Experimental Research on the Properties and Formulation of Fly Ash Based Geopolymer Grouting Material
Experimental Research on the Properties and Formulation of Fly Ash Based Geopolymer Grouting...
Zeng, Qingwei;Gao, Peiwei;Li, Kuan;Dong, Guoqing;Jin, Guanglai;Sun, Xuewei;Zhao, Jingwei;Chen, Lifeng
2022-04-19 00:00:00
buildings Article Experimental Research on the Properties and Formulation of Fly Ash Based Geopolymer Grouting Material 1 , 2 1 , 1 , 2 1 2 1 , 2 3 Qingwei Zeng , Peiwei Gao *, Kuan Li , Guoqing Dong , Guanglai Jin , Xuewei Sun , Jingwei Zhao 2 , and Lifeng Chen * Department of Civil and Airport Engineering, College of Civil Aviation, Nanjing University of Aeronautics and Astronautics, Nanjing 211106, China; zqw@sinoroad.com (Q.Z.); likuan@sinoroad.com (K.L.); donggq@nuaa.edu.cn (G.D.); sxw@sinoroad.com (X.S.) Jiangsu Sinoroad Engineering Technology Research Institute, Nanjing 211899, China; jgl@sinoroad.com School of Transportation, Southeast University, Nanjing 211189, China; zhaojw_6204@eyou.com * Correspondence: gpw1963@nuaa.edu.cn (P.G.); clf@sinoroad.com (L.C.) Abstract: This paper experimentally investigated the effects of varying contents of Na O in a modified sodium silicate, sodium silicate moduli (M ), and contents of granulated blast furnace slag (GBFS) on the compressive strength and drying shrinkage of fly ash (FA)-based geopolymer grouting materials at different ages. X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDS) were used to study the influences of different amounts of GBFS on the microstructure and product compositions of FA-based geopolymer grouting materials. The results show that the content of Na O in modified sodium silicate, M 2 s , and the content of GBFS play a significant role in compressive strength and drying shrinkage of FA-based geopolymer grouting materials. In addition, the influence of M as well as the content of GBFS on the compressive strength and drying shrinkage of FA-based geopolymer grouting materials was deeply affected by curing age. The micro-performance tests and analysis clearly showed that Citation: Zeng, Q.; Gao, P.; Li, K.; incorporating 30 wt% GBFS can decrease the proportion of pores with large pore sizes, improve pore Dong, G.; Jin, G.; Sun, X.; Zhao, J.; size distribution, and enhance the solubility of FA and further promote the formation of C-A-S-H gel Chen, L. Experimental Research on the Properties and Formulation of Fly within FA-based geopolymer grouting materials. Ash Based Geopolymer Grouting Material. Buildings 2022, 12, 503. Keywords: geopolymer; sodium silicate modulus; granulated blast furnace slag; compressive https://doi.org/10.3390/ strength; microstructure buildings12050503 Academic Editor: Francesco Colangelo 1. Introduction Received: 21 February 2022 Under the action of long-term harsh weather and traffic load, defects such as damage, Accepted: 15 April 2022 decline of skid resistance, and cracks will gradually appear on many roads. Traditional Published: 19 April 2022 pavement maintenance techniques generally adopt the method of first excavating to remove Publisher’s Note: MDPI stays neutral the damaged parts and then filling with new materials [1,2]. However, due to disadvan- with regard to jurisdictional claims in tages, such as long cycle, high cost, and traffic impact, such a method fails to fix the damage; published maps and institutional affil- therefore, how to treat subgrade diseases and solve the problem of insufficient subgrade iations. bearing capacity has become a great difficulty faced by road managers. As a type of liquid slurry, grouting materials have the advantages of high fluidity, permeability, and compactness. The slurry penetrating the structure can be used for filling and squeezes air and water in gaps to occupy the available space and decrease porosity Copyright: © 2022 by the authors. at cracks, thus improving the strength of the overall structure. Therefore, they are widely Licensee MDPI, Basel, Switzerland. used to repair defects of buildings, such as subgrades, bridges, and coal mines [3–6]. This article is an open access article Trenchless grouting reinforcement technology has gradually become the preferred scheme distributed under the terms and for subgrade reinforcement due to its advantages, such as simplicity of construction, rapid conditions of the Creative Commons re-opening to traffic, and low price. Geopolymers, firstly proposed by Davidovits, are Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ amorphous aluminosilicate gels depolymerised and repolymerised from aluminosilicate- 4.0/). rich materials that serve as raw materials under the action of an alkali activator. As inorganic Buildings 2022, 12, 503. https://doi.org/10.3390/buildings12050503 https://www.mdpi.com/journal/buildings Buildings 2022, 12, 503 2 of 12 polymer materials, geopolymers demonstrate a chain structure and have excellent acid and alkali corrosion resistance, rapid hardening, and high-temperature resistance [7–10]. With the rapid development of industrialisation, a lot of industrial wastes, such as fly ash (FA) and slag, are produced. Relevant studies indicate that furnace slag contains many glassy substances with pozzolanic activity which weakly react with water. However, activated by alkaline or acidic substances, such as sodium silicate, Ca(OH) , and NaOH, the active glassy substances in furnace slag are chemically activated to form gel products [11,12]. Under the action of a chemical activator, FA is chemically activated, and the resulting aluminosilicate gel can significantly improve the durability of activated products [13–15]. Scholars around the world have conducted experimental research on the performance of geopolymer grouting materials. Güllü [16] compared and investigated rheological properties of geopolymer grouting materials and FA cement-based grouting materials under different water-to-binder ratios. The research results show that geopolymer grouting materials exhibit better adaptability in material selection compared with cement-based grouting materials. Aboulayt [17] experimentally studied the rheological properties of geopolymer grouting materials formed by mixing metakaolin, FA, and stabiliser. The results implied that the addition of xanthan gum has a weak effect on the polymerisation, while it has positive effects on the stability of the grouting materials by acting on the activation solution. Roviello et al. [18] obtained a new hybrid material by synthesising a copolymer via a mixture of a polymer and an alkaline solution. Compared with pure geopolymer materials, the new material has a highly interpenetrating structure, excellent physical and mechanical properties, as well as better applicability to heat resistance and bonding of building structures. Furthermore, in terms of the effects of the activator on the performance of geopolymer grouting materials, Fernandez-Jimenez [19] investigated the influences of types of activator on the microstructure and mechanical properties of grouting materials. The research results suggested that an activator containing soluble Si is conducive to improving the chemical reaction of polymers and the strength of corresponding specimens. Criado [20–22] also found that the content and compositions of reaction products are closely related to the content of soluble Si in the activator, and the more aluminium silicate gel is produced, the higher the strength of the grouting materials. When hydroxide was selected as the activator, Lloyd [23] found that a small number of crystals with a large gap appear on the surface of FA, which greatly decreases the strength of specimens of grouting materials. Regarding the effects of mineral raw materials on the performance of geopolymer grouting materials, Yang et al. [24] fabricated FA microspheres through electrostatic adsorption and added them to an alkali-activated FA slag, which greatly improved the rheological properties of the geopolymer grouting materials. Amin et al. [25] explored influences of the content of sodium silicate solution on the fluidity of activated slag and found that the fluidity decreased with increasing amounts of sodium silicate solution. When 5% silica fume was added, the working performance of the grouting materials was improved. In the past few years, there have also been numerous reports on the shrinkage of geopolymers and their influencing factors. For example, with the increase in slag content or the concentration of the alkaline activator, Xu et al. [26] found that geopolymerization is accelerated and the shrinkage value increases. When basalt fiber was incorporated, it was also found that the capillary pores within geopolymers were improved and the pore network was refined, which generated a positive effect on shrinkage [27]. In addition, Xiang et al. [28] reported that the incorporation of Fuller-fine sand helps to increase the demand for “chemically combined” water within geopolymers, reducing the evaporation of water in a dry environment and further improving drying shrinkage. At present, there have been few studies examining the effects of activators and mineral raw materials on the performance of geopolymer grouting materials. In this research, new FA-based geopolymer grouting materials were prepared by chemically activating FA and solid wastes of granulated blast furnace slag (GBFS) using modified sodium silicate. Eight different mixing ratios were designed to evaluate the influences of the content of Na O in modified sodium silicate, sodium silicate modulus (M ), and the content of GBFS on the s Buildings 2022, 11, x FOR PEER REVIEW 3 of 12 At present, there have been few studies examining the effects of activators and mineral raw materials on the performance of geopolymer grouting materials. In this research, new FA-based geopolymer grouting materials were prepared by chemically activating FA and solid wastes of granulated blast furnace slag (GBFS) using modified Buildings 2022, 12, 503 3 of 12 sodium silicate. Eight different mixing ratios were designed to evaluate the influences of the content of Na2O in modified sodium silicate, sodium silicate modulus (Ms), and the content of GBFS on the compressive strength and drying shrinkage of FA-based compressive strength and drying shrinkage of FA-based geopolymer grouting materials geopolymer grouting materials at different ages. In addition, microstructures and product at different ages. In addition, microstructures and product compositions of FA-based compositions of FA-based geopolymer grouting materials under different contents of geopolymer grouting materials under different contents of GBFS were further studied by GBFS were further studied by using X-ray diffraction (XRD), mercury intrusion using X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and scanning electron porosimetry (MIP), and scanning electron microscopy–energy dispersive X-ray microscopy–energy dispersive X-ray spectroscopy (SEM–EDS). spectroscopy (SEM–EDS). 2. Experimental Program 2. Experimental Program 2.1. Materials 2.1. Materials In this research, FA and GBFS were used as ash raw materials. The chemical com- positions In thiand s res cea ontents rch, Fof A a FA nd G andBF GBFS S were determined used as a using sh raan w m X-ray ateria fluor ls. T escence he chem (XRF) ical diffraction analyser are listed in Table 1. The particle size distributions of FA and GBFS compositions and contents of FA and GBFS determined using an X-ray fluorescence (XRF) were studied with a Mastersizer 2000 laser particle sizer and the median diameters (D ) diffraction analyser are listed in Table 1. The particle size distributions of FA and GBFS of FA and GBFS were 10.80 m and 11.4 m, respectively. The XRD analysis of FA and were studied with a Mastersizer 2000 laser particle sizer and the median diameters (D50) GBFS is demonstrated in Figure 1. Figure 1a shows that FA contains mullite and quartz of FA and GBFS were 10.80 μm and 11.4 μm, respectively. The XRD analysis of FA and and that a hump appears within 15 2q 35 , indicating that FA includes several glassy GBFS is demonstrated in Figure 1. Figure 1a shows that FA contains mullite and quartz substances. As displayed in Figure 1b, diffuse scattering peaks occur within 20 2q 40 , and that a hump appears within 15° ≤ 2θ ≤ 35°, indicating that FA includes several glassy suggesting that glassy substances are present in GBFS. Furthermore, a diffraction peak substances. As displayed in Figure 1b, diffuse scattering peaks occur within 20° ≤ 2θ ≤ 40°, is seen at 2q = 29.5 (d = 0.30284 nm), indicating that merwinite is contained in GBFS. A suggesting that glassy substances are present in GBFS. Furthermore, a diffraction peak is diffraction peak appears at 2q = 31.3 (d = 0.28545 nm), suggesting that GBFS contains seen at 2θ = 29.5° (d = 0.30284 nm), indicating that merwinite is contained in GBFS. A akermanite or gehlenite. diffraction peak appears at 2θ = 31.3° (d = 0.28545 nm), suggesting that GBFS contains akermanite or gehlenite. Table 1. Chemical composition of FA and GBFS (wt%). Table 1. Chemical composition of FA and GBFS (wt%). Material SiO Al O CaO MgO Na O K O MnO P O TiO SO LOI 2 2 3 2 2 2 5 2 3 Material SiO2 Al2O3 CaO MgO Na2O K2O MnO P2O5 TiO2 SO3 LOI FA 50.62 21.97 7.18 9.17 2.12 1.33 - - 0.79 2.16 0.77 FA 50.62 21.97 7.18 9.17 2.12 1.33 - - 0.79 2.16 0.77 GBFS 33.00 14.82 0.23 40.80 - - 0.32 0.01 0.66 - 2.31 GBFS 33.00 14.82 0.23 40.80 - - 0.32 0.01 0.66 - 2.31 F Figure igure 1 1. . X XRD RD a analysis: nalysis: ((a a)) F FA A; ; ((b b)) G GBFS. BFS. Industrial sodium silicate used in this study was provided by Nanjing Daoqin Indus- Industrial sodium silicate used in this study was provided by Nanjing Daoqin trial Co., Ltd. (Nanjing, China), with the contents of SiO , Na O, and H O being 26.2, 8.5, 2 2 2 Industrial Co., Ltd. (Nanjing, China), with the contents of SiO2, Na2O, and H2O being 26.2, and 65.3 wt%. The solid sodium hydroxide with a purity 96% and deionised water were 8.5, and 65.3 wt%. The solid sodium hydroxide with a purity ≥96% and deionised water provided by Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). The modified were provided by Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). The sodium silicates with moduli (M ) of 1.2, 1.4, and 1.6, and Na O contents of 6, 9, and 12 wt% s 2 modified sodium silicates with moduli (Ms) of 1.2, 1.4, and 1.6, and Na2O contents of 6, 9, were prepared by adding solid sodium hydroxide and deionised water into industrial and 12 wt% were prepared by adding solid sodium hydroxide and deionised water into sodium silicate. All modified sodium silicates were allowed to stand for 24 h before use and recovered to room temperature. 2.2. Specimen Preparation and Testing Programs In the present study, the composite powder composed of FA and GBFS was chemi- cally activated with the modified sodium silicate. Eight types of grouting materials were prepared according to the mass ratio of water to composite powder (W/S) of 0.45. Figure 2 Buildings 2022, 11, x FOR PEER REVIEW 4 of 12 industrial sodium silicate. All modified sodium silicates were allowed to stand for 24 h before use and recovered to room temperature. 2.2. Specimen Preparation and Testing Programs In the present study, the composite powder composed of FA and GBFS was chemically activated with the modified sodium silicate. Eight types of grouting materials Buildings 2022, 12, 503 4 of 12 were prepared according to the mass ratio of water to composite powder (W/S) of 0.45. Figure 2 illustrates the nomenclature of grouting materials and Table 2 lists the mix proportions of the grouting materials. The grouting materials were injected into cubic illustrates the nomenclature of grouting materials and Table 2 lists the mix proportions of moulds measuring 30 mm × 30 mm × 30 mm and prismatic moulds measuring 20 mm × the grouting materials. The grouting materials were injected into cubic moulds measuring 20 mm × 80 mm after uniform stirring with a cement paste mixer, respectively. All 30 mm 30 mm 30 mm and prismatic moulds measuring 20 mm 20 mm 80 mm specimens were immediately wrapped with polyethylene films and then placed in the after uniform stirring with a cement paste mixer, respectively. All specimens were immedi- curing chamber (20 ± 1 °C, RH ≥ 95%) for curing for 24 h before being demoulded. ately wrapped with polyethylene films and then placed in the curing chamber (20 1 C, RH 95%) for curing for 24 h before being demoulded. Figure 2. N Figure omencl 2. atu Nomenclatur re of groutin egof mgr ate outing rials. materials. Table 2. Mix proportions for FA-based geopolymer grouting materials. Table 2. Mix proportions for FA-based geopolymer grouting materials. Composite Powder Modified Sodium Silicate Composite Powder Modified Sodium Silicate b No. Mix W/S FA (wt%) GBFS (wt%) Ms Na2O (wt%) SiO2 (wt%) H2O (wt%) No. Mix W/S GBFS Na O SiO 2 2 1 G-6-1.4 100 0 1.4 6.0 8.4 93.6 0.45 FA (wt%) M H O (wt%) (wt%) (wt%) (wt%) 2 G-9-1.2 100 0 1.2 9.0 10.8 89.8 0.45 3 G-9-1.4 100 0 1.4 9.0 12.6 99.5 0.45 1 G-6-1.4 100 0 1.4 6.0 8.4 93.6 0.45 4 G-9-1.6 100 0 1.6 9.0 14.4 101.0 0.45 2 G-9-1.2 100 0 1.2 9.0 10.8 89.8 0.45 5 G-12-1.4 100 0 1.4 12.0 16.8 105.4 0.45 3 G-9-1.4 100 0 1.4 9.0 12.6 99.5 0.45 6 G-9-1.2-10 90 10 1.2 9.0 10.8 89.8 0.45 4 G-9-1.6 100 0 1.6 9.0 14.4 101.0 0.45 7 G-9-1.2-20 80 20 1.2 9.0 10.8 89.8 0.45 5 G-12-1.4 100 0 1.4 12.0 16.8 105.4 0.45 8 G-9-1.2-30 70 30 1.2 9.0 10.8 89.8 0.45 6 G-9-1.2-10 90 10 1.2 9.0 10.8 89.8 0.45 Notes: (a) The contents of compositions in modified sodium silicate are expressed by the mass of 7 G-9-1.2-20 80 20 1.2 9.0 10.8 89.8 0.45 composite powder; (b) W/S represents the mass ratio of water to composite powder. 8 G-9-1.2-30 70 30 1.2 9.0 10.8 89.8 0.45 Notes: (a) The contents of compositions in modified sodium silicate are expressed by the mass of composite The dem powder; oulded c (b) W/S ub repr ic s esents pecim the en mass s were p ratio of la water ced ito n t composite he curinpowder g cham . ber for curing for 7, 28, and 90 days, respectively. According to the relevant test methods in GB/T 17671-2020 The demoulded cubic specimens were placed in the curing chamber for curing for [29], the compressive strength of the cubic specimens cured for 7, 28, and 90 days was 7, 28, and 90 days, respectively. According to the relevant test methods in GB/T 17671- measured with an electro-hydraulic cement compressive tester (TYA-100C). Each 2020 [29], the compressive strength of the cubic specimens cured for 7, 28, and 90 days compressive strength value was measured based on three specimens. was measured with an electro-hydraulic cement compressive tester (TYA-100C). Each The drying shrinkage of the grouting materials at different ages was tested based on compressive strength value was measured based on three specimens. the prismatic specimens. The initial length (L0) of the demoulded specimen was first The drying shrinkage of the grouting materials at different ages was tested based measured using a comparator by referring to relevant test methods in JC/T 603-2004 [30]. on the prismatic specimens. The initial length (L ) of the demoulded specimen was first Thereafter, the specimen was placed in a curing box to allow continued curing for 2, 3, 7, measured using a comparator by referring to relevant test methods in JC/T 603-2004 [30]. 14, 21, 28, 56, 90, and 180 days at 20 ± 2 °C and RH = 45 ± 5%. After curing, the lengths (Lt) Thereafter, the specimen was placed in a curing box to allow continued curing for 2, 3, 7, 14, of the specimens at different ages were measured. The drying shrinkage of the specimen 21, 28, 56, 90, and 180 days at 20 2 C and RH = 45 5%. After curing, the lengths (L ) of was calculated in accordance with Equation (1): the specimens at different ages were measured. The drying shrinkage of the specimen was L − L 0 t calculated in accordance with Equation (1): S = ×100% (1) L L where St is the drying shrinkage percentage of the sp 0 ecim t en at each age (%) and Le denotes S = 100% (1) the effective length of the specimen (75 mm). e where S is the drying shrinkage percentage of the specimen at each age (%) and L denotes t e the effective length of the specimen (75 mm). To study the microstructure of the grouting materials, samples were taken from the crushed rectangular specimen that had been cured for 28 days, immersed in absolute ethanol for 24 h and then dried in a vacuum at 40 C for 24 h. The XRD test was then used to analyse the phases of the specimen under the scanning range of 5 to 85 at a scanning rate of 10 /min. An MIP test was conducted on the grouting materials with a 60-GT automatic mercury porosimeter to study the micropore structure. The microstructures of Buildings 2022, 11, x FOR PEER REVIEW 5 of 12 To study the microstructure of the grouting materials, samples were taken from the crushed rectangular specimen that had been cured for 28 days, immersed in absolute ethanol for 24 h and then dried in a vacuum at 40 °C for 24 h. The XRD test was then used to analyse the phases of the specimen under the scanning range of 5° to 85° at a scanning Buildings 2022, 12, 503 5 of 12 rate of 10°/min. An MIP test was conducted on the grouting materials with a 60-GT automatic mercury porosimeter to study the micropore structure. The microstructures of the specimens were observed through the SEM–EDS test and the types of reaction the specimens were observed through the SEM–EDS test and the types of reaction products products were determined according to elemental compositions in the microstructure. were determined according to elemental compositions in the microstructure. 3. Results and Discussion 3. Results and Discussion 3.1. Compressive Strength 3.1. Compressive Strength The compressive strengths of FA-based geopolymer grouting materials cured for 7, The compressive strengths of FA-based geopolymer grouting materials cured for 7, 28, and 90 days with different contents of Na2O, Ms, and contents of GBFS are displayed 28, and 90 days with different contents of Na O, M and contents of GBFS are displayed s , in Figure 3. Figure 3a shows that as the content of Na2O in modified sodium silicate in Figure 3. Figure 3a shows that as the content of Na O in modified sodium silicate increased from 6.0 to 12.0 wt%, the compressive strength of the grouting materials cured increased from 6.0 to 12.0 wt%, the compressive strength of the grouting materials cured for 7, 28, and 90 days increased from 6.0 to 14.1 MPa, from 12.6 to 24.4 MPa, and from 16.7 for 7, 28, and 90 days increased from 6.0 to 14.1 MPa, from 12.6 to 24.4 MPa, and from 16.7 to 39.0 MPa, respectively. These findings indicate that the increased content of Na2O in to 39.0 MPa, respectively. These findings indicate that the increased content of Na O in the modified sodium silicate is conducive to improving the compressive strength of the the modified sodium silicate is conducive to improving the compressive strength of the grouting materials. The main reasons for this are as follows: on the one hand, the higher grouting materials. The main reasons for this are as follows: on the one hand, the higher the content of Na2O in modified sodium silicate as the activator, the more alkaline the the content of Na O in modified sodium silicate as the activator, the more alkaline the geopolymer system, which promotes the full dissolution of raw materials. The increase in geopolymer system, which promotes the full dissolution of raw materials. The increase the dissolution of Si and Al promotes continuous polymerization, resulting in more gel in the dissolution of Si and Al promotes continuous polymerization, resulting in more gel phases. On the other hand, the higher the content of Na2O, the higher the content of SiO2 phases. On the other hand, the higher the content of Na O, the higher the content of SiO 2 2 that plays a role in cementation in the modified sodium silicate. The generation of a lot of that plays a role in cementation in the modified sodium silicate. The generation of a lot of gel phases results in denser grouting materials, thus increasing their compressive gel phases results in denser grouting materials, thus increasing their compressive strength. strength. In addition, the formation of hydrated ions by Na ions and more water is In addition, the formation of hydrated ions by Na ions and more water is conducive to conducive to decreasing the content of free water as well as the content of microscopic decreasing the content of free water as well as the content of microscopic pores in the pores in the internal structure induced by water evaporation, further slowing down the internal structure induced by water evaporation, further slowing down the generation of generation of microcracks and strength loss to a certain extent. microcracks and strength loss to a certain extent. (a) (b) (c) Figure 3. Effects of different factors on the compressive strength of FA-based geopolymers: (a) content of Na O; (b) M ; (c) content of GBFS. 2 s As illustrated in Figure 3b, with the increase in M from 1.2 to 1.6, the compressive strength of FA-based geopolymer grouting materials cured for 7 and 28 days increased by 2.5 and 1.5 MPa from 9.6 to 12.1 MPa and from 18.6 to 20.1 MPa, respectively. It is Buildings 2022, 12, 503 6 of 12 noteworthy that the compressive strength after curing for 28 days decreased slightly when the M was 1.4. The compressive strength of the grouting materials cured for 90 days first increased, then decreased, and increased by 0.52 MPa with the increase in M . It can be inferred that for the grouting materials at an early age, increasing the modulus of the activator was beneficial in that it slightly increased the compressive strength. However, the compressive strength decreased with the increase in the modulus of the activator for the grouting materials at the later age. Sodium silicate is an important cementing agent. When keeping the W/S and content of Na O unchanged, the larger M is, the higher the 2 s content of silica oligomer in modified sodium silicate. Many silica oligomers precipitate on the surface of undissolved FA particles, which improves the compressive strength of the grouting materials. When M is high, [Al(OH) ] produced through dissolution is immediately saturated by [Si(OH) ]. The subsequent polycondensation occurs between [Si(OH) ] and [Si(OH) ] with a high reaction activation energy. This prolongs the setting 4 4 and hardening time of FA-based geopolymer grouting material, which is not conducive to practical engineering applications. Figure 3c shows the compressive strength of FA-based geopolymer grouting materials cured for 7, 28, and 90 days after adding different amounts of GBFS: as the amount of GBFS increased from 0 to 30 wt%, the compressive strength of the grouting materials cured for 7, 28, and 90 days increased by 195%, 101%, and 88%, respectively, suggesting that the addition of GBFS was conducive to improving the compressive strength of the grouting materials. However, the increasing amplitude in compressive strength decreased slightly with the increase in curing age. 3.2. Drying Shrinkage Figure 4 shows the drying shrinkage of FA-based geopolymer grouting materials under different amounts of Na O, M , and amounts of GBFS. From Figure 4a, the content 2 s of Na O in the modified sodium silicate exhibits a significant effect on the drying shrinkage of the grouting materials under a certain M . For instance, the drying shrinkage percentage of the grouting materials was merely increased by about 0.07% at an age of 180 days when the content of Na O increased from 6 to 9 wt%. When the content of Na O increased 2 2 from 9 to 12 wt%, the drying shrinkage percentage increased by 0.36%. The generation of a certain amount of shrinkage is closely related to two types of driving forces, namely, the pore pressure and the steric hydration forces induced by the interactions between ions [31]. On the one hand, as mentioned above, increasing the content of Na O is conducive to decreasing the internal porosity of the material and making the internal structure more dense, which may contribute to a smaller radius of the menisci formed within the grouting material and further induce a high pore pressure, resulting in increased autogenous shrink- age. On the other hand, with the increase in Na O content, there were large amounts of Na ions in the initial solution. With the progress of polymerization, the reduction in the concentration of Na ions and the hydration shells essentially led to a decrease in the steric hydration force. Consequently, the surrounding gel pores were close to each other, which was manifested in the increase in the drying shrinkage of the specimen. The changes in the drying shrinkage of the grouting materials with age under dif- ferent M are illustrated in Figure 4b: the drying shrinkage of the grouting materials first decreased, then increased with the increase in M . When M increased from 1.2 to 1.6, the s s corresponding drying shrinkage of the grouting materials at the age of 180 days decreased from 0.29% to 0.15%, then increased to 0.29%. In addition, comparison of Figure 4a,b shows that the content of Na O in the modified sodium silicate exerted a more significant influence on the drying shrinkage of the grouting materials than M . The changes in the drying shrinkage of FA-based geopolymer grouting materials with age under different contents of GBFS are shown in Figure 4c. As the content of GBFS increased, the drying shrinkage of the grouting materials uniformly decreased. As the content of GBFS increased from 0 to 30 wt%, the drying shrinkage decreased by 28% from 0.29% to 0.21%. The reaction product of the grouting materials was N-A-S (H) gel. Buildings 2022, 12, 503 7 of 12 The gel contained many gel pores and capillary pores, and a large capillary force during dehydration shrinks and cracks the materials. After adding GBFS, the reaction product of the grouting materials (N-A-S (H) gel) contained some C-A-S-H gel. Compared with the Buildings 2022, 11, x FOR PEER REVIEW 7 of 12 N-A-S (H) gel, the resulting C-A-S-H gel had the higher elastic modulus, which is beneficial for inhibiting the shrinkage of gel materials. (a) (b) (c) Figure 4. Influences of different factors on the drying shrinkage of FA-based geopolymer grouting Figure 4. Influences of different factors on the drying shrinkage of FA-based geopolymer grouting materials: (a) content of Na2O; (b) Ms; (c) content of GBFS. materials: (a) content of Na O; (b) M ; (c) content of GBFS. 2 s 3.3. XRD The c Analysis hanges in the drying shrinkage of the grouting materials with age under different Ms are illustrated in Figure 4b: the drying shrinkage of the grouting materials Figure 5 displays the XRD patterns of FA-based geopolymer grouting materials under first decreased, then increased with the increase in Ms. When Ms increased from 1.2 to 1.6, different contents of Na O, M , and contents of GBFS. The turning point in the chart (for 2 s the corresponding drying shrinkage of the grouting materials at the age of 180 days FA-based material) is widened and shifts to a higher angle after activation with modified decreased from 0.29% to 0.15%, then increased to 0.29%. In addition, comparison of Figure sodium silicate, suggesting the formation of N-A-S (H) gel due to alkali excitation [8]. As 4a,b shows that the content of Na2O in the modified sodium silicate exerted a more displayed in Figure 5a, it can be observed that XRD patterns of FA-based geopolymer significant influence on the drying shrinkage of the grouting materials than Ms. grouting materials under different contents of Na O and M are basically consistent. The The changes in the drying shrinkage of FA-based geopolymer grouting materials original quartz and mullite in the fly ash still existed in the diffraction spectrum of the with age under different contents of GBFS are shown in Figure 4c. As the content of GBFS geopolymerisation products and the corresponding positions of the characteristic peaks did incrnot ease change, d, the dbut ryinthe g sh intensity rinkage of of each the gr characte outing ristic materpeak ials uwas nifordif mly ferd ent. ecreXRD ased.cannot As the ef co fectively ntent of characterise GBFS increas phase ed from compositions 0 to 30 wt%, t ofhF e dry A-based ing sh geopolymer rinkage decr gr ea outing sed bymaterials 28% from 0.29% to 0.21%. The reaction product of the grouting materials was N-A-S (H) gel. The gel with N-A-S (H) gel as the main product. contAs aine shown d manin y ge Figur l peor5eb, s a quartz nd cap and illarmullite y pores, phases and a wer laerge still capr pilla esent ry f inorFce A-based during geopolymerisation dehydration shrink pr s a oducts nd cra after cks th adding e materi 0–30 als. A wt% fter a GBFS. ddin W g G ith Bthe FS, t incr he rea ease ctin ion the pro content duct of of GBFS, the diffraction intensities of quartz and mullite phases gradually decreased, the grouting materials (N-A-S (H) gel) contained some C-A-S-H gel. Compared with the indicating that these two phases did not participate in geopolymerisation. Furthermore, it N-A-S (H) gel, the resulting C-A-S-H gel had the higher elastic modulus, which is can be inferred that the addition of GBFS increases the solubility of FA, thus improving beneficial for inhibiting the shrinkage of gel materials. the reaction of many FA-based polymer grouting materials. Moreover, the proportion of amorphous products significantly increased. Figure 5b shows that the hump widened and 3.3. XRD Analysis Figure 5 displays the XRD patterns of FA-based geopolymer grouting materials under different contents of Na2O, Ms, and contents of GBFS. The turning point in the chart (for FA-based material) is widened and shifts to a higher angle after activation with modified sodium silicate, suggesting the formation of N-A-S (H) gel due to alkali excitation [8]. As displayed in Figure 5a, it can be observed that XRD patterns of FA-based geopolymer grouting materials under different contents of Na2O and Ms are basically Buildings 2022, 11, x FOR PEER REVIEW 8 of 12 Buildings 2022, 12, 503 8 of 12 consistent. The original quartz and mullite in the fly ash still existed in the diffraction spectrum of the geopolymerisation products and the corresponding positions of the moved to a higher angle with the increase in the content of GBFS. This is mainly because a 2+ characteristic peaks did not change, but the intensity of each characteristic peak was large amount of Ca in GBFS dissolves and participates in geopolymerisation, so that the different. XRD cannot effectively characterise phase compositions of FA-based product of FA-based geopolymer grouting materials partially converts from N-A-S(H) gel geopolymer grouting materials with N-A-S (H) gel as the main product. to C-A-S-H gel. (b) (a) Q-Quartz Q-Quartz M-Mullite M-Mullite M M M M G-9-12-30 G-12-14 G-9-12-20 G-6-14 G-9-16 G-9-14 G-9-12-10 G-9-12 G-9-12 FA 10 20 30 40 50 60 70 10 20 30 40 50 60 70 2θ/° 2θ/° Figure 5. XRD analysis of FA-based geopolymer grouting materials: (a) parameters of modified Figure 5. XRD analysis of FA-based geopolymer grouting materials: (a) parameters of modified sodium silicate; (b) content of GBFS. sodium silicate; (b) content of GBFS. 3.4. MIP Analysis As shown in Figure 5b, quartz and mullite phases were still present in FA-based geopolymerisation products after adding 0–30 wt% GBFS. With the increase in the content The MIP test results of FA-based geopolymer grouting materials G-9-12 and G-9-12- of GBFS, the diffraction intensities of quartz and mullite phases gradually decreased, 30 are shown in Figure 6. As displayed in Figure 6a, double peaks appear in the pore indicating that these two phases did not participate in geopolymerisation. Furthermore, size distribution of G-9-12 but not that for G-9-12-30 because many coalesced pores are it can be inferred that the addition of GBFS increases the solubility of FA, thus improving present in such polymers [32]. On the one hand, after being modified by 30 wt% GBFS, the reaction of many FA-based polymer grouting materials. Moreover, the proportion of the chemical reaction of FA-based geopolymers was more complete and more reaction amorphous products significantly increased. Figure 5b shows that the hump widened and products filled gaps inside the materials to make the structure more compact. On the other mov hand, edGBFS to a hplays igher a an rg ole le w initmicr h the o-aggr increa egate se in t filling he cont and entcan of GB also FSdecr . Thiease s is ma the inl por y b osity ecaus of e 2+ a large amount of Ca in GBFS dissolves and participates in geopolymerisation, so that grouting materials to a certain extent. Figure 6b shows the proportion of volumes of pores t with he pro dif d fer ucent t of F sizes A-bin ase G-9-12 d geopand olym G-9-12-30. er groutinAfter g matadding erials pa 30 rtia wt% lly cGBFS, onvertthe s fro pr m oportion N-A-S(H) of ge por l t es o C smaller -A-S-H than gel.10 nm in the grouting materials increased from 6.83% to 27.28%, whereas those of pores with sizes of 10–20, 20–50, 50–100, and larger than 100 nm decreased by 3 51.56%, .4. MIP79.06%, Analysi79.14%, s and 57.41%, respectively. The proportion of pores larger than 50 nm decreased from 43.16% to 23.24%. This implies that the addition of 30 wt% GBFS improves The MIP test results of FA-based geopolymer grouting materials G-9-12 and G-9-12- the pore size distribution of FA-based geopolymer grouting materials. It is inferred that 30 are shown in Figure 6. As displayed in Figure 6a, double peaks appear in the pore size the microstructure of the grouting materials to which 30 wt% GBFS has been added is distribution of G-9-12 but not that for G-9-12-30 because many coalesced pores are present Buildings 2022, 11, x FOR PEER REVIEW 9 of 12 more compact and suffers less drying shrinkage compared with grouting materials without in such polymers [32]. On the one hand, after being modified by 30 wt% GBFS, the added GBFS. chemical reaction of FA-based geopolymers was more complete and more reaction products filled gaps inside the materials to make the structure more compact. On the other hand, GBFS plays a role in micro-aggregate filling and can also decrease the porosity of grouting materials to a certain extent. Figure 6b shows the proportion of volumes of pores with different sizes in G-9-12 and G-9-12-30. After adding 30 wt% GBFS, the proportion of pores smaller than 10 nm in the grouting materials increased from 6.83% to 27.28%, whereas those of pores with sizes of 10–20, 20–50, 50–100, and larger than 100 nm decreased by 51.56%, 79.06%, 79.14%, and 57.41%, respectively. The proportion of pores larger than 50 nm decreased from 43.16% to 23.24%. This implies that the addition of 30 wt% GBFS improves the pore size distribution of FA-based geopolymer grouting materials. It is inferred that the microstructure of the grouting materials to which 30 wt% GBFS has been added is more compact and suffers less drying shrinkage compared with grouting materials without added GBFS. (a) (b) Figure 6. Pore size distribution of FA-based geopolymer grouting materials: (a) differential curves Figure 6. Pore size distribution of FA-based geopolymer grouting materials: (a) differential curves of of pore size distribution; (b) proportion of pores. pore size distribution; (b) proportion of pores. 3.5. SEM–EDS Analysis Figures 7 and 8 display SEM–EDS patterns of FA-based geopolymer grouting materials G-9-12 and G-9-12-30, respectively. FA-based geopolymer grouting materials present a “chocolate cookie” structure: many undissolved FA particles are embedded in gel products or spall in the sample preparation process to leave different sizes of pores; flocculent or crystalline substances aggregate on the surface of some undissolved FA particles. In addition, there are many networked cracks in the gel products of FA-based geopolymer grouting materials, some of which are coalesced. A large gap exists between a lot of incomplete FA particles and gel products, mainly due to the dehydration and shrinkage of gel products. The research on the microstructure of geopolymers also shows that the geopolymerisation products produced by dissolution and condensation are unable to fill pores produced by the dissolution of FA particles [33]. (a) (b) (c) (d) Figure 7. SEM–EDS patterns of G-9-12: (a) SEM image (×500); (b) SEM image (×3000); (c) elemental composition: Area A; (d) elemental composition: Area B. Buildings 2022, 11, x FOR PEER REVIEW 9 of 12 (a) (b) Buildings 2022, 12, 503 9 of 12 Figure 6. Pore size distribution of FA-based geopolymer grouting materials: (a) differential curves of pore size distribution; (b) proportion of pores. 33.5. .5. SSEM–EDS EM–EDS A Analysis nalysis Figu Figurre ess 7 7 and and 8 8 display displa SEM–EDS y SEM–E patterns DS patt of erFns A-based of FAgeopolymer -based geop gr olouting ymer g materials routing m G-9-12 aterials and G-G-9-12-30, 9-12 and G r-espectively 9-12-30, resp . FeA-based ctively. FA geopolymer -based geogr po outing lymer materials grouting m pra esent terials a “chocolate cookie” structure: many undissolved FA particles are embedded in gel products present a “chocolate cookie” structure: many undissolved FA particles are embedded in ge orl p spall rodu in cts o ther sp sample all in t pr heparation e sample p pr reocess paratio ton p leave rocedif ss t fer o le ent ave sizes diffe of ren por t siz es; es o flocculent f pores; or crystalline substances aggregate on the surface of some undissolved FA particles. In flocculent or crystalline substances aggregate on the surface of some undissolved FA addition, there are many networked cracks in the gel products of FA-based geopolymer particles. In addition, there are many networked cracks in the gel products of FA-based grouting materials, some of which are coalesced. A large gap exists between a lot of geopolymer grouting materials, some of which are coalesced. A large gap exists between incomplete FA particles and gel products, mainly due to the dehydration and shrinkage a lot of incomplete FA particles and gel products, mainly due to the dehydration and of gel products. The research on the microstructure of geopolymers also shows that the shrinkage of gel products. The research on the microstructure of geopolymers also shows geopolymerisation products produced by dissolution and condensation are unable to fill that the geopolymerisation products produced by dissolution and condensation are pores produced by the dissolution of FA particles [33]. unable to fill pores produced by the dissolution of FA particles [33]. (a) (b) (c) (d) Figure 7. SEM–EDS patterns of G-9-12: (a) SEM image (×500); (b) SEM image (×3000); (c) elemental Figure 7. SEM–EDS patterns of G-9-12: (a) SEM image (500); (b) SEM image (3000); (c) elemental composition: Area A; (d) elemental composition: Area B. composition: Area A; (d) elemental composition: Area B. The main elemental composition in matrix A of the FA-based geopolymer grouting ma- terials G-9-12 was Na K Ca Mg AlSi Fe , which contained C-A-S-H and N-A- 2.88 0.12 1.28 0.13 4.17 0.37 S(H) gel products. The main elemental composition in floccule B was Na K Ca Mg 2.13 0.06 0.93 0.15 AlSi Fe , which also contained C-A-S-H and N-A-S (H) gel products. Both A and B 3.63 0.30 were the result of the accumulation of gel particles, but the density of A was higher than that of B. It is speculated that the amount of free water in B was higher, resulting in a loose structure. Compared with G-9-12, G-9-12-30 with the content of GBFS of 30 wt% has a more compact structure and contains fewer undissolved FA particles. The reaction activity of GBFS is much higher than FA, and glassy substances in GBFS are dissolved in activator 2+ 2+ solution, producing a large amount of Ca . On the one hand, the dissolved Ca from GBFS can replace some charge-balancing Na ions in the N-A-S (H) gel network, resulting 2+ in the gradual conversion of N-A-S (H) gel into C-A-S-H gel [32]. On the other hand, Ca can decrease the bond energy of Si , Al , and O , thus promoting the dissolution of 2P 2P 1S glassy substances in FA. Adding an appropriate amount of GBFS is conducive to improving the compactness of the microstructure of FA-based geopolymer growing materials [34]. Buildings 2022, 12, 503 10 of 12 Buildings 2022, 11, x FOR PEER REVIEW 10 of 12 (a) (b) 1000 1000 C D Si 800 800 Atom % Si Atom % 600 600 Si:Al:Fe:Na:K:Ca:Mg O Al Si:Al:Fe:Na:Ca:Mg =39.57:11.36:1.39:22.74:0.59:20.56:2.01 Mg =25.82:21.86:4.99:12.55:14.54:18.84 400 400 Na Ca Al Ca Na 200 200 Pt Mg Pt C S Fe S Ca Fe Ca Fe 0 0 0 2 4 6 0 2 4 6 keV keV (c) (d) Figure 8. SEM–EDS patterns of G-9-12-30: (a) SEM image (×500); (b) SEM image (×3000); (c) Figure 8. SEM–EDS patterns of G-9-12-30: (a) SEM image (500); (b) SEM image (3000); elemental composition: Area C; (d) elemental composition: Area D. (c) elemental composition: Area C; (d) elemental composition: Area D. The main elemental composition in matrix A of the FA-based geopolymer grouting The main elemental composition in matrix C of G-9-12-30 was Na K Ca Mg 2.00 0.05 1.81 0.18 materials G-9-12 was Na2.88K0.12Ca1.28Mg0.13AlSi4.17Fe0.37, which contained C-A-S-H and N- AlSi Fe , which consisted of C-A-S-H and N-A-S (H) gel products. The mushroom- 3.48 0.12 A-S(H) gel products. The main elemental composition in floccule B was shaped floccule mainly comprised Na Ca Mg AlSi Fe as well as C-A-S-H and 0.57 0.67 0.86 1.18 0.23 Na2.13K0.06Ca0.93Mg0.15AlSi3.63Fe0.30, which also contained C-A-S-H and N-A-S (H) gel N-A-S (H) gel products. In comparison with G-9-12, the calcium content in the matrix of products. Both A and B were the result of the accumulation of gel particles, but the density G-9-12-30 increased significantly. Therefore, it is inferred that the proportion of C-A-S-H of A was higher than that of B. It is speculated that the amount of free water in B was gel in its products increased significantly. higher, resulting in a loose structure. 4. Conclusions Compared with G-9-12, G-9-12-30 with the content of GBFS of 30 wt% has a more comp Based act stron uctexperimental ure and contar in esear s few ch erand und theor issolv etical ed FA analysis, particlethe s. Tfollowing he reaction conclusions activity of GBFS is much higher than FA, and glassy substances in GBFS are dissolved in activator are obtained: 2+ 2+ solution, producing a large amount of Ca . On the one hand, the dissolved Ca from When the sodium silicate modulus is certain, increasing the content of Na O in the G modified BFS can rep sodium lace s silicate ome chis arconducive ge-balancin to g N enhancing a ions in t the hecompr N-A-S e ( ssive H) ge str l n ength etworof k, r FA-based esulting 2+ in geopolymer the graduagr l couting onversio materials. n of N-A-W S ( ith H)the gel in incr toease C-Ain -S-sodium H gel [32 silicate ]. On the modulus, other hathe nd, C com- a pressive strength of grouting materials with early curing age improved slightly, whereas can decrease the bond energy of Si2P, Al2P, and O1S, thus promoting the dissolution of the compressive strength of grouting materials with a high curing age first increased and glassy substances in FA. Adding an appropriate amount of GBFS is conducive to then decreased. As the GBFS content ranged from 0 to 30 wt%, a significant increase improving the compactness of the microstructure of FA-based geopolymer growing was observed in the compressive strength of grouting materials; however, the increasing materials [34]. amplitude slowed down with curing age. The main elemental composition in matrix C of G-9-12-30 was With the content of Na O ranging from 9 to 12 wt%, the drying shrinkage of FA-based Na2.00K0.05Ca1.81Mg0.18AlSi3.48Fe 2 0.12, which consisted of C-A-S-H and N-A-S (H) gel products. geopolymer grouting materials showed a significant increase. It was observed that the The mushroom-shaped floccule mainly comprised Na0.57Ca0.67Mg0.86AlSi1.18Fe0.23 as well as drying shrinkage of FA-based geopolymer grouting materials was decreased with the C-A-S-H and N-A-S (H) gel products. In comparison with G-9-12, the calcium content in increase in sodium silicate modulus and then significantly increased when the sodium the matrix of G-9-12-30 increased significantly. Therefore, it is inferred that the proportion silicate modulus was 1.6. The improvement of GBFS content has a positive effect on the of C-A-S-H gel in its products increased significantly. drying shrinkage of FA-based geopolymer grouting materials. XRD analysis shows that, with the increase in Na O content and sodium silicate modulus, the positions of the characteristic peaks of quartz and mullite do not change, and the main difference is that each characteristic peak shows a certain difference in intensity. Buildings 2022, 12, 503 11 of 12 The increase in GBFS content could improve the solubility of FA and further promote the formation of C-A-S-H gel. MIP and SEM–EDS analysis revealed that the incorporation of GBFS with a content of 30% helped to reduce the proportion of pores with large pore size and further improved the pore size distribution in the grouting materials as well as the conversion of the reaction products of FA-based geopolymer grouting materials from the main N-A-S(H) gel to both N-A-S(H) and C-A-S-H gel. Author Contributions: Q.Z., resources, investigation, writing—original draft, editing and formal analysis; P.G., supervision, validation, methodology and funding acquisition; K.L., G.D., G.J., X.S., J.Z. and L.C., data curation, project administration. All authors have read and agreed to the published version of the manuscript. Funding: This project was support by the Jiangsu Province International Science and Technology Cooperation Project (BZ2019060), the Tian Expressway Group Technology Project (GS-YY-YH-2021-775), and the Science and Technology Project of CCCC Third Highway Engineering (3GS-TL-JS-04-2021). Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data presented in this study are available on request from the correspondence author. Conflicts of Interest: The authors declare no conflict of interest. References 1. Mo, H.; Alengaram, U.J.; Jumaat, M.Z. Structural performance of reinforced geopolymer concrete members: A review. Constr. Build. Mater. 2016, 120, 251–264. [CrossRef] 2. Chen, C.; Habert, G.; Bouzidi, Y.; Jullien, A. Environmental impact of cement production: Detail of the different processes and cement plant variability evaluation. J. Clean. Prod. 2010, 18, 478–485. [CrossRef] 3. Yang, Z.; Zhang, X.; Liu, X.; Guan, X.; Zhang, C.; Niu, Y. Flexible and stretchable polyurethane/waterglass grouting material. Constr. Build. Mater. 2017, 138, 240–246. [CrossRef] 4. Güllü, H. On the viscous behavior of cement mixtures with clay, sand, lime and bottom ash for jet grouting. Constr. Build. Mater. 2015, 93, 891–910. [CrossRef] 5. Canakci, H.; Güllü, H.; Dwle, M. Effect of glass powder added grout for deep mixing of marginal sand with clay. Arab. J. Sci. Eng. 2018, 43, 1583–1595. [CrossRef] 6. Gao, P.W.; Zhong, J.J.; Deng, Y.S.; Xu, X.F.; Li, M.Y.; Zhang, J. Preparation and microstructure analysis of high performance lightweight grouting materials. J. East China Jiaotong Univ. 2021, 38, 29–35. 7. Davidovits, J. Geopolymer: Inorganic polymeric new materials. J. Ther. Anal. 1991, 37, 1633–1639. [CrossRef] 8. Duxson, P.; Fernandez-Jimenez, A.; Provis, J.L. Geopolymer technology: The current state of the art. J. Mater. Sci. 2007, 42, 2917–2933. [CrossRef] 9. Duxson, P.; Provis, J.L.; Luckey, G.C. The role of inorganic polymer technology in the development of ‘green concrete’. Cem. Concr. Res. 2007, 37, 1590–1597. [CrossRef] 10. Liang, G.W.; Li, H.X.; Zhu, H.J.; Liu, T.J.; Chen, Q.; Guo, H.H. Reuse of waste glass powder in alkali-activated metakaolin/fly ash pastes: Physical properties, reaction kinetics and microstructure. Resour. Conserv. Recycl. 2021, 173, 105721. [CrossRef] 11. Li, C.; Sun, H.; Li, L. A review: The comparison between alkali-activated slag (Si + Ca) and metakaolin (Si + Al) cements. Cem. Concr. Res. 2010, 40, 1341–1349. [CrossRef] 12. Davidovits, J. Geopolymer Chemistry and Applications; Geopolymer Institute: Saint-Quentin, France, 2008. 13. Provis, J.L.; Duxson, P.; Deventer, J.S.J.V. The role of mathematical modelling and gel chemistry in advancing geopolymer technology. Chem. Eng. Res. Des. 2005, 83, 853–860. [CrossRef] 14. Provis, J.L.; Bernal, S.A. Geopolymers and Related Alkali-Activated Materials. Annu. Rev. Mater. Res. 2014, 44, 299–327. [CrossRef] 15. Myers, R.J.; Bernal, S.A.; San Nicolas, R. Generalized structural description of calcium-sodium aluminosilicate hydrate gels: The cross-linked substituted tobermorite model. Langmuir 2013, 29, 5294–5306. [CrossRef] 16. Güllü, H.; Cevik, A.; Al-Ezzi, K.M.A. On the rheology of using geopolymer for grouting: A comparative study with cement-based grout included fly ash and cold bonded fly ash. Constr. Build. Mater. 2019, 196, 594–610. [CrossRef] 17. Aboulayt, A.; Jaafri, R.; Samouh, H. Stability of a new geopolymer grout: Rheological and mechanical performances of metakaolin- fly ash binary mixtures. Constr. Build. Mater. 2018, 181, 420–436. [CrossRef] 18. Roviello, G.; Menna, C.; Tarallo, O.; Ricciotti, L. Preparation, structure and properties of hybrid materials based on geopolymers and polysiloxanes. Mater. Des. 2015, 87, 82–94. [CrossRef] Buildings 2022, 12, 503 12 of 12 19. Fernandez-Jimenez, A.; Palomo, A. Composition and microstructure of alkali activated fly ash binder: Effect of the activator. Cem. Concr. Res. 2005, 35, 1984–1992. [CrossRef] 20. Criado, M.; Fernandez-Jimenez, A.; de la Torre, A.G.; Aranda, M.A.G.; Palomo, A. An XRD study of the effect of the SiO /Na O 2 2 ration on the alkali activation of fly ash. Cem. Concr. Res. 2007, 37, 671–679. [CrossRef] 21. Criado, M.; Fernandez-Jimenez, A.; Palomo, A. Alkali activation of fly ash: Effect of the SiO /Na O ratio PartI: FTIR study. 2 2 Microporous Mesoporous Mater. 2007, 106, 180–191. [CrossRef] 22. Criado, M.; Fernandez-Jimenez, A.; Palomo, A.; Sobrados, I.; Sanz, J. Effect of the SiO /Na O ratio on the alkali activation of fly 2 2 ash. PartII: 29Si MAS-NMR Survey. Microporous Mesoporous Mater. 2008, 109, 525–534. [CrossRef] 23. Lloyd, R.R.; Provis, J.L.; Devevter, J.S.J.V. Microscopy and microanalysis of inorganic polymer cements. 2: The gel binder. J. Mater. Sci. 2009, 44, 620–631. [CrossRef] 24. Yang, T.; Zhu, H.; Zhang, Z.H. Effect of fly ash microsphere on the rheology and microstructure of alkali-activated fly ash/slag pastes. Cem. Concr. Res. 2018, 109, 198–207. [CrossRef] 25. Amin, M.M.; Mohammad, B.; Alireza, J. Feasibility of Alkali-Activated Slag Pasteas Injection Material for Rehabilitation of Concrete Structures. J. Mater. Civ. Eng. 2018, 30, 04018252. 26. Xu, J.; Kang, A.H.; Wu, Z.G.; Xiao, P.; Li, B.; Lu, Y.M. Reseach on the formulation and properties of a high-performance geopolymer grouting material based on slag and fly ash. KSCE J. Civ. Eng. 2021, 25, 3437–3447. [CrossRef] 27. Xu, J.; Kang, A.H.; Wu, Z.G.; Xiao, P.; Gong, Y.F. Effect of high-calcium basalt fiber on the workability, menchanical properties and microstructure of slag-fly ash geopolymer grouting material. Constr. Build. Mater. 2021, 302, 124089. [CrossRef] 28. Xiang, J.X.; Liu, L.P.; Cui, X.M.; He, Y.; Zheng, G.J.; Shi, C.J. Effect of fuller-fine sand on rheological, drying shrinkage, and microstructural properties of metakaolin-based geopolymer grouting materials. Cem. Concr. Compos. 2019, 104, 103381. [CrossRef] 29. GB/T 17671-2020; Methods of Testing Cements-Determination of Strength. Standards Press of China: Beijing, China, 2020. 30. JC/T 603-2004; Standard Test Method for Drying Shrinkage of Mortar. Standards Press of China: Beijing, China, 2004. 31. Li, Z.M.; Lu, T.S.; Liang, X.H.; Dong, H.; Ye, G. Mechanisms of autogenous shrinkage of alkali-activated slag and fly ash pastes. Cem. Concr. Res. 2020, 135, 106107. [CrossRef] 32. Duxson, P.; Provis, J.L.; Lukey, G.C. Understanding the relationship between geopolymer compositing, microstructure and mechanical properties. Colloids Surf. A 2005, 269, 47–58. [CrossRef] 33. Lloyd, R.R.; Provis, J.L.; Smeaton, K.J. Spatial distribution of pores in fly ash-based inorganic polymer gels visualised by Wood’s metal intrusion. Microporous Mesoporous Mater. 2009, 126, 32–39. [CrossRef] 34. Provis, J.L.; Myers, R.J.; White, C.E. X-ray microtomography shows pore structure and tortuosity in alkali-activated binders. Cem. Concr. Res. 2012, 42, 855–864. [CrossRef]
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