Silica Fume in Geopolymers: A Comprehensive Review of Its Effects on Properties 3031332180, 9783031332180

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SpringerBriefs in Applied Sciences and Technology Alaa M. Rashad

Silica Fume in Geopolymers A Comprehensive Review of Its Effects on Properties

SpringerBriefs in Applied Sciences and Technology

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Alaa M. Rashad

Silica Fume in Geopolymers A Comprehensive Review of Its Effects on Properties

Alaa M. Rashad Building Materials Research and Quality Control Institute Housing and Building National Research Center (HBRC) Cairo, Egypt

ISSN 2191-530X ISSN 2191-5318 (electronic) SpringerBriefs in Applied Sciences and Technology ISBN 978-3-031-33218-0 ISBN 978-3-031-33219-7 (eBook) https://doi.org/10.1007/978-3-031-33219-7 © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 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, expressed 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

As known, the production of Portland cement (PC) currently is approximately 4.6 billion tonnes/year, and it is anticipated to reach approximately 6.0 billion tonnes by 2050. A great deal of hazardous gases such as sulphur dioxide, carbon dioxide and nitrogen oxide is released during cement manufacture, which makes it one of the most polluting industries. The industry of cement consumes approximately 4427 MJ/ tonne of energy, which represents 12–15% of the total energy used worldwide. This industry needs a tremendous amount of virgin materials (approximately 1.5 tonnes for every tonne of cement produced). As a result, cement production may lead to a shortage of virgin materials. Thus, it is useful to replace cement by alkali-activated cement or geopolymer. Return back to 1930, Kuhl studied the behaviour of setting of slag powder activated with solution of caustic potash. This was the first time of using alkali cement. In 1937, Chassevent used soda and caustic potash to measure the reactivity of slag powder. In 1940, Purdon conducted the first comprehensive laboratory study on cements free from clinker made of slag and either caustic alkalis or caustic soda manufactured by an alkaline salt and a base. In 1957, Glukhovsky made binders from calcium free or low basic calcium aluminosilicates activated with alkali metal solution. Since that date, the manufacture of alkali-activated materials or geopolymers has been receiving higher attention due to the growing request for novel construction materials that produce low emissions of greenhouse gas during manufacture. Generally, alkaliactivated materials are manufactured by activating aluminosilicate materials such as slag, fly ash and metakaolin with alkaline activator. Because the fact that recent studies do not intend to obtain new type of binder, they focus on how to develop and improve the properties of geopolymers. In recent developments, numerous studies have been implemented to obtain superior properties of various types of geopolymer by incorporating silica fume (SF). Due to its microsize and high amorphous silica, SF can be recycled into geopolymers in three various forms: as an additive to the precursor or as a part of a precursor, as a part of an activator or as a foaming agent. In this book, the available most recent developments in different types of geopolymer containing SF were compiled and deep analysed. Chapter 1 focused on the importance of using geopolymer as an alternative to PC, the importance of v

vi

Preface

using SF in PC and geopolymers as well as the properties of SF. Chapter 2 focused on the effect of SF on the fresh and the hardened properties of various geopolymer types when it was used as a part of precursor. These hardened properties contain mechanical and durability properties. Chapter 3 focused on the importance of using SF as a part of alkali activator on the properties of geopolymers. Chapter 4 focused on the importance of using SF as a foaming agent on the density and thermal properties of the geopolymers. Chapter 5 focused on general view of the results mentioned in the previous chapters and recommendation for future work. Finally, Chap. 6 focused on the general conclusions or remarks of incorporating SF into geopolymers. Cairo, Egypt

Alaa M. Rashad

Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 6

2 Silica Fume as a Part of Precursor/An Additive . . . . . . . . . . . . . . . . . . . 2.1 Workability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Setting Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Compressive Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.1 Slag Precursor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.2 Fly Ash Precursor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.3 Metakaolin Precursor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.4 Slag/Fly Ash Precursor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.5 Other Precursors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 Flexural Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6 Splitting Tensile Strength and Elastic Modulus . . . . . . . . . . . . . . . . 2.7 Toughness and Abrasion Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . 2.8 Water Absorption, Porosity and Water Penetration Depth . . . . . . . . 2.9 Fire Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.10 Other Durability Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9 9 16 17 20 20 29 38 44 52 53 57 63 63 71 75 81

3 Silica Fume as an Activator Component . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

85 93

4 Silica Fume as a Foaming Agent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 5 General Perspective and Suggestions for Upcoming Work . . . . . . . . . . 103 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 6 General Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

vii

Chapter 1

Introduction

Abstract Silica fume (SF) is a by-product of ferrosilicon alloys or the silicon metal industry. Due to its high fineness and amorphous silica, it is widely used in Portland cement (PC) systems as a cementitious material to enhance the durability and mechanical properties. In recent developments, numerous studies have been implemented to obtain superior properties of various types of geopolymer by incorporating SF. On the whole, SF can be recycled into geopolymers in three various forms: as an additive to the precursor or as a part of a precursor, as a part of an activator or as a foaming agent. Recycling SF into various geopolymer types may have a positive effect or an adverse effect. This mainly depends on precursor/SF fineness, activator concentration and type, activator/binder ratio, testing age, curing condition, SF amount and Si/Al ratio. The target of this document is to review, summarize and analyse the past studies focused on the effect of SF, in its three various forms, on the properties of geopolymers. Keywords Silica fume · Geopolymers · Fresh properties · Hardened properties · Activator component · Foaming agent

Despite Portland cement (PC) is widely used in infrastructures and buildings, its industry pollutes the environment and consumes huge amounts of energy and natural raw materials [1]. Thus, blended cement was used to partially solve these defects [2–4]. If cement can be fully replaced by other eco-friendly binders, the defects resulting from the cement industry can be fully solved. These eco-friendly binders are named geopolymers. Geopolymer is a binder based on the reaction between an alkali activator and an aluminosilicate. Using geopolymers instead of PC can limit greenhouse gas emissions by ~ 73% and energy consumption by ~ 43% [5], but the costs may be 39% higher or 7% lower than those of PC. This mainly depends on the precursor type [6]. Since the knowledge of geopolymer, improvements have been made to obtain better properties. For these proposals, several tactics were used such as adding various types of nanoparticles [7], introducing various types of fibres [8, 9], incorporating various types of cementitious materials [1, 10] and chemical admixtures [1]. One selection to get superior properties is to blend the main precursor © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. M. Rashad, Silica Fume in Geopolymers, SpringerBriefs in Applied Sciences and Technology, https://doi.org/10.1007/978-3-031-33219-7_1

1

2

1 Introduction

with ultra-fine material such as SF. As known, NaOH and sodium silicate are widely used as activators for geopolymers due to their better achieved strength. However, the production of these activators is energy-intensive [11, 12]. In the case of sodium silicate, it is produced by the fusion of sand and CaCO3 at ~ 1350–1450 °C pursued by liquefying the glass formed at ~ 140–160 °C in an autoclave under steam pressure [13]. This procedure emits a large CO2 amount [14]. Therefore, if sodium silicate can be replaced by by-product material such as SF, lower CO2 emissions and cost can be obtained. Silica fume (SF) is an extremely fine non-crystalline silica generated in electric arc furnace as a by-product of alloys containing silicon or elemental silicon production. When ferrosilicon alloys or silicon metals were produced that were used in steel production, aluminium production, fabrication of computer chips and silicones production, SF was formed as a by-product. Condensed SF, volatilized silica, silica dust and microsilica are other names of SF. The colour of SF is regularly grey (Fig. 1.1) [15] or greyish black, whilst its morphology shape is spherical (Fig. 1.2) [16]. Figure 1.3 confirms that SF is an amorphous material [17]. Its specific gravity varies from 2.04 [18], 2.15 [19], 2.2 [15, 17, 20–23], 2.23 [24], 2.28 [25], 2.32 [26], 2.6 [27] to 2.64 [28]. Its bulk density densified, as-produced and slurry are 720– 480, 430–130 and 1440–1320 kg/m3 , respectively, whilst its typical particle size and surface area are < 1 µm and 30,000–13,000 m2 /kg, respectively [29]. SF is a rich material with amorphous silica and contains small amounts of magnesium, iron and alkali oxides as shown in Table 1.1. Due to its better properties, it can be classified as a pozzolanic material agreeing with ASTM C1240 and used as a cementitious material for PC systems to reach superior properties [29–33]. SF plays three protuberant rules in the cement matrix. Firstly, it can improve the rheological properties by its lubricating effect. Secondly, it can improve packing density by its filling effect. Thirdly, it can enhance C–S–H by its pozzolanic activity [34]. The literature has numerous studies focused on the effect of SF on the hardened and fresh properties of conventional PC systems. Recently, SF was used in geopolymers in three different forms. Firstly, it can be used as a part of a precursor or an additive. Secondly, it can be used as a part of an activator. Thirdly, it can be used as a foaming agent. It was reported that the cost of production of geopolymer concrete containing fly ash (FA) and SF is cheaper than that of neat FA geopolymer concrete. The global warming of FA geopolymer concrete can be decreased from 148 kg CO2 -e to 133 and 135 with the inclusion of SF [24]. In the same style, it was reported that the activator of NaOH-SF showed lower CO2 emissions and cost compared to that of NaOH-sodium silicate [35]. Therefore, in principle, the use of SF in geopolymer is more environmentally friendly and less cost. So far, there is no document concerned with studying the effect of SF (in its three forms) on the properties of geopolymers. Thus, the target of this book is to summarize and analyse the past studies focused on the effect of SF as a part of precursor, as a part of activator and as a foaming agent on the properties of geopolymers.

1 Introduction Fig. 1.1 View of SF [15]. Reprinted with permission from Springer publisher

Fig. 1.2 SF morphology [16]. Reprinted with permission from Elsevier publisher

Fig. 1.3 XRF pattern of SF [17]. Reprinted with permission from American Concrete Institute publisher

3

97.1

96.57

90

88.5

95.2

90.01

95.38

96.1

94.14

90.01

94.5

96.81

94.49

95.72

93.67

96.7

93.34

91.57

95.1

94.58

Wetzel and Middendorf [36]

Cheah et al. [25]

Ramezanianpour and Moeini [37]

Escalante-Garcia et al. [38]

Zhu et al. [39]

Liu et al. [40]

Saludung et al. [41]

Živica [42]

Zhang et al. [43]

Cong and Mei [44]

Elyamany et al. [45]

Alanazi et al. [46]

Duan et al. [47]

Okoye et al. [48]

Luna-Galiano [18]

Wang et al. [49]

Uysal et al. [21]

Alcamand et al. [50]

Javed et al. [51]

SiO2

21.08

0.7

0.38

0.62

0.43

0.83

0.09

0.07

0.25

0.27

1.04

0.13

0.73

–

1.04

–

1.4

1.2

0.06

0.1

Al2 O3

Oxide (%)

Billong et al. [20]

References

Table 1.1 Chemical composition of SF

1.45

0.4

0.32

0.99

0.51

0.31

0.23

0.5

0.16

–

0.63

0.13

0.27

1.84

0.63

0.98

1.5

1

0.51

–

CaO

0.06

1.1

0.15

1.75

0.5

1.3

0.63

0.1

0.45

0.83

0.61

0.18

1.4

0.61

0.61

1

2.1

2

0.06

0.2

Fe2 O3

0.41

0.8

4.05

0.58

0.39

0.84

0.37

0.62

0.26

0.97

0.21

0.18

0.42

0.26

0.21

0.23

2

0.6

0.25

0.15

MgO

0.14

0.3

–

–

–

0.16

0.01

0.11

0.14

–

0.83

0.28

0.2

–

0.83

0.02

–

0.5

0.12

0.06

SO3

0.11

–

–

–

–

–

0.04

–

–

–

0.01

–

–

–

0.01

–

–

–

–

P2 O5

–

0.05

–

0.14

–

0.84

0.02

–

–

–

–

–

–

–

–

–

–

0.02

–

MnO

–

–

–

–

–

–

0.01

–

–

–

0.12

–

–

–

0.12

0.15

–

0.01

0.06

TiO2

0.23

–

0.55

0.68

0.2

0.4

0.09

0.09

0.14

0.54

0.19

–

–

0.16

0.19

0.91

–

0.8

0.16

–

Na2 O

0.64

1.33

2.58

1.89

0.79

1.1

0.26

0.54

0.28

–

0.32

–

0.74

0.85

0.32

1.03

0.75

–

0.73

–

K2 O

(continued)

1.79

–

1.68

–

1.48

2.1

2.53

3.21

1.3

1.9

5.34

2.35

1.68

0.9

5.34

0.2

3

–

1.41

0.08

L.O.I

4 1 Introduction

94.5

92.26

96.1

93.35

Matalkah et al. [19]

Rashad et al. [15], Morsy et al. [54, 55]

Liu et al. [56]

SiO2

2.96

0.5

0.89

1.03

Al2 O3

Oxide (%)

Seleem et al. [52, 53]

References

Table 1.1 (continued)

0.63

0.21

0.49

1.1

CaO

0.14

0.7

1.97

0.78

Fe2 O3

0.75

0.48

0.96

0.46

MgO

–

0.1

0.33

0.08

SO3

–

–

–

–

P2 O5

–

–

–

–

MnO

–

–

–

–

TiO2

–

0.31

0.42

0.27

Na2 O

0.59

0.49

1.31

0.43

K2 O

–

1.14

4.96

1.31

L.O.I

1 Introduction 5

6

1 Introduction

References 1. A.M. Rashad, A comprehensive overview about the influence of different additives on the properties of alkali-activated slag—a guide for civil engineer. Constr. Build. Mater. 47, 29–55 (2013) 2. A.M. Rashad, A brief on high-volume class F fly ash as cement replacement—a guide for civil engineer. Int. J. Sustain. Built Environ. 4(2), 278–306 (2015) 3. A.M. Rashad, An overview on rheology, mechanical properties and durability of high-volume slag used as a cement replacement in paste, mortar and concrete. Constr. Build. Mater. 187, 89–117 (2018) 4. A.M. Rashad, Metakaolin as cementitious material: history, scours, production and composition—a comprehensive overview. Constr. Build. Mater. 41, 303–318 (2013) 5. A.M. Rashad, Additives to increase carbonation resistance of slag activated with sodium sulfate. ACI Mater. J. 119(2) (2022) 6. B.C. McLellan, R.P. Williams, J. Lay, A. Van Riessen, G.D. Corder, Costs and carbon emissions for geopolymer pastes in comparison to ordinary Portland cement. J. Clean. Prod. 19(9–10), 1080–1090 (2011) 7. A.M. Rashad, Effect of nanoparticles on the properties of geopolymer materials. Mag. Concr. Res. 71(24), 1283–1301 (2019) 8. A.M. Rashad, The effect of polypropylene, polyvinyl-alcohol, carbon and glass fibres on geopolymers properties. Mater. Sci. Technol. 35(2), 127–146 (2019) 9. A.M. Rashad, Effect of steel fibers on geopolymer properties—the best synopsis for civil engineer. Constr. Build. Mater. 246, 118534 (2020) 10. A.M. Rashad, Effect of limestone powder on the properties of alkali-activated materials—a critical overview. Constr. Build. Mater. 356, 129188 (2022) 11. A. Rashad, Y. Bai, P. Basheer, N. Milestone, N. Collier, Hydration and properties of sodium sulfate activated slag. Cem. Concr. Compos. 37, 20–29 (2013) 12. A.M. Rashad, Y. Bai, Effect of slag fineness and Na2 SO4 concentration on carbonation of Na2 SO4 -activated slag. ACI Mater. J. 120(1) (2023) 13. C. Shi, A. Fernández-Jiménez, Stabilization/solidification of hazardous and radioactive wastes with alkali-activated cements. J. Hazard. Mater. 137(3), 1656–1663 (2006) 14. R. Vinai, M. Soutsos, Production of sodium silicate powder from waste glass cullet for alkali activation of alternative binders. Cem. Concr. Res. 116, 45–56 (2019) 15. A.M. Rashad, G.M. Essa, W. Morsi, Traditional cementitious materials for thermal insulation. Arab. J. Sci. Eng., 1–13 (2022) 16. Y. Cheng, P. Cong, Q. Zhao, H. Hao, L. Mei, A. Zhang, Z. Han, M. Hu, Study on the effectiveness of silica fume-derived activator as a substitute for water glass in fly ash-based geopolymer. J. Build. Eng. 51, 104228 (2022) 17. A.M. Rashad, Y.A. Mosleh, Effect of tidal zone and seawater attack on alkali-activated blended slag pastes. ACI Mater. J. 119(2) (2022) 18. Y. Luna-Galiano, C. Leiva, C. Arenas, C. Fernández-Pereira, Fly ash based geopolymeric foams using silica fume as pore generation agent. Phys. Mech. Acoust. Prop. J. Non-Crystal. Solids 500, 196–204 (2018) 19. F. Matalkah, A. Ababneh, R. Aqel, Efflorescence control in calcined kaolin-based geopolymer using silica fume and OPC. J. Mater. Civ. Eng. 33(6), 04021119 (2021) 20. N. Billong, J. Oti, J. Kinuthia, Using silica fume based activator in sustainable geopolymer binder for building application. Constr. Build. Mater. 275, 122177 (2021) 21. M. Uysal, M.M. Al-mashhadani, Y. Aygörmez, O. Canpolat, Effect of using colemanite waste and silica fume as partial replacement on the performance of metakaolin-based geopolymer mortars. Constr. Build. Mater. 176, 271–282 (2018) 22. Y. Jaradat, F. Matalkah, Effects of micro silica on the compressive strength and absorption characteristics of olive biomass ash-based geopolymer. Case Stud. Constr. Mater. 18, e01870 (2023)

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7

23. A.M. Rashad, Possibility of producing thermal insulation materials from cementitious materials without foaming agent or lightweight aggregate. Environ. Sci. Pollut. Res. 29(3), 3784–3793 (2022) 24. R. Bajpai, K. Choudhary, A. Srivastava, K.S. Sangwan, M. Singh, Environmental impact assessment of fly ash and silica fume based geopolymer concrete. J. Clean. Prod. 254, 120147 (2020) 25. C.B. Cheah, L.E. Tan, M. Ramli, The engineering properties and microstructure of sodium carbonate activated fly ash/slag blended mortars with silica fume. Compos. B Eng. 160, 558–572 (2019) 26. A.M. Rashad, M.H. Khalil, A preliminary study of alkali-activated slag blended with silica fume under the effect of thermal loads and thermal shock cycles. Constr. Build. Mater. 40, 522–532 (2013) 27. R.P. Singh, K.R. Vanapalli, V.R.S. Cheela, S.R. Peddireddy, H.B. Sharma, B. Mohanty, Fly ash, GGBS, and silica fume based geopolymer concrete with recycled aggregates: Properties and environmental impacts. Constr. Build. Mater. 378, 131168 (2023) 28. P. Kathirvel, G. Murali, Effect of using available GGBFS, silica fume, quartz powder and steel fibres on the fracture behavior of sustainable reactive powder concrete. Constr. Build. Mater. 375, 130997 (2023) 29. R. Siddique, Utilization of silica fume in concrete: review of hardened properties. Resour. Conserv. Recycl. 55(11), 923–932 (2011) 30. M.I. Khan, R. Siddique, Utilization of silica fume in concrete: review of durability properties. Resour. Conserv. Recycl. 57, 30–35 (2011) 31. A.M. Rashad, H.E.-D.H. Seleem, A.F. Shaheen, Effect of silica fume and slag on compressive strength and abrasion resistance of HVFA concrete. Int. J. Concr. Struct. Mater. 8, 69–81 (2014) 32. A.M. Rashad, Potential use of silica fume coupled with slag in HVFA concrete exposed to elevated temperatures. J. Mater. Civ. Eng. 27(11), 04015019 (2015) 33. A.M. Rashad, An exploratory study on high-volume fly ash concrete incorporating silica fume subjected to thermal loads. J. Clean. Prod. 87, 735–744 (2015) 34. J.R. Liew, M.-X. Xiong, B.-L. Lai, Design of Steel-Concrete Composite Structures Using High-Strength Materials (Woodhead Publishing, 2021) 35. X. Dai, S. Aydın, M.Y. Yardımcı, K. Lesage, G. De Schutter, Rheology and microstructure of alkali-activated slag cements produced with silica fume activator. Cem. Concr. Compos. 125, 104303 (2022) 36. A. Wetzel, B. Middendorf, Influence of silica fume on properties of fresh and hardened ultrahigh performance concrete based on alkali-activated slag. Cem. Concr. Compos. 100, 53–59 (2019) 37. C.S. Thunuguntla, T.G. Rao, Effect of mix design parameters on mechanical and durability properties of alkali activated slag concrete. Constr. Build. Mater. 193, 173–188 (2018) 38. J.I. Escalante-Garcia, V.M. Palacios-Villanueva, A.V. Gorokhovsky, G. Mendoza-Suárez, A.F. Fuentes, Characteristics of a NaOH-activated blast furnace slag blended with a fine particle silica waste. J. Am. Ceram. Soc. 85(7), 1788–1792 (2002) 39. Y. Zhu, M.A. Longhi, A. Wang, D. Hou, H. Wang, Z. Zhang, Alkali leaching features of 3-yearold alkali activated fly ash-slag-silica fume: for a better understanding of stability. Compos. B Eng. 230, 109469 (2022) 40. Y. Liu, C. Shi, Z. Zhang, N. Li, D. Shi, Mechanical and fracture properties of ultra-high performance geopolymer concrete: effects of steel fiber and silica fume. Cem. Concr. Compos. 12, 103665 (2020) 41. A. Saludung, T. Azeyanagi, Y. Ogawa, K. Kawai, Effect of silica fume on efflorescence formation and alkali leaching of alkali-activated slag. J. Clean. Prod. 315, 128210 (2021) 42. V.R. Živica, Effectiveness of new silica fume alkali activator. Cem. Concr. Compos. 28(1), 21–25 (2006) 43. Z. Zhang, L. Li, X. Ma, H. Wang, Compositional, microstructural and mechanical properties of ambient condition cured alkali-activated cement. Constr. Build. Mater. 113, 237–245 (2016)

8

1 Introduction

44. P. Cong, L. Mei, Using silica fume for improvement of fly ash/slag based geopolymer activated with calcium carbide residue and gypsum. Constr. Build. Mater. 275, 122171 (2021) 45. H.E. Elyamany, M. Abd Elmoaty, A.M. Elshaboury, Setting time and 7-day strength of geopolymer mortar with various binders. Constr. Build. Mater. 187, 974–983 (2018) 46. H. Alanazi, J. Hu, Y.-R. Kim, Effect of slag, silica fume, and metakaolin on properties and performance of alkali-activated fly ash cured at ambient temperature. Constr. Build. Mater. 197, 747–756 (2019) 47. P. Duan, C. Yan, W. Zhou, Compressive strength and microstructure of fly ash based geopolymer blended with silica fume under thermal cycle. Cem. Concr. Compos. 78, 108–119 (2017) 48. F. Okoye, J. Durgaprasad, N. Singh, Effect of silica fume on the mechanical properties of fly ash based-geopolymer concrete. Ceram. Int. 42(2), 3000–3006 (2016) 49. F. Wang, X. Sun, Z. Tao, Z. Pan, Effect of silica fume on compressive strength of ultra-highperformance concrete made of calcium aluminate cement/fly ash based geopolymer. J. Build. Eng., 105398 (2022) 50. H.A. Alcamand, P.H. Borges, F.A. Silva, A.C.C. Trindade, The effect of matrix composition and calcium content on the sulfate durability of metakaolin and metakaolin/slag alkali-activated mortars. Ceram. Int. 44(5), 5037–5044 (2018) 51. U. Javed, F.U.A. Shaikh, P.K. Sarker, Microstructural investigation of lithium slag geopolymer pastes containing silica fume and fly ash as additive chemical modifiers. Cem. Concr. Compos. 134, 104736 (2022) 52. H.E.D.H. Seleem, A.M. Rashad, T. Elsokary, Effect of elevated temperature on physicomechanical properties of blended cement concrete. Constr. Build. Mater. 25(2), 1009–1017 (2011) 53. H.E.-D.H. Seleem, A.M. Rashad, B.A. El-Sabbagh, Durability and strength evaluation of highperformance concrete in marine structures. Constr. Build. Mater. 24(6), 878–884 (2010) 54. M. Morsy, S. Shebl, A. Rashad, Effect of fire on microstructure and mechanical properties of blended cement pastes containing metakaolin and silica fume. Asian J. Civ. Eng. Build. Hous. 9, 93–105 (2008) 55. M. Morsy, A. Rashad, S. Shebl, Effect of elevated temperature on compressive strength of blended cement mortar. Build. Res. J. 56(2–3), 173–185 (2008) 56. X. Liu, C. Hu, L. Chu, Microstructure, compressive strength and sound insulation property of fly ash-based geopolymeric foams with silica fume as foaming agent. Materials 13(14), 3215 (2020)

Chapter 2

Silica Fume as a Part of Precursor/An Additive

Abstract Due to the prospective properties of silica fume (SF), it is frequently used in Portland cement (PC) systems as a supplementary cementitious ingredient to improve the mechanical and durability properties. In recent developments, numerous studies have been implemented to obtain superior properties of various types of geopolymer by incorporating SF. In spite of SF can be incorporated into geopolymers in various forms, most of the past studies employed it as a part of precursor/an additive. However, recycling SF as a cementitious material (as a part of precursor) into various geopolymer types may have a positive effect or an adverse effect. This mainly depends on precursor/SF fineness, activator concentration and type, activator/binder ratio, testing age, curing condition, SF amount and Si/Al ratio. The target of this part is to review, summarize and analyse the past studies focused on the effect of SF, as an additive or a part of precursor, on workability, setting time, density, mechanical strength and different durability aspects of various types of geopolymer. Keywords Silica fume · Geopolymers · Fresh properties · Mechanical strength · Durability

2.1 Workability Rashad [1] found 9.1% reduction in the workability of slag activated with Na2 SO4 by partially replacing slag with 5% SF. Ramezanianpour and Moeini [2] found 2.7%, 10.81% and 13.51% higher flowability of alkali-activated slag (AAS) mortar mixtures activated with NaOH and sodium silicate solution (activator/binder = 0.9) with including 5%, 7.5% and 10% SF (size 2.5 μm), respectively. When the activator/binder ratio was 1, the flowability was increased by 4.35%, 0% and 4.35%, respectively. When KOH and sodium silicate solution was used as an alkaline activator (activator/binder = 0.9), the incorporation of 5%, 7.5% and 10% SF increased the flowability by 4.55%, 4.55% and 9.1%, respectively, whilst the flowability was increased by 4.17% with the incorporation of any ratio of SF when activator/binder ratio was 1. Kanaan and Soliman [3] found ~ 29.4%, ~ 7.5% and ~ 0.8% reduction in the flowability of AAS mortar mixtures activated with anhydrous sodium © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. M. Rashad, Silica Fume in Geopolymers, SpringerBriefs in Applied Sciences and Technology, https://doi.org/10.1007/978-3-031-33219-7_2

9

10

2 Silica Fume as a Part of Precursor/An Additive

metasilicate and sodium carbonate by partially replacing slag (fineness 585 m2 /kg) with 10% SF (fineness 19,530 m2 /kg) when the activator concentration was 16%, 20% and 25%, respectively. Wetzel and Middendorf [4] found 117.39%, 117.39% and 60.87% higher slump of AAS mortar mixtures activated with potassium/sodium hydroxide and potassium/sodium waterglass containing 10%, 15% and 20% SF (fineness 21,800 m2 /kg), by volume, compared to that containing 5% SF. Kathirvel and Murali [5] found a slight higher flowability of AAS reactive powder concrete mixtures by partially replacing slag (size 1358.3 nm) with 15% and 30% SF (size 962.3 nm). Cheah et al. [6] found 3.7% and 11.11% higher flowability of 40% slag/60% fly ash (FA) geopolymer mortar mixtures activated with Na2 CO3 and Na2 SiO3 with the incorporation of 6 and 8% SF (fineness 30,000–13,000 m2 /kg), whilst the incorporation of 10% SF reduced it by 3.7%. Contrarily, the incorporation of 2% and 4% SF did not show any change in the flowability. Zhang et al. [7] partially replaced FA in 40% slag/60% FA geopolymer paste mixtures activated with NaOH and sodium silicate solution by 5–15% SF. The results showed good workability with the incorporation of 0% and 5% SF, whilst the incorporation of 10% and 15% SF led to low workability. Singh et al. [8] found 0%, 5.55%, 11.11% and 16.67% reduction in the workability of 50% slag/50% FA geopolymer concrete mixtures activated with NaOH and sodium silicate solution by partially replacing slag with 5%, 10%, 15% and 20% SF, respectively. Liu et al. [9] prepared a mortar mixture from slag/FA/5% SF and 2% steel fibres activated with NaOH and waterglass solution. The slag/FA was partially replaced with 10%, 20% and 30% SF. The results showed 6.4% higher flowability by partially replacing slag (fineness 446 m2 /kg) and FA (fineness 290 m2 /kg) with 10% SF (fineness 18,650 m2 /kg), whilst the inclusion of 20% and 30% SF decreased it by 5.56% and 32.9%, respectively. Alanazi et al. [10] found a reduction in the flowability of FA geopolymer mortar mixtures activated with NaOH and sodium silicate solution by partially replacing FA with 5% and 10% SF. As the SF amount increased, the flowability decreased. When the sodium silicate/NaOH ratio was 1, the reduction in the flowability with the incorporation 5% and 10% SF was ~ 8.8% and ~ 23.7%, respectively, whilst the reduction reached ~ 2.1% and ~ 23.5, respectively, when sodium silicate/NaOH ratio was 2.5. Jena and Panigrahi [11] found 6.56%, 18% and 27.87% reduction in the workability of FA geopolymer concrete mixtures activated with NaOH and sodium silicate solution by partially replacing FA with 5%, 10% and 15% SF, respectively. Okoye et al. [12] found 0%, ~ 10%, ~ 15% and 50% reduction in the workability of FA geopolymer concrete mixtures activated with NaOH and sodium silicate solution by partially replacing FA with 5%, 10%, 15% and 20% SF, respectively. Sukontasukkul et al. [13] found 12.73%, 19.1% and 34.54% reduction in the flowability of FA geopolymer mortar mixtures activated with NaOH and sodium silicate solution by partially replacing FA with 10%, 20% and 30% SF, respectively. Das et al. [14] prepared FA/lime/SF geopolymer concrete mixtures activated with NaOH and sodium silicate solution. The results showed that the workability increased with increasing SF ratio. The slump of the mixtures made of 10% lime beside 3% and 2% SF was 93% and 50% higher than that made of 1% SF, respectively. Wang et al. [15] prepared ultra-high performance concrete (UHPC) geopolymer mixtures from

2.1 Workability

11

FA/calcium aluminate cement (CAC) activated with NaOH and sodium silicate solution. When the ratio of cement was 10%, the inclusion of 5% and 10% SF increased the flowability even though its surface area (19,020 m2 /kg) is higher than that of FA (1120 m2 /kg) and cement (1600 m2 /kg), whilst the inclusion of 15% and 20% SF decreased it. When the ratio of cement was 20%, the inclusion of 5–20% SF increased the flowability. Batista et al. [16] found 2.63% higher spread of metakaolin (MK) (size 2.12 μm) geopolymer mortar mixture activated with NaOH and sodium silicate solution with the inclusion of 4% SF (size 0.37 μm), whilst the inclusion of 7% SF decreased it by 1.3%. Rashad and Zeedan [17] reported higher workability of MK geopolymer paste mixtures activated with sodium silicate by partially replacing MK with 5–25% SF even though the fineness of SF is higher than that of MK. When 25% of the activator was used, the incorporation of 5%, 10%, 15%, 20% and 25% SF increased the flow by 17.86%, 28.57%, 42.86%, 50% and 57.14%, respectively, whilst the flow was increased by 2.63%, 5.26%, 7.9%, 10.53% and 13.16%, respectively, when 50% of activator was used (Fig. 2.1). Albidah et al. [18] found ~ 28.57% lower workability of MK geopolymer concrete mixture activated with NaOH and sodium silicate solution by partially replacing MK (size 32.33 μm) with 5% SF (size 64.96 μm), whilst the incorporation of 10%, 20% and 30% SF increased the workability by 85.7%, 171.4% and 214.3%, respectively. They related this improvement to the large size of SF. Table 2.1 briefs the results of this part. Based on the discussion so far, it is evident that the incorporation of SF may increase or decrease the mixture workability. This depends on precursor type and fineness, activator concentration and type as well as SF amount and fineness. As shown in Fig. 2.2, when slag or MK was used as a precursor, the incorporation of SF increased the workability even though the SF fineness is higher than that of slag or MK. This improvement could be attributed to the smooth spherical SF particles 120

50% activator

25% activator

100

Flow (%)

80 60 40 20 0 0

5

10

15

20

25

SF content (%) Fig. 2.1 Effect of SF on MK geopolymer mixtures workability activated with different concentrations of sodium silicate [17]. Reprinted with permission from American Concrete Institute publisher

NaOH and sodium 5, 7.5 silicate solution and 10 Anhydrous sodium 10 metasilicate and sodium carbonate

Potassium/sodium hydroxide and potassium/sodium waterglass

25.97 μm

585 m2 /kg

390 m2 /kg

–

–

Slag

Slag

Slag

Slag

Slag/FA

Slag/FA

Slag/FA

Ramezanianpour and Moeini [2]

Kanaan and Soliman [3]

Wetzel and Middendorf [4]

Kathirvel and Murali [5]

Cheah et al. [6]

Zhang et al. [7] NaOH and sodium 10 and silicate solution 15

NaOH and sodium 5 silicate solution

–

–

Sodium carbonate 6 and 8 30,000–13,000 m2 /kg and sodium silicate solution

465/324.4 m2 /kg

962.3 nm

NaOH and sodium 15 and silicate 30

21,800 m2 /kg

19,530 m2 /kg

2.5 μm

22,000 m2 /kg

1358.3 nm

10, 15 and 20

5

Na2 SO4

500 m2 /kg

Slag

Rashad [1]

SF (%) SF size/surface area

Activator

Precursor size/surface area

Precursor

References

Table 2.1 Effect of SF on the mixture workability

Paste

Paste

Mortar

Reactive powder concrete

Mortar

Mortar

Mortar

Paste

Type

Decreased workability

Increased workability

Increased flowability

Increased workability

Increased workability

Decreased flowability

Increased flowability

Decreased workability

Effect

Low

Good

(continued)

3.7 and 11.11

~ 2.4 and ~ 1.2

117.39, 117.39 and 60.87

~ 29.4%, ~ 7.5% and ~ 0.8% (according to activator concentration)

2.7, 10.81 and 13.5

9.1

Ratio

12 2 Silica Fume as a Part of Precursor/An Additive

NaOH and sodium 4 silicate solution NaOH and sodium 7 silicate solution

2.12 μm

2.12 μm

MK

MK

Batista et al. [16]

NaOH and sodium 5, 10, silicate solution 15 and 20 NaOH and sodium 10, 20 silicate solution and 30

FA

Sukontasukkul et al. [13]

–

–

FA

Okoye et al. [12]

NaOH and sodium 5, 10 silicate solution and 15

8 μm

FA

Jena and Panigrahi [11]

NaOH and sodium 5 and silicate solution 10

–

FA

NaOH and sodium 5 and silicate solution 10

NaOH and 20 and waterglass solution 30

17.9/36.94/0.15 μm

Slag/FA/SF

–

NaOH and 10 waterglass solution

17.9/36.94/0.15 μm

Slag/FA/SF

Liu et al. [9]

Alanazi et al. [10] FA

NaOH and sodium 5, 10, silicate solution 15 and 20

– /45 μm

Slag/FA

Singh et al. [8]

0.37 μm

0.37 μm

–

–

–

–

–

18,650 m2 /kg

0.15 μm

0.12 μm

SF (%) SF size/surface area

Activator

Precursor size/surface area

Precursor

References

Table 2.1 (continued)

Mortar

Mortar

Mortar

Concrete

Concrete

Mortar

Mortar

Mortar

Mortar

Concrete

Type

Decreased workability

Increased workability

Decreased flowability

Decreased workability

Decreased workability

Decreased flowability

Decreased flowability

Decreased flowability

Increased flowability

Decreased workability

Effect

1.3

2.63

(continued)

12.73, 19.1 and 34.54

0, ~ 10, ~ 15 and 50

6.56, 18 and 27.87

~ 2.1 and ~ 23.5

~ 8.8 and ~ 23.7

5.56 and 32.9

6.4

0, 5.55, 11.11 and 16.67

Ratio

2.1 Workability 13

NaOH and sodium 5 silicate solution NaOH and sodium 10, 20 silicate solution and 30

32.33 μm

32.33 μm

MK

MK

Albidah et al. [18]

Sodium silicate

460 m2 /kg

MK

5, 10, 15, 20 and 25

5, 10, 15, 20 and 25

Sodium silicate

460 m2 /kg

MK

Rashad and Zeedan [17]

64.96 μm

64.96 mm

20,200 m2 /kg

20,200 m2 /kg

SF (%) SF size/surface area

Activator

Precursor size/surface area

Precursor

References

Table 2.1 (continued)

Concrete

Concrete

Paste

Paste

Type

Increased workability

Decreased workability

Increased flowability

Increased flowability

Effect

85.7, 171.4 and 214.3%

~ 28.57

2.63, 5.26, 7.9, 10.53 and 13.16 (50% activator)

17.86, 28.57, 42.86, 50 and 57.14 (25% activator)

Ratio

14 2 Silica Fume as a Part of Precursor/An Additive

2.1 Workability

15

Relative workability (%)

350

Slag Slag/FA FA MK

300 250 200 150 100 50 0 0

5

10

15

20

25

30

SF (%) Fig. 2.2 Effect of SF on the workability of different types of geopolymer [1–6, 8–13, 16–18]

Fig. 2.3 Percentage of studies of different media for workability

11.76

41.18

Paste Mortar Concrete 47.06

compared to the jagged and irregular shape of slag particles [19] or the platelet MK particles [20]. The spherical particles can act as a bouncing ball between other solid particles. This can lead to the friction force reduction between the particles. Contrarily, the high amount of SF reduced the flowability due to its higher surface area [15]. On the other hand, when FA was used as a precursor, the incorporation of SF decreased the workability. This could be attributed to the geometry of FA particles that can perform as ball bearings [21]. These ball bearings have a positive effect on the mixture rheology [22]. In addition, the small particle size of SF has an adverse effect on the workability. As a matter of fact, about 47.06%, 41.18% and 11.76% of the cited references focused on mortar, concrete and paste mixtures, respectively (Fig. 2.3), whilst 27.78%, 22.22%, 22.22%, 16.67% and 11.11% of them used slag, FA, slag/FA, MK and other precursors, respectively (Fig. 2.4).

16

2 Silica Fume as a Part of Precursor/An Additive

Fig. 2.4 Percentage of studies of different precursors for workability

11.11 27.78 Slag FA MK Slag/FA

22.22

16.67

22.22

2.2 Setting Time Wetzel and Middendorf [4] found 19%, 28.57% and 38.1% longer setting time of AAS mortar mixtures containing 10%, 15% and 20% SF (fineness 21,800 m2 /kg) compared to that containing 5% SF. Elyamany et al. [23] found longer setting time of 50% slag/50% FA geopolymer mortar mixtures activated with NaOH by partially replacing slag with 15% SF. When 16 M NaOH was used, the incorporation of 15% SF prolonged the initial and final time by ~ 71.4% and ~ 20%, respectively. Cheah et al. [6] found shorter setting time of 40% slag/60% FA geopolymer paste mixtures activated with Na2 CO3 and Na2 SiO3 by adding 4–10% SF. The addition of 4%, 6%, 8% and 10% SF (fineness 30,000–13,000 m2 /kg) shortened the initial setting time by 9.8%, 5.88%, 13.73% and 23.92%, respectively, whilst the final setting time was shortened by 11.11%, 8.33%, 11.11% and 12.78%, respectively. There is no change in the final setting time with the addition of 2% SF, whilst the initial setting time was prolonged by 7.84%. Sukontasukkul et al. [13] found 26.67%, 40% and 66.67% longer final setting time of FA geopolymer mortar mixtures activated with NaOH and sodium silicate solution by partially replacing slag with 10%, 20% and 30% SF, respectively. Das et al. [14] prepared FA/lime/SF geopolymer concrete mixtures activated with NaOH and sodium silicate solution. The results showed that the initial and final setting time increased with increasing SF ratio. The final setting time of the mixtures made of 5% lime beside 3% and 2% SF was 36% and 13% longer than that made of 1% SF, respectively. Liang et al. [24] found general increase in the period of initial and final setting time of MK geopolymer paste mixtures activated with NaOH and sodium silicate solution by partially replacing MK (size 39.8 μm) with 10–40% SF (size 31.3 μm). The incorporation of 10%, 20%, 30% and 40% SF increased the initial setting time by ~ 4.95%, ~ 18.8%, ~ 33.7% and 48.5%, respectively. The incorporation of 10% SF shortened the final setting time by ~ 5.56%, whilst the incorporation of 20%, 30% and 40% prolonged it by ~ 5.56%, ~ 18.5% and ~ 32.6%, respectively. Javed et al. [25] found 9.49% and 5.94% shorter initial and final setting time of calcined lithium

2.3 Density

17

slag geopolymer paste mixture activated with NaOH and sodium silicate solution by partially replacing lithium slag (size 43.15 μm) with 20% SF (fineness 15–30 m2 /kg), respectively. Contrarily, the incorporation of 30% SF prolonged the initial and final setting time by 8.88% and 10.4%, respectively, whilst the incorporation of 40% prolonged it by 18.59% and 21.2%, respectively. Table 2.2 briefs the results of this part. Based on the discussion so far, it is evident that there is no clear trend about the effect of SF on the setting time of the mixture. Some studies reported that the incorporation of SF prolonged the setting time [4, 23], whilst Cheah et al. [6] reported opposite finding. Along the same lines, the results reported by Liang et al. [24] revealed longer initial setting time, but shorter final setting time with the incorporation of SF. These results are opposite to the findings obtained by Javed et al. [25]. These conflicting results indicate that more studies are required. As a matter of fact, about 57.14%, 28.56% and 14.29% of the cited references focused on paste, mortar and concrete, respectively (Fig. 2.5).

2.3 Density Wetzel and Middendorf [4] found 4% and 8.46% higher packing density of AAS mortar mixtures containing 10% and 15% SF (fineness 21,800 m2 /kg), by volume, compared to that containing 5% SF. Hossein et al. [26] found an increase in the 7–90 days density of 50% slag/50% rockwool geopolymer pastes activated with NaOH and waterglass solution by partially replacing rockwool by 2% SF, whilst the incorporation of 4% and 6% SF decreased it. Yavuz et al. [27] found 11.59%, 10.9%, 19.6% and 26.8% increment in the 28 days apparent density of FA geopolymer pastes activated with NaOH and sodium silicate solution by partially replacing FA with 25%, 50%, 75% and 100% SF, respectively. The specimens were cured at 65 °C for 24 h. Yong-Sing et al. [28] found an increase in the bulk density of 60% FA/40% ladle furnace slag geopolymer pastes activated with NaOH and sodium silicate solution by adding 1–3% SF, whilst the addition of 4% SF decreased it. The bulk density of the control was 2140 kg/m3 , whilst it was 2172–2274 kg/m3 by adding 1–3% SF. On the other hand, the addition of 4% SF decreased it by 2%. Batista et al. [16] found 0.83% and 1.13% reduction in the 28 days apparent dry density of MK geopolymer mortars activated with NaOH and sodium silicate solution by partially replacing MK (size 2.12 μm) with 4% and 7% SF (size 0.37 μm), respectively. Alcamand et al. [29] found 12.4% reduction in the density of MK geopolymer mortars activated with NaOH and sodium silicate solution (SiO2 /Al2 O3 = 3) by partially replacing MK with 20% SF (SiO2 /Al2 O3 = 3.9). Albidah et al. [18] found 4.5%, 1.1%, 2.66% and 1.86% reduction in the fresh bulk density of MK geopolymer concrete mixtures activated with NaOH and sodium silicate solution by partially replacing MK (size 32.33 μm) with 5%, 10%, 20% and 30% SF (size 64.96 μm), respectively, The incorporation of 5% SF decreased the 28 days bulk density by 0.87%, whilst the incorporation of 10%, 20% and 30% SF increased it by 3.57%, 2.3% and 3.2%, respectively. Based

Sodium carbonate 4, 6, 8 and sodium silicate and 10 solution

465/324.4 m2 /kg

Slag/FA

NaOH and sodium silicate solution NaOH and sodium silicate solution NaOH and sodium silicate solution

–

39.8 μm

39.8 μm

Liang et al. [24] MK

MK

Sukontasukkul et al. [13]

FA

Sodium carbonate 4, 6, 8 and sodium silicate and 10 solution

465/324.4 m2 /kg

Slag/FA

Cheah et al. [6]

NaOH

–

Slag/FA

NaOH

–

Slag/FA

Elyamany et al. [23]

10

10, 20, 30 and 40

10, 20 and 30

15

15

10, 15 and 20

Potassium/sodium hydroxide and potassium/sodium waterglass

390 m2 /kg

Slag

Wetzel and Middendorf [4]

SF (%)

Activator

Precursor size/surface area

Precursor

References

Table 2.2 Effect of SF on the setting time of AAM mixtures

31.3 μm

31.3 μm

–

30,000–13,000 m2 /kg

30,000–13,000 m2 /kg

–

–

21,800 m2 /kg

SF size/surface area

Paste

Paste

Mortar

Mortar

Mortar

Mortar

Mortar

Mortar

Type

Shortened final setting time

Prolonged initial setting time

Prolonged final setting time

Shortened final setting time

Shortened initial setting time

Prolonged final setting time

Prolonged initial setting time

Prolonged setting time

Effect

~ 5.56

(continued)

~ 4.95, ~ 18.8, ~ 33.7 and 48.5

26.67, 40 and 66.67

11.11, 8.33, 11.11

9.8, 5.88, 13.73 and 23.92

~ 20

71.4

19, 28.57 and 38.1

Ratio

18 2 Silica Fume as a Part of Precursor/An Additive

Javed et al. [25]

References Activator NaOH and sodium silicate solution NaOH and sodium silicate solution

NaOH and sodium silicate solution NaOH and sodium silicate solution

Precursor size/surface area

39.8 μm

43.15 μm

43.15 μm

43.15 μm

Precursor

MK

Calcined lithium slag

Calcined lithium slag

Calcined lithium slag

Table 2.2 (continued)

40

30

20

20, 30 and 40

SF (%)

15–30 m2 /kg

15–30 m2 /kg

15–30 m2 /kg

31.3 μm

SF size/surface area

Paste

Paste

Paste

Paste

Type

Prolonged final setting time

Prolonged final setting time

Shortened initial and final setting time

Prolonged final setting time

Effect

18.59 and 21.2

8.88 and 10.4

9.49 and 5.94

~ 5.56, ~ 18.5 and ~ 32.6

Ratio

2.3 Density 19

20 Fig. 2.5 Percentage of studies of different media for setting time

2 Silica Fume as a Part of Precursor/An Additive

14.29 28.57 Paste Mortar Concrete

57.14

on the mentioned studies, it is evident that the incorporation of SF in the matrix may increase or decrease the density, and this mainly depends on the precursor type, amount of SF and curing temperature.

2.4 Compressive Strength 2.4.1 Slag Precursor Rashad [1] found 42.1%, 56%, 29.2%, 35.27% and 56.95% enhancement in the 3, 7, 28, 56 and 91 days compressive strength of slag activated with Na2 SO4 by partially replacing slag with 5% SF. Rashad and Mosleh [30] found 9.73% and 15.86% increase in the 7 days compressive strength of slag pastes activated with sodium silicate by partially replacing slag with 5% and 10% SF, whilst the 28 days was increased by 21.42% and 21.73%, respectively. Rashad [31] found 24.57% reduction in the 28 days compressive strength of slag pastes activated with Na2 SO4 by partially replacing slag with 10% SF. Kanaan and Soliman [3] prepared AAS mortars activated with anhydrous sodium metasilicate and sodium carbonate. Different activator concentrations of 16%, 20% and 25% were used. The slag (fineness 585 m2 /kg) was partially replaced with 10% SF (fineness 19,530 m2 /kg). When 16% and 20% activator concentrations were used, the results showed 0% and ~ 26.25 reduction in the 7 days compressive strength of AAS mortars with the inclusion of 10% SF, respectively, whilst it was enhanced by ~ 11.75% when 25% concentration of activator was used. At the age of 28 days, when 20% activator concentration was used, the incorporation of 10% SF decreased the compressive strength by 8%. When 16% and 25% activator concentrations were used, the incorporation of 10% SF increased the compressive strength by 19.31% and 40.75%, respectively. Ramezanianpour and Moeini [2] found 9.92%, 10.92% and 9.68% enhancement in the 28 days compressive strength of AAS mortars activated with NaOH and sodium silicate solution (activator/binder = 0.9) with the incorporation of 5%, 7.5% and 10% SF (size 2.5 μm),

2.4 Compressive Strength

21

respectively, whilst the 90 days compressive strength was enhanced by 11.03%, 19.2% and 0.38%, respectively. The 7 days compressive strength was reduced by 17.5%, 6.25% and 15.3% with the incorporation of 5%, 7.5% and 10% SF, respectively. The incorporation of 7.5% SF increased the 3 days compressive strength by 5.39%, whilst the incorporation of 5% and 10% SF decreased it by 8.82% and 9.8%, respectively. When the activator/binder ratio was 1, the incorporation of 5% increased the 3 days compressive strength by 3.1%, whilst the incorporation of 7.5% and 10% decreased it by 20.1% and 20.5%, respectively. The 7 days compressive strength was reduced by 2.95%, 22.29% and 18.7% with the incorporation of 5%, 7.5% and 10% SF. The incorporation of 7.5% SF decreased the 28 days compressive strength by 9.88%, whilst the incorporation of 5% and 10% SF increased it by 5.43% and 2.96%, respectively. When KOH and sodium silicate solution was used as an alkaline activator (activator/binder = 0.9), the incorporation of 5%, 7.5% and 10% SF decreased the 3 days compressive strength by 11.93%, 16.77% and 31.29%, respectively. The incorporation of 7.5% increased the 7 days compressive strength by 12.4%, whilst the incorporation of 5% and 10% decreased it by 7.82% and 10.78%, respectively. The incorporation of 5%, 7.5% and 10% SF increased the 28 days compressive strength by 17.16%, 8.69% and 0.42%, respectively. The incorporation of 5% and 7.5% SF increased the 90 days compressive strength by 4.65% and 5.31%, respectively, whilst the incorporation of 10% SF decreased it by 4.48%. When the activator/binder ratio of 1 was used, the incorporation of 5%, 7.5% and 10% SF decreased the 3 days compressive strength by 15.5%, 13.1% and 11%, respectively, whilst the 7 days compressive strength was decreased by 14.1%, 11% and 13.45%, respectively. The 28 days compressive strength was reduced by 4.1%, 9.68% and 6.67% with the incorporation of 5%, 7.5% and 10% SF, respectively, whilst the 90 days compressive strength was enhanced by 48.1%, 18.96% and 16.11%, respectively (slag fineness = 338.3 m2 /kg, size 25.97 μm and SF size 2.5 μm). Rashad and Khalil [32] found 152%, 105.9% and 91.3% enhancement in the 7 days compressive strength of AAS pastes activated with sodium silicate by partially replacing slag with 5%, 10% and 15% SF, respectively, whilst the 28 days compressive strength was enhanced by 150%, 103.8% and 87.57%, respectively. Rostami and Behfarnia [33] found 12.79%, 24.33% and 27.9% enhancement in the 28 days compressive strength of AAS concretes activated with NaOH and sodium silicate solution by partially replacing slag (fineness 450 m2 /kg) with 5%, 10% and 15% SF (fineness N/A), respectively, whilst the 90 days compressive strength was enhanced by 22.73%, 28.1% and 32.37%, respectively, when water curing was used. When the plastic cover was used for curing, the incorporation of 5%, 10% and 15% SF increased the 28 days compressive strength by 12.5%, 19.64% and 23.21%, respectively, whilst the 90 days compressive strength was enhanced by 12.1%, 20.7% and 25.86%, respectively. Escalante-Garcia et al. [34] reported that partially replacing slag in AAS mortars activated with NaOH by 5–15% SF enhanced the 3–90 days compressive strength, whilst partially replacing slag with 20% SF decreased it. The incorporation of 5%, 10% and 15% SF enhanced the 1 day compressive strength by ~ 15%, ~ 16.6% and ~ 28.3%, respectively, whilst the 7 days compressive strength

22

2 Silica Fume as a Part of Precursor/An Additive

was enhanced by ~ 5.7%, ~ 13.7% and 13.7%, respectively. The 28 days compressive strength was enhanced by ~ 1.12%, ~ 6.2% and ~ 6.2% with the incorporation of 5%, 10% and 15% SF, respectively, whilst the 90 days compressive strength was enhanced by ~ 4.5%, ~ 8.6% and ~ 12.1%, respectively. The incorporation of 20% SF decreased the 1, 7, 28 and 90 days compressive strength by ~ 10.8%, ~ 21.5%, ~ 0% and ~ 5.5%, respectively. Sun et al. [35] prepared AAS mortars activated with NaOH containing tailing as a fine aggregate. The slag (fineness 397 m2 /kg) was partially replaced with 5–20% SF (fineness 414.3 m2 /kg). The results showed 6.33%, 10.23%, 3.12% and 16% enhancement in the 3, 7, 14 and 28 days compressive strength with the inclusion of 5% SF, respectively. The inclusion of 10% SF increased the 7 days compressive strength by 9.47%, whilst the 3, 14 and 28 days compressive strength was reduced by 0.63%, 11.05% and 11.41%, respectively. The incorporation of 15% SF decreased the 3, 7, 14 and 28 days compressive strength by 28.48%, 14.77%, 20.4% and 23.91%, respectively, whilst the inclusion of 20% SF decreased it by 34.81%, 34.37%, 46.46% and 44.56%, respectively. Wetzel and Middendorf [4] found 12.35%, 19.22% and 5.14% higher 28 days compressive strength of AAS mortars activated with potassium/sodium hydroxide and potassium/sodium waterglass containing 10%, 15% and 20% SF (fineness 21,800 m2 /kg), by volume, compared to that containing 5% SF. Kathirvel and Murali [5] found 20.3% and 34.6% higher 28 days compressive strength of AAS reactive powder concrete specimens activated with NaOH and sodium silicate solution by partially replacing slag (size 1358.3 nm) with 15% and 30% SF (size 962.3 nm), respectively. A similar trend of strength enhancement was observed at the age of 7 days. Table 2.3 briefs the results of this part. Based on the discussion so far, it is evident that there are conflicting results about the effect of SF on AAS matrices compressive strength (Fig. 2.6), but most of them (about 54.55%) [1, 4, 5, 30, 32, 33] reported a positive effect, whilst about 9.09% of them [31] reported a negative effect (Fig. 2.6). Other studies (about 36.36%) [2, 3, 34, 35] reported that the incorporation of SF into AAS matrices may have a positive effect or a negative effect on the compressive strength (Fig. 2.7). This depends on slag/SF fineness, activator concentration and type, activator/binder ratio, testing age, curing condition and SF amount. On the whole, it is better not to increase the proportion of SF by more than 15% to obtain better strength. Sun et al. [35] related the improvement in the strength with the incorporation of SF to the filling effect of SF on pores that can densify the microstructure, whilst they related the reduction in the strength to the formation of thaumasite which reduced C–S–H and led to the formation of microcracks. Rashad and Mosleh [30], Rashad and Khalil [32] and Rashad [1] related this improvement to the SF fineness that can block the voids producing denser and more compact microstructure (Fig. 2.8) (Fig. 2.9). Rostami and Behfarnia [33] related this enhancement to the higher C–S–H gel and filling the pores caused by SF. Rashad and Khalil [32] related this improvement to the nucleation sites of the reactions caused by SF. The filling effect of SF can fill the voids and improve the pore size/shape distribution. However, in most cases, the incorporation of SF at ratios > 15% may cause an adverse effect. This could be attributed to the increase of fine particles and silica ratio that may lead to the increase of the number of unreacted particles [17, 36, 37] and the formation of pores [17, 38, 39]. As a matter of fact,

Sodium silicate Sodium silicate Na2 SO4 Anhydrous sodium 10 metasilicate and sodium carbonate Anhydrous sodium 10 metasilicate and sodium carbonate Anhydrous sodium 10 metasilicate and sodium carbonate Anhydrous sodium 10 metasilicate and sodium carbonate

300 m2 /kg

300 m2 /kg

450 m2 /kg

585 m2 /kg

585 m2 /kg

585 m2 /kg

585 m2 /kg

Slag

Slag

Slag

Slag

Slag

Slag

Slag

Rashad and Mosleh [30]

Rashad [31]

Kanaan and Soliman [3]

10

5 and 10

5 and 10

5

Na2 SO4

500 m2 /kg

Slag

Rashad [1]

SF (%)

Activator

Precursor size/fineness

Precursor

Reference

Table 2.3 Effect of SF on the compressive strength of AAS matrices

19,530 m2 /kg

19,530 m2 /kg

19,530 m2 /kg

19,530 m2 /kg

22,000 m2 /kg

20,000 m2 /kg

20,000 m2 /kg

22,000 m2 /kg

SF size/fineness

Mortar

Mortar

Mortar

Mortar

Paste

Paste

Paste

Paste

Type

28

28

7

7

28

28

7

3, 7, 28, 56 and 91

Age (day)

Increased

Decreased

Increased

Decreased

Decreased

Increased

Increased

Increased

Effect

(continued)

19.31 and 40.75 (16% and 25% activator concentrations)

8 (20% activator concentration)

~ 11.75 (25% activator concentration)

0 and ~ 26.25 (16% and 20% activator concentrations)

24.57

21.42 and 21.73

9.73 and 15.86

42.1, 56, 29.2, 35.27 and 56.95

Ratio

2.4 Compressive Strength 23

Activator NaOH and sodium silicate solution NaOH and sodium silicate solution NaOH and sodium silicate solution NaOH and sodium silicate solution

NaOH and sodium silicate solution

NaOH and sodium silicate solution NaOH and sodium silicate solution NaOH and sodium silicate solution

Precursor size/fineness

25.97 μm

25.97 μm

25.97 μm

25.97 μm

25.97 μm

25.97 μm

25.97 μm

25.97 μm

Precursor

Slag

Slag

Slag

Slag

Slag

Slag

Slag

Slag

Reference

Ramezanianpour and Moeini [2]

Table 2.3 (continued)

5, 7.5 and 10

7.5 and 10

5

5, 7.5 and 10

5, 7.5 and 10

5, 7.5 and 10

7.5

5 and 10

SF (%)

2.5 μm

2.5 μm

2.5 μm

2.5 μm

2.5 μm

2.5 μm

2.5 μm

2.5 μm

SF size/fineness

Mortar

Mortar

Mortar

Mortar

Mortar

Mortar

Mortar

Mortar

Type

7

3

3

90

28

7

3

3

Age (day)

Decreased

Decreased

Increased

Increased

Increased

Decreased

Increased

Decreased

Effect

(continued)

2.95, 22.29 and 18.7 (activator/binder 1)

20.1 and 20.5 (activator/binder 1)

3.1 (activator/binder 1)

11.03, 19.2 and 0.38 (activator/binder 0.9)

9.92, 10.92 and 9.68 (activator/binder 0.9)

17.5, 6.25 and 15.3 (activator/binder 0.9)

5.39 (activator/binder 0.9)

8.82 and 9.8 (activator/binder 0.9)

Ratio

24 2 Silica Fume as a Part of Precursor/An Additive

Reference Activator NaOH and sodium silicate solution NaOH and sodium silicate solution KOH and sodium silicate solution

KOH and sodium silicate solution KOH and sodium silicate solution KOH and sodium silicate solution

KOH and sodium silicate solution KOH and sodium silicate solution

Precursor size/fineness

25.97 μm

25.97 μm

25.97 μm

25.97 μm

25.97 μm

25.97 μm

25.97 μm

25.97 μm

Precursor

Slag

Slag

Slag

Slag

Slag

Slag

Slag

Slag

Table 2.3 (continued)

10

5 and 7.5

5, 7.5 and 10

7.5

5 and 10

5, 7.5 and 10

7.5

5 and 10

SF (%)

2.5 μm

2.5 μm

2.5 μm

2.5 μm

2.5 μm

2.5 μm

2.5 μm

2.5 μm

SF size/fineness

Mortar

Mortar

Mortar

Mortar

Mortar

Mortar

Mortar

Mortar

Type

90

90

28

7

7

3

28

28

Age (day)

Decreased

Increased

Increased

Increased

Decreased

Decreased

Decreased

Increased

Effect

(continued)

4.48 (activator/binder 0.9)

4.65 and 5.31 (activator/binder 0.9)

17.16, 8.69 and 0.42 (activator/binder 0.9)

12.4 (activator/binder 0.9)

7.82 and 10.78 (activator/binder 0.9)

11.93, 16.77 and 31.29 (activator/binder 0.9)

9.88 (activator/binder 1)

5.43 and 2.96 (activator/binder 1)

Ratio

2.4 Compressive Strength 25

KOH and sodium silicate solution KOH and sodium silicate solution KOH and sodium silicate solution KOH and sodium silicate solution Sodium silicate Sodium silicate NaOH and sodium silicate solution NaOH and sodium silicate solution NaOH and sodium silicate solution

25.97 μm

25.97 μm

25.97 μm

25.97 μm

300 m2 /kg

300 m2 /kg

450 m2 /kg

450 m2 /kg

450 m2 /kg

Slag

Slag

Slag

Slag

Rashad and Khalil Slag [32]

Slag

Slag

Slag

Slag

Rostami and Behfarnia [33]

Activator

Precursor size/fineness

Precursor

Reference

Table 2.3 (continued)

5, 10 and 15

5, 10 and 15

5, 10 and 15

5, 10 and 15

5, 10 and 15

5, 7.5 and 10

5, 7.5 and 10

5, 7.5 and 10

5, 7.5 and 10

SF (%)

–

–

–

202,000 cm2 /g

202,000 cm2 /g

2.5 μm

2.5 μm

2.5 μm

2.5 μm

SF size/fineness

Concrete

Concrete

Concrete

Paste

Paste

Mortar

Mortar

Mortar

Mortar

Type

28

90

28

28

7

90

28

7

3

Age (day)

Increased

Increased

Increased

Increased

Increased

Increased

Decreased

Decreased

Decreased

Effect

(continued)

12.5, 19.64 and 23.21 (plastic cover curing)

By 22.73, 28.1 and 32.37 (water curing)

12.79, 24.33 and 27.9 (water curing)

150, 103.8 and 87.57

152, 105.9 and 91.3

48.1, 18.96 and 16.11 (activator/binder 1)

4.1%, 9.68% and 6.67 (activator/binder 1)

14.1, 11 and 13.45 (activator/binder 1)

15.5%, 13.1% and 11 (activator/binder 1)

Ratio

26 2 Silica Fume as a Part of Precursor/An Additive

Sun et al. [35]

Escalante-Garcia et al. [34]

Reference Activator NaOH and sodium silicate solution NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH

Precursor size/fineness

450 m2 /kg

450 m2 /kg

450 m2 /kg

450 m2 /kg

450 m2 /kg

450 m2 /kg

397 m2 /kg

397 m2 /kg

m2 /kg

397

397 m2 /kg

397 m2 /kg

Precursor

Slag

Slag

Slag

Slag

Slag

Slag

Slag

Slag

Slag

Slag

Slag

Table 2.3 (continued)

20

15

10

10

5

20

5, 10 and 15

5, 10 and 15

5, 10 and 15

5, 10 and 15

5, 10 and 15

SF (%)

414.3 m2 /kg

414.3 m2 /kg

414.3

m2 /kg

414.3 m2 /kg

414.3 m2 /kg

–

–

–

–

–

–

SF size/fineness

Mortar

Mortar

Mortar

Mortar

Mortar

Mortar

Mortar

Mortar

Mortar

Mortar

Concrete

Type

Increased

Increased

Decreased

Increased

Increased

Increased

Increased

Increased

Effect

3, 7, 14 and 28

3, 7, 14 and 28

Decreased

Decreased

3, 14 and Decreased 28

14

3, 7, 14 and 28

1, 7, 28 and 90

90

28

7

1

90

Age (day)

(continued)

34.81, 34.37, 46.46 and 44.56

28.48, 14.77, 20.4 and 23.91

0.63, 11.05 and 11.41

9.47

6.33, 10.23, 3.12 and 16

~ 10.8, ~ 21.5, ~ 0 and ~ 5.5

~ 4.5, ~ 8.6 and ~ 12.1

~ 1.12, ~ 6.2 and ~ 6.2

~ 5.7, ~ 13.7 and 13.7

~ 15, ~ 16.6 and ~ 28.3

12.1, 20.7 and 25.86 (plastic cover curing)

Ratio

2.4 Compressive Strength 27

Potassium/sodium hydroxide and potassium/sodium waterglass

390 m2 /kg

1358.3 nm

1358.3 nm

Slag

Slag

Slag

Wetzel and Middendorf [4]

Kathirvel and Murali [5] NaOH and sodium silicate

NaOH and sodium silicate

Activator

Precursor size/fineness

Precursor

Reference

Table 2.3 (continued)

15 and 30

15 and 30

10, 15 and 20

SF (%)

962.3 nm

962.3 nm

21,800 m2 /kg

SF size/fineness

Reactive powder concrete

Reactive powder concrete

Mortar

Type

28

7

28

Age (day)

Increased

Increased

Increased

Effect

20.3 and 34.6

~ 14.3 and ~ 28%

12.35, 19.22 and 5.14

Ratio

28 2 Silica Fume as a Part of Precursor/An Additive

2.4 Compressive Strength

29

Relative compressive strength (%)

300 250 200 150 100 50 0 0

5

10

15

20

SF (%) Fig. 2.6 Effect of SF on slag geopolymers compressive strength [1–5, 30–35]

Fig. 2.7 Percentage of studies about the effect of SF on slag geopolymers compressive strength

Increased

36.36

Decreased Increased/ decreased

54.55

9.09

about 45.45%, 36.36% and 18.18% of the cited references in this part focused on mortar, paste and concrete, respectively (Fig. 2.10).

2.4.2 Fly Ash Precursor Nuruddin et al. [40] partially replaced FA in FA geopolymer concretes activated with NaOH and sodium silicate solution by 3%, 5% and 7% SF. In the case of ambient curing, the results showed lower 3–90 days compressive strength with the inclusion of 5% SF, whilst the inclusion of 3% and 7% SF increased it. The inclusion of 3% showed the highest strength. In the case of hot gunny curing, the results showed

30

2 Silica Fume as a Part of Precursor/An Additive

1 1

2

2

(a)

(b)

Fig. 2.8 SEM images of AAS paste samples without (a) and with (b) 5% SF [32]. Reprinted with permission from Elsevier publisher

Fig. 2.9 SEM images of AAS paste samples without (a) and with (b) 5% SF [1]. Reprinted with permission from Elsevier publisher Fig. 2.10 Percentage of studies of different media for slag geopolymers compressive strength containing SF

18.18 Paste Mortar Concrete

45.45

36.36

2.4 Compressive Strength

31

higher compressive strength with the inclusion of 3–7% SF. The inclusion of 7% SF showed the highest strength. In the case of ambient curing, the incorporation of 3% SF increased the 1, 7, 28, 56 and 90 days compressive strength by ~ 56.3%, ~ 75%, ~ 50%, ~ 41% and ~ 37.5%, respectively, whilst the incorporation of 7% increased it by ~ 56.3%, ~ 28.6%, ~ 35%, ~ 31.8% and ~ 25%, respectively. Contrarily, the incorporation of 5% SF decreased it by ~ 46.9%, 28.6%, ~ 38.7%, ~ 31.8% and ~ 33.3%, respectively. In the case of hot gunny curing, the incorporation of 3% SF increased the 1, 7, 28, 56 and 90 days compressive strength by ~ 0%, ~ 0%, ~ 6.7%, 12.5% and ~ 11.1%, respectively, whilst the incorporation of 5% SF increased it by ~ 60%, ~ 60%, ~ 73.3%, ~ 100% and ~ 87.2%, respectively, whilst the incorporation of 7% SF increased it by ~ 140%, ~ 100%, ~ 90%, ~ 100% and ~ 90.3%, respectively. Alanazi et al. [10] found a reduction in the 1–28 days compressive strength of FA geopolymer mortars activated with NaOH and sodium silicate solution cured at ambient temperature by partially replacing FA with 5% and 10% SF. This reduction depended on the ratio of sodium silicate/NaOH. When this ratio was 1, the incorporation of 5% decreased the 1, 3, 7 and 28 days compressive strength by ~ 11.1%, ~ 30%, ~ 12.2% and ~ 18.9%, respectively, whilst the incorporation of 10% decreased it by ~ 11.1%, ~ 32%, ~ 13.2% and ~ 27%, respectively. When the sodium silicate/NaOH ratio was 2.5, the incorporation of 5% SF decreased the 1, 3, 7 and 28 days compressive strength by ~ 18.75%, ~ 0%, ~ 0% and ~ 25%, respectively, whilst the incorporation of 10% SF decreased it by ~ 18.75%, ~ 0%, ~ 0% and ~ 30%, respectively. Vaibhav et al. [41] found 3.22% reduction in the 7 days compressive strength of FA geopolymer mortars activated with NaOH and sodium silicate solution by partially replacing FA with 10% SF, whilst the 28 days compressive strength was enhanced by 28.9%. When M sand was replaced by 25%, 75% and 100% recycled fine aggregate, the incorporation of SF increased the 7 days compressive strength by 47.68%, 15.58% and 13.33%, respectively, whilst the 7 days compressive strength of the specimens containing 50% M sand/50% recycled fine aggregate was decreased by 25.2% with the inclusion of SF. When M sand was replaced by 25% and 50% recycled fine aggregate, the 28 days compressive strength was enhanced by 4.53% and 1.53% with the inclusion of SF, respectively, whilst replacing M sand with 75% and 100% recycled fine aggregate led to 26.23% and 14.97% reduction in the compressive strength with the inclusion SF, respectively. Jena and Panigrahi [11] partially replaced FA in FA geopolymer concretes activated with NaOH and sodium silicate solution by 5–15% SF. After casting, the specimens were cured at room temperature for 24 h followed by 70 °C for 24 h, then at laboratory temperature. The results showed 6.84%, 9.92% and 2.26% enhancement in the 7 days compressive strength with the incorporation of 5%, 10% and 15% SF, respectively, whilst the 28 days compressive strength was enhanced by 8.7%, 9.7% and 3.5%, respectively. The 90 days compressive strength was enhanced by 3.8%, 7.13% and 1.2%, respectively. Bajpai et al. [42] found 5.5% reduction in the 28 days compressive strength of FA geopolymer paver block concrete specimens activated with NaOH and sodium silicate solution by partially replacing FA (fineness 399.7 m2 /kg) with ~ 22% SF (fineness 21,170 m2 /kg). Sukontasukkul et al. [13] found 36.16% enhancement in the 28 days compressive strength of FA

32

2 Silica Fume as a Part of Precursor/An Additive

geopolymer mortars activated with NaOH and sodium silicate solution by partially replacing FA with 10% SF, whilst the inclusion of 20% and 30% SF decreased it by 18.64% and 48%, respectively, when curing temperature was 23–28 °C. Contrarily, when the specimens were cured at 60 for 24 h, the inclusion of 10%, 20% and 30% SF decreased the 28 days compressive strength by 73.6%, 82% and 84.27%, respectively. Duan et al. [43] found 6.7%, 23.2% and 44.1% enhancement in the 28 days compressive strength of FA geopolymer pastes activated with NaOH and waterglass solution by partially replacing FA (size 3.39 μm) with 10%, 20% and 30% SF (size 1.44 μm), respectively. The specimens were cured at 25 °C with 70% RH for 24 h, then at 20 °C with 95% RH. Okoye et al. [12] found higher compressive strength of FA geopolymer concretes activated with NaOH and sodium silicate solution cured at 100 °C for 72 h by partially replacing FA with 5–40% SF. The 3 days compressive strength was enhanced by 46.5%, 22.9%, 46.5% and 110% with the inclusion of 5%, 10%, 20%, 30% and 40% SF, respectively, whilst the 28 days compressive strength was enhanced by 1.5%, 9.3%, 12.4% and 51.2%, respectively. Yavuz et al. [27] prepared geopolymer pastes from FA/SF at ratios of 100/0, 75/25, 50/50, 25/75 and 0/100 activated with NaOH and sodium silicate solution. The specimens were cured at 65 °C for 24 h. The results showed 134.63% and 48.9% enhancement in the 28 days compressive strength with the inclusion of 25% and 50% SF, respectively, whilst the inclusion of 75% and 100% SF decreased it by 7.13% and 42.43%, respectively. Table 2.4 briefs the results of this part. Based on the discussion so far, it is evident that there are conflicting results about the effect of SF on FA geopolymers compressive strength (Fig. 2.11). There are about 33.3% of the recorded studies reported a positive effect of SF on FA geopolymers compressive strength [11, 12, 43], whilst about 22.22% of them reported a negative effect [10, 42]. Other studies (about 44.44%) [13, 27, 40, 41] reported that the incorporation of SF into FA geopolymers may have a positive effect or a negative effect on the compressive strength (Fig. 2.12). This depends on FA/SF fineness, activator concentration and type, activator/binder ratio, testing age, curing condition and SF amount. On the whole, it is better not to increase the proportion of SF by more than 10% to obtain better strength. Alanazi et al. [10] and Duan et al. [43] related this improvement to the denser microstructure and packing effect of the fine SF. SF can act as a microaggregate filler leading to dispersion in the matrix and filling the inner space inside the microstructure. Okoye et al. [12] related this improvement to the existence of silicate ions in the alkali solution. Sukontasukkul et al. [13] related this improvement to increasing reaction products. However, higher ratios of SF (≥ 20%) may cause an adverse effect. Alanazi et al. [10] related this adverse effect to the low CaO and Al2 O3 content in SF. The incorporation of SF led to a reduction in the alkalinity which therefore decreased the dissolution of FA. Sukontasukkul et al. [13] related this reduction to the excessive SiO2 amount which led to cracking and expansion. As a matter of fact, about 44.44%, 33.33% and 22.22% of the cited references in this part focused on mortar, concrete and paste, respectively (Fig. 2.13).

–

–

–

–

–

FA

FA

FA

FA

FA

Precursor size/fineness

–

Precursor

Nuruddin et al. FA [40]

References

NaOH and sodium silicate solution

NaOH and sodium silicate solution

NaOH and sodium silicate solution

NaOH and sodium silicate solution

NaOH and sodium silicate solution

NaOH and sodium silicate solution

Activator

7

5

3

7

5

3

SF (%)

–

–

–

–

–

–

SF size/fineness

Table 2.4 Effect of SF on the compressive strength of FA geopolymer matrices

Concrete

Concrete

Concrete

Concrete

Concrete

Concrete

Type

1, 7, 28, 56 and 90

1, 7, 28, 56 and 90

1, 7, 28, 56 and 90

1, 7, 28, 56 and 90

1, 7, 28, 56 and 90

1, 7, 28, 56 and 90

Age (day)

Hot gunny

Hot gunny

Hot gunny

Ambient

Ambient

Ambient

Curing

Increased

Increased

Increased

Increased

Decreased

Increased

Effect

(continued)

~ 140, ~ 100, ~ 90, ~ 100 and ~ 90.3 (hot gunny curing)

~ 60, ~ 60, ~ 73.3, ~ 100 and ~ 87.2 (hot gunny curing)

~ 0%, ~ 0%, ~ 6.7%, 12.5% and ~ 11.1% (hot gunny curing)

~ 56.3, ~ 28.6, ~ 35, ~ 31.8 and ~ 25 (ambient curing)

~ 46.9, 28.6, ~ 38.7, ~ 31.8 and ~ 33.3 (ambient curing)

~ 56.3, ~ 75, ~ 50, ~ 41 and ~ 37.5 (ambient curing)

Ratio

2.4 Compressive Strength 33

Jena and Panigrahi [11]

NaOH and sodium silicate solution NaOH and sodium silicate solution NaOH and sodium silicate solution

–

8 μm

8 μm

FA

FA

FA

NaOH and sodium silicate solution

NaOH and sodium silicate solution

–

–

FA

NaOH and sodium silicate solution

Activator

FA

–

FA

Alanazi et al. [10]

Vaibhav et al. [41]

Precursor size/fineness

Precursor

References

Table 2.4 (continued)

–

–

–

–

SF size/fineness

5, 10 – and 15

5, 10 – and 15

10

10

10

5

SF (%)

Concrete

Concrete

Mortar

Mortar

Mortar

Mortar

Type

28

7

28

7

1, 3, 7 and 28

1, 3, 7 and 28

Age (day)

70 °C for 24 h

70 °C for 24 h

Ambient

Ambient

Ambient

Ambient

Curing

Increased

Increased

Increased

Decreased

Decreased

Decreased

Effect

8.7, 9.7 and 3.5

(continued)

6.84, 9.92 and 2.26

28.8

3.22

~ 11.1, ~ 32, ~ 13.2 and ~ 27

~ 11.1, ~ 30, ~ 12.2 and ~ 18.9

Ratio

34 2 Silica Fume as a Part of Precursor/An Additive

Okoye et al. [12]

FA

–

With NaOH and waterglass solution

3.39 μm

Duan et al. [43] FA

NaOH and sodium silicate solution

–

FA

NaOH and sodium silicate solution

NaOH and sodium silicate solution

–

FA

NaOH and sodium silicate solution

399.7 m2 /kg

Sukontasukkul et al. [13]

NaOH and sodium silicate solution

8 μm

FA

FA

Activator

Precursor size/fineness

Precursor

Bajpai et al. [42]

References

Table 2.4 (continued) SF size/fineness

10, 20, 30 and 40

10, 20 and 30

20 and 30

10

~ 22

–

1.44 μm

–

–

21,170 m2 /kg

5, 10 – and 15

SF (%)

Mortar

Paste

Mortar

Mortar

Concrete

Concrete

Type

3

28

28

28

28

90

Age (day)

100 °C for 72 h

20 °C, 95% RH

23–28 °C

23–28 °C

60 °C for 12 h

70 °C for 24 h

Curing

Increased

Increased

Decreased

Increased

Decreased

Increased

Effect

(continued)

46.5%, 22.9%, 46.5% and 110

6.7%, 23.2% and 44.1

18.64 and 48

36.16

5.5

3.8, 7.13 and 1.2

Ratio

2.4 Compressive Strength 35

Precursor size/fineness

–

–

Precursor

FA

FA

References

Yavuz et al. [27]

Table 2.4 (continued)

NaOH and sodium silicate solution

NaOH and sodium silicate solution

Activator

75 and 100

25 and 50

SF (%)

–

–

SF size/fineness

Paste

Paste

Type

28

28

Age (day)

65 °C for 24

65 °C for 24

Curing

Decreased

Increased

Effect

7.13% and 42.43

134.63% and 48.9

Ratio

36 2 Silica Fume as a Part of Precursor/An Additive

2.4 Compressive Strength

37

Relative compressive strength (%)

300 250 200 150 100 50 0 0

10

20

30

40

50

60

70

80

90

100

SF (%) Fig. 2.11 Effect of SF on FA geopolymers compressive strength [10–13, 27, 40–43] Fig. 2.12 Percentage of studies about the effect of SF on FA geopolymers compressive strength

33.33

Increased 44.44

Decreased Increased/dec reased 22.22

Fig. 2.13 Percentage of studies of different media for FA geopolymers compressive strength containing SF

22.22 33.33 Paste Mortar Concrete

44.44

38

2 Silica Fume as a Part of Precursor/An Additive

2.4.3 Metakaolin Precursor Batista et al. [16] found ~ 9.48% and ~ 17.24% reduction in the 28 days compressive strength of MK geopolymer mortars activated with NaOH and sodium silicate solution by partially replacing MK (size 2.12 μm) with 4% and 7% SF (size 0.37 μm), respectively. Matalkah et al. [44] found 28.6%, 14.5% and 7.7% enhancement in the 7 days compressive strength of calcined kaolin geopolymer mortars activated with NaOH and sodium silicate solution by partially replacing calcined kaolin (size < 75 μm) with 5%, 10% and 15% SF (fineness 0.1365 m2 /g), respectively. The specimens were cured at room temperature for 24 h, then at 23 °C ± 2 °C with 95% ± 3% RH. Rashad and Zeedan [17] found 115.13%, 209.6%, 330.17%, 423% and 343.3% higher 7 days compressive strength of MK geopolymer pastes activated with 25% sodium silicate by partially replacing MK with 5%, 10%, 15%, 20% and 25% SF, respectively, whilst the 28 days compressive strength was enhanced by 253.24%, 316.34%, 371.23%, 523.9% and 445.9%, respectively (Fig. 2.14). Contrarily, the incorporation of 5%, 10%, 15%, 20% and 25% SF decreased the 7 days compressive strength by 8.13, 17.36%, 25.83%, 35.81% and 38.56%, whilst the 28 days compressive strength was decreased by 11.6%, 17.95%, 23.43%, 30.31% and 36.96%, respectively, when 50% of sodium silicate was used (Fig. 2.15). Alcamand et al. [29] found ~ 5.4% reduction in the 28 days compressive strength of MK geopolymer mortars activated with NaOH and sodium silicate solution (SiO2 /Al2 O3 = 3) by partially replacing MK (size ~ 0.1–11 μm) with 20% SF (size ~ 0.03–2 μm) (SiO2 /Al2 O3 = 3.9).

Compressive strength (MPa)

120 7-d

28-d

100 80 60 40 20 0 0

5

10

15

20

25

Silica fume (%) Fig. 2.14 Effect of low activator concentration (i.e. low Si/Al ratio) on the compressive strength of MK geopolymer cement containing SF [17]. Reprinted with permission from American Concrete Institute publisher

2.4 Compressive Strength

39

Compressive strength (MPa)

120

7-d

28-d

100 80 60 40 20 0 0

5

10

15

20

25

Silica fume (%) Fig. 2.15 Effect of high activator concentration (i.e. high Si/Al ratio) on the compressive strength of MK geopolymer cement containing SF [17]. Reprinted with permission from American Concrete Institute publisher

Uysal et al. [45] found 5.35% and 8.55% enhancement in the 7 days compressive strength of MK geopolymer mortars activated with NaOH and sodium silicate solution by partially replacing MK with 10% and 20% SF (fineness 20,000 m2 /kg), respectively, whilst the inclusion of 30% and 40% SF decreased it by 25.73% and 28.71%, respectively. The inclusion of 20% SF increased the 28 days compressive strength by 11.48%, whilst the inclusion of 10%, 30% and 40% decreased it by 1.04%, 23.74% and 27.45%, respectively. Albidah et al. [18] found 15.7%, 14.9%, 36.6% and 68.8% reduction in the 28 days compressive strength of MK geopolymer concretes activated with NaOH and sodium silicate solution by partially replacing MK (size 32.33 μm) with 5%, 10%, 20% and 30% SF (size 64.96 μm), respectively. Aygörmez et al. [46] prepared MK geopolymer mortars activated with NaOH and sodium silicate solution. The specimens were cured at 60 °C for 72 h. The MK was partially replaced with 10–40% SF. The 28 days compressive strength was enhanced by 11.48%, with the inclusion of 20% SF, whilst the inclusion of 10%, 30% and 40% SF decreased it by 1%, 23.74% and 27.45%, respectively. Liang et al. [24] prepared MK geopolymer pastes activated with NaOH and sodium silicate solution. The MK (size 39.8 μm) was partially replaced with 10–40% SF (size 31.3 μm). The specimens were cured in steam at 50 °C up to testing age. The incorporation of 10%, 20% and 30% SF increased the 3 days compressive strength by 24.18%, 22.73% and 7%, respectively, whilst the incorporation of 40% SF decreased it by 11.64%. The incorporation of 10% SF increased the 7 days compressive strength by 10.17%, whilst the incorporation of 20%, 30% and 40% SF decreased it by 0.39%, 4.11% and 14.7%, respectively. Table 2.5 briefs the results of this part. Based on the discussion so far, it is evident that there are conflicting results about the effect of SF on MK geopolymers compressive strength (Fig. 2.16). There are

Activator NaOH and sodium silicate solution NaOH and sodium silicate solution Sodium silicate

Sodium silicate

Sodium silicate

Sodium silicate

Precursor size/fineness

2.12 μm

< 75 μm

460 m2 /kg

460 m2 /kg

460 m2 /kg

460 m2 /kg

Precursor

MK

Calcined kaolin

MK

MK

MK

MK

References

Batista et al. [16]

Matalkah et al. [44]

Rashad and Zeedan [17]

5, 10, 15, 20 and 25

5, 10, 15, 20 and 25

5, 10, 15, 20 and 25

5, 10, 15, 20 and 25

5, 10 and 15

4 and 7

SF (%)

20,200 m2 /kg

20,200 m2 /kg

20,200 m2 /kg

20,200 m2 /kg

0.1365 m2 /g

0.37 μm

SF size/fineness

Table 2.5 Effect of SF on the compressive strength of MK geopolymer matrices

Paste

Paste

Paste

Paste

Mortar

Mortar

Type

28

7

28

7

7

28

Age (day)

50 °C

50 °C

50 °C

50 °C

23 °C, 95% RH

Ambient

Curing

Decreased

Decreased

Increased

Increased

Increased

Decreased

Effect

(continued)

11.6, 17.95, 23.43, 30.31 and 36.96 (50% activator)

8.13, 17.36, 25.83, 35.81 and 38.56 (50% activator)

253.24, 316.34, 371.23, 523.9 and 445.9 (25% activator)

115.13, 209.6, 330.17, 423 and 343.3 (25% activator)

28.6, 14.5 and 7.7

~ 9.48 and ~ 17.24

Ratio

40 2 Silica Fume as a Part of Precursor/An Additive

NaOH and sodium silicate solution NaOH and sodium silicate solution

–

–

–

–

32.33 μm

MK

MK

MK

MK

Uysal et al. [45]

Albidah et al. MK [18]

NaOH and sodium silicate solution

~ 0.1–11 μm

MK

Alcamand et al. [29]

NaOH and sodium silicate solution

NaOH and sodium silicate solution

NaOH and sodium silicate solution

Activator

Precursor size/fineness

Precursor

References

Table 2.5 (continued)

Mortar

Mortar

Mortar

Mortar

20,000 m2 /kg

20,000 m2 /kg

20,000 m2 /kg

20,000 m2 /kg

Concrete

Mortar

Type

~ 0.03–2 μm

SF size/fineness

5, 10, 20 64.96 μm and 30

20

10, 30 and 40

30 and 40

10 and 20

20

SF (%)

28

28

28

7

7

28

Age (day)

24 °C, with 20% RH

60 °C for 72 h

60 °C for 72 h

60 °C for 72 h

60 °C for 72 h

Room

Curing

Decreased

Increased

Decreased

Decreased

Increased

Decreased

Effect

(continued)

15.7, 14.9, 36.6 and 68.8

11.48

1.04, 23.74 and 27.45

25.73 and 28.71

5.35 and 8.55

~ 5.4

Ratio

2.4 Compressive Strength 41

NaOH and sodium silicate solution NaOH and sodium silicate solution NaOH and sodium silicate solution NaOH and sodium silicate solution NaOH and sodium silicate solution NaOH and sodium silicate solution

~ 45 μm

~ 45 μm

39.8 μm

39.8 μm

39.8 μm

39.8 μm

MK

MK

MK

MK

MK

MK

Aygörmez et al. [46]

Liang et al. [24]

Activator

Precursor size/fineness

Precursor

References

Table 2.5 (continued)

20, 30 and 40

10

40

10, 20 and 30

20

10, 30 and 40

SF (%)

31.3 μm

31.3 μm

31.3 μm

31.3 μm

–

–

SF size/fineness

Paste

Paste

Paste

Paste

Mortar

Mortar

Type

7

7

3

3

28

28

Age (day)

50 °C steam

50 °C steam

50 °C steam

50 °C steam

60 °C for 72 h

60 °C for 72 h

Curing

Decreased

Increased

Decreased

Increased

Increased

Decreased

Effect

0.39, 4.11 and 14.7

10.17

11.6

24.18, 22.73 and 7

11.48

1, 23.74 and 27.45

Ratio

42 2 Silica Fume as a Part of Precursor/An Additive

2.4 Compressive Strength

43

about 12.5% of the recorded studies reported a positive effect, whilst about 37.5% of them reported a negative effect. Other studies reported that the incorporation of SF into MK geopolymers may have a positive effect or a negative effect on the compressive strength (Fig. 2.17). This depends on MK/SF fineness, activator concentration and type, activator/binder ratio, testing age, curing condition, SF amount/fineness and Si/Al molar ratio [47]. The later factor (Si/Al) has a considerable effect on compressive strength [17]. Duxson et al. [48] and Riahi et al. [49] emphasized that increasing Si/Al ratio up to a certain level led to increasing the compressive strength. Additional increasing Si/Al ratio led to decreasing the compressive strength. De Silva et al. [37] supposed that the later ages compressive strength values were enhanced due to increasing Si/Al molar ratios up to 3.8. A higher molar ratio led to overcoming polysialatesiloxo (Si–O–Si)/polysialatedisiloxo structures in geopolymer lattice on polysialate (Si–O–Al) structures [49]. On the whole, it is better not to increase the molar ratio than 3.91 to obtain better strength [17]. Matalkah et al. [44] related this improvement to the good dispersion of the amorphous SF particles that generated denser microstructure by filling the inner pores. Rashad and Zeedan [17] related this improvement to the reduction in the pores due to the SF filling effect (Fig. 2.18). However, higher molar ratios can cause an adverse effect due to the formation of pores [17, 38, 39] (Fig. 2.19), an increase in the porosity [16, 50–52], a decrease in gel formation/stability [36, 37] and a decrease in the solution pH value [53]. As a matter of fact, about 62.5%, 25% and 12.5% of the cited references in this part focused on mortar, paste and concrete, respectively (Fig. 2.20).

Relative compressive strength (%)

700 600 500 400 300 200 100 0 0

10

20

30

40

SF (%) Fig. 2.16 Effect of SF on MK geopolymers compressive strength [16–18, 24, 29, 44–46]

44

2 Silica Fume as a Part of Precursor/An Additive

12.50 Increased 50.00

Decreased Increased/dec 37.50 reased

Fig. 2.17 Percentage of studies about the effect of SF on MK geopolymers compressive strength

Pores

a) 0.25F0

b) 0.25F20

Fig. 2.18 SEM images of MK paste samples activated with 25% sodium silicate without (a) and with 20% SF (b) [17]. Reprinted with permission from American Concrete Institute publisher

2.4.4 Slag/Fly Ash Precursor Cong and Mei [54] prepared 20% slag/80% FA geopolymer pastes activated with gypsum and calcium carbide residue. The FA was partially replaced with 2–6% SF. The specimens were cured at 50 °C for 24 h. The results showed that the incorporation of 2%, 4% and 6% SF increased the 3 days compressive strength by ~ 8.7%, ~ 13% and ~ 30.43%, respectively, whilst the 28 days compressive strength was enhanced by ~ 4%, ~ 10% and ~ 25%, respectively. The 56 days compressive strength was enhanced by ~ 4.62%, ~ 16.9% and ~ 32.3% with the inclusion of 2%, 4% and 6% SF, respectively. Cheah et al. [6] found higher 7–90 days compressive strength of 40% slag/60% FA geopolymer mortars activated with Na2 CO3 and sodium silicate with

2.4 Compressive Strength

45

Pores

GP gel

a) 0.5F0

b) 0.5F5

Fig. 2.19 SEM images of MK paste samples activated with 50% sodium silicate without (a) and with 5% SF (b) [17]. Reprinted with permission from American Concrete Institute publisher

Fig. 2.20 Percentage of studies of different media for MK geopolymers compressive strength containing SF

12.50 25.00 Paste Mortar Concrete

62.50

the incorporation of 2–6% SF (fineness 30,000–13,000 m2 /kg). The incorporation of 2% SF increased the 7, 14, 28 and 90 days compressive strength by ~ 17.7%, ~ 70%, ~ 19.35% and ~ 3.75%, respectively, whilst the incorporation of 4% SF increased it by ~ 37.8%, ~ 67.5%, ~ 8.1% and ~ 3.75%, respectively. The incorporation of 6% SF increased it by ~ 0%, ~ 95%, ~ 37.1% and ~ 2.5%, respectively. The incorporation of 8% SF decreased 7, 28 and 90 days by ~ 6.7%, ~ 6.4% and ~ 22.5%, respectively, whilst the 14 days compressive strength was enhanced by ~ 27.5%. The incorporation of 10% SF increased the 7, 14 and 28 days compressive strength by ~ 28.8%, ~ 75% and ~ 22.6%, respectively, whilst the 90 days compressive strength was decreased by ~ 31.2%. Zhang et al. [7] partially replaced FA in 40% slag/60% FA geopolymer pastes activated with NaOH and sodium silicate solution by 5–15% SF. The results showed no obvious change in the 7–360 days compressive strength with the inclusion of

46

2 Silica Fume as a Part of Precursor/An Additive

SF. They also partially replaced slag in 40% slag/60% FA with 5% and 10% SF. The results showed a reduction in the 7–360 days compressive strength with the inclusion of SF. The results obtained by Zhu et al. [55] showed comparable 7– 1080 days compressive strength of 40% slag/60% FA pastes activated with NaOH and sodium silicate solution with the incorporation of 5–15% SF. Elyamany et al. [23] found ~ 12.72%, ~ 20%, ~ 14.3% and ~ 7.5% higher 7 days compressive strength of 50% slag/50% FA geopolymer mortars activated with NaOH by partially replacing slag with 15% SF when 10, 12, 14 and 16 M of NaOH was used, respectively. The alkaline solution/binder ratio was 0.35, and the specimens were cured at 60 °C for 48 h. They also found ~ 10%, ~ 5.9%, ~ 6.7% and ~ 3.8% enhancement in the compressive strength when alkaline solution/binder ratios were 0.35, 0.4, 0.45 and 0.5, respectively. The molarity of NaOH was 16, and the specimens were cured at 60 °C for 48 h. Singh et al. [8] found 4.23%, 15.77%, 28.1% and 10.38% higher 7 days compressive strength of 50% slag/50% FA geopolymer concrete mixtures activated with NaOH and sodium silicate solution by partially replacing slag with 5%, 10%, 15% and 20% SF, respectively, whilst the 28 days compressive strength was enhanced by 3.35%, 17.7%, 24.88% and 13.64%, respectively. Zhang et al. [56] found 13.51%, 20.26%, 22.14% and 22.33% reduction in the 7 days compressive strength of 60% slag/40% FA geopolymer pastes activated with NaOH and waterglass solution by adding 5%, 10%, 15% and 20% SF, respectively. The addition of 5%, 10% and 15% SF decreased the 28 days compressive strength by 13.51%, 20.26%, 22.14% and 22.33%, respectively, whilst the addition of 20% SF increased it by 8.53%. Liu et al. [9] prepared mortar specimens from slag/FA/5% SF and 2% steel fibres activated with NaOH and waterglass solution. The slag/FA was partially replaced with 10%, 20% and 30% SF (size 0.15 μm = 18,650 m2 /kg). The results showed that the inclusion of 10% SF sharply decreased the compressive strength by 18.4%, whilst 20% and 30% SF increased it by ~ 7.8% and ~ 18%, respectively. Table 2.6 briefs the results of this part. Based on the discussion so far, it is evident that most of the studies reported a positive effect of SF on slag/FA geopolymers compressive strength (Fig. 2.21). The obtained results are affected by slag/FA/SF fineness, activator concentration and type, activator/binder ratio, testing age, curing condition and Si/Al molar ratio. On the whole, it is better not to increase the proportion of SF by more than 10% to obtain superior strength. Cong and Mei [54] related this superior strength to the denser microstructure caused by SF particles that can act as microaggregates to fill the voids. Cheah et al. [6] related this improvement to the pore refinements of paste and paste/aggregate interfacial transition zone (ITZ). The excessive ratio of SF brought an adverse effect due to hindering the geopolymerization process resulting from the sharp increase of the Si/Al ratio. Elyamany et al. [23] related this improvement to the increased reactivity of the slag and microstructure densely caused by SF (Fig. 2.22). However, in some cases, the incorporation of SF may decrease the compressive strength. Cheah et al. [6] related this reduction to the hinder of geopolymerization process caused by spiked higher Si/Al ratio beyond the optimal. As a matter of fact, about 37.5%, 50% and 12.5% of the cited references in this part focused on mortar, paste and concrete, respectively (Fig. 2.23).

Sodium carbonate and sodium silicate solution Sodium carbonate and sodium silicate solution

–

465/324.4 m2 /kg

465/324.4 m2 /kg

Slag/FA

Slag/FA

Slag/FA

Cheah et al. [6]

Gypsum and calcium carbide residue

–

Slag/FA

Gypsum and calcium carbide residue

Gypsum and calcium carbide residue

–

Slag/FA

Cong and Mei [54]

Activator

Precursor size/fineness

References Precursor

4

2

Paste

Paste

Paste

Type

30,000–13,000 Mortar m2 /kg

30,000–13,000 Mortar m2 /kg

2, 4 – and 6

2, 4 – and 6

2, 4 – and 6

SF SF (%) size/fineness

Table 2.6 Effect of SF on the compressive strength of slag/FA geopolymer matrices

7, 14, 28 and 90

7, 14, 28 and 90

56

28

3

Age (day)

Increased

Increased

Increased

Effect

Polyethylene Increased film wrap

Polyethylene Increased film wrap

50 °C for 24 h

50 °C for 24 h

50 °C for 24 h

Curing

(continued)

~ 37.8, ~ 67.5, ~ 8.1 and ~ 3.75

~ 17.7, ~ 70, ~ 19.35 and ~ 3.75

~ 4.62, ~ 16.9 and ~ 32.3

~ 4%, ~ 10 and ~ 25

~ 8.7, ~ 13 and ~ 30.43

Ratio

2.4 Compressive Strength 47

Activator Sodium carbonate and sodium silicate solution Sodium carbonate and sodium silicate solution Sodium carbonate and sodium silicate solution Sodium carbonate and sodium silicate solution

Precursor size/fineness

465/324.4 m2 /kg

465/324.4 m2 /kg

465/324.4 m2 /kg

465/324.4 m2 /kg

Slag/FA

Slag/FA

Slag/FA

Slag/FA

References Precursor

Table 2.6 (continued)

10

8

8

6

Type

30,000–13,000 Mortar m2 /kg

30,000–13,000 Mortar m2 /kg

30,000–13,000 Mortar m2 /kg

30,000–13,000 Mortar m2 /kg

SF SF (%) size/fineness

7, 14 and 28

14

7, 28 and 90

7, 14, 28 and 90

Age (day)

Effect

~ 0, ~ 95, ~ 37.1 and ~ 2.5

Ratio

Polyethylene Increased film wrap

Polyethylene Increased film wrap

(continued)

~ 28.8, ~ 75 and ~ 22.6

~ 27.5

Polyethylene Decreased ~ 6.7, ~ 6.4 and ~ film wrap 22.5

Polyethylene Increased film wrap

Curing

48 2 Silica Fume as a Part of Precursor/An Additive

NaOH

NaOH and sodium silicate solution

–

–

–

–

– /45 μm

Slag/FA

Slag/FA

Slag/FA

Slag/FA

Zhang et al. [7]

Zhu et al. [55]

Elyamany et al. [23]

Singh et al. Slag/FA [8]

Sodium carbonate and sodium silicate solution

465/324.4 m2 /kg

Slag/FA

NaOH

NaOH and sodium silicate solution

NaOH and sodium silicate solution

Activator

Precursor size/fineness

References Precursor

Table 2.6 (continued)

5, 10, 15 and 20

15

15

5, 10 and 15

5, 10 and 15

10

Type

0.12 μm

–

–

–

–

7

7

Effect

Ratio

Ambient

Ambient

60 °C for 48 h

60 °C for 48 h

Increased

Increased

Increased

No obvious change

No obvious change

(continued)

4.23, 15.77, 28.1 and 10.38

~ 10, ~ 5.9, ~ 6.7 and ~ 3.8 (w/b 0.35, 0.4, 0.45 and 0.5)

12.72, 20, 14.3 and 7.5 (for 10, 12, 14 and 16 M)

~0

~0

Polyethylene Decreased ~ 31.2 film wrap

Curing

7–1080 Ambient

7–360

90

Age (day)

Concrete 7

Mortar

Mortar

Paste

Paste

30,000–13,000 Mortar m2 /kg

SF SF (%) size/fineness

2.4 Compressive Strength 49

Liu et al. [9]

Zhang et al. [56] NaOH and 5, waterglass 10, solution 15 and 20 NaOH and 5, waterglass 10 solution and 15 NaOH and 20 waterglass solution

428/– m2 /kg

428/– m2 /kg

428/– m2 /kg

Slag/FA

Slag/FA

Slag/FA

0.15 μm

0.15 μm

Slag/FA/SF 17.9/36.94/0,15 μm NaOH and 20 waterglass and solution 30

21,000 m2 /kg

21,000 m2 /kg

21,000 m2 /kg

0.12 μm

Slag/FA/SF 17.9/36.94/0,15 μm NaOH and 10 waterglass solution

5, 10, 15 and 20

NaOH and sodium silicate solution

Slag/FA

– /45 μm

SF SF (%) size/fineness

Activator

Precursor size/fineness

References Precursor

Table 2.6 (continued) Age (day)

Mortar

Mortar

Paste

Paste

Paste

–

–

28

28

7

Concrete 28

Type

80 °C for 24 h

80 °C for 24 h

20 with 95% RH

20 with 95% RH

20 with 95% RH

Ambient

Curing

3.35, 17.7, 24.88 and 13.64

Ratio

8.53

Increased

~ 7.8 and ~ 18

Decreased 18.4

Increased

Decreased 1, 22.5 and 7.17

Decreased 13.51, 20.26, 22.14 and 22.33

Increased

Effect

50 2 Silica Fume as a Part of Precursor/An Additive

2.4 Compressive Strength

51

Relative compressive strength (%)

250 200 150 100 50 0 0

10

20

30

SF (%) Fig. 2.21 Effect of SF on slag/FA geopolymers compressive strength [6–9, 23, 54–56]

Fig. 2.22 SEM images of FA (a) 50% FA/50% slag (b) and 50% FA/35% slag/15% SF (c) geopolymer mortar samples [23]. Reprinted with permission from Elsevier publisher Fig. 2.23 Percentage of studies of different media for slag/FA geopolymers compressive strength containing SF

12.50

Paste Mortar 37.50

Concrete

50.00

52

2 Silica Fume as a Part of Precursor/An Additive

2.4.5 Other Precursors Das et al. [14] prepared FA/lime/SF geopolymer concrete specimens activated with NaOH and sodium silicate solution. The results showed that the 28 days compressive strength was increased with including 2% and 3% SF when the ratio of lime was 7.5% and 10%, respectively, compared to those containing 1% SF. Wang et al. [15] prepared UHPC geopolymer specimens from FA/ CAC activated with NaOH and sodium silicate solution. When the ratio of cement was 10%, the inclusion of 5% and 10% SF increased the 7 days compressive strength by 11.46% and ~ 3.75%, respectively, whilst the inclusion of 15% and 20% SF decreased it by ~ 10.54% and 14%, respectively. The 28 days compressive strength was enhanced by ~ 10%, ~ 11.25%, ~ 3.75% and ~ 12.5% with the inclusion of 5%, 10%, 15% and 20% SF, respectively. When the ratio of cement was 20%, the inclusion of 5–20% SF increased the 7 and 28 days compressive strength. The 7 day compressive strength was enhanced by ~ 5%, ~ 12.5%, ~ 13.75% and ~ 22.2% with the incorporation of 5%, 10%, 15% and 20% SF, respectively, whilst the 28 days compressive strength was enhanced by ~ 11%, ~ 20%, ~ 27.5% and ~ 34.3%, respectively. Ye and Huang [57] found a general enhancement in the 3–28 days compressive strength of 70% FA/30% cement pastes activated with different activators (NaOH, Na2 SO4 and Na2 CO3 ) by partially replacing cement with 10% SF. The 3, 7, 21 and 28 days compressive strength of the specimens activated with NaOH was enhanced by ~ 50%, ~ 53%, ~ 50% and ~ 55%, respectively, whilst it was enhanced by ~ 25%, ~ 53.8%, ~ 30.4% and ~ 16.4% when Na2 SO4 was used, respectively. The compressive strength of the specimens activated with Na2 CO3 was enhanced by ~ 19%, ~ 105%, 53% and ~ 40.6%, respectively. Hossein et al. [26] found higher 7–90 days compressive strength of 5% slag/50% rockwool geopolymer pastes activated with NaOH and waterglass solution by partially replacing rockwool with 2% SF, whilst partially replacing rockwool with 4% and 6% SF decreased it. Zakira et al. [58] found 10.85% and 2.4% enhancement in the 3 and 28 days compressive strength of 50% slag/50% red mud geopolymer pastes activated with NaOH and sodium silicate solution by partially replacing red mud with 10% SF, respectively. Jaradat and Matalkah [59] found 9%, 16%, ~ 3.26% and ~ 3.2% enhancement in the 28 days compressive strength of 40% olive biomass ash (OBA)/60% kaolin geopolymer mortars activated with NaOH and sodium silicate solution by partially replacing the mixed precursors with 5%, 10%, 15% and 20% SF, respectively, when curing temperature was 25 °C, whilst a reduction of ~ 14.3%, ~ 21.4%, ~ 28.57% and ~ 33.9% was obtained when the specimens were cured at 60 °C for 24 h, respectively. Javed et al. [25] found 125.72%, 254% and 270% enhancement in the 28 days compressive strength of calcined lithium slag geopolymer pastes activated with NaOH and sodium silicate solution by partially replacing slag with 20%, 30% and 40% SF (fineness 15–30 m2 /kg), respectively, when the specimens were cured at 25 °C with 55% RH, whilst the compressive strength was enhanced by 18.27%, 34.62% and 53.9%, respectively, when the specimens were cured at 70 °C for 24 h, then at 25 °C with 55% RH. The lesser enhancement in the strength of specimens cured at 70 °C compared to those

2.5 Flexural Strength

53

cured at 20 °C is attributed to the formation of cracks. Yu et al. [60] prepared fluid catalytic cracking (FCC) waste catalyst geopolymer pastes activated with NaOH and sodium silicate solution. The specimens were cured at 80 °C for 4 h, then at 20 ± 2 °C with RH ≥ 95%. The results showed an enhancement in the compressive strength by 84.2, 475.4, 188 and 176.2 folds when the FCC waste catalyst was replaced with 20%, 50%, 80% and 100% SF, respectively. Table 2.7 briefs the effect of SF on other types of geopolymer compressive strength. Based on the discussion so far, it is evident that it is possible to enhance the compressive strength of geopolymers based on unconventional precursors by incorporating SF (Fig. 2.24). The optimum ratio of SF varies according to the type of precursor. For example, when FA/lime was used as a precursor, it is better to use 2– 3% SF, whilst 2% SF was recommended when slag/rockwool was used as a precursor. In this manner, when FA/calcium aluminate cement was used as a precursor, it is better to use 20% SF, whilst 10% SF was recommended when BOA/kaolin or slag/red mud was used as a precursor. When calcined lithium slag was used as a precursor, it is better to use 40% SF, whilst 50% SF was recommended when FCC waste catalyst was used as a precursor.

2.5 Flexural Strength Yong-Sing et al. [28] found ~ 3.8–16.7% reduction in the 28 days flexural strength of 60% FA/40% ladle furnace slag geopolymer pastes activated with NaOH and sodium silicate solution by adding 1–3% SF, whilst adding 4% SF decreased it by ~ 12.8%. Cheah et al. [6] found higher 7–90 days flexural strength of 40% slag/60% FA geopolymer mortar mixtures activated with Na2 CO3 and sodium silicate with the incorporation of 2–6% SF (fineness 30,000–13,000 m2 /kg). Singh et al. [8] found 0.76%, 3.6%, 10% and 1.5% higher 28 days flexural strength of 50% slag/50% FA geopolymer concrete mixtures activated with NaOH and sodium silicate solution by partially replacing slag with 5%, 10%, 15% and 20% SF, respectively. Elyamany et al. [23] found ~ 21.25%, ~ 8.5% and ~ 31.6% enhancement in the 7 days flexural strength of 50% FA/50% slag geopolymer mortars activated with NaOH by partially replacing slag with 15% SF when the specimens cured at 30, 60 and 90 °C for 48 h, respectively. The molarity of NaOH was 16 M, and the alkaline solution/binder ratio was 0.35. Jena and Panigrahi [11] found 5.9%, 14.71% and 2.94% enhancement in the 28 days flexural strength of FA geopolymer concretes activated with NaOH and sodium silicate solution by partially replacing FA with 5%, 10% and 15% SF, respectively. All specimens were cured at room temperature for 24 h followed by 70 °C for 24 h, then at laboratory temperature. Bajpai et al. [42] found 1.63% reduction in the 28 days flexural strength of FA geopolymer paver block concrete specimens with rectangular shape activated with NaOH and sodium silicate solution by partially replacing FA (fineness 399.7 m2 /kg) with ~ 22% SF (fineness 21,170 m2 /kg). Sukontasukkul et al. [13] found 31.82% and 18.18% enhancement in the 28 days flexural strength of FA geopolymer mortars activated with NaOH and sodium silicate solution by partially

Hossein et al. [26]

Slag/rockwool

NaOH and waterglass

Na2 CO3

FA/cement

NaOH and sodium silicate solution

FA/CAC

Na2 SO4

NaOH and sodium silicate solution

FA/CAC

FA/cement

NaOH and sodium silicate solution

FA/CAC

NaOH

NaOH and sodium silicate solution

FA/CAC

FA/cement

NaOH and sodium silicate solution

Wang et al. [15] FA/CAC

Ye and Huang [57]

Activator

NaOH and sodium silicate solution

Precursor

FA/lime

References

Das et al. [14]

Type Concrete

Concrete

2

10

10

10

Paste

Paste

Paste

Paste

5, 10, 15 Concrete and 20

5, 10, 15 Concrete and 20

5, 10, 15 Concrete and 20

15 and 20

5 and 10 Concrete

2 and 3

SF (%)

Table 2.7 Effect of SF on the compressive strength of other geopolymer types Age (day)

Curing

20 °C

20 °C

20 °C

20 °C

20 °C

Ambient

7, 14, 28 and 90

60 °C for 1 day

3, 7, 21 and 28 Room

3, 7, 21 and 28 Room

3, 7, 21 and 28 Room

28

7

28

7

7

7

Effect

Increased

Increased

Increased

Increased

Increased (cement ratio 20%)

Increased (cement ratio 20%)

Increased (cement ratio 10%)

Decreased (cement ratio 10%)

Increased (cement ratio 10%)

Increased (cement ratio 10%)

(continued)

12.48, 13.92, 15.23 and 17.8

~ 19, ~ 105, 53 and ~ 40.6

~ 25, ~ 53.8, ~ 30.4 and ~ 16.4

~ 50, ~ 53, ~ 50 and ~ 55

~ 11, ~ 20, ~ 27.5 and ~ 34.3

~ 5, ~ 12.5, ~ 13.75 and ~ 22.2

~ 10, ~ 11.25, ~ 3.75 and ~ 12.5

~ 10.54 and 14

11.46 and ~ 3.75

Ratio/fold

54 2 Silica Fume as a Part of Precursor/An Additive

FCC waste catalyst

NaOH and sodium silicate solution

NaOH and sodium silicate solution

Calcined lithium slag

Yu et al. [60]

NaOH and sodium silicate solution

NaOH and sodium silicate solution

OBA/kaolin

Javed et al. [25] Calcined lithium slag

NaOH and sodium silicate solution

OBA/kaolin

Jaradat and Matalkah [59]

NaOH and waterglass

Slag/rockwool

NaOH and sodium silicate

NaOH and waterglass

Slag/rockwool

Slag/red mud

Activator

Precursor

Zakira et al. [58]

References

Table 2.7 (continued)

Paste

Paste

Paste

Type

20, 50, 80 and 100

20, 30 and 40

20, 30 and 40

Paste

Paste

Paste

5, 10, 15 Mortar and 20

5, 10, 15 Mortar and 20

10

6

4

SF (%)

70 °C for 24 h 80 °C for 4 h

20 °C, RH ≥ 95

25 °C, 55% RH

60 °C for 24 h

25 °C

60 °C

60 °C for 1 day

60 °C for 1 day

Curing

28

28

28

28

3 and 28

7, 14, 28 and 90

7, 14, 28 and 90

Age (day)

Increased

Increased

Increased

Decreased

Increased

Increased

Decreased

Decreased

Effect

84.2, 475.4, 188 and 176.2 folds

18.27, 34.62 and 53.9

125.72, 254 and 270

~ 14.3, ~ 21.4, ~ 28.57 and ~ 33.9

9, 16, ~ 3.26 and ~ 3.2

10.85 and 2.4

30.33, 29.21, 29.37 and 29.29

17.85, 17.75, 16.29 and 14.76

Ratio/fold

2.5 Flexural Strength 55

56

2 Silica Fume as a Part of Precursor/An Additive 400

FA/CAC FA/cement Slag/rockwool Slag/red mud OBA/kaolin Calcined lithium slag

Relative workability (%)

350 300 250 200 150 100 50 0 0

10

20

30

40

SF (%) Fig. 2.24 Effect of SF the compressive strength of geopolymers based on unconventional precursors [15, 25, 26, 57–59]

replacing FA with 10% and 20% SF, whilst the inclusion of 30% SF decreased it by 6.82%, when curing temperature was 23–28 °C. Contrarily, when the specimens were cured at 60 for 24 h, the inclusion of 10%, 20% and 30% SF decreased the 28 days flexural strength by 22.72%, 27.27% and 31.82%, respectively. Liu et al. [9] prepared mortar specimens from slag/FA/5% SF and 2% steel fibres activated with NaOH and waterglass solution. The slag/FA was partially replaced with 10%, 20% and 30% SF (size 0.15 μm = 18,650 m2 /kg). The results showed that the inclusion of 10% SF decreased the flexural strength by 8.75%, whilst the inclusion of 20% and 30% increased it by 7.5% and 44.4%, respectively. Okoye et al. [12] reported that the incorporation of 5% and 10% SF into FA geopolymer concretes activated with NaOH and sodium silicate solution cured at 100 °C for 72 h did not show a change in the 28 days flexural strength, whilst the incorporation of 30% and 40% SF increased it by ~ 5.4% and ~ 15.6%, respectively. Uysal et al. [45] found 17.42%, 29.41% and 3.85% enhancement in the 7 days flexural strength of MK geopolymer mortars activated with NaOH and sodium silicate solution by partially replacing MK with 10%, 20% and 30% SF, respectively, whilst the inclusion of 40% SF decreased it by 6.79%. The inclusion of 10%, 20% and 30% SF increased the 28 days flexural strength by 26.29%, 29.44% and 3.15%, respectively, whilst the inclusion of 40% SF decreased it by 0.45%. Aygörmez et al. [46] prepared MK geopolymer mortars activated with NaOH and sodium silicate solution. The specimens were cured at 60 °C for 72 h. The MK was partially replaced with 10–40% SF. The 28 days flexural strength was enhanced by 26.27 and 29.43% with the inclusion of 10 and 20% SF, whilst the inclusion of 30 and 40% SF did not show an essential change in the strength. Yavuz et al. [27] found 114.4%, 83% and 32.9% enhancement in the 28 days flexural strength of FA geopolymer pastes activated with NaOH and sodium silicate solution by partially replacing FA with

2.6 Splitting Tensile Strength and Elastic Modulus

57

25%, 50% and 75% SF, respectively, whilst the inclusion of 100% SF decreased it by 93.83%. The specimens were cured at 65 °C for 24 h. Table 2.8 briefs the results of this part. Based on the discussion so far, it is evident that there are conflicting results about the effect of SF on geopolymers flexural strength (Fig. 2.25), but most of them (about 50%) [6, 8, 11, 12, 23, 46] reported a positive effect. However, other studies (about 41.67%) [9, 13, 27, 28, 45] reported that the incorporation of SF may have a positive effect or a negative effect on the flexural strength (Fig. 2.26). This depends on precursor type/fineness, activator concentration and type, activator/binder ratio, testing age, curing condition and SF amount/fineness. On the whole, it is better not to increase the proportion of SF by more than 30% to obtain superior flexural strength. This improvement is attributed to the filling effect of SF in the voids [11]. As a matter of fact, about 50%, 16.67% and 33.33% of the cited references in this part focused on mortar, paste and concrete, respectively (Fig. 2.27).

2.6 Splitting Tensile Strength and Elastic Modulus Jena and Panigrahi [11] found 9.7%, 15.6% and 10.5% enhancement in the 28 days splitting tensile strength of FA geopolymer concretes activated with NaOH and sodium silicate solution by partially replacing FA with 5%, 10% and 15% SF, respectively. All specimens were cured at room temperature for 24 h followed by 70 °C for 24 h, then at laboratory temperature. Okoye et al. [12] reported that the incorporation of 5% and 10% SF into FA geopolymer concretes activated with NaOH and sodium silicate solution cured at 100 °C for 72 h did not show a change in the 28 days splitting tensile strength, whilst the incorporation of 30% and 40% SF increased it by ~ 5% and ~ 19.6%, respectively. Singh et al. [8] found 6.13%, 4.6%, 14.44% and 3.1% higher 28 days splitting tensile strength of 50% slag/50% FA geopolymer concrete specimens activated with NaOH and sodium silicate solution by partially replacing slag with 5%, 10%, 15% and 20% SF, respectively. Albidah et al. [18] found a reduction in the 28 days splitting tensile strength of MK geopolymer concretes activated with NaOH and sodium silicate solution by partially replacing MK (size 32.33 μm) with 5–30% SF (size 64.96 μm). Liu et al. [9] prepared geopolymer mortar specimens from slag/FA/5% SF and 2% steel fibres activated with NaOH and waterglass solution. The slag/FA was partially replaced with 5%, 10%, 20% and 30% SF (size 0.15 μm = 18,650 m2 /kg). The inclusion of 10% SF decreased the splitting tensile strength by 36.4%, whilst the inclusion of 20% and 30% increased it by 1.75% and 43.6%, respectively, compared to that containing 5% SF. The inclusion of 10% SF decreased the elastic modules by 21.2%, whilst the inclusion of 20% and 30% increased it by ~ 13.8% and ~ 10.3%, respectively, compared to that containing 5% SF. Batista et al. [16] found ~ 4.6% and ~ 6.15% higher 28 days modulus of elasticity of MK geopolymer mortars activated with NaOH and sodium silicate solution by partially replacing MK (size 2.12 μm) with 4% and 7% SF (size 0.37 μm), respectively. The specimens were cured at ambient temperature. Table 2.9 briefs the results

Elyamany et al. [23]

Slag/FA

–

NaOH

NaOH and sodium silicate solution

– /45 μm

Singh et al. [8] Slag/FA

15

5, 10, 15 and 20

2–6

Sodium carbonate and sodium silicate solution

465/324.4 m2 /kg

Slag/FA

NaOH and 4 sodium silicate solution

d10 36.3/35.6 μm

FA/ladle slag

Cheah et al. [6]

NaOH and 1, 2 sodium and silicate 3 solution

d10 36.3/35.6 μm

FA/ladle slag

Yong-Sing et al. [28]

SF (%)

Activator

Precursor size/fineness

Precursor

References

Table 2.8 Effect of SF on the flexural strength of geopolymer matrices

Paste

Paste

Type

–

0.12 μm

Mortar

7

~ 3.8, ~ 6.3 and ~ 16.7

Ratio

30, 60 and 90 °C for 48 h

Ambient

Increased

Increased

(continued)

~ 21.25, ~ 8.5 and ~ 31.6

0.76, 3.6, 10 and 1.5

60 °C for 6 h Decreased ~ 12.8

60 °C for 6 h Increased

Effect

7, 14, Polyethylene Increased 28 film wrap and 90

28

28

Age Curing (day)

Concrete 28

30,000–13,000 m2 /kg Mortar

0.007 μm

0.007 μm

SF size/fineness

58 2 Silica Fume as a Part of Precursor/An Additive

–

FA

NaOH and sodium silicate solution

10, 20 and 30

NaOH and 30 sodium silicate solution

NaOH and 10 sodium and silicate 20 solution

Slag/FA/SF 17.9/36.94/0.15 μm NaOH and 10 waterglass solution

–

FA

Liu et al. [9]

–

Sukontasukkul FA et al. [13]

NaOH and ~ 22 21,170 m2 /kg sodium silicate solution

399.7 m2 /kg

FA

0.15 μm

–

–

–

–

Bajpai et al. [42]

5, 10 and 15

NaOH and sodium silicate solution

8 μm

FA

SF size/fineness

Jena and Panigrahi [11]

SF (%)

Activator

Precursor size/fineness

Precursor

References

Table 2.8 (continued)

Mortar

Mortar

Mortar

Mortar

–

28

28

28

Concrete 28

80 °C for 24 h

60 for 24 h

23–28 °C

23–28 °C

60 °C for 12 h

Room temperature for 24 h followed by 70 °C for 24 h

Age Curing (day)

Concrete 28

Type

5.9, 14.71 and 2.94

Ratio

31.82 and 18.18

(continued)

Decreased 8.75

Decreased 22.72, 27.27 and 31.82

Decreased 6.82

Increased

Decreased 1.63

Increased

Effect

2.6 Splitting Tensile Strength and Elastic Modulus 59

Uysal et al. [45]

Okoye et al. [12]

References

Precursor size/fineness

Activator

SF (%)

–

–

–

MK

MK

–

FA

MK

–

FA

10, 20 and 30

NaOH and sodium silicate solution

10, 20 and 30

NaOH and 40 sodium silicate solution

NaOH and sodium silicate solution

NaOH and 30 sodium and silicate 40 solution

NaOH and 10 sodium and silicate 20 solution

Slag/FA/SF 17.9/36.94/0.15 μm NaOH and 20 waterglass and solution 30

Precursor

Table 2.8 (continued)

–

Mortar

Mortar

Mortar

20,000 m2 /kg

20,000 m2 /kg

20,000 m2 /kg

28

7

7

Concrete 28

60 °C for 72 h

60 °C for 72 h

60 °C for 72 h

100 °C for 72 h

100 °C for 72 h

80 °C for 24 h

Age Curing (day)

Concrete 28

Mortar

Type

–

–

0.15 μm

SF size/fineness

7.5 and 44.4

Ratio

17.42, 29.41 and 3.85%

~ 5.4 and ~ 15.6

Increased

(continued)

26.29, 29.44 and 3.15

Decreased 6.79

Increased

Increased

No change ~ 0, ~ 0

Increased

Effect

60 2 Silica Fume as a Part of Precursor/An Additive

Yavuz et al. [27]

Aygörmez et al. [46]

References

–

FA

25, 50 and 75

NaOH and 100 sodium silicate solution

NaOH and sodium silicate solution

NaOH and 30 sodium and silicate 40 solution

~ 45 μm

MK

–

NaOH and 10 sodium and silicate 20 solution

~ 45 μm

MK

FA

NaOH and 40 sodium silicate solution

–

SF (%)

MK

Activator

Precursor size/fineness

Precursor

Table 2.8 (continued)

–

–

–

Paste

Paste

Mortar

Mortar

Mortar

20,000 m2 /kg

–

Type

SF size/fineness

28

28

28

28

28

65 °C for 24

65 °C for 24

60 °C for 72 h

60 °C for 72 h

60 °C for 72 h

Age Curing (day)

Ratio

26.27 and 29.43

114.4, 83 and 32.9

Decreased 93.83

Increased

No change ~ 0 and ~ 0

Increased

Decreased 0.45

Effect

2.6 Splitting Tensile Strength and Elastic Modulus 61

62

2 Silica Fume as a Part of Precursor/An Additive

Relative flexural strength (%)

250 200 150 100 50 0 0

10

20

30

40

50

60

70

80

90

100

SF (%) Fig. 2.25 Effect of SF on geopolymers flexural strength [8, 9, 11–13, 23, 27, 28, 42, 45, 46] Fig. 2.26 Percentage of studies about the effect of SF on geopolymers flexural strength

Increased 41.67

Decreased Increased/dec reased

8.33

Fig. 2.27 Percentage of studies of different media for geopolymers flexural strength containing SF

16.67 33.33 Paste Mortar Concrete

50.00

50.00

2.8 Water Absorption, Porosity and Water Penetration Depth

63

of this part. Based on the discussion so far, it is evident that the splitting strength is mainly affected by precursor type, SF amount and curing temperature, whilst no clear trend can be drawn from the effect of SF on elastic modulus due to the limited number of the available studies.

2.7 Toughness and Abrasion Resistance Batista et al. [16] found 13.5% lower 28 days toughness of MK geopolymer mortars activated with NaOH and sodium silicate solution by partially replacing MK (size 2.12 μm) with 4% SF (size 0.37 μm), whilst the inclusion of 7% SF increased it by 9.65%. The specimens were cured at ambient temperature. Contrarily, Sukontasukkul et al. [13] found 4.8%, 9.2% and 8.6 folds higher 28 days toughness of FA geopolymer mortars activated with NaOH and sodium silicate solution by partially replacing slag with 10%, 20% and 30% SF, respectively, when curing temperature was 23–28 °C, whilst 5.4, 11.6 and 14.8 folds were obtained when the specimens were cured at 60 °C for 24 h. Uysal et al. [45] found 20% and 37.65% reduction in the weight loss of MK geopolymer mortars activated with NaOH and sodium silicate solution by partially replacing MK with 10% and 20% SF due to abrasion, respectively, whilst the inclusion of 30% and 40% SF showed a negative effect. Albidah et al. [18] found 50% and 30% reduction in the weight loss of MK geopolymer concrete specimens activated with NaOH and sodium silicate solution with the inclusion of 5% and 10% SF due to abrasion, whilst the inclusion of 20% and 30% SF increased it by 40% and 390%, respectively. Bajpai et al. [42] found 0.44% reduction in the weight loss of FA geopolymer paver block concrete specimens activated with NaOH and sodium silicate solution after abrasion by partially replacing FA with ~ 22% SF. Based on the discussion so far, it is evident that there are few studies focused on the effect of SF on toughness and abrasion resistance. Thus, no clear conclusions can be obtained.

2.8 Water Absorption, Porosity and Water Penetration Depth Yong-Sing et al. [28] found 4.14–9.84% and 9.9–18.81% reduction in the 28 days apparent porosity and water absorption of 60% FA/40% ladle furnace slag geopolymer pastes activated with NaOH and sodium silicate solution by adding 1–3% SF, respectively, whilst adding 4% SF decreased it by ~ 3.63 and ~ 15.84%, respectively. Alanazi et al. [10] found lower 28 days porosity (27.9%) of 95% FA/5% SF geopolymer mortars activated with NaOH and sodium silicate solution cured at ambient temperature compared to those containing 100% FA cured at 60 °C for 24 h (32.5%). Hossein et al. [26] found 23.14% and 2% higher porosity at the ages of 7 and 28 days of slag/rockwool geopolymer pastes activated with NaOH and waterglass

NaOH and sodium silicate solution NaOH and waterglass solution

32.33 μm

17.9/36.94/0.15 μm

Liu et al. [9] Slag/FA/SF

MK

Albidah et al. [18]

NaOH and sodium silicate solution

– /45 μm

Slag/FA

Singh et al. [8]

NaOH and sodium silicate solution

–

FA

NaOH and sodium silicate solution

–

NaOH and sodium silicate solution

8 μm

FA

Jena and Panigrahi [11]

Okoye et al. FA [12]

Activator

Precursor size/fineness

Precursor

References SF size/fineness

–

10

0.15 μm

5, 10, 64.96 μm 20 and 30

5, 10, 0.12 μm 15 and 20

30 and – 40

5 and 10

5, 10 – and 15

SF (%)

Mortar

Concrete

Concrete

Concrete

Concrete

Concrete

Type

Table 2.9 Effect of SF on the splitting tensile strength and elastic modulus of geopolymers matrices

–

28

28

28

28

28

Age (day)

Effect

80 °C for 24 h

24 °C, with 20% RH

Ambient

Decreased splitting strength

Decreased splitting strength

Increased splitting strength

100 °C for 72 h Increased splitting strength

100 °C for 72 h No effect on splitting strength

Room Increase temperature for splitting 24 h followed strength by 70 °C for 24 h

Curing

(continued)

36.4

6.13, 4.6, 14.44 and 3.1

5 and ~ 19.6

–

9.7, 15.6 and 10.5

Ratio

64 2 Silica Fume as a Part of Precursor/An Additive

Activator NaOH and waterglass solution NaOH and waterglass solution NaOH and waterglass solution NaOH and sodium silicate solution

Precursor size/fineness

17.9/36.94/0.15 μm

17.9/36.94/0.15 μm

17.9/36.94/0.15 μm

2.12 μm

Precursor

Slag/FA/SF

Slag/FA/SF

Slag/FA/SF

Batista et al. MK [16]

References

Table 2.9 (continued) SF size/fineness

0.15 μm

4 and 7

0.37 μm

15 and 0.15 μm 30

10

15 and 0.15 μm 30

SF (%)

Mortar

Mortar

Mortar

Mortar

Type

28

–

–

–

Age (day)

Ambient

80 °C for 24 h

80 °C for 24 h

80 °C for 24 h

Curing

Increased elastic modulus

Increased elastic modulus

Decreased elastic modulus

Increased splitting strength

Effect

~ 4.6 and ~ 6.15

~ 13.8 and ~ 10.3

21.2

1.75% and 43.6

Ratio

2.8 Water Absorption, Porosity and Water Penetration Depth 65

66

2 Silica Fume as a Part of Precursor/An Additive

solution by partially replacing rockwool with 2% SF, respectively, whilst the porosity was decreased by 4.2% and 17.1% at the ages of 14 and 90 days, respectively. The incorporation of 4% SF increased the porosity at the ages of 7, 14, 28 and 90 days by 61.32%, 71.93%, 98.26% and 170.14%, respectively, whilst the incorporation of 6% SF increased it by 34.55%, 53.95%, 98.53% and 182%, respectively. Rostami and Behfarnia [33] found 12.97%, 19.25% and 23.85% reduction in the short-term water absorption of AAS concretes activated with NaOH and sodium silicate solution by partially replacing slag with 5%, 10% and 15% SF, respectively, whilst the 28 days water absorption was decreased by 5.97%, 9.7% and 13.1%, respectively. They also found 27%, 49.1% and 63.33% reduction in the 28 days water penetration depth with the incorporation of 5%, 10% and 15% SF, respectively. Albidah et al. [18] found 4.2%, 3.55%, 7.89% and 23.68% reduction in the 28 days water absorption of MK geopolymer concretes activated with NaOH and sodium silicate solution by partially replacing MK (size 32.33 μm) with 5%, 10%, 20% and 30% SF (size 64.96 μm), respectively. Uysal et al. [45] found 3.83%, 7.1%, 10.1% and 13.9% reduction in the 28 days water absorption of MK geopolymer mortars activated with NaOH and sodium silicate solution by partially replacing MK with 10%, 20%, 30% and 40% SF, respectively. Bajpai et al. [42] found 9.17% reduction in water absorption of FA geopolymer paver block concrete specimens activated with NaOH and sodium silicate solution after abrasion by partially replacing FA with ~ 22% SF. Yavuz et al. [27] found 35.9%, 45.41%, 55.74% and 62.63% reduction in the 28 days water absorption of FA geopolymer pastes activated with NaOH and sodium silicate solution by partially replacing FA with 25%, 50%, 75% and 100% SF, respectively, whilst the total porosity was decreased by 24.86%, 19.26%, 37.87% and 55.51%, respectively. Contrarily, Batista et al. [16] found 2.17% and 3.91% higher 28 days water absorption of MK geopolymer mortars activated with NaOH and sodium silicate solution by partially replacing MK (size 2.12 μm) with 4% and 7% SF (size 0.37 μm), respectively, whilst the apparent porosity was increased by 0.71% and 2.13%, respectively. Saludung et al. [61] found higher 28 days water absorption of AAS pastes activated with NaOH and sodium silicate solution by partially replacing slag with 5–15% SF. The plain specimens showed the lowest water absorption (3.51%) and total pore volume. The incorporation of 5%, 10% and 15% SF increased the water absorption by ~ 22.5%, ~ 102.3% and ~ 79.5%, respectively. Alcamand et al. [29] found 50.42% higher 28 days oxygen permeability of MK geopolymer mortars activated with NaOH and sodium silicate solution (SiO2 /Al2 O3 = 3) by partially replacing MK with 20% SF (SiO2 /Al2 O3 = 3.9). Table 2.10 briefs the obtained results of this part. Based on the discussion so far, it is evident that there are conflicting results about the effect of SF on geopolymers water absorption and porosity, of which about 63.63% of these results confirmed a positive effect, whilst about 27.27% of them confirmed a negative effect. This depends on precursor type/fineness, activator concentration and type, activator/binder ratio, testing age, curing condition and SF amount/fineness. Rostami and Behfarnia [33] related the positive effect of MK on water absorption to the pores filled with SF. Uysal et al. [45] related this positive effect to SF fineness. Yavuz et al. [27] related this positive effect to the less porous

d10 36.3/35.6 μm

d10 36.3/35.6 μm

d10 36.3/35.6 μm

FA/ladle slag

FA/ladle slag

FA/ladle slag

–

d10 36.3/35.6 μm

FA/ladle slag

Yong-Sing et al. [28]

Alanazi et al. FA [10]

Precursor size/fineness

Precursor

References

NaOH and sodium silicate solution

NaOH and sodium silicate solution

NaOH and sodium silicate solution

NaOH and sodium silicate solution

NaOH and sodium silicate solution

Activator

5

4

4

1–3

1–3

Paste

Paste

0.007 μm

0.007 μm

Mortar

Paste

0.007 μm

–

Paste

Type

0.007 μm

SF (%) SF size/fineness

Table 2.10 Effect of SF on water absorption and porosity of different geopolymer matrices

28

28

28

28

28

Age (day)

Ambient

60 °C for 6h

60 °C for 6h

60 °C for 6h

60 °C for 6h

Curing

Decreased porosity

Decreased water absorption

Decreased porosity

Decreased water absorption

Decreased porosity

Effect

(continued)

14.15

~ 15.84

~ 3.63

9.9–18.81

4.14–9.84

Ratio

2.8 Water Absorption, Porosity and Water Penetration Depth 67

NaOH and waterglass NaOH and waterglass NaOH and waterglass NaOH and waterglass NaOH and sodium silicate solution NaOH and sodium silicate solution NaOH and sodium silicate solution

456/– m2 /kg

456/– m2 /kg

456/– m2 /kg

456/– m2 /kg

450 m2 /kg

450 m2 /kg

450 m2 /kg

Hossein et al. Slag/rockwool [26] found

Slag/rockwool

Slag/rockwool

Slag/rockwool

Slag

Slag

Slag

Rostami and Behfarnia [33]

Activator

Precursor

Precursor size/fineness

References

Table 2.10 (continued)

5, 10 and 15

5, 10 and 15

5, 10 and 15

6

4

2

2

–

–

–

20,000 m2 /kg

20,000 m2 /kg

20,000 m2 /kg

20,000 m2 /kg

SF (%) SF size/fineness

Concrete

Concrete

Concrete

Paste

Paste

Paste

Paste

Type

28

28

Short term

7, 14, 28 and 90

7, 14, 28 and 90

14 and 90

7 and 28

Age (day)

Water

Water

Water

60 °C for 1 day

60 °C for 1 day

60 °C for 1 day

60 °C for 1 day

Curing

Decreased water penetration depth

Decreased water absorption

Decreased water absorption

Increased porosity

Increased porosity

Decreased porosity

Increased porosity

Effect

(continued)

27, 49.1 and 63.33

5.97, 9.7 and 13.1

12.97, 19.25 and 23.85

34.55, 53.95, 98.53 and 182

61.32, 71.93, 98.26 and 170.14

4.2 and 17.1

23.14 and 2

Ratio

68 2 Silica Fume as a Part of Precursor/An Additive

NaOH and sodium silicate solution NaOH and sodium silicate solution NaOH and sodium silicate solution

32.33 μm

–

399.7 m2 /kg

–

–

Albidah et al. MK [18]

MK

FA

FA

FA

Uysal et al. [45]

Bajpai et al. [42]

Yavuz et al. [27]

NaOH and sodium silicate solution

NaOH and sodium silicate solution

Activator

Precursor

Precursor size/fineness

References

Table 2.10 (continued)

25, 50 and 75

25, 50 and 75

~ 22

10, 20 and 30

5, 10, 20 and 30

–

–

Paste

Paste

Concrete

Mortar

20,000 m2 /kg

21,170 m2 /kg

Concrete

Type

64.96 μm

SF (%) SF size/fineness

28

28

28

28

28

Age (day)

Decreased water absorption

Decreased water absorption

Decreased water absorption

Effect

35.9, 45.41, 55.74 and 62.63

9.17

3.83, 7.1, 10.1 and 13.9

4.2, 3.55, 7.89 and 23.68

Ratio

(continued)

65 °C for 24 Decreased 24.86%, total porosity 19.26%, 37.87% and 55.51%

65 °C for 24 Decreased water absorption

60 °C for 12 h

60 °C for 72 h

24 °C, with 20% RH

Curing

2.8 Water Absorption, Porosity and Water Penetration Depth 69

Activator NaOH and sodium silicate solution NaOH and sodium silicate solution NaOH and sodium silicate solution

Precursor size/fineness

2.12 μm

417 m2 /kg

~ 0.1–11 μm

Precursor

MK

Slag

MK

References

Batista et al. [16]

Saludung et al. [61]

Alcamand et al. [29]

Table 2.10 (continued)

20

5, 10 and 15

~ 0.03–2 μm

16.3 m2 /g

4 and 7 0.37 μm

SF (%) SF size/fineness

Mortar

Paste

Mortar

Type

28

28

28

Age (day)

Room

Sealed at 20 °C

Ambient

Curing

Increased oxygen permeability

Increased water absorption

Increased water absorption

Effect

50.42

~ 22.5, ~ 102.3 and ~ 79.5

2.17 and 3.91

Ratio

70 2 Silica Fume as a Part of Precursor/An Additive

2.9 Fire Resistance

71

and denser microstructure caused by SF. However, other studies reported a negative effect of SF on water absorption and porosity. Saludung et al. [61] related this negative effect to the increase of the total paste pore volume with the incorporation of SF. Alcamand et al. [29] related this negative effect to the incomplete dissolution of SF.

2.9 Fire Resistance Yong-Sing et al. [28] reported that adding 3% SF into 60% FA/40% ladle furnace slag activated with NaOH and sodium silicate solution increased flexural strength by 16.7%, 29%, 43.7%, 53.4% and 77.3% after exposure to 300, 600, 900 and 1000 °C, respectively, whilst the addition of 3% SF decreased it by 57.1% after exposure to 1100 °C. They related this positive effect of SF to its high Si content which increased the geopolymer compactness. In addition, SF fineness supplied a clamping of sliding surfaces and increased fire resistance. Contrarily, the addition of SF has a negative effect at 1100 °C due to the crack formation and higher thermal shrinkage degree. The results obtained by Jaradat and Matalkah [59] showed that there is no obvious change in the residual compressive strength of 40% OBA/60% kaolin geopolymer mortars activated with NaOH and sodium silicate solution with the incorporation of 5–20% SF after exposure to 200–400 °C when the initial curing temperature was 25 °C or 60 °C for 24 h. Contrarily, the incorporation of 10% and 15% SF increased the residual strength after exposure to 800 °C in both curing conditions. Duan et al. [43] exposed FA geopolymer pastes with/without SF activated by NaOH and waterglass solution to 7, 28 and 56 thermal cycles at 200, 400 and 800 °C. The results showed 8.11%, 27.87% and 53.97% enhancement in the compressive strength after exposure to 7 thermal cycles at 200 °C with the inclusion 10%, 20% and 30% SF, respectively, whilst the enhancement after exposure to 28 thermal cycles was 7.78%, 24% and 48.48%, respectively, and the enhancement after exposure to 56 cycles was 6.29%, 30.8% and 51.66%, respectively. A similar trend of the results was observed after exposure to thermal cycles at 400 and 800 °C. They related this improvement to the microstructure optimization and refining the pores with the inclusion of SF. The incorporation of SF can produce homogenous, denser and fewer cracks in the microstructure. Aygörmez et al. [46] found lower compressive strength and flexural strength loss of MK geopolymer mortars activated with NaOH and sodium silicate solution after exposure to 300–900 °C with the inclusion of 10% and 20% SF. After exposure to 300 °C, the compressive strength loss of the control was reduced from 32.61% to 31.15% and 31.07% with the inclusion of 10% and 20% SF, respectively, whilst the flexural strength loss was reduced from 54.77% to 51.11% and 49.19%, respectively. After exposure to 600 °C, the compressive strength loss of the control was reduced from 55.15% to 51.89% and 50.37% with the inclusion of 10% and 20% SF, respectively, whilst the flexural strength loss was reduced from 69.54% to 67.48% and 66.89%, respectively. After exposure to 900 °C, the compressive strength loss of the control was reduced from 86% to 82.89% and 82.4% with the inclusion of

72

2 Silica Fume as a Part of Precursor/An Additive

10% and 20% SF, respectively, whilst the flexural strength loss was reduced from 84.95% to 82.92% and 80.59%, respectively. Rashad and Zeedan [17] found higher fire resistance of MK geopolymer pastes activated with 25% sodium silicate by partially replacing MK with 5–25% SF, whilst lower fire resistance was obtained with the inclusion of SF when 50% of sodium silicate was used. They confirmed that the incorporation of SF into MK geopolymers may increase or decrease the compressive strength after exposure to elevated temperatures. This depends on the ratio of Si/Al. Rashad and Khalil [32] found higher fire resistance of AAS pastes activated with sodium silicate by partially replacing slag with 5–15% SF after exposure to 200–800 °C. The incorporation of 5% SF showed the highest residual strength followed by those containing 10%, 15% and 0%. Contrarily, the incorporation of SF decreased fire resistance after exposure to 1000 °C (Fig. 2.28). They also found an adverse effect of SF on thermal shock resistance (exposed the specimens to 800 °C for 40 min, then quenching them in water for 5 min). The specimens free from SF exhibited 7 cycles, whilst those containing SF exhibited 4 cycles only. Table 2.11 briefs the obtained results of this part. Based on the discussion so far, it is evident that the effect of SF on geopolymers thermal resistance could be affected by precursor type, activator concentration and type, Si/Al ratio, Na/Si ratio, SF amount and curing condition. When slag was used as a precursor, the incorporation of SF has a positive effect on fire resistance up to 800 °C, whilst it has an adverse effect at 1000 °C [32]. When MK was used as a precursor, the incorporation of SF may increase or decrease fire resistance. This depends on activator concentration (i.e. Si/Al ratio). When a higher activator concentration was used (i.e. higher Si/Al ratio), the incorporation of SF decreased the fire resistance due to the formation of pores and microcracks [17]. When FA was used as a precursor, the incorporation of SF increased thermal cycles resistance due

Residual compressive strength (MPa)

40

SF0

SF5

SF10

SF15

35 30 25 20 15 10 5 0 0

200

400

600

800

1000

Temperature (oC) Fig. 2.28 Effect of SF on the residual compressive strength of AAS pastes [32]. Reprinted with permission from Elsevier publisher

Duan et al. [43]

FA

OBA/kaolin

3.39 μm With NaOH and waterglass solution

NaOH and sodium silicate solution

10, 20 and 30

5, 10, 15 and 20

5, 10, 15 and 20

2650/1340 m2 /kg

OBA/kaolin

Jaradat and Matalkah [59] NaOH and sodium silicate solution

1–3

d10 36.3/35.6 μm NaOH and sodium silicate solution

FA/ladle slag

SF (%)

Yong-Sing et al. [28]

Activator

Precursor size/fineness

Precursor

References

Table 2.11 Effect of SF on fire resistance of different geopolymer matrices

1.44 μm

13,650 m2 /kg

0.007 μm

SF size/fineness

Paste

Mortar

Mortar

Paste

Type

20 °C, 95% RH

60 °C for 24 h

25 °C

60 °C for 6 h

Curing

• Increased thermal cycles resistance up to 800 °C (continued)

• No obvious change in the residual strength at 200–600 °C • 10 and 15% SF increased residual strength at 800 °C

• No obvious change in the residual strength at 200–600 °C • 15 and 10% SF increased residual strength at 800 °C

• Increased fire resistance up to 1000 °C • Decreased fire resistance at 1100 °C

Effect

2.9 Fire Resistance 73

Sodium silicate

Sodium silicate

Sodium silicate

460 m2 /kg

460 m2 /kg

300 m2 /kg

MK

MK

Rashad and Zeedan [17]

Slag

NaOH and sodium silicate solution

~ 45 μm

MK

Aygörmez et al. [46]

Rashad and Khalil [32]

Activator

Precursor size/fineness

Precursor

References

Table 2.11 (continued)

5, 10 and 15

5, 10, 15, 20 and 25

5, 10, 15, 20 and 25

10 and 20

SF (%)

202,000 cm2 /g

20,200 m2 /kg

20,200 m2 /kg

–

SF size/fineness

Paste

Paste

Paste

Mortar

Type

40 °C

50 °C

50 °C

60 °C for 72 h

Curing

• Increased fire resistance up to 800 °C • Decreased fire resistance at 1000 °C • Decreased thermal shock resistance

• Decreased fire resistance (up to 1000 °C) (when 50% activator was used)

• Increased fire resistance (up to 1000 °C) (when 25% activator was used)

• Increased fire resistance (900 °C)

Effect

74 2 Silica Fume as a Part of Precursor/An Additive

2.10 Other Durability Aspects

75

to less cracks, homogenous and denser microstructure [43]. When FA/ladle furnace slag was used as a precursor, the addition of 3% SF increased fire resistance up to 1000 °C due to its high Si content and fineness. Contrarily, the addition of SF showed a negative effect at 1100 °C due to the crack formation and higher thermal shrinkage degree [28]. When OBA/kaolin was used as a precursor, the incorporation of 10% and 15% has a positive effect in increasing fire resistance at 800 °C, but there is no effect after exposure to 200–400 °C [59].

2.10 Other Durability Aspects Okoye et al. [62] prepared FA/SF geopolymer concretes activated with NaOH and sodium silicate solution. The ratios of FA/SF were 100/0, 90/10 and 80/20. The specimens were cured at 100 °C for 72 h. After 28 curing days, the specimens were immersed in 5% sodium chloride (NaCl) and 2% sulphuric acid (H2 SO4 ) for up to 90 days. The results showed lower weight loss and lower compressive strength loss of the specimens with the inclusion of SF. The incorporation of 20% SF showed the best resistance to NaCl and H2 SO4 . They related this improvement to the formation of N–A–S–H gel and C–A–S–H gel. Okoye et al. [12] reported that 60% FA/40% SF geopolymer concretes showed quite durability in the presence of 5% Na2 SO4 , 2% H2 SO4 and 5% NaCl. Alcamand et al. [29] found a reduction in the 5% MgSO4 resistance of MK geopolymer mortars activated with NaOH and sodium silicate solution (SiO2 /Al2 O3 = 3) by partially replacing MK with 20% SF (SiO2 /Al2 O3 = 3.9). The reduction in the compressive strength of MK specimens was increased by 5.02% and 5.57% after exposure to MgSO4 for 30 and 90 days, respectively, whilst 7.27% reduction was obtained after exposure for 180 days. Contrarily, the specimens containing SF showed a reduction of 13.5%, 10.84% and 0.76% after exposure for 30, 90 and 180 days, respectively. Zhu et al. [55] found lower leaching of 60% FA/40% slag pastes activated with sodium silicate by partially replacing FA or slag with 10% SF. Saludung et al. [61] reported that the AAS pastes activated with NaOH and sodium silicate solution showed the highest leaching, whilst partially replacing slag (fineness 417 m2 /kg) with 15% SF (fineness 16,300 m2 /kg) showed the lowest leaching. The specimens containing 0% SF showed the highest leaching of sodium silicate resulting from the excessive amount of unreacted sodium. They also found a reduction in the efflorescence of the AAS pastes by partially replacing slag with 5%, 10% and 15% SF. This reduction could be attributed to the formation of crystals. Matalkah et al. [44] found 52.27%, 47% and 39.39% reduction in the carbonate and bicarbonate concentration of calcined kaolin geopolymer mortars activated with NaOH and sodium silicate solution by partially replacing calcined kaolin with 5%, 10% and 15% SF, respectively. This means that SF can decrease the efflorescence formation and 5% is the optimum. Rashad and Mosleh [30] found higher compressive strength of AAS pastes

76

2 Silica Fume as a Part of Precursor/An Additive

activated with sodium silicate exposed to seawater attack and simulated tidal zone for 12 M by partially replacing slag with 5% and 10% SF. After exposure to 12 M of simulated tidal and seawater attack, the incorporation of 10% SF enhanced the compressive strength by 21.3% and 15.33%, respectively. Bajpai et al. [42] found 6.17% reduction in the weight loss of FA geopolymer paver block concrete specimens activated with NaOH and sodium silicate solution after exposure to 25 freeze/thaw cycles by partially replacing FA with ~ 22% SF. Aygörmez et al. [46] found higher compressive strength and flexural strength of MK geopolymer mortars activated with NaOH and sodium silicate solution after exposure to 56 and 300 freezing/thawing cycles as well as 5–25 wetting/drying cycles with the inclusion of 10% and 20% SF. Liang et al. [24] found higher resistance of 25 and 50 freezing/thawing cycles of MK geopolymer pastes activated with NaOH and sodium silicate solution by partially replacing MK (size 39.8 μm) with 10% SF (size 31.3 μm), whilst the incorporation of 20–40% SF showed a negative effect. The suitable ratio of SF can reduce porosity and refine pores. Rostami and Behfarnia [33] found 31.83%, 37% and 48.26% reduction in the 28 days charge passed (Coulombs) of AAS concretes activated with NaOH and sodium silicate solution by partially replacing slag with 5%, 10% and 15% SF, respectively, whilst the 90 days charge passed was decreased by 26.68%, 38.48% and 49.61%, respectively. Alanazi et al. [10] found higher surface resistivity of FA geopolymer mortars activated with NaOH and sodium silicate solution cured at ambient temperature by partially replacing FA with 5% and 10% SF. They related this improvement to the reduction in the permeability and free metal ions (Na+ ) in the pore solution due to the high silica ratio in SF. The reaction between Na2 O and SiO2 in an alkaline solution led to an increase of the surface resistivity and a decrease of the conductivity. Rashad [1] found 33%, 25%, 24% and 21% higher drying shrinkage of slag pastes activated with Na2 SO4 by partially replacing slag with 5% SF after 32, 60, 95 and 200 days of drying, respectively. Ye and Huang [57] found 2–4 times higher drying shrinkage of 70% FA/30% cement pastes activated with either NaOH, Na2 SO4 or Na2 CO3 by partially replacing cement with 10% SF. The specimens activated with NaOH showed the highest shrinkage followed by those activated with Na2 CO3 and Na2 SO4 , respectively. Contrarily, Zhang et al. [56] found reduction in the drying shrinkage of 60% slag/40% FA geopolymer pastes by adding 5–20% SF. The drying shrinkage decreased with increasing SF ratio. Rashad [31] found higher carbonation resistance of slag pastes activated with Na2 SO4 by partially replacing slag with 10% SF. The carbonation depth after exposure to accelerated carbonation for 8 weeks was decreased from 15.31 mm (for the control) to 2.23 mm with the incorporation of 10% SF with a reduction rate of 85.46%. This improvement is attributed to the denser microstructure caused by including SF (Fig. 2.29). Table. 2.12 briefs the obtained results of this part.

2.10 Other Durability Aspects

77

Fig. 2.29 SEM images of 100% slag (a) and 90% slag/10% SF (b) paste samples after 8 weeks of accelerated carbonation [31]. Reprinted with permission from American Concrete Institute publisher

Based on the discussion so far, it is evident that even though there are two studies [12, 62] reported higher NaCl and H2 SO4 resistance of geopolymer with the incorporation of SF, there is a study [29] reported adverse effect of SF on MgSO4 geopolymers resistance. There is confirmation from two studies that SF has a positive effect in decreasing leaching [55, 61] and efflorescence [44, 61]. Saludung et al. [61] related this improvement to the reduction in the number of unreacted sodium particles with the incorporation of SF, of which increasing unreacted sodium particles led to higher leaching and efflorescence. Matalkah et al. [44] related the positive effect of SF on efflorescence to the filled pores by unreacted particles of SF and the formation of more hydration products that enhanced the microstructure. Rashad and Mosleh [30] related the superior compressive strength of AAS pastes containing 5% and 10% SF over the control after exposure to 12 M of seawater attack and simulated tidal zone to the filling effect of SF and the modified pore size distribution and pore shape caused by SF. There is one study reported higher freezing/thawing resistance of geopolymers with the incorporation of 10% and 20% [46], whilst another one [24] reported an adverse effect of 20–40% SF. Thus, this property still needs more studies to get clear results. The incorporation of SF has a positive effect on the charge passed due to filling the pores [33] and surface resistance due to the reduction of Na+ in the solution of the pore resulting from the higher SiO2 content and the paste permeability reduction [10]. There is too limited number of studies in the literature focused on the effect of SF on the drying shrinkage [1, 56, 57] and carbonation resistance of geopolymers [31]. Thus, clear conclusions cannot be drawn.

Matalkah et al. [44]

NaOH and sodium silicate solution NaOH and sodium silicate solution NaOH and sodium silicate solution

417 m2 /kg

417 m2 /kg

< 75 μm

Slag

Slag

Calcined kaolin

Saludung et al. [61]

NaOH and sodium silicate solution

–

Slag/FA

Zhu et al. [55]

NaOH and sodium silicate solution

~ 0.1–11 μm

MK

Alcamand et al. [29]

NaOH and sodium silicate solution

–

NaOH and sodium silicate solution

Activator

Okoye et al. [12] FA

Precursor size/fineness

–

Precursor

Okoye et al. [62] FA

References

5, 10 and 15

5, 10 and 15

15

10

20

40

10 and 20

SF (%)

0.1365 m2 /g

16.3 m2 /g

16.3 m2 /g

–

~ 0.03–2 μm

–

–

SF size/fineness

Table 2.12 Effect of SF on different durability aspects of different geopolymer matrices

Mortar

Paste

Paste

Paste

Mortar

Concrete

Concrete

Type

23 °C, 95% RH

Sealed at 20 °C

Sealed at 20 °C

Ambient

Room

100 °C for 72 h

100 °C for 72 h

Curing

(continued)

• Decreased efflorescence

• Decreased efflorescence

• Decreased leaching

• Decreased leaching

• Decreased MgSO4 resistance

• Increased NaCl, Na2 SO4 and H2 SO4 resistance

• Increased NaCl and H2 SO4 resistance

Effect

78 2 Silica Fume as a Part of Precursor/An Additive

NaOH and sodium silicate solution

NaOH and sodium silicate solution

–

NaOH and sodium silicate solution

39.8 μm

MK

FA

NaOH and sodium silicate solution

39.8 μm

MK

Liang et al. [24]

Alanazi et al. [10]

NaOH and sodium silicate solution

~ 45 μm

MK

Aygörmez et al. [46]

450 m2 /kg

NaOH and sodium silicate solution

399.7 m2 /kg

Bajpai et al. [42] FA

Slag

Sodium silicate

300 m2 /kg

Slag

Rashad and Mosleh [30]

Rostami and Behfarnia [33]

Activator

Precursor size/fineness

Precursor

References

Table 2.12 (continued)

5 and 10

5, 7.5 and 10

20–40

10

10 and 20

~ 22

5 and 10

SF (%)

–

–

31.3 μm

31.3 μm

–

21,170 m2 /kg

20,000 m2 /kg

SF size/fineness

Mortar

Concrete

Paste

Paste

Mortar

Concrete

Paste

Type

• Increased freezing/thawing resistance

• Increased freezing/thawing and wetting/drying resistance

• Increased the resistance of freezing/thawing

• Increased seawater attack resistance and resistance of simulated tidal

Effect

Ambient

Water

(continued)

• Increased surface resistance

• Decreased charge passed

50 oC steam • Decreased freezing/thawing resistance

50 °C steam

60 °C for 72 h

60 °C for 12 h

18 °C

Curing

2.10 Other Durability Aspects 79

Na2 SO4

450 m2 /kg

Rashad [31]

Slag

NaOH and waterglass solution

428/– m2 /kg

Zhang et al. [56] Slag/FA

FA/cement

Ye and Huang [57] NaOH Na2 SO4 Na2 CO3

Na2 SO4

500 m2 /kg

Slag

Rashad [1]

–

Activator

Precursor size/fineness

Precursor

References

Table 2.12 (continued)

10

5, 10, 15 and 20

10

5

SF (%)

22,000 m2 /kg

21,000 m2 /kg

–

22,000 m2 /kg

SF size/fineness

Paste

Paste

Paste

Paste

Type

40 °C

20 °C with 95% RH

Room

40 °C

Curing

• Increased carbonation resistance

• Decreased drying shrinkage

• Increased drying shrinkage

• Increased drying shrinkage

Effect

80 2 Silica Fume as a Part of Precursor/An Additive

References

81

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20. A.M. Rashad, D.M. Sadek, An investigation on Portland cement replaced by high-volume GGBS pastes modified with micro-sized metakaolin subjected to elevated temperatures. Int. J. Sustain. Built Environ. 6(1), 91–101 (2017) 21. A.M. Rashad, A comprehensive overview about the influence of different admixtures and additives on the properties of alkali-activated fly ash. Mater. Des. 53, 1005–1025 (2014) 22. A.M. Rashad, S.A. Khafaga, M. Gharieb, Valorization of fly ash as an additive for electric arc furnace slag geopolymer cement. Constr. Build. Mater. 294, 123570 (2021) 23. H.E. Elyamany, M. Abd Elmoaty, A.M. Elshaboury, Setting time and 7-day strength of geopolymer mortar with various binders. Constr. Build. Mater. 187, 974–983 (2018) 24. G. Liang, H. Zhu, H. Li, T. Liu, H. Guo, Comparative study on the effects of rice husk ash and silica fume on the freezing resistance of metakaolin-based geopolymer. Constr. Build. Mater. 293, 123486 (2021) 25. U. Javed, F.U.A. Shaikh, P.K. Sarker, Microstructural investigation of lithium slag geopolymer pastes containing silica fume and fly ash as additive chemical modifiers. Cem. Concr. Compos. 134, 104736 (2022) 26. H.A. Hossein, E.M. Hamzawy, G.T. El-Bassyouni, B.S. Nabawy, Mechanical and physical properties of synthetic sustainable geopolymer binders manufactured using rockwool, granulated slag, and silica fume. Constr. Build. Mater. 367, 130143 (2023) 27. E. Yavuz, N.I.K. Gul, N.U. Kockal, Characterization of class C and F fly ashes based geopolymers incorporating silica fume. Ceram. Int. 48(21), 32213–32225 (2022) 28. N. Yong-Sing, Y.-M. Liew, H. Cheng-Yong, M.M.A.B. Abdullah, C. Rojviriya, M.S. Khalid, O. Shee-Ween, O. Wan-En, H. Yong-Jie, Interaction of silica fume on flexural properties of 10 mm-thickness geopolymers based on fly ash and ladle furnace slag under the thermal conditions. J. Build. Eng. 69, 106331 (2023) 29. H.A. Alcamand, P.H. Borges, F.A. Silva, A.C.C. Trindade, The effect of matrix composition and calcium content on the sulfate durability of metakaolin and metakaolin/slag alkali-activated mortars. Ceram. Int. 44(5), 5037–5044 (2018) 30. A.M. Rashad, Y.A. Mosleh, Effect of tidal zone and seawater attack on alkali-activated blended slag pastes. ACI Mater. J. 119(2) (2022) 31. A.M. Rashad, Additives to increase carbonation resistance of slag activated with sodium sulfate. ACI Mater. J. 119(2) (2022) 32. A.M. Rashad, M.H. Khalil, A preliminary study of alkali-activated slag blended with silica fume under the effect of thermal loads and thermal shock cycles. Constr. Build. Mater. 40, 522–532 (2013) 33. M. Rostami, K. Behfarnia, The effect of silica fume on durability of alkali activated slag concrete. Constr. Build. Mater. 134, 262–268 (2017) 34. J.I. Escalante-Garcia, V.M. Palacios-Villanueva, A.V. Gorokhovsky, G. Mendoza-Suárez, A.F. Fuentes, Characteristics of a NaOH-activated blast furnace slag blended with a fine particle silica waste. J. Am. Ceram. Soc. 85(7), 1788–1792 (2002) 35. Q. Sun, T. Li, B. Liang, Preparation of a new type of cemented paste backfill with an alkaliactivated silica fume and slag composite binder. Materials 13(2), 372 (2020) 36. H. Wang, H. Li, F. Yan, Synthesis and mechanical properties of metakaolinite-based geopolymer. Colloids Surf. A 268(1–3), 1–6 (2005) 37. P. De Silva, K. Sagoe-Crenstil, V. Sirivivatnanon, Kinetics of geopolymerization: role of Al2 O3 and SiO2 . Cem. Concr. Res. 37(4), 512–518 (2007) 38. M. Lahoti, P. Narang, K.H. Tan, E.-H. Yang, Mix design factors and strength prediction of metakaolin-based geopolymer. Ceram. Int. 43(14), 11433–11441 (2017) 39. R. Pouhet, M. Cyr, R. Bucher, Influence of the initial water content in flash calcined metakaolinbased geopolymer. Constr. Build. Mater. 201, 421–429 (2019) 40. F. Nuruddin, Compressive strength and microstructure of polymeric concrete incorporating fly ash and silica fume. Can. J. Civ. Eng. 1(1) (2010) 41. K.S. Vaibhav, M. Nagaladinni, M. Madhushree, B. Priya, Effect of silica fume on fly ash based geopolymer mortar with recycled aggregates, in Sustainable Construction and Building Materials (Springer, 2019), pp. 595–602

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Chapter 3

Silica Fume as an Activator Component

Abstract As known, NaOH and sodium silicate are widely used as alkaline activators for preparing geopolymers due to better obtained strength. Unfortunately, the manufacture of these activators is somewhat costly and requires a lot of energy. This is particularly true for sodium silicate, which is made by melting sodium carbonate and sand at 1350–1450 °C, then dissolving the glass that is created in an autoclave at 140–160 °C under the prober steam pressure. This procedure generates a lot of CO2 emissions. Employing by-product material such as silica fume (SF) as a part of activator may mitigate these problems. In this part, the earlier studies that used SF as a part of activator were collected. The effect of this activator on the properties of different geopolymer types was reviewed, summarized and analysed. Keywords Silica fume · Geopolymers · Activator component · NaOH · KOH · Sodium silicate

Assi et al. [1] activated FA geopolymer pastes with SF and NaOH. There were three types of curing named ambient curing, water curing and heat curing at 75 °C for 48 h. The results showed 505 and 565 min initial and final setting time for the paste cured at ambient temperature, respectively. The 28 days compressive strength was ~ 18.9, ~ 46.7 and ~ 15 MPa for the specimens cured at ambient temperature, heat curing and water curing, respectively. Cheng et al. [2] employed SF as an activator instead of waterglass. Different ratios of SF (2–11%) were mixed with different concentrations of NaOH (4–12 M) to prepare the alkaline activator solutions. FA geopolymer pastes were activated with SF-NaOH as well as NaOH (12 M) coupled with waterglass solution. The sealing curing was used for all specimens. The results showed a reduction in the setting time with increasing NaOH concentration when 8% SF was used. The setting time of the specimens prepared by NaOH and waterglass solution was still shorter than those prepared by SF coupled with NaOH. The results showed that the specimens activated with NaOH and waterglass solution exhibited the highest 3–90 days compressive strength followed by those activated with 8% SF coupled with 12 M NaOH. At the age of 90 days, the specimens activated with 8% SF coupled with 12 M NaOH exhibited compressive strength of 58 MPa. Wu et al. [3] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. M. Rashad, Silica Fume in Geopolymers, SpringerBriefs in Applied Sciences and Technology, https://doi.org/10.1007/978-3-031-33219-7_3

85

86

3 Silica Fume as an Activator Component

compared the compressive strength and crack width of FA/slag/calcined magnesite geopolymer concretes activated with SF coupled with NaOH with those activated with NaOH and sodium silicate solution. The specimens were cured at ambient temperature. The results showed similar compressive strength and less surface crack of specimens activated with NaOH-SF compared to those activated with NaOHsodium silicate solution. At the age of 7 days, the compressive strength of specimens activated with SF-NaOH reached 43.36 MPa. Adeleke et al. [4] prepared an activator from SF and NaOH to activate slag concretes. Different ratios of activator/precursor and SF/NaOH were used. The results showed higher workability with higher activator/precursor ratio. The compressive and tensile strengths were affected by activator/precursor ratio and SF/NaOH ratio, but activator/precursor ratio is more effective. Dai et al. [5] prepared an activator from a combination of SF (size 7.8 µm) and NaOH to activate slag (size 9 µm) pastes. The results showed longer setting time, better workability retention, lower drying shrinkage, higher mechanical strength, well-packed microstructure and fewer microcracks of the pastes activated with NaOH-SF compared to those activated with NaOH and sodium silicate solution. When Si/Na ratio was 1.2, the 2, 7 and 28 days compressive strength of specimens activated with NaOH and SF was enhanced by 20.12%, 4% and 4.9% compared to those activated with NaOH and sodium silicate solution, respectively, whilst the flexural strength was enhanced by 17.1%, 9.88% and 17.44%, respectively. They also found lower CO2 emissions and cost of SF compared to sodium silicate. Billong et al. [6] prepared an activator from a combination of SF and NaOH (10 M) with 1:1 volume proportion for slag and MK geopolymer pastes. The results showed a comparable setting time of the pastes activated with NaOH-SF compared to those activated with NaOH and sodium silicate solution. The pastes activated with NaOH-SF showed a slightly higher compressive strength than those activated with NaOH and sodium silicate solution. The MK geopolymer and AAS pastes activated with NaOH-SF showed 6.82% higher and 18% lower tensile strength than those activated with NaOH and sodium silicate solution, respectively. The MK geopolymer pastes activated with NaOH-SF showed ~ 8.7% lower water absorption than those activated with NaOH and sodium silicate solution, whilst AAS pastes showed comparable water absorption. Bernal et al. [7] reported that MK/slag geopolymer pastes activated with NaOH and SF (size 64.1 µm) showed similar reaction products to those activated with NaOH and sodium silicate solution. Oshani et al. [8] activated MK geopolymer pastes with 5–25% SF and NaOH. The curing temperatures were 60, 70 or 80 °C for 3 h, whilst Na2 O/Al2 O3 ratios were 0.8, 1 or 1.2. The results showed higher compressive strength with higher SF ratios up to 15%. Increasing SF ratios up to 25% led to a slight strength reduction. As the ratio of Na2 O/Al2 O3 increased, the compressive strength increased. Nmiri et al. [9] activated MK geopolymer pastes with sole NaOH and NaOH coupled with sodium silicate. The MK was partially replaced with 2%, 6% and 10% SF. The SF was employed as a part of the activator combined with NaOH. Compared to the specimens activated with NaOH and sodium silicate solution, the results showed that using 2% and 6% SF as a part of the activator increased the compressive strength by ~ 37.12% and ~ 71.4%, respectively, whilst

3 Silica Fume as an Activator Component

87

using 10% SF as a part of activator decreased it by 29.48%. The apparent density was reduced by 4%, 0.9% and 3.57% when 2%, 6% and 10% SF were used as a part of the activator, respectively, whilst the total porosity was decreased by 21%, 12.71% and 6.91%, respectively. Compared to the specimens activated with NaOH, using 2% and 10% SF as a part of the activator decreased the compressive strength by 17% and 57.13%, respectively, whilst using 6% SF increased it by 3.7%. Using 2% and 10% SF as a part of the activator decreased the apparent density by 2.27% and 1.82%, respectively, whilst using 6% SF increased it by 0.91%. The total porosity was increased by 3.27% and 10.13% when 6% and 10% SF was used as a part of the activator, respectively, whilst using 2% SF decreased it by 6.53%. The specimens were cured at room temperature. Bezerra et al. [10] found faster setting time of MK geopolymer paste mixture activated with NaOH and SF compared with that activated with NaOH and sodium silicate solution, whilst comparable compressive strength was obtained. Villaquirán-Caicedo and de Gutiérrez [11] prepared MK geopolymer pastes activated with potassium silicate or KOH and SF. The specimens were cured at 70 °C for 20 h. The results showed ~ 55% and ~ 26.25% higher compressive strength of the specimens activated with KOH + 50% SF and KOH + 100% SF compared to those activated with potassium silicate, respectively. A similar trend of results was obtained by Mónica and Villaquirán-Caicedo [12], but the compressive strength decreased with increasing hydration time. Table 3.1 briefs the obtained results of this part. Based on the discussion so far, it is evident that SF can be combined with NaOH or KOH to prepare an activator solution instead of using sodium silicate or potassium silicate. The obtained results mainly depend on precursor type/fineness, NaOH or KOH concentration, SF amount/fineness, testing age and curing condition. Using NaOH-SF activator instead of NaOH-sodium silicate solution one may improve workability, prolong setting time, decrease drying shrinkage, decrease microcracks, increase flexural strength, increase compressive strength, decrease CO2 emissions, decrease cost [5], decrease porosity and density [9] when slag or MK was used as a precursor. The workability improvement could be attributed to the formation of silica-based complex which can be absorbed to the grain surface and act as a superplasticizer as a result of steric repulsion [9]. The prolonged setting time could be attributed to the high Si/Na value when SF was used as a part of the activator [5]. The strength improvement may be due to the obtained densified microstructure [13]. The lower drying shrinkage could be attributed to the effect of pore refining of undissolved SF particles [5]. When FA was used as a precursor, using NaOH-SF activator instead of NaOH-waterglass solution one may decrease compressive strength and prolong setting time. The strength reduction could be related to the lower concentration of silica tetrahedron at the beginning of reaction. The longer setting time could be related to the slow dissolution of FA at the early stage caused by SF dissolution.

FA/slag/calcined magnesite

Wu et al. [3]

NaOH

NaOH

NaOH

FA

FA

NaOH

FA

Cheng et al. [2]

NaOH

FA

Assi et al. [1]

Helpful activator

Precursor

References

Table 3.1 Effect of SF as a part of activator on the properties of geopolymers

Concrete

Paste

Paste

Paste

Paste

Type

Ambient

Sealed

75 °C for 48 h

Water

Ambient

Curing condition

(continued)

Compared to NaOH and sodium silicate . Decreased surface crack . Similar compressive strength

Compared to NaOH and waterglass . Prolonged setting time . Decreased 3–90 days compressive strength

. The obtained compressive strength was ~ 46.7 MPa

. The obtained compressive strength was ~ 15 MPa

. The obtained initial and final setting time was 505 and 565 min . The obtained compressive strength was ~ 18.9 MPa

Effect

88 3 Silica Fume as an Activator Component

Precursor

Slag

Slag

References

Adeleke et al. [4]

Dai et al. [5]

Table 3.1 (continued)

NaOH

NaOH

Helpful activator

Paste

Concrete

Type

20 °C

20 °C with 90% RH

Curing condition

(continued)

Compared to NaOH and sodium silicate . Better workability . Prolonged setting time . Decreased drying shrinkage . Decreased microcracks . Increased 2, 7 and 28 days compressive strength by 20.12%, 4% and 4.9%, respectively . Increased 2, 7 and 28 days flexural strength by 17.1%, 9.88% and 17.44, respectively . Lower CO2 emissions and cost

. Workability increased with increasing activator/precursor ratio . Compressive and tensile strengths were affected by activator/precursor ratio and SF/NaOH ratio, but activator/precursor ratio is more effective

Effect

3 Silica Fume as an Activator Component 89

MK/slag

MK

Oshani et al. [8]

NaOH

NaOH

NaOH

MK

Bernal et al. [7]

NaOH

Slag

Billong et al. [6]

Helpful activator

Precursor

References

Table 3.1 (continued)

Paste

Paste

Paste

Paste

Type

60, 70 or 80 °C for 3 h

60 °C, > 90% RH for 24 h

23 °C, 70% RH

23 °C, 70% RH

Curing condition

. The obtained compressive increased with increasing SF ratio up to 15% . Increasing SF ratios up to 25% led to a slight strength reduction (continued)

Compared to NaOH and sodium silicate . Similar reaction products

Compared to NaOH and sodium silicate . Slightly increased compressive strength . Increased tensile strength by 6.82% . Decreased water absorption by ~ 8.7%

Compared to NaOH and sodium silicate . Slightly increased compressive strength . Decreased tensile strength by 18% . Comparable water absorption

Effect

90 3 Silica Fume as an Activator Component

Precursor

MK

References

Nmiri et al. [9]

Table 3.1 (continued) NaOH

Helpful activator Paste

Type Room

Curing condition

Compared to NaOH and sodium silicate . 2% and 6% SF increased compressive strength by ~ 37.12% and ~ 71.4%, respectively, whilst 10% SF decreased it by 29.48% . 2%, 6% and 10% decreased the apparent density by 4%, 0.9% and 3.57%, respectively . 2%, 6% and 10% decreased total porosity by 21%, 12.71% and 6.91% Compared to NaOH . 2% and 6% SF decreased compressive strength by 17% and 57.13%, respectively, whilst 10% increased it by 3.7% . 2% and 6% SF decreased apparent density by 2.27% and 1.82%, respectively, whilst 10% increased it by 0.91% . 2% SF decreased total porosity by 6.53%, whilst 6% and 10% SF increased it by 3.27% and 10.13%, respectively (continued)

Effect

3 Silica Fume as an Activator Component 91

Precursor

MK

MK

MK

References

Bezerra et al. [10]

Villaquirán-Caicedo and de Gutiérrez [11]

Mónica and Villaquirán-Caicedo [12]

Table 3.1 (continued)

KOH

KOH

NaOH

Helpful activator

Paste

Paste

Paste

Type

70 °C for 20 h

70 °C for 20 h

40 °C for 24 h

Curing condition

Compared to potassium silicate . Prolonged setting time (at 25 °C) . 50% and 100% SF increased the compressive strength

Compared to potassium silicate . 50% and 100% SF increased the compressive strength by ~ 55% and ~ 26.25%

. Faster setting time . Comparable compressive strength . Higher elastic modulus

Effect

92 3 Silica Fume as an Activator Component

References

93

References 1. L.N. Assi, E.E. Deaver, P. Ziehl, Using sucrose for improvement of initial and final setting times of silica fume-based activating solution of fly ash geopolymer concrete. Constr. Build. Mater. 191, 47–55 (2018) 2. Y. Cheng, P. Cong, Q. Zhao, H. Hao, L. Mei, A. Zhang, Z. Han, M. Hu, Study on the effectiveness of silica fume-derived activator as a substitute for water glass in fly ash-based geopolymer. J. Build. Eng. 51, 104228 (2022) 3. X. Wu, Y. Shen, L. Hu, Performance of geopolymer concrete activated by sodium silicate and silica fume activator. Case Stud. Constr. Mater. 17, e01513 (2022) 4. B.O. Adeleke, J.M. Kinuthia, J. Oti, M. Ebailila, Physico-mechanical evaluation of geopolymer concrete activated by sodium hydroxide and silica fume-synthesised sodium silicate solution. Materials 16(6), 2400 (2023) 5. X. Dai, S. Aydın, M.Y. Yardımcı, K. Lesage, G. De Schutter, Rheology and microstructure of alkali-activated slag cements produced with silica fume activator. Cem. Concr. Compos. 125, 104303 (2022) 6. N. Billong, J. Oti, J. Kinuthia, Using silica fume based activator in sustainable geopolymer binder for building application. Constr. Build. Mater. 275, 122177 (2021) 7. S.A. Bernal, E.D. Rodríguez, R. Mejia de Gutiérrez, J.L. Provis, S. Delvasto, Activation of metakaolin/slag blends using alkaline solutions based on chemically modified silica fume and rice husk ash. Waste Biomass Valori. 3(1), 99–108 (2012) 8. F. Oshani, A. Allahverdi, A. Kargari, N.M. Mahmoodi, Effect of preparation parameters on properties of metakaolin-based geopolymer activated by silica fume-sodium hydroxide alkaline blend. J. Build. Eng. 60, 104984 (2022) 9. A. Nmiri, M. Duc, N. Hamdi, O. Yazoghli-Marzouk, E. Srasra, Replacement of alkali silicate solution with silica fume in metakaolin-based geopolymers. Int. J. Miner. Metall. Mater. 26(5), 555–564 (2019) 10. B. Bezerra, M. Morelli, A. Luz, Effect of reactive silica sources on the properties of Nametakaolin-based geopolymer binder. Constr. Build. Mater. 364, 129989 (2023) 11. M. Villaquirán-Caicedo, R.M. de Gutiérrez, Synthesis of ceramic materials from ecofriendly geopolymer precursors. Mater. Lett. 230, 300–304 (2018) 12. M.A. Villaquirán-Caicedo, Studying different silica sources for preparation of alternative waterglass used in preparation of binary geopolymer binders from metakaolin/boiler slag. Constr. Build. Mater. 227, 116621 (2019) 13. V.R. Živica, Effectiveness of new silica fume alkali activator. Cem. Concr. Compos. 28(1), 21–25 (2006)

Chapter 4

Silica Fume as a Foaming Agent

Abstract The incorporation of foaming or blowing agent in the geopolymer can produce porous microstructure, which improves the effectiveness of its thermal insulation. Improving the thermal insulation effectiveness can save energy and absorb acoustic. The target of this part is to review, summarize and analyse the past studies focused on the effect of SF, as a foaming agent, on density, porosity, thermal conductivity, sound absorption and compressive strength of various types of geopolymer. Keywords Silica fume · Foaming agent · Thermal conductivity · Porosity · Density · Sound absorption

Delair et al. [1] reported that the incorporation of SF into MK geopolymer pastes activated with NaOH or KOH dissolved in sodium silicate or potassium silicate can produce insulating material with thermal conductivity < 0.2 W/mK. Youmoue et al. [2] employed 13% SF into MK geopolymer pastes activated with NaOH and sodium silicate solution as a foaming agent. The specimens were cured at 70 °C for < 24 h. The incorporation of SF increased the porosity from 15% (for the control) to 68%. The incorporation of SF decreased the bulk density from 1.78 g/cm3 (for the control) to 0.65 g/cm3 , whilst the compressive strength was decreased from 66 MPa (for the control) to 1 MPa. Prud’homme et al. [3] reported that 18% SF can be employed as a foaming agent for different types of clay (MK, kaolin, illite and montmorillonite) geopolymer pastes activated with KOH and potassium silicate solution. The specimens were cured at 70 °C for 4 h. Prud’homme et al. [4] reported that SF (5– 18%) can be employed as a foaming agent for MK geopolymer pastes activated with KOH and potassium silicate solution. The specimens were cured at 70 °C for 4 h. The obtained thermal conductivity results were in the range of 0.24–0.22 W/mK. Sawan et al. [5] prepared a foaming agent from SF/MK activated with NaOH and sodium silicate solution. The specimens were cured at 70 °C for 24 h. The obtained apparent porosity was 22%, 25% and 28% when SF/MK ratios were 2.5%/97.5%, 5%/95% and 7.5%/92.5%, respectively, whilst the bulk densities were 1.353, 1.077 and 0.96 g/cm3 , respectively, and the compressive strength values were 10, 9.4 and © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. M. Rashad, Silica Fume in Geopolymers, SpringerBriefs in Applied Sciences and Technology, https://doi.org/10.1007/978-3-031-33219-7_4

95

96

4 Silica Fume as a Foaming Agent

6.5 MPa, respectively. Henon et al. [6] reported that SF can be employed as a foaming agent for MK geopolymer pastes activated with KOH and potassium silicate solution. The specimens were cured at different temperatures (25, 50 and 70 °C) for different periods. The obtained apparent densities were in the range of 0.85–0.4 g/cm3 , whilst the thermal conductivities were in the range of 0.35–0.12 W/mK. Škvára et al. [7] employed 5% and 10% SF into FA geopolymer pastes activated with NaOH and waterglass solution as a foaming agent. Compared to the specimens foamed by Al powder, the specimens foamed by SF showed higher compressive strength and higher thermal conductivity (~0.105 compared to ~ 0.095 W/mK), but similar pore sizes were observed. They noted that the foamed specimens can resist elevated temperature up to 1000 °C. Luna-Galiano [8] employed SF as a foaming agent for FA geopolymer pastes activated with KOH or potassium silicate. The FA was partially replaced with SF at ratios of 20% and 40%. The setting temperature was 40 or 70 °C. The incorporation of 20% and 40% SF increased the open porosity from 11.5% (for the control) to 18.1% and 28.9%, respectively, as shown in Fig. 4.1, whilst the density was reduced from 1.4 g/cm3 (for the control) to 1.17 and 1.07 g/cm3 , respectively, the 28 days compressive strength was decreased from ~ 12.1 MPa (for the control) to ~ 8.8 MPa and ~ 7 MPa, respectively, and the noise reduction coefficient was increased from 0.08 (for the control) to 0.14 and 0.21, respectively, when setting temperature was 40 °C and alkaline activator was potassium silicate. When the setting temperature was 70 °C and the alkaline activator was potassium silicate, the incorporation of 20% SF increased the open porosity from 11.5% (for the control) to 36.2%, whilst the density was reduced from 1.4 g/m3 (for the control) to 0.97 g/cm3 , the 28 days compressive strength was decreased from ~ 12.1 MPa (for the control) to ~ 4 MPa, and the noise reduction coefficient was increased from 0.08 (for the control) to 0.23. When the setting temperature was 40 °C and the alkaline activator was KOH, the incorporation of 20% SF increased the open porosity from 11.5% (for the control) to 20.1%, whilst the density was reduced from 1.4 g/m3 (for the control) to 1.12 g/cm3 , the 28 days compressive strength was decreased from ~ 12.1 MPa (for the control) to ~ 6.25 MPa, and the noise reduction coefficient was increased from 0.08 (for the control) to 0.16. The results revealed that higher SF ratio and setting temperature led to higher sound absorption. Liu et al. [9] employed SF as a foaming agent for FA geopolymer pastes activated with either NaOH or waterglass. The FA was partially replaced with 15%, 30% and 45% SF. The specimens were cured at 80 °C for 24 h, then at ambient temperature. The results showed a reduction in the compressive strength and density, whilst the porosity was increased with the incorporation of foaming agent (SF). The porosity reached to ~ 41.25% and ~ 31.25% with the incorporation of 45% SF for specimens activated with NaOH and waterglass, respectively, whilst the density reached ~ 0.98 g/cm3 and ~ 1.29 g/cm3 , respectively. When waterglass was used as an activator, the 28 days compressive strength was decreased by ~ 39%, ~ 55.8% and 61.41% with the incorporation of 15%, 30% and 45% SF, respectively, whilst it was decreased by ~ 50%, ~ 80% and 84.7%, respectively, when NaOH was used as an activator. When waterglass was used as an activator, the incorporation of 45% SF increased the porosity by 2.63 times, whilst it was increased by 3.02 times when NaOH was used as an activator. When waterglass

4 Silica Fume as a Foaming Agent

Without SF cured at 40 oC

Containing 20% SF cured at 40 oC

97

Containing 40% SF cured at 40 oC

Containing 20% SF cured at 70 oC

Fig. 4.1 View of sample without/with SF foaming agent cured at different temperatures [8]. Reprinted with permission from Elsevier publisher

was used as an activator, the incorporation of 45% SF decreased the density by ~ 16% times, whilst it was decreased by ~ 36.5% times when NaOH was used as an activator. The results also showed an increase in the absorption of sound with the incorporation of SF, which led to good sound insulation. When NaOH was used as an alkaline activator, the incorporation of 15%, 30% and 45% SF increased the mean sound insulation value by 10.37%, 18.32% and 25.26%, respectively, whilst it was increased by 15.1%, 18.52% and 33.13% when waterglass was used as an alkaline activator, respectively. The results revealed that using NaOH as an activator is more effective than waterglass in thermal insulation and sound absorption applications. Shakouri et al. [10] prepared a foaming agent from SF and NaOH by thermal treatment. The SF was mixed with different concentrations of NaOH (4–16 M). The specimens were cured at different temperatures (60, 80 and 100 °C) and then heated at different temperatures (200–500 °C). The results showed that higher heat treatment and activator concentration led to lower density. The obtained thermal conductivity and compressive strength were in the range of 0.04–0.1 W/mK and 0.15–0.75 MPa, respectively. The high porosity and low density of < 94% and > 85 kg/m3 can be obtained, respectively. Table 4.1 briefs the obtained results of this part. Based on the discussion so far, it is evident that SF can be used as a foaming or blowing agent to produce lightweight and thermal insulating composites similar to other foaming agent types [11–14]. The properties of the obtained composites depend mainly on the precursor type/fineness, activator concentration and type, SF

Precursor

MK

MK

MK

MK

MK

FA

References

Delair et al. [1]

Youmoue et al. [2]

Prud’homme et al. [4]

Sawan et al. [5]

Henon et al. [6]

Škvára et al. [7]

13

NA

SF (%)

NaOH and waterglass solution

5 and 10

KOH and potassium silicate solution 18

KOH and potassium silicate solution 2.5–7.5

KOH and potassium silicate solution 5–18

NaOH and sodium silicate solution

NaOH or KOH and sodium silicate or potassium silicate

Activator

Table 4.1 Effect of SF as a foaming agent on the properties of geopolymers

Paste

Paste

Paste

Paste

Paste

Paste

Type

80 °C for 12 h

25, 50 and 70 °C

70 °C for 24 h

70 °C for 4 h

70 °C < 24 h

70 °C

Curing condition

(continued)

. The obtained thermal conductivity ~ 0.105 W/mK . Resist elevated temperature up to 1000 °C

. The obtained thermal conductivity 0.35–0.12 W/mK . The obtained apparent density 0.85–0.4 g/cm3

. The obtained porosity 22–28% . The obtained bulk density 0.96–1.353 g/cm3 . The obtained compressive strength 6.5–10 MPa

. The obtained thermal conductivity 0.24–0.22 W/mK

. The obtained porosity 68% . The obtained bulk density 0.65 g/cm3 . The obtained compressive strength 1 MPa

. The obtained thermal conductivity < 0.2 W/mK

Main results

98 4 Silica Fume as a Foaming Agent

KOH

Potassium silicate solution

Potassium silicate solution

Potassium silicate solution

FA

FA

FA

FA

Luna-Galiano [8]

Activator

Precursor

References

Table 4.1 (continued)

40

20

20

20

SF (%)

Paste

Paste

Paste

Paste

Type

40

70

40

40

Curing condition

(continued)

. The obtained open porosity 28.9% . The obtained density 1.07 g/cm3 . The obtained compressive strength ~ 7 MPa . The noise reduction coefficient increased by ~ 2.63 times

. The obtained open porosity 36.2% . The obtained density 0.97 g/cm3 . The obtained compressive strength ~ 4 MPa . The noise reduction coefficient increased by ~ 2.88 times

. The obtained open porosity 18.1% . The obtained density 1.17 g/cm3 . The obtained compressive strength ~ 8.8 MPa . The noise reduction coefficient increased by 1.75 times

. The obtained total porosity 20.1% . The obtained density 1.12 g/cm3 . The obtained compressive strength ~ 6.25 MPa . The noise reduction coefficient increased by 2.0 times

Main results

4 Silica Fume as a Foaming Agent 99

Precursor

FA

–

References

Liu et al. [9]

Shakouri et al. [10]

Table 4.1 (continued)

100

15, 30 and 45

Waterglass

NaOH

15, 30 and 45

SF (%)

NaOH

Activator

Paste

Paste

Paste

Type

60, 80 and 100 °C

80 °C for 24 h

80 °C for 24 h

Curing condition

. The obtained thermal conductivity 0.04–0.1 W/mK . The obtained porosity < 94% . The obtained density > 85 kg/m3

. Increased porosity up to 2.63 times . Decreased compressive strength up to 61.41% . Decreased density up to ~ 16% . Increased mean sound insulation value by 15.1, 18.52 and 33.13%

. Increased porosity up to 3.02 times . Decreased compressive strength up to 84.7% . Decreased density up to ~ 36.5% . Increased mean sound insulation value by 10.37, 18.32 and 25.26%

Main results

100 4 Silica Fume as a Foaming Agent

References

101

amount/fineness and curing condition. The formation of the foam is due to releasing H2 by silicon (from SF) oxidation and water reduction producing Si(OH)4 as follows: Si + 4H2 O → Si(OH)4 + 2H2 [4]. When MK was used as a precursor, the thermal conductivity of 0.24–0.22, 0.35– 0.12 W/mK, bulk density of 0.84–0.4, 0.96–1.35 g/cm3 and porosity of 22–68% can be obtained when SF was employed as a foaming agent [1, 2, 4–6]. Prud’homme et al. [3] related this improvement in thermal insulation to the formation of pores due to the dihydrogen (H2 ) formed by water (Si0 → 4e− + Si4+ ) and silicon oxidation (4e− + 4H2 O → 4OH− + 2H2 ) to form Si(OH)4 (Si0 + 4H2 O → Si(OH)4 + 2H2 ). The production of H2 can act as a foaming agent. Henon et al. [6] related the improvement in the thermal conductivity to the porosity generated from the liberated molecular hydrogen formed from the oxidation of free silicon inside SF. When FA was used as a precursor, total porosity of 20.1%, open porosity of 18.1%, 36.2%, 28.9%, porosity of ~ 31.25%, ~ 41.25% and density of 1.12, 1.17, 1.07, ~ 1.29 and ~ 0.98 g/cm3 can be obtained when SF was employed as a foaming agent [8, 9]. The thermal conductivity, porosity and density of SF used as a foaming agent can reach as low as 0.4–0.1 W/mK, < 94% and > 85%, respectively [10].

References 1. S. Delair, É. Prud’homme, C. Peyratout, A. Smith, P. Michaud, L. Eloy, E. Joussein, S. Rossignol, Durability of inorganic foam in solution: the role of alkali elements in the geopolymer network. Corros. Sci. 59, 213–221 (2012) 2. M. Youmoue, R.T. Tene Fongang, A. Gharzouni, R.C. Kaze, E. Kamseu, V.M. Sglavo, I. Tonle Kenfack, B. Nait-Ali, S. Rossignol, Effect of silica and lignocellulosic additives on the formation and the distribution of meso and macropores in foam metakaolin-based geopolymer filters for dyes and wastewater filtration. SN Appl. Sci. 2, 1–20 (2020) 3. E. Prud’Homme, P. Michaud, E. Joussein, C. Peyratout, A. Smith, S. Rossignol, In situ inorganic foams prepared from various clays at low temperature. Appl. Clay Sci. 51(1–2), 15–22 (2011) 4. E. Prud’homme, P. Michaud, E. Joussein, C. Peyratout, A. Smith, S. Arrii-Clacens, J.-M. Clacens, S. Rossignol, Silica fume as porogent agent in geo-materials at low temperature. J. Eur. Ceram. Soc. 30(7), 1641–1648 (2010) 5. S.A. Sawan, M. Zawrah, R. Khattab, A.A. Abdel-Shafi, In-situ formation of geopolymer foams through addition of silica fume: preparation and sinterability. Mater. Chem. Phys. 239, 121998 (2020) 6. J. Henon, A. Alzina, J. Absi, D.S. Smith, S. Rossignol, Potassium geopolymer foams made with silica fume pore forming agent for thermal insulation. J. Porous Mater. 20(1), 37–46 (2013) 7. Š František, Š Rostislav, T. Zdenˇek, S. Petr, Š Vít, Z. Zuzana, Preparation and properties of fly ashbased geopolymer foams. Ceram. Silik. 58(3), 188–197 (2014) 8. Y. Luna-Galiano, C. Leiva, C. Arenas, C. Fernández-Pereira, Fly ash based geopolymeric foams using silica fume as pore generation agent. Phys. Mech. Acoust. Prop. J. Non-Cryst. Solids 500, 196–204 (2018) 9. X. Liu, C. Hu, L. Chu, Microstructure, compressive strength and sound insulation property of fly ash-based geopolymeric foams with silica fume as foaming agent. Materials 13(14), 3215 (2020) 10. S. Shakouri, Ö. Bayer, S.T. Erdo˘gan, Development of silica fume-based geopolymer foams. Constr. Build. Mater. 260, 120442 (2020)

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11. Z. Zhang, J.L. Provis, A. Reid, H. Wang, Geopolymer foam concrete: an emerging material for sustainable construction. Constr. Build. Mater. 56, 113–127 (2014) 12. M. Morsy, A.M. Rashad, H. Shoukry, M. Mokhtar, Potential use of limestone in metakaolinbased geopolymer activated with H3 PO4 for thermal insulation. Constr. Build. Mater. 229, 117088 (2019) 13. A.M. Rashad, M. Gharieb, H. Shoukry, M. Mokhtar, Valorization of sugar beet waste as a foaming agent for metakaolin geopolymer activated with phosphoric acid. Constr. Build. Mater. 344, 128240 (2022) 14. A.M. Rashad, A.M. Abd El Fattah, W. Morsi, Aluminum dross for thermal insulation and acoustic absorption of alkali-activated slag mortars. ACI Mater. J. 119(4), 151–164 (2022)

Chapter 5

General Perspective and Suggestions for Upcoming Work

Abstract In spite of silica fume (SF) can be incorporated into different geopolymer types as a part of precursor, as a part of activator or as a foaming agent, most of the earlier studies employed SF as a part of cementitious material (as a part of precursor or an additive) (~ 74.1%), whilst employing it as a part of activator came in the second place (14.81%). Finally, employing SF as a foaming agent came in the last place (11.11%). In this part, the percentage of studies about the effect of SF as a part of precursor on each property of geopolymers was established and compared. The effect of SF in its three forms (part of precursor, part of activator and foaming agent) on the various geopolymer types was summarized. Keywords Silica fume · Cementitious material · Activator component · Foaming agent · Statistics

Generally, SF can be employed in geopolymers in three primary forms: as a part of a precursor or an additive, as a component of the activator and as a foaming agent. In view of Fig. 5.1, numerous of the past studies (74.07%) favoured using SF as a part of a precursor, whilst about 14.81% and 11.11% of them favoured using SF as a component of activator and as a foaming agent, respectively. The paste studies agreed that the incorporation of SF in the slag or MK geopolymer mixtures increased the workability even though the SF is finer than the slag of MK. This improvement is attributed to the smooth spherical SF particles compared to the jagged and irregular shape of slag particles or the platelet MK particles. Conversely, the incorporation of SF in FA geopolymer mixtures decreased the workability due to the geometry of FA particles that can perform as ball bearings that have a positive effect on the mixture rheology. No clear trend can be drawn about the effect of SF on setting time due to the conflicting results. By presenting the compressive strength results of slag (Fig. 2.6), FA (Fig. 2.11), MK (Fig. 2.16) and slag/FA (Fig. 2.21) geopolymers in one Fig. (Fig. 5.2). One should be aware that, even though there are conflicting results about the effect of SF on geopolymers compressive strength, in most cases, the incorporation of SF up to 15%, 10%, 20% and 10% has a positive effect on the compressive strength of slag, FA, MK and slag/FA geopolymers, respectively. Regardless of the precursor © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. M. Rashad, Silica Fume in Geopolymers, SpringerBriefs in Applied Sciences and Technology, https://doi.org/10.1007/978-3-031-33219-7_5

103

104

5 General Perspective and Suggestions for Upcoming Work

Fig. 5.1 Percentage of studies about used SF as a part of precursor, as a part of an activator an as a foaming agent

type, numerous past studies (about 43.59%) confirmed higher compressive strength with the incorporation of SF, whilst only about 16% confirmed lower compressive strength. However, about 41% of these studies indicated that the incorporation of SF may decrease or increase the compressive strength (Fig. 5.3). This mainly depends on precursor type/fineness, activator concentration and type, activator/binder ratio, testing age, curing condition, SF amount/fineness and Si/Al molar ratio. There are numerous studies confirmed lower water absorption and porosity of geopolymer with the incorporation of SF up to 15%. The incorporation of SF up to 15% can decrease leaching, decrease efflorescence and increase freezing/thawing resistance, whilst SF up to 10% can decrease charge passed and increase surface resistance. The incorporation of SF up to 15% increased fire resistance up to 800 °C, but at 1000 °C showed a negative effect in slag geopolymer. The incorporation of SF up to 25% may decrease or increase MK geopolymer fire resistance according to activator concentration (i.e. Si/Al). According to the current survey, the majority of earlier studies on the effect of SF, which was used as a part of precursor, on the compressive strength of geopolymers focused on slag precursor (around 26.19%), followed by FA precursor (around 21.43%), MK precursor (around 19.05%) and slag/FA precursor (around 19.053%), whilst other precursor types received less attention such as FA/cement (around 2.38%), FA/CAC (around 2.38%), slag/rockwool (around 2.38%), slag/red mud (around 2.38%), OBA/kaolin (around 2.38%) and calcined lithium slag (around 2.38%) as shown in Fig. 5.4.

5 General Perspective and Suggestions for Upcoming Work

Relative compressive strength (%)

700

105 Slag FA MK Slag/FA FA/cement FA/CAC Slag/rockwool Slag/red mud OBA/kaolin Calcined lithium slag

600 500 400 300 200 100 0 0

10

20

30

40

50

60

70

80

90

100

SF (%) Fig. 5.2 Effect of SF on geopolymers compressive strength [1–42]

Fig. 5.3 Percentage of studies about the effect of SF on geopolymers compressive strength

As a matter of fact, about 38.52%, 12.59%, 8.89%, 8.15% and 5.19% of the cited references that used SF as a part of precursor focused on compressive strength, workability, flexural strength, water absorption/porosity and setting time, respectively, as shown in Fig. 5.5, whilst some properties received less attention such as fire resistance (3.7%), splitting tensile strength (3.7%), chemical resistance (2.22%),

106

5 General Perspective and Suggestions for Upcoming Work

Fig. 5.4 Relative research number of geopolymers based on different types of the precursor containing SF

freezing/thawing resistance (2.22%), abrasion resistance (2.22%), drying shrinkage (2.22%), toughness (1.48%), elastic modulus (1.48%), leaching (1.48%), efflorescence (1.48%), seawater attack/simulated tidal resistance (0.74%), wetting/drying resistance (0.74%), surface resistance (0.74%), carbonation resistance (0.74%) and thermal shock resistance (0.74%). Thus, it is recommended to increase the number of studies to cover this shortage. SF can be used with NaOH instead of sodium silicate or with KOH instead of potassium silicate to activate different precursor types. The obtained results mainly depend on precursor type/fineness, NaOH or KOH concentration, SF amount/fineness, testing age and curing condition. When slag or MK was used as a precursor, using NaOH-SF activator instead of NaOH-sodium silicate one showed benefits in workability, strength, drying shrinkage, microcracks, CO2 emissions and cost. Contrarily, when FA was used as a precursor, using NaOH-SF activator instead of NaOH-sodium silicate one showed an adverse effect on strength. SF can be used as a foaming agent for MK and FA geopolymers. The obtained results mainly depend on precursor type/fineness, activator concentration and type, SF amount/fineness and curing condition. Low thermal conductivity, low density and high porosity can be obtained by employing SF as a foaming agent.

References

107

Fig. 5.5 Percentage of studies about the effect of SF as a part of precursor on properties of geopolymers

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9. P. Kathirvel, G. Murali, Effect of using available GGBFS, silica fume, quartz powder and steel fibres on the fracture behavior of sustainable reactive powder concrete. Constr. Build. Mater. 375, 130997 (2023) 10. A. Wetzel, B. Middendorf, Influence of silica fume on properties of fresh and hardened ultrahigh performance concrete based on alkali-activated slag. Cem. Concr. Compos. 100, 53–59 (2019) 11. C.S. Thunuguntla, T.G. Rao, Effect of mix design parameters on mechanical and durability properties of alkali activated slag concrete. Constr. Build. Mater. 193, 173–188 (2018) 12. J.I. Escalante-Garcia, V.M. Palacios-Villanueva, A.V. Gorokhovsky, G. Mendoza-Suárez, A.F. Fuentes, Characteristics of a NaOH-activated blast furnace slag blended with a fine particle silica waste. J. Am. Ceram. Soc. 85(7), 1788–1792 (2002) 13. Y. Zhu, M.A. Longhi, A. Wang, D. Hou, H. Wang, Z. Zhang, Alkali leaching features of 3-yearold alkali activated fly ash-slag-silica fume: for a better understanding of stability. Compos. B Eng. 230, 109469 (2022) 14. Y. Liu, C. Shi, Z. Zhang, N. Li, D. Shi, Mechanical and fracture properties of ultra-high performance geopolymer concrete: effects of steel fiber and silica fume. Cem. Concr. Compos. 112, 103665 (2020) 15. Z. Zhang, L. Li, X. Ma, H. Wang, Compositional, microstructural and mechanical properties of ambient condition cured alkali-activated cement. Constr. Build. Mater. 113, 237–245 (2016) 16. P. Cong, L. Mei, Using silica fume for improvement of fly ash/slag based geopolymer activated with calcium carbide residue and gypsum. Constr. Build. Mater. 275, 122171 (2021) 17. H.E. Elyamany, M. Abd Elmoaty, A.M. Elshaboury, Setting time and 7-day strength of geopolymer mortar with various binders, Constr. Build. Mater. 187, 974–983 (2018) 18. H. Alanazi, J. Hu, Y.-R. Kim, Effect of slag, silica fume, and metakaolin on properties and performance of alkali-activated fly ash cured at ambient temperature. Constr. Build. Mater. 197, 747–756 (2019) 19. P. Duan, C. Yan, W. Zhou, Compressive strength and microstructure of fly ash based geopolymer blended with silica fume under thermal cycle. Cem. Concr. Compos. 78, 108–119 (2017) 20. F. Okoye, J. Durgaprasad, N. Singh, Effect of silica fume on the mechanical properties of fly ash based-geopolymer concrete. Ceram. Int. 42(2), 3000–3006 (2016) 21. F. Wang, X. Sun, Z. Tao, Z. Pan, Effect of silica fume on compressive strength of ultra-highperformance concrete made of calcium aluminate cement/fly ash based geopolymer. J. Build. Eng. 62, 105398 (2022) 22. H.A. Alcamand, P.H. Borges, F.A. Silva, A.C.C. Trindade, The effect of matrix composition and calcium content on the sulfate durability of metakaolin and metakaolin/slag alkali-activated mortars. Ceram. Int. 44(5), 5037–5044 (2018) 23. U. Javed, F.U.A. Shaikh, P.K. Sarker, Microstructural investigation of lithium slag geopolymer pastes containing silica fume and fly ash as additive chemical modifiers. Cem. Concr. Compos. 134, 104736 (2022) 24. A.M. Rashad, Influence of different additives on the properties of sodium sulfate activated slag. Constr. Build. Mater. 79, 379–389 (2015) 25. D.M. Kanaan, A.M. Soliman, Performance of one-part alkali-activated self-consolidated mortar. ACI Mater. J. 119(2) (2022) 26. S. Jena, R. Panigrahi, Performance evaluation of sustainable geopolymer concrete produced from ferrochrome slag and silica fume. Eur. J. Environ. Civ. Eng. 26(11), 5204–5220 (2022) 27. P. Sukontasukkul, P. Chindaprasirt, P. Pongsopha, T. Phoo-Ngernkham, W. Tangchirapat, N. Banthia, Effect of fly ash/silica fume ratio and curing condition on mechanical properties of fiber-reinforced geopolymer. J. Sustain. Cem. Based Mater. 9(4), 218–232 (2020) 28. R.P. Batista, A.C.C. Trindade, P.H. Borges, F. de Andrade Silva, Silica fume as precursor in the development of sustainable and high-performance MK-based alkali-activated materials reinforced with short PVA fibers. Front. Mater. 6, 77 (2019) 29. A.M. Rashad, S.R. Zeedan, Effect of silica fume and activator concentration on metakaolin geopolymer exposed to thermal loads. Mater. J. (2022)

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Chapter 6

General Remarks

Abstract Herein, the incorporation of SF as a part of a precursor, as a part of activator and as a foaming agent for geopolymers has been comprehensively reviewed, summarized and analysed. The main outcomes can be briefed as follows.

1.

2. 3.

4.

5.

6.

7.

8. 9.

The incorporation of SF showed a positive effect on the workability of slag and MK geopolymer mixtures but showed an adverse effect on the workability of FA ones. No clear effect of SF on the setting time of geopolymers due to varying results. The incorporation of SF in geopolymer may increase or decrease the density and splitting tensile strength. This mainly depends on the precursor type, amount of SF and curing temperature. Generally, the mechanical strength and other properties were affected by precursor type/fineness, SF amount/fineness, activator concentration and type, activator/binder ratio, testing age, Si/Al ratio and curing condition. Despite there are conflicting results about the effect of SF on AAS matrices compressive strength, most of these results showed a positive effect. On the whole, it is better not to increase the proportion of SF by more than 15% to obtain better strength. Despite there are conflicting results about the effect of SF on FA geopolymers compressive strength, it is better not to increase the proportion of SF more than 10% to obtain better strength. Despite there are conflicting results about the effect of SF on MK geopolymers compressive strength, it is better not to increase the proportion of SF by more than 20% to obtain better strength. Most studies found a better effect of SF on slag/FA geopolymers compressive strength. It is better not to increase the proportion of SF by more than 10%. Despite there are conflicting results about the effect of SF on geopolymers flexural strength, most of these results showed a positive effect. It is better not to increase the proportion of SF by more than 30%.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. M. Rashad, Silica Fume in Geopolymers, SpringerBriefs in Applied Sciences and Technology, https://doi.org/10.1007/978-3-031-33219-7_6

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10. No clear trend can be drawn from the effect of SF on elastic modulus, toughness, abrasion resistance, carbonation resistance, drying shrinkage, surface resistance, wetting/drying resistance, seawater attack resistance, simulated tidal resistance, charge passed, chemical resistance and thermal shock resistance due to the limited number of the available studies. 11. There are conflicting results about the effect of SF on geopolymers water absorption and porosity, of which 63.63% of them showed a positive effect, whilst about 27.27% of them showed a negative effect. 12. The incorporation of SF decreased leaching and efflorescence due to the reduction in the number of unreacted sodium particles and pores. 13. Fire resistance of geopolymers including SF mainly depended on the precursor type/fineness, SF amount/fineness, activator concentration and type, activator/binder ratio, testing age, Si/Al ratio and curing condition. When slag was used as a precursor, the incorporation of SF has a positive effect on fire resistance up to 800 °C, whilst it has an adverse effect at 1000 °C. When MK was used as a precursor, the incorporation of SF may increase or decrease fire resistance. This mainly depended on activator concentration (i.e. Si/Al ratio). When FA/ladle furnace slag was used as a precursor, the addition of 3% SF has a positive effect on fire resistance up to 1000 °C due to its high Si and fineness, whilst it has a negative effect at 1100 °C due to crack formation and higher thermal shrinkage degree. 14. The positive effect of SF on durability and mechanical properties could be attributed to the filling effect of SF on pores that can act as macroaggregates and densify the microstructure and the nucleation sites. On the contrary, the negative effect of SF could be attributed to the increase of fine particles and silica ratio that may lead to the increase in the number of unreacted particles. The excessive SiO2 amount led to cracking and expansion. The incorporation of SF led to a reduction in the alkalinity which therefore decreased the dissolution. 15. SF can be combined with NaOH instead of sodium silicate or with KOH instead of potassium silicate to activate different types of precursor. Using NaOH-SF activator instead of NaOH-sodium silicate one may improve workability, prolong setting time, decrease drying shrinkage, decrease microcracks, increase flexural strength, decrease porosity, increase compressive strength, decrease density, decrease CO2 emissions and decrease cost when slag or MK was used as a precursor. When FA was used as a precursor, using NaOH-SF activator instead of NaOH-waterglass one may decrease compressive strength and prolong setting time. 16. SF can be used as a foaming agent for MK and FA geopolymers. The properties of the obtained composites depended mainly on the precursor type/fineness, activator concentration and type, SF amount/fineness and curing condition. When MK was used as a precursor, thermal conductivity of 0.24–0.22, 0.35– 0.12 W/mK, bulk density of 0.84–0.4, 0.96–1.35 g/cm3 and porosity of 22–28% can be obtained when SF was employed as a foaming agent. When FA was used as a precursor, total porosity of 20.1%, open porosity of 18.1, 36.2, 28.9% and density of 1.12, 1.17 and 1.07 g/cm3 can be obtained when SF was employed

6 General Remarks

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as a foaming agent. The thermal conductivity, porosity and density of SF used as a foaming agent can reach as low as 0.4–0.1 W/mK, < 94% and > 85%, respectively.