Performance Optimization and Characterization of Soda Residue-Fly Ash Geopolymer Paste for Goaf Backfill: Beta-Hemihydrate Gypsum Alternative to Sodium Silicate

Wang, Haoyu; Zhao, Xianhui; Zhou, Boyu; Yao, Lin; Gao, Han

doi:10.3390/ma13245604

Cited by 18 publications

(22 citation statements)

References 34 publications

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“…The SR was used with blend of FFA and alkali-activator solution to prepare the geopolymer grouting paste for goaf backfill [25]. The prepared paste occurs the chemical reaction of geopolymerization between Si-O and Al-O bonds to generate the mixtures of (Ca, Na)-containing aluminosilicate polymer gel (N,C)-A-S-H and calcium silicate hydrated gel C-S-H. Additionally, the SR also was used with FFA, beta-hemihydrate gypsum and alkali-activator solution, to manufacture the geopolymer slurry for goaf backfill [49]. The reaction mechanism of geopolymerization and hydration process still happen to form the coexistence of (N,C)-A-S-H and C-S-H gels, along with the hydration of gypsum.…”

Section: Discussionmentioning

confidence: 99%

Resistance of Soda Residue–Fly Ash Based Geopolymer Mortar to Acid and Sulfate Environments

et al. 2021

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The early mechanical performances of low-calcium fly ash (FFA)-based geopolymer (FFA–GEO) mortar can be enhanced by soda residue (SR). However, the resistance of SR–FFA–GEO mortar to acid or sulfate environments is unclear, owing to the various inorganic calcium salts in SR. The aim of this study was to investigate the long-term mechanical strengths of up to 360 d and evaluate the resistance of SR–FFA–GEO mortar to 5% HCl and 5% Na2SO4 environments through the losses in compressive strength and mass. Scanning Electron Microscopy (SEM), Energy-Dispersive Spectroscopy (EDS) and Fourier Transform Infrared Spectrometer (FTIR) experiments were conducted for the SR–FFA–GEO mortars, both before and after chemical attack, to clarify the attack mechanism. The results show that the resistances of the SR–FFA–GEO mortar with 20% SR (namely M10) to 5% HCl and 5% Na2SO4 environments are superior to those of cement mortar. The environmental HCl reacts with the calcites in SR to produce CaCl2, CO2 and H2O to form more pores under HCl attack, and the environmental Na+ cations from Na2SO4 go into Si-O-Al network structure, to further enhance the strength of mortar under Na2SO4 attack. These results provide the experimental basis for the durability optimization of SR–FFA–GEO mortars.

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Section: Discussionmentioning

confidence: 99%

Resistance of Soda Residue–Fly Ash Based Geopolymer Mortar to Acid and Sulfate Environments

et al. 2021

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“…Due to the poor cementation derived from the extremely low 28 day and 90 day UCS s, the fluidity of the mixture increases with the addition of FAI, but the pH and EC of the mixture decrease. In G1, high-calcium-based slags such as CS, SR, and BRS have a slow hydrated reaction with low-calcium FAII [ 5 , 7 , 37 ], and it is not obvious for GP, as an addition, to promote faster hydration to achieve better strength in a higher W/B of paste [ 30 ]. Subsequently, the nature of the hydration in G2 does not alter when low-calcium FAI is added to mixture G1.…”

Section: Resultsmentioning

confidence: 99%

“…The range study revealed that the fluidity and 28 d UCS increased and then decreased as the SR-FA ratio increased, with the greatest fluidity and strength occurring at an SR-FA ratio of 2:3 [ 7 ]. Then, 10% GP was substituted for Na 2 SiO 3 in SR-FA-based geopolymer paste for goaf backfill, with a high fluidity of 196–222 mm and a suitable 28-d UCS of 0.92 MPa [ 30 ]. It was determined that 10% GP improved fluidity and UCS sufficiently to meet the performance criteria of goaf backfill material.…”

Section: Introductionmentioning

confidence: 99%

“…To fabricate geopolymer production, RM was combined with FA employing a composite activator [ 15 , 23 , 36 ]. The Ca(OH) 2 and CaO are suitable alternatives to alkaline activators for the admixture or activator because their ingredients are significantly less expensive than NaOH and Na 2 SiO 3 [ 30 , 37 ]. Currently, the commercialization of the alkali-activated binder is still a long way off due to the following challenges: (1) the development of new chemical admixtures; (2) the ensuring of workability, durability, and in-service track record; and (3) the lack of a detailed chemical understanding of the materials’ properties [ 12 ].…”

Section: Introductionmentioning

confidence: 99%

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Properties and Cementation Mechanism of Geopolymer Backfill Paste Incorporating Diverse Industrial Solid Wastes

Wang¹,

Zhao

Wang³

et al. 2023

Materials

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Industrialization has resulted in a large number of industrial waste slags being produced, which severely pollute the environment. This urgently needs resourceful treatment. The objective of this paper is to investigate the preparation, performance, and cementation mechanism of a novel geopolymer backfill paste for goaf. We reused diverse industrial waste slags based on low-calcium silica–alumina precursors (two fly ashes FAI, FAII, and red mud RM), high-calcium-based slags (carbide slag CS, soda residue SR, briquette residue slag BRS, and granulated blast furnace slag GBFS), and two additives (gypsum powder GP and lime powder LP). The hardening of backfill pastes was investigated by analyzing the effects of FAI, GBFS, RM, and LP on physical and chemical performance. The cementation mechanism of the prepared backfill paste was revealed through morphology, mineralogy, and chemical products through the use of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). The results show that the prepared backfill paste incorporating various solid wastes (FAI, FAII, RM, CS, SR, GBFS, RBS, etc.) yields a 28-d compressive strength of 2.1 MPa (higher than the required value of 0.6 MPa) and a fluidity of 201 mm. Geopolymer gels (N,C)-A-S-H, calcium silicate hydrated C-S-H, and calcium aluminosilicate hydrated C-A-S-H gels serve as chemical cementers, whereas unreacted particles serve as physical filler skeletons. These findings provide an experimental and theoretical basis for the interchangeable use of various identical component solid wastes in backfill engineering materials.

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“…A Quanta FEG450 scanning electron microscope was employed together with an energy dispersive spectroscopy (Hillsboro, OR, USA). The detection method was as follows: the area-scanning technique was used to determine the position of product gels in binders, and then the EDS spectra of representative points were obtained to analyze the gel products [17,19,42]. The samples were used for detection with gold spray pretreatment.…”

Section: Characterization Of Microstructure and Gel Productmentioning

confidence: 99%

Long-Term Physical and Mechanical Properties and Microstructures of Fly-Ash-Based Geopolymer Composite Incorporating Carbide Slag

Zhao

Wang²,

Jiang³

et al. 2021

Materials

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The long-term property development of fly ash (FA)-based geopolymer (FA–GEO) incorporating industrial solid waste carbide slag (CS) for up to 360 d is still unclear. The objective of this study was to investigate the fresh, physical, and mechanical properties and microstructures of FA–GEO composites with CS and to evaluate the effects of CS when the composites were cured for 360 d. FA–GEO composites with CS were manufactured using FA (as an aluminosilicate precursor), CS (as a calcium additive), NaOH solution (as an alkali activator), and standard sand (as a fine aggregate). The fresh property and long-term physical properties were measured, including fluidity, bulk density, porosity, and drying shrinkage. The flexural and compressive strengths at 60 d and 360 d were tested. Furthermore, the microstructures and gel products were characterized by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The results show that the additional 20.0% CS reduces the fluidity and increases the conductivity of FA–GEO composites. Bulk densities were decreased, porosities were increased, and drying shrinkages were decreased as the CS content was increased from 0.0% to 20.0% at 360 d. Room temperature is a better curing condition to obtain a higher long-term mechanical strength. The addition of 20.0% CS is more beneficial to the improvement of long-term flexural strength and toughness at room temperature. The gel products in CS–FA–GEO with 20.0% CS are mainly determined as the mixtures of sodium aluminosilicate (N–A–S–H) gel and calcium silicate hydration (C–S–H) gel, besides the surficial pan-alkali. The research results provide an experimental basis for the reuse of CS in various scenarios.

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Performance Optimization and Characterization of Soda Residue-Fly Ash Geopolymer Paste for Goaf Backfill: Beta-Hemihydrate Gypsum Alternative to Sodium Silicate

Cited by 18 publications

References 34 publications

Resistance of Soda Residue–Fly Ash Based Geopolymer Mortar to Acid and Sulfate Environments

Resistance of Soda Residue–Fly Ash Based Geopolymer Mortar to Acid and Sulfate Environments

Properties and Cementation Mechanism of Geopolymer Backfill Paste Incorporating Diverse Industrial Solid Wastes

Long-Term Physical and Mechanical Properties and Microstructures of Fly-Ash-Based Geopolymer Composite Incorporating Carbide Slag

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