Low Calcium Fly Ash/Slag Geopolymer: History
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Subjects: Construction & Building Technology
Contributor:
Salem Aldawsari

Geopolymer has a lower footprint in terms of CO2 emissions and has been considered as an alternative for ordinary portland cement (OPC), which is known for its significant contribution to carbon dioxide emissions.

  • geopolymer
  • alkali activated
  • fly ash
  • slag

1. Introduction

Building materials have evolved over centuries during the history of construction to improve various housing needs and to meet contemporary demands. One of these evolving materials is concrete, which has survived for centuries due to its high performance and long lifespan. Concrete is a composite material, primarily made from ordinary Portland cement, water, coarse aggregate, and fine aggregate. Nowadays, Portland cement is the main binder for ordinary concrete (OPC) and it has been produced extensively as it is considered one of the most dominant binders in the building industry. In the nineteenth century, when producers and consumers demanded strength and stabilization despite their pronounced environmental effects, Portland cement was the breakthrough technology and contributed to advances in the field of materials science [1]. The excessive production of Portland cement contributes to high amounts of carbon dioxide (CO2) being released into the atmosphere. Carbon dioxide is a notable pollutant and contributes approximately 0.95 tons of CO2 emissions for each ton of Portland cement produced [2]. The Portland cement industry contributes significantly to CO2 emissions globally, with values ranging from 5% to 7% [3]. Although the demand for Portland cement continues to exist, concern about environmental issues is rising, and the affected industries are currently identifying alternative solutions in the light of global warming [4].
Throughout the past decades, researchers have shifted more toward sustainable materials through either the partial or full replacement of OPC with more environmentally friendly alternatives. Some of the most promising alternatives, which may replace significant volumes of Portland cement in the future, are geopolymer materials due to their low shrinkage, sulfate resistance, early strength gain, corrosion resistance, and long-term properties [5]. In the 1970s, Joseph Davidovits [6] developed and named geopolymer; however, the constituents of similar materials have evolved since the 1950s in the Soviet Union, where the term “soil cement” was used [7]. Geopolymer materials consist primarily of an aluminosilicate source and liquid alkaline constituents. Alkaline liquids are used to activate the aluminosilicate materials to form three-dimensional structure products. Aluminum and silicate exist abundantly in nature or can easily be obtained from industrial by-products such as fly ash, blast furnace slag, rice husk ash, and other materials that offer sufficient alumina and silica content to provide pozzolanic properties. Alkaline solutions such as sodium hydroxide (NaOH), sodium silicate (Na2SiO3), potassium hydroxide (KOH), and potassium silicate (K2SiO3) are commonly used activators. Alkaline activators are used to liberate silicon (Si) and aluminium (Al) from the aluminosilicate species. When Si and Al are released, a supersaturated aluminosilicate solution is created, which subsequently contributes to gel formation with large complex networks [8]. Davidovits [9] defined the three-dimensional structure of silico-aluminate by semi-crystalline to amorphous of types poly(sialate) (-Si-O-Al-O-), poly(sialate-siloxo) (-Si-O-Al-O-Si-O-), poly(sialate-disiloxo) (-Si-O-Al-O-Si-O-Si-O-), and he suggested a general empirical formula of polysialate:
where M is the alkaline element, n is the degree of polymerization, and z takes on one of the following values—1, 2, or 3. Geopolymer materials have been found to possess similar or superior properties (strength, shrinkage, fire resistance, and chemical resistance) when compared to ordinary Portland cement [10][11][12][13][14]. Though geopolymer materials have been heavily researched throughout the recent decades and new developments have led to significant improvements, the lack of standards and long-term experience have increased the uncertainty about the ability of geopolymers to survive for a long-term lifespan.
Although OPC has been researched and successfully used for almost 170 years, the molecular-scale mechanism that occurs during OPC hardening is still not fully understood [15]. Portland cement had been studied and researched for decades until it advanced to what is seen today in industrial, residential, and commercial buildings, and yet it has an established reputation and researchers have obtained a well-developed understanding of its characteristics. As geopolymer research has taken many different directions and paths over the years, it is crucial to reevaluate the state of the art and comprehensively summarize the most significant findings.
Fly ash and slag have been used extensively as raw materials in geopolymers, either in combination with each other or separately. Because the presented work reflects on fly ash and slag as the primary binders, a brief introduction to these two materials in regard to their production, as well as their physical and compositional properties, is presented below. Fly ash is a by-product formed during the burning process of pulverized coal for the generation of electricity and has pozzolanic properties that make it suitable for use in concrete. Fly ash is defined by ASTM-International [16] as “finely divided residue that results from the process of combustion of ground or powdered coal and that is transported by flue gases”. Because fly ash particles solidify in the air, where they seek the lowest energy state, they are spherical in nature, as shown in Figure 1a, and fine spherical particles are separated from flue gases by collective systems or electrostatic participators [17].
Materials 15 00876 g001 550
Figure 1. Particle shapes of (a) fly ash (Reprinted with permission from Ref. [18]. Copyright 2012 Ann E. Benbow) and (b) ground-granulated blast-furnace slag (GGBFS) (Reprinted with permission from Ref. [19]. Copyright 2018 Elsevier).
Fly ash mainly consists of silicon (SiO2), aluminum (Al2O3), iron (Fe2O3), and calcium oxide (CaO), as well as some minor components such as potassium, magnesium, sodium, sulfur, and titanium. The most common fly ashes are classified by ASTM-International [20] as class F fly ash and class C fly ash. Class F fly ash has a low calcium oxide (CaO) content, which differentiates it from class C fly ash, with a higher amount of CaO. The CaO content for class F fly ash should not exceed a maximum of 18%, whereas class C may exceed this value, according to [20]. Both classes must contained a minimum of 50% silica, aluminum, and iron contents, and a maximum of 5%, 3%, and 6% for sulfur trioxide (SO3), moisture content, and loss on ignition, respectively. These values and limits do not predict the performance of the fly ash, but rather help in characterizing the uniformity and the composition of the material [20].
Steel slag is formed during the manufacturing of iron and steel as a by-product that mainly consists of SiO2, Al2O3, Fe2O3, CaO, magnesium oxide (MgO), and minor amounts of sulfur trioxide (SO3), titanium dioxide (TO2), and potassium oxide (K2O). The formation of steel slag occurs during iron manufacturing in a basic oxygen furnace (BOF) or during steel production from scrap in an electric arc furnace (EAF). In a BOF, oxygen is used to expel impure components such as silicon, carbon, phosphorus, and manganese. These impurities then join with lime and dolomitic lime to create slag. In EAF, liquid slags floats on top of the molten steel, which can be separated and dispersed by tilting the EAF such that the upper layer of slag leaves the EAF, whereas the molten steel remains in the vessel. The molten material is skimmed off and left to cool down to become slag [21]. For granulated blast-furnace slag with cementitious properties, the manufacturing depends on the rapid quenching of the molten slag by means of water or air quenching to ensure that the material reaches the glassy state. Water quenching using high-pressure water jets is considered the most effective process because it produces a higher amount of glass structures in the slag [22]. After quenching the molten slag by means of powerful water jets in the granulator, granulated blast furnace slag (GBFS) is formed [22], and then due to the grinding process, ground granulated blast furnace slag (GGBFS) particles are mostly angular, as shown in Figure 1b. ASTM-International [16] defines this material as “the glassy, granular material formed when molten blast-furnace slag is rapidly chilled, as by immersion in water”.
In addition to the processing conditions, variations in the constituent materials of geopolymers, such as fly ash, slag, and alkaline liquids, contribute significantly to the different physical properties and characteristics of geopolymers. For example, shrinkage, fire resistance, setting time, thermal conductivity, and compressive strength [8] are all affected by the properties of the individual constituent materials. The addition of ground granulated blast furnace slag to fly ash-based geopolymers has enhanced their mechanical properties [13][23], reduced setting time [24][25][26] and leading to decreased permeability [23][27][28]. However, replacing fly ash partially with GGBFS produces more gel phases and complex system structures, with increased shrinkage [29][30]. Furthermore, GGBFS, alkaline activator, and the activator concentration substantially affect the setting time. The correlation between these factors and setting time requires further evaluation to achieve a comprehensive overview of the preceding research studies. In this context, it seems essential to find the optimum replacement of fly ash by slag [24][26][29][31], alkaline liquid ratios [24][31][32], solution concentrations [26][31], and key parameters that influence the blended system to attain an optimum setting time and to better predict how these systems form and behave in engineering applications. Accordingly,  targeting the use of low-calcium class-F fly ash in combination with ground granulated blast furnace slag because the separate use of fly ash-based or slag-based geopolymers are well-developed topics in the literature, whereas the heterodyne effect has not yet been properly studied. Although the mechanical properties of the blended fly ash and slag system has been researched extensively [33][34][35][36][37], its microstructure and durability are not fully established topics and require further evaluation.

2. Low Calcium Fly Ash/Slag Geopolymer

Low-calcium fly-ash-based geopolymer has a slow setting time [24][25][35] and requires heat curing to accelerate the hardening process [25][38]. Adding slag, on the contrary, leads to a more rapid setting time [25][29][39]. Combining these two binders revealed positive effects on setting time, mechanical strength, permeability, and durability in aggressive environments. Significant changes in the fresh properties and the microstructure formation can be traced back to the addition of slag, which in turn affects the hardened properties of the fly-ash-slag geopolymer; specifically, characteristics such as setting time, gel phases, matrix density, shrinkage, and permeability are improved in the binary system.
Based on the rapid setting time induced through the use of slag, it now appears to be clear that the high calcium composition from slag reacts rapidly with the available silica offered by sodium silicate in the alkaline solution. Numerous studies used sodium silicate and sodium hydroxide as the alkaline activator, and the setting time decreases in most cases when the ratio of sodium silicate to sodium hydroxide increases [24][32]. This is due to the higher amount of soluble silica offered by the alkaline solution, which accelerates the rate of the setting time and contributes to the final gels formed [32][39]. The Ca/Si ratio in the formed C-S-H gel in slag-based geopolymer is lower than that formed in ordinary Portland cement, and by introducing class-F fly ash into the reaction, the Ca/Si ratio is made substantially smaller than what is normally formed in OPC. The decrease in the Ca/Si ratio could be attributed to the substitution of Al+3 for Si+4 in the calcium-rich phase [40]. Although the addition of slag to fly-ash-based geopolymer significantly accelerates the setting time, increases mechanical strength, and densifies the final gels, it may also negatively contribute to volume instability [13][29] and crack initiation [31]. The literature has shown that shrinkage of the hardened system as a result of a larger substitution of fly ash with slag may lead to crack propagation. Accordingly, it appears to be crucial to determine the proper replacement ratio limitations to optimize the desired characteristics in the combined system.
The multi-gel phases formed within the fly ash-slag system produce a more intricate and denser microstructure, which ultimately improves the permeability. Permeability is an essential material property because it controls the flow paths for aggressive solutions that penetrate and harm the concrete. The literature clearly demonstrate that the coexistence of geopolymeric gel phases (N-A-S-H or K-A-S-H) and calcium-rich gel phases leads to a substantial reduction in permeability. When these gels form in one system, they produce a denser microstructure, which eventually contributes to low permeability. Because focusing on durability concerning chloride ingress, sulfate attack, and carbonatation, permeability is discussed in the context of these aspects. For chloride environments, different standards designed to evaluate the durability of OPC systems—including NordTest NT Build 492, ASTM-International [41] (withdrawn in 2019), and ASTM-International [42]—have been utilized to analyze the ingress of chloride into fly ash/slag geopolymers. Among the factors that contribute to chloride ingression, the fly-ash-to-slag ratios and the maturity of the reaction products substantially affect the chloride penetration depths. According to the literature about chloride attacks on fly ash/slag-based geopolymers, the consensus is that chloride resistance is affected by the curing duration [43], curing temperature [43], pore structure [10][43][44], fly ash/slag ratio [10][12][45][44], liquid/binder ratio [10], and the maturity of the formed products [12]. Furthermore, porosity and tortuosity are both significant factors in chloride resistance [10]. An important finding by Zhu et al. [10] demonstrated that Cl− penetration not only relates to porosity but also to the tortuosity of the formed structure. Thus, a reduction in the porosity and an increased tortuosity lead to an improved resistance to Cl− migration. The inclusion of slag improves the pore structure system, such as the porosity and tortuosity, which leads to low permeability and increases the chloride penetration resistance.
As permeability plays a significant role in chloride ingression, sulfate attack and carbonatation are also affected by the pore structure of fly ash/slag-based geopolymer systems. Sulfate ions penetrate fly ash/slag geopolymer and cause the formation of gypsum and/or ettringite, which contribute to the expansion or contraction of the affected concrete element. Expansion or contraction induces micro- and major cracks, which ultimately may cause the disintegration of the whole structure. The ingression of sodium sulfate solutions in fly ash/slag geopolymers is less aggressive on the formed microstructure and some studies have identified negligible or positive gains in the mechanical strength [46][47]. On the other hand, magnesium sulfate solution contributes to gypsum and ettringite formation, which induced the expansion and deterioration of the structure [48][46]. For carbonatation, adding slag to the fly-ash-based geopolymer system positively affects the carbonatation resistance [49][50]. The decrease in the apparent volume of permeable voids (AVPV) resulting from higher substitution of slag shows a positive effect and a strong correlation between carbonatation resistance and AVPV [49]. Gel phases formed after the addition of slag are denser, and therefore decrease the permeable voids through which CO2 travels to penetrate the matrix. The reaction products formed throughout this process produce natron, huntite, and calcium carbonate, which may lead to the decomposition of the hydrated products [51][52]. Although slag affects the corbonatation behavior as described above, other factors such as exposure duration, carbon dioxide concentration, and curing conditions significantly impact the carbonatation process. Evaluating material parameters that induce internal or external changes in the sulfate environment or carbonatation process is critical when designing fly ash/slag geopolymers.
Fly ash/slag-based geopolymer properties vary according to the fly ash/slag ratio, liquid/binder ratio, available soluble silica, pore structure, and curing conditions and duration. The formation of C-S-H or C-A-S-H gel phases in fly-ash-based geopolymers leads to low permeability, which in turn increases the resistance to aggressive solutions that may deteriorate the reinforcement steel or the concrete matrix. This reduction in permeability increases durability in aggressive environments (sulfate or chloride ions), as well as the resistance to carbonatation in carbon-rich environments. However, it should be noted that the replacement quantity of slag should be constrained to limit crack initiation due to shrinkage susceptibility. The addition of slag to low-calcium fly ash-based geopolymer densifies the microstructural system and increases the uptake of calcium-substituting alkalis, which leads to C-A-S-H formation [53]. Substituting alkalis for calcium due to the higher affinity of calcium to silicon, which leads to the formation of C-A-S-H, may delay the hydration of N-A-S-H or K-A-S-H [54]. Delaying the formation of N-A-S-H or K-A-S-H may lead to lower strength gains and delay the ultimate strength of these materials at later ages.
The interactions and mechanisms of calcium-rich phases (C-S-H and C-A-S-H) and N-A-S-H or K-A-S-H are complex due to the multiple factors involved in the reactions that mainly include alkaline solution materials, the chemical compositions of fly ash and slag, the concentrations and proportions of materials in the alkaline solution, the ratios of fly ash/slag and alkaline activator/binder. Despite previous extensive studies, in which researchers have attempted to evaluate pore structure [12][28], gel phase formations and structures [55][53][56], elemental compositions [56][57], and microstructural density [26][58], the exact mechanisms underlying the interaction between fly ash/slag blended systems and alkaline activators remains unclear.

This entry is adapted from the peer-reviewed paper 10.3390/ma15030876

References

  1. Shi, C.; Jiménez, A.F.; Palomo, A. New cements for the 21st century: The pursuit of an alternative to Portland cement. Cem. Concr. Res. 2011, 41, 750–763.
  2. Davidovits, J. Geopolymer Cement. A Review; Technical Papers; Geopolymer Institute: Saint-Quentin, France, 2013; pp. 1–11.
  3. McLellan, B.C.; Williams, R.P.; Lay, J.; Van Riessen, A.; Corder, G.D. Costs and carbon emissions for geopolymer pastes in comparison to ordinary portland cement. J. Clean. Prod. 2011, 19, 1080–1090.
  4. Huntzinger, D.N.; Eatmon, T.D. A life-cycle assessment of Portland cement manufacturing: Comparing the traditional process with alternative technologies. J. Clean. Prod. 2009, 17, 668–675.
  5. Davidovits, J. Geopolymeric reactions in archaeological cements and in modern blended cements. Concr. Int. 1987, 9, 23–29.
  6. Davidovits, J. Chemistry of geopolymeric systems, terminology. Geopolymer 1999, 99, 9–39.
  7. Motorwala, A.; Shah, V.; Kammula, R.; Nannapaneni, P.; Raijiwala, D. ALKALI activated FLY-ASH based geopolymer concrete. Int. J. Emerg. Technol. Adv. Eng. 2013, 3, 159–166.
  8. Duxson, P.; Fernández-Jiménez, A.; Provis, J.L.; Lukey, G.C.; Palomo, A.; van Deventer, J.S. Geopolymer technology: The current state of the art. J. Mater. Sci. 2007, 42, 2917–2933.
  9. Davidovits, J. Geopolymers: Inorganic polymeric new materials. J. Therm. Anal. Calorim. 1991, 37, 1633–1656.
  10. Zhu, H.; Zhang, Z.; Zhu, Y.; Tian, L. Durability of alkali-activated fly ash concrete: Chloride penetration in pastes and mortars. Constr. Build. Mater. 2014, 65, 51–59.
  11. Deb, P.S.; Nath, P.; Sarker, P.K. The effects of ground granulated blast-furnace slag blending with fly ash and activator content on the workability and strength properties of geopolymer concrete cured at ambient temperature. Mater. Des. (1980–2015) 2014, 62, 32–39.
  12. Ismail, I.; Bernal, S.A.; Provis, J.L.; San Nicolas, R.; Brice, D.G.; Kilcullen, A.R.; Hamdan, S.; van Deventer, J.S. Influence of fly ash on the water and chloride permeability of alkali-activated slag mortars and concretes. Constr. Build. Mater. 2013, 48, 1187–1201.
  13. Shang, J.; Dai, J.G.; Zhao, T.J.; Guo, S.Y.; Zhang, P.; Mu, B. Alternation of traditional cement mortars using fly ash-based geopolymer mortars modified by slag. J. Clean. Prod. 2018, 203, 746–756.
  14. Kong, D.L.; Sanjayan, J.G. Effect of elevated temperatures on geopolymer paste, mortar and concrete. Cem. Concr. Res. 2010, 40, 334–339.
  15. Van Deventer, J.S.; Provis, J.L.; Duxson, P.; Brice, D.G. Chemical research and climate change as drivers in the commercial adoption of alkali activated materials. Waste Biomass Valoriz. 2010, 1, 145–155.
  16. ASTM C294-19Standard Terminology Relating to Concrete and Concrete Aggregates, ASTM-International: West Conshohocken, PA, USA, 2019.
  17. Hardjito, D. Studies of Fly Ash-Based Geopolymer Concrete. Ph.D. Thesis, Curtin University, Bentley, WA, Australia, 2005.
  18. Snellings, R.; Mertens, G.; Elsen, J. Supplementary cementitious materials. Rev. Mineral. Geochem. 2012, 74, 211–278.
  19. Ramezanianpour, A.A.; Moeini, M.A. Mechanical and durability properties of alkali activated slag coating mortars containing nanosilica and silica fume. Constr. Build. Mater. 2018, 163, 611–621.
  20. ASTM C618-19Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete, ASTM-International: West Conshohocken, PA, USA, 2019.
  21. Shi, C. Steel slag—Its production, processing, characteristics, and cementitious properties. J. Mater. Civ. Eng. 2004, 16, 230–236.
  22. Hogan, F.; Meusel, J. Evaluation for durability and strength development of a ground granulated blast furnace slag. Cem. Concr. Aggreg. 1981, 3, 40–52.
  23. Škvára, F.; Kopeckỳ, L.; Nemecek, J.; Bittnar, Z. Microstructure of geopolymer materials based on fly ash. Ceramics-Silikaty 2006, 50, 208–215.
  24. Hadi, M.N.; Zhang, H.; Parkinson, S. Optimum mix design of geopolymer pastes and concretes cured in ambient condition based on compressive strength, setting time and workability. J. Build. Eng. 2019, 23, 301–313.
  25. Jang, J.G.; Lee, N.; Lee, H.K. Fresh and hardened properties of alkali-activated fly ash/slag pastes with superplasticizers. Constr. Build. Mater. 2014, 50, 169–176.
  26. Saha, S.; Rajasekaran, C. Enhancement of the properties of fly ash based geopolymer paste by incorporating ground granulated blast furnace slag. Constr. Build. Mater. 2017, 146, 615–620.
  27. Li, Z.; Liu, S. Influence of slag as additive on compressive strength of fly ash-based geopolymer. J. Mater. Civ. Eng. 2007, 19, 470–474.
  28. Deb, P.; Nath, P.; Sarker, P. Properties of fly ash and slag blended geopolymer concrete cured at ambient temperature. In New Developments in Structural Engineering and Construction; University of Hawaii: Manoa, HI, USA, 2013; pp. 571–576.
  29. Fang, G.; Bahrami, H.; Zhang, M. Mechanisms of autogenous shrinkage of alkali-activated fly ash-slag pastes cured at ambient temperature within 24 h. Constr. Build. Mater. 2018, 171, 377–387.
  30. Nedeljković, M.; Li, Z.; Ye, G. Setting, strength, and autogenous shrinkage of alkali-activated fly ash and slag pastes: Effect of slag content. Materials 2018, 11, 2121.
  31. Lee, N.; Lee, H.K. Setting and mechanical properties of alkali-activated fly ash/slag concrete manufactured at room temperature. Constr. Build. Mater. 2013, 47, 1201–1209.
  32. Nath, P.; Sarker, P.K. Effect of GGBFS on setting, workability and early strength properties of fly ash geopolymer concrete cured in ambient condition. Constr. Build. Mater. 2014, 66, 163–171.
  33. Kurtoglu, A.E.; Alzeebaree, R.; Aljumaili, O.; Nis, A.; Gulsan, M.E.; Humur, G.; Cevik, A. Mechanical and durability properties of fly ash and slag based geopolymer concrete. Adv. Concr. Constr. 2018, 6, 345.
  34. Fang, G.; Ho, W.K.; Tu, W.; Zhang, M. Workability and mechanical properties of alkali-activated fly ash-slag concrete cured at ambient temperature. Constr. Build. Mater. 2018, 172, 476–487.
  35. Kumar, S.; Kumar, R.; Mehrotra, S. Influence of granulated blast furnace slag on the reaction, structure and properties of fly ash based geopolymer. J. Mater. Sci. 2010, 45, 607–615.
  36. Krishnaraja, A.; Sathishkumar, N.; Kumar, T.S.; Kumar, P.D. Mechanical behaviour of geopolymer concrete under ambient curing. Int. J. Sci. Eng. Technol. 2014, 3, 130–132.
  37. Puertas, F.; Martinez-Ramirez, S.; Alonso, S.; Vazquez, T. Alkali-activated fly ash/slag cements: Strength behaviour and hydration products. Cem. Concr. Res. 2000, 30, 1625–1632.
  38. Hardjito, D.; Cheak, C.C.; Ing, C.H.L. Strength and setting times of low calcium fly ash-based geopolymer mortar. Mod. Appl. Sci. 2008, 2, 3–11.
  39. Criado, M.; Fernández-Jiménez, A.; Palomo, A. Alkali activation of fly ash: Effect of the SiO2/Na2O ratio: Part I: FTIR study. Microporous Mesoporous Mater. 2007, 106, 180–191.
  40. Puertas, F.; Palacios, M.; Manzano, H.; Dolado, J.; Rico, A.; Rodríguez, J. A model for the CASH gel formed in alkali-activated slag cements. J. Eur. Ceram. Soc. 2011, 31, 2043–2056.
  41. ASTM C1543-10Standard Test Method for Determining the Penetration of Chloride Ion into Concrete by Ponding (Withdrawn 2019), ASTM-International: West Conshohocken, PA, USA, 2019.
  42. ASTM C1556Standard Test Method for Determining the Apparent Chloride Diffusion Coefficient of Cementitious Mixtures by Bulk Diffusion, ASTM-International: West Conshohocken, PA, USA, 2011.
  43. Noushini, A.; Castel, A.; Aldred, J.; Rawal, A. Chloride diffusion resistance and chloride binding capacity of fly ash-based geopolymer concrete. Cem. Concr. Compos. 2020, 105, 103290.
  44. Yang, T.; Yao, X.; Zhang, Z. Quantification of chloride diffusion in fly ash–slag-based geopolymers by X-ray fluorescence (XRF). Constr. Build. Mater. 2014, 69, 109–115.
  45. Rajagopalan, G. Durability of alumina silicate concrete based on slag/fly ash blends against corrosion. Eng. Constr. Archit. Manag. 2019, 26, 1641–1651.
  46. Ismail, I.; Bernal, S.A.; Provis, J.L.; Hamdan, S.; van Deventer, J.S. Microstructural changes in alkali activated fly ash/slag geopolymers with sulfate exposure. Mater. Struct. 2013, 46, 361–373.
  47. Džunuzović, N.; Komljenović, M.; Nikolić, V.; Ivanović, T. External sulfate attack on alkali-activated fly ash-blast furnace slag composite. Constr. Build. Mater. 2017, 157, 737–747.
  48. Gopalakrishnan, R.; Chinnaraju, K. Durability of ambient cured alumina silicate concrete based on slag/fly ash blends against sulfate environment. Constr. Build. Mater. 2019, 204, 70–83.
  49. Pasupathy, K.; Berndt, M.; Castel, A.; Sanjayan, J.; Pathmanathan, R. Carbonation of a blended slag-fly ash geopolymer concrete in field conditions after 8 years. Constr. Build. Mater. 2016, 125, 661–669.
  50. Zhuguo, L.; Sha, L. Carbonation resistance of fly ash and blast furnace slag based geopolymer concrete. Constr. Build. Mater. 2018, 163, 668–680.
  51. Khan, M.; Castel, A.; Noushini, A. Carbonation of a low-calcium fly ash geopolymer concrete. Mag. Concr. Res. 2017, 69, 24–34.
  52. Bernal, S.A.; Provis, J.L.; Walkley, B.; San Nicolas, R.; Gehman, J.D.; Brice, D.G.; Kilcullen, A.R.; Duxson, P.; van Deventer, J.S. Gel nanostructure in alkali-activated binders based on slag and fly ash, and effects of accelerated carbonation. Cem. Concr. Res. 2013, 53, 127–144.
  53. Garcia-Lodeiro, I.; Palomo, A.; Fernández-Jiménez, A.; Macphee, D. Compatibility studies between NASH and CASH gels. Study in the ternary diagram Na2O–CaO–Al2O3–SiO2–H2O. Cem. Concr. Res. 2011, 41, 923–931.
  54. Ye, H.; Radlińska, A. Fly ash-slag interaction during alkaline activation: Influence of activators on phase assemblage and microstructure formation. Constr. Build. Mater. 2016, 122, 594–606.
  55. Puligilla, S.; Mondal, P. Role of slag in microstructural development and hardening of fly ash-slag geopolymer. Cem. Concr. Res. 2013, 43, 70–80.
  56. Walkley, B.; San Nicolas, R.; Sani, M.A.; Rees, G.J.; Hanna, J.V.; van Deventer, J.S.; Provis, J.L. Phase evolution of C-(N)-ASH/NASH gel blends investigated via alkali-activation of synthetic calcium aluminosilicate precursors. Cem. Concr. Res. 2016, 89, 120–135.
  57. Ismail, I.; Bernal, S.A.; Provis, J.L.; San Nicolas, R.; Hamdan, S.; van Deventer, J.S. Modification of phase evolution in alkali-activated blast furnace slag by the incorporation of fly ash. Cem. Concr. Compos. 2014, 45, 125–135.
  58. Qiu, J.; Zhao, Y.; Xing, J.; Sun, X. Fly Ash/Blast Furnace Slag-Based Geopolymer as a Potential Binder for Mine Backfilling: Effect of Binder Type and Activator Concentration. Adv. Mater. Sci. Eng. 2019, 2019, 2028109.
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