Sulfate and chloride resistance of bottom ash doped slag-based geopolymer composites

Abstract

Keywords: Geopolymer; Slag; Bottom Ash; Magnesium Sulfate; Sodium Sulfate; Sodium Chloride

Introduction

Geopolymer creates an alternative product by causing lower carbon emissions, unlike Portland cement-based binders. Geopolymer products are produced using precursor materials containing amorphous aluminosilicate in their structure. In addition, an alkali activator (chemical liquid solution providing high pH) consisting of a

mixture of silicate and hydroxide is used in geopolymerization. While a ceramic-like amorphous microstructure is formed by the reaction between the binder material and the activator, this reaction also includes melting and condensation [1]. As the information about the solutions it brings to carbon dioxide emission has expanded, the search for replacing alternative binders with cement has accelerated. Bakis

*Corresponding author. *E-mail address: aygormez@yildiz.edu.tr This paper was recommended for publication in revised form by Regional Editor Metin Tülü Published by Yıldız Technical University Press, İstanbul, Turkey Copyright 2021, Yıldız Technical University. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).

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et al. [2] produced 8 different series by replacing normal strength control concrete with pumice. By using fiber and city water, 86.55 MPa of compressive strength and 11.12 MPa of flexural strength were obtained. Bayraktar et al. [3] investigated the stabilization of electric arc furnace powders obtained during steel production from scrap metals with different ratios of cement and low-grade MgO. It has been determined that the environmental performance or structural properties were suitable if the electric arc furnace powders were used at a percentage of 30% by weight. Uslu et al. [4] did not encounter any significant problems when the chemical treatment sludge produced in the automotive factory was used up to 10% as a raw material component in brick manufacturing. In addition to the use of substitute materials in this way instead of cement, the production of geopolymer has also created an environmentally important alternative. Slag is a waste product from the pig iron production process, which consists mainly of calcium-magnesium alumino-silicate glass. The structure, properties, and chemical composition vary depending on the raw materials and industrial process. The most commonly used slag is blast furnace slag. As a result of the main reactions for alkali-activated slag, high strength results were obtained due to the calcium silicate hydrate (C–S–H) product. However, despite high strength, drying shrinkage values​​ were high due to insufficient workability and rapid setting [5-6]. Bottom ash is a granular, dark gray, and porous material obtained during the coal burning process. Since the bottom ash has an aluminum oxide-silicate structure, geopolymerization can be performed between alkaline solution and aluminosilicate with alkali activation [7]. It has been tried in the production of geopolymer, especially after it has been made fine-grained. Higher-strength values ​​were obtained under room conditions and heat curing [8-9]. However, durability studies are limited, especially in the case of bottom ash use. More research needs to be done on this subject. Sulfate attack is one of the vitally important durability indexes for concrete and mortar materials. In studies of sulfate attack on conventional Portland Cement concrete, the reaction between sulfate-containing solutions and hydration products has a complex mechanism [1011]. Bakharev et al. [12] determined that the performance of geopolymers against sulfate attack was different. The main parameters affecting the stability of geopolymer composites are the cation and concentration in the sulfate environment and the alkali activator type. It has been observed that geopolymer mixtures prepared using only sodium hydroxide were more stable against sulfate attack than the samples prepared together with sodium silicate and hydroxide or prepared by using potassium silicate and hydroxide together. When the performance research of geopolymers exposed to 5% magnesium sulfate and 5% sodium sulfate solutions in different combinations was carried out, it was seen that the changes in the composite

samples were small and the fluctuations in the mechanical properties were highest in the series in which the two solutions were used together. Fernández-Jiménez et al. [13] investigated the resistance of fly ash-based alkali-activated samples to the effect of sulfate. After fluctuation in the first stages, an increase in strength was detected both in air-cured samples and in samples kept in 4.4% Na2SO4 solutions. After being kept in Na2SO4 solution for 365 days, it was observed that the crystals of Na2SO4 salts formed in the pores, and some deterioration occurred in this situation. Despite this situation, it has been observed that alkalized materials perform satisfactorily. High solution concentrations have not been studied much, although the real environment tends to be more complex and extreme and this poses greater challenges for concrete and mortar structures. A large number of performance studies have been conducted against the effects of chloride and sulfate on geopolymer composites and Portland Cement-based samples. Although there are many studies on the performance of geopolymer composites against these effects, studies on the reinforcement of slag-based geopolymers with bottom ash are limited. In this study, the performance of slagbased geopolymer samples containing up to 30% bottom ash was investigated, while their behavior under the influence of chloride and sulfate with a concentration of 15%, as opposed to solution attacks with low concentrations, was also investigated. Thus, it enables researchers in the construction industry to make promising designs for various applications. Three different periods were used to test the geopolymer samples. 2, 6, and 10-month solution attacks were made. After the completion of each solution period, the changes in flexural strength, compressive strength, and weight were investigated. In addition, SEM and XRD analyzes were conducted for examining the magnesium sulfate effect, and a visual inspection was performed after the magnesium sulfate test.

Materials And Methods

Materials The main binder material was used as slag for this study. The specific gravity value of the slag is 2.91 and the total silica + alumina + iron oxide ratio is 54.8%. The important feature of the slag is its calcium content and accordingly, it shortens the setting time. Bottom ash was used as the other binding material. In order to increase the reactivity of the bottom ash, it was ground to a 5% residue on a 45 µm sieve. The specific gravity of the bottom ash is 2.3. It was made into smaller particles to have a high specific surface. Due to this situation, it has become more reactive. The Blaine fineness values of bottom ash and slag are 5300 cm2/g and 4500 cm2/g, respectively. The chemical composition of the binders used is shown in Table 1.

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Table 1. Binder materials’ chemical analysis Chemical analysis, %

Rilem sand was used as the aggregate, and the unit weight and specific gravity values are 1.35 kg/m3 and 2.6, respectively. Rilem sand has a water absorption rate of 1.276% and its properties comply with BS EN 196-1. A mixture of sodium silicate and hydroxide was used to prepare the activator. The SiO2/Na2O ratio was 3.29 in sodium silicate and the hydroxide was prepared as 12M. Specimen Mix Design Within the scope of the geopolymer mortar study, slag and bottom ash were used as binding materials, standard sand as aggregate, and sodium silicate and hydroxide as activators. The sodium silicate/sodium hydroxide ratio was kept as 2:1, the aggregate/binder material was 2.5:1, and the binder material/activator ratio was 1:0.7, while water was evaluated only for preparing sodium hydroxide solution. Extra water wasn’t added and a superplasticizer was added to keep the binder/activator ratio constant. For this reason, the activator/binder ratio was used instead of the water/ binder ratio in the traditional Portland Cement based mortar. In total, 5 series were prepared and the mixture amounts for standard 450 g were summarized in Figure 1.

In addition, a detailed mixture description was made for the mortar sample containing 100% slag, and the difference in the other series was in the amount of bottom ash. For the control mixture containing 100% slag, sodium hydroxide solution was prepared as 12M the day before. The hydroxide solution cooled at room temperature was first mixed with sodium silicate solution on the day of mixing. Here, the sodium silicate/sodium hydroxide ratio was taken as 2:1 and the activator was prepared. Then, a mixer drill was used for mixing the activator with 450 g of slag. The activator/binder material ratio was taken as 0.7:1. At the last stage, Rilem sand was added to the mixture at a ratio of 2.5:1 aggregate/binder, and the mixture was continued until a homogeneous mixture was obtained with a mixer drill. Two types of molds, 40 x 40 x 160 mm prism and 50 mm cube molds, were used. The homogeneous mixture was placed in the molds in two stages and vibration was applied at each stage. After the vibration was applied, the specimens were hardened in the mold for 2 hours. The samples were taken out of the mold at the end of this period with the early setting property of slag. After demolding, the specimens were retained at room temperature and relative

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humidity (50±4%) for 28 days. Then, durability tests were started. The details are given in Table 2. Along with the control series, the other four series were prepared using bottom ash (7.5%, 15%, 22.5%, and 30%).

be dissolved at a higher rate by the geopolymerization process. Due to the hydration products obtained with MgO and CaO, the slag had a driving force in geopolymerization. Due to the slag, more CSH, CASH, and NASH formations were observed, while a more homogeneous and dense structure was formed by connecting the voids between the unreacted particles and different hydrated phases. In this way, slag-based geopolymer mortars could be cured at room conditions without the need for temperature curing. However, slag-based geopolymer mortars had disadvantages such as early hardening, rapid slump loss, and workability. Alternative binders should be investigated in this situation [14-18]. Bottom ash was used for this purpose. When the bottom ash, whose pozzolanic reaction was increased by bringing it to high fineness, was used up to 15%, it formed an increase in the strength results. Having a high percentage of silica and alumina was an important factor in this case. These components supported the formation of geopolymerization products (CSH, CASH, and NASH) that strengthened strength development by reacting with alkali silicate solutions. In addition, by increasing the free calcium ion (Ca2+) ratio in the composition, bottom ash supported the formation of calcium silicate hydrate (CSH) gel as a result of the reaction with the silicate. In addition, its high thinness also played a role in the development of strength by showing a filling effect. Using it at a higher ratio caused a decrease in strength. Its high thinness increased the specific surface area while increasing the need for activators. While the decrease in flowability and workability created a more hollow structure, it also caused a decrease in strength [15, 19-22]. Figures have been studied in detail. It was observed that the geopolymer composites gained strength after the solution effect period of 2 months was completed. This showed that the initial solution effect helped the geopolymerization to continue. Particularly, the calcium expansion products from the slag reacted with sulfate and chloride crystals to renew the pore structure, increasing the compactness of the geopolymer structure [23]. After 2 months, chloride and sulfate attacks increased, creating more porosity, and microcracks also increased. Thus, strength losses started to be seen due to erosion. If the magnesium sulfate solution was taken as a basis, the fluctuations in the strength results can be explained. There are two kinds of movements. The first of these movements was the transition of alkali ions to the solution by leaving the sample, and the second was the diffusion of Mg into the sample [12, 24]. At first, the second movement provided the continuation of the geopolymerization, but later it caused a loss of strength with deterioration. Waiting in the oven before the test allowed the samples to absorb the solutions better. The temperature increased the void ratio and increased the absorption tendency. After 2 months, the formation of gypsum and ettringite in the pores increased the microcracks, while the transition of alkalis to the solution increased the strength loss [12, 25]. When comparing the solutions, it was seen that the most

Test Procedure Three different 15% solutions (sodium chloride and sulfate, and magnesium sulfate) were prepared for durability tests and poured into plastic storage boxes. The prepared samples were first kept in an oven for one day at 105oC. The main reason for this was to increase the efficiency of the solution by increasing its absorption. Solution concentration and pH values must ​​ be maintained to create a homogeneous structure in the test. Therefore, the solutions were renewed at the end of the 1st, 2nd, and 6th months. 4 units of solution for 1 unit of the sample were placed in the plastic box. The samples were taken out of the plastic boxes after 2 months, 6 months, and 10 months and left to dry by keeping at room temperature. A wire brush was used for cleaning the outer surface after the specimens dried. The flexural strength, compressive strength, and weight changes at the end of three different periods were compared with the 28-day conditions. The compressive strength was found using cube specimens (50 mm) and the flexural strength was found using prism specimens (40x40x160 mm). Three samples were used for the tests and the final values were ​​ found according to the average. In addition, microstructural analyzes were also applied to the samples. After the magnesium sulfate test, a visual inspection was done. The SEM and XRD analyzes were conducted according to the magnesium sulfate test.

Results And Discussion

Strength Results The mechanical properties of the slag-based geopolymer composites produced by adding bottom ash and the results of the residual compressive strength after chloride and sulfate attacks are given together (Figures 2-4). When the details are examined, the interactions between the slag and the bottom ash are explained: Slag was an important geopolymer binder material due to its oxide components and mineralogical structure. It contained a significant amount of basic oxides such as CaO and MgO, which could

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aggressive solution was magnesium sulfate. Due to this situation, the most mechanical losses were due to magnesium sulfate. The chloride ions’ smaller size resulted in higher penetration. So, the highest strength increases were in sodium chloride solution [26-27].

After 2, 6, and 10 months, residual compressive strengths of 43.92 MPa, 28.51 MPa, and 19.06 MPa were obtained for the 15BA sample under the influence of magnesium sulfate. After 2, 6, and 10 months, residual compressive strengths of 47.83 MPa, 32.23 MPa, and 24.81 MPa were obtained

Figure 2. Compressive strength results with magnesium sulfate exposure.

Figure 3. Compressive strength results with sodium sulfate exposure.

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Figure 4. Compressive strength results with sodium chloride exposure. for the 15BA sample under the influence of sodium sulfate. After 2, 6, and 10 months, residual compressive strengths of 54.23 MPa, 43.96 MPa, and 35.45 MPa were obtained for the 15BA sample under the influence of sodium chloride.

The 28-day flexural strengths of the bottom ash reinforced samples are given in comparison with the results after the effect of sulfate and chloride (Figures 5-7). The flexural strength results showed a decrease directly after solution

Figure 5. Flexural strength results with magnesium sulfate exposure.

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Figure 6. Flexural strength results with sodium sulfate exposure.

Figure 7. Flexural strength results with sodium chloride exposure.

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attacks, in contrast to the compressive strength results [25]. Thus, it was determined that the sensitivity of the flexural strength results was higher. The microcrack propagation in porous structures played an important role in the decrease in flexural strength [26]. In the order of flexural strength results, parallelism was observed with the compressive strengths. This was due to the properties of the solutions. After 2, 6, and 10 months, residual flexural strengths of 6.52 MPa, 4.98 MPa, and 3.26 MPa were obtained for the 15BA sample under the influence of magnesium sulfate. After 2, 6, and 10 months, residual flexural strengths of 7.32 MPa, 5.73 MPa, and 4.45 MPa were obtained for the 15BA sample under the influence of sodium sulfate. After 2, 6, and 10 months, residual flexural strengths of 7.74 MPa,

Conclusion

For this study, the feasibility of bottom ash reinforcement in the production of slag-based geopolymer composites and the performance of the obtained product against the effect of sulfate and chloride in 10 months were investigated, and the stated results were found: According to the preliminary test results, a 15% bottom ash substitution was found to be critical in terms of mechanical properties. The utilization of higher bottom ash reduced flowability and workability and resulted in poor performance. For sample 7.5BA, the increased percentages for compressive and flexural strengths according to the control sample were 7.15% and 5.55%, respectively. For sample 15BA, the increase percentages for compressive and flexural strengths according to the control sample were 14.21% and 8.75%, respectively. While investigating the performance of geopolymer samples against solutions, increases were observed in the compressive strength and weight values over 2 months, while these increases were replaced by a decrease in the following periods. Fluctuations in mechanical properties occurred due to the transitions between the solution and matrix. In addition, being kept in an oven before durability tests facilitated the absorption of the solution. In the next days, the formation of ettringite and gypsum was also effective in the formation of micro-cracks, together with the transition of alkalis to the solution. The small size of the chloride ions resulted in greater penetration. Magnesium sulfate was known to be more aggressive than sodium sulfate. These conditions ensured

Data Availability Statement

The authors confirm that the data that supports the findings of this study are available within the article. Raw data that support the finding of this study are available from the corresponding author, upon reasonable request.

Conflict Of Interest

The author declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Ethics

There are no ethical issues with the publication of this manuscript.

References

1. Bayraktar AC, Avsar E, Toroz I, Alp K, Hanedar A. [17] Nis A, Altundal MB. Mechanical strength degrada- Stabilization and solidification of electric arc fur- tion of slag and fly ash based geopolymer specimens nace dust originating from steel industry by using exposed to sulfuric acid attack. Sigma J Eng Nat Sci low grade MgO. Arch Environ Prot 2015;41:62−66. 2019;37:917−926. [CrossRef] [18] Aygormez, Y. Performance of ambient and freez-
2. Uslu E, Avşar E, Toröz İ. Otomotiv endüstrisi kimyasal ing-thawing cured metazeolite and slag based geo- arıtma çamurlarının tuğla üretiminde kullanılabil- polymer composites against elevated temperatures. irliğinin ürün kalitesi yönünden araştırılması. Sigma Rev Constr 2021;20:145−162. [CrossRef] J Eng Nat Sci 2010;3:141−148. [Turkish] [19] Wongsa A, Boonserm K, Waisurasingha C, Sata V,
3. Chi M, Huang R. Inding mechanism and properties Chindaprasirt P. Use of municipal solid waste incin- of alkali-activated fly ash/slag mortars. Constr Build erator (MSWI) bottom ash in high calcium fly ash Mater 2013;40:291−298. [CrossRef] geopolymer matrix. J Clean Prod 2017;148:49−59.
4. Marjanović N, Komljenović M, Baščarević Z, Nikolić [CrossRef] V, Petrović R. Physical-mechanical and microstruc- [20] Kumar ML, Revathi V. Metakaolin bottom ash blend tural properties of alkali-activated fly ash-blast furnace geopolymer mortar-A feasibility study. Constr Build slag blends. Ceram Int 2015;41:1421−1435. [CrossRef] Mater 2016;114:1−5. [CrossRef]
5. Zarina Y, Mohd Mustafa ABA, Kamarudin H, [21] Deraman LM, Al Bakri Abdullah MM, Liew YM, Khairul Nizar I, Andrei Victor S, Petricǎ V, et al. Hussin K, Yahya Z. A review on processing and Chemical and physical characterization of boiler ash properties of bottom ash based geopolymer materi- from palm oil industry waste for geopolymer com- als. Key Eng Mater 2015;660:3−8. [CrossRef] posite. Rev Chim 2013;64:1408−1412. [22] Hosseini S, Brake NA, Nikookar M, Gunaydin-Sen
6. Kim SH, Ryu GS, Koh KT, Lee JH. Flowability O, Snyder H. A. (2021). Mechanochemically acti- and strength development characteristics of bot- vated bottom ash-fly ash geopolymer. Cem Concr tom ash based geopolymer. Int J Civ Environ Eng Compos 2021;118:103976. [CrossRef] 2012;6:852−857. [23] Duan P, Yan C, Zhou W. Influence of partial
7. Revathi V, Saravanakumar R, Thaarrini J. Effect of replacement of fly ash by metakaolin on mechan- molar ratio of SiO2/Na2O, Na2SiO3/NaOH ratio ical properties and microstructure of fly ash geo- and curing mode on the compressive strength of polymer paste exposed to sulfate attack. Ceram Int ground bottom ash geopolymer mortar. Int J Earth 2016;42:3504−3517. [CrossRef] Sci Eng 2014;7:1511−1516. [24] Elyamany HE, Abd Elmoaty M, Elshaboury AM.
8. Guo L, Wu YY, Xu F, Song XT, Ye JY, Duan P, et al. Magnesium sulfate resistance of geopolymer mortar. Sulfate resistance of hybrid fiber reinforced metaka- Constr Build Mater 2018;184:111−127. [CrossRef] olin geopolymer composites. Compos Part B Eng [25] Thokchom S, Ghosh P, Ghosh S. Performance of fly 2020;183:1−10. [CrossRef] ash based geopolymer mortars in sulphate solution.
9. Santhanam M, Cohen MD, Olek J. Mechanism J Eng Sci Technol Rev 2010;3:36−40. [CrossRef] of sulfate attack: a fresh look. Cem Concr Res [26] Zhang HY, Kodur V, Wu B, Cao L, Qi SL. 2003;33:341−346. [CrossRef] Comparative thermal and mechanical performance
10. Bakharev T. Durability of geopolymer materials of geopolymers derived from metakaolin and fly in sodium and magnesium sulfate solutions. Cem ash. J Mater Civ Eng 2016;28:04015092. [CrossRef] Concr Res 2005;35:1233−1246. [CrossRef] [27] Škvára F, Jílek T, Kopecký L. Geopolymer materials
11. Fernandez-Jimenez A, García-Lodeiro I, Palomo A. based on fly ash. Ceram Silik 2005;49:195−204. Durability of alkali activated fly ash cementitious [28] Rashidian-Dezfouli H, Rangaraju PR. A compara- materials. J Mater Sci 2007;42:3055−3065. [CrossRef] tive study on the durability of geopolymers produced
12. Ionescu BA, Lăzărescu AV, Hegyi A. The possibil- with ground glass fiber, fly ash, and glass-powder ity of using slag for the production of geopolymer in sodium sulfate solution. Constr Build Mater materials and its influence on mechanical perfor- 2017;153:996−1009. [CrossRef] mances-A review. Proceedings 2020;63:30. [CrossRef] [29] Kwasny J, Aiken TA, Soutsos MN, McIntosh JA,
13. Thaarrini J, Ramasamy V. Properties of foundry sand, Cleland DJ. Sulfate and acid resistance of litho- ground granulated blast furnace slag and bottom ash marge-based geopolymer mortars. Constr Build based geopolymers under ambient conditions. Period Mater 2018;166:537−553. [CrossRef] Polytech Civ Eng 2016;60:159−168. [CrossRef] [30] Müllauer W, Beddoe RE, Heinz D. Sulfate
14. Qiu J, Zhao Y, Xing J, Sun X. Fly ash/blast furnace attack expansion mechanisms. Cem Concr Res slag-based geopolymer as a potential binder for mine 2013;52:208−215. [CrossRef] backfilling: effect of binder type and activator con- [31] Maes M, De Belie N. Resistance of concrete and mor- centration. Adv Mater Sci Eng 2019;2019:2028109. tar against combined attack of chloride and sodium [CrossRef] sulphate. Cem Concr Compos 2014;53:59−72. [CrossRef] Sigma J Eng Nat Sci, Vol. 41, No. 2, pp. 288−301, April, 2023 301
15. Sata V, Sathonsaowaphak A, Chindaprasirt P. [38] Salami BA, Johari MAM, Ahmad ZA, Maslehuddin Resistance of lignite bottom ash geopolymer mor- M. Durability performance of palm oil fuel ash- tar to sulfate and sulfuric acid attack. Cem Concr based engineered alkaline-activated cementitious Compos 2012;34:700−708. [CrossRef] composite (POFA-EACC) mortar in sulfate envi-
16. Karakoc MB, Turkmen I, Maras MM, Kantarci F, ronment. Constr Build Mater 2017;131:229−244. Demirboga R. Sulfate resistance of ferrochrome [CrossRef] slag based geopolymer concrete. Ceram Int [39] Ismail I, Bernal SA, Provis JL, Hamdan S, van 2016;42:1254−1260. [CrossRef] Deventer JS. Microstructural changes in alkali acti-
17. Chindaprasirt P, Kanchanda P, Sathonsaowaphak A, vated fly ash/slag geopolymers with sulfate expo- Cao HT. Sulfate resistance of blended cements con- sure. Mater Struct 2013;46:361−373. [CrossRef] taining fly ash and rice husk ash. Constr Build Mater [40] Aygormez Y, Canpolat O, Al-mashhadani MM, 2007;21:1356−1361. [CrossRef] Uysal M. Elevated temperature, freezing-thawing
18. Ren D, Yan C, Duan P, Zhang Z, Li L, Yan Z. and wetting-drying effects on polypropylene fiber Durability performances of wollastonite, tremolite reinforced metakaolin based geopolymer compos- and basalt fiber-reinforced metakaolin geopoly- ites. Constr Build Mater 2020;235:117502. [CrossRef] mer composites under sulfate and chloride attack. [41] Atahan HN, Arslan KM. Improved durability of Constr Build Mater 2017;134:56−66. [CrossRef] cement mortars exposed to external sulfate attack:
19. Arslan AA, Uysal M, Yılmaz A, Al-mashhadani MM, The role of nano & micro additives. Sustain Cities Canpolat O, Sahin F, et al. Influence of wetting-dry- Soc 2016;22:40−48. [CrossRef] ing curing system on the performance of fiber rein- [42] Yıldırım Ozen M, Dur F, Kunt K, Derun E. Evaluation forced metakaolin-based geopolymer composites. of gold mine tailings in cement mortar: investiga- Constr Build Mater 2019;225:909−926. [CrossRef] tion of effects of chemical admixtures. Sigma J Eng
20. He J, Zhang J, Yu Y, Zhang G. The strength and micro- Nat Sci 2020;38:2155−2168. structure of two geopolymers derived from metaka- olin and red mud-fly ash admixture: a comparative study. Constr Build Mater 2012;30:80−91. [CrossRef]

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