Calcium Aluminum Silicate Hydrate Research Articles

All-solid-waste cementitious materials for grouting: Effects of alkali content and elemental ratios on performance and sustainability

The use of all-solid waste cementitious materials (ACM) in coal mine grouting backfill offers substantial green, low-carbon, and energy-saving benefits. This study systematically examines the effects of combining carbide slag (CS), fly ash (FA), and ground granulated blast furnace slag (GGBS) on the strength, workability, hydration characteristics, and microstructure of ACM. The utilization of sulfur-containing CS was achieved. The detrimental effects of delayed FA reaction and prolonged setting time can be mitigated by the introduction of high alkalinity or an increase in the Ca/Si ratio. The compressive strength may also be enhanced. The addition of excessive alkalinity (10 %) will result in a prolongation of the setting time. The primary hydration products include calcium aluminum silicate hydrate and magnesium-aluminum layered double hydroxide. Low Ca/Si ratios favor alkali metal ion charge balance, facilitating the transformation of silicate gels from single to double chains, while excessively high ratios reduce polymerization. Gmelinite forms when the (Ca+Na)/(Al+Si) ratio exceeds 1.6, and high NaOH concentrations inhibit ettringite formation. Validation shows that a GGBS:FA:CS= 3:1:3 mix with 4 % alkali binder (Group A2) meets mine grouting backfill criteria, with 80 % lower carbon emissions, 68 % lower energy intensity, and 50 % lower cost than cement. This research offers a viable pathway for the comprehensive utilization of multi-solid waste in mining applications.

Enhancing geopolymer mortars for environmental sustainability: A novel approach using frits and ceramic waste

This study investigates the potential of transparent frits as a sustainable aluminosilicate precursor to enhance geopolymer mortars, aiming to reduce environmental impact by repurposing industrial waste. White ceramic waste (WCP) and frits (F) were assessed for their ability to improve mortar properties while contributing to eco-friendly construction materials. The optimal mixture, containing 50% F and 50% WCP, achieved a compressive strength of 38.71 MPa and displayed a dense microstructure. In contrast, mortars made entirely from WCP had higher porosity of 19.12% and lower compressive strength of 9.89 MPa. Although 100% F mortars gained strength more slowly, they eventually outperformed the WCP mortars, demonstrating higher compressive strength and forming a honeycomb-like calcium-aluminum-silicate-hydrate (C-A-S-H) structure. These results highlight the environmental benefits of using frits to improve both the mechanical and structural properties of geopolymer mortars. By incorporating industrial waste materials, this approach offers a sustainable solution for producing high-performance, eco-friendly construction materials, paving the way for further green innovations in geopolymer technology.

Comparison of the efficacy of carbonation and conventional curing for remediation of copper-contaminated soils by ladle slag

Soil contamination poses an increasing challenge for global sustainable development. Traditional remediation methods, such as using ordinary Portland cement (OPC) for treating contaminated soils, are limited by high CO2 emissions, significant energy consumption, and natural resource depletion. A sustainable approach utilizing steel production waste (ladle slag, LS) to efficiently remediate copper (Cu)-contaminated soils was proposed in this study. The efficacy of this remediation using carbonation and conventional curing methods was compared. Cu-contaminated soils, spiked with varying initial concentrations, were treated with 10 % LS and subjected to both conventional and carbonation curing for different durations. Leaching behavior, strength development, and chemical and mineral properties of LS-remediated Cu-contaminated soils were assessed. The results demonstrated that both CO2 and conventional curing significantly reduced Cu leaching in contaminated soils by 4–5 orders of magnitude compared to untreated soils. CO2 curing achieved these reductions in a shorter time (56–72 hours) than conventional curing (28–56 days). Additionally, CO2 curing sequestered up to 8 % CO2 in the soils. However, higher Cu concentrations hindered carbonation reactions, lowering CO2 sequestration. While CO2 curing improved soil strength, increased initial Cu concentration diminished this effect. During CO2 curing, the formation of Ca- and Mg-carbonates contributed to microstructural densification and binding, thereby improving strength. These carbonates also encapsulated Cu, preventing its leaching. In contrast, the addition of Cu enhanced hydration reactions and improved the strength development of Cu-contaminated soils subjected to conventional curing. Conventional curing produced calcium aluminum silicate hydrate, which effectively bound soil particles, filled pores, and encapsulated Cu, reducing its leaching.

Hydration process and fluoride solidification mechanism of multi-source solid waste-based phosphogypsum cemented paste backfill under CaO modification

The large-scale, environmentally friendly utilization of phosphogypsum (PG) remains a global challenge. PG cemented paste backfill (PCPB) is a promising method to manage PG, but using ordinary Portland cement as the binder has drawbacks such as high cost, low mechanical strength, and high fluoride leaching risk. This paper presents a multi-source solid waste-based PCPB (MPCPB) material that enhances mechanical properties and reduces fluoride leaching risks. In MPCPB, industrial waste residues like steel slag (SS) and ground granulated blast furnace slag (GBFS) are used as precursors (SS: GBFS = 1:2). Additionally, 4–8 wt% CaO (relative to the dry weight of PG) is used as a neutralizing modifier and alkaline activator. The results indicate that an optimal amount of CaO can neutralize the residual acidity of PG, provide sufficient Ca(OH)2 for MPCPB hydration, and react with PG to produce significant amounts of AFt. Furthermore, CaO promotes the geopolymerization reaction between SS and GBFS, generating more calcium silicate hydrate (C-S-H) and calcium aluminate silicate hydrate (C-A-S-H) gels. Fluoride stabilization in MPCPB results from synergistic effects involving hydration reactions, complexation, ionic mobility, rearrangement, and physical adsorption. Notably, CaO enhances the conversion of free fluoride ions into stable compounds like fluorapatite, fluorite (CaF2), [AlF6]3-, and [FeF6]3- complexes. This approach offers a cost-effective, environmentally friendly, and efficient solution to the PG stockpiling challenge.

The Influence of Particle Size and Calcium Content on Performance Characteristics of Metakaolin- and Fly-Ash-Based Geopolymer Gels.

This research systematically investigates the influence of raw material particle size and calcium content on the geopolymerization process to gain insight into the physical and mechanical properties of geopolymer gels, including setting time, fluidity, pore structure, compressive strength, and leaching characteristics of encapsulated Cr3+ heavy metal ions. Utilizing a diverse range of particle sizes of metakaolin (MK; 3.75, 7.5, and 12 µm) and fly ash (FA; 18, 45, and 75 µm), along with varied calcium levels, this study assesses the dual impact of these factors on the final properties of both metakaolin- and fly-ash-based geopolymers. Employing sophisticated analytical techniques such as Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and Nuclear Magnetic Resonance (NMR), the research meticulously documents alterations in chemical bonding, micro-morphology, and pore structures. Key findings reveal that reducing the size of MK and FA particles to 3.75 and 18 µm, respectively, enhances the compressive strength of their matrices by 128.37 and 297.58%, respectively, compared to their original values (63.59 and 33.87 MPa, respectively) at larger particle sizes. While smaller particle sizes significantly bolster compressive strength, they adversely affect slurry flow and reduce the leaching rates of Cr3+ from MK- and FA-based matrices, reaching 0.42 and 0.75 mg/L at 3.75 and 18 µm, respectively. Conversely, increased calcium content markedly enhances setting times and contributes to the formation of dense microstructures through the production of calcium aluminate silicate hydrate (C-A-S-H) gels, thus improving the overall curing performance and durability of the materials. These insights underline the importance of fine-tuning particle size and calcium content to optimize geopolymer formulations, offering substantial benefits for varied engineering applications and promoting more sustainable construction practices.

Studies on the performance of alkali-activated aluminosilicate geopolymer mortar against exposure to acid, sulfate, and elevated temperature

An alkali-activated aluminosilicate is a group of materials that have the potential to reduce the carbon footprint of the construction industry. Several combinations of materials have been explored for producing alkali-activated aluminosilicate geopolymer mortars, emphasizing the need to understand their resistance to chemical attack and elevated temperatures to ensure long-term durability. The present study prepared fly ash-based alkali-activated aluminosilicate mortar using fly ash (FA) and ground granulated blast furnace slag (GGBS) without heat curing. Properties such as compressive strength and weight loss were evaluated after chemical attack and exposure to high temperatures (200° to 1000°), and compared with PC mortars. The result shows that fly ash and GGBS-based alkali-activated aluminosilicate mortar (AAAM) exhibit better resistance to chemical attack and high temperatures than conventional mortar. Specifically, after 180 days of acid exposure, PCM showed a mass loss of 5.06% and compressive strength loss of 85%, while AAAM had a mass loss of 2.88% and compressive strength loss of 71%. Sulfate exposure led to a mass gain of 55.77% for PCM and 27.35% for AAAM, with compressive strength losses of 55.77% for PCM and 27.35% for AAAM. Elevated temperatures (1000°) resulted in a compressive strength loss of 68% for PCM and 45% for AAAM. To substantiate these results, X-ray diffraction (XRD) and Fourier Transformation Infrared Spectroscopy (FTIR) were used to study the changes in the bonding behavior of C-A-S-H (Calcium-Aluminate-Silicate-Hydrate) and N-A-S-H (Sodium-Aluminate-Silicate-Hydrate) when exposed to chemical attack and elevated temperatures.

Improvement of strength and microstructure of low-carbon cementitious materials with high volume of calcined coal gangue

The accumulation of coal gangue poses significant environmental challenges due to its massive volume and low reactivity. This study investigates the influence of calcium hydroxide (Ca(OH)₂) and gypsum on the mechanical properties, hydration, and pore structure of low-carbon cementitious materials incorporating high volumes of calcined coal gangue (CCG) and limestone. The results showed that the addition of Ca(OH)₂ significantly increased compressive strength, with a 19 % improvement at 28 days in LCC-40-P mix, which contained 40 % cement and 2.73 % Ca(OH)₂ by weight. The incorporation of 10 % gypsum in the LCC-40-P mix and 20 % gypsum in the LCC-70 mix (containing 70 % cement without Ca(OH)₂) effectively refined the pore structure, reduced overall porosity, and enhanced the material's density and mechanical properties, resulting in compressive strengths of 38.4 MPa (72 % of the strength of Portland cement) and 50.2 MPa (94 % of the strength of Portland cement) at 28 days, respectively. Microstructure and hydration heat tests showed that the addition of Ca(OH)₂ accelerates the hydration reaction and significantly enhanced compressive strength by ensuring sufficient Ca(OH)₂ for pozzolanic reactions, leading to the formation of additional calcium silicate hydrate, calcium aluminate silicate hydrate and carboaluminate phases. Gypsum refined the pore structure by shifting the pore size distribution towards smaller sizes, reducing overall porosity, and increasing the proportion of gel and small capillary pores. These findings highlight the potential of using CCG with optimized additives to develop sustainable, low-carbon construction materials with enhanced performance characteristics.

Formation of calcium-aluminum-silicate-hydrate (C-A-S-H) in iron ore tailings ceramsite and its influence on cement hydration degree

This study explores the application potential of iron ore tailing (IOT) ceramsites in cement and concrete. It focuses on elucidating the pozzolanic reaction of ceramsite and its impact on the hydration kinetics of cement paste. The results showed that the active substances inof ceramsite dissolve in an alkaline environment and bind with Ca2+ in the cement solution to form a robust structure with needle-like C-A-S-H as the framework and layer-like C-A-S-H as the core-shell. Ceramsite slightly delayed the end of the induction period and significantly increased the total heat of hydration, thereby enhancing cement paste hydration. The compressive strength and degree of hydration exhibited a linear correlation. The C-A-S-H structure effectively enhances the strength of the cement paste within 100 μm of the ceramsite, with the strengthening effect extending up to 700 μm after 3 days. This study underscores the significant potential of IOT ceramsites in the concrete industry.

A novel approach for high-efficient activation of large-volume slag cement towards a lower-carbon future in cement industry

Substituting ordinary Portland cement (OPC) with supplementary cementitious materials (SCMs) is a widely adopted strategy in the cement industry to reduce CO2 emissions. However, the low reactivity of SCMs often results in delayed early strength development when used in large quantities. This study aims to substitute 70 % of OPC with ground granulated blast furnace slag (GGBFS) and efficiently activate this system through calcium-ferrite-silicate-hydrates/polycarboxylate ether (C-F-S-H/PCE) nanocomposites and sodium sulfate. The findings indicate that the combined use of both activators has a significant positive effect on the strength development of this low-carbon cement, demonstrating comparable performance to OPC without any substitution. This can be attributed to the effective enhancement of the reactivity of the low-carbon cement, particularly GGBFS. Furthermore, the utilization of C-F-S-H/PCE nanocomposites improves the polymerization degree and leads to a more compact morphology of the calcium-aluminum-silicate-hydrates (C-A-S-H) gel without affecting the Al/Si. The proposed activation approach provides a foundation for the large-volume utilization of GGBFS and other SCMs in cement-based materials and holds enormous potential for reducing CO2 emissions in cement industry.

Utilization of industrial waste sodium sulfate for calcined clay-based sustainable binder

This study explored the utilization of industrial waste Na2SO4 to develop a calcined clay-based sustainable cementitious composite inspired by ancient Roman concrete. Na2SO4 with or without the addition of NaCl was utilized, keeping the total Na2O quantity constant, and their performances at the macro and micro scale were compared. A separate set of samples was prepared using seawater. A medium-grade calcined clay, along with lime, was utilized as the binder. The salts were first dissolved in water and then used as the mixing water for sample preparation. A diverse array of characterization methods was utilized, encompassing thermogravimetric analysis, chemical extraction, X-ray diffraction (XRD), and Backscattered Scanning electron microscopy (SEM). It was observed that the salt-containing batches achieved compressive strength faster than the seawater samples. However, the strength remained in a comparable range (∼30 MPa) for all the samples after 28 days of curing. The initial strength of salt-containing samples was attributed to the formation of gypsum, ettringite, and hydrocalumite. Additionally, the geopolymer gel and calcium aluminum silicate hydrate (C-A-S-H) gel phases were present in all samples. Finally, this study also showed that lime-clay mortars can achieve a reduction in carbon footprint of up to 50 % compared to ordinary portland cement (OPC) mortars.

Preparation and Immobilization Mechanism of Red Mud/Steel Slag-Based Geopolymers for Solidifying/Stabilizing Pb-Contaminated Soil.

Pb-contaminated soil poses serious hazards to humans and ecosystems and is in urgent need of remediation. However, the extensive use of traditional curing materials such as ordinary Portland cement (OPC) has negatively impacted global ecology and the climate, so there is a need to explore low-carbon and efficient green cementitious materials for the immobilization of Pb-contaminated soils. A red mud/steel slag-based (RM/SS) geopolymer was designed and the potential use of solidifying/stabilizing heavy metal Pb pollution was studied. The Box-Behnken design (BBD) model was used to design the response surface, and the optimal preparation conditions of RM/SS geopolymer (RSGP) were predicted by software of Design-Expert 8.0.6.1. The microstructure and phase composition of RSGP were studied by X-ray diffractometer, Fourier transform infrared spectrometer, scanning electron microscopy and X-ray photoelectron spectroscopy, and the immobilization mechanism of RSGP to Pb was revealed. The results showed that when the liquid-solid ratio is 0.76, the mass fraction of RM is 79.82% and the modulus of alkali activator is 1.21, the maximum unconfined compressive strength (UCS) of the solidified soil sample is 3.42 MPa and the immobilization efficiency of Pb is 71.95%. The main hydration products of RSGP are calcium aluminum silicate hydrate, calcium silicate hydrate and nekoite, which can fill the cracks in the soil, form dense structures and enhance the UCS of the solidified soil. Pb is mainly removed by lattice immobilization, that is, Pb participates in geopolymerization by replacing Na and Ca to form Si-O-Pb or Al-O-Pb. The remaining part of Pb is physically wrapped in geopolymer and forms Pb(OH)2 precipitate in a high-alkali environment.

Influence of Silica Modulus on the Activation of Amorphous Wollastonitic Hydraulic Binders with Different Alumina Content: Study of Hydration Reaction and Paste Performance.

This study investigates how different sodium silicate SiO2/Na2O MS ratios (0.75, 0.9, and 1.2) affect the hydration behavior of amorphous wollastonitic hydraulic (AWH) binders containing various amounts of Al2O3 content (4, 7, 10, and 12%wt). The effects of and interaction between the MS ratio of the activator and the Al2O3 content of the sample on the hydration reaction and paste performance were investigated. The reaction was followed by calorimetry, and the pastes' compressive strength performances were tested at different curing times (2, 7, and 28 days). The hydrated pastes were characterized by FTIR, thermogravimetry analysis, and X-ray diffraction. The calorimetric results show that a higher Al2O3 cContent and a higher MS ratio result in a longer induction period. In terms of paste performance, an increase of the Al2O3 coupled with an activation with a 1.2 MS ratio results in a lower compressive strength after 28 days of hydration; the results range from 76 to 52 MPa. A decrease of the MS ratio to 0.9 allowed the obtention of a narrower range of results, from 76 to 69 MPa. Even though a decrease of the MS ratio to 0.75 led to higher hydration kinetics and high compressive strength results at early ages, at 28 days of curing, a decrease in compressive strength was observed. This may be a consequence of the fast kinetic of the mixture, since the rapid growth of hydration products may inhibit the dissolution at later ages and increase the porosity of the paste. Moreover, the high Al intake in the hydration product, facilitated by the high sodium content of the activator, promotes the formation of a higher number of calcium aluminate silicate hydrate structures (C-A-S-H) to the detriment of calcium silicate hydrate structures (C-S-H), decreasing the compressive strength of the samples. The TGA results indicate that the samples hydrated with the MS075 solution resulted in a higher number of hydrated products at early ages, while the samples hydrated with the MS09 and MS1.2 solutions exhibit a steady increase with curing time. Hence, an equilibrium in the hydration kinetic promoted by Si saturation-undersaturation appears to be fundamental in this system, which is influenced by both the MS ratio and the Al(OH)4- content in solution. The results of this study suggest that for this type of binder, optimal performance can be achieved by decreasing the MS ratio to 0.9. This composition allows for a controlled kinetic and overall higher compressive strength results in pastes produced with this AWH precursor.

Design and characterization of solid waste based self-healing artificial aggregate

A novel type of solid waste based artificial aggregate which holds promise for a good synergy between mechanical properties and self-healing capacity is designed with using the core-shell structure concept. The artificial aggregate is designed with a high self-healing potential core and a high strength shell, to achieve the high-performance application of artificial aggregates in concrete. The basic properties and potential self-healing capacity of artificial aggregates were comprehensively analyzed. The results indicated that the artificial aggregates were eligible considering the 28-d single particle compressive strength of exceeding 5.0 MPa, low water absorption and high volumetric stability. The crack-healing ratio of artificial aggregate is up to 94.5 % after 7-d curing in the simulated concrete pore solution (i.e., saturated Ca(OH)2 solution). The primary self-healing product was detected as calcium-aluminate-silicate-hydrate (C-A-S-H) gel due to the secondary hydration reactions of core materials.

Study on the synergistic effects of OPC and silica fume on the mechanical and microstructural properties of geopolymer mortar

This study investigated the synergistic effects of ordinary Portland cement (OPC) and silica fume (SF) in fly ash-based geopolymer mortar (FA-GPM). The research comprehensively evaluated the impact of replacing fly ash (FA) with varying proportions of OPC and SF on the flowability and mechanical properties of the geopolymer mortar (GPM). Furthermore, this study analyzed the interaction mechanisms of these effects by examining the microstructure and hydration products. The results showed that increasing amounts of SF initially enhanced but subsequently reduced flowability, while the inclusion of OPC consistently decreased it. The combination of SF and OPC significantly improved the mechanical performance and microstructure of the GPM. Optimal mechanical performance, with compressive strengths of 37.66 MPa at 7 days and 50.52 MPa at 28 days, was achieved by adding 10% SF and 20% OPC. Microstructural analysis revealed that using OPC and SF together enhanced the dissolution of alumino-silicate materials in the alkaline activating solution, leading to increased polymerization reactions in the GPM. This process resulted in the formation of calcium-alumino-silicate-hydrate (C-A-S-H) gel, sodium-alumino-silicate-hydrate (N-A-S-H) gel, and calcium-silicate-hydrate (C-S-H) gel, creating a denser structure with reduced porosity and enhanced mechanical properties. This study highlights the advantages of incorporating SF and OPC into FA-GPM, providing valuable insights for further research and practical applications of geopolymer materials.

From marble waste to monocarboaluminate binder: role of sodium aluminate composition, calcined clay type, and curing temperature

This study focuses on the synthesis of a monocarboaluminate (MCA)-based binder by treating marble waste (MW) powder with sodium aluminate (SA). The aim is to investigate the influence of various parameters, including the alumina modulus (M A) of SA, different contents of calcined clays with varying alumina levels, and curing temperatures, on the performance and phase composition of the resulting binder. The results demonstrate that the combination of SA and MW leads to the formation of an MCA-based binder, which exhibits a high compressive strength of up to 28 MPa after seven days of curing. Additional phases such as gibbsite, pirssonite, and gaylussite are observed, indicating the occurrence of a cationic exchange reaction between MW and SA, as confirmed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The stability of the resulting binder is primarily influenced by the M A value, with higher values associated with greater stability. Regardless of the type of calcined clay used, incorporating calcined clay results in the formation of a calcium aluminate silicate hydrate (CSAH) phase alongside MCA, contributing to the improved stability of the hardened binder over time. Notably, calcined clay with a higher alumina content exhibits the highest strength at all curing ages. Furthermore, increasing the curing temperature up to 100 °C significantly enhances the early strength, which correlates with the formation of the kotoite phase at the expense of the MCA phase.

Phenomenological description of the effect of glass dissolution on cement paste evolution in an integrated glass dissolution experiment

The interaction between nuclear glass surrogate and ordinary Portland cement (OPC) was investigated through integrated static leach tests conducted at ambient temperature. Tests were performed in stainless-steel cells in which OPC hydrated cement pastes were separated from glass powders by a stainless-steel filter. This article gives a phenomenological description of the processes affecting the hydrated cement paste arising from glass dissolution. The results show that the ingress of Si from glass dissolution leads to the degradation of the cement paste over a distance of 100–200 μm within 900 days of interaction. The Hardened Cement Paste (HCP) is affected by two main processes, which are the pozzolanic reaction and the alkali-silica reaction (ASR). These processes lead to porosity changes of HCP in contact with the stainless-steel filter and significant changes in the diffusive properties of the HCP. Especially, the effect of such processes on boron and lithium retention was studied and showed that precipitation of ASR-like gel and low Ca/Si C–S–H (Calcium Silicate Hydrate) highly retain these two elements. In the presence of an Al-rich glass (SM539), ASR is unlikely due to the preferential formation of C-A-S-H (Calcium Aluminium Silicate Hydrate).

Synthesis of Eggshell Powder and GGBS Geopolymer Designed by the Taguchi Method

This research endeavors to develop a geopolymer mortar synthesized from eggshell powder and ground granulated blast-furnace slag, utilizing the Taguchi L25 optimization technique to refine the synthesis process across molarity (A), precursor ratio (B) and curing duration (C). Analyzed at five distinct levels across 25 experimental setups, denoted as A1B1C1 through A5B5C5, these variables were rigorously tested. Compressive-strength measurement was employed as a criterion to assess the performance of three samples from each setup, alongside setting-time evaluation to ascertain the geopolymer concrete's workability. Optimal results were observed with a 60% eggshell to 40% slag ratio (A5B1C5), yielding the highest average compressive strength of 49.5 MPa after a curing period of 56 days. Conversely, a mix comprising 100% eggshell (A2B5C1) manifested the lowest compressive strength of 5 MPa at a 3-day curing period. Taguchi's signal-to-noise ratio analysis pinpointed the precursor ratio as a crucial determinant of compressive strength. Additionally, setting-time investigations revealed A5B1C5 as exhibiting the most advantageous initial and final setting times of 15 minutes and 30 minutes, respectively, compared to the protracted durations of 240 minutes and 540 minutes for A2B5C1. Through comprehensive chemical, micro-structural and mineralogical characterizations via X-ray fluorescence, Scanning Electron Microscopy (SEM) and X-ray diffraction, it was found that an increased proportion of ground granulated blastfurnace slag relative to eggshell enhances surface smoothness and density, indicative of successful polymerization. This was further corroborated by X-ray diffraction, which confirmed the formation of sodium alumina-silicate hydrate, calcium aluminum silicate hydrate and calcium silicate hydrate gels. Consequently, the study substantiates the potential of employing eggshell powder and ground granulated blast-furnace slag in the sustainable fabrication of geopolymers from waste materials. Keywords: Geopolymers, GGBFS, Eggshell, Taguchi Method, Compressive strength

Feasibility of using building-related construction and demolition waste-derived geopolymer for subgrade soil stabilization

A high-value utilization approach is essential to improve the utilization rate of building-related construction and demolition waste (brCDW). This study developed a novel approach by synthesizing a brCDW-derived geopolymer to stabilize high liquid limit subgrade soil. The unconfined compressive strength (UCS) test, shear strength test, resilient modulus test, and permanent strain test were conducted to investigate the effects of brCDW-derived geopolymer dosage, curing time, stress state, and moisture condition on the engineering properties of geopolymer stabilized soil. These test results demonstrated that increasing the geopolymer dosage effectively improved the UCS, shear strength and resilient modulus of stabilized soil and reduced the permanent strain of stabilized soil. The 8% brCDW-derived geopolymer provided adequate UCS, shear strength, resilient modulus, and resistance to permanent strain for stabilized soil, which showed the most economical improvement. Mechanistic-empirical models were employed to accurately estimate the stress-dependent resilient modulus and permanent strain of geopolymer stabilized soil at any given stress state. The Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) test were performed to investigate the strengthening mechanism of brCDW-derived geopolymer stabilization of subgrade soil. The SEM test results indicated that the porosity of stabilized soil was significantly decreased when the geopolymer dosage increased to 8%. The EDS test results demonstrated that the predominant gel types generated from the geopolymer stabilization might be Calcium–Aluminum-Silicate-Hydrate (C-A-S-H), Calcium-Silicate-Hydrate (C–S–H), and Calcium-Aluminate-Hydrate (C-A-H) gels. There was also a small amount of Sodium-Alumino-Silicate-Hydrate (N-A-S-H) gel detected in the geopolymer stabilized soil. Finally, the sustainability of brCDW-derived geopolymer stabilization approach was assessed in terms of material production cost, carbon dioxide emission, and energy consumption. The brCDW-derived geopolymer was proven as a sustainable stabilizer for subgrade soil.

Effect of Iron Ore and Copper Ore Tailings on Engineering Properties and Hydration Products of Sustainable Cement Mortar

Abstract The prohibition of river sand mining has drawn the attention of researchers in finding practicable alternatives. In the approach of finding these alternatives, it is essential to ensure minimal or zero impairment to the ecological balance, which can be mainly attained by making use of industrial waste/byproducts. The wastes from the mining industry are the major contributors in causing impairment to the environment, and their influence on the stability of mortars on using as fine aggregates needs to be systematically investigated with the view of long-term performance concerns. Thus, the present study explores the applicability of mine tailings and finding the optimum dosage in cement mortars by investigating the engineering properties and microstructure development with the aid of qualitative and quantitative analysis associated with hydration products. The studies confirm that the increased consumption of portlandite for secondary hydration reactions followed by the additional formation of calcium silicate hydrate (CSH) and calcium aluminum silicate hydrate (CASH) phases in mine tailing-based mortars helped in achieving a quality microstructure. These additional formations of CSH and CASH phases are also confirmed through Fourier transform infrared spectroscopy by identifying the shift of Si-O-Si stretching vibration bands toward a lower wavenumber. The lowering of calcium/silicate atomic ratio and increased formation of mineralogical compounds related to CSH and CASH in x-ray diffraction patterns also confirms the same. Gismondine, chabazite, and hillebrandite are the additional phases formed and found to take part in refining the pore structure. This enhanced performance of mine tailing mortars was also verified with the aid of a modified Andreasen and Andersen particle packing model. The formation of high-quality microstructure is reflected in the hardened properties of optimized cement mortar in the proportion of 20 % for iron ore tailing and 30 % for copper ore tailing.

Investigating the impact of alkaline activator on the sustainability potential of geopolymer and alternative hybrid materials

Geopolymer binders are considered highly sustainable due to their utilization of industrial wastes. However, previous studies highlight the limited industrial-scale applications of geopolymers. Therefore, this study critically investigates the strength, cost, and environmental impact of geopolymers and alternative hybrid cement mixes to provide a complete picture for the sustainability analysis. Geopolymers and hybrid cement mixes are designed with varying proportions of alkaline activator (sodium hydroxide 5–25 wt%) and ordinary Portland cement (OPC) (15–35 wt%) respectively for the comparative analysis. The strength characteristics of designed mixes have been assessed by analyzing their compressive strength and microstructure. A comparative economic assessment has been made by contemplating the manufacturing and production costs of different materials used in geopolymer and hybrid cement mixes. ReCiPe Midpoint Life cycle assessment (LCA) has been performed to examine the environmental performance by considering the manufacturing and production processes of various binder and aggregate materials used in geopolymer and hybrid cement mixes. Mechanical and microstructural analysis shows that hybrid cement mix with 35 wt% of OPC yields the highest strength due to the formation of excess calcium aluminum silicate hydrate (C-A-S-H) and calcium silicate hydrate (C–S–H) gels than geopolymer mix containing 25 wt% of NaOH. Economic and life cycle assessment reveals that the geopolymer mix with 5 wt% NaOH offers the lowest cost and environmental impact as compared to others containing higher proportions of alkaline activator and OPC. Owing to the conflicting nature of the results, multi-criteria decision making approach has been used which presents the hybrid cement mix (with 35 wt% OPC) as the optimal and sustainable solution for the construction applications. The study's findings offer a sustainable direction for the construction industry by suggesting the application of hybrid concretes.