Building Pathology, Durability and Service Life [1st ed.] 9783030473013, 9783030473020

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Building Pathology and Rehabilitation

João M. P. Q. Delgado   Editor

Building Pathology, Durability and Service Life

Building Pathology and Rehabilitation Volume 12

Series Editors Vasco Peixoto de Freitas, University of Porto, Porto, Portugal Aníbal Costa, Aveiro, Portugal João M. P. Q. Delgado

, University of Porto, Porto, Portugal

This book series addresses the areas of building pathologies and rehabilitation of the constructed heritage, strategies, diagnostic and design methodologies, the appropriately of existing regulations for rehabilitation, energy efficiency, adaptive rehabilitation, rehabilitation technologies and analysis of case studies. The topics of Building Pathology and Rehabilitation include but are not limited to - hygrothermal behaviour - structural pathologies (e.g. stone, wood, mortar, concrete, etc…) diagnostic techniques - costs of pathology - responsibilities, guarantees and insurance - analysis of case studies - construction code - rehabilitation technologies architecture and rehabilitation project - materials and their suitability - building performance simulation and energy efficiency - durability and service life.

More information about this series at http://www.springer.com/series/10019

João M. P. Q. Delgado Editor

Building Pathology, Durability and Service Life

123

Editor João M. P. Q. Delgado CONSTRUCT-LFC Department of Civil Engineering Faculty of Engineering University of Porto Porto, Portugal

ISSN 2194-9832 ISSN 2194-9840 (electronic) Building Pathology and Rehabilitation ISBN 978-3-030-47301-3 ISBN 978-3-030-47302-0 (eBook) https://doi.org/10.1007/978-3-030-47302-0 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2020 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Preface

Building pathology is the scientific of building failures, with emphasis on building defects and performance, to help create the right remedial and management resolutions. The principles upon which building pathology is based rely on a detailed knowledge of how a building is designed, constructed, used and changed, and various mechanisms by which its structural, material and environmental conditions can be affected. The evolution of degradation can be interpreted as the continuous reduction in performance over time. If the performance decreases below the functionality limits, the functional service life limit is reached. The eventual identification of potential hidden defects is extremely useful, which can compromise the building’s performance and, if identified late, can have very costly repairs or be out of warranty terms. A typical example is the corrosion by the salt attack which is one of the most common forms of degradation of material properties due to interaction with the environment. The main purpose of this book, Building Pathology, Durability and Service Life, is to provide a collection of recent research works to contribute to the systematization and dissemination of knowledge related to building pathologies (structural and hygrothermal), salt attack and corrosion, durability and service life prediction. It includes a set of new developments in the field of structural and hygrothermal building pathologies, corrosion by salt attack, durability and service life prediction, namely in concrete structures. The book is divided into seven chapters that intend to be a resume of the current state of knowledge for benefit of professional colleagues, scientists, students, practitioners, lecturers and other interested parties to network. At the same time, these topics will be going to the encounter of a variety of scientific and engineering disciplines, such as civil, materials and mechanical engineering. Porto, Portugal

João M. P. Q. Delgado

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Contents

Durability and Service Life Prediction of Reinforced Concrete Frames Subjected to Chloride Corrosion and Mechanical Loading . . . . . . . . . . Carlos Alberto Caldeira Brant, Karolinne Oliveira Coelho, Edna Possan, Edson Denner Leonel, and Julio Flórez-López Service Life and Durability of Reinforced Concrete Structures Present in Marine Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carlos Eduardo Tino Balestra Salt Attack, Durability and Service Life of Concrete Structures . . . . . . Wellington Mazer, Alessandra Monique Weber, Carlos Alberto Brunhara, and Juliana McCartney Fonseca Guidelines for Inspection and Receipt of Reinforced Concrete Structures in Newly Constructed Buildings . . . . . . . . . . . . . . . . . . . . . . Marcus Vinícius Fernandes Grossi

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41 57

73

Application of the Degradation Measurement Method in the Study of Facade Service Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 E. Bauer, J. S. de Souza, and C. B. Piazzarollo The Influence of Mass Tourism and Hygroscopic Inertia in Relative Humidity Fluctuations of Museums Located in Historical Buildings . . . 121 C. Ferreira, V. P. de Freitas, and João M. P. Q. Delgado Residual Safety in One-Way Slabs with Severe Corrosion . . . . . . . . . . . 145 Jose Vercher, Enrique Gil, Ángeles Mas, and Carlos Lerma

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Durability and Service Life Prediction of Reinforced Concrete Frames Subjected to Chloride Corrosion and Mechanical Loading Carlos Alberto Caldeira Brant, Karolinne Oliveira Coelho, Edna Possan, Edson Denner Leonel, and Julio Flórez-López Abstract The objective of this work is to propose a mathematical model for the prediction of service life in reinforced concrete frames subjected to chloride corrosion and mechanical loading. Corrosion causes the reduction of the cross section of the steel bars and decreases the yield stress; mechanical loading produces concrete cracking and yield of the reinforcement. For the modeling of the structural behavior, this research is based on lumped damage mechanics. As a theoretical basis for the proposed mathematical model, some concepts and laws of the thermodynamics of frames are also introduced. The model proposed in this work is called elastoplastic with damage and corrosion, and the internal variables used are plastic rotation, damage level and corrosion level. The propagation of damage causes an acceleration of the evolution of corrosion and the constant that characterizes this relationship can be identified experimentally. The proposed model was used for the simulation of a reinforced concrete frame. In the example, corrosion evolution causes increments of cracking and the evolution of the damage accelerates the corrosion process. Keywords Durability · Service life prediction · Reinforced concrete · Chloride corrosion

C. A. C. Brant · E. Possan (B) · J. Flórez-López University of Latin American Integration, Foz do Iguaçu, Brazil e-mail: [email protected] C. A. C. Brant e-mail: [email protected] J. Flórez-López e-mail: [email protected] K. O. Coelho State University of Campinas, Campinas, Brazil e-mail: [email protected] E. D. Leonel University of São Paulo, São Paulo, Brazil e-mail: [email protected] © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2020 J. M. P. Q. Delgado (ed.), Building Pathology, Durability and Service Life, Building Pathology and Rehabilitation 12, https://doi.org/10.1007/978-3-030-47302-0_1

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1 Introduction Corrosion is one of the most common forms of degradation of material properties due to interaction with the environment. Inevitably, this deterioration can occur in several types of materials, as in polymeric insulation present in the spinning of aging aircraft or even in selective-dissecting ceramics. However, corrosion is mainly associated with metallic materials. Koch (2002) shows that in the United States roughly US$ 276 billion per year is required to cover corrosion processes, focusing mainly on maintenance of utilities, transportation and infrastructure. For Shaw and Kelly (2006), as well as death and taxes, the corrosion of materials is inevitable but something that must be delayed or minimized, and for this, it is necessary to understand how to deal with this phenomenon. For the authors, the fundamental cause of all corrosion is the Gibbs free energy variation of the system. In this sense, the production of the metal alloys involves the addition of energy to the system, so that as a result of the thermodynamic struggle, over time, the metal is naturally driven to return to its more stable state (low energy oxide). Corrosion corresponds to this process of returning to the oxide form. As infrastructures worldwide grow older, more failures due to corrosion can be expected to occur. As mentioned by Shaw and Kelly (2006), the replacement of all bridges and pipelines would obviously be expensive and unnecessary, since it is understood that most of these infrastructures may still be in good working order. The challenge of finding out which ones are failing and how long they can last is the function of the “service life prediction”. Possan et al. (2018) report that the service life involves of measuring the expected life of a structure or its parts, throughout its life cycle. Thus, this work considers the subject of corrosion-cracking coupling in reinforced concrete structures, since in the perspective of civil engineering and structures, concrete undoubtedly stands as one of the most used materials in the world. In this chapter, only the chloride corrosion mechanism is considered. The concrete-reinforcing bond strength ensures that the steel bars work only with the deformation of the concrete surrounding them. Thus, even if the structure possesses deformed regions subjected to cracking of the concrete, it will be able to ensure adequate resistance to the external forces. In addition, the concrete around the reinforcement, besides having the function of adhesion, also serves to protect the steel bars against corrosion. Through experimental works, Suzuki et al. (1990), Pettersson and Jorgensen (1996), Scott and Alexander (2007) and Otieno et al. (2010) showed that the greater the crack widths in concrete structures the higher the rate of evolution of reinforcement corrosion due to the presence of chloride ions (pit). Thus, the propagation of damage favors the penetration of aggressive agents in contact with the reinforcement that decreases the durability of structures and the shortening of service life due to acceleration of corrosion. In this context, because it is a probabilistic phenomenon that depends on environmental factors, structural characteristics and time exposed, the structural analysis

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that contemplates the corrosion of the reinforcement is linked to high complexity in simulations. However, through the theoretical basis offered by thermodynamics of solids and frames, it is foreseen the possibility of making a mechanical model of analysis of reinforced concrete structures that take into account the coupling of concrete cracking-corrosion of the reinforcement. Disregarding the effect of concrete cracking, some models propose the empirical calculation of the corrosion rate of steel reinforcement caused by the presence of chloride ions (Otieno et al. 2012; Yalcyn and Ergun 1996; Liu and Weyers 1998; Vu and Stewart 2000; Martínez and Andrade 2009). Yalcyn and Ergun (1996) model was developed in studies on experimental accelerated corrosion tests because of chloride ions and acetate ions. Liu and Weyers (1998) developed a model based on statistical analysis of experimental results obtained for a 5 year accelerated corrosion test programmed for 44 no cracked bridge slabs. The model by Vu and Stewart (2000) assumes that the availability of oxygen on the surface of steel bars is the governing factor of the corrosive process. This model has the water/cement factor (w/c) and the reinforcement cover thickness (cob) as input parameters. As conditions for the use of this method, the relative humidity values should be around 75% and the ambient temperature around 20 °C. The model of Martínez and Andrade (2009) can be used to represent the average annual rate of corrosion due to the effect of chloride ions and it is based on the resistivity of concrete. Using any of the models to obtain the corrosion rate associated with the presence of chloride ions, the calculation of the maximum pit depth can be made according to the proposals developed by Val and Melchers (1997) and Stewart (2004). Coelho (2017) pioneered the analysis of corrosion-cracking behavior in reinforced concrete structures through lumped damage mechanics. The lumped damage theory is based on fracture and classic damage mechanics. It provides a framework of relative simplicity and significant theoretical consistency at the same time (FlórezLópez et al. 2015) by combining these theories with the plastic hinge concept. Coelho modeled the reduction of the cross section of the reinforcement and the penalization of the yield function due to corrosion evolution. Due to the low computational cost associated with lumped damage theory, probabilistic structural analyses were feasible through the Monte Carlo simulation method, proving that this theory and probabilistic analysis can work well together. This work generalizes the results presented in Coelho (2017) and is based too on the study done by Brant (2019). Brant proposed a thermodynamic of frames based the theory of thermodynamics of solids. The author validates the thermodynamics of frames with auxiliary models consolidated in the literature: perfect elastoplastic model, elastoplastic model with linear kinematic hardening, elastic model with damage, elastoplastic model with linear kinematic hardening and damage. Through the development of this thermodynamics, the author performs the structural analysis of a frame considering the evolution of pit corrosion. The present research proposes to study the coupling of the reinforcement corrosion in the structural analysis, through lumped damage mechanics, and to develop a thermodynamically admissible model that contemplates as internal variables: plasticity, damage and corrosion. As novelties of this research, we intend to consider the

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evolution of the corrosion in the structural analysis and to incorporate the influence of concrete cracking on the corrosion rates. For this, it is necessary to make the experimental identification of the constant that relates the propagation of the damage with the increase of the pit corrosion evolution. Finally, this work proposes a mathematical model for the coupling of corrosion by the effect of chloride ions, cracking and plasticity in the analysis of reinforced concrete structures. This formulation permits the incorporation of any model of pitting corrosion in the literature for analysis of complex structures subject to chemical and mechanical loading. This chapter is organized as follows. Section 2 reviews some corrosion laws described in the literature and shows that they can be written in a unified way. Section 3 describes the theory of thermodynamics of frames. Section 4 proposes a new model of the behavior of RC frame elements undergoing corrosion, cracking and plasticity. Section 5 presents a numerical example of a reinforced concrete frame subjected to thermo-mechanical loadings. Lastly, Sect. 6 includes some final remarks and conclusions.

2 Review of Laws of Corrosion by Chloride Ions 2.1 Corrosion Current Density Corrosion due to the action of chloride ions often occurs at concentrated points of reinforcement in reinforced concrete structures (pit corrosion). The corrosion current density (i cor ) is one of the most important parameters of interest for this kind of corrosion. It is expressed in units of µA/cm2 . The corrosion current density can be turned into pit depth in a steel bar (p). The maximum pit depth can be calculated using the formulation developed by Val and Melchers (1997), apud Stewart (2004), below. p = 0.0116i cor Rel(ttr − tini )

(1)

where p is the depth of the pit (mm), Rel is the relationship between the maximum depth of the pit and the average depth, ttr is the elapsed time (years) and tini is the start time for corrosion (years). The Rel parameter is considered probabilistic, but according to Stewart (2004) a simplification for the variable equal to 5.08 can be adopted. The number 0.0116 is responsible for the transformation from µA/cm2 to mm/yr. To obtain i cor there are many models available in the literature. Otieno et al. (2011) present a critical view of some of those laws. They are presented in the following sections.

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2.2 Yalcyn and Ergun’s Model (1996) This model was developed in studies on experimental accelerated corrosion tests due to the effects of chloride ions and acetate ions. Equation (2) presents the calculation of the corrosion current density caused by the presence of chloride ions obtained by the authors.  0, if ttr < tini i cor = (2) i 0 e−CY E ttr , if ttr ≥ tini where ttr is the elapsed time (days), i 0 is the associated initial corrosion rate and CY E is a constant that depends on material and cross-section properties: the degree of pore saturation, the pH, the permeability and the thickness of the concrete covering. The authors propose a value for constant CY E equal to 1.1 × 10−3 day−1 .

2.3 Liu and Weyers’ Model (1998) The development of this empirical model is based on statistical analysis of experimental results. The results were obtained for an accelerated corrosion test over 5 years and included 44 un-cracked bridge slabs:  i cor =

0, if ttr < tini i 0 + 290.91(ttr − tini )−0.215 , if ttr ≥ tini

(3)

i 0 = 102.47 + 10.09 ln(1.69Cl) − 39, 038.96T −1 − 0.0015Rc where Cl is the total chloride content in the steel bars (kg/m3 ), T is the surface temperature of the steel (K) and Rc is the resistivity of the concrete cover (). Time is measure in years. Notice that this model depends on the thermochemical forces associated with chloride ion concentration and temperature; and concrete properties: resistivity of the concrete cover.

2.4 Vu and Stewart’s Model (2000) The authors assume that the availability of oxygen on the surface of steel bars is the governing factor of the corrosive process. The model has the water/cement factor (w/c) and the reinforcement cover thickness (cov) as input parameters (Eq. 4). As conditions for the use of this method, the relative humidity values should be around 75% and the ambient temperature around 20 °C.

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The reinforcement cover is measured in cm and time in years. In this model, the empirical development by Liu and Weyers (1998) is considered, in which the corrosion rate decreases exponentially over time. This model depends on the properties of concrete: water-cement ratio; and section properties: thickness of the reinforcement cover. ⎧ if ttr < tini ⎨ 0, (4) i cor = i 0 , if tini ≤ ttr < 0.57 + tini ⎩ 0.85i 0 (ttr − tini )−0.29 , if ttr ≥ 0.57 + tini −1.64  37.8 · 1 − wc i0 = cov

2.5 A General Formulation of Normalized Corrosion Rate The normalized corrosion rate is defined as equal to the pit depth rate p˙ divided by the diameter of the steel bar φ. This variable rate can be obtained from the expressions presented in the previous paragraphs. In general terms, the normalized corrosion rate is a function of thermochemical forces, concrete properties, section properties and time defined by some function O = O(CF, CP, SP, t). This expression does not consider the influence of cracking on the corrosion evolution:  · 0.0116Rel i˙cor cor (ttr − tini ) + i cor p˙ , if ttr ≥ tini O= = φ φ

(5)

Thus, for each i cor model a different function O is obtained. These functions can be seen in Table 1. Table 1 Models for computing function O Models

O = O(CF, CP, SP, t)

Yalcyn and Ergun (1996)

0 0.06i 0 e−CY E ttr φ

[1 − CY E ln(e)(ttr − tini )]

ttr < tini ttr ≥ tini

Liu and Weyers (1998)

0

ttr < tini ttr ≥ tini

Vu and Stewart (2000)

0

ttr < tini tini ≤ ttr < 0.57 + tini ttr ≥ 0.57 + tini

 0.06i 0 +13.46(ttr −tini )−0.215 φ 0.06i 0 φ 0.036i 0 (ttr −tini )−0.29 φ

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3 Thermodynamics of Frames 3.1 The Principle of Virtual Work The virtual power of external forces ( Pˆext ) is associated with the virtual velocities {U˙ˆ }, according to Eq. (6). Pˆext = {U˙ˆ }t {P}

(6)

where the vector {P} corresponds to the equivalent external nodal forces. The symbols aˆ and a˙ refer, respectively, to virtuality and time derivative for a given variable a. The matrix {U˙ˆ } derives from the displacement matrix {U} for a plane frame structure, as shown in Fig. 1. The generalized displacement matrix {U} is assembled for the whole structure, composed of elements and nodes, whose identifiers were defined by b and mn, respectively (Eq. 7). The horizontal displacement is given by u, the vertical displacement by w and the rotation by θ . Fig. 1 Representation of possible displacement and rotations in the node

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Fig. 2 Representation of possible forces and moment in the node

⎧ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨

⎫ u1 ⎪ ⎪ ⎪ w1 ⎪ ⎪ ⎪ ⎪ ⎪ θ1 ⎪ ⎪ ⎪ ⎪ u2 ⎪ ⎪ ⎪ ⎬ . {U } = ⎪ . ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ . ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ u ⎪ mn ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ w mn ⎪ ⎪ ⎪ ⎩ ⎭ θmn

(7)

The external force matrix {P} accounts for all external loads and reactions applied to nodes of the structure. Figure 2 illustrates these nodal loadings on a frame node. The matrix {P} is represented by Eq. (8) below. ⎧ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨

⎫ Pu 1 ⎪ ⎪ ⎪ Pw1 ⎪ ⎪ ⎪ ⎪ ⎪ Pθ1 ⎪ ⎪ ⎪ ⎪ Pu 2 ⎪ ⎪ ⎪ ⎬ . {P} = ⎪ . ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ . ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ Pu ⎪ mn ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ Pw mn ⎪ ⎪ ⎪ ⎩ ⎭ Pθmn

(8)

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where Pu mn is the horizontal external force, Pwmn is the vertical external force and Pθmn the external bending moment acting on the node mn of the structure. The virtual power of the deformations ( Pˆde f ) is defined for the frame structure according to Eq. (9). Pˆde f =

m  b=1

b Pˆde f =

m  · t  ˆ {M}b  b=1

(9)

b

· ˆ and {M} correspond, respectively, to the generalized virtual deforVectors  mation rate and the generalized stresses of a frame element b. The parameter m is the number of the of the frame.  elements ·  ˆ come from the generalized deformation matrix {} for a plane The matrices  frame element, as shown in Fig. 3 and Eq. (10). ⎧ ⎫ ⎨ φi ⎬ {}b = φ j ⎩ ⎭ δ

(10)

where φi and φ j represent the relative rotations at nodes i and j, respectively, and δ is the elongation of the element b. The relationship between generalized displacements and deformations is denoted kinematic equations and can be obtained from geometrical considerations: {}b = [B]b {U } Fig. 3 Generalized deformations in a frame element

(11)

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Fig. 4 Generalized stresses in a frame element

where [B]b is the transformation kinematic matrix to element b (Eq. 12). ⎡

⎤ cos αb b b 0 . . . senα − cosL bαb 1 . . . − senα 0 ... Lb Lb Lb ⎢ ⎥ cos αb b b − cosL bαb 0 . . . − senα 1 ...⎦ ⎣ 0 . . . senα Lb Lb Lb 0 . . . − cos αb −senαb 0 . . . cos αb senαb 0 . . .

(12)

1, . . . , 3i − 2, 3i − 1, 3i, . . . , 3j − 2, 3j − 1, 3j, . . . where α and L are, respectively, the angle of the cord of element b with respect to the reference coordinate system (X) and L its length. The generalized stress matrix {M} is formed by the internal bending moments at nodes i and j (m i and m j ) and the axial force at the frame element b(n), according to Fig. 4 and Eq. (13). ⎧ ⎫ ⎨ mi ⎬ {M}b = m j ⎩ ⎭ n

(13)

by the product between The virtual power of the forces of inertia ( Pˆine )is given  ·

t

Uˆ

, mass matrix [Mass] and

 t ·   Pˆine Uˆ [Mass] U¨

(14)

the vector transposed from the virtual velocities   vector acceleration of the structure U¨ :

The equilibrium equation of the structure is obtained from the principle of virtual powers: Pˆext = Pˆde f + Pˆine ⇒ {P} =

m    [B]tb {M}b + [Mass] U¨ b=1

(15)

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3.2 Principles of Thermodynamics for a Frame Structure The development of thermodynamics of frames is based on the fundamentals of thermodynamics of solids, revised from the books of Lemaitre and Chaboche (1990) and Proença (2000). The first principle of thermodynamics is described by Eq. (16), where E˙ is the rate of variation of the internal energy, K˙ is the rate of variation of the kinetic energy, Pext is the power of the external forces and Q is the amount of heat yielded or received by the structure E˙ + K˙ = Pext + Q

(16)

Combining the first principle of thermodynamics, the principle of virtual powers and the equality between the rate of variation of kinetic energy and the power of inertia forces ( K˙ = Pine ), we obtain Eq. (17), which represents the accumulated internal energy for the entire structure. E˙ = Pde f + Q

(17)

m  ˙ Assuming that E˙ = m b=1 E b and Q = b=1 Q b , the following equation (Eq. 18) relates the respective energy rates with the power of the deformations for each frame element b. · ·  t b ˙ E b = Pde f + Q b ↔ E b =  b {M}b + Q b

(18)

The second principle of thermodynamics is represented by Eq. (19), which is proposed for each element from the expression presented in Swalin (1972). This inequality can be rearranged as a function of the internal energy rate (Eq. 20). ·

Sb −

Qb ≥0 Tb

· ·  t ˙ {M}b − E b ≥ 0 Tb Sb +  b

(19) (20)

·

where Sb is the entropy rate and the Tb is the absolute mean temperature for a plane frame element b.

3.3 The Gibbs Energy as a Thermodynamic Potential The Gibbs free energy (gb ) of a frame element is associated with the internal energy (E b ), entropy (Sb ) and deformations of the element () adapting the results provided

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by Lubarda (2004) to frame structures. It is also possible to make use of Gibbs energy with negative signal (G b = −gb ), this was done in order to obtain an expression of positive energy dissipation: G b = −gb = −E b + Tb Sb + {}tb {M}b

(21)

The Gibbs free energy will be used as thermodynamic potential. Thus, it is postulated that the Gibbs energy is a function of the generalized stresses ({M}b ), the temperature (Tb ) and the internal variables (Vα ) (Eq. 22). G b = G b (Mb , Tb , Vα )

(22)

From the derivative of Eq. (21) in time and replacing the internal energy in the inequality (20), we obtain the expression represented in Eq. (23). This inequality results from the combination of the first and second principles of thermodynamics and the Gibbs free energy. · ·   G b − Tb Sb − {}tb M˙ b ≥ 0

(23)

Now, through Eq. (23), it is possible to verify whether a given physical model is thermodynamically admissible or not. Deriving the energy potential (Eq. 22) with respect to time, we obtain the following equation (Eq. 24). 

·

Gb =

∂G b ∂M

t

     ∂G b · ∂G b t · ˙ Tb + Vα M b+ ∂ Tb ∂ Vα b

(24)

·

Introducing G b in the inequality (23) gives: 

∂G b ∂M



t − {}b

  M˙ b +



    · ∂G b ∂G b t · − Sb Tb + Vα ≥ 0 ∂ Tb ∂ Vα b

(25)

For a reversible process, the equality in Eq. (25) occurs, and the rates of variation ·

of the internal variables become equal to zero (Vα = 0): 

∂G b ∂M

t

 − {}b

  M˙ b +



 · ∂G b − Sb Tb = 0 ∂ Tb ·

(26)

Considering a process that is also isothermal (Tb = 0), the following expression results.   ∂G b {}b = (27) ∂M

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In a reversible process, only with temperature change ( Mb = 0), the following formulated expression is obtained. sb =

∂G b ∂ Tb

(28)

According to thermodynamics of solids, the relationships (27) and (28) can be generalized to any thermodynamic process. Thus, it results in the energy dissipation equation for any process, reversible or irreversible, that is represented by Eqs. (29) or (30). 

∂G b ∂ Vα

t 

· Vα

 ≥0

(29)

or   · {Aα }t Vα ≥ 0

(30)

where Aα is the thermodynamic forces associated with the internal variables Vα . Therefore, the state laws are obtained by deriving Gibbs’ free energy with respect to the internal variables of interest. The relationships that arise are as follows Eqs. (31) to (33). 

∂G b ∂M

 = {}b

∂G b = Sb ∂ Tb   ∂G b = {Aα } ∂ Vα

(31) (32) (33)

It is observed the cause-effect relations between the internal variables and those derived from the Gibbs potential: {M} ↔ {}; Tb ↔ Sb ; {Vα } ↔ {Aα }. Thus, for each state or internal variables (Vα ) there is an associated thermodynamic force Aα . The inequality obtained in Eqs. (29) or (30) states that energy dissipation must occur in inelastic processes, where in this case inequality is necessarily positive. For elastic processes, inequality will assume null value. Models that verify this condition are called “thermodynamically admissible”.

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3.4 Thermodynamic Formulation of the Direct Stiffness Method The direct stiffness method is a well-known algorithm for the analysis of elastic frames. This procedure can be derived from the following Gibbs potential: Gb =

1 {M}t [F0 ]{M} + {M}t {0 } 2

(34)

where [F0 ] is the flexibility matrix of frame element and {0 } is denoted initial deformation matrix. The latter is the consequence of the distributed forces on the element. For instance, in the case of a homogeneous element (elasticity modulus E c ) of constant inertia I subjected to constant distributed forces p, those matrices have the following expressions: ⎡ ⎢ [F0 ] = ⎣

L −L 3E c I 6E c I −L L 6E c I 3E c I

0

0

⎤ 0 ⎥ 0 ⎦

{0 } =

L AE c

⎧ ⎪ ⎨

⎫ ⎪ ⎬

⎩

⎪ ⎭

pL 3 24E c I 3 − pL ⎪ 24Ec I

0

(35)

Notice that in this particular case, the Gibbs energy becomes the complementary strain energy used in the classical formulations. The state law (31) gives the constitutive model for an elastic frame element: {} = [F0 ]{M} + {0 }

(36)

In the classic theory of structures, the constitutive Eq. (36) is usually presented in terms of stiffness and not flexibility: {M} = [E 0 ]{} + {M0 }

(37)

where [E 0 ] is the elasticity matrix of frame element and {M0 } is denoted initial moment matrix. ⎡ 4Ec I 2Ec I ⎤ 0 L L (38) [E 0 ] = [F0 ]−1 = ⎣ 2ELc I 4ELc I 0 ⎦ AE c 0 0 L ⎧ ⎫ pL 2 ⎪ ⎨ − 12 ⎪ ⎬ pL 2 {M0 } = −[F0 ]−1 {0 } = ⎪ ⎪ ⎩ 12 0 ⎭ The combination of the constitutive Eq. (38), the kinematic Eq. (11) and the equilibrium Eq. (15) leads to the conventional expressions:

Durability and Service Life Prediction of Reinforced Concrete …

[K 0 ]{U } = {F} [K 0 ] =

m 

[B]t [E 0 ][B]

15

(39) (40)

b=1

{F} = {P} −

m 

[B]t {M0 }

(41)

b=1

Notice that [K 0 ] is the conventional stiffness matrix and {F} the matrix of external forces that include nodal forces and the loads distributed on the elements. This model has not internal variables because it has not energy dissipation.

3.5 Thermodynamic Formulation of Elasto-Plastic Frames Elasto-plastic concepts are frequently used in the design of reinforced concrete structures and the seismic analysis of frames. In this section the classic model is formulated within the thermodynamic framework. Consider the lumped plasticity model shown in Fig. 5. Each frame member is the assemblage of an elastic beam-column and two perfectly plastic hinges located at the ends of the element. The Gibbs potential for this model is given by: Gb =

  1 {M}t [F0 ]{M} + {M}t {0 } + {M}t  p 2

(42)

Notice that this potential includes one internal variable: the generalized plastic deformation matrix { p }. This new potential leads to the following state laws: Fig. 5 Representation of the internal variables of the elastoplastic model

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 {} =

∂G b ∂M

 

  = [F0 ]{M} + {0 } +  p ∂G b ∂φ p

(43)

 = {M}

(44)

Thus, the thermodynamic force associated to plastic rotations is the generalized stress matrix {M}. Then, the energy dissipation for this model is given by:   {M}t  p ≥ 0

(45)

The constitutive equations are now composed by the state laws and the plasticity evolution laws. The latter are defined by the introduction of yield functions of the plastic hinge that in the case of perfectly plastic hinges have the following expression: f i = |m i | − k0 ≤ 0

(46)

where k0 is, in this case, equal to the ultimate moment of the cross-section. Actually, in real RC structures, the ultimate moments under positive or negative actions are usually different. For the sake of simplicity, this chapter will deal only with monotonic or constant loadings and it will not be necessary to consider different resistances as a function of the sign of the moment in the formulation. The plastic rotation evolution law for a hinge is derived from the conventional normality rule and the consistence condition: ⎧ ⎨ λi = 0 i f f i < 0 or f˙i < 0 ∂ f i p ˙ φi = λi ; (47) λ > 0 i f f i = 0 and f˙i = 0 ⎩ i ∂m i f i > 0 impossible It can now be shown that this model is thermodynamically admissible (see Brant 2019).

3.6 The Generalized Griffith Criterion for Frame Structures The Griffith criterion is a well-known principle of the fracture mechanics. It establishes the conditions for crack propagation based on an energy balance. This formulation can also be extended to the case of frame structures. Once again, a frame member is assumed to be the assemblage of an elastic beamcolumn and two inelastic hinges (i and j). Concrete cracking is represented by damage internal variables (di and d j ) that can take values between 0 and 1 as shown in Fig. 6. In the case of a pure concrete element, the thermodynamic potential for this model is represented by Eq. (48).

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Fig. 6 Representation of the internal variable of the brittle damage model

Gb =

1 {M}t [F(D)]{M} + {M}t {0 } 2

(48)

  where (D) = di , d j is the damage matrix of the element and [F(D)] is the flexibility matrix with damage that has the following expression: ⎡ ⎢ [F(D)] = ⎣

−L L 3E c I (1−di ) 6E c I −L L 6E c I 3E c I (1−d j )

0

0

⎤ 0 0 ⎥ ⎦

(49)

L AE c

This flexibility matrix is obtained from a well-known principle of damage mechanics: the hypothesis of deformation equivalence (Flórez-López et al. 2015). By deriving the potential in relation to the moment, the associated elasticity law is obtained (Eq. 50). 

∂G b ∂M

 = [F(D)]{M} + {0 } = {}

(50)

The derivative of the Gibbs energy with respect to damage determines the thermodynamic force related to cracking (Eq. 51). 

∂G b ∂d

 =

⎧ ⎨ ⎩

Lm i2 6E c I (1−di )2 Lm 2j 6E c I (1−d j )

2

⎫ ⎬ ⎭

= {Y }

(51)

Notice that the thermodynamic force Yi corresponds in this case to the energy release rate or crack driving moment of an inelastic hinge. The Griffith criterion for an inelastic hinge can be written as: ⎧ if Yi < R0 or Y˙i < 0 ⎨ d˙i = 0 i f Yi = R0 and Y˙i = 0 d˙ > 0 ⎩ i Yi > R0 or d˙i < 0 impossible

(52)

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It can also be shown that this model is thermodynamically admissible (see Brant 2019).

4 A Lumped Model Coupling Damage, Plasticity and Corrosion 4.1 Internal Variables This model is a generalization of the lumped damage constitutive equations described by Flórez-López et al. (2015). The new constitutive law considers plastic rotations { p } and cracking of the concrete {D}; it also includes as internal variable the corrosion of the reinforcement by chloride ions {C}. These variables are lumped at the inelastic hinges as shown in Fig. 7.   {C}t = ci , c j

(53)

The level of corrosion (cor or ci for any node i) is defined by Eq. (54). ci = cor =

p¯ φ¯

(54)

In which p¯ is the average pit depth and φ¯ is the original steel average diameter in the cross section of the element under analysis. Notice that the corrosion internal variable is simply a normalized pit depth. The effective area, i.e. the total steel area less the corroded area, can be related to the new internal variable according to Eq. (55): Ae f

A0 = π



√ K cor + π − arcsin 2cor −cor 2 + 1, if cor < √ K cor + arcsin 2cor −cor 2 + 1, if cor ≥

Fig. 7 Internal variables of the elastoplastic model with plasticity, damage and corrosion

√ 2 √2 2 2

(55)

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Fig. 8 Cinematics of a corroded steel bar

K cor = −4cor 2 arcsin

  −cor 2 + 1 + 2cor −cor 2 + 1

where Ae f is the effective cross-sectional area of the reinforcement (discounted corroded area) and A0 is the original steel area. Equation (55) was obtained according to the cinematics of corrosion proposed by Val and Melchers (1997), apud Stewart (2004) that is presented in Fig. 8.   {C}t = ci , c j

(53)

Thus, the variables ci and c j represent the corrosion levels of the reinforcement in the respective hinge and assume values between 0 and 1, such that the closer to 1, the more the steel bar will be corroded in that position of the structure. As presented in Sect. 2, it is assumed that corrosion laws can be presented in a unified way as some function O of thermochemical forces CF, concrete properties CP, section properties SP and time: O = O(C F, C P, S P, t)

(56)

4.2 Gibbs Potential The thermodynamic potential representing this model is in the form of a function G b = G b ({M}, { p }, {D}, {C}):   1 {M}t [F(D)]{M} − I (D, C) + {M}t φ p 2   {O}t {C} 1  t − φ p [H (D, C)] φ p + 2 ξ

Gb =

(57)

The new model is based on the hypothesis of equivalence in deformations too, thus the flexibility matrix [F(D)] has the same expression presented in Sect. 3.6 (Eq. 49). However, the presence of the steel reinforcement produces an increment in the crack resistance that is represented by the function I (D, C). Based on the lumped damage

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constitutive law (Flórez-López et al. 2015), the following expression is considered:  1    1 I (D, C) = − q(ci )ln 2 (1 − di ) − q c j ln 2 1 − d j 2 2

(58)

where q(ci ) is a parameter that depends on the corrosion internal variable. The matrix [H (D, C)] corresponds to a kinematic hardening term that is assumed to depend on damage and plastic rotations: ⎡

⎤ 0   0 (1 − di )h i (ci )  [H (D, C)] = ⎣ 0 1 − dj h j cj 0 ⎦ 0 0 0

(59)

  Finally, the matrix {O}t = Oi , O j represents the value of the function O at the hinges i and j of the element. In most cases the function O assumes the same value for all the inelastic hinges of a structure. However, there could be some exceptions, for instance semi-submersed structures.

4.3 State Law and Thermodynamic Forces Associated to the Internal Variables By deriving the Gibbs potential in relation to the generalized stresses, the elasticity law is obtained (Eq. 60). 

∂G b ∂M



  = [F(D)]{M} +  p = {}

(60)

The derivative of G b with respect  to the plastic rotations defines the thermodynamic forces related to plasticity A p : 

 Ap =



∂G b ∂ p



⎧ p ⎫ m − − d (1 )h(c )φ ⎨ i i i i      p⎬  = {M} − [H (D, C)]  p = m j − 1 − d j h c j φ j (61) ⎩ ⎭ n

In addition, deriving the Gibbs energy with respect to the damage gives the thermodynamic force related to the damage {Ad }:  {Ad } =

∂G b ∂d



⎧ ⎨

 p 2 ⎫ i) ⎬ − q(ci ) ln(1−d + 21 h(ci ) φi (1−di ) =   ln(1−d j ) 1   p 2 ⎩ + 2h cj φj ⎭ 2 − q cj (1−d j ) 6E c I (1−d j ) Lm i2 6E c I (1−di )2 Lm 2j

(62)

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21

Finally, deriving Gb in with respect to the corrosion variables gives the corrosion driving force, denoted {Ac } (Eq. 63).  {Ac } =

∂G b ∂cor



!   {O} 1  p t ∂ H (D, C)  p  ∂ I (D, C) =−   − + 2 ∂cor ∂cor ξ

(63)

4.4 Damage Evolution Law The damage evolution law of the new model has the same form of the one in the lumped damage constitutive law (Flórez-López et al. 2015) that disregards the influence of the plastic rotations on damage evolution. Thus, the damage driving moments {Yi } are now rewritten as:  p 2 Lm i2 1 1 ln(1 − di ) Yi = Adi − h(ci ) φi = − q(ci ) 2 2 2 3E I (1 − di ) (1 − di )

(64)

Then, the damage evolution law is expressed as a generalized Griffith criterion as in Sect. 3.6: ⎧ if Yi < R0 or Y˙i < 0 ⎨ d˙i = 0 (65) i f Yi = R0 and Y˙i = 0 d˙i > 0 ⎩ ˙ Yi > R0 or di < 0 impossible

4.5 Computation of the Parameters q and R0 as a Function of the Corrosion Level and the Axial Force The damage evolution law presented in the previous section introduces two parameters q(ci ) and R0 . One of them is assumed to be a function of the corrosion internal variable. This section proposes a rational procedure for the determination of their values. Consider the Griffith equation Yi = R0 for any hinge i: m i2 =

6E c I(1 − di )2 6q E c I R0 + (1 − di )ln(1 − di ) L L

(66)

Equation (66) represents a relationship between moment and damage as the one presented in Fig. 9. Notice that theses curves have two points that can be computed using the procedures indicated in the codes for reinforced concrete design for the particular case of zero corrosion: the first cracking moment Mcr and the ultimate moment Mu .

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Fig. 9 Bending moment to damage ratio for an inelastic hinge

Thus, when the damage associated with Eq. (66) is zero, the bending moment is equal to the critical moment Mcr , therefore: R0 =

2 L Mcr 6E c I

(67)

The ultimate moment occurs at the maximum of the curve in Fig. 9. Therefore: ⎧ ⎨ ⎩

"

∂m i2 " =0 ∂di "d =d i u 6E c I(1−du )2 2 Mu = L

R0 +

6q E c I L (1

− du ) ln(1 − du )

(68)

This system of equations permits the computation of the values of q and du . However the codes do not explicitly include steel corrosion in the procedures for the determination of the properties Mcr and Mu . It is then proposed to modify the conventional algorithm according the scheme presented in Fig. 10.

Fig. 10 Stress and strain distributions in a RC section for a Mcr , b Mu

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23

Where Ae f is the effective steel area computed using Eq. (55); f t is the concrete cracking stress in tension, εcu is the ultimate strain in concrete; the curvature χu is equal to the concrete ultimate strain over the depth of the neutral axis; εs is the strain in steel bar; f c is the concrete stress. Finally, f s is the steel stress that is computed according to Eq. (69). ⎧ ⎪ i f εs < ε y (cor ) ⎨ E s εs ,  fu − f y  f s = f y + εup −ε y εs − ε y , i f ε y (cor ) ≤ εs < εup (cor ) ⎪ ⎩ f u (cor ), i f εup (cor ) ≤ εs

(69)

where E s is modulus of elasticity of the steel. The ultimate stress f u (cor ) and ultimate strain reinforcement εu (cor ) are represented schematically in Fig. 11 (see Brant 2019). Equations (70)–(74) enable the respective calculation of f y (cor ), ε y (cor ), εup (cor ), f u (cor ) and εu (cor ). f y (cor ) = (1 − 0.81cor ) f y0 ε y (cor ) =

f y (cor ) Es

(70) (71)

εup (cor ) = (1 − 1.72cor )εup0

(72)

f u (cor ) = (1 − 0.90cor ) f u0

(73)

Fig. 11 Stress × strain behavior of longitudinal bars

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Fig. 12 Example structure

εu (cor ) = (1 − 2.30cor )εu0

(74)

where f y0 is the yielding strength of the steel bar, εup0 is the ultimate strain of the steel bar, f u0 is the ultimate strength of the steel bar and εu0 is the ultimate strain of the steel bar. All these values correspond to the un-corroded state. The functions (70) to (74) were obtained for values of corrosion less than 30% and it should not be applied for higher levels of pitting corrosion. This methodology was applied to a specimen tested by Kearsley and Joyce (2014) that is presented in Fig. 12. The characteristic resistances of the materials are equal to 27.04 MPa for concrete and 500 MPa for steel. This procedure permits the determination of generalized interaction diagrams for the critical and ultimate moments presented, respectively, in Figs. 13 and 14. Thus, using Eqs. (67) and (68), it is also possible to obtain the interaction diagrams of R0 (cor, N ) and q(cor, N ) (see Figs. 15 and 16).

4.6 Plastic Rotation Evolution Law The following yield function of an inelastic hinge with corrosion is introduced: " " " p" f i = " A pi " − (1 − di )k0 (ci ) = "m i − (1 − di )h(ci )φi " − (1 − di )k0 (ci ) and fi ≤ 0

(75)

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25

Fig. 13 Interaction diagram between Mcr , cor and N

Fig. 14 Interaction diagram between Mu , cor and N

This yield function can also be justified on the basis of the hypothesis of equivalence in deformation (Flórez-López et al. 2015). Then, the same law indicated in Sect. 3.5 can be used to describe the evolution of the plastic rotations: ⎧ ⎨ λi = 0 i f f i < 0 or f˙i < 0 ∂ fi p φ˙ i = λi ; λ > 0 i f f i = 0 and f˙i = 0 ⎩ i ∂ A pi f i > 0 impossible

(76)

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Fig. 15 Interaction diagram between R0 , cor and N

Fig. 16 Interaction diagram between q, cor and N

The yield function (75) introduces two additional parameters that depend on the corrosion level and the axial force: h and ko. The next section describes a systematic procedure for their determination.

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27

4.7 Computation of the Parameters h and k0 Figure 17 shows the graph corresponding to the equation: p

f i = m i − (1 − di )hφi − (1 − di )k0 = 0

(77)

Again, two characteristic points of this curve can be identified: (0, M p ) and (φ pu , Mu ), where M p is the yield or first plastic moment of the cross-section and φ pu is the plastic rotation associated to the ultimate moment. These two new parameters allows for the computation of the parameters h and k0 . Indeed, the expression p f i = 0 (Eq. 78) for φi = 0 and m i = M p leads to: k0 =

Mp 1 − dp

(78)

where d p is the value of damage associated to the yield moment through Eq. (66). The first plastic moment for a corroded RC element can be obtained on the basis of the scheme presented in Fig. 18. Finally, the value of h obtained from Eq. (77) for m i = Mu : Fig. 17 Bending moment to plastic rotation for an inelastic hinge

Fig. 18 Stress and strain distributions in a RC section for M p

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Fig. 19 Interaction diagram between K 0 , cor and N

h=

1 φ pu



Mp Mu − 1 − du 1 − dp

 (79)

The plastic rotation that corresponds to the ultimate moment can be computed by Eq. (80) below. φ pu = (χu − χ p )L p

(80)

where the curvatures χu and χ p are represented in Figs. 10 and 18. The parameter L p refers to the length of the plastic hinge that can be obtained using any standard expression of the theory of reinforced concrete structures (Park and Paulay 1975). Thus, for a plane frame structure subjected to pitting corrosion it is possible to compute an interaction diagram of k0 (cor, N ) and h(cor, N ) as it can be seen in Figs. 19 and 20.

4.8 Corrosion Evolution Law For the sake of simplicity, the evolution of damage and plastic rotation were described using time-independent laws. This is not possible for the corrosion internal variable since constant chemical forces induce a continuous increment of corrosion. Thus, the new evolution law needs to be time-dependent. It is then proposed to use the following expression:   ∂q ∂h 2 2 − φ p (1 − di ) c˙i = ξ Aci = Oi + ξ ln (1 − di ) ∂ci ∂ci

(81)

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29

Fig. 20 Interaction diagram between h, cor and N

Notice that for a value ξ = 0, corrosion evolution is given by the phenomenological law defined by the function O. For positive values of the parameter ξ , Eq. (81) generalizes the law including an acceleration of corrosion due to concrete cracking ∂q ∂h and ∂c in Eq. (81) can be easily or yield of the reinforcement. The derivatives ∂c i i computed from the interaction diagrams presented in Figs. 16 and 20.

4.9 Experimental Identification of Parameter ξ Otieno et al. (2010) carried out a study showing the influence of different crack width on corrosion propagation. In the experimental analysis, Cracks were produced by loading a RC beam under a three-point flexural machine. Then, the specimens were subjected to a chemical loading. Figure 21 shows the experimental results Fig. 21 Corrosion rates in cracked RC specimen, Otieno et al. (2010)

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reported in that work. This figure permits the identification of the current densities for different values of cracking state, represented in this case by the crack width. In this section, it is presented the identification of the parameter ξ considering the particular case of an element with concrete cracking but no yield of the reinforcement. Let be i 0 the initial corrosion current density of the element with no cracks (d = 0) and i 0d I the observed initial current density for a specific cracking value dI. Integration on time of the corrosion evolution law (81) allows for the computation of the corrosion current density as a function of the parameter ξ . It is then obtained the following expression:   ∂q 0.0116Rel(i 0d I − i 0 ) ξ = ∂c ∅¯ · ln 2 (1 − d I )

(82)

where the term 0.0116Rel is the same that was introduced in Sect. 2.1. Therefore, the corrosion evolution law for an inelastic hinge is becomes: c˙i = Oi +

0.0116Rel(i 0d I − i 0 ) 2 ln (1 − di ) ∅¯ · ln 2 (1 − d I )

(83)

Notice that the values of i 0 , i 0d I and dI can be identified in tests like the one represented in Fig. 21. Observe that for d i = 0, the initial corrosion evolution given by Eq. (83) is governed by the current density i 0 . In the particular case of d i = d I , the initial corrosion evolution depends only on i 0d I . If concrete damage and steel yielding happen simultaneously, the corrosion evolution law is given by:   0.0116Rel(i 0d I − i 0 ) ∂h ∂q 2 2 ln (1 − di ) − φ p (1 − di ) / c˙i = Oi + ∂ci ∂ci ∅¯ · ln 2 (1 − d I )

(84)

It can also be shown that the new model proposed in this Sect. 4 is thermodynamically admissible (Brant 2019).

5 Numerical Simulations 5.1 Simulation of a Test by Otieno et al. (2010) The objective of this section was to reproduce the PC-55 experiment by Otieno et al. (2010), by means of a numerical simulation using the corrosion-cracking coupling model proposed in this work. The structure to be analyzed is a reinforced concrete simply supported beam with characteristic concrete strength equal to 32.5 MPa and yield stress equal to 550 MPa. This beam can be seen in Fig. 22.

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31

Fig. 22 Beam to be analyzed

It was imposed a load P equal to 19.2 kN in order generate a damage of 0.28 at hinge 2, which corresponds to a crack width of, approximately, 0.40 mm. After the application of this loading the structure was subjected to a chemical loading that generates an initial corrosion current density of 0.1 µA/cm2 in the undamaged hinge and 0.87 µA/cm2 in the cracked one as indicated in Fig. 21. The time to start corrosion of the reinforcement was two weeks. The results are shown in the graph in Fig. 23. It shows corrosion evolution in hinge 1 (c11 ) and hinge 2 (c12 ).

5.2 Application of the Model in the Analysis of a Reinforced Concrete Frame In this section, the analysis of a reinforced concrete frame is presented (see Fig. 24). The strength of concrete is 32.5 MPa and yield stress of the steel bars is 550 MPa, as in Otieno et al. (2010). The structure was first subjected to the permanent load: g = 19.0 kN/m. The bending moment distribution corresponding to an elastic analysis is shown in Fig. 25. The mesh of three elements and four nodes, which was used for the inelastic analysis, is also presented in Fig. 25. Nodes 1 and 4 correspond to the frame supports, node 2 to position where the value of the elastic positive moment was maximum in the beam and node 3 to position where there is the connection between beam and column. Then the force was kept constant during the rest of the simulation. Next, a corrosion process based on the experimental results presented in Fig. 21 was initiated. Therefore, the initiation time was equal to 2 weeks, the initial corrosion density for

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Fig. 23 Corrosion simulation in cracked RC example beam

the un-damaged stated is equal to 0.1 and 0.87 µA/cm2 for a damage of 0.28. It was assumed that the corrosion evolution follows the Vu and Stewart’s model (Eq. 4). The analysis of the structure followed the flowchart represented in Fig. 26. The results of the analysis are presented in Figs. 27, 28, 29, 30 and 31. Figure 27 shows the damage distribution map at the end of the simulation (60 years) and Fig. 28 its evolution on time. Two plastic hinges were activated due to corrosion propagation at points 12 and 22 of the structure. This happened after 45 years of corrosion and can be seen in Fig. 29. Corrosion evolution is presented in Fig. 30. Notice that the corrosion state variable increases much faster in the damaged hinges as theoretically expected, since the cracking of the concrete facilitates the penetration of aggressive agents from the medium (chloride ions, in this case). Finally, the evolution of the corrosion current density (i cor ) is presented in Fig. 31. Notice that the graph of the current densities for the hinges with low or no damage follows the evolution predicted by the Vu and Stewart’s model. The behavior is completely different for the hinges at the maximum bending-moment section. The new model predicts an acceleration of the corrosion current density. Its initial value is neither the un-cracked one (0.10 µA/cm2 ) nor the identification one (0.87 µA/cm2 )

Durability and Service Life Prediction of Reinforced Concrete …

33

Fig. 24 Frame to be analyzed

Fig. 25 Elastic bending moment diagram

but it was computed by the model taking into account that the damage produced by the mechanical load was not 0 or 0.28.

6 Final Remarks and Conclusions Two main ideas are proposed in this chapter. The first one is a procedure for the inclusion of any corrosion current density law that could be presented as a function O into the analysis of complex structures. As a result, a specific corrosion law can be

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Fig. 26 Schematic flow diagram of the model

Fig. 27 Damage map in the frame

transform into damage and plastic rotation values as well as service life prediction. For this analysis, only the blueprint of the structure and the history of thermochemical and mechanical loadings are needed. The end of the service life of a structure can be defined in many ways; for instance, when some critical damage value is reached; or more conservatively, when plasticity appears in the structure for the first time. The procedure also permits an estimation of the time for the total collapse due to the

Durability and Service Life Prediction of Reinforced Concrete …

35

Fig. 28 Damage evolution in time

advent of a plastic mechanism. The last example of this chapter intends to show how this service life could be determined. The second idea of the chapter is a rational procedure for the generalization of the current densities laws in order to include the effect of initial cracking and cracking evolution of the concrete. This procedure is based on the concepts of the thermodynamics of frames and a Gibbs energy potential. For the extension, only the values of the current density for two damage states are needed. On the other hand, this chapter does not deal with very important aspects of the corrosion phenomena. The first is the initiation time that in this chapter is considered as data of the problem. The determination of the initiation time and the influence of concrete cracking on it is a complex phenomenon that perhaps admits a thermodynamic analysis as the one used in this chapter. The second aspect is that chloride induced is not the only corrosion mechanism. Others equally important, as carbonation of concrete, were completely ignored. Even within the scope of this work there are some limiting aspects. The first one is the restrictions of the empirical expressions (70) to (74). These equations can be improved using a more general experimental data base and a more sophisticated interpolation procedure. The second one is the use of time-independent models for

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Fig. 29 Plasticity values in time

the generalized deformation, plasticity and damage. It is true that, as the phenomena occurs in very long periods of time, time-independent can be a good approximation. However, the parameters and values used in the simulations should be adjusted accordingly and this is a subject that was not treated in the chapter.

Durability and Service Life Prediction of Reinforced Concrete …

Fig. 30 Corrosion evolution

Fig. 31 Corrosion rates simulation in cracked RC frame

37

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C. A. C. Brant et al.

Acknowledgements We should thank the Coordination for the Improvement of Higher Education Personnel (CAPES) and the National Council for Scientific and Technological Development (CNPq) for the support and funding of the study.

References Brant CAC (2019) Formulação termodinâmica do acoplamento corrosão-fissuração em estruturas de concreto armado. Dissertação de mestrado em preparação. UNILA-PPGECI, Foz do Iguaçu, pp 1–129 Coelho KO (2017) Modelos numéricos aplicados à modelagem probabilística da degradação mecânica do concreto e corrosão de armaduras. Dissertação de Metrado (Mestrado em engenharia de estruturas). São Carlos, pp 25–35 Flórez-López J, Marante ME, Picón R (2015) Fracture and damage mechanics for structural engineering of frames. IGI Global, Hershey, pp 1–83 Kearsley EP, Joyce A (2014) Effect of corrosion products on bond strength and flexural behaviour of reinforced concrete slabs. J South Afr Inst Civ Eng 56(2):21–29 Koch GH (2002) Historic congressional study: corrosion cost and preventive strategies in the United States. A supplement to materials performance. NACE International, Houston Lemaitre J, Chaboche JL (1990) Mechanics of solid materials. Cambridge University Press, New York, pp 37–65 Liu Y, Weyers RE (1998) Modelling the time-to-corrosion cracking in chloride contaminated reinforced concrete structures. ACI Mater J Lubarda VA (2004) On thermodynamic potentials in linear thermoelasticity. Int J Solids Struct 41:7377–7398 Martínez I, Andrade C (2009) Examples of reinforcement corrosion monitoring by embedded sensors in concrete structures. Cem Concr Compos 31 Otieno MB, Alexander MG, Beushausen HD (2010) Corrosion in cracked and uncracked—influence of crack width, concrete quality and crack reopening. Mag Concr Res 6(62):393–404 Otieno M, Beushausen H, Alexander M (2011) Prediction of corrosion rate in RC structures—a critical review. In: Modelling of corroding concrete structures, Spain Otieno M, Beushausen H, Alexander M (2012) Prediction of corrosion rate in reinforced concrete structures—a critical review and preliminary results. Mater Corros 63(9):777–790 Park R, Paulay T (1975) Reinforced concrete structures. Christchurch Pettersson K, Jorgensen O (1996) The effect of cracks on reinforcement corrosion in highperformance concrete in a marine environment. In: Proceedings of the 3rd ACI/CANMET international conference on the performance os concrete in the marine environment, St. Andrews-by-the-Sea, Canada Possan E, Andrade JJO, Dal Molin DCC (2018) A conceptual framework for service life prediction of reinforced concrete structures. J Build Pathol Rehabil 3:1–11 Proença SPB (2000) Fundamentos da termodinâmica dos sólidos. Apostila: introdução à mecânica do dano e fraturamento. EESC-USP, São Carlos, p 10 Scott AN, Alexander MG (2007) The influence of binder type, cracking and cover on corrosion rates of steel in chloride-contaminated concrete. Mag Concr Res Shaw BA, Kelly RG (2006) What is corrosion? Electrochem Soc Interface 24–26 Stewart MG (2004) Spatial variability of pitting corrosion and its influence on structural fragility and reliability of RC beams in flexure. Struct Saf 454 Suzuki K et al (1990) Mechanism of steel corrosion in cracked concrete. In: Corrosion of reinforcement in concrete. Society of Chemical Industry, London Swalin RA (1972) Thermodynamics of solids, 2nd edn. Wiley-VCH, Minneapolis

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Val DV, Melchers RE (1997) Reliability of deteriorating RC slab bridges. J Struct Eng ASCE 123(12):1638–1644. https://doi.org/10.1061/(ASCE)0733-9445(1997)123:12(1638) Vu KAT, Stewart MG (2000) Structural reliability of concrete bridges including improved chlorideinduced corrosion models. Struct Saf 22:313–333 Yalcyn H, Ergun M (1996) The prediction of corrosion rates of reinforcing steels in concrete

Service Life and Durability of Reinforced Concrete Structures Present in Marine Environment Carlos Eduardo Tino Balestra

Abstract Reinforced concrete structures present in the marine environment are subject to physical attacks, due to the waves collision against the concrete structures, and chemical attacks, due to the presence of the different ions present in seawater that react both with the concrete and the reinforcement leading to structure’s degradation. In this sense, marine environment is characterized as one of the most aggressive to coastal reinforced concrete infrastructures. Thus, this chapter deals with the aggressiveness of the marine environment towards these structures, taking into account since the different mechanisms of substance penetration in the different marine aggressive zones up to recent empirical models for service life prediction of structures present in this environment. It is expected to contribute to a better understanding of the marine environment effects on the degradation of reinforced concrete structures, allowing the managers responsible for the conservation of these structures to have a bibliographic tool easy to read that helps in their decision making about the service life of concrete structures present in marine environment. Keywords Marine environment · Reinforced concrete structures · Chlorides · Sulfates · Service life · Durability

1 Introduction A significant portion of the cities in the world have been developed in coastal regions due to the historical and economic importance of navigation. Thus, to support this maritime modal, maritime structures have been built, playing an important role in trade relations between nations until nowadays. Considering the known of mechanical concrete properties and its resistance against water and fire combined with easy workability and low materials cost, several marine infrastructures have been built in reinforced or prestressed concrete (Mehta and Monteiro 2006). In the context of reinforced concrete structures present in the marine environment, and therefore susceptible to degradation in this environment, we can mention C. E. T. Balestra (B) Federal University of Technology—Paraná, Toledo, Brazil e-mail: [email protected] © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2020 J. M. P. Q. Delgado (ed.), Building Pathology, Durability and Service Life, Building Pathology and Rehabilitation 12, https://doi.org/10.1007/978-3-030-47302-0_2

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the existence of structures for different purposes, such as nuclear power generation plants, piers, bridges and off-shore platforms destined for the oil and gas extraction that can be built kilometers far from the coast. In addition to these, in recent years the construction of offshore platforms to allocate new airports, power plants and garbage dumps should be considered (Mehta and Monteiro 2006; Oh and Jang 2007; Li and Shao 2014; Samarakoon and Ratnayake 2013; Da Costa et al. 2013). It should be first pointed that the high alkaline pH of the solution present in the concrete pores (pH 12–13) protects the reinforcement against the corrosion effects through the formation of an iron oxide film that coats and protects the bars inside concrete. This film, called passive film, has a thickness varying between 10 and 50 μm and, in high alkaline medium; it is impermeable and highly adherent to the bars surface. In this sense, it is possible to consider that reinforcements in concrete are protected both chemically and physically, chemically through the passive film, and physically, due to the concrete cover layer. The joint action of these protection mechanisms guarantees, in theory, the structural safety of a reinforced concrete structure, ensuring the maintenance of the steel cross section and complete adherence and, consequently, transmission of loads in the steel-concrete system (Mehta and Monteiro 2006; Apostolopoulos 2009; Apostolopoulos et al. 2013; Han et al. 2014). Although, concrete is a cementitious material that presents an interconnected pores network and voids due to spaces not occupied by cement hydration products. In this case, aggressive environmental agents, as chlorides, sulfates and magnesium, ends up penetrating and reacting both with the hydrated constituents of the Portland cement paste (by hydrolysis of cement paste components or cation-exchange reactions for example) and/or with the reinforcement (leading to its corrosion) (Mehta and Monteiro 2006; Claisse 2019). Furthermore, almost all chemical elements present in the periodic table are present in seawater, with emphasis on the presence of chlorides, sulfates and magnesium. In this way, the iteration of these aggressive constituents with the concrete or the reinforcement ends up leading to the degradation of the concrete structures present in the marine environment. The distribution of the main chemical elements present in seawater is shown in Fig. 1 (Silva 2011). Fig. 1 Main chemical elements present in seawater (Silva 2011)

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Fig. 2 Marine aggressive zones. Adapted from Mehta and Monteiro (2006)

Overall, the marine environment can be subdivided into four main aggressive zones: the submerse zone, the tidal zone, the splash zone and the marine atmosphere zone (DuraCrete 1999). In this sense, a structural element as a pillar, for example, can having segments present in more than one aggressive zone, therefore being subject to different aggressiveness level in the marine environment depending on its position in relation to these zones. Taking a pillar as an example, Fig. 2 shows a representation of these four marine aggressive zones (Mehta and Monteiro 2006). In the submerse zone the structure (or its respective segment) remains constantly below the minimum level reached by the tide or, in other words, completely submerged. In this case, due to the low oxygen availability, reinforcement corrosion is not frequently observed, consequently, the attacks on concrete structures concentrated in the reactions resulting from the iteration of the hydrated constituents of the cement paste with chemical elements present in sea water, for example, sulfates and magnesium. In other marine aggressive zones, reinforcement corrosion is a frequent phenomenon to be observed (Mehta and Monteiro 2006; Claisse 2019; Andrade 2001). The sulfate attack comes mainly from reactions involving calcium hydroxide and hydrated calcium aluminate in the hardened cement paste, leading to the expansion and cracking of the concrete due to the formation of gypsum and calcium sulfoaluminates. In addition, the attack by sulfates can also lead to a loss of cohesion between cement hydration products, resulting in concrete mass loss and strength. In the case of magnesium, this, in addition to being able to react with calcium hydroxide and form soluble salts, the attack of this ion extends to hydrated calcium silicate (C–S– H), where calcium ions can be partially or totally replaced by magnesium through cation-exchange reaction, leading to a reduction in the concrete properties (Mehta and Monteiro 2006; Claisse 2019; Neville and Brooks 2010; Maes and De Belie 2014).

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The tide zone comprises the maximum and minimum levels reached respectively by high and low tide. This is one of the most aggressive zone from the reinforcement corrosion perspective, since this zone is subject to wetting and drying cycles that enhance the chlorides penetration (Chlorides are the main agent responsible for the reinforcement corrosion process in marine environment) through the pore network in the layers closest to the concrete surface known as the convection zone. In addition, the structures present in this zone are subject to the mechanical action of the waves, which produces an abrasion effect on the concrete surface (Safehian and Ramezanianpour 2014). During the wetting cycles, water containing aggressive agents penetrates through the concrete pores due to capillary tensions acting in the capillary pores. This is the mainly way how chlorides can ingress into concrete, leading to the structure degradation by reinforcement corrosion. On the other hand, during the drying periods, water present in the concrete pores is lost through evaporation, consequently the salt concentration increase in the concrete pores in the convection zone. The continuous process of wetting drying cycles contributes to increase the chloride concentration in the concrete pores (Mehta and Monteiro 2006; Neville and Brooks 2010). The wetting drying cycles are also active in the splash zone that is located above the high tide level. In this case, the breaking of the sea waves ends up generating the splashes that reach the structures. The height of this aggressive zone is dependent on the sea agitation and the intensity of breaking waves; however it has been observed that in general this zone is located close to 50 cm above the maximum level of the tide zone. Splash zone is a very aggressive zone for reinforced concrete structures from the reinforcement corrosion perspective, since, in addition to the wetting and drying cycles, there is also a high availability of chlorides and oxygen for the corrosion reactions. In this way, it is possible to affirm that tidal and splash zones are the most aggressive zones from the reinforcement corrosion perspective (Valipour et al. 2014; Guimarães et al. 2003). Finally, in the marine atmosphere zone, the structures do not come into direct contact with sea water, but are subject to the effects of the salt fog present in this environment. This fog, is constituted of saline droplets (mainly composed of sodium chloride from sea) formed due to the breaking waves. This saline droplet are carried by the winds actions and can be deposited on concrete surfaces up to 1.5 km from the coast (depending on intensity of the winds, the presence of obstacles such as trees and the gravitational forces acting on the droplets as a function of their mass). Thus, buildings located relatively far from the sea (approximately 1 km) are also subject to these attacks, justifying the degradation of structures in the coastal cities that are not in direct contact with sea water (Meira et al. 2010, 2014). Regarding the reinforcement corrosion of concrete structures present in the marine environment, the chlorides present in the water and in the sea fog are the main agents responsible for triggering the degradation process. When chlorides reach a certain concentration in the reinforcement region (see Table 1), they trigger a type of corrosion known as pits (Fig. 3) that are characterized by located corrosion points on the surface of the reinforcement that deepen as the corrosive process progresses (Meira et al. 2010, 2014; Zezza and Macri 1995).

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Fig. 3 Small reinforcement pit corrosion detail observed in optical micrograph image

When chloride concentration exceeds a certain value (detailed in Table 1), called as chlorides threshold, the passive film is locally destroyed even the medium showing highly alkaline pH values. By the way, there is a local acidification on the reinforcement surface and a self-catalytic process of iron chloride formation is started. In other words, after breaking the passive film, chlorides (Cl− ) combine with metallic iron (Fe2+ ) producing iron chloride (FeCl2 ) and, consequently, removing the metallic material from the reinforcement. This FeCl2 dissociates in the solution present in the concrete pores allowing the formation of iron oxides and hydroxides (FeO·(H2 O)x ) Table 1 Chlorides threshold values according to standards Standard

Chloride threshold

Observation

BS 8500-1 (British Standard 2006)

0.4%

In relation to cement mass

ACI 318 (American Concrete Institute 2011)

0.15%

In relation to cement mass

EN 206-1 (European Standard 2006)

0.4%

In relation to cement mass

EN 206-1 (European Standard 2006)

0.2%

In relation to cement mass using sulfate resistance cement

NBR 12655 (Brazilian Association of Technical Standards 2015)

≤0.15%

In relation to cement mass for structures exposed to chlorides

JSCE SP-2 (Japan Society of Civil Engineering 2005)

0.60 kg/m3

In relation to concrete mass

CEB-FIB, Bulletin nº 183 (Comité Euro-International Du Béton 1992)

0.05 at 0.1%

In relation to concrete mass

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C. E. T. Balestra

with the hydroxyls (OH− ) present in the solution pores. These iron oxides and hydroxides, called as corrosion products, are deposited in the vicinity of reinforcements, allowing the chlorides to return to metallic surface in order to continue the corrosion in a self-catalytic process (Mehta and Monteiro 2006). Chlorides threshold to break the passive film and start the reinforcement corrosion is presented by different standards, as shown in Table 1, however, in the literature itself different values are observed in relation to this limit concentration, since this concentration is affected by the characteristics of the concrete (carbonation, cement type, for example) and the iron composition. In any case, the limit value equal to 0.4% in relation to cement mass has been an accepted value for a significant part of the researches observed in the literature for non-carbonated concretes. It is worth mentioning that pitting corrosion in the marine environment, due to the chlorides action, leads to intense and rapid structure degradation, leading to a fast decrease of the load carrying capacity of the structure, which can cause sudden collapases in extreme cases. This is the reason why reinforcement corrosion in structures present in the marine environment has been the subject for the development of several research fronts. Reinforcement corrosion is one of the main pathologies observed in reinforced concrete structures. The corrosion effects lead to the formation of corrosion products composed of iron oxides and hydroxides that have expansive characteristics, that is, its present a higher volume in relation to the metal consumed in the corrosion process may even reaching variations of up to 600% in relation to the metal originally consumed in the process, as seen in Fig. 4. From this corrosion mechanism, three intervening factors are preponderant and should be pointed (Mehta and Monteiro 2006; Apostolopoulos 2009; Apostolopoulos et al. 2013; Han et al. 2014; Claisse

Fig. 4 Volumetric expansion caused by corrosion products. Adapted from Mehta and Monteiro (2006)

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2019; Safehian and Ramezanianpour 2014; Valipour et al. 2014; Guimarães et al. 2003; Meira et al. 2010, 2014): 1. As the corrosive process develops, there is a progressive reduction in the reinforcement’s cross section, leading to a continuous process of mechanical properties decrease, mainly regarding its ductility (ability to withstand strains without fracture). 2. Reinforcement corrosion products are deposited around the bars, exerting tensions in the radial direction to the reinforcement axis. These stresses are not supported by the limited plastic strain presented by concrete and ends up leading to cracking and subsequent detachment of the cover layer. 3. As the corrosion products are deposited on reinforcements, the monolithism (the adherence between the bars and concrete) is impaired, impacting the internal load transfer between them. Studies have shown that pitting corrosion ends up significantly reducing the mechanical properties of steel bars when subjected to tensile stress, mainly regarding the ductility of the bars. In this case, pitting corrosion can generate different geometric defects in the bars as it deepen, that is, the pits can be small in diameter, but deeper or, on the other hand, being shallow and wide. Anyway, pits generate geometric defects by changing the position of the reinforcement axis, generating eccentricities that impair reducing the reinforcement mechanical properties, as shown in Fig. 5 (Zhu and François 2014). One way to analyze the corrosion impacts on the mechanical properties of reinforcement is through the corrosion degree, defined as the bars mass variation (Fig. 6) (Apostolopoulos 2009; Apostolopoulos et al. 2013). However, although this is the most commonly used methodology to analyze the decrease in the mechanical properties of the corroded bars, this analysis type is not able to observe the damage produced by corrosion pits in the reinforcement cross section, since it is not possible to determine the pits depth. For this reason, the interpretation of the analyzed data using corrosion degree should be done judicious by Engineers (Balestra et al. 2016). Anyway, it is consensual in the literature that corrosion leads to a decrease in the mechanical properties of reinforcement as the corrosion degree increases, regardless

Fig. 5 Representation of geometry and axis eccentricities produced by pitting corrosion

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Fig. 6 Representation of corrosion effects on mechanical properties of corroded reinforcement

of whether the analyzes are conducted by accelerated processes in laboratory (using salt spray chamber or mechanical simulations) or by natural corrosion processes (Mehta and Monteiro 2006; Apostolopoulos 2009; Apostolopoulos et al. 2013; Han et al. 2014; Claisse 2019; Safehian and Ramezanianpour 2014; Valipour et al. 2014; Guimarães et al. 2003; Meira et al. 2010, 2014; Zhu and François 2014; Balestra et al. 2016).

2 Aggressive Environment Agents: Penetration Mechanism Regarding the mechanisms of fluid penetration in concrete, it should pointed that most of the transport mechanisms in porous media result from a potential generator of a mass flow (Eq. 1), consequently, this mass flow is dependent of the potential gradient allied to the material properties at a given depth. In this way, the distribution, dimension and interconnectivity between the pores play a key role for the penetration of aggressive substances from the environment into concrete (Nilsson and Tang 1996).   qm = −Kψ · ∂ψ /∂x

(1)

where qm is the mass flow; kψ is the material’s properties coefficient; ∂ψ is the Potential gradient and x is the Depth. For concrete structures present in the four marine aggressive zones, we can highlight the permeability, capillary absorption and ionic diffusion as the main active mechanisms for penetration of aggressive ions as chlorides, sulfates and magnesium. The first mechanism occurs through hydraulic pressure gradients and, in general, occurs in submerged structures (submerse zone), being governed by Darcy’s laws where the coefficient related to the material’s properties takes into account

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the relationship between its permeability and the viscosity of the penetrating fluid (Nilsson and Tang 1996; Nepomucemo 2005). The capillary absorption mechanism is related to capillary tension acting in the concrete pores. In general, this mechanism occurs in the concrete layers (unsaturated concrete) closest to the surface in marine aggressive zones subject to wetting and drying cycles. On this point, during wetting periods, when water comes into contact with concrete surface, aggressive ions as chlorides in the marine environment penetrate together with water in the microstructure concrete pores through capillary tension, while in the drying periods, the water flow is reversed due to the drying of the concrete pores, leaving chlorides present in the concrete pores. In this sense, with each cycle, the chloride concentration increases inside the concrete up to a certain limit depending on the concrete characteristics and its ability to store chlorides in the pores (Mehta and Monteiro 2006; Neville and Brooks 2010). At this point, the author of this chapter has already observed chloride concentrations up to 1.6% in relation to the concrete mass in field structures present for more than 40 years in splash zone (Balestra et al. 2019a). Furthermore, the concrete layers closest to surface where the predominant water absorption mechanism is known as convection zone, where it is possible to observe an increase in the concentration of chlorides up to a maximum concentration (peak) in chloride profiles. Chloride profiles are representations of the variation in chloride concentration as a function of depth from the concrete surface, as shown in Fig. 7 (Andrade et al. 2015). The most commonly method to determine total chloride concentration in concrete is related to the use of a silver nitrate solution in powder concrete samples (RILEM Recommendation 2010). The third mechanism is governed by the first and second Fick’s Law of diffusion, which characterize mass flows due to concentration gradients. This mechanism, in general, occurs in the concrete inner layers due to the difference in concentration between the layers closest to the surface and the deeper concrete layers. In the chloride profiles, this diffusion zone, where diffusion mechanism is predominant, is observed after the peak of maximum chloride concentration, considering that the mobility of Fig. 7 Chloride profile representation

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the chlorides is more difficult and slower in this concrete region (Vieira et al. 2018; Wang et al. 2018; Othmen et al. 2018). Chloride profiles represented in Fig. 7 have been used for mathematical modelling in order to estimate the service life of reinforced concrete structures present in marine environment. In this sense, the most common analysis performed with chloride profiles consists in consider only diffusion zone. For this the concentration axis is positioned in the peak, being the analysis performed using the Second Fick’s Law solution (Eq. 2) considering predominantly the diffusion zone (Liang et al. 1999). One explanation about this issue is related to the reinforcement position since, in general, they are located in diffusion zone. Furthermore, as convection zone is subject to wetting drying cycles, chloride concentration in this zone can significant varies during the cycle’s occurrence. However, empirical models already exist, as through the Modified Holliday Equation (Eq. 3), based on field structures present for more than 40 years in marine aggressive zone (Balestra et al. 2019a). This model can take into account the convection zone without the transference of the concentration axis to the peak. Although Eq. (3) has been recently presented in the literature, more studies are necessary in different conditions of exposure.  √  C(x, t) = Cs + (Ci−Cs) · erfc x/ (4Dt)

(2)

    C(x, t) = 1/ R1 · 1 + (x − R3)2 /(Dt)

(3)

where C(x, t) is the chloride concentration in concrete in relation to depth (x) and time (t); Ci is the initial chloride concentration in concrete; Cs is the surface chloride concentration in concrete; erfc (z) is the Gauss error function; x is the concrete depth from surface (in centimeters in Eq. 3); t is the time; D is the diffusion coefficient in concrete; 1/R1 is the maximum chloride concentration at the peak; and R3 is the peak position from the concrete surface (in centimeters). In addition to these points, another consideration refers to the iteration between chlorides and cement hydration products. In the specific case, as chlorides penetrate through the pore network, these combine with the aluminate phases forming Friedel’s salt (C3 A·CaCl2 ·10H2 O) and Kuzel’s salt (3CaO·Fen On + 1 ·CaCl2 ·10H2 O) restricting chloride mobility through concrete pores delaying its arrival to the region of the reinforcements to trigger the corrosive process. However, effects, such as concrete carbonation, can ends up causing the release of these chlorides, making them free to move and participate in the corrosive process of the bars. The image detection of Friedel’s and Kuzel’s salt by SEM (Scanning Electron Microscopy) and the knowledge about the mechanism that influence the stability of these salts are still a challenge and have been the subject of researches (Backus et al. 2013; Kuosa et al. 2014; Saillio et al. 2014).

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3 Evaluation of Concrete Structures by Nondestructive Test The evaluation of field structures can be carried out through tests that can require the extraction of concrete cores and subsequently analysis in the laboratory, however, often due to the difficulties observed in field, such as accessibility to certain points of a structure with equipment for the extraction of concrete cores, the presence of reinforcements that can be sectioned in the act of collecting concrete cores and time consuming for analysis, ends up making this an difficult issue. In this way, nondestructive tests have been performed in field structures since the methodologies are simple and fast reliable results can be obtained, where emphasis has been given to concrete electrical resistivity for the analysis of durability and service life of these structures (Nguyen et al. 2017, 2018). The electrical resistivity is a material’s property and is governed from Ohm’s Law, dealing with the material’s resistance to the electric charge flow. Concrete, when it is wet, behaves like a semiconductor with electrical resistivity of the order of 104 . cm and, when dried, it acts as an electrical insulator, with resistivity of the order of 1011 . cm. As the reinforcement corrosion is a predominantly electrochemical process that occurs in an aqueous medium, the determination of the electrical resistivity allows to indirectly evaluating the chloride ions mobility through the pore network of the hardened concrete, being possible to analyze the protection degree of the concrete against the reinforcement corrosion (Neville and Brooks 2010). For the evaluation of the concrete electrical resistivity, the four-point method proposed by F. Wenner in 1915 has been the most used. The method is simple and based on the contact of four electrodes on the material surface, where, the external electrodes generate a current that is measured by the internal ones, determining the electrical resistivity of the material as represented in Fig. 8 (Chen et al. 2014; Sengul 2014). In this sense, several standards and studies have correlated the probable corrosion rate with the concrete electrical resistivity, as shown in Table 2.

Fig. 8 Representation of the concrete electrical resistivity test

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Table 2 Values of electrical resistivity (k cm) associated with the probability of corrosion occurring Reinforcement corrosion probability

References

Very high

High

Moderate

Low

Very low

Negligible

–

100

RILEM TC 154-EMC (RILEM Recommendation 2010)

–

20

–

CEB 192 (Comité Euro-International Du Béton 1989)

–

141.1

Azarsa and Gupta (2017)

–

12

–

–

Smith et al. (2004)

100

Polder (2001)

80

Balestra et al. (2019b)

4 Conclusions Marine environment is characterized as one of the most aggressive environment to reinforced concrete structures, since the iteration between sulfate and magnesium ions and cement matrix and the iteration between chloride ions and the reinforcements, end up leading to both degradation. In this sense, the main conclusions that can be draw from this chapter can be listed below: • The iteration between sulfates and magnesium ions present in sea water with cement matriz ends up leading to concrete cracking due to their reactions with the hydrated constituents of the Portland cement paste. In this case, cracking enhance the ingress of these and other ions, allowing the faster degradation of the inner concrete layers. • Reinforcement corrosion has a significant impact on bars mechanical properties, mainly regarding its ductility. As the corrosion degree intensifies, the mechanical properties of the reinforcements are lower and, consequently, the safety and structural bearing capacity of the structures decrease. • The main penetration mechanisms into concrete are permeability, capillary absorption and ionic diffusion. In this case, the performance of wetting and drying cycles, in non-submerged structures, ends up potentiating the penetration of aggressive agents such as chlorides that promotes reinforcement corrosion. • Regarding chlorides penetration modeled from chloride profiles, although the durability modeling have been performed by diffusion analysis through the displacement of the concentration axis to the chloride profile peak position, there are already empirical mathematical models capable of taking into account the effects observed in the convection zone for field structures analysis as the Modified Holliday Equation presented in Balestra et al. (2019a).

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• Concrete electrical resistivity has been used as one of the main non-destructive techniques for structural analysis, since it is a simple technique with fast reliable results. In this case, several technical standards have pointed closed values relating the electrical resistivity with the probable reinforcement corrosion risk.

References American Concrete Institute (2011) ACI 318: 2011: building code requirements for structural concrete. American Concrete Institute, Farmington Hills Andrade JJO (2001) Contribution to service life prediction of reinforced concrete structures attacked by reinforcement corrosion: initiation by chlorides. Doctoral thesis, Federal University of Rio Grande do Sul, Porto Alegre, pp 277f (in Portuguese) Andrade C, Climent MA, De Vera G (2015) Procedure for calculating the chloride diffusion coefficient and surface concentration from a profile having a maximum beyond the concrete surface. Mater Struct 48:863–869 Apostolopoulos CA (2009) The influence of corrosion and cross-section diameter on the mechanical properties of B500c steel. J Mater Eng Perform 18(2):190–195 Apostolopoulos CA, Demis S, Papadakis VG (2013) Chloride-induced corrosion of steel reinforcement: mechanical performance and pit depth analysis. Constr Build Mater 38:139–146 Azarsa P, Gupta R (2017) Electrical resistivity of concrete for durability evaluation: a review. Adv Mater Sci Eng 1–30 Backus J et al (2013) Exposure of mortars to cyclic chloride ingress and carbonation. Adv Cem Res 25(1):3–11 Balestra CET et al (2016) Corrosion degree effect on nominal and effective strengths of reinforcement naturally corroded. J Mater Civ Eng 28(10):04016103 Balestra CET, Reichert TA, Pansera WA, Savaris G (2019a) Chloride profile modeling contemplating the convection zone based on concrete structures present for more than 40 years in different marine aggressive zones. Constr Build Mater 198:345–358 Balestra CET, Nakano AY, Savaris G, Medeiros-Junior RA (2019b) Reinforcement corrosion risk of marine concrete structures evaluated through electrical resistivity: proposal of parameters based on field structures. Ocean Eng 187:106167 Brazilian Association of Technical Standards (2015) NBR 12655:2015. Portland cement concrete: preparing, control, receive and acceptance. Rio de Janeiro, 29 pp (in Portuguese) British Standard (2006) BS 8500-1: 2006: concrete: complementary British Standard to BS EN 206-1: part 1: method of specifying and guidance for the specifier, 2nd edn. London, 66 pp Chen CT, Chang JJ, Yeih W (2014) The effects of specimen parameters on the resistivity of concrete. Constr Build Mater 71:35–43 Claisse P (2019) Materials of civil construction, 1st edn. Elsevier, London, 540 pp Comité Euro-International Du Béton (1989) Bulletin D’ information Nº 192: 1989: diagnostic and assessment of concrete structures. Thomas Telford Services, Lausanne, 130 pp Comité Euro-International Du Béton (1992) Bulletin D’ information Nº 183: 1992: durable concrete structures, 2nd edn. Telford Services, Lausanne, 122 pp Da Costa A et al (2013) Modelling of chloride penetration into non-saturated concrete: case study application for real marine offshore structures. Constr Build Mater 43:217–224 DuraCrete (1999) Models for environmental actions on concrete structures: DuraCrete, probabilistic performance based durability design of concrete structures [S.l.]. CUR, 273 pp. ISBN 9789037604009 European Standard (2006) EN 206-1: 2006: concrete: part 1: specification, performance, production and conformity. London

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Guimarães ATC, Castagno JRR, Helene PRL (2003) Intensity of chloride attack: considerations about concrete distance in relation to sea water. Teor Prát Eng Civ 3:73–79 (in Portuguese) Han SJ et al (2014) Degradation of flexural strength in reinforced concrete members caused by steel corrosion. Constr Build Mater 54:572–583 Japan Society of Civil Engineering (2005) JSCE SP-2: 2005: standards on test method for diffusion coefficient of chloride ion in concrete. Concrete Committee, Tokyo, 57 pp Kuosa H et al (2014) Effect of coupled deterioration by freeze-thaw, carbonation and chlorides on concrete service life. Cem Concr Compos 47:32–40 Li J, Shao W (2014) The effect of chloride binding on the predicted service life of RC pipe piles exposed to marine environments. Ocean Eng 88:55–62 Liang MT et al (1999) Service life prediction of reinforced concrete structures. Cem Concr Res 29:1141–1418 Maes M, De Belie N (2014) Resistance of concrete and mortar against combined attack of chloride and sodium sulphate. Cem Concr Compos 53:59–72 Mehta PK, Monteiro PJM (2006) Concrete: microstructure, properties and materials, 3th edn. McGraw Hill, New York, 674 pp Meira GR et al (2010) Durability of concrete structures in marine atmosphere zones: the use of chloride deposition rate on the wet candle as an environmental indicator. Cem Concr Compos 32:427–435 Meira GR et al (2014) Analysis of chloride threshold from laboratory and field experiments in marine atmosphere zone. Constr Build Mater 55:289–298 Nepomucemo AA (2005) Concrete mechanism of fluid transport, Chap 26. In: Isaia GC (ed) Concrete: education, research and realizations, vol 2. IBRACON, São Paulo, pp 793–828 Neville AM, Brooks JJ (2010) Concrete technology, 2nd edn. Pearson, London, 448 pp Nguyen AQ, Klyz G, Derby F, Balayssac J-P (2017) Evaluation of water content gradient using a new configuration of linear array four-point probe for electrical resistivity measurement. Cem Concr Compos 83:308–322 Nguyen AQ, Klyz G, Derby F, Balayssac J-P (2018) Assessment of the electrochemical state os steel in water saturated concrete by resistivity measurement. Constr Build Mater 171:455–466 Nilsson LO, Tang L (1996) Transport mechanisms in porous materials: an introduction to their basic laws and correlations. In: International congress on modeling of microstructure and its potential for studying transport properties and durability. Proceedings [S.l.]. Kluwer, Saint-Rémy-lésChevreuse, pp 289–311 Oh BH, Jang SY (2007) Effect of material and environmental parameters on chloride penetration profiles in concrete structures. Cem Concr Res 37:47–53 Othmen S, Bonnet F, Schoef S (2018) Statistical investigation of different analysis methods for chloride profiles within a real structure in a marine environment. Ocean Eng 157:96–107 Polder RB (2001) Test methods for onsite measurement of resistivity of concrete—a RILEM TC— 154. Constr Build Mater 15:125–131 RILEM Recommendation (2010) TC154-EMC: electrochemical techniques for measuring metallic corrosion. Mater Struct 33:603–611 Safehian M, Ramezanianpour AA (2014) Assessment of service life models for determination of chloride penetration into silica fume concrete in the severe marine environmental condition. Constr Build Mater 48:287–294 Saillio M, Baroghel-Bouny V, Barbeon F (2014) Chloride binding in sound and carbonated cementitious materials with various types of binder. Constr Build Mater 68:82–91 Samarakoon SMSM, Ratnayake RM (2013) Residual service life prediction of offshore concrete structures with chloride-induced damage: the state of the art. In: 2013 32nd international conference on ocean, offshore and Arctic engineering. Proceedings. ASME, New York Sengul O (2014) Use of electrical resistivity as an indicator for durability. Constr Build Mater 73:434–441 Silva CAR (2011) Chemical oceanography, 1st edn. Interciência, Rio de Janeiro, 218 pp

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Smith KM, Schokker AJ, Tikalsky PJ (2004) Performance of supplementary cementitious materials in concrete resistivity and corrosion monitoring evaluations. ACI Mater J 101(5):385–390 Valipour M, Shekarchi M, Ghods P (2014) Comparative studies of experimental and numerical techniques in measurement of corrosion rate and time-to-corrosion-initiation of rebar in concrete in marine environments. Cem Concr Compos 48:98–107 Vieira DR, Moreira ALR, Calmon JL, Dominicini WK (2018) Service life modeling of a bridge in a tropical marine environment for durable design. Constr Build Mater 163:315–325 Wang Y, Wu L, Wang Y, Li Q, Xiao Z (2018) Prediction model of long-term chloride diffusion into plain concrete considering the effect of the heterogeneity of materials exposed to marine tidal zone. Constr Build Mater 159:297–315 Zezza F, Macri F (1995) Marine aerosol and stone decay. Sci Total Environ 167:123–143 Zhu W, François R (2014) Experimental investigation of the relationship between residual crosssection shapes and the ductility of corroded bars. Constr Build Mater 69:335–345

Salt Attack, Durability and Service Life of Concrete Structures Wellington Mazer, Alessandra Monique Weber, Carlos Alberto Brunhara, and Juliana McCartney Fonseca

Abstract The chapter in this book presents concepts on the durability of concrete structures directly relating to deterioration due to the attack of chloride and sulfate salts. The matter becomes necessary due to the aggressive conditions that the structure may be exposed to. In the case of sulfates, these can be present in soils, acid rain, sewage and the sea. Marine environments, on the other hand, are mainly responsible for the penetration of chlorides in concrete, another situation is the free chloride that can be present in the concrete mass and react when in large quantities. We covered the operation of chloride attack and sulfate attack, the calculation models and related life prediction and some recent studies to understand the behavior of buildings in the long term. This study becomes relevant for understanding the deterioration mechanisms that compromise durability. Keywords Sulphate attack · Chloride ion · Durability · Service life · Concrete structures

1 Introduction A reinforced concrete structure, in addition to mechanical resistance, must have adequate durability, which consists of resisting the environmental actions of the environment where it is inserted, during the period of its useful life.

W. Mazer (B) · A. M. Weber · C. A. Brunhara · J. M. Fonseca Federal University of Technology-Paraná, Apucarana, Brazil e-mail: [email protected] A. M. Weber e-mail: [email protected] C. A. Brunhara e-mail: [email protected] J. M. Fonseca e-mail: [email protected] © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2020 J. M. P. Q. Delgado (ed.), Building Pathology, Durability and Service Life, Building Pathology and Rehabilitation 12, https://doi.org/10.1007/978-3-030-47302-0_3

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According to the American Concrete Institute (2001), the durability of concrete can be defined as the ability to resist any deterioration process, for example, the action of weather, chemical agents and abrasion. Thus, it is stated that knowing the durability and useful life of the structures is of paramount importance to prevent pathological manifestations and to understand the behavior of buildings in the long term (Medeiros et al. 2011). Environmental conditions can accelerate the deterioration of a reinforced concrete structure due to its level of aggressiveness. Some of these regions are industrial environments, marine regions and cities with high levels of air pollution. Among the various deterioration agents existing in these environments are the action of sulfates, which causes the deterioration of concrete, and chloride ions, which cause the corrosion of reinforcement. According to Alexander and Beushausen (2019) corrosion occurs due to a reaction that leads to the loss of the protective oxide layer of the steel. The presence of chlorides is one of the causes of the corrosion process in reinforced concrete structures; the structure will be exposed to the action of chlorides in marine environments mainly (Aguiar 2014). The speed of entry of aggressive agents such as sulfates and chlorides depends on the present amount of these agents, on the permeability of the concrete and on the humidity (Aguiar 2014). As it are talking about the entrance of external agents in the concrete, the concrete covering has a fundamental role in the useful life of the structure, being as important the quality of the material as the depth of this layer (Alexander and Beushausen 2019). Figure 1 illustrates these important elements in the concrete cover layer. The prediction of the useful life given through calculation models is of fundamental importance for professionals in the area of concrete structures to understand the mechanisms of deterioration. This modeling foreseeing corrosion according to Félix et al. (2018) happens in two stages, the initiation and the propagation. Fig. 1 Schematic of cover layer of concrete. Source Alexander and Beushausen 2019)

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The FIB Bulletin (2006) presents deterioration prediction models, such as carbonation and chloride ingress. Lifetime designs are usually based on the period of onset of corrosion, according to authors Alexander and Beushausen (2019).

2 Sulfate Action 2.1 General Concepts According Costa (2004), among the various salts that produce harmful effects on concrete, sulfates stand out, which may have an internal or external origin to concrete. The sources of internal sulfates are the various additions present in clinker and cement (Skalny et al. 2002), whereas the external sources can be water in the soil, acid rain, sewage, and sea, among others. The degradation of the concrete due to the attack of sulfates can manifest itself through the expansion and cracking of the concrete or through the loss of mass and strength. When in solution, the magnesium, calcium, potassium, sodium and ammonium sulfates can react with the hydrated cement paste and the consequence is the breakdown of the concrete after some time. The most well-known means of sulfates attack on concrete are reactions with the hydration products of aluminates producing secondary ettringite and reactions with calcium hydroxide producing gypsum (Costa 2004). According to Mehta and Monteiro (2008) the intensity and the process of attack of sulfates varies with the concentration of the ion and the composition of the cement paste. High levels of C3 A and calcium hydroxide in the Portland cement paste increase its susceptibility to attack by sulfates (Lee and Lee 2007). In addition to C3 A, the relationship between C3 S/C2 S silicates also has an influence on the resistance of cements to attack by sulfates, and the higher this relationship, the greater the susceptibility to attack by sulfates (Al-Amoudi 2002). According to Lee and Lee (2007), C3 S hydration produces 61% C–S–H and 39% CH, while C2 S hydration produces 82% C–S–H and 18% CH. Considering that the strength of the hardened cement paste is reduced when in the presence of CH, it is expected that cements containing a greater amount of C2 S will be more resistant in environments rich in sulfates. The main types of sulfates that attack the cement paste are calcium (CaSO4 ), sodium (Na2 SO4 ) and magnesium (MgSO4 ) sulfates, in an increasing order of aggressiveness. Due to its low solubility in water, CaSO4 is considered the least aggressive sulfate to the cement paste, however there are studies that consider that the high alkalinity of the cement increases the solubility of these ions, allowing the attack to the cement paste (Drimalas et al. 2011). In Eq. 1, the reaction of CaSO4 with C3 A is presented to form the secondary ettringite, causing the expansion and cracking of the cement paste.

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3(CaSO2 · 2H2 O) + 4CaO · Al2 O3 · 19H2 O + 17H2 O → 3CaO · Al2 O3 · 3CaSO4 · 32H2 O

(1)

The Na2 SO4 can react with CH forming gypsum, as indicated in Eq. 2, and with the aluminate phases forming ettringite, as presented in Eqs. 3 and 4 (Drimalas et al. 2011; Piasta et al. 2014). Ca(OH)2 + Na2 SO4 · H2 O → CaSO4 · H2 O ↓ +2NaOH

(2)

2Na2 SO4 + 3CaO · Al2 O3 · CaSO4 · 12H2 O + 2Ca(OH)2 + 2H2 O → 3CaO · Al2 O3 · 3CaSO4 · 32H2 O + 2NaO

(3)

3Na2 SO4 + 2(4CaO · Al2 O3 · 19H2 O) + 14H2 O →   3CaO · Al2 O3 · 3CaSO4 · 32H2 O + 2 Al(OH)3 6NaOH

(4)

The MgSO4 , due to its high solubility in water, is the type of sulfate that produces the greatest deterioration of the cement paste and can react with all cement hydration products. MgSO4 can generate the decomposition of the C–S–H phase of the cement paste, forming expansive compounds, producing brucite (Mg(OH)2 ) and hydrated magnesium silicate (M–S–H) (Liu et al. 2013). As an example of the possible reactions of MgSO4 with the hydrated cement paste compounds, in Eq. 5 the reaction with ettringite is presented and in Eq. 6 the reaction with C–S–H. (CaO)3 Al2 O3 · CaSO4 · 12H2 O + 2MgSO4 + 2Ca(OH)2 + 20H2 O . → (CaO)3 Al2 O3 · 3CaSO4 · 32H2 O + 2Mg(OH)2 ↓

(5)

xMg2+ + xSO2_ 4 + xCaO · SiO2 · aq + 3xH2 O → xCaSO4 · 2H2 O + xMg(OH)2 + SiO2 · aq

(6)

Due to the low solubility of Mg(OH)2 , it precipitates in all reactions of magnesium sulfate with calcium hydroxide or any other phase of the cement paste that contains calcium. The more compacted layer of brucite can slow up the attack forward at first. However, the pH of the solution tends to decrease with the release of Mg2+ ions and the acidity of the solution tends to accelerate the dissociation of calcium ions from the phases present in e cement paste, promoting an increase in gypsum formation. With this, there is a depletion of Ca(OH)2 in the medium and the decalcification of C–S–H begins to occur, which is converted to M–S–H, which does not have any type of binding properties with the other phases of the concrete (Drimalas et al. 2011; Piasta et al. 2014).

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2.2 Durability Models Models that simulate the attack mechanisms are important to understand how the reactions occur, being able to quantitatively predict the products of these deleterious reactions in the concrete. Lorente et al. (2011) analyze the results of the transfer sulfate sodium and magnesium in the pores of concrete comparing models the migration of the magnetic field and natural diffusion. In the first, it was based on the principle that sulfate is an ionic species, so an electric field was used to induce migration and reactions (inspired by classic chloride migration models), while in diffusion, which occurs naturally, starting from a more concentrated (external) to less concentrated (internal) region, sulfate reacts with the cementitious matrix. The tests proved that in the migration, the penetration depth of the sulfate is greater with MgSO4 , while in the diffusion, the reaction products are greater when Na+ is the counter-ion. This can be explained due to the kinetics of brucite formation slower than the sulfate penetration time under an electric field. The ion diffusion mechanism in concrete can be modeled using Fick’s second law. Of the existing models, the authors Sun et al. (2013) innovate in order to consider the effect of the evolution of sulfate ion diffusion related to the immersion time and concentration of sulfate ions, whose damage evolution has been proven through ultrasonic measurements. A numerical method was used to solve the nonlinear parabolic differential equation that describes the diffusion by sulfate ions, later with experiments to validate the model. It was then obtained functions that describe the evolution of the damage induced by the sulfate that significantly accelerates the penetration of sulfate ions when the concentration of sulfate is high and/or immersion time is greater. Campos et al. (2016) proposed a kinetic model with the objective of predicting the evolution and distribution of the internal sulfate attack on conventional concrete and dams, considering two pyrrhotite oxidants, usually contained in contaminated aggregates, which in the presence of water and oxygen react and can form expansive products. The models were validated through measurements in real dams. It was found that, while in conventional concrete, oxygen is the main oxidant, with exponential kinetic evolution over time, in concrete in dams, Fe3+ is the main oxidant, with kinetic evolution in the form of “S”. The fact can be explained by the pH of the aggregates, which determines the main oxidant of pyrrhotite (oxygen: pH > 4 and Fe3+ : pH < 4). In conventional concrete, aggregates are surrounded by cement paste, becoming alkaline. While in the case of dams, larger aggregates are not influenced by the structure’s pH, remaining acidic. Most of the existing mechanical models of external diffusion sulfate attack, applied even at the structural level, do not consider the varying humidity conditions. Cefis and Comi (2017) developed a model that simulates the mechanical effects of expansion in partially saturated conditions, considering that the effect of formation of ettringite, based on results obtained by simplified diffusion models, implies the

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formation of chemicals accounted for by the amount of aluminates that cause volumetric deformation in the concrete. Chemical and mechanical damage describe the formation of micro-cracks that decrease the elastic properties of concrete. Feng et al. (2018) developed a model microstructural linear elastic finite element that calculates the force driving the growth expanding the phase aft external attack sulfate in cement paste, which, although it has a wide range of compositions, is governed the mostly by the stage of formation of etringita. Crystallization pressure and stress fields are tracked in the microstructure on a micrometer scale. The damage initially caused by the expansion, in addition to causing damage to the physical properties, that is, the linear elastic properties in the microstructure; they also cause rheological changes in the progressive reactions that will attack the innermost region of the concrete, through mechanisms based on the concentration of sulfate ions and changes in the pH in the aqueous solution within the porous structure. It is observed when soluble carbonates are present, confirming reductions in pH of the pore solution, which usually accompanies the input sulfates, there is a destabilizing significantly from calcium monosulfoaluminate, becoming spontaneously AFt without adding extra sulfate. Therefore, the progress of phase transformations and expansion of the surface into the porous material is dictated by the input rate of fronts of concentration of sulfate ions and pH, which are not essentially coincident. The behavior within the first 100 µm surface provide information on the concentration of sulfate, concentration of carbonate and pH on the microstructure and a substantial material expansion.

2.3 Studies Carried Out Studies were carried out using 3 types of Brazilian cements, designated CP-II F 32, CP-IV and CP-V, subjected to attack by 3 types of sulfates, CaSO4 , Na2 SO4 and MgSO4 , for 5 months, with a concentration of 10% in relation to the body of water. A high concentration was chosen to accelerate the degradation of the cement. For the study, mortar specimens were used in the mix 1:3, with a ratio of w/c 0.5. Table 1 shows the composition of the cements used, with CP-IV cement considered resistant to sulfates.

Table 1 Chemical composition of cements Al2 O3 (%)

SiO2 (%)

Fe2 O3 (%)

CaO (%)

CP-II F32

4.25

18.62

2.88

61.03

CP-IV

9.79

28.99

4.07

45.45

CP-V

4.30

18.96

2.95

60.76

Source Schiavini (2018)

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A

B

C

D

63

Fig. 2 SEM images of CP-IV

In Fig. 2, it is possible to observe the SEM images of the CP-IV cement after the 5 months of attack of the different types of sulfates, comparing with a sample free of attack. Figure 2a represents the image of the microstructure of the reference CP-IV, where it is possible to observe C–S–H formations, a fact confirmed by the high presence of Ca and Si indicated in the EDS. In Fig. 2b, which represents the image of CP-IV that suffered CaSO4 attack, in addition to C–S–H it is also possible to observe the formation of ettringite. The sample subjected to the attack of Na2 SO4 is represented in Fig. 2c where the formation of Portlandite is observed, and it is not possible to evidence the attack by sulfates. The 2D image represents the sample subjected to the attack of MgSO4 where it is possible to observe the formation of monosulfate and brucite, however in the formation of monosulfate, according to EDS results, Ca was replaced by Mg. The results presented above indicate the greater aggressiveness of MgSO4 when compared with other types of sulfates, even in a sulfate-resistant cement. It is also possible to check the resistance of the 3 types of cements against MgSO4 attack, as illustrated in Fig. 3. In Fig. 3a, which is an image of the CP-II F32 cement, it is possible to observe the formation of ettringite and the EDS indicates a small presence of Mg. The CP-IV cement is represented in Fig. 3b and, as mentioned above, presents the formation of monosulfate and brucite. CP-V cement is illustrated in Fig. 3c where it is possible

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C

B

Fig. 3 SEM image of the MgSO4 attack on different types of cement

Table 2 Sulfate concentration in cement samples

CaSO4

Na2 SO4

MgSO4

CP-II F32

0.50

1.23

1.81

CP-IV

0.41

0.82

1.40

CP-V

0.56

0.98

1.47

Source Schiavini (2018)

to observe the formation of monosulfate with a large amount of Mg, according to an analysis by EDS. In addition to the SEM images, the amounts of sulfates that penetrated the samples were also determined using the APHA Method 4500—SO4 2− , from ASTM, as shown in Table 2. By the sulfate concentrations determined in the mortar samples, it is possible to observe that MgSO4 presents greater aggressiveness and that CP-IV has the highest resistance to attack by the 3 types of sulfates used. In addition to the laboratory experiment, a study was also carried out on a 18year-old construction work on a sewage treatment plant that used CP-IV cement, sulfate resistance, with an w/c = 0.45 ratio with a compressive strength of 42 MPa (Mazer et al. 2019). According Rheinheimer and Khoe (2013), the sewage from this sewage treatment plant has a sulfate concentration less than 200 mg/L and according to NBR 12.655 (ABNT 2006) this condition represents a moderate aggressiveness, however the average sulfate content found in analysis of 4 samples was 7.84%, at a depth of up to 5 cm and a porosity of 12.76%, determined by mercury intrusion (Mazer et al. 2019).

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3 Chloride Action 3.1 General Concepts The action of aggressive agents on reinforced concrete causes its degradation, which, according to Johnson (1969) and Martin-Pérez et al. (2000), has as its main symptoms cracks, disintegration and stains. According to Martin-Pérez et al. (2000) reinforcement corrosion due to the action of chloride ions is a major cause of degradation of reinforced concrete structures. This corrosion is the result of an electrochemical process, accompanied by anodic and cathodic reactions. According to Mehta (1982) the reactions that occur due to the action of the chloride ions are presented in Eqs. 7 and 8: • Anodic reaction involving Cl− ions

Fe + 2Cl− → FeCl2 → Fe++ + 2Cl− + 2e−

(7)

• Cathodic reaction

1 O2 + H2 O + 2e− → 2(OH)− 2

(8)

The corrosion of reinforcement in environments subjected to the action of chlorides has been studied by several authors, among which, Otieno et al. (2016) studied the phenomenon in a laboratory and natural environment considering the parameters of covering, crack opening and concrete quality, it is not possible to infer the results in the natural environment from the laboratory results. Bouteiller et al. (2016), on the other hand, verified the influence of temperature and relative humidity, verifying that higher temperatures and relative humidity in 80% showed higher corrosion rates of the reinforcement. Several studies (Castro-Borges et al. 2013; Kuosa et al. 2013; Medeiros-Junior et al. 2015) demonstrate that the main factors influencing the chloride penetration in concrete are the type of cement, the chloride diffusion coefficient, the water/cement ratio, the curing of concrete, the surface concentration of chlorides, the exposure conditions, the relative humidity, and the ambient temperature. Pradelle et al. (2017) performed a sensitivity analysis on some models and observed that the thickness of the reinforcement covering and the concentration of chlorides had a greater influence on the useful life of the structures than the chloride diffusion coefficient. Considering the influence of the marine aggressiveness zone, Zhu et al. (2016) analyzed, for 28 years, beams subjected to the action of saline fog and observed that after 1 year of exposure, the concentration of chlorides near the reinforcement

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was higher than the limit established by RILEM and that these beams showed loss of rigidity and load capacity due to the cracking and corrosion process of the reinforcement over time. Valipour et al. (2014) evaluated reinforced concrete specimens exposed to tidal and splash zones for 650 days and found that the corrosion rate was higher in the splash zone than in the tidal zone. Once the chloride ions have penetrated the concrete structures, they can be found in two different forms: combined with the cement hydration compounds physically or chemically, or free in the concrete pores, the latter being the ones that act in the process corrosion resistance. Determination of the content of free chloride ions in concrete is not common because the carbonation process can release combined chloride ions (Kropp and Hilsdorf 1995), thus it is common to establish models for predicting useful life based on the amount of total chloride ions in the concrete. However, Mohammed and Hamada (2003) established relationships between the total amount of chloride ions and the amount of free chloride ions for different types of Japanese cements, among which are mentioned: common Portland cement (OPC), moderate heat cement hydration (MH), the initial high strength cement (HES), and a cement with a high content of C3 A (AL). For all cements surveyed, the authors found linear relationships between the amounts of total and free chloride ions, as indicated in the equations below: O PC: Ct = 1.1597C f

R 2 = 0.94

(9)

H E S: Ct = 1.1390C f

R 2 = 0.97

(10)

M H : Ct = 1.1266C f

R 2 = 0.87

(11)

AL: Ct = 1.4821C f

R 2 = 0.98

(12)

where Ct corresponds to the total amount of chloride ions and Cf is the amount of free chloride ions in the concrete. In the expressions above, it is observed that cement with a high C3 A content has a lower Cf /Ct ratio, indicating a better ability of Chloride ions to combine with hydrated cement compounds, in particular aluminate compounds. The ability to combine Chloride ions in concrete depends mainly on the amount of C3 A, for the formation of Friedel’s Salt (3CaO·Al2 O3 ·CaCl2 ·10H2 O) (Kropp and Hilsdorf 1995). Many of the models used to determinate the chloride penetration profile in concrete structures is based on Fick’s laws (Andrade et al. 1997; Liang and Lin 2003; Sun et al. 2012; Petcherdchoo 2013). Some of those models consider the diffusion coefficient as constant in time. However, this argument is not valid for concrete because studies show variations in the chloride diffusion coefficient according to the penetration depth, the degree of cement hydration, with the surface concentration of chlorides,

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with the temperature, and with the pH of the concrete (Mazer 2010; Nogueira and Leonel 2013; Safehian and Ramezanianpour 2013). In the search for a better model of the chloride penetration profile, some studies (Val and Trapper 2008; Bastidas-Arteaga et al. 2011; Andrade et al. 2013) have shown deterministic or probabilistic models for describing the transport mechanism of chlorides in concrete. In this context, the chaos theory is a good option for developing the concrete technology. Another option is the use of fractals as a way to model the diffusion process. The flexibility of fuzzy logic is also a good feature to work with subjective and qualitative parameters. Thus, the models with applications in the concrete technology that contains a mathematical approach using fuzzy logic, chaos theory and fractals, are few and recent (Anoop et al. 2002; Altmann et al. 2012; Anoop and Raghuprasad 2012; Mazer et al. 2017).

3.2 Durability Models The durability models existing for determining the useful life of concrete due to chloride penetration are mostly based on the 2nd Fick’s Law, indicated in Eq. 13. ∂ 2C ∂C = Da 2 ∂t ∂x

(13)

where ∂C/∂t represents the change in concentration over time; Da is the apparent diffusion coefficient, in cm2 /s and ∂ 2 C/∂x2 is the mass flow gradient. It is also possible to observe that the chloride diffusion coefficient is constant. Some existing models are presented below. Saetta et al. (1993) developed a model that uses environmental parameters in its formulation, presented in Eq. 14. Ct ∂ω ∂Ct = −div[Da · ∇Ct ] + ∂t α ∂t

(14)

where Ct is the total chloride ion concentration in kg/m3 ; Da is the apparent diffusion coefficient in m2 /s; α is a capacity factor; and ω represents the amount of water. This model considers, in addition to the diffusion coefficient of chlorides as a function of time, environmental parameters such as temperature and relative humidity, which are implicit in the parameters Da and ω, given by:   ω = ωsat h 1.16h 3 − 1.05h 2 − 0.11h + 1 Da =

Di α

(15) (16)

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where ωsat is the amount of evaporable water from the concrete; h is the relative humidity; and Di represents the diffusion coefficient admitted as the base coefficient, given by: Di = Di,r e f f 1 (T ) f 2 (te ) f 3 (h)

(17)

where Di,ref representing the diffusion coefficient evaluated for a temperature T = 23 °C, relative humidity h = 100% and degree of hydration of the cement at 28 days. The functions f1 , f2 and f3 consider the influence of temperature T, maturation time t and relative humidity h, respectively. The synergistic effect of the CO2 action, chloride and sulfate ions was modeled by Liang and Lin (2003), considering the unidimensional action of aggressive agents. The proposed model is given by: ∂ 2C ∂C ∂C = Ds 2 − υ − KT C ∂t ∂x ∂x

(18)

with initial and boundary conditions: C(x, 0) = Ci; C(0, t) = Cs and C(L , t) = C f

(19)

where C is the concentration of chemical corrosive; Ci , Cs and Cf are the initial concentration of contaminants in the concrete, on the concrete surface and at the interface between the concrete and the reinforcement; Ds represents the diffusion coefficient; ν is the average speed of water in the pore structure of concrete; KT is the first order decay constant at temperature T; L is the thickness of the reinforcement covering; x is the depth; and t is the time. For the case of the existence of only Chloride ions, this model comes down to 2nd Fick’s Law. Anoop et al. (2002) applied the concepts of Fuzzy Logic to consider the effects of environmental factors in the initiation and propagation of corrosion by chloride ions in reinforced concrete elements. Initially, the authors applied the concepts of Fuzzy Sets to environmental characteristics such as temperature, relative humidity and degree of wetting and drying, defining an Environmental Aggression Factor (EAF). After a first stage of modeling, the authors define the concrete class and the water/cement ratio, according to current regulations, and it is then possible to determine the minimum thickness of the reinforcement covering. To determine the time required for corrosion to start, the authors apply the 2nd Fick’s Law:   −2  d2 −1 cs − cr er f ti = 4D cs

(20)

where d is the thickness of the chloride ion free coating; D is the Chloride Diffusion coefficient, in cm2 /s; erf is Gauss’s error function; cs represents the surface concentration of chloride ions; and cr is the critical concentration of chloride ions.

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3.3 Studies Carried Out Guzzo (2018) evaluated the depth of chloride penetration and the concentration of chlorides in a conventional concrete with 25 MPa of compressive strength and in a Reactive Powder Concrete (RPC) with 174 MPa of strength, exposed for 24 months to a 5% chloride solution in relation to body of water. The author observed a concentration of total chlorides of 0.86% in conventional concrete and 0.88% in RPC, in relation to the cement mass. In a first analysis it is believed that there are no differences between the two types of concrete, however in conventional concrete, the penetration of chlorides reached a depth of 4.83 mm and in RPC it was 1.41 mm. Mazer (2010) analyzed the influence of temperature and the region of exposure on the penetration of chlorides in conventional concretes with 30 MPa of compressive strength. The author evaluated the temperatures of 15, 20, 25 and 30 °C, in the regions of submerged exposure, level variation and atmospheric zone, at the ages of 6, 12 and 18 months. The author observed that the increase in the ambient temperature leads to an increase in the chloride diffusion coefficient. It was also observed that the wetting and drying cycle of the region of water level variation influenced the concentration of chlorides in the region. In addition, the penetration rate from 6 months to 12 months was higher than the penetration rate from 12 to 18 months.

4 Conclusions The approach explored in this work provides a perspective for understanding the mechanisms of concrete deterioration through aggressive sulfate and chloride environments. The phenomena are complex, depending on several factors such as temperature, pH, degree of hydration of the cement compounds, time, types of reagents involved, concrete coverage, concrete permeability. In this sense, it was proven that the mathematical models mentioned here are essential to try to understand the mechanisms of diffusion and reaction over time. Although it recognizes a remarkable advance in the understanding of the durability and useful life of concrete structures, many studies should be done to improve the methodologies of investigation and understanding of these phenomena. Most of the models that are used to estimate the penetration of aggressive agents and to predict durability and useful life are based on Fick’s Laws, often considering the diffusion coefficients of aggressive agents constant over time (although they are variable), and still disregarding the use of other important variables. Therefore, it is admitted the importance of developing improved methodologies to represent the nature, diffusion and reaction of aggressive agents in the most realistic way possible, consecutive deteriorations from the first reaction that gave rise to disintegration, in a quantitative and qualitative way.

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References Aguiar JE (2014) Patologia e Durabilidade das Estruturas de Concreto. Notas de aula (Especialização em Construção Civil). Universidade Federal de Minas Gerais, Escola de Engenharia, Belo Horizonte, 298 p Al-Amoudi OSB (2002) Attack on plain and blended cements exposed to aggressive sulfate environments. Cem Concr Compos 24:305–316 Alexander M, Beushausen H (2019) Durability, service life prediction, and modelling for reinforced concrete structures—review and critique. Cem Concr Res 122:17–29 Altmann F, Sickrt JU, Mechtcherine V, Kaliske M (2012) A fuzzy-probabilistic durability concept for strain-hardening cement-based composites (SHCC) exposed to chlorides. Part 1: Concept development. Cem Concr Compos 34:754–762 American Concrete Institute (2001) Committee 201.2R. Guide to durable concrete. ACI Manual of Concrete Practice. Detroit, 42 p Andrade MC, Diez JM, Cruz Alonso M (1997) Mathematical modeling of a concrete surface “Skin Effect” on diffusion in chloride contaminated media. Adv Cem Based Mater 6:39–44 Andrade C, Prieto M, Tanner P, Tavares F, D’andrea R (2013) Testing and modelling chloride penetration into concrete. Construct Build Mater 93:9–18 Anoop MB, Rao KB, Rao TVSRA (2002) Application of fuzzy sets for estimating service life of reinforced concrete structural members in corrosive environments. Eng Struct Anoop MB, Raghuprasad BK (2012) A refined methodology for durability-based service life estimation of reinforced concrete structural elements considering fuzzy and random uncertainties. Comput Aided Civil Infrastruct Eng 27:170–186 Associação Brasileira de Normas Técnicas (2006) ABNT NBR 12655: Concreto de Cimento Portland – Preparo, Controle e Recebimento - Procedimento. Rio de Janeiro Bastidas-Arteaga E, Chateauneuf A, Sanchez-Silva M, Bressolette P, Schoefs F (2011) A comprehensive probabilistic model for chloride ingress in unsaturated concrete. Eng Struct 33:720–730 Bouteiller V, Marie-Victoire E, Cremona C (2016) Mathematical relation of steel thickness loss with time related to reinforced concrete contaminated by chlorides. Constr Build Mater 124:764–775 Campos A, López CM, Aguado A (2016) Diffusion–reaction model for the internal sulfate attack in concrete. Constr Build Mater 102:531–540 Castro-Borges P, Balancán-Zapata M, López-González A (2013) Analysis of tools to evaluate chloride threshold for corrosion onset of reinforced concrete in tropical marine environment of Yucatán, México. J Chem 1–8 Cefis N, Comi C (2017) Chemo-mechanical modelling of the external sulfate attack in concrete. Cem Concr Res 93:57–70 Costa RM (2004) Análise de Propriedades Mecânicas do Concreto Deteriorado Pela Ação de Sulfato Mediante Utilização do UPV. Tese de Doutorado em Engenharia de Estruturas - Escola de Engenharia da Universidade Federal de Minas Gerais Drimalas T, Clement JC, Folliard KJ, Dhole R, Thomas MDA (2011) Technical Report 04889-1. Laboratory and Field Evaluations of External Sulfate Attack in Concrete. Center for Transportation Research, Austin, 190 p Félix EF et al (2018) Análise da vida útil de estruturas de concreto armado sob corrosão uniforme por meio de um modelo com RNA acoplado ao MEF. Revista de la Asociación Latinoamericana de Control de Calidad, Patología y Recuperación de la Construcción-ALCONPAT 8(1):1–15 Feng P, Liu J, She W, Hong J (2018) A model investigation of the mechanisms of external sulfate attack on Portland cement binders. Constr Build Mater 175:629–642 FIB, Model code for service life design, Switzerland, fib bulletin 34, 2006 Guzzo G (2018) Avaliação do comportamento do concreto convencional e do concreto de ultra alto desempenho frente à contaminação por cloretos. Trabalho de Conclusão de Curso, UTFPR, Curitiba

Salt Attack, Durability and Service Life of Concrete Structures

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Johnson SM (1969) Dégradation, entretien et reparation des ouvrages du genie civil, Eyrolles, 1a. edição, Paris Kropp J, Hilsdorf HK (1955) Performance criteria for concrete durability. Rilem Report 12, London Kuosa H, Ferreira RM, Holt E, Leivo M, Vesikari E (2013) Effect of coupled deterioration by freeze-thaw, carbonation and chlorides on concrete service life. Cem Concr Compos 47:32–40 Lee ST, Lee SH (2007) Sulfate attack and the role of cement compositions. J Korean Ceram Soc 44(9):465–470 Liu Z, Deng D, De Schutter G, Yu Z (2013) The effect of MgSO4 on thaumasite formation. Cem Concr Compos 35:102–108 Liang M, Lin S (2003) Modeling the transport f multiple corrosive chemicals in concrete structures: synergetic effect study. Cem Concr Res 33:1917–1924 Lorente S, Yssorche-Cubaynes MP, Auger J (2011) Sulfate transfer through concrete: migration and diffusion results. Cement Concr Compos 33:735–741 Martin-Pérez B, Zibara H, Hooton RD, Thomas MDA (2000) A study of the effect of chloride binding on service life prediction. Cem Concr Res 30:1215–1223 Mazer W (2010) Metodologia para a previsão da penetração de íons cloretos em estruturas de concreto armado utilizando a Lógica Difusa. Tese de doutorado, ITA, São José dos Campos, SP Mazer W, Lima MG, Medeiros-Junior RA (2017) Fuzzy logic for estimating chloride diffusion in concrete. Struct Build Mazer W, Araújo JM, Medeiros A, Weber AM (2019) Evaluation of sulfate ions in degrading armed concrete structures of a sewage treatment station: case study. J Build Pathol Rehabil Medeiros MHF, Andrade JJO, Helene P (2011) Durabilidade e vida útil das estruturas de concreto. Concreto: ciência e tecnologia 1:773–808 Medeiros-Junior RA, Lima MG, Brito PC, Medeiros MHF (2015) Chloride penetration into concrete in an offshore platform—Analysis of exposure conditions. Ocean Eng 103:78–87 Mehta K (1982) Durability of concrete in marine environment—a review. In: Performance of concrete in marine environment, ACI, pp 1–20 Mehta PK, Monteiro JM (2008) Concreto: estrutura, propriedades e materiais. 2nd edn. IBRACON. São Paulo Mohammen TU, Hamada H (2003) Relationship between free chloride and total chloride contents in concrete. Cem Concr Res 33:1487–1490 Nogueira CG, Leonel ED (2013) Probabilistic models applied to safety assessment of reinforced concrete structures subject to chloride ingress. Eng Fail Anal 31:76–89 Otieno M, Beushausen H, Alexander M (2016) Chloride-induced corrosion of steel in cracked concrete—Part I: Experimental studies under accelerated and natural marine environments. Cem Concr Res 79:373–385 Petcherdchoo A (2013) Time dependent models of apparent diffusion coefficient and surface chloride for chloride transport in fly ash concrete. Constr Build Mater 38:497–507 Piasta W, Marczewska J, Jaworska M (2014) Some aspects and mechanisms of sulfate attack. Struct Environ 6:19–24 Pradelle S, Thiéry M, Baroghel-Bouny V (2017) Sensitivity analysis of chloride ingress models: case of concretes immersed in seawater. Constr Build Mater 136:44–56 Rheinheimer B, Khoe SS (2013) Ataque por Sulfatos em Estações de Tratamento de Efluentes. Trabalho de Conclusão de Curso (Graduação) – Curso Superior de Engenharia Civil. Universidade Federal do Paraná, Curitiba, Brasil Saetta A et al (1993) Analysis of chloride diffusion into partially saturated concrete. ACI Mater J 90(5):441–451 Safehian M, Ramezanianpour AA (2013) Assessment of service life models for determination of chloride penetration into silica fume concrete in the severe marine environmental condition. Constr Build Mater 48:287–294 Schiavini DN (2018) Análise de diferentes tipos de cimento na resistência ao ataque por sulfatos. Trabalho de Conclusão de Curso, UTFPR, Curitiba

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Skalny J, Marchand J, Odler I (2002) Sulfate attack on concrete. Son Press 1ª Ed. London and New York Sun YM, Liang MT, Chang TP (2012) Time/depth dependent diffusion and chemical reaction model of chloride transportation in concrete. Appl Math Model 36:1114–1122 Sun C, Chen J, Zhu J, Zang M, Ye J (2013) A new diffusion model of sulfate ions in concrete. Constr Build Mater 39:39–45 Val DV, Trapper PA (2008) Probabilistic evaluation of initiation time of chloride induced corrosion. Reliabil Eng Syst Saf 93:364–372 Valipour M, Shekarchi M, Ghods P (2014) Comparative studies of experimental and numerical techniques in measurement of corrosion rate and time-to-corrosion-initiation of rebar in concrete in marine environments. Cement Concr Compos 48:98–107 Zhu W, François R, Fang Q, Zhang D (2016) Influence of long-term chloride diffusion in concrete and the resulting corrosion of reinforcement on the serviceability of RC beams. Cement Concr Compos 71:144–152

Guidelines for Inspection and Receipt of Reinforced Concrete Structures in Newly Constructed Buildings Marcus Vinícius Fernandes Grossi

Abstract The purchase of real estate is an important decision, besides being costly, it must fulfill the legitimate needs and expectations of buyers, which means that it must bring comfort, safety and resistance. Therefore, receipt inspections are useful in several situations, and may be demanded by developers, builders, consumers, financing agents, insurance companies and even public entities to reduce uncertainties. The buyer have to inspect the property and formally point out any irregularities identified before formalizing the possession. Among the various systems present in a building, the structure is the system that represents greater importance in aspects related to security. In order to collaborate in this process, an excerpt from this author the master’s thesis (GROSSI 2019) was proposed, proposing guidelines and methods of inspection and receiving newly built housing, based on technical standards, legislation and established building techniques. It is a very important topic, where there are many studies aimed at building inspection during use, however, with few references related to the receipt of newly constructed buildings. The elaboration of the mentioned work was based on a broad bibliographic search, contemplating procedures for carrying out incoming inspections, covering aesthetic, functional aspects, safety in use and operation, compliance with technical standards and applicable legislation, contributing to assess the apparent building conditions of conformity and performance before its use. Keywords Structural inspection · Receiving buildings · Reinforced concrete structure

1 Introduction The purchase of real estate is an important decision and must be supported by knowledge of property physical condition. The professional technical knowledge is the safest way to make this decision (AS 4349-1 2007). The advantages of inspection by specialized professionals are that they have technical training and experience to M. V. F. Grossi (B) University of São Paulo (USP), São Paulo, Brazil e-mail: [email protected] © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2020 J. M. P. Q. Delgado (ed.), Building Pathology, Durability and Service Life, Building Pathology and Rehabilitation 12, https://doi.org/10.1007/978-3-030-47302-0_4

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Fig. 1 Armor cover measurement using pacometer

prospect for constructive irregularities, which, being identified early in the building’s useful life, bring many advantages to everyone involved. The eventual identification of potential hidden defects is extremely useful, which can compromise the building’s performance and, if identified late, can have very costly repairs or be out of warranty terms. Latent defects is by definition any anomaly or failure that manifests itself only after a period of use or exposure, or whose identification becomes difficult for a layman, such as: • inadequate slope of the ramp for disabled people access, which is easy to verify (identifiable only by visual inspection), however, requires knowledge of its mandatory nature; • reinforcement cover less than that specified in the project and/or technical standard, which will decrease the useful structure life and will only manifest itself after some period of time (Fig. 1). This chapter summarizes a thesis section that was developed on the necessary requirements to carry out a complete building receipt inspection, addressing aspects in addition to pathological manifestations (apparent defect), but also points a potential pathological manifestations appearance (latent defect) and non-conformities to legal and normative requirements, covering aesthetic, functional and safety aspects in use and operation, contributing to assess the conditions of conformity and apparent performance of the building structure before its use starts. In this proposal for the inspection scope and receipt, it is intended to be more comprehensive than those carried out in the activities of: (a) commissioning (Silva and Couto 2012); (b) quality control inspection of the final product (Finger et al. 2015; PMBOK 2012); (c) cadastral inspection provided by NBR 9452 (ABNT 2016); (d) home inspection or pre-purchase inspection (AS 4349-1 2007; Teixeira and Santos 2015), since all of these revolve around symptomatic problems and/or limited performance criteria. It is emphasized that this work does not aim to generate an inspection method that certifies full structure conformity within the requirements of any local law, regulation, ordinance, law or statute; serving as a guarantee against problems in the

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building future, due to the various physical, technical limitations etc., serving as a tool to reduce the uncertainties (risks) on apparent performance of the building structure.

2 Inspection and Receipt Guidelines The following is a proposal for the scope, procedures and methods for carrying out the inspection and receipt of reinforced concrete structures in buildings.

2.1 Scope of Inspection It is necessary to define the scope in order to know the inspection objectives expected by the customer. In this way, the scope and inspection scope must be clearly defined by the client, so that the inspector can carry out the inspection as expected. However, it is prudent for the inspector to advise on the definition of this scope as follows (AS 4349-0 2007; Singapore 2012). The inspection and receipt of newly constructed reinforced concrete structures must cover the surroundings, the implantation and all the apparent construction systems of the building, in order to have a holistic building view, since the building does not exist isolated from the environment (Table 1). The inspection can also be divided into areas, and it is recommended that in the case of inspections restricted to certain areas, their adjacent areas should also be inspected. The scope of building evaluation must consider: • Building performance requirements, systems and subsystems (Table 3); • Users’ needs and requirements (Table 2); • Local legal and regulatory requirements.

2.2 Inspection and Receipt Process The proposed receiving stages basically consist, after the construction is completed, of inspection and receipt activities, and irregularities evaluation. If the building acceptance opinion is not carried out, and irregularities are present, it is assessed whether they jeopardize safety or habitability. If they do not harm, the partial acceptance opinion is carried out. If they harm, the building refusal opinion is issued. In cases of partial acceptance or refusal, the builder have to make the necessary corrections and submit the building again to the inspection and receiving activity, as shown in Fig. 2. The proposed inspection and receipt process involves the steps described in Fig. 3.

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Table 1 Relevant elements to be inspected in a newly constructed building Place

Relevant elements for inspection

Surroundings (~30 m radius)

• Neighboring buildings with great noise generation, shadow projection, etc. • Traffic density, road conditions and sidewalks • Urban drainage/flood risk • Climate conditions • Topography, geology • Fauna, flora and water courses • Neighborhood activities that may cause violence, pollution, insecurity, etc.

Implantation

• • • • •

Building

• • • • • • •

2.2.1

Currencies Topography, geology Vegetation and water courses Easement area Preservation area

Foundation and Structure Floors Vertical seals Coverages Hydrosanitary Combustible gas Electrical, telecommunication and atmospheric discharge protection system • Vertical transport systems • Environmental conditioning • Fire protection

Documents Collection and Analysis

The first step in the process should be the request for access to consult and analyze the documents described in the applicable technical standards. This relationship must be adequate according to the type and complexity of building, its installations and construction systems and the characteristics of state and municipality legal requirements as well. Documents can be delivered electronically, as long as it is possible to view them free of charge to users. For example, the projects delivery in PDF format, as opposed to DWG, or the delivery in DWG together with free viewer software. Failure to provide any of documents should be considered as non-compliance. The documents analysis should not be restricted to just checking the existence record, but analyzing its content in comparison with the normative and legal requirements, and with the real conditions of the building when the inspection was carried out, as follows: 1. Sales material: check if the building structure has the characteristics, areas, finishes, systems and equipment as presented in the advertising material, the

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Table 2 User needs and demands Requirements Safety

Habitability

Sustainability

User Needs Structural security

Mechanical resistance, static and dynamic actions; climatic effects (fatigue)

Fire safety

Flame spread risk; physiological effects (smoke control and ventilation); Alarm time, evacuation time and survival time

Safety in use and operation

Protection against explosions and burns; protection against mechanical movements; protection against electric shocks; protection against radioactivity; safety during movements and circulation; safety against human or animal intrusion

Watertightness

Watertight; airtight; dust intrusion control

Thermal performance

Air temperature and thermal radiation control

Acoustic performance

Noise control (continuous and intermittent); sound intelligibility; reverberation time

Luminous performance

Natural and artificial lighting control; insolation; illuminance contrast level; possibility of darkening; aspects of finish (color, texture, regularity); visual contact (internally and with the outside world)

Health, hygiene and air quality

Facilities for human body care; clean water supply; evacuation of waste water; materials and smoke; ventilation; odour control; toxic gas control

Functionality and accessibility

Number; size; geometry and spaces interrelations; services and equipment provision; flexibility

Tactile and anthropodynamic comfort

Limitations of accelerations and vibrations; aspect of human resistance and maneuverability; roughness and flexibility of surfaces; humidity and temperature on surfaces; absence of static electricity discharges

Resistance

Life-long performance conservation

Maintainability

Possibility of maintenance and replacement

Environmental appropriateness

Minimize changes, environmental impacts during the life cycle of the building, as well as the consumption of natural resources

Source ISO 19208 (2016)

x

x

User demands

Structure as vertical sealing

Structure as roof

Subsystems/elements

Structure as roof

Source Adapted from Gonçalves et al. (2003)

x

x

x x

x

x

x

x

Resistance

Watertightness

x

x

x

Structure as vertical sealing

x

Tactile and anthropodynamic comfort

x

x

x

Safety in use and operation

Structure as floor

Functionality and accessibility

x

x

x

x

Fire safety

x

Health, hygiene and air quality

x

x

x

x

Structural performance

Structure

Luminous performance

x

x

Structure as floor

Aesthetic appearance

User demands

Structure

Subsystems/elements

Table 3 Performance requirements of building structures

x

x

x

x

Maintainability

x

x

Thermal performance

Environmental appropriateness

x

x

x

Acoustic performance

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Fig. 2 Step flow for accepting or refusing on receiving newly constructed buildings

Fig. 3 Inspection process flow and newly building receiving

2. 3. 4. 5. 6.

7.

8.

purchase and sale commitment contract, the descriptive memorial, the plans and other documents related to the edification sale; Documents incorporation: verify that the building structure has the correct registration of characteristics, areas and environments; Documents to start the work: check if the building structure has the permition and execution licenses issued by the municipal, state and federal agencies; Technical responsibility record: verify that all projects and services performed have a qualified technical person in charge; Projects and memorials: verify that the information and details contained in the projects, which can be evidenced in the sensory survey, were obeyed as provided; Documents delivery: check if the building structure has the necessary permits and licenses, as well as if there are the minimum documents to carry out its correct use, operation and maintenance; Test reports, opinions and certificates: verify that the documents have the minimum necessary information, defining the test method used, the samples characterization, the results obtained and the technical person responsible for the performance; also verify the test results satisfy the criteria defined in the respective standards and/or projects; Documents after construction delivery: verify that the delivery of all documents, equipment and accessories provided has been formalized and that the building’s legal representative inspected and accepted the building structure (the

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inspection and acceptance of the legal representative can be replaced by the inspection provided for in work that gave rise to this chapter, when the contractor is the user). To assess the documents related to the reinforced concrete structure system, the criteria of applicable technical standards must be observed, assessing whether the system has the appropriate documentation, and the items in Table 4 must be observed.

2.2.2

Survey of the History and Complications of the Work

Whenever it is possible, it is important that data collection be carried out, through interviews and/or questioning during the survey activities. The objective is to obtain information about the building and its history, so that better understood its design, construction systems, construction sequence, construction techniques and used materials. Knowing those information it is possible identify significant occurrences, such as: construction company/contractor alteration, delays in execution, degradation signs of any system, possible interventions, among others; and, also, to become aware of any problems already identified by third parties.

2.2.3

Organoleptic Survey of Surroundings, Implantation and Construction

In the inspection stage, information should be collected to characterize anomalies, their respective extent, probable causes, corrective actions and their severity (ABNT NBR 16747 2018). Therefore, a quantitative and non-qualitative survey should be carried out, since the objective is to identify all possible problems and their respective locations. The inspection is the stage in which the inspector physically approaches the building, and is strictly sensory (visual, tactile, olfactory, audible and palatable), with vision being the main and most used sense (Amaral 2013); however, the other senses are also very important, as examples (Amaral 2013): • Tactile evaluation: passing your hand over a coating surface allows you to assess the existence of dust or breakdown; • Olfactory evaluation: the existence of high humidity in closed environments can be detected by smell, or the existence of leaks from the fuel gas network; • Audible evaluation: the existence of noise in an electrical panel that may indicate poor contact or installation overload, or water leakage from the hydraulic network; • Palatable evaluation: it is the least usual for obvious reasons, but in the case of water-soluble efflorescence, it can present different flavors. For example, the sodium sulfate from the block plaster has a characteristically salty taste, while the calcium sulfate from the block does not have a very noticeable flavor.

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Table 4 Document checklist: reinforced concrete structures Requirement

Verification item

Structural performance

Third party technical design evaluation opinion

Evidence answered? NA

YES

Registered the technical standards of reference in design Adequate consideration of wind action Proper consideration of earthquakes The memorial calculation design and the respective executive drawings, with necessary technical information Resistance

Recorded system and subsystems life expectancy Correct environmental aggressiveness class (EAC) (Table 5) Concrete specification (maximum large aggregate size) Concrete specification (type of cement compatible with surroundings) Concrete specification (additions and/or additives compatible with surroundings) Concrete specification (water/cement ratio compatible with EAC) (Table 6) Concrete specification (minimum cement consumption compatible with EAC) (Table 6) Concrete specification (fck compatible with EAC) (Table 6) EAC compatible reinforcement cover (macro and micro areas), special attention for pillars in contact with the ground and reservoir cover (Table 7) Preventive measures for alkali-aggregate reaction

Fire safety

Complying with fire resistance requirements

Use and operation safety

Vehicle fall protection (h = 50 cm) in parking lots

Source Repette (1991), ABNT NBR 15575-5 (2013); ABNT NBR 6118 (2014) NA not applicable; NI not inspectable

NO

NI

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Table 5 Environmental aggressiveness class—EAC EAC

Aggressiveness

Environment type general classification

Deterioration risk

Content of CO2 g (%)

Content of Cl−g (mg/L)

I

Weak

Rural

Insignificant

≤3

≤200

Immersed II

Moderated

Urbana,b

Small

≤3

3

>500

Industriala,b Watertight partsd IV

Very strong

Industriala,b Salt spraya, e Freezingf

a A microclimate with a milder aggressiveness class (one class above) can be admitted for dry indoor

environments (rooms, bedrooms, bathrooms, kitchens and service areas of residential apartments and commercial complexes or environments with mortar-coated concrete and paint) b A milder class of aggressiveness (one class at the top) can be admitted in constructions of dry climate regions, with average relative air humidity less than or equal to 65%, parts of the structure protected from rain in predominantly dry environments or regions where it rarely rains c Chemically aggressive environments, industrial tanks, electroplating, bleaching in pulp and paper industries, fertilizer warehouses, chemical industries, sewage treatment stations, etc d Conditions where low water permeability concrete is required, e.g. in water tanks, nonwaterproofed slabs, etc. e Exposure to chlorides from chemical de-icing agents, salts, salt water, seawater, or splashes or sprays of these agents f Exposure to freezing and defrosting processes in wet conditions or to chemical defrosting agents g Non-standard but reference values for field surveys and measurements Source Thomaz (2001, p. 177), ABNT NBR 6118 (2014, p. 17), ABNT NBR 12655 (2015, p. 12) Table 6 Correspondence between the EAC and the concrete quality Concrete

Type

Environmental aggressiveness class I

II

III

IV

Water/cement ratio in mass

Reinforced concrete

≤0.65

≤0.60

≤0.55

≤0.45

Projected concrete

≤0.60

≤0.55

≤0.50

≤0.45

Concrete class

Reinforced concrete

≥C20

≥C25

≥C30

≥C40

Projected concrete

≥C25

≥C30

≥C35

≥C40

≥260

≥280

≥320

≥360

Portland cement consumption

(kg/m3 )

Source ABNT NBR 12655 (2015, p. 12)

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Table 7 Correspondence between EAC and cnom para c = 10 mm Structure type

Component or element

Environmental aggressiveness class I

II

III

IVa

Nominal coverage (mm) Reinforced concrete

Projected concreted

Slabb

20

25

35

45

Beam/pillar

25

30

40

50

Structural elements in ground contactc

30

30

40

50

Slab

25

30

40

50

Beam/pillar

30

35

45

55

Source Adapted from ABNT NBR 6118 (2014, p. 20) a On surfaces exposed to aggressive environments, such as reservoirs, water and sewage treatment plants, sewage ducts, effluent channels and other works in chemically and intensely aggressive environments, the coatings of aggressiveness class IV must be attended b For slabs and beams upper face that will be coated with screed mortar, carpet and wood-type dry final coatings, cladding and finishing mortar, such as high performance floors, ceramic floors, asphalt floors and others, the requirements of this table can be replaced by the coverings calculated according to bar or sheath diameter, respecting a cnom ≥ 15 mm c In the section of pillars in ground contact next to foundation elements, the reinforcement must have a nominal cover ≥45 mm d Nominal sheath or wire, cable and rope coverage. The passive reinforcement cover must respect the reinforced concrete coverings Notes (1) In order to field verification, the minimum reinforcement coverage is the lowest value that must be respected throughout the entire element considered. This constitutes an acceptance criterion; (2) The cover values in the table indicate design values (cnom ± 10 mm), so when checking in the field, consider the cover values above by subtracting 10 mm

The survey should try to identify potential influences and risks, focusing on all environment elements, implementation and apparent systems, so that the following items are registered, analyzed and verified: (a) (b) (c) (d) (e)

complete completion of all services execution; pathological manifestations, finish irregularities and vices1 or apparent vices2 ; aspects that may compromise the health and users safety; aspects that may compromise the use, operation and maintenance of building; meeting the performance requirements of ISO 19208 (2016);

1 Vices:

anomalies that affect the performance of products or services, or make them inadequate for their intended purpose, causing inconvenience or material damage to the consumer. They may arise from design or execution failure, or from defective information about their use or maintenance (ABNT NBR 13752 1996, p. 5). 2 Apparent vices: these are the ostensible constructive faults, easily detectable even by nonprofessionals under construction. Examples: broken or stained glass, different shades in the coating or painting, wrongly applied decorated tile, breaking the scheme of projected geometric design, lack of mirrors in the electrical installations, detached or cracked doors, leaks existing at the time of delivery, finishing material used different from that in the sales memorial, etc. (Grandiski 2018, p. 83).

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Fig. 4 Example of potential hidden defect: rainwater runoff concentration point, which can create hygroscopic cracking and early coating degradation

(f) compliance with the requirements of technical standards and legislation (in force at the time of the project protocol in the responsible bodies); (g) functioning of equipment and systems. It is important to note that an organoleptic survey is not able to identify hidden flaws, which require verification through other survey methods, such as, for example, a concrete failure in an apparent structure; that do not cause changes in the construction elements; or, also, addictions that have not shown apparent signs, such as infiltrations. In some cases it is possible to identify unfavorable construction aspects, where the action of degradation mechanisms and impairment of resistance is expected, which would be called potential latent defect, such as, for example, a concentration point of runoff (Fig. 4). To evaluate the system of reinforced concrete structures, the criteria of applicable technical standards must be observed, assessing whether the system is apparently stable, resistant, fire-safe, durable and without apparent anomalies, and the items in Table 8 have to be observed in field inspections. Below, from Figs. 5, 6, 7, 8, 9 and 10, some anomalies examples in reinforced concrete structure system are presented, which should be observed in inspection and reception activities.

2.2.4

Carrying Out Measurements, Tests and Quick Trials

The measurements performance, tests and expedited trials serve as a complement to organoleptic survey, quantifying impressions and often analyzing aspects not perceptible to the human senses, serving as an extension of inspector’s ability to grasp reality, being recommended the harmonization of its use (Lichtenstein 1986). Table 10 presents simple utensils, which allow the maximum amount of useful information to be extracted from the building. Most constructive anomalies can be

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Table 8 In loco inspection checklist: reinforced concrete structures Requirement

Verification item

Evidence answered? NA

Aesthetics

YES

NO

NI

Completed services and clean environments No efflorescence formation (Fig. 6)

Structural

No noticeable geometric irregularities No cracks above those tolerated in fences due to structure movement No compromises in doors and windows operation due to structure movement Position and dimensions of holes in structural parts compared to those foreseen in the design

Watertightness

No points with water accumulation on structure Platiband tops and walls protected by sills, ruffs, etc. All joints subject to the action of water properly sealed and watertight Drainage and ventilation openings in structural elements where there is the possibility of water accumulation or high moisture content (Fig. 7)

Health and hygiene

No place with moisture favouring or forming bacteria, algae, moulds

Resistance

No possibility of attack by sulphates, if so, with the appropriate protections No risk of leaching from water (Fig. 5) No cracks in the apparent parts above the tolerable (Table 9) (Figs. 8 and 9) Adequate surface protection of exposed concrete No spots with corrosion signs (orange spots, longitudinal cracks in the frame, concrete cover stripping, exposed steel) (continued)

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Table 8 (continued) Requirement

Verification item

Evidence answered? NA

YES

NO

NI

No concrete faulty points/exposed steel (Fig. 10) No points with displating, delamination, peeling, erosion, disintegration Maintainability

No remnants of concrete forming Provided access for inspection and maintenance of parts of the structure with a shorter service life than the whole, such as support appliances, coffins, inserts, waterproofing and others

NA not applicable; NI not inspectionable Source Repette (1991), Thomaz (2001), Husni et al. (2003), ABNT NBR 14931 (2004), ABNT NBR 6118 (2014)

Table 9 Resistance requirements related to cracking and armor protection as a function of the EAC Type of structural concrete

Environmental aggressiveness class and protrusion type

Characteristic cracks opening in concrete surface (wk )

Simple concrete

EAC I a IV

Absent

Reinforced concrete

EAC I

≤0.4 mm

EAC II e III

≤0.3 mm

EAC IV

≤0.2 mm

Protruded concrete level 1 (partial protension)

Pre-tension with EAC I or post-tension with EAC I and II

≤0.2 mm

Protruded concrete level 2 (limited protension)

Pre-tension with EAC II or post-tension with EAC III and IV

0.0 mm

Protruded concrete level 3 (full protrusion)

Pre-tension with EAC III and IV

0.0 mm

Note For EAC-III and IV environmental aggressiveness classes, non-standard ropes are required to have special protection in the region of their anchors Source Adapted from ABNT NBR 6118 (2014, p. 80)

identified in case of doubts in sensory field inspections, or when a more detailed analysis of the system is requested (Amaral 2013).

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Fig. 5 Moisture and orange spot on beam and roof slab of 1st subsoil and diagonal shear cracking on beam

In addition to these utensils, others of an equally simple and small size could be added. All of them are packed in a suitcase and will be used in most cases (Lichtenstein 1986). The performance of expedited tests is not mandatory, but recommendable, since it contributes significantly to expand the inspector’s ability to understand and identify anomalies. To evaluate the system of reinforced concrete structures one must observe the criteria of the applicable technical standards, assessing whether the system meets the expected behavior in expedited tests according to the items in Table 11. In case of doubts in sensory field inspections, or when a more detailed system analysis is requested, some measurements and expedited tests should be performed for a better system evaluation: • Apparent concrete part displacements in comparison with the allowable valleys in Table 12. This measurement can be carried out with instructions that make it possible to compare the parts external faces, with a vertical or horizontal reference, such as: hose levels, bubble levels, plumb lines, rulers, topographic equipment, laser levels, etc. It should be noted that the reference lines arrangement should allow the evaluation of the faces parallel to the axis of lower part inertia, also avoiding that the forms openings are confused with plumb distortions (Repette 1991, p. 16).

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Fig. 6 Efflorescence in reinforced concrete beam

• Dimensional deviations of exposed concrete parts compared to the permissible values in Tables 13 and 14. This measurement can be carried out with instruments that make it possible to compare the height, width and length of the parts with a graduated reference, such as tape or laser scales, graduated rulers, hand squares, calipers, etc. • The reinforcement covering of the apparent structural parts can be verified by non-destructive and destructive tests, the latter not being indicated for inspection and receipt purposes, with the results compared to those foreseen in the project and/or Table 7. Within the non-destructive tests, the analysis can be performed with instruments that allow the verification of the position and depth of the steel bars, the most portable and financially accessible being the pacometer (Fig. 1). It should be noted that due care must be taken with the calibration and accuracy of the equipment, for correct data analysis. • The relative humidity content can be verified by means of instruments that allow the measurement of UR, such as the thermometer or psychrometer (Fig. 11), and verified if the microclimates of the building are equivalent to those predicted in the project in comparison with Table 5. The measurement should be performed at the most critical sites identified by the sensory field survey. • The CO2 content can be verified by means of instruments that make it possible to measure the CO2 content, and check whether the microclimates of the building are equivalent to those predicted in the project in comparison with Table 5. The

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Fig. 7 Non-ventilated barrel with water condensation on ceiling

measurement should be performed in the most critical locations, such as parking lots, close to gas-fired equipment, external areas, etc. • The carbonation depth can be evaluated by the colorimetri-co method, qualitative pH indication described in BS EN 14630 (2006), by performing a small fracture of the concrete piece, or extraction of testimony, following the application of a 1% diluted phenolphthalein solution, which reacts with the concrete leaving the carbonated region (pH ≤ 9) colourless, and the region still alkaline in pink/magenta (Fig. 12). • The presence or depth of free chlorides can be evaluated by the qualitative colorimetric method of the Italian standard UNI 7928 (1978)—even if the only existing standard reference is cancelled—by performing a small fracture of the concrete piece, extraction of the testimony, or dust removal with a drill; then a 0.1 M silver nitrate solution dissolved in aqueous solution is applied; where free chlorides are present a white precipitate (silver chloride) is formed and in the region without chlorides or with combined chlorides a brown precipitate (silver oxide) is formed, according to Fig. 13 (Real et al. 2015). If free chlorides are present, a laboratory test for water soluble chloride ion content should be performed using the ASTM C 1218 method, and the levels found should be compared with the limits in Table 15.

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Subtitle A

B

Plastic

C

D

E

F

G

H

Plastic Thermal shrinkage laying retraction Source: CANOVAS (1994, p. 122).

I

J

K

Long-term drying shrinkage

Mapped

L

M

Armor Corrosion

N RAA

Fig. 8 Typical frequent cracks in reinforced concrete structures

2.2.5

Classification of Non-conformities and Anomalies

The non-conformities and anomalies found in the previous steps should be classified as follows (ABNT NBR 16747 2018; CIB 1993): 1. Non-conformities are characterized by non-compliance with any legal, regulatory or user performance criteria; 2. Anomalies are classified by origin (Fig. 14): • Environment: when the origin of performance loss is due to causes arising from buildings or neighboring areas not foreseeable in project; • Land: when the origin of performance loss was due to causes originating from soil, topography etc., not predictable in project; • Exposure to environment: when the origin of performance loss was due to causes originated from the environment, not predictable in a project; • Project: when the origin of performance loss was due to error, inadequacy or lack of project information; • Execution: when the origin of performance loss was due to imperfection or error in execution or assembly, or also due to inadequacy in the transportation or storage of materials and components;

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Fig. 9 Crack thickness measurement with fissurometer by comparison showing an 0.2 mm opening

• Material: when the origin of performance loss was due to manufacturing error of the element or component. This problems classification is important in order to identify their legal obligation, as well as to know the problem origin: • Identify its extent, as it may be present in only one place at the time of inspection, but hidden in other places. Example: execution problems can be linked to a person or team and, in this way, the areas they executed will be tracked; in case of a project error, the areas that were specified in the same way will be identified; • Identify the provider or service provider responsible, to define who will perform the repair and/or financial disbursement. Example: in case of a material problem, the repair costs will be at manufacturer expense; • Identify the origin, to subsidize the identification of root cause, so that actions can be taken to avoid recurrence in other constructions, projects or lots of material.

2.2.6

Classification of Apparent Performance State

It is recommended to classify in a general way each one of the building’s constructive systems regarding the apparent performance state, based on identified anomalies and

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Fig. 10 Concreting nest on underside of exposed steel beam

non-conformities, taking into account the deterioration degree, the users risk and the use capacity loss and operation of some system, according to Table 16.

2.2.7

Priority Organization

Recommendations for action to correct and repair the problems observed should be organized at priority levels, taking into account the risk of each one, so that the corrective action plan is oriented. It is suggested that the preliminary risk analysis (APR) proposed in Table 17 be applied, which defines priorities according to their probability of occurrence compared to their harmful consequence.

2.2.8

Definition of Correction and Repair Actions

At this stage the corrective actions should be defined; they should be objective and simple, guiding the action taken by the person responsible for the correction, with the objective of identifying “what to do” and not “how to do it”. This can be, for example, a further investigation indication of problem cause, or the need indication for further study (ABNT NBR 16747 2018).

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Table 10 Relevant tools to assist the survey activities Tool

Use and application

Photo or video camera

Register of sites surveyed and anomalies identified

Borescope (predial endoscope)

Internal visualization of places where direct vision is not possible, such as linings, pipes, etc.

Drone

External visualization of places where access is impossible, unsafe or difficult, such as roofing, high facades etc.

Binoculars

Quick external visualization of distant places, such as facades, etc.

Magnifier

More detailed visualization of cracks, anomalies, etc.

Stem with mirror

Quick visualization of places of difficult access, such as facades visualized by the internal part of the building, between ceilings, etc.

Ruler

Expedited detection of flatness, such as floor and wall cladding, linings, etc.

Square

Expedited detection of orthogonality, such as corners of walls and ceilings, etc.

Level with bubble

Expedited detection of unevenness, such as falling of floor, levelling of benches, etc.

Plumb

Expedited detection of unevenness, such as wall plumbing, walls, etc.

Fissurometer

Expedited measurement of crack widths, by comparison

Graduated wedge

Execution of expeditious measurements of openings, such as cracks, gaps between floorboards, etc.

Pachymeter

Execution of expeditious dimensional measurements and surveys

Tape measure

Execution of expedited dimensional measurements and surveys

Compass

Geographical orientation, for solar incidence determination

Hammer and pointer

Auxiliary in taking samples, breaking coatings, etc.

Rigid polyethylene hammer

Performing rapid percussion tests to identify poorly adhered coatings

Screwdriver

Auxiliary in the opening of passage boxes, electrical panels; and execution of expedited tests of surface resistance of coatings, etc.

Spatula

Auxiliary in the removal of samples, breaking of coatings, etc.; and execution of expedited tests of surface resistance of coatings, etc.

Bucket

Performing expedited tests of floor fall, assisting in the identification of cracks with water spray on the lining, etc.

Bristle or brush

Cleaning of surfaces to be visualized, localized removal of debris or coatings, etc.

Lantern

Lighting of the site and the elements to be surveyed (continued)

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Table 10 (continued) Tool

Use and application

Ladder

Provide access to roofs, trapdoors, ceilings, etc.

Multimeter

Execution of expeditious measurements of current, voltage, resistance, etc.

Thermographic camera

Execution of expeditious tests of surface temperature to identify overheating of equipment and electrical devices and cables, leakage of currents, poorly adhered coatings on facades, humidity, thermal bridges, etc.

Moisture meter

Performing expedited measurements of the surface moisture content of walls, floors, ceilings, etc., to help identify the cause/origin of moisture

Thermohigrometer

Performing expeditious measurements of air temperature and humidity content

Fuel gas detector

Execution of expeditious measurements to identify leaks in gas installations, gas equipment, etc.

Pacometer

Execution of expeditious measurements of metallic or energized elements without the need for direct access, such as measurement of reinforcement cover, identification of embedded electrical network, etc.

Manometer

Execution of expedited pressure measurements of cold water, hot water, gas, etc.

Tablet/smartphone

Facilitating transport and consultation of projects, standards, documents, etc.

Sketch, leaves and pen

Assist in recording anomalies, drawing up sketches, identifying photographs, etc.

Pencil or chalk

Identify the construction elements with anomalies

Personal protective equipment

Security to perform the survey activities, access in high places, etc.

Note Instruments and equipment must be in good condition and calibrated in laboratories accredited by BNTL (Brazilian Network of Testing Laboratories) or with traceable measurement standards, within the tolerance criteria of deviation from national and international standards and within the validity period Source Lichtenstein (1986), AMARAL (2013)

In cases where the problem resolution is not feasible, the owner should be asked to value the damage caused and/or actions to mitigate it, such as, for example, reducing the value as a execution result of an environment with a smaller size than that contracted.

2.2.9

Issuance of Technical Opinion for Inspection and Receipt

The inspection and receipt must be registered, creating a technical inspection opinion and receipt, which will serve as a precautionary state record of building on the

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Table 11 Checklist of expedited tests: reinforced concrete structures Requirement

Verification item

Evidence answered? NA

Structural

YES

NO

NI

No movement of the apparent parts above the tolerable (Table 12) No plumbing deviations of pillars and apparent wall above the tolerable (Table 12) No dimensional or rental deviation of the apparent parts above the tolerable (Tables 13 and 14)

Resistance

Armor cover according to design and/or Table 7 (Fig. 1) Relative moisture content of the medium (Table 5) (Fig. 12) CO2 content of the medium (Table 5) Carbonation depth in reinforced concrete parts (Fig. 13) Depth or presence of free chlorides in reinforced concrete parts (Table 15) (Fig. 14) No dimensional or rental deviation of the apparent parts above the tolerable (Tables 13 and 14)

Source Repette (1991), ABNT NBR 14931 (2004), ABNT NBR 6118 (2014)

date of its completion and also as a basis for action to correct and repair identified problems. Therefore, the opinion must be thoroughly elaborated, having the anomalies well identified as to location and extension, being able to make use of sketches, illustrations, abundant photographic register, etc. The technical report of receiving inspection should be structured as follows (ABNT NBR 13752 1996; ABNT NBR 14724 2011; ABNT NBR 16747 2018; AS 4349-0 2007; ASTM E2270-14 2016; Singapore 2012): • • • •

Cover Summary Errata (where applicable) Introduction – Objective: inspection objective description, for example, inspection and receipt of common areas, or the private unit number “x”, etc.; – Applicant: applicant identification and/or contractor; – Owner: building legal representative identification; – Object inspected: description of building technical characteristics, for example, location, date of approved project at city hall, date of residence, date of condominium installation, number of buildings, number of floors, number of units, built area, building use, environments description per floor, construction systems description, etc.;

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Table 12 Limits for molded structures displacements in loco Reason for limitation

Example

Displacement to consider

Avoid psychological insecurity

Visible structural elements

Total

Sensory acceptability

Vibrations felt on the floor by users

Due to accidental loads

Surfaces that should drain water

Penthouses and balconies

Floors that must remain flat

Gymnasiums and bowling alleys



250



350

Total



250

Total



Occurred after the floor construction Avoid fissures and damages

Vertical seals

Ceiling linings

a The

Boundary shift

Masonry, frames, and cladding

After the construction of the wall

Lightweight partitions and telescopic frames

Occurring after the installation of the partition

Lateral movement of buildings

Caused by the action of wind for frequent combination (ψ1 = 0.30)

Vertical thermal movements

Caused by temperature difference

Horizontal thermal movements

Caused by temperature difference

Glued coatings

Occurred after the construction of the lining

Hanging or jointing coatings

Occurred after the construction of the lining

a

350 + inverse deflection b  600 

c 500 e 10 mm and θ = 0.0017 radd



250 e 25 mm

H 1700 e H 850 between floorsf g  400 e 15 mm Hi

500



350



175

surfaces must be sufficiently inclined or the intended displacement compensated for by inverse deflection so that no water accumulates b The displacements can be partially compensated by the specification of inverse deflection. However, the isolated  action of inverse deflection may not cause a deviation from the plane greater than  350 c The span  must be taken in the direction in which the wall or partition develops d Rotation on wall-mounted elements e H is the total building height and H the gap between two neighbouring floors i f This limit applies to the lateral displacement between two consecutive floors, due to the action of horizontal actions. Displacements due to axial deformation of the pillars cannot be included. The limit also applies to the relative vertical displacement of the ends of lintels connected to two bracing walls, when Hi represents the length of the lintel g The value  refers to the distance between the external pillar and the first internal pillar Notes 1. All displacement limit values assume  span elements supported at both ends by supports that do not move. In the case of overhangs, the span equivalent to be considered must be twice the length of the overhangs 2. In the case of surface elements, the prescribed limits consider that the  value is the smallest span, except in cases of verification of walls and partitions, where the direction in which the wall or partition develops is of interest, this value being limited to twice the smallest span 3. The total displacement must be obtained from the combination of characteristic actions weighted by the coefficients defined in ANBR NBR 6118 (2014) 4. Excessive displacements may be partially compensated by inverse deflection Source Adapted ABNT NBR 6118 (2014, p. 77), Thomaz (2001)

Guidelines for Inspection and Receipt of Reinforced Concrete … Table 13 Dimensional tolerances for cross-sections of linear structural elements (columns and beams) and for the thickness of surface structural elements (slabs and walls)

Dimension (a)

97 Tolerance

a ≤ 60 cm

±5 mm

60 cm < a ≤ 120 cm

±7 mm

120 cm < a ≤ 250 cm

±10 mm

a > 250 cm

±0.4% of dimension

Source ABNT NBR 14931 (2004)

Table 14 Dimensional tolerances for length of linear structural elements (columns and beams)

Dimension ()

Tolerance

 ≤3m

±5 mm

3m 15 m

±20 mm

Note The dimensional tolerance of overlapped linear elements should be considered over the overall dimension Source ABNT NBR 14931 (2004)

Fig. 11 Thermohygrometer example

– Inspection method: documental analysis, historical survey, sensory inspection, expedited tests, etc.; – Diligences: date of interviews, surveys, tests, etc.; environmental conditions at survey time/tests, when relevant. • Data presentation and analysis – Documents analysis: available documentation requested versus made, description of possible lack of documents, description of documents analysis, with possible irregularities;

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Fig. 12 Carbonation depth test with phenolphthalein application

Fig. 13 Test for free chlorides presence by silver nitrate application of, free chlorides (white) and combined or absent chlorides (brown). Source Medeiros et al. (2009)

– Inspection: description of anomalies and non-conformities identified in each environment, with respective classification regarding origin/non fulfillment of requirement; – Inspection limitations: identification of any area or item (within the inspection scope) that was not inspected, the reasons that prevented the inspection;

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Table 15 Maximum chloride ion content for concrete reinforcement protection Structure service conditions

Chloride ion content (Cl− ) in concrete (% over the cement mass)

All

Protruded concrete

≤0.05%

III e IV

Reinforced concrete exposed to chlorides in operating conditions of structure

≤0.15%

II

Reinforced concrete not exposed to chlorides in operating conditions of structure

≤0.30%

I

Reinforced concrete in mild exposure conditions (dry or protected from moisture in service conditions of structure)

≤0.40%

EAC

Source ABNT NBR 12655 (2015, p. 13)

Fig. 14 Diagram of anomalies causes and non-conformities at receiving buildings stage Source CIB (1993), Ishikawa (1990)

– Apparent state of performance classification: indicate the construction systems performance class of each existing/inspected; – Priorities organization: describe all problems with the respective degrees of priority; – Recommendations for correction: describe the actions to correct and repair each problem identified; • Conclusion – Indication of extent to which scope of inspection has been fulfilled and, if appropriate under the inspection contract terms; – Recommendations for an additional inspection or evaluation to be carried out by an expert; – Conclusions regarding the inspection objective, with enough information to allow the client to briefly understand the overall construction result; – Technical inspection opinion date;

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Table 16 Apparent state performance rating Rating

Description

Appropriate performance (class 1)

Suitable performance for use, when the system or element does not present any situation or manifestation that prevents the normal building use from the safety point of view, habitability and durability requirements

Regular performance (class 2)

Performance requires corrective and/or preventive recommendations, when the system or element does not present a situation that prevents the normal building use, does not present a situation that harms the safety, habitability or durability for users, but requires preventive and/or corrective interventions resulting from the observations made during the inspection, in order to prevent and/or correct failures with aesthetic repercussions, pathological manifestations or factors that jeopardize performance

Improper performance (classe 3)

Inadequate performance when the pathological manifestations detected jeopardize the safety and/or health of users

Source ABNT NBR 16747 (2018)

Table 17 Proposed heading for organising priorities according to risk Anomaly/non-conformity

Origin

Probability

Consequence

Risk

Corrective Actions

Identified at Sects. 2.2.1–2.2.4 item

Defined at Sect. 2.2.5 item

Define according to Table 18

Define according to Sect. 2.2.6 item

Define according to Table 18

Defined at Sect. 2.2.8 item

Source Scabbia (2004)

Table 18 Risk matrix for irregularities classification Risk matrix Probability

Consequences (according to Table 16) Class 1

Class 2

Class 3

3—High

Medium

High

High

2—Medium

Low

Medium

High

1—Low

Low

Low

Medium

Source Scabbia (2004)

– Technical manager signature, full name, professional council registration number; • References • Glossary (optional) • Appendices (where applicable)

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– Detailed photographic report and sketches identifying the anomalies and general building state; – Test results and tests performed; • Annexes (when applicable) – Laboratory tests, calculation memorials, relevant documents etc. – Register of Technical Responsibility, issued by the person responsible for inspection and receipt.

3 Final Considerations Due to the large number and complexity of requirements for receiving a building structure, when applying the inspection method suggested here, its scope may vary according to the need for greater or lesser analysis depth, and may cover from one to all building systems, defined by contractor, and its cost-benefit should be considered. It should be emphasized that some aspects may lead to an impediment to inspection, for some of the following reasons: • physical impediment, because it is not accessible to direct sensory inspection or out of reach or any equipment capacity (e.g., characteristics of concrete used in foundation). In these cases, the item cannot be reproved, but the risks of this noninspection can be analysed, if they can be monitored, mitigated, etc. It could also be recommended the cracks instrumentation (gypsum seals, installation of inclinometers, bases for measurements with micrometers, etc.) and/or the execution of inspection wells, in case anomalies in the superstructure and masonry were found to be caused by foundation accommodation; • temporal impediment, as it was a record that should have been generated during one of design or construction stages (e.g.: characterization of environmental aggressiveness at the time of design, or piles load test). In these cases, alternative analyses should be performed that approximate the expected result at the correct age, or if this is not possible, the item may be disapproved—if evidence is required by the constructor; • technical impediment, due to lack of inspector technical qualification (e.g.: civil engineer inspector is not qualified to inspect large electrical installations, elevators, etc.). In this case it is necessary to hire a multidisciplinary team; • financial hindrance, due to lack of monetary resources to hire the adequate inspection scope (e.g.: necessary laboratory tests, reprocessing of the structure calculation or further investigation of a certain system). In this case, one should proceed in the same way as in the case of access lack. Through practical experiences, it is possible to verify that in some cases the solution will be unfeasible due to technical, financial, or logistical aspects. In this case, the risks to users should be analyzed and mitigation actions should be adopted;

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for example, not dimensioning the structure for the required time of fire resistance (RTFR), one can include active measures of fire protection, such as sprinklers or fire resistant coatings application. Financial losses to owners can also be assessed by compensating them monetarily or by performing counterpart trading (e.g., price reduction due to environment execution with a smaller size than that sold).

References Amaral SFM (2013) Inspeção e diagnóstico de edifícios recentes: Estudo de um caso real. 2013. 293 f. Dissertação (Mestrado) - Curso de Engenharia Civil: Edificações, Departamento de Engenharia Civil, Instituto Superior de Engenharia de Lisboa, Lisboa American Society for Testing and Materials (2016) ASTM E2270-14: Standard practice for periodic inspection of building facades for unsafe conditions. Pensilvânia Associação Brasileira De Normas Técnicas (2014) NBR 6118: Projeto de estruturas de concreto Procedimento. Rio de Janeiro, 238 p Associação Brasileira De Normas Técnicas (2016) NBR 9452: Inspeção de pontes, viadutos e passarelas de concreto — Procedimento. Rio de Janeiro, 48 p Associação Brasileira De Normas Técnicas (2015) NBR 12655: Concreto de cimento Portland Preparo, controle, recebimento e aceitação - Procedimento. Rio de Janeiro, 23 p Associação Brasileira De Normas Técnicas (1996) NBR 13752: Perícia de engenharia na construção civil. Rio de Janeiro, 8 p Associação Brasileira De Normas Técnicas (2011) NBR14724: Informação e documentação Trabalhos acadêmicos – Apresentação. Rio de Janeiro, 11 p Associação Brasileira De Normas Técnicas (2004) NBR 14931: Execução de estruturas de concreto - Procedimento. Rio de Janeiro, 53 p Associação Brasileira De Normas Técnicas (2013) NBR 15575-1: Edificações habitacionais — Desempenho - Parte 1: Requisitos gerais. Rio de Janeiro, 71 p Associação Brasileira De Normas Técnicas (2013) NBR 15575-5: Edificações habitacionais — Desempenho - Parte 5: Requisitos para os sistemas de coberturas. Rio de Janeiro, 71 p Associação Brasileira De Normas Técnicas (2018) NBR 16747: Inspeção predial - Diretrizes, conceitos, terminologia, requisitos e procedimento. Rio de Janeiro, 22 p. (Projeto de elaboração) Australian Standard (2007) AS 4349-0: Inspection of buildings—Part 0: general requirements. Sydney Australian Standard (2007) AS 4349-1: Inspection of buildings—Part 0: Pre-purchase inspections— residential buildings. Sydney Bristish Standards Institution (2006) BS EN 14630: products and systems for the protection and repair of concrete structures: test methods: determination of carbonation depth in hardened concrete by the phenolphthalein method. London, United Kingdom Canovas (1994) Manuel Fernandez. Patologia y Terapêutica Del Hormigon Armado, 4th edn. Rugarte, Madrid, 487 p Finger FB, González MS, Kern AP (2015) Control de la obra terminada: Inspección final de calidad en un proyecto de interés social. Revista Ingeniería de Construcción, Santiago, v. 30, n. 2, pp 147–153, 11 June 2015 Gonçalves OM, John VM, Picchi FA (2003) Normas técnicas para avaliação de sistemas construtivos inovadores para habitações. In: Roman H, Bonin LC (eds) Normalização e Certificação na Construção Habitacional. ANTAC, Porto Alegre. Cap. 3. Pp 42–53. (Coleção Habitare, v. 3) Grandiski P (2018) Problemas Construtivos-I: aspectos técnico-legais da construção civil, 11th edn. Oficina de textos, São Paulo, 356 p Grossi MVF (2017) Análise de um edifício em concreto armado com problemas de corrosão de armaduras. In: 2º Simpósio Paranaense de Patologia das Construções (2º SPPC), 2017,

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Curitiba. Anais… Curitiba: Editora Cubo, pp 34–47. http://doi.editoracubo.com.br/10.4322/ 2SPPC.2017.004 Grossi MVF (2018) Assistência técnica de construção de edifícios. AEA, São Paulo. 676 slides. Aula do curso livre de assistência técnica de construção de edifícios Grossi MVF (2019) Diretrizes para inspeção e recebimento de edificações habitacionais recémconstruídas. 446 f. Dissertação (Mestrado) - Curso de Habitação: Planejamento e Tecnologia, Instituto de Pesquisas Tecnológicas do Estado de São Paulo – IPT, São Paulo Husni R et al (2003) Ações sobre as estruturas de concreto. In: Helene PRdL et al (Org.). Manual de reabilitação de estruturas de concreto: Reparo, reforço e proteção. São Paulo: Red Rehabilitar, 2003, pp 37–104. Tradução Osvando Braga Junior INTERNATIONAL COUNCIL FOR RESEARCH AND INNOVATION IN BUILDING AND CONSTRUCTION (CIB). W086 Building patholoy: A state-of-the-art report. Holanda: CIB, 1993 International Organization for Standardization (2016) ISO 19208: framework for specifying performance in buildings. Suíça, 24 p Ishikawa K (1990) Introduction to quality control, 448 p (Tradução J. H. Loftus) Lichtenstein NB (1986) Patologia das construções. São Paulo: Departamento de Engenharia de Construção Civil da Escola Politécnica da Universidade de São Paulo, 35 p. Boletim técnico 06 Medeiros MHF, Hoppe Filho J, Helene P (2009) Influence of the slice position on chloride migration tests for concrete in marine conditions. Marine Struct [s.l.] 22(2):128–141, abr. Elsevier BV. http:// dx.doi.org/10.1016/j.marstruc.2008.09.003 PROJECT MANAGEMENT INSTITUTE (2012) A guide to the project management body of knowledge: PMBOK Guide, 4th edn. Saraiva, São Paulo, p 125 Real LV et al (2015) AgNO3 spray method for measurement of chloride penetration: the state of art. Revista ALCONPAT, [s.l.] 5(2):149–159, 30 maio 2015. Revista ALCONPAT. http://dx.doi. org/10.21041/ra.v5i2.84 Repette WL (1991) Contribuição à inspeção e avaliação da segurança de estruturas acabadas de concreto armado. Rio Grande do Sul, 1991. 169 f. Dissertação (Mestrado) - Curso de PósGraduação em Engenharia Civil, Universidade Federal do Rio Grande do Sul, Porto Alegre Scabbia ALG (2004) Aplicação de análise preliminar de perigos (APP) no gerenciamento de riscos de incêndios originados em instalações elétricas de baixa tensão. 237 f. Dissertação (Mestrado) Curso de Habitação: Planejamento e Tecnologia, Instituto de Pesquisas Tecnológicas do Estado de São Paulo, São Paulo Silva FMM, Couto JPPM (2012) Conceito e estado internacional da atividade de building commissioning. Guimarães: Universidade do Minho, 175 p. (Workshop Construção e Reabilitação Sustentáveis: Soluções Eficientes para um Mercado em Crise) Singapore, Building and Construction Authority (2012) Periodic structural inspection of existing buildings: guideline for structural engineers. Singapore Teixeira R, Santos JdC (2015) Inspeção para compra de imóveis: a consultoria de engenheiros e arquitetos durante a compra de imóveis: os conceitos de home inspection para profissionais do Brasil. PINI, São Paulo, 89 p Thomaz E (2001) Tecnologia, gerenciamento e qualidade na construção. PINI, São Paulo, 451 p Italian Standard UNI 7928 (1978). Determination of chloride ion penetration. Roma

Application of the Degradation Measurement Method in the Study of Facade Service Life E. Bauer, J. S. de Souza, and C. B. Piazzarollo

Abstract The degradation of buildings needs to be investigated more and more, mainly due to the increasing demands of performance and service life specified for the facades. Otherwise, the definitions of rehabilitation and pathology are increasingly associated with the evolution of performance over time. Measuring the degradation allows to evaluate the service condition of the component, identifying whether it has already reached or exceeded the specified service life. The aim of this chapter is to describe the Degradation Measurement Method developed to quantify the degradation in facades. Guidelines for anomaly inspection, mapping and quantification operations are presented, as well as for calculating the FGD indicator. An application is made with the purpose of exemplification in two degraded samples, as well as the application to identify the service life value for several samples is also presented. The daily use of this methodology has allowed constant improvements and also the development of more accurate models to quantify the degradation. Keywords Facade · Service life · Degradation measurement · Anomalies

1 Introduction The degradation of the building results from the action of various agents relevant to the exposure and use of different elements and systems that compose it. The evolution of degradation can be interpreted as the continuous reduction in performance over time. If the performance decreases below the functionality limits, the functional service life limit is reached. The same reasoning can be done in relation to degradation, that is, once the critical limits are reached, the service life limit is determined (Shohet et al. E. Bauer (B) · J. S. de Souza · C. B. Piazzarollo Department of Civil and Environment Engineering, University of Brasília, Brasília, Brazil e-mail: [email protected] J. S. de Souza e-mail: [email protected] C. B. Piazzarollo e-mail: [email protected] © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2020 J. M. P. Q. Delgado (ed.), Building Pathology, Durability and Service Life, Building Pathology and Rehabilitation 12, https://doi.org/10.1007/978-3-030-47302-0_5

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1999; Flores-Colen and de Brito 2010). The life can be understood at a functional level, that is, meeting a predetermined minimum performance level. It can also be considered under the aspect of obsolescence, that is, when functions and performance are enhanced, or even when more attractive technical and economic solutions appear (Lee 2018). From the perspective of aesthetics, the life of a building can also be determined by changes in its functions, architectural patterns and other aspects during the period of use. The process is always complex, since it involves many variables, several of which are difficult to quantify and model. Degradation agents, generally classified as: mechanical, electromagnetic, thermal, chemical and biological, vary depending on the climate, country, geographical aspects, and also depending on the materials and design definitions. The active mechanisms then become specific to the agents and intensity of action, and also to the nature and behavior of materials and components. For example, on a facade, ultraviolet radiation is an important agent for polymeric paintings, while it has little effect on the degradation of ceramic tiles. The sensitivity of a facade is, therefore, due to the quantity and intensity of the action (cycles, time of exposure) and also the propensity to degradation of the materials and elements (porosity, ductility, rigidity) by a certain mechanism (Flores et al. 2010; Souza et al. 2018a). The building’s facade is a peculiar element, since: it is responsible for a large set of different functions (protection, waterproofing, ventilation), it has a large number of different elements (masonry, windows, claddings); and it can also be subdivided into several zones (top, corners and ends, balconies, openings, continuous walls and transition between floors). All these different characteristics make the response to a given degradation agent unique for each case (ISO/DIS 15686-2 2012). The most important agents of facades are the climatic ones. Thus, both solar radiation and driving rain are seen as agents responsible for most mechanisms (Silvestre and De Brito 2009; Bauer et al. 2015; Souza et al. 2018b). The radiation, which is distinguished for each cardinal orientation of the facades, influences the thermal behavior, affecting the displacements and thermo-mechanical efforts that can mainly cause cracking and detachment (Nascimento et al. 2016; Zanoni et al. 2018). The effect of radiation is cyclical, that is, each day there is an incidence of the agent. Facades with greater exposure have greater degradation (Souza et al. 2016). The driving rain is dependent on the precipitation, direction and intensity of the winds, as well as on the topography, height and aerodynamics of the building. It also has preferred cardinal orientations in function of the microclimate of each location. The wetting of the facades can lead to different displacements, cracking, infiltrations, and can increase the effects of detachment and thermal shock. A major advance in the study of quantification of actions of climatic agents and the building’s response to them, is the use of hygrothermal simulation. Bauer and collaborators (Zanoni 2015; Nascimento 2016; Piazzarollo 2019; Souza 2019), using the WUFI system, have associated climatic action to degradation, identifying, among other aspects, the differences in the mechanisms in relation to the cardinal orientation of the facades. This approach is very useful, both in the study of degradation and in

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the evaluation of new building projects, where it is possible to evaluate the expected service life for each proposed solution. The quantification of the degradation of a facade sample can be used for several purposes, where it stands out: mapping of anomalies, classification of degradation, evaluation of service life, among others. To study the service life of prolonged exposures, a quantification is frequently performed through inspections. To study the service life, the ISO/DP 15686-2 (2002) proposes: field exposure, inspection of buildings, exposure in experimental buildings and in use exposure. For the case of inspection of buildings in use, although it is often difficult to obtain the history of the inspected component, it has the advantage of obtaining a direct correlation between the state of degradation of the component and the environmental conditions of exposure and use. In this context, the Degradation Measurement Method (DMM) is intended to quantify the degradation based on facade inspection and anomaly mapping. One of the main results of this method is to allow the elaboration of degradation curves which are expressed as a function of time, as shown in Fig. 1. In such cases, several samples of buildings of different ages may have their degradation quantified. The evolution of this over time is the facade degradation curve. As can be seen in Fig. 1, when quantifying the General Degradation Factor (FGD) of several building samples, it is possible to identify trends of evolution. When making a new inspection of a facade sample, one can determine if the evolution follows the standards and also to prospect on what is the service life of the sample or when it was reached.

Fig. 1 Facade degradation evolution over time

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2 Degradation Measurement Method The Degradation Measurement Method (DMM) was developed by Bauer and collaborators (Silva 2014; Souza 2016) at the University of Brasília (Brazil) to quantify the facade degradation. The focus of the method is the degradation, that is, the quantifications are based on the study of anomalies and degraded regions. The DMM consists of a set of investigation and analysis procedures that allow to obtain degradation quantification indices. For this, some basic steps are defined, namely: • Classification of anomalies—where the observed anomalies are classified into four main groups (detachment, cracks, joint defects, stains). This definition is supported by extensive study of characterization of the facade of anomalies developed in Brasilia, Brazil (Bauer et al. 2011). • Standardization and adequate definition of samples. • Field inspection using: techniques for capturing and orthogonalizing digital images, laser scanning, infrared thermography and physical inspection when necessary. • Definition and mapping of anomalies in scale for each sample. • Quantification of the degree of degradation by calculating the indicators.

2.1 Sampling and Mapping A particularity of the DMM sampling is the division of the facade into facade samples. From another perspective, several methods quantify the degradation of the entire facade (Magos et al. 2016; Galbusera et al. 2014; Prieto et al. 2018). The use of DMM facade samples allows more specific investigations such as: • Study and define preferential degradation zones (Piazzarollo 2019). • Observe the variability of the degradation along the facade. • Compare different behaviors of architectural elements (continuous facade, gables, stairs). The definition of the samples is a preliminary step to field inspection. Figure 2 exemplifies the subdivision of the facade into samples. Sample A1 is in a gable element, samples A2 and A5 are in the continuous facade element, and sample A3 and A4 are in the staircase element. The criteria for defining the samples allows a standardization of the methodology, which is interesting, for example, for comparing the results between buildings with different design. The criteria are shown in Table 1. Once the samples are defined, the following steps are the inspection, identification and mapping of anomalies. In the case of images, an orthogonalization of the same is made in order to be able to elaborate sketches on an appropriate scale. Figure 3 exemplifies these steps until the quantification of anomalies.

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Fig. 2 Example of the definition of facade samples

Table 1 Sample configuration criteria Criteria

Description

1

Maximum area of 300 m2

2

Minimum area of 50 m2

3

The sample must be on the same plane. Plan changes constitute another sample

4

If there are structural joints, the sample limit must coincide with them. It is not allowed to define a sample that exceeds the structural joint

5

The sample must be inserted in the same architectural element (facade, gable, stairs). It is not allowed to define samples in 2 or more elements

The entire quantification is expressed in terms of the sample’s degraded area. This is achieved by overlapping a 0.50 m × 0.50 m mesh (in scale) on the mapping (Fig. 3d). Area units (mesh) are then accounted for each anomaly found. This way of quantization, as well as the mesh size, is defined from extensive study developed by Silva (2014). Linear or localized anomalies are also quantified by the set of area units (mesh) where they are manifested. With this form of accounting, the aim is to simplify the quantification of degraded areas in the sample. If the user already has a mapping with the quantification of the degraded areas, for each group of anomalies, he can use it without problems.

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Fig. 3 Details of the sample definition: obtaining the digital image (a), orthogonalization (b), sketch (c), and quantification with mesh overlay (d)

2.2 Degradation Indicators For quantification it is necessary to preliminarily group the anomalies. Some studies carried out in Brasília-Brazil have identified the main anomalies. Souza (2019) in an investigation of more than 350 samples of buildings in use, aged between 10 and 50 years, observes the distribution illustrated in Fig. 4. It is identified that inside the degraded area, the detachment group has the highest indexes, followed by cracks. The characterization of anomalies, in order to classify what should be detailed in the mapping, is done in four groups, as described in Table 2.

Fig. 4 Occurrence of facade anomalies in Brasilia-Brazil

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Table 2 Classification and grouping of facade anomalies Anomalies group

Description

1. Detachment (DT)

It involves all the anomalies associated with the detachment of the facade tile, regardless of the cause (stress, strain, displacement, failures in the execution, among others), and regardless of how it occurs (on the surface, in the mortar base, among others)

2. Crack (CR)

Crack anomalies in the ceramic cladding, regardless of its manifestation and origin, as well as the zone of the facade where it occurs

3. Joint (JO)

Anomalies observed at any joints in the facade. Any situation is computed, such as: cracking and removal of the filling material, failures in the sealants, among others

4. Stain (ST)

Surface stains of any nature such as efflorescence, damp, among others

Two indicators are defined in the quantitative analysis. The first, Damage Factor (FD), is calculated directly after quantification, according to Eq. (1). For each group of anomalies (Table 2), the degraded areas of the sample are added and divided by the total area of the sample. It is interesting, for each sample, to calculate the FD for each group of anomalies in order to classify the type of degradation. In this assessment, the degraded area of each group is divided by the total area of the sample. The sum of all FD (n) corresponds to FD (Eq. 2). FD =

(Aan(DT ) + Aan(C R) + Aan(J O) + Aan(ST ) ) × 100 At

(1)

where: FD is the sample damage factor; Aan (n) is the degraded area in the sample by the group n anomalies (DT, CR, JO, ST) (m2 ); n is the classification group of the observed anomaly (Table 1), and At is the total area of the sample (m2 ). F D = F D(DT ) + F D(C R) + F D(J O) + F D(ST )

(2)

where: FD is the sample damage factor, FD(DT) is the detachment damage factor, FD(CR) is the crack damage factor, FD(JO) is the joint damage factor, and FD(ST) is the stain damage factor. FD is mainly used to assess the incidence occurrence. It can be applied to study the incidence of each group of anomalies. In calculating the FD for each facade zone, it is possible to identify the most degraded zone. In the same way, one can proceed to study the impact on each element of architecture (for example: facade, gable, staircase). The second indicator is the General Degradation Factor (FGD). It is a model based on the studies by Gaspar and Brito (2008), Bordalo et al. (2011) and Gaspar (2009) and proposed by Silva (2014) and Souza (2019) in Brazil. It consists of calculating the weighted degradation related to the types of anomalies observed in the inspection process. This factor makes it possible, through a weighted list of the observed anomalies, to quantify the degradation of each facade sample. FGD is

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calculated according to Eq. 3.  FGD =

Aan(n) · G (n) · R I(n)  At · G max

 (3)

where: FGD is the General Degradation Factor, Aan(n) is the area damaged by an anomaly in group n (m2 ), G(n) is the gravity factor of the anomaly (n) (1, 2, 3 or 4) (Table 4), RI(n) is a weighting factor of the relative importance of each  anomaly observed (Table 5), At is the total area of the facade sample (m2 ) and Gmax is the sum of the severity factors equivalent to the level of the greater gravity (4 + 4 + 3 + 3) considering the groups in Table 2. The FGD with its gravity (G) and relative importance (RI) factors consider the observed degradation of the sample. The FGD also expresses the degradation in relation to the worst possible condition, that is, multiplying the sample area (A t ) in the denominator by the sum of the highest possible values of the gravity index ( Gmax ). Thus, it is possible, for example, to compare samples from different buildings in different degrees of degradation, as well as in different architectural elements. The gravity factor (G) assumes values from 1 to 4, in a similar way as ISO/DIS 15686-7 (2006) establishes when discussing the influence of degradation on the service life of the building. As shown in Table 3, four conditions (A, B, C, D) are associated with G values, for each group of anomalies (Table 2). Table 3 describes the classification criteria for the gravity index. For the definition of the G value, Table 4 specifies the criteria according to the sample FD for each anomaly group. It is observed that the simple presence of detachments or cracks already classifies these anomalies as condition B. Likewise, there is no reason to classify stains and joints in condition D, since they do not evendefine collapse or ruin. Adding the highest G values for all anomalies, we have the Gmax that corresponds to 14 (4 + 4 + 3 + 3) and is constant in Eq. 3. Table 3 Description of the degradation conditions and the gravity factor (G) Conditions

G

Description

A

1

Good service conditions in which possible anomalies do not impair the functionality and durability of the system. There is no risk to the safety of users and preventive maintenance is suggested

B

2

Presence of localized anomalies that impair functionality, but do not impair the durability and safety of users. Predictive maintenance is suggested in periodic maintenance to assess system performance

C

3

Generalized and simultaneous presence of anomalies that impair the functionality, durability and security of the system. Corrective maintenance procedures are suggested

D

4

Widespread incidence of anomalies that impair functionality, safety and durability, presenting a risk of collapse or ruin of the system. In this condition, rehabilitation or restoration of the system is necessary

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Table 4 Criteria for defining the gravity factor G Condition

G

FD (%) Detachment

Crack

Joint

Stain

A

1

–

–

FD(JO) < 10

FD(ST) < 10

B

2

0 < FD(DT) < 5

0 < FD(CR) < 20

10 ≤ FD(JO) < 30

10 ≤ FD(ST) < 30

C

3

5 ≤ FD(DT) < 30

20 ≤ FD(CR) < 50

30 ≤ FD(JO)

30 ≤ FD(ST)

D

4

30 ≤ FD(DT)

50 ≤ FD(CR )

Table 5 Relative importance factor (RI) for each group of anomalies RI

Detachment

Crack

Joint

Stain

1.00

0.77

0.28

0.11

The relative importance (RI) between groups of anomalies in ceramic cladding systems is determined through correlation matrices. To obtain the RI factor, the relationship between the anomalies and their causes and the relationship between the anomalies and how they affect the degree of performance is analyzed. Souza (2019) developed a broad investigation that allows the presentation of RI values for ceramic facades, as shown in Table 5. Table 5 shows that the detachment has the highest RI value. Thus, for example, for joints, in calculating the FGD (Eq. 2) the importance in relation to detachment is 0.28.

2.3 Application Example The first data to obtain is the sample area. Then, the degraded areas are quantified for each group of anomalies and the FD for the anomalies (FD(DT), FD(CR) , FD(JO) , FD(ST)) ) is calculated, respectively, according to Eq. (1). This done, it is possible to determine the G, using Table 4. Another factor to be defined is the RI, which is obtained in Table 5 for each type of anomaly. The last step is the calculation of the FGD using Eq. (3). To exemplify the calculation of the FGD, the following is an example of two samples, in particular Sample 1 and Sample 2. Figure 5 shows the mappings of the samples which differ in their total area and also in the constitution of the elements of facade. The degraded areas are also different in the samples. Table 6 shows the calculation routine until the FGD values are obtained.

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Fig. 5 Anomalies mapping of samples 1 and 2

3 Service Life Limit One of the most important parameters to be defined when using service life prediction models is the limit state of degradation, that is, the maximum acceptable level of degradation (Branco et al. 2013). Under the focus of the functional life of the facades, it is possible to identify conditions in which the FGD can define the degradation limit. Souza (2019) developed an investigative procedure in order to define the limit state, based on a wide field investigation. The criteria for determining the service life limit of ceramic facades are based on samples, investigated in the field and considers the following conditions: • Ascertaining the extension and disposition of anomalies on the facade, with the purpose of identifying whether the anomalies are present in several floors and zones of the façade, which characterizes a generalized degradation; • Identification of maintenance histories, in order to observe if the performance of punctual maintenance corrected the existing degradation during the life of the building; • Observation of the conditions associated with the expected performance with the intention of verifying whether the existing anomalies impair the functionality and durability of the facade, besides to possibly causing risks to the safety of users. As a result of this analysis, it is possible to define ranges of FGD values for each of the conditions set out in Table 3. Table 7 specifies these values. Figure 6 shows the limits discussed in the evolution of degradation over time. It is important to observe that, in the model of the degradation curve, the limit of service life is reached at an age close to 24 years, as identified in Fig. 6.

Application of the Degradation Measurement Method … Table 6 Degradation indicator calculation spreadsheet

115 Sample 1

Sample 2

Sample área (At)

(m2 )

358.25

150.25

Detachment (Aan(DT) )

(m2 )

94.50

43.25

Crack (Aan(CR) )

(m2 )

6.00

1.00

Joint (Aan(JO) )

(m2 )

0.00

6.50

Stain (Aan(ST) )

(m2 )

0.00

0.00

Total degraded área (Aan)

(m2 )

100.50

50.75

FD(DT)

(%)

26.4

28.8

FD(CR)

(%)

1.7

0.7

FD(JO)

(%)

0.0

4.3

FD(ST)

(%)

0.0

0.0

FD

(%)

28.1

33.8

Detachment

3

3

Crack

2

2

Joint

–

1

Stain  Gmáx

–

–

14

14

Damage factor (FD) (Eq. 1)

Gravity factor (G) (Table 4)

Relative importance factor (RI) (Table 5) Detachment

1.00

1.00

Crack

0.77

0.77

Joint

0.28

0.28

Stain

0.11

0.11

0.058

0.063

General degradation factor

FGD

The final result of the FGD calculation for each sample is highlighted.

Table 7 FGD intervals for each degradation condition

Conditions

FGD

A

0.169

The Conditions shown in Fig. 6 and Table 7 indicate ranges of degradation. Over time, the degradation increases, and goes beyond the limits of each condition, changing its situation. Thus we have:

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Fig. 6 Degradation over time associated with 4 limit conditions

• The Condition A is defined as a slight degradation condition. Samples with FGD values below 0.003 are classified under this condition. • Condition B shows localized degradation, but without prejudice to performance. Thus, FGD values are between 0.003 and 0.049. • In Condition C, the acceptable degradation limit is exceeded, with loss of functionality and safety, that is, the limit state of degradation is exceeded. Samples with FGD values are between 0.050 and 0.169 are classified under Condition C. • Condition D indicates severe degradation with great damage to performance and safety, in which intensive rehabilitation must be carried out. In this condition, samples of FGD values are greater than 0.169 are included. The definition of the FGD limit (0.050), which characterizes the limit state of degradation, allows applying several methodologies to define the service life. The graphical method, in which a simple regression model is obtained allows to obtain a trend curve, which requiring a database of several samples with different ages. When the model curve reaches the FGD limit value (0.050), the service life time is identified. An example of this analysis can be seen in Fig. 7, where the evolution of the FGD of a set of samples is shown, where the samples are subdivided according to the cardinal orientation. In Fig. 7, it can be seen that the service life of the facades is differentiated according to the orientation, with the shortest being oriented to north and the biggest oriented to the west. This difference is approximately 12 years. The observed evolution allows to conclude that for the younger ages (0–10 years) the values of FGD are relatively low, with no predominance of trend. For more advanced ages (40 years) it is observed that the north and west orientations are predominant in relation to FGD values. Another important observation is that degradation is a cumulative process, that is, it grows and increases in speed with the evolution of time.

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Fig. 7 Evolution of degradation—influence of cardinal orientation

4 Conclusions The development of DMM, its analysis and indicators were obtained through a gradual evolution of several studies, with different approaches and objectives. Studying degradation is a very complex task, but developing a methodology that allows comparing results from different buildings, different cities or countries, is a study that never ends, since there will always be a new necessary approach, new challenges in relation to the mechanisms of degradation, among other various aspects. It is possible to conduct several important investigations, such as associating degradation (FGD) with the quantification of climatic degradation agents. Hygrothermal simulation brings several contributions to this approach. Another approach parallel to this theme is the service life forecast in the design phase. Based on the models and algorithms developed and adapted, it is already possible to act on this important theme. As for the FGD indicator and its formulation and parameterization, it seeks to properly contemplate the main anomalies, considering their specific importance. It is certainly possible to quantify the degradation with this methodology. The challenges proposed converge to improve the accuracy of models to the study of more samples in the field, also differentiating other regions with different degradation agents. The Degradation Measurement Method already allows efforts to be directed towards the construction of a normative document that will use the results of these investigations to improve the projects, the construction process, the rehabilitation and ultimately to improve the use of the building.

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References Bauer E, Castro EK, Antunes JR, Leal FE (2011) Identification and quantification of failure modes of new buildings facades in Brasília. In: 12th DBMC: durability of building materials and components, pp 1089–1096 Bauer E, Castro EK, Silva MNB (2015) Estimate of the facades degradation with ceramic cladding: study of Brasilia buildings. Cerâmica 6:151–159 [in Portuguese] Bordalo R, De Brito J, Gaspar PL, Silva A (2011) Service life prediction modelling of adhesive ceramic tiling systems. Build Res Inf 39:66–78 Branco F, Paulo P, Garrido M (2013) Service life in civil construction. In: Internacional boletín técnico asociación latinoamericana de control de calidad. Patología y Recuperación de la Construcción Alconpat, pp 1–22 (in Portuguese) Flores-Colen IS, De Brito J (2010) A systematic approach for maintenance budgeting of buildings façades based on predictive and preventive strategies. Constr Build Mater 24(9):1718–1729 Flores-Colen I, De Brito J, Freitas VP (2010) Discussion of criteria for prioritization of predictive maintenance of building façades: survey of 30 experts. J Perform Constr Facil 24(4):337–344 Galbusera MM, De Brito J, Silva A (2014) The importance of the quality of sampling in service life prediction. Constr Build Mater 66:19–29 Gaspar P (2009) Vida útil das construções: Desenvolvimento de uma metodologia para a estimativa da durabilidade de elementos da construção. Aplicação a rebocos de edifícios correntes. Tesis Doctoral. Instituto Superior Técnico, Universidade Técnica de Lisboa. Portugal (in Portuguese) Gaspar P, De Brito J (2008) Quantifying environmental effects on cement-rendered facades: a comparison between different degradation indicators. Build Environ 43(11):1818–1828 ISO/DIS 15686-7 (2006) Buildings and constructed assets—Service life planning. Part 7: Performance evaluation for feedback of service life data from practice ISO/DIS 15686-2 (2012) Buildings and constructed assets—Service life planning. Part 2: Service life prediction procedures Lee JS (2018) Value engineering for defect prevention on building façade. J Constr Eng Manage 144(8):04018069 Magos M, De Brito J, Gaspar PL, Silva A (2016) Application of the factor method to the prediction of the service life of external paint finishes on façades. Mater Struct 49(12):5209–5225 Nascimento MLM (2016) Application of hygrothermal simulation on investigation of building facades degradation. Tesis Master. Universidade de Brasília, Brasil (in Portuguese) Nascimento MLM, Bauer E, Souza JS, Zanoni VAG (2016) Wind-driven rain incidence parameters obtained by hygrothermal simulation. J Build Pathol Rehabil 1(1):5 Piazzarollo CB (2019) Study of the progression and severity of degradation in different facade component zones. Tesis Master. Universidade de Brasília, Brasil (in Portuguese) Prieto AJ, Silva A, De Brito J, Macias-Bernal JM (2018) Serviceability of facade claddings. Build Res Inf 46(2):179–190 Shohet IM, Rosenfeld Y, Puterman M, Gilboa E (1999) Deterioration patterns for maintenance management—A methodological approach. In: 8th DBMC: durability of building materials and components, pp 1666–1678 Silva MNB (2014) Quantitative evaluation of degradation and service life of facade coatings: application to Brasilia/DF’s case. Tesis Doctoral. Universidade de Brasília, Brasil (in Portuguese) Silvestre JD, De Brito J (2009) Ceramic tiling inspection system. Constr Build Mater 23(2):653–668 Souza JS (2016) Evolution of facade degradation: effect of degradation agents and elements constituents. Tesis Master. Universidade de Brasília, Brasil (in Portuguese) Souza JS (2019) Impact of degradation factors on service life of buildings’ facades. Tesis Doctoral. Universidade de Brasília, Brasil (in Portuguese) Souza JS, Bauer E, Nascimento MLM, Capuzzo VM, Zanoni VA (2016) Study of damage distribution and intensity in regions of the facade. J Build Pathol Rehabil 1(1):3 Souza JS, Silva A, De Brito J, Bauer E (2018a) Service life prediction of ceramic tiling systems in Brasília-Brazil using the factor method. Constr Build Mater 192:38–49

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Souza JS, Silva A, De Brito J, Bauer E (2018b) Application of a graphical method to predict the service life of adhesive ceramic external wall claddings in the city of Brasília, Brazil. J Build Eng 19:1–13 Zanoni VAG (2015) Influence of climatic degradation agents on the hygrothermal behavior of facades in Brasília. Tesis Doctoral. Universidade de Brasília, Brasil (in Portuguese) Zanoni VAG, Sanchez JMM, Bauer E (2018) Evaluation of methods for measuring driving rain on buildings facades. PARC Pesquisa em Arquitetura e Construção 9(2):122–132

The Influence of Mass Tourism and Hygroscopic Inertia in Relative Humidity Fluctuations of Museums Located in Historical Buildings C. Ferreira, V. P. de Freitas, and João M. P. Q. Delgado

Abstract The preservation of artefacts in museum collections is profoundly affected by fluctuations in temperature and, especially, relative humidity (RH). Since the late nineteenth century, many studies have been carried out into the best way to control hygrothermal conditions. In old buildings located in maritime temperate climate zones (as Portugal) with strong thermal inertia, and which have low ventilation rate (relative to the volume and number of visitors) daily and seasonal hygroscopic inertia may help to assure the maintenance of RH stabilization conditions. The use of expensive active systems may be minimized through passive behaviour of internal finishing building materials. In order to assess the risk of mass tourism and hygroscopic inertia of finishing materials associated with the hygrothermal behaviour of museums, an analysis of several numerical scenarios with a different number of occupants (visitors per hour), different Portuguese climatic zones and finishing materials in order to quantify the risks associated with the fluctuations of relative humidity in a museum. The results of sensitivity studies performed are presented for the case of a museum located in Porto and Lisboa. Keywords Mass tourism · Hygroscopic inertia · Relative humidity · Museums · Collections preservation

1 Introduction One of the main functions of museums all over the world is the conservation of artefact collections. This complex work includes, among other things, the control of C. Ferreira · V. P. de Freitas · J. M. P. Q. Delgado (B) Civil Engineering Department, Faculty of Engineering, CONSTRUCT-LFC, University of Porto, 4200-465 Porto, Portugal e-mail: [email protected] C. Ferreira e-mail: [email protected] V. P. de Freitas e-mail: [email protected] © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2020 J. M. P. Q. Delgado (ed.), Building Pathology, Durability and Service Life, Building Pathology and Rehabilitation 12, https://doi.org/10.1007/978-3-030-47302-0_6

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the interior climate conditions (i.e., temperature, T, and particularly relative humidity, RH) inside the museum buildings (MacIntyre 1934; Rawlins 1942; Thomson 1986). In the rehabilitation of museums in old buildings, active systems for interior climate control have generally been favoured over passive ones. However, in countries with a temperate climate, such as Portugal, and more precisely the city of Porto [classification: 3C (ASHRAE 2013)], hygroscopic inertia combined with adequate ventilation may help control relative humidity fluctuations in old buildings without need for complex active systems. Hygroscopic inertia refers to the capacity of a room to store excess moisture from the air and restore it to the atmosphere when the relative air humidity is low. The finishing’s and the stored materials used in the rooms are one of the main factors responsible for the storage and restitution of humidity. Hygroscopic inertia may be assessed over short periods of time (short-cycle hygroscopic inertia of rooms) and for longer periods (long-cycle hygroscopic inertia of rooms). In the Laboratory of Building Physics, at Faculty of Engineering of University of Porto (FEUP), important research has been carried out in the domain of daily (i.e. short-cycle) hygroscopic inertia in order to quantify the performance of render materials (through parameters that indicate their water vapour adsorption and restitution capacity), find models with which to assess the influence of daily hygroscopic inertia upon peaks of relative humidity, and develop experimental studies to measure the phenomenon and validate the models (Freitas and Abrantes 1988; Ramos 2007; Delgado et al. 2009; Ramos and Freitas 2009). It is crucial the control of relative humidity and temperature fluctuations to preserve the museum’s collections. Today, there are advanced hygrothermal simulation tools to predict the climate inside, taking into account the geometry of the building, the finishing materials, the ventilation and the occupancy. In the last years, our research group has validated the hygrothermal numerical simulation model (Wufi-Plus), in different museums, by comparing numerical and experimental results of interior climate, using for this purpose several sensors. The mass tourism has led to an exponential increase in museums occupancy with serious consequences on indoor temperature and relative humidity change that may put at risk the preservation of the exhibited collections. In order to assess the risk of mass tourism and hygroscopic inertia of finishing materials associated with the hygrothermal behaviour of museums, an advanced hygrothermal numerical simulation model was used to evaluate those risks, for a generic museum room (model) located in a historical building of different Portuguese climatic zones.

2 Literature Review There have always been concerns about the climate conditions in museums. In the first century BC, Vitruvius mentioned the need to ensure wholesome conditions in the rooms where collections were kept and should be mentioned the care taken by

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the first collectors in the rooms where they kept their objects and in the options taken by Elias Ashmolean in the construction of the Ashmolean Museum of Oxford, in 1683 (Casanovas 2006). Between 1908 and 1978, several researchers defined the best recommendations that fit their museum’s reality. In 1908, the Boston Museum of Fine Arts installed a humidification central heating system that led McCabe to define that the best relative humidity value, for paintings and other artworks of art, was between 55 and 60% and with a recommended temperature in the range of human comfort zone (Erhardt et al. 2007). In 1934, John MacIntyre suggested that the interior environment should be controlled and maintained during the winter months at a temperature of 16 °C and relative humidity values between 55 and 60% (MacIntyre 1934). In 1942, Rawlins suggested that the most acceptable environmental conditions for art objects are 16 °C (60 °F) and 60% (Rawlins 1942). During World War II, a great part of the British Museum collection survived in very good conditions, in a limestone quarry in Westwood—Wiltshir, with the suggested temperature and relative humidity. This fact contributed to the inevitable success of rule 60:60 (Oddy 2001). In 1978, the book published by Garry Thomson gave priority to the museum’s collections over its visitors and concluded that the control of relative humidity is much more important than the control of temperature (Thomson 1986). Between 1993 and 1994, Michalski contributed to an alteration of the dominant mind set by asserting that in museums there is no ideal relative humidity, but rather minimum and maximum values, and acceptable fluctuations that minimize the various types of deteriorations (Michalski 1994). Till then, the defined reference values of temperature and relative humidity were considered to be valid for any museum in any part of the world, whatever the exterior climate and the background of the collections and buildings. In 1999, ASHRAE included in their manual for the first time a chapter devoted to museums, libraries and storages, in which they presented a methodology for the control of interior climate conditions based on reference values, maximum admissible fluctuations, and the risks and benefits for the collections, associated to each option (ASHRAE 2015). Between 1999 and 2001, a European research project identified the main sources of risk to cultural heritage due to the unconscious use of technology and mass tourism. The results showed that museums located in historical buildings benefited from the heat and humidity storage action of their thick walls and the hygroscopic materials used in the renders inside the building. In other words, air conditioning systems may be dangerous for the museum’s objects, as it causes alterations in the temperature and humidity gradients over short spaces of time (Camuffo et al. 2001). Another way of defining the hygrothermal conditions in museums is the proofed fluctuation method, proposed by Michalski in 1993 and 2004 (Michalski 2007). This method consists of defining the maximum temperature and relative humidity fluctuations to which the collection or object was subjected in the past, and if the future climate conditions do not exceed the range defined by past conditions, then the risk of future mechanical damage is negligible (Michalski 2007; The Getty Conservation Institute 2007).

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Since 2008, various working groups, as the Bizot Group, the National Museum Directors’ Conference—NMDC, the Environment Guidelines: Opportunities and Risks - EGOR and the Boston Museum of Fine Arts, have been rethinking and debating specific policies and approaches for the environmental conditions required by the museum’s objects, taken into account the energy efficiency, reduction of CO2 emissions and adaptation to climate change (http://www.nationalmuseums.org.uk/ what-we-do/contributing-sector/environmental-conditions/). In 2010, the CEN published a European norm (EN 15757), which established temperature and relative humidity specifications in order to limit the physical damage to organic hygroscopic materials (CEN (European Committee for Standardization) 2010). Then in 2012, the British Standards Institute published a specification that provided a series of requirements for the environmental conditions of storage, display and loan applicable to all types and sizes of collections (Group 2010). In 2009, the National Museum Directors’ Conference (NMDC) guidelines suggested a stable RH in the range between 40 and 60% and a stable temperature in the range 16–25 °C as interim guidelines for objects containing hygroscopic materials (Atkinson 2014). In 2014, IIC and ICOM-CC 2014 declaration on environmental guidelines state that guidelines for environmental conditions for permanent display and storage should be achievable for the local climate (Bickersteth 2016). From 2003 to 2007, the International Research Project “Annex 41 - MOIST-ENG” deepens the knowledge on the heat, air and humidity balance of the entire building and its effect on the interior environment and energy consumption (Woloszyn and Rode 2008). At Subtask 4, it was addressed the recommended values of temperature and relative humidity for the interior of museums, by several authors and entities (International Council of Museums—ICOM, Garry Thomson, German-speaking countries, Burmester and ASHRAE) (Holm 2008). It can be considered that, in addition to the developments summarized here, there is a need for an advanced hygrothermal approach to this problem that could enable the effect of hygroscopic inertia upon relative humidity peaks to be quantified. This work allows us to quantify the importance of hygroscopic inertia in museums housed in older buildings, of temperate climates, to demonstrate that it is possible to reduce relative humidity fluctuations inside museums and display cases using only passive techniques such as the use of hygroscopic finishing materials and ventilation control, and to propose a methodology for pre-sizing hygroscopic finishing materials and for quantifying the class of interior atmosphere of a space.

3 Laboratory Experiments 3.1 RHS Parameter Relative humidity stabilization parameter (RHS) consists of the sum over a year of the absolute differences between the 90 day mean seasonal relative humidity and the

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relative humidity in each hour, 8760     R H i,seasonal − R Hi  RHS =

(1)

i=1

This parameter allows quantifying the greater or lesser relative humidity stabilization over a year. To estimate the seasonal change in the climate, a running average (R H i,seasonal,90d ) is calculated for each hour and consists of the arithmetic average of the hourly values of 45 days or 1080 h before, and 45 days or 1080 h after [see Eq. (2)]. This period is centred, which means for each value looking back one month and a half and looking forward one month and a half. R H i,seasonal,90d =

i+1080  1 R Ha 2161 a=i−1080

(2)

3.2 Materials and Methods A coating material, normally, used in the rehabilitation of historical buildings, was selected to evaluate the hygroscopic behaviour, as well as the contribution to the control of indoor relative humidity. The material selected, with a thickness of 15 mm, was a 1.5 mm diameter wood fibers panels agglomerated with white cement (material B). From the experimental results reported in Table 1 it is possible to observe that Material B is very permeable to water vapour, and δp is dependent on the prevailing relative humidity and generally changes rapidly at high RH. This material presents a greater amount of adsorbed water vapour (MBV) for the relative humidity range of 33–75%, with 94.7 g/m2 (2.25 g/m2 %RH). Nordtest report (Rode et al. 2005) classified the capacity of materials to buffer moisture of indoor, according to their MBV obtained from MBV test with range of 33–75% RH. As so, Material B is classified as excellent materials (MBV > 2 g/m2 %RH) to buffer moisture of indoor. Finally, this experiments allowed concluding that Material B presents a hygroscopic capacity of 0.07 kg/m2 (calculated by the product of equilibrium moisture content with material density and thickness at different RH’s) for a relative humidity variation between 50 and 70%. The flux chamber (see Fig. 1), with dimensions 1500 × 524 × 584 mm3 , was installed in a climatic chamber with controlled temperature (T in the range 15– 35 °C) and relative humidity (RH in the range 30–90%). The temperature and relative humidity could be controlled by fixing values or using programmable cycles including variation of one or both parameters. The ventilation system presents two points, inside the flux chamber, to extracts the air and an inlet on top allows for the

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Table 1 Hygroscopic properties of the selected material Properties

Material B

Density, ρ (kg/m3 )

450

Porosity, ε (−)

0.38

Heat capacity, cp (J/kgK)

2800

Thermal conductivity, λ W/mK)

0.100

Water vapor permeability, δ p (kg/ms Pa)

4.13 ± 0.21 × 10−11 (dry) 1.37 ± 0.51 × 10−10 (wet)

Water vapor diffusion resistance factor, μ (−)

4.63 ± 0.24 (dry cup) 1.40 ± 0.05 (wet cup)

Equivalent air layer thickness, sd (m)

0.08 ± 0.012 (dry cup) 0.02 ± 0.001 (wet cup)

Moisture Buffer Value, MBV (g/m2 %RH)

2.25 (or 94.6 g/m2 ) (Excellent)

Hygroscopic sorption curve (u, ϕ)

10 Adsorption - Material B

u (kg/kg%)

8 6 4 2 0 0

20

40

60

Relative Humidity (%)

Fig. 1 Sketch of the flux chamber

80

100

The Influence of Mass Tourism and Hygroscopic Inertia …

30

Fig. 2 Flux chamber exterior climate (summer and winter cycles)

60

Summer cycle

29

55

28

50

27

45

26

40

25 24

0

Relative Humidity Temperature 1 2 3 4 5

RH (%)

T (ºC)

127

35 6

7

8

30

Time (days) 23 22

60

21

55

20

50

19

45 Relative Humidity Temperature

18 17

0

1

2

3

4

RH (%)

T (ºC)

65

Winter cycle

40 5

6

7

35

Time (days)

air to get in and at the same time prevents pressure differences. The flux chamber inlet air comes directly from the climatic chamber and its characteristics are known, whereby infiltration through the openings does not affect the overall balances of heat, air, and moisture. The air flux value is controlled by flow meters with a range of air exchange rate (ach) of 0.26–17 h−1 . The flux chamber was subject to a different cycle of exterior climate generated by the surrounding climatic chamber, and it was tested with an hourly air change rate of 0.26 and 0.65 h−1 , and an area of 0.75 m2 of hygroscopic coating material. The exterior climate was defined based on the average climatic conditions inside a museum located in the city of Porto, and consisted of the definition of summer and winter cycles, as sketched in Fig. 2. The tested configurations analysed in the flux chamber are described in Table 2.

3.3 Experimental Results In Fig. 3 and Table 3 are presented the results of the temperature and relative humidity obtained for the tested configurations, with different air change rate, and for the summer cycle and winter cycle. The main conclusions were:

128 Table 2 Configurations tested in the flux chamber

C. Ferreira et al. Refs.

Climatic chamber

Flux chamber

Cycle

ach (h−1 )

Hygroscopic material

Conf. 2.1

Summer

0.26

–

Conf. 2.3

Summer

0.65

–

Conf. 2.5

Summer

0.26

0.75 m2 of Material B

Conf. 2.7

Summer

0.65

0.75 m2 of Material B

Conf. 2.2

Winter

0.26

–

Conf. 2.4

Winter

0.65

–

Conf. 2.6

Winter

0.26

0.75 m2 of Material B

Conf. 2.8

Winter

0.65

0.75 m2 of Material B

• The test results carried out in the flux chamber demonstrate that the introduction of the hygroscopic coating material (Material B) influences the fluctuation of the relative humidity inside the flux chamber; • This influence is visible when comparing the variation between the maximum and minimum relative humidity—RH of Conf. 2.1 and Conf. 2.5 or Conf. 2.3 and Conf. 2.7 (summer cycle); and Conf. 2.2 and Conf. 2.6 or Conf. 2.4 and Conf. 2.8 (winter cycle), with different air change rates. Hygroscopic capacity (C apHyg ) was calculated for the different configurations tested using Eq. (3), and the results obtained described in Table 3:    CapHyg g/m3 % RH =

M BVi × Si

i

V

(3)

where MBV i is the Moisture Buffer Value of the finishing material (g/m2* %RH), S i is the surface area (m2 ) and V is the volume (m3 ) of the flux chamber.

4 Numerical Simulation The main objective is to evaluate the performance of the museum rooms with different hygroscopic finishing materials and ventilation rates. The governing equations for moisture and energy transfer are, respectively,

The Influence of Mass Tourism and Hygroscopic Inertia … Fig. 3 Temperature and relative humidity variation observed, with ach = 0.26 h−1

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Table 3 Hygroscopic capacity, maximum, minimum and average values of relative humidity obtained in the flux chamber, for summer and winter cycle, with different air change rate Relative humidity

Ext. clim.

2.1 0.26 h−1

2.3 0.65 h−1

2.5 0.26 h−1

2.7 0.65 h−1

C apHyg (g/m3 % RH)

–

0.00

Maximum

62.34

57.16

58.91

53.16

54.45

Minimum

35.48

43.17

40.66

47.47

47.22

Average

50.76

49.70

49.84

50.08

50.26

St. Dev.

4.60

2.816

3.547

1.21

1.596

RH

26.86

13.99

18.25

5.69

7.23

RHS

–

21,286

26,051

10,513

14,166

2.2 0.26 h−1

2.4 0.65 h−1

2.6 0.26 h−1

2.8 0.65 h−1

Relative humidity C apHyg (g/m3

% RH)

Ext. clim.

3.68

–

0.00

Maximum

69.93

57.51

60.61

56.05

3.68 57.44

Minimum

45.06

48.71

48.05

51.58

51.25

Average

55.66

54.37

54.69

54.24

54.97

St. dev.

4.253

2.765

3.359

1.209

1.846

RH

24.87

8.79

12.56

4.47

6.19

RHS

–

21,286

26,051

10,513

14,166

  ∂w ∂φ = ∇ Dφ ∇φ + δp ∇(φ psat ) ∂φ ∂t

(4)

  ∂ H ∂T = ∇(λ∇T ) + h v ∇ δp ∇(φ psat ) ∂ T ∂t

(5)

where w is water content (kg/m3 ), ϕ is the relative humidity (%), t is the time (s), Dϕ is the liquid conduction coefficient (kg/ms), δ p is the vapour permeability (kg/m s Pa), psat is the saturation vapour pressure (Pa), H is the enthalpy (J/m3 ), T is the temperature in Kelvin and hv is the latent heat of phase change (J/kg). The water vapour diffusion resistance factor, μ, used by WUFI is given by, μ=

2.0 × 10−7 T 0.81 /Pn δa = δp δp

(6)

where Pn is the normal atmospheric pressure (Pa). At each representative node of the building zone, the following balance equations were applied in order to obtain the indoor conditions, temperature and relative humidity, of each zone (Fraunhofer-Institut für Bauphysik 2010), ρc p V

   dTi = A j U j T j − Ti + Q sol + Q il + Q vent dt j

(7)

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Fig. 4 Model building used in this study

V

 dwi = A j gwj + nV (wa − wi ) + W M P + Wvent dt j

(8)

where ρ is the bulk density (kg/m3 ), cp is the specific heat capacity (J/kg K), V is the volume (m3 ), T i is the indoor air temperature (K), t is the time (s), Aj is the superficial area (m2 ), U j is the thermal transmission coefficient (W/m2 K), T j is the superficial temperature (K), Qsol is the direct solar energy (W), Qil is the internal gains with people, lighting and equipment’s (W), Qvent is the heat gains or losses due ventilation (W), wi is the absolute indoor air humidity (kg/m3 ), gwj is the moisture flow from the interior surface to the room (kg/sm2 ), wa is the absolute air humidity (kg/m3 ), W MP is the moisture production (kg/h) and W vent is the moisture gains or losses due ventilation (kg/h). For each element, the Eqs. (4) and (6) are solved simultaneously, obtaining the surface conditions of temperature and relative humidity. The internal conditions (T and RH) are obtained by solving Eqs. (7) and (8). The strong dependence between the two sets of equations implies an iterative calculation of the internal temperature and relative humidity (Casanovas 2006). The boundary conditions associated to the outside and inside climates and the constitution of the building’s envelope are required. Thus, data concerning the building model (see Fig. 4), geometry of the envelope (materials and their properties), exterior climate ventilation and internal gains (number of visitors) were introduced into the model.

4.1 Numerical Analyse In accordance with the experimental results, a preliminary numerical study was conducted using Wufi-Plus hygrothermal model of advanced numerical simulation

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(Fraunhofer-Institut für Bauphysik 2010). The main objective is to evaluate the performance of the museum rooms with different hygroscopic finishing materials, ventilation rates and occupancy, specifically in terms of temperature and relative humidity fluctuations. For this purpose, Table 4 presents several variables of the outdoor climate tested according to the specific weather files used. In this preliminary analysis only the two Portuguese cities with more tourism were considered. As regards the envelope, Table 5 gives a brief description of the constitution of each component and the material used in the final rendering. The properties of these materials were not determined experimentally. Instead, the database of the program Wufi-Pus was used, which contained selected materials with similar properties to the finishing materials existing in the museum. Table 6 shows the properties of the finishing materials used for interior layer with higher relevance for the hygrothermal calculation. A ventilation rates (0.24 and 0.98 h−1 ) were specified as well as internal gains resultant from lighting, 9 W/m2 during opening hours (from 10:00 to 18:00 and the only day closed for visitors was considered to be Monday) and 2 W/m2 selected for the remaining period. Regarding occupancy, different numbers were chosen (5, 10 and 20 visitors per hour), and considering that each visit have a duration of 20 min and a typical year with 308 days of being open to the public, it results in a range of visitors annually between 36,960 and 147,840. Several parameters were used to obtain the internal gains, namely a metabolic rate of 1.28 met and a heat gain of 134 W, in which 60% is sensible heat and 40% is latent heat. Sensible heat is directly related to temperature (50% radiant and 50% convective). Considering the ventilation flow of 0.26 h−1 and taking into account that each visitor releases 70 g/h of water vapour in the duration of 8 h (BS 2011), the internal water vapour gain is given by: Table 4 External climate considering the climatic data used in the simulation (annual values) District

Climatic zone

Temperature (°C)

Relative humidity (%)

Mean

Maximum

Minimum

Mean

Maximum

Minimum

Lisboa

I1–V2

16.6

32.0

3.7

78.4

98.0

32.6

Porto

I2–V1

15.2

38.4

0.3

73.3

99.0

9.40

Table 5 Constitution of each component and respective finishing material (base scenario) Component

Description

Finishing material

Outer walls

Granite walls with ETICS

Lime mortar with painting

Inner walls

Granite walls with lime-based rendering on both surfaces

Lime mortar with painting

Roof

Ceiling in gypsum board plus thermal insulation

Gypsum board with painting

Floor

Reinforced concrete slab

Old Oak without varnish

0.70 15

Thermal conductivity (W/m K)

Water vapour diffusion resistance factor (−)

Hygroscopic sorption curve

850

Specific heat capacity (J/kg K)

1785

Lime mortar 0.28

(kg/m3 )

Porosity (−)

Bulk density

Properties

8.3

0.20

850

0.65

850

Gypsum board

Table 6 Main properties of the hygroscopic finishing materials used in numerical simulation

223

0.1522

1600

0.35

740

Old oak

See Table 1

Material B

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I nter.Gain =

n.ω.h ach.V.24

(9)

where n is the number of visitors, ω the water vapour produced by each visitor (70 g/h), h the number of hours of the visit (8 h), ach the ventilation rate (0.26 h−1 ), V the room volume (206 m3 ) and 24 the factor used to obtain the mean hygrometry.

5 Results and Discussion Tables 7, 8, 9 and 10 present the indoor climate characterization, specifically concerning temperature and relative humidity, in order to better perceive the implications associated with the different variables analysed in performed simulations. Figures 5 and 6 show, as example for Porto, the seasonal temperature and relative humidity obtained for the different scenarios studied. It is possible to observe an increase of temperature and RH with the number of visitors, however, the increase of RH is significantly lesser when the museum room used hygroscopic materials, namely with an ach = 0.24 h−1 . More in detail, the results show: • An increase of the average temperature and relative humidity with the number of visitors per hour, for an ach = 0.24 h−1 , however, for an ach = 0.98 h−1 , the average temperature increases and the RH decreases; • When the ach value is 0.24 h−1 and buffering material B is used on the walls and ceilings, the value of parameter RHS drops, in average, by 27% compared to when the original materials are used; • When the ach value is 0.98 h−1 and buffering material B is used the value of parameter RHS reduces, in average, by 22% compared to when the original materials are used; • When the ach value is 0.24 h−1 and buffering material B is used on the walls and ceilings, the difference between the maximum and minimum relative humidity ranged between 28.4% and 40.0% compared to the range between 38.1% and 53.3%. • When the ach value is 0.98 h−1 and buffering material B is used the difference between the maximum and minimum RH ranged between 45.8 and 65.3% compared to the range between 53.8 and 71.9%.

5.1 ASHRAE Classification Tables 11, 12, 13 and 14 show the numerical results for the general climate risk assessment method of the museum room analysed, according to ASHRAE method (ASHRAE 2015).

9.83

12.87

56,967

H R sazonal

RHS

9.13

RH (%)

62.03

3.92

RH (%)

T (°C)

17.71

85.31

T (°C)

25.20

RH (%)

33.75

RH (%)

T (°C)

10.27

T (°C)

53,756

9.14

9.84

8.55

3.95

69.04

19.00

93.28

27.08

40.00

11.33

54,533

13.40

9.67

8.94

3.97

74.82

20.24

95.94

28.88

45.00

12.34

52,320

17.66

9.43

9.50

4.04

83.32

22.62

99.01

32.23

50.63

14.18

39,032

11,13

9.76

6.60

3.89

59.66

18.33

76.56

25.75

38.28

10.70

35,857

8.06

9.70

5.98

3.92

64.69

20.06

81.72

28.25

45.78

12.11

5

0

20

Base scenario + Mat. B 10

0

5

Base scenario

T sazonal

St. dev.

Average

Max.

Min.

Variables/No. visitors per hour

Table 7 Temperature and relative humidity results for Porto with different visitors per hour and ach = 0.24 h−1

38,052

9.61

9.57

6.42

3.97

68.49

21.68

86.09

30.63

49.69

13.32

10

45,865

9.66

9.15

7.09

4.09

72.48

24.83

91.41

34.97

54.53

15.78

20

The Influence of Mass Tourism and Hygroscopic Inertia … 135

10.00

14.49

81,258

H R sazonal

RHS

12.51

RH (%)

64.87

4.03

RH (%)

T (°C)

16.93

95.63

T (°C)

25.52

RH (%)

23.75

RH (%)

T (°C)

8.83

T (°C)

76,885

12.72

10.01

11.84

4.06

64.29

17.89

95.63

26.92

27.19

9.61

74,472

11.53

10.00

11.47

4.11

63.64

18.81

95.47

28.25

26.72

10.39

74,756

10.31

9.93

11.38

4.24

62.49

20.52

95.00

30.98

25.78

11.80

67,305

13.05

10.00

9.88

4.09

62.52

18.32

89.38

27.78

29.22

9.45

62,889

11.42

10.01

9.42

4.17

61.22

19.42

87.66

29.50

28.75

10.31

5

0

20

Base scenario + Mat. B 10

0

5

Base scenario

T sazonal

St. dev.

Average

Max.

Min.

Variables/No. visitors per hour

Table 8 Temperature and relative humidity results for Porto with different visitors per hour and ach = 0.98 h−1

60,031

9.97

10.02

9.02

4.39

58.51

21.56

84.69

33.02

27.19

11.99

10

57,760

8.72

9.99

7.09

4.09

72.48

24.83

91.41

34.97

54.53

15.78

20

136 C. Ferreira et al.

10.78

12.22

37,175

H R sazonal

RHS

6.83

RH (%)

63.13

4.31

RH (%)

T (°C)

18.71

81.88

T (°C)

26.06

RH (%)

43.75

RH (%)

T (°C)

11.88

T (°C)

36,964

17.11

10.75

8.21

4.33

69.01

20.10

89.69

28.02

48.44

13.05

40,617

20.77

10.67

9.73

4.35

73.27

21.56

95.31

30.01

50.00

14.22

49,420

25.67

10.75

12.08

4.49

78.06

24.57

98.75

34.07

48.13

16.56

23,403

10,73

10,57

5.19

4.29

60.60

19.36

74.38

26.84

45.94

12.50

23,975

14.44

10.67

6.55

4.31

64.88

21.10

81.56

29.34

50.63

13.75

5

0

20

Base scenario + Mat. B 10

0

5

Base scenario

T sazonal

St. dev.

Average

Max.

Min.

Variables/No. visitors per hour

Table 9 Temperature and relative humidity results for Lisboa with different visitors per hour and ach = 0.24 h−1

30,718

16.62

10.56

7.79

4.35

68.02

22.74

86.25

31.77

51.25

15.00

10

41,750

17.92

10.42

8.83

4.48

68.63

26.64

89.69

36.77

49.69

18.05

20

The Influence of Mass Tourism and Hygroscopic Inertia … 137

10.92

14.02

55,004

H R sazonal

RHS

9.17

RH (%)

65.96

4.39

RH (%)

T (°C)

17.95

92.50

T (°C)

26.22

RH (%)

36.09

RH (%)

T (°C)

10.51

T (°C)

53,093

14.76

10.93

9.15

4.43

65.11

18.91

93.13

27.63

38.13

11.17

53,046

15.34

10.94

9.33

4.48

64.16

19.86

93.75

29.07

40.00

11.88

56,460

16.07

10.98

9.92

4.61

61.44

21.89

92.81

32.00

37.19

13.36

43,290

13.28

10.91

7.74

4.40

64.79

18.23

86.41

26.77

37.50

10.47

40,883

13.89

10.93

7.66

4.46

63.34

19.34

85.63

28.52

38.44

11.17

5

0

20

Base scenario + Mat. B 10

0

5

Base scenario

T sazonal

St. dev.

Average

Max.

Min.

Variables/No. visitors per hour

Table 10 Temperature and relative humidity results for Lisboa with different visitors per hour and ach = 0.98 h−1

40,084

14.32

10.95

7.72

4.54

61.80

20.45

85.16

30.28

39.22

11.88

10

41,247

14.56

10.95

7.96

4.75

58.38

22.70

83.28

33.88

37.50

13.44

20

138 C. Ferreira et al.

The Influence of Mass Tourism and Hygroscopic Inertia … 40

Temperature (ºC)

35

Base, N=0 Base, N=5 Base, N=10 Base, N=20

139

Base+Mat.B, N=0 Base+Mat.B, N=5 Base+Mat.B, N=10 Base+Mat.B, N=20

30 25 20

15 10 5

0

100

Relative Humidity (%)

90 80

70 60 50 40 30 20 10 0

Base, N=0 Base, N=5 Base, N=10 Base, N=20

Base+Mat.B, N=0 Base+Mat.B, N=5 Base+Mat.B, N=10 Base+Mat.B, N=20

Fig. 5 Numerical results for Porto, with and without buffering materials, different number of visitors per hour and ach = 0.24 h−1 (seasonal exterior T and RH marked as a yellow line)

It is possible to observe that from the comparison between the three most stringent classes (Classes AA to A) the one that manages to verify, for the vast majority of simulations, an acceptance above 50% of the time according to their limits, regarding the variations in the resulting internal temperature and relative humidity, is class A. On the other hand, class B, the one that is generally most suitable for historical

140

C. Ferreira et al. 40 35

Base, N=0 Base, N=5 Base, N=10 Base, N=20

Base+Mat.B, N=0 Base+Mat.B, N=5 Base+Mat.B, N=10 Base+Mat.B, N=20

Temperature (ºC)

30 25 20 15 10 5 0

100

Relative Humidity (%)

90 80 70 60 50 40 30 20 10 0

Base, N=0 Base, N=5 Base, N=10 Base, N=20

Base+Mat.B, N=0 Base+Mat.B, N=5 Base+Mat.B, N=10 Base+Mat.B, N=20

Fig. 6 Numerical results for Porto, with and without buffering materials, different number of visitors per hour and ach = 0.98 h−1 (seasonal exterior T and RH marked as a yellow line)

The Influence of Mass Tourism and Hygroscopic Inertia …

141

Table 11 ASHRAE indoor climate risk assessment methodology for Porto with different visitors per hour and ach = 0.24 h−1

Nº visitors 0 5 10 20

Scenario

ASHRAE climate classes (%) AA

As

A

B

C

D

Base scenario

38

41

64

78

92

92

Base + Mat. B

49

55

77

93

93

100

Base scenario

41

42

65

79

72

77

Base + Mat. B

51

58

77

95

84

96

Base scenario

33

39

60

80

41

51

Base + Mat. B

46

52

68

94

59

84

Base scenario

16

27

32

76

8

21

Base + Mat. B

30

31

43

90

30

64

Scale: 0

10

20

30

40

50

60

70

80

90

100

Table 12 ASHRAE indoor climate risk assessment methodology for Porto with different visitors per hour and ach = 0.98 h−1

Nº visitors 0

5 10 20

Scenario

ASHRAE climate classes (%) AA

As

A

B

C

D

Base scenario

27

27

48

61

80

80

Base + Mat. B

32

32

55

70

86

87

Base scenario

29

29

50

63

81

83

Base + Mat. B

34

34

56

73

88

91

Base scenario

29

29

50

65

79

85

Base + Mat. B

34

34

54

75

84

94

Base scenario

23

24

42

65

71

87

Base + Mat. B

26

28

44

76

71

96

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Table 13 ASHRAE indoor climate risk assessment methodology for Lisboa with different visitors per hour and ach = 0.24 h−1

Nº visitors 0 5 10 20

Scenario

ASHRAE climate classes (%) AA

As

A

B

C

D

Base scenario

52

65

84

95

93

97

Base + Mat. B

64

87

94

100

88

100

Base scenario

41

63

72

96

56

75

Base + Mat. B

47

82

83

100

68

95

Base scenario

30

56

58

93

25

55

Base + Mat. B

37

68

66

100

44

80

Base scenario

12

26

25

76

7

40

Base + Mat. B

23

31

36

94

26

75

Table 14 ASHRAE indoor climate risk assessment methodology for Lisboa with different visitors per hour and ach = 0.98 h−1

Nº visitors 0 5 10

20

Scenario

ASHRAE climate classes (%) AA

As

A

B

C

D

Base scenario

36

45

69

80

80

82

Base + Mat. B

44

54

76

90

87

91

Base scenario

35

46

68

80

77

85

Base + Mat. B

42

55

73

91

82

94

Base scenario

33

45

63

80

70

87

Base + Mat. B

37

53

66

91

74

95

Base scenario

25

33

43

77

57

89

Base + Mat. B

26

38

44

90

61

98

buildings, presents an acceptable performance for this first consideration, with percentages closely from 76% to 100% of permanence, for ach = 0.24 h−1 and 61% to 91%, for ach = 0.98 h−1 . As it was to be expected, the increase in the number visitors per hour inflicts a decrease in acceptance for the presented classes of climate control. An important issue observed is the fact that, for the same air change rate, when the buffering material B is used in the walls and ceilings, the museum room meet

The Influence of Mass Tourism and Hygroscopic Inertia …

143

class A or higher in more 22% (in average) of the time compared to when the original materials are used, for ach = 0.24 h−1 , and in more than 12%, for ach = 0.98 h−1 .

6 Conclusions This work presents a study of the influence of hygroscopic materials with different characteristics in stabilizing the relative humidity, when ventilation flows are reduced. When this particular buffering material was analysed numerically, as part of the walls and ceiling of the museum room, the difference between the maximum and minimum interior relative humidity decreases in more than 10%, for an ach = 0.24 h−1 . These results show that it is possible used passive technique for controlling/mitigating relative humidity in storage rooms, inside museums, when ventilation flows are reduced.

References ASHRAE (2013) Climatic data for building design standards (ANSI approved). ASHRAE 169:2013 ASHRAE (2015) Heating, ventilating, and air-conditioning applications. Chapter: museums, galleries, archives, and libraries. In: ASHRAE handbook. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta Atkinson JK (2014) Environmental conditions for the safeguarding of collections: a background to the current debate on the control of relative humidity and temperature. Stud Conserv 59(4):205– 212 Bickersteth J (2016) IIC and ICOM-CC 2014 declaration on environmental guidelines. Stud Conserv 61(S1):12–17 BS 5250 (2011) Code of practice for control of condensation in buildings. British Standards Institution BSI Group (2010) New initiative on environmental conditions for cultural collections. http://www. bsigroup.com (Press Release July 2010) Camuffo D, Grieken RV, Busse H-J, Sturaro G, Valentino A, Bernardi A, Blades N, Shooter D, Gysels K, Deutsch F, Wieser M, Kim O, Ulrych U (2001) Environmental monitoring in four European museums. Atmos Environ 35(1):S127–S140 Casanovas L (2006) Preventive conservation and preservation of works of art: environmental conditions and museum spaces in Portugal. Ph.D. dissertation, Faculdade de Letras de Lisboa, Portugal CEN (European Committee for Standardization) (2010) Conservation of cultural property—Specifications for temperature and relative humidity to limit climate-induced mechanical damage in organic hygroscopic materials. EN 15757: 2010 Delgado JMPQ, Ramos NMM, Freitas VP (2009) Can moisture buffer performance be estimated from sorption kinetics? J Build Phys 29(4):281–299 Erhardt D, Tumosa CS, Mecklenburg MF (2007) Applying science to the question of museum climate. In: Padfield T, Borchersen K (eds) Contributions to the museum microclimates conference. The National Museum of Denmark, Copenhagen Fraunhofer-Institut für Bauphysik (2010) Fundamentals of WUFI-plus. seminar: simultaneous calculation of transient hygrothermal conditions of indoor spaces and building envelopes. Holzerkirchen, Germany

144

C. Ferreira et al.

Freitas VP, Abrantes V (1988) Étude expérimentale de l’humidité de l’air dans l’intérieur dês bâtiments. Influence du comportement hygroscopique des matériaux. In: Proceedings of healthy buildings’88, vol 2. CIB, pp 201–209 Holm A (2008) Annex 41 whole building heat, air, moisture response—Subtask 4—Applications, Indoor environment, energy, durability. International Energy Agency, Executive Committee on Energy, Conservation in Buildings and Community Systems. ISBN 978-90-334-7061-5 MacIntyre J (1934) Some problems connected with atmospheric humidity. Some notes on atmospheric humidity in relation to works of art. Courtauld Institute of Art, London, UK, pp 7–16 Michalski S (1994) Relative humidity and temperature guidelines: what’s happening? http://www. cci-icc.gc.ca/crc/cidb/document-eng.aspx?Document_ID=118. Accessed on 06 June 2017 Michalski S (2007) The ideal climate, risk management, the ASHRAE chapter, proofed fluctuations, and toward a full risk analysis model. In: Contribution to the experts’ roundtable on sustainable climate management strategies. Tenerife, Spain Oddy A (2001) The three wise men and the 60:60 rule. In: Occasional Paper no. 145. British Museum, London Ramos NMM (2007) The importance of hygroscopic inertia in the hygrothermal behaviour of buildings. Ph.D. dissertation, Faculdade de Engenharia da Universidade do Porto, Portugal Ramos NMM, Freitas VP (2009) An experimental device for the measurement of hygroscopic inertia influence on RH variation. J Building Phys 33(2):157–170 Rawlins FIG (1942) The control of temperature and humidity in relation to works of art. Mus J 41:279–283 Reviewing environmental conditions: NMDC guiding principles for reducing museums’ carbon footprint. In: National museum directors’ conference. http://www.nationalmuseums.org.uk/whatwe-do/contributing-sector/environmental-conditions/. Accessed on 06 June 2017 Rode C, Peuhkuri R, Mortensen L, Hansen K, Time B, Gus-Tavsen A, Svennberg K, Arfvidsson J, Harderup L, Ojanen T, Ahonnen J (2005) Moisture buffering of building materials. Report BYG-DTU R-126, Department of Civil Engineering, DTU, Lyngby, Denmark The Getty Conservation Institute (2007) Experts’ roundtable on sustainable climate management strategies—Alternative climate controls for historic buildings. http://www.getty. edu/conservation/our_projects/science/climate/climate_experts_roundtable.html#proceedings. Accessed on 06 June 2017 Thomson G (1986) The museum environment, 2nd edn. Elsevier Butterworth-Heinemann, Oxford Woloszyn M, Rode C (2008) Annex 41 whole building heat, air, moisture response—Subtask 1— Modelling principles and common exercises. International Energy Agency, Executive Committee on Energy, Conservation in Buildings and Community Systems. ISBN 978-90-334-7057-8

Residual Safety in One-Way Slabs with Severe Corrosion Jose Vercher, Enrique Gil, Ángeles Mas, and Carlos Lerma

Abstract There are numerous cases of slabs with corrosion in their joists, in which the constructive elements that rest on them do not show remarkable damage. Sometimes, even with all the lower reinforcement corroded in all the joists, there is no alarming cracking in flooring or partition walls. This research provides support for making expert decisions about the corroded slabs, from the initial tasks of diagnosis until late intervention criteria, by evaluating the remaining safety of the most common slabs in residential buildings: the reinforced concrete one-way slabs with in situ and precast joists, having the most usual thickness. The remaining safety assessment has been performed by the analysis of complete building models, where each element is in its real position and appears when real construction dictates. ACI-318 load test is used as a criterion for acceptance or rejection of an existing structure. The assessment of the Load Factor (LF), which quantifies the remaining safety and gives the necessary order of magnitude in the intervention, is developed in this research. Keywords Corrosion · Experiments · Slabs · Joists · Numerical analysis

1 Introduction The slab is the structural element that first receives the vertical loads in a building. Most residential buildings in Spain contain slabs that are formed by reinforced or prestressed concrete joists and compression layer. J. Vercher (B) · Á. Mas · C. Lerma Department of Architectural Constructions, Universitat Politècnica de València, València, Spain e-mail: [email protected] Á. Mas e-mail: [email protected] C. Lerma e-mail: [email protected] E. Gil Department of Structural Constructions, Universitat Politècnica de València, València, Spain e-mail: [email protected] © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2020 J. M. P. Q. Delgado (ed.), Building Pathology, Durability and Service Life, Building Pathology and Rehabilitation 12, https://doi.org/10.1007/978-3-030-47302-0_7

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All the elements included in a building, both constructive and structural, over time are subject to a series of external aggressions, which cause their damage. The rehabilitation and maintenance of buildings represents practically 50% of the activity of the construction sector in Spain (SEOPAN 2018). The deterioration of the slabs is the most frequent damage in reinforced concrete buildings, and the one that has the greatest impact in case of repair or intervention, because its cracking or excessive deformation affects the majority of construction elements, which it serves as support, such as the partition walls, the flooring, the false ceiling or the facades. In Spain, lesions appear in 25.6% of the floors. The type of structure most affected by corrosion are unidirectional slabs, which are the most common, representing 68% of pathological situations (Vieitez and Ramírez 1984). One of the most frequent damages in the unidirectional slabs, together with the excessive deformation, is the corrosion of the lower reinforcement of the joists, sometimes favored by the use of aluminous cement, leading to the bond loss between steel and concrete, the cover spalling, and even breakage of the reinforcement due to severe corrosion. In some of these cases there are no excessive deformations or cracking in the rest of the construction elements, and therefore the damaged joists are discovered in a casual way, motivated for example by the demolition of the false ceiling due to a change of use in the building. The influence of bond deterioration is much more critical than the loss of steel section (Mangat and Elgarf 1999). The problem of identifying the bond properties is far from being solved. The present investigation assumes the complete loss of bond, to help understand the worst possible scenario. There are very few studies in the research publications of structural pathology that address the issue of residual safety. The few existing works are concerned with assessing the behavior and residual safety in isolated joists, individually, and without forming a set with the rest of the elements that make up a slab in reality (Río et al. 2000; Di Evangelista et al. 2011; Coronelli and Gambarova 2004). In this way, the additional resistance mechanisms that appear in reality as part of a complete building are not being evaluated (arch effect, membrane, struts and ties). When analyzing the structures in space, it is verified that the stresses in the continuous slabs are distributed in a markedly different way from that obtained by the linear calculation methods (Calavera 2003). The evaluation of the built structures, with their present damages, as well as the possibilities of reinforcement and repair, has established itself as a branch of knowledge that is expanding (del Río 2008). In this way, this work aims to assess the remaining safety of unidirectional slabs with severe joists corrosion, conducting a three-dimensional study on entire buildings. In all the literature studied, the analysis and testing of the entire building with corrosion in the slabs has not been seen, taking into account the construction process, the load history and the deterioration phenomenon. A large variety of cases have been evaluated in this study in terms of the number of corroded joists and their position within the slab, both for cases of reinforced and prestressed joists. The tools used in the evaluation of the remaining safety are the Load Factor and the load test of the American standard ACI-318 (American Concrete Institute 2008). In this investigation, the simulation of models

Residual Safety in One-Way Slabs with Severe Corrosion

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with complete corrosion is loaded to the final load. The load at admissible active deflection with respect to the service load gives an estimation of the remaining safety.

2 Materials and Methods This section describes in detail the methodology used in this work, from the geometry and materials studied, to the great validation work carried out, the used load steps and the way in which to evaluate the residual safety. It is necessary to emphasize that because they are intended to study complete buildings, it is not possible to perform real tests due to their high cost of time and economic. Due to this, a numerical study is carried out, using complete building models. In order to extract valid results, extensive validation work must be carried out previously, both of the properties of the materials and of the behavior of the different elements that appear in the building in an isolated way.

2.1 Materials Properties Virtually all materials have a first range of elastic behavior. However, in this work it is very important to correctly characterize the behavior of the material throughout its load range, since the models will collapse to assess the remaining safety. No confidence margins or reduction coefficients are used. Being a research topic and wanting to reach the real result as accurately as possible, average strength values are used, non-characteristic strength values, as is the case in structural design (Ingeciber 2008). It is necessary to properly calibrate the properties of the materials to obtain results consistent with the actual behavior, and that the conclusions drawn from the work are valid. It is essential to define the properties of the three materials that appear in the analyzed models (concrete, steel and masonry) in the most real way possible. This work includes the real behavior of the materials, the non-linearity, the approach of the balance in the deformed structure, the cracking and crushing of the concrete, the yielding and the creep of the reinforcement. Concrete is characterized by the simplification proposed by EHE-08 (Ministerio de Fomento 2008), where the behavior model is represented by a parabola of degree n and a rectilinear segment. The behavior of steel has also been simplified to a bilinear curve, so that it adequately represents its elastic and plastic range. And the masonry is a heterogeneous element. It is a non-linear, anisotropic material, which exhibits different directional properties, because the mortar joints act as planes of weakness or fragility (Dilrukshi et al. 2010). Macro-modeling is used in this work, because the fundamental objective is to evaluate the safety of the slab. The enclosure is intended

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Table 1 Materials properties Material

Concrete HA-30

Steel HP-40

B-500-SD

Masonry Y-1860-C

ρ (KN/m3 )

25

25

78.5

78.5

14

fcm (MPa)

38

48

–

–

4

E (GPa)

28.6

30.9

200

200

2

ftm (MPa)

3.39

3.96

–

–

0.2

fy (MPa)

–

–

500

1581

–

E tang (GPa)

–

–

3

3

–

to intervene (Cubel et al. 2012), with its own weight and its contribution of stiffness, but in this case it is not essential to evaluate its own safety. Table 1 shows all the properties of the materials used in the investigation. It should be remembered that two types of concrete are used, pouring in situ and prefabricated in prestressed joists. Likewise, two types of steels are used, without tension and with initial tension.

2.2 Geometry Complete three-dimensional models of buildings are analyzed, where the slabs evaluated are in the real position, with the restrictions that originate from the rest of the construction elements. This is the reason why the ceramic facade is included, since it is a very important element in the real behavior of a structure. The model is made with total precision, building the concrete elements and placing the corrugated steel reinforcements in their exact position. The analyzed model consists of a generic three-story residential building, three openings in the direction of the beams and three openings in the direction of the joists, with conventional spans. The structure is porticoed, made with flat beams and one-way slab. Taking advantage of the analysis of a building with double symmetry, a quarter of the building has been modeled (Fig. 1). The geometric characteristics of the model are: • • • • • • •

Inter-story clearance: 2.64 m Spans of beams to the column axes: 4.47–5.22–4.47 m Spans of joists to the column axes: 4.92 m Spacing between joists axes: 0.69 m Slab thickness: 0.30 m Compression layer: 5 cm thick with ∅5 wire mesh with a spacing of 25 cm Flat beams, columns and reinforced and prestressed joists geometry can be seen in Fig. 2 • The 18 cm thick facade has conventional hollows.

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Fig. 1 Geometry of a quarter of the building

Fig. 2 Geometry of structural elements

This work covers the most common cases of slabs, such as the 30 cm thickness unidirectional ones, with reinforced or prestressed joists. Corrosion appears on floor 2 to have a situation with continuity both below and above. The remaining safety of

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Fig. 3 Designation of squares and bays

cases with 3 contiguous joists with extreme corrosion at the lower reinforcement in different positions of the slab, and cases with all joists corroded in a bay is analyzed. As can be seen in Fig. 3, the evaluated building has 4 type squares: corner square (1), joist end square (2), beam end square (3) and center square (4). In addition, it has two outer bays and a central bay, for cases of corrosion of all joists. Specimens A and C correspond to the models in which corrosion appears on the outer bay, in the case of reinforced and prestressed slabs respectively. In addition, the specimens B and D correspond to the models in which the corrosion appears on the central bay. Healthy cases, cases with all nerves corroded in a bay and cases with corrosion in the 3 central joists of each square are studied. The influence of the cover spalling on the reinforced slabs, and the influence of the cover spalling and the number of levels of prestressed tendons on the prestressed slabs are also analyzed. This influence is evaluated in squares 2 and 4, which are the most dominant in outer and central bay respectively. The nomenclature of the specimens can be seen in Table 2 can be seen in Results and Discussion section.

2.3 Methodology It must be remembered that it has been necessary an exhaustive work of validation of the behavior of the materials and of isolated elements submitted to the different types of solicitations, even with corrosion. This previous work is necessary to be able to achieve the real behavior of the complete building model, where the additional resistance mechanisms appear, and the remaining safety can be evaluated in cases of damage. In order to validate the results and conclusions obtained, and to verify the accuracy of the hypotheses of the cases carried out, the models and materials have been

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calibrated with research by other authors (Vercher 2013). Various investigations of simple elements with different types of failure are studied, to have the wide range of possible failures of the materials covered. The basis of the calibration has been represented by four works, where the subject studied is: bending with failure domain governed by concrete (Barbosa and Ribeiro 1998), bending with failure domain governed by steel (Fanning 2001), compression (Tavio and Tata 2009), and bending of prestressed elements with corrosion (Rodriguez et al. 1997; Coronelli and Gambarova 2004). In order to achieve residual safety values as close to reality as possible, it is necessary to detail very well the process of loading and appearance of the construction elements. The steps are detailed below: • Prestressed joists, in the cases of slabs with prefabricated joists: appearance of the finite three-dimensional concrete elements of the joists in their real position, with the prestressing forces. • Load-bearing structure (3500 N/m2 ): appearance of the finite three-dimensional concrete elements and the bar elements that represent the reinforcements in their real position, with their own weight. • Flooring (+1000 N/m2 = 4500 N/m2 ): simulated with an increase in load on the slabs. • Facade: appearance of the finite three-dimensional elements of the facade with its own weight. It provides stiffness preventing the rotation and the descent of the perimeter of the slabs. • Partition walls (+1000 N/m2 = 5500 N/m2 ): simulated with an increase in load on the slabs. When the partition walls appear, the active deflection with respect to the partition walls begins to occur. This deflection is limited to L/400 by Spanish standard EHE-08 (Ministerio de Fomento 2008), with L being the span in meters. This deflection is used to quantify the Load Factor (LF). This factor is developed in the work of Vercher (2013) and helps the responsible technician to quantify the remaining safety and to have a magnitude of the necessary intervention. • Service load (+600 N/m2 = 6100 N/m2 ): simulated with an increase in load on the slabs. Service load is the load value with which the structure will be subjected throughout its service life. The live load in Spain is 2000 N/m2 in residential buildings, according to the technical building code CTE-06 (Ministerio de Vivienda 2006). The entire slab is not loaded with this load continuously. According to this standard, the quasi-permanent value of the live load is the value that is exceeded during 50% of the reference time, and its value is 600 N/m2 . Therefore, the service load is composed of the overall dead load and the quasipermanent part of the live load. During the service life is when there are corrosion problems. Therefore, the corrosion is simulated in the next step. • Corrosion, in damaged cases: the complete loss of the lower reinforcement of certain joists is simulated, with cover spalling in some cases. • Remaining live load (+1400 N/m2 = 7500 N/m2 ): simulated with an increase in load on the slabs.

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• Load until failure: the study area is loaded until the collapse, to assess the remaining load capacity in each case. The way in which the residual safety is evaluated is by studying two aspects in the load-vertical displacement curves. These curves are represented for the significant points in each case, and the load test according to ACI-318 (American Concrete Institute 2008) and the Load Factor (LF) are analyzed. The ACI-318 load test determines whether an existing structure can continue in use. The slab or affected area of a slab is loaded with a certain load, and the increase in deflection experienced with this load increase is measured. If the deflection increase is greater than the limit, the recovery in the discharge must be measured. In this way, slabs with sufficient stiffness and healthy flexible slabs are accepted. The Load Factor (LF) estimation quantifies the load that a specific specimen supports before reaching a limit state with respect to the service load. This factor is based on the admissible active deflection with respect to the partition walls, of the EHE-08 standard (Ministerio de Fomento 2008). The load that supports each specimen is analyzed when it has reached the permissible limit for this deflection, and is related to the service load. In this way, the remaining safety can be estimated in each case.

3 Results and Discussion The ACI-318 standard has a section that evaluates the strength of existing structures, and describes a load test so that a construction can continue in use. This standard determines the total load of the test, using the equation Qt = 0.85(1.4D + 1.7L), where D is the total of dead loads and L is the total of live loads. In the studied building, D is 5500 N/m2 and L is 2000 N/m2 . Therefore, the total test load is 9435 N/m2 . The deflection increase produced from the existence of only the dead loads (5500 N/m2 ) to the final test load (9435 N/m2 ) is limited by max ≤ lt 2 /(20,000h), so that the structure is suitable to continue in use. The span between pillars in the studied models is 4.92 m, and the slab thickness is 0.30 m, so the deflection increase limit is equal to 4.03 mm. Figures 4a and 5a show this study at point 1 for reinforced and prestressed specimens. Thus, the specimens in which the increase in vertical deflection is less than 4.03 mm are suitable to continue in use. If the deflection increase produced by the load test is greater than 4.03 mm, the recovery percentage of the deflection when unloading must be at least 75%. In this way, the structure

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Fig. 4 Load-vertical displacement curves for reinforced slabs at point 1

can continue in use. If a building does not meet the ACI-318 load test, it should be considered that it cannot continue in use. In addition, in order to quantify the residual safety of each specimen, the Load Factor (LF) is evaluated. The active deflection with respect to the partition walls begins to be produced from the construction of the partition walls, that is, when the models are loaded with 4500 N/m2 . It is necessary to measure the slab deflection when the partition walls (4500 N/m2 ) appear, and calculate the admissible active deflection with respect to the partition walls, which will be allowed from that point.

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Fig. 5 Load-vertical displacement curves for prestressed slabs at point 1

For a span between pillar axes of 4.92 m, the permissible active deflection is 1.23 cm. This value is obtained by the limitation of the EHE-08 (Ministerio de Fomento 2008) of L/400. The remaining safety coefficient is obtained by relating the load with which each specimen reaches the permissible active deflection with respect to the partition walls and the value of the service load, 6100 N/m2 . Figures 4b and 5b show this study at point 1 for reinforced and prestressed specimens.

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Table 2 Reinforced one-way slabs specimens, load factor values and ACI-318 load test Specimen

Damaged area

Corrosion

Spalling

Load factor (LF)

ACI-318 load test

A.1

Outer bay

Healthy

Without

2.35

Positive

A.2

Outer bay

All joists

Without

1.50

Negative

A.3

Square 1

3 central joists

Without

2.15

Negative

A.4.1

Square 2

3 central joists

Without

2.00

Negative

A.4.2

Square 2

3 central joists

Central

1.96

Negative

A.4.3

Square 2

3 central joists

Total

1.88

Negative

B.1

Central bay

Healthy

Without

2.71

Positive

B.2

Central bay

All joists

Without

2.01

Negative

B.3

Square 3

3 central joists

Without

2.63

Positive

B.4.1

Square 4

3 central joists

Without

2.39

Positive

B.4.2

Square 4

3 central joists

Central

2.38

Negative

B.4.3

Square 4

3 central joists

Total

2.30

Negative

L F = Q pad /Q ser vice This section shows the load-vertical displacement curves of the various specimens evaluated, as well as the tables with all the results obtained (Tables 2 and 3). Table 4 summarizes Load Factor values. Not all curves are presented due to extension issues. Looking at the curves, it can be seen that point 2 (center point of square 2) is more restrictive on the outer bay, and point 4 (center point of square 4) is more restrictive on the central bay. This is due to the geometry of the building. All prestressed specimens meet the ACI-318 load test. The same does not happen in cases of reinforced slabs, where the specimens with corrosion in all the joists of a bay do not meet, and for cases of corrosion in 3 adjacent joists only meet the cases without cover spalling in squares 3 and 4 (Figs. 6, 7, 8, 9, 10 and 11).

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Table 3 Pre-stressed one-way slabs specimens, load factor values and ACI-318 load test Specimen

Damaged area

Corrosion

Spalling

Healthy tendon levels

Load factor (LF)

ACI-318 load test

C.1

Outer bay

Healthy

Without

2

2.68

Positive

C.2

Outer bay

All joists

Without

2

2.15

Positive

C.3

Square 1

3 central joists

Without

2

2.59

Positive

C.4.1

Square 2

3 central joists

Without

2

2.48

Positive

C.4.2

Square 2

3 central joists

Central

2

2.47

Positive

C.4.3

Square 2

3 central joists

Total

2

2.46

Positive

C.4.4

Square 2

3 central joists

Total

1

2.14

Positive

D.1

Central bay

Healthy

Without

2

3.07

Positive

D.2

Central bay

All joists

Without

2

2.47

Positive

D.3

Square 3

3 central joists

Without

2

3.04

Positive

D.4.1

Square 4

3 central joists

Without

2

2.99

Positive

D.4.2

Square 4

3 central joists

Central

2

2.94

Positive

D.4.3

Square 4

3 central joists

Total

2

2.84

Positive

D.4.4

Square 4

3 central joists

Total

1

2.53

Positive

Table 4 Load factor values Reinforced-30

Prestressed-30

Healthy specimens

2.35–2.71

2.68–3.07

Specimens with a full corroded bay

1.50–2.01

2.15–2.47

Specimens with corrosion in 3 adjacent joists

1.88–2.63

2.14–3.04

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Fig. 6 Load-vertical displacement curves for reinforced slabs at point 2

Fig. 7 Load-vertical displacement curves for reinforced slabs at point 3

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Fig. 8 Load-vertical displacement curves for reinforced slabs at point 4

Fig. 9 Load-vertical displacement curves for pre-stressed slabs at point 2

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Fig. 10 Load-vertical displacement curves for pre-stressed slabs at point 3

Fig. 11 Load-vertical displacement curves for pre-stressed slabs at point 4

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4 Conclusions In case of severe corrosion with cover spalling of the lower reinforcement of the joists of a unidirectional slab, there is a greater load capacity, and therefore greater safety, in the cases of pre-stressed joists. This is because the in situ reinforced joists do not have more bar levels, and the precast joists have upper tendons necessary for the balance of the section, which remain healthy, and begin to withstand tensions, thus possessing certain load capacity. The cover spalling has a greater influence on the slabs executed with reinforced joists. For example, at point 2 (center point of square 2) the Load Factor values for cases without spalling, with central spalling and with total spalling for the 30 cm reinforced slab are 2.00, 1.96 and 1.88; while in the case of the pre-stressed slab of the same thickness the values are 2.48, 2.47 and 2.46. The number of levels of pre-stressed tendons that remain healthy is more decisive than the amount of cover spalling in precast joists slabs. The Load Factor values approach 2.50 when there are two healthy levels and 2.14 when there is one healthy level, in cases of three joists with corrosion in square 2. The loss of stiffness caused by corrosion can be analyzed by studying the yielding step and the subsequent change of slope in the load-displacement curves. This loss of stiffness is almost immediate in the models of reinforced slabs, in which when the yielding step appears, there is virtually no security with respect to the service load (6100 N/m2 ). On the other hand, in cases of pre-stressed slabs, an instantaneous deflection caused by corrosion appears, but then the initial slope, that of the elastic section, is practically retaken. They have a high bearing capacity. Regardless of the number of joists with corrosion, much safety information can be obtained by estimating the point of the curve in which the construction is located. If the value is within the first range of slopes, repair and measures to achieve sufficient security are easily attainable. However, if the point is on the final slope of the curve, then very strict safety measures are needed. By means of the methodology described in this work, the responsible technician has an adequate tool for the intervention of slabs. Previously, a data collection task must be carried out regarding the geometry, the properties of the materials and the location and level of corrosion in the joists. However, the decision is the responsibility of the expert, so it is advisable to carry out a complete slab repair project, to restore the safety values used during the design phase.

References American Concrete Institute (2008) Building code requeriments for structural concrete ACI 318-08 and commentary. Strength evaluation of existing structures. ACI, Michigan Barbosa AF, Ribeiro GO (1998) Analysis of reinforced concrete structures using Ansys nonlinear concrete model. Comput Mech 8:1–7

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Calavera J (2003) Cálculo, construcción, patología y rehabilitación de forjados de edificación. INTEMAC, Madrid Coronelli D, Gambarova P (2004) Structural assessment of corroded reinforced concrete beams: modeling guidelines. J Struct Eng 130:1214–1224 Cubel F, Mas A, Vercher J et al (2012) Design and construction recommendations for brick enclosures with continuous air chamber. Constr Build Mater 36:151–164 del Río A (2008) Patología, reparación y refuerzo de estructuras de hormigón armado de edificación. ETS Arquitectura (UPM), Madrid Di Evangelista A, De Leonardis A, Valente C et al (2011) Design and testing of corrosion damaged prestressed concrete joists: the Pescara Benchmark. J Phys Conf Ser 305:10 Dilrukshi KG, Dias WP, Rajapakse RK (2010) Numerical modelling of cracks in masonry walls due to thermal movements in an overlying slab. Eng Struct 32:1411–1422 Fanning P (2001) Nonlinear models of reinforced and post-tensioned concrete beams. Electr J Struct Eng 2:111–119 Ingeciber SA (2008) Elemento Solid65. Recomendaciones de uso con ANSYS/CivilFEM. Ingeciber SA, Madrid Mangat P, Elgarf M (1999) Flexural strength of concrete beams with corroding reinforcement. ACI Struct J 96:149–158 Ministerio de Fomento (2008) Instrucción de Hormigón Estructural (EHE-08). Boletín Oficial del Estado, Madrid Ministerio de Vivienda (2006) Código Técnico de la Edificación (CTE). Boletín Oficial del Estado, Madrid Río O, Alonso C, Andrade C et al (2000) Comportamiento de la reparación localizada de viguetas armadas afectadas por corrosión. Horm Acer 217:101–110 Rodriguez J, Ortega LM, Casal J (1997) Load carrying capacity of concrete structures with corroded reinforcement. Constr Build Mater 11:239–248 SEOPAN (2018) Construcción e infraestructuras: Estadísticas 2018 y previsiones para 2019. Asociación de Empresas Constructoras y Concesionarias de Infraestructuras. Available at https://seopan.es/wp-content/uploads/2019/07/Informe-Estad%C3%ADstico-SEOPAN2018_2019.pdf. Cited 22 Oct 2019 Tavio T, Tata A (2009) Predicting nonlinear behavior and stress-strain relationship of rectangular confined reinforced concrete columns with Ansys. Civ Eng Dim 11:23–31 Vercher J (2013) Seguridad residual en los forjados con corrosión severa. Universitat Politècnica de València, Valencia https://doi.org/10.4995/Thesis/10251/27705 Vieitez JA, Ramírez JL (1984) Patología de la Construcción en España: Aproximación Estadística. Resumen Tesis Doctoral. Inf Constr 36:5–15