Calcium Aluminum Silicate Hydrate Research Articles

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.

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.

Effect of blast furnace slag substitution for cement in carbon-reduced and low-cost solidified/stabilized cementitious materials

The development of low-carbon cementitious materials involves the selection of the appropriate raw materials and the transformation of the hydration mechanism. In this study, low-carbon and low-cost cementitious materials were prepared using municipal solid waste incineration fly ash (MSWI FA), blast furnace slag (BFS), and desulfurization gypsum (DFG) as raw materials to reduce clinker usage. Results showed that the compressive strength of K5 (mass ratio of BFS: DFG: MSWI FA = 7:1:2) after 360 d of curing was 41.49 MPa, with a low leaching concentration of heavy metal residues that meet groundwater Class II standards, a dioxin content of only 25 ngTEG/kg, and a stable pH value ranging between 11 and 11.5. Microscopic analysis revealed a continuous decrease in the Ca/Si atomic ratios of K4 (mass ratio of BFS: DFG: MSWI FA: P·I 42.5 = 42:10:20:28) and K5, i.e., 1.18–1.54 and 1.04–1.23, respectively, with the increase in the hydration age. The highest Al/Si atomic ratio of K5, i.e., 0.26–0.31, was observed with the strongest conversion trend of calcium–silicate–hydrate gel into calcium–aluminum–silicate–hydrate gel, and the network structure of sodium–(calcium)–aluminum–silicate–hydrate gel zeolite-like phase was generated. The water-to-binder (WTB) mass ratio of 0.35 was determined to be more suitable for the K4 and K5 systems and resulted in a 56.83% and 90.82% reduction in half-life t∂ compared with the WTB ratio of 0.5, respectively. Notably, the value of the reaction velocity constant K in the induction period was 10 times that of K1, and the autocatalytic reaction controlled the value of N to < 1. The X-ray absorption near-edge structure indicated that Zn solidification produced Zn2SiO4 with a small solubility product. The production of 1 t of K5 emitted only 10.83 kg/t of CO2, which was 40 times less than that of K1. Overall, K5 provides the highest economic benefit at 40.08 USD/t, and the clinker-free cementitious system with multisolid waste synergy has significant advantages in terms of solidifying harmful substances, reducing carbon emissions, and lowering costs.

Application of SCMs and seawater to cement-bonded calcareous sand: Macro performance, micro mechanism, and strength prediction

Cement-bonded calcareous sand (C-BCS) demonstrates promising potential for marine island construction due to its exceptional mechanical properties. However, challenges such as freshwater scarcity and the erosive effects of seawater hinder the extensive utilization of C-BCS. To address this, this study comprehensively examines the feasibility of incorporating supplementary cementitious materials (SCMs) and seawater in C-BCS, focusing on macroscopic properties, microscopic mechanisms, and strength prediction. Macroscopic tests reveal that blast furnace slag and silica fume effectively enhance the hydration process and mechanical properties of C-BCS. Moreover, the cemented specimens developed in this study partially meet the strength standards for road pavement sub-base and airport runway upper-base applications. Microscopic analyses indicate that calcareous sand serves as a plentiful source of calcium, facilitating the formation of calcium aluminate silicate hydrate (C-A-S-H) and tobermorite when combined with Al2O3 and reactive SiO2 from slag and silica fume. This enhances the mechanical properties of the samples and their resistance against seawater erosion. Additionally, a back propagation (BP) neural network model accurately predicts the unconfined compressive strength of the cemented specimens. The findings of this study support the broader implementation of SCMs and seawater in practical island engineering projects involving C-BCS.

Hydration kinetics of cation exchanged clinoptilolite zeolite based cementitious materials

This paper provides information on the global reaction path and hydration kinetics of a natural clinoptilolite-Ca zeolite blended portland cementitious system. The replacement of up to 20% as-received clinoptilolite-Ca zeolite with portland cement substantially minimized the tricalcium aluminate (C3A) peak heat of hydration as observed using isothermal calorimetry. Inductively coupled plasma-optical emission spectrometry results showed that the zeolite-blended samples had a higher initial chemical dissolution of calcium and aluminate; but subsequently, the consumption of both was higher compared to the neat cement control sample, likely due to the formation of new hydration reaction products, indicating an interaction between cement and clinoptilolite-Ca zeolite. Clinoptilolite-Ca zeolite transformed into clinoptilolite-Na zeolite using NaOH and NaCl solutions showed a distinct aluminate (C3A) peak heat flow, indicating a different reaction path compared to clinoptilolite-Ca zeolite. Micro-chemical analysis using energy dispersive spectroscopy suggests a different hydration reaction mechanism for both calcium and sodium-based zeolite, along with the possibility of reduction in the formation of C–S–H, ettringite, and monosulfate due to the formation of new hydration products. The clinoptilolite-Ca zeolite consumed significantly higher aluminate contents leading to the formation of amorphous calcium-aluminum-silicate-hydrate (C-A-S-H) gels, which consequently reduced the aluminate-related reaction (C3A) heat flow in the system. In contrast, the clinoptilolite-Na zeolite released sodium ions through cation exchange to produce sodium aluminosilicate hydrate (N-A-S-H) in the blended system, which did not interfere with the C3A peak heat flow during the hydration process.

The Performance and Reaction Mechanism of Untreated Steel Slag Used as a Microexpanding Agent in Fly Ash-Based Geopolymers

Steel slag is an industrial by-product of the steelmaking process, which is under-utilized and of low value due to its characteristics. Alkali-activated technology offers the possibility of high utilization and increased value of steel slag. A geopolymer composition was composed of steel slag, fly ash, and calcium hydroxide. Four experimental groups utilizing steel slag to substitute fly ash are established based on varying replacement levels: 35%, 40%, 45%, and 50% by mass. The final samples were characterized by compressive strength tests, and Fourier-transform infrared spectroscopy measurements, thermogravimetric measurements, scanning electron microscopy with energy dispersive spectroscopy, X-ray diffraction, and mercury intrusion porosimetry were used to investigate the chemical composition and microstructure of the final products. Higher steel slag/fly ash ratios lead to a lower bulk density and lower compressive strength. The compressive strength ranges from 3.7 MPa to 5.6 MPa, and the bulk density ranges from 0.85 g/cm3 to 1.13 g/cm3. Microstructural and energy-dispersive X-ray spectroscopy analyses show that the final geopolymer products were a type of composite consisting of both calcium aluminate silicate hydrate and sodium aluminate silicate hydrate, with the unreacted crystalline phases acting as fillers.

Performance assessment and cost-benefit analysis of low-carbon binders containing calcined sediments from Chorfa II dam as new building materials

Recently, considerable attention has been given to the valorization of dredged sediments around the world, which are considered waste. The reuse of dredged sediments has significantly contributed to Sustainable Development Goals. However, the efficiency and cost assessments of calcined sediments as a partial replacement for cement are not well understood. In this present investigation, the use of calcined sediments from dams as a green construction material on the properties of eco-pastes and mortars formulation is explored. Properties measurements, microscopic observation, eco-strength efficiency, and cost assessments were performed on fresh, hardened mortars in order to valorize calcined sediments in the cement industry. The best findings for the compressive and tensile strengths of mortars containing calcined sediments were obtained after 180 days, which was compared to the control mortar. Furthermore, microscopic analyses showed that an increase in the substitution rates of calcined sediment resulted in the increasing germination of calcium aluminate silicate hydrate gel (C-A-S-H) and calcium silicate hydrate gel (C-S-H). The control mortar showed an efficiency of 0.0902 MPa/kgCO2 eq for 28 days while the eco-strength efficiency of mortars containing 5%, 15%, and 25% of calcined sediments presented an efficiency of 0.0920 MPa/kgCO2 eq, 0.0922 MPa/kgCO2 eq, and 0.0997 MPa/kgCO2 eq, which represents an increase of 1.9%, 2.21% and 10.51%, respectively. However, the replacement of cement with calcined sediments up to a rate of 25% decreases embodied carbon. In conclusion, the cost of treatment of one (1) ton of sediments is lower than cement, which represents a reduction from 81.96% to 86%.

Atomistic investigation of surface modification effect on interfacial properties of CNTs reinforced AAS geopolymer

To prolong the life of eco-friendly alkali-activated slag-based (AAS) geopolymers, carbon nanotubes (CNTs) have been adopted as reinforcements due to their outstanding properties. However, the hydrophobic nature of CNTs poses challenges in establishing a strong interfacial compatibility with the hydrophilic calcium-aluminum-silicate-hydrate (C-A-S-H) gel, which plays a crucial role in determining the strength of these geopolymers. This disparity leads to inadequate interfacial adhesion between CNTs and C-A-S-H gel, primarily resulting in material failure at the interface of CNTs reinforced AAS geopolymers. Despite employing various surface modification techniques to address this issue, the precise impact of functional groups on the interfacial interaction at the nanoscale between CNTs and C-A-S-H gels remains uncertain. In this work, the atomistic-scale impact of functional groups on the interfacial properties between CNTs and C-A-S-H gels has been investigated. Compared to unmodified CNTs, CNTs functionalized with carboxyl groups exhibit a remarkable 16.9 % increase in the maximum pull stress during the pull-out process, whereas those functionalized with hydroxyl groups show a more modest 3.5 % improvement. Water molecules gradually desorb from the functionalized CNTs and re-adsorb onto the C-A-S-H structure during the pull-out process, which consumes energy. Functional groups amplify this effect by involving more water molecules in these dynamic processes during interface failure. These findings provide valuable theoretical guidance for optimizing the surface modification techniques of CNTs and underscore the untapped potential of CNTs in enhancing the performance of AAS geopolymer composites.

Design and characterization of iron–calcium–aluminium–silicate–hydrate as low-temperature binder

This work aims to synthesize new cementitious materials (binders) using marble powder, rice husk ash, activated laterite and NaOH solution by applying low energy process. The binder was used to stabilize solid precursors (laterite and pozzolan). To achieve this objective, calcium–silicate–hydrate (CSH) was first synthesized at different temperatures (26, 50, 80 and 100 °C). The best physical–mechanical properties were chosen to produce iron–calcium–aluminium–silicate–hydrate [Fe–C(A)SH] at different concentrations of sodium hydroxide solution: 4, 5, 6 M. Finally, the formulated binder at 6 M of NaOH solution was used to stabilize laterite and pozzolans at the following proportions 20%, 30%, 40% and 50%. The samples were characterized after 28 days of curing at room temperature. FT-infrared spectroscopy, X-ray diffraction, and environmental scanning electron microscope ESEM-EDS permitted to confirm the formation of CSH, and Fe–C(A)SH. The mechanical test used to evaluate the performance showed that the incorporation of 10% iron-rich laterite into CSH increased the strength up to 42.93 MPa and the addition of Fe–C(A)SH in the laterite/pozzolans increased the compressive strength of the final product (15.34 and 15.8 MPa for laterite and pozzolan, respectively). The highest concentration (6 M) increases the alkalinity and reduces the efficiency of silicate polymerization affecting the final structural compound. From the results, low-energy Fe–C(A)SH-based cement and stabilized compounds appeared promising for the development of sustainable infrastructures.

Effect of mix proportion parameters on chloride erosion resistance of fly ash/slag-based engineered geopolymer composites

The incorporation of ground granulated blast furnace slags (GGBS) into fly ash-based engineered geopolymer composites (EGC) was explored to enhance their resistance against chloride-induced erosion. An investigation was conducted to understand how variations in the slag content, the water-to-binder ratio, the quantity of alkali activator, and the inclusion of polyethylene fibers affect the EGC's ability to resist chloride erosion. The study found an enhancement in the chloride erosion resistance with an increase in the water-binder ratio from 0.32 to 0.38. Conversely, the resistance decreased when the proportion of slag was raised from 40% to 100%, when the alkali activator content went up from 4% to 6%, and when the percentage of polyethylene fibers grew from 1.0% to 2.0%. Microstructural analyses revealed that a higher water-binder ratio of 0.38 reduced the peak intensity of calcium aluminate silicate hydrate, increasing the porosity and, thereby, compromising the chloride erosion resistance of the EGC. In contrast, increasing the slag content, alkali activator, and polyethylene fiber percentage generated the reverse effect, reinforcing the material's resistance to chloride penetration. The optimized EGC demonstrated promising chloride erosion resistance with a low chloride diffusion coefficient of 0.0661 × 10−12 m2/s, paired with robust mechanical properties including compressive strength ranging from 70 to 80 MPa, ultimate tensile strength between 5 and 6 MPa, and ultimate tensile strain reaching up to 8%.

Recycling of phosphogypsum and clay by-products from phosphate mines for sustainable alkali-activated construction materials

This work investigated the recycling the large quantities of phosphogypsum, generated by phosphoric acid plants, by exploring its potential use as a precursor in alkali-activated materials. The alkali-activation involved using phosphogypsum and calcined clays as precursors and an alkaline activator. The compressive strength of elaborated materials was evaluated after 28 days of curing. Additionally, various techniques were used to characterize the diverse samples. The results demonstrated the effectiveness of the alkaline activation process to induce the formation of Calcium Aluminum Silicate Hydrate and Sodium Aluminum Silicate Hydrate gels in the elaborated samples. The samples with 22.4% phosphogypsum, 11.28 M NaOH, and a liquid/solid ratio of 0.86 presented the maximum compressive strength of 27.3 MPa as they presented a more dense and less porous structure. The Toxicity Characteristic Leaching Procedure test showed no release of harmful substances. These findings suggest that phosphogypsum could be recycled in alkali-activation technology in the construction industry.

Mechanical and Microstructural Properties of Bamboo Fiber-Reinforced Concrete Containing a Blend of Waste Marble Powder and Waste Glass Powder

Using blended supplementary cementitious materials in the production of concrete has a contribution to make in reducing cement consumption, as well as having a negative environmental impact. The main objective of this study was to investigate the mechanical and microstructural properties of bamboo fiber-reinforced concrete containing a blend of waste marble powder (WMP) and waste glass powder (WGP) as a partial replacement for cement. To achieve these objectives, the physical and chemical properties of concrete ingredients were studied. The design mix was done as per the American Concrete Institute (ACI) mixing procedure by using 5%, 10%, 15%, and 20% blended WMP and WGP as a replacement for cement and 0.75% bamboo fiber as an addition. The mechanical tests were conducted after samples were cured for 7 and 28 days in water. The microstructural properties of the hardened concrete from three different mixes were also determined for the 28-day cured specimens. The study result indicated improvement in compressive strength, shear stress, and bond stress at M2 (10%), whereas maximum splitting tensile strength was achieved at M1 (5%). Moreover, scanning electron microscopy (SEM) showed a denser microstructure, whereas X-ray diffraction (XRD) illustrated portlandite, calcium aluminum silicate, quartz, and calcium silicate hydrate as common phases of the concrete structure. Eventually, the experimental finding implied that using a 10% blend of WMP and WGP as a partial replacement for cement and 0.75% bamboo fiber improves fresh and hardened concrete properties.

Strength characteristics of marine clay mixed with coal ash and cement with microstructural verification

This study uses coal ash obtained from the Tanjung Bin coal power plant consisting of a mixture of fly ash and bottom ash at different ratios. Such mixtures will be used with the minimum amount of Ordinary Portland Cement to stabilise marine clay. Compaction data corresponding to a mixture of coal ash and OPC mixed with marine clay soil provides 1535 and 1600 kg/ MDD and 18–22.2% OMC ranges, as additive percentages are increased. The unconfined compressive strength test indicated the highest increase at 50BA:50FA ratio with a value of 536 kPa at 15% of additive. The strength of the treated soil sample would also increase with increasing additive percentage and curing period. The XRD of untreated soil sample indicates composition intensity for minerals like quartz, mica, kaolinite, calcite, montmorillonite, and muscovite generally decreased with curing time; on the other hand, halloysite composition reduced. However, a new mineral is formed: calcium aluminium silicate hydroxide hydrate. Moreover, the FESEM results show that the treated marine clay surface particles looked denser with time. Structural voids were also reduced. In line with the XRD and FESEM test outcomes, the EDX results indicated that the formed cementitious products comprised calcium aluminate silicate hydrate.

Improvement of cemented rockfill by premixing low-alkalinity activator and fly ash for recycling gangue and partially replacing cement

Recycling mining wastes such as gangue for cemented rockfill is a key approach for sustainable development while ensuring the safety of underground structures in the mining industry. However, achieving sufficient strength for this low-cost material remains a fundamental challenge. This study explores an approach to strengthen cemented rockfill by using well-graded gangue, and by partially replacing Portland cement with fly ash and a premixed low-alkalinity activator. The effects of activator dosage and curing time on mechanical properties, composition and microstructure of cemented rockfill were investigated through uniaxial compression, XRD, FTIR, TG/DTG, MIP and SEM-EDS analyses. Results show overall improvements in the performance of cemented rockfill despite its low cement content, and the use of a low-cost low-alkaline activator. The 28-d compressive strength improved by over 30 % to reach 8 MPa with only 7.7 % wt. Portland cement and incorporating more than 60 % wt. of waste gangue in its mix composition. The main source of strength is calcium silicate hydrate and calcium aluminate silicate hydrate, the latter playing an increasing contribution with longer curing due to fly ash activation. Addition of premixed activator to fly ash enhanced the formation of Ca6Si6O17(OH)2, and CaO∙Al2O3∙xSiO2∙yH2O. Activator causes densification of the microstructure and this occurs predominantly on pores smaller than 1 μm. The optimum mix having the highest performance-cost ratio contains between 10 % and 15 % activator. This work reveals an effective and low-cost method of premixing fly ash with a low-alkalinity activator for recycling mining wastes and reducing cement.

Experimental study of mixtures soil-industrial waste using simplex design for application in paving

The large amount of solid waste generated by industry is a concern for society. A possible solution is to incorporate these wastes into soils to improve their properties and contribute to sustainable development. The objective of this research was to conduct an experimental study on the chemical stabilization of two samples of tropical soils using two industrial wastes, electric arc furnace slag (EAFS) and fly ash (FA), using a design of experiments (DoE) of mixtures in a simplex centroid network. Seven mixtures were determined from the DoE for each soil sample. Using specimens of these mixes prepared at optimum moisture content, after a curing period of 7 days in a humid chamber, the properties were evaluated: unconfined compressive strength (UCS), California Bearing Ratio (CBR), and resilient modulus (RM). An improvement in the evaluated mechanical properties was observed with the addition of waste, especially with the addition of EAFS. The statistical software Minitab 18 allowed to obtain response surfaces for each mechanical property studied as a function of the pseudo-components of the mixtures. To determine the proportion of components that optimized the soil-waste mixtures, the desirability function was used, which resulted in the proportions of 80% soil, 20% EAFS, and 0% FA for both soil samples. Based on SEM and XRD tests, it was found that calcium silicate hydrate (C–S–H), calcium aluminate silicate hydrate (C-A-S-H), and calcium aluminate hydrate (C-A-H) were formed, which were responsible for improving the mechanical strength. The use of industrial waste to stabilize tropical soils with low bearing capacity proved to be a technically and environmentally viable alternative.

Influence of partial cement substitution by ground blast furnace slag on the mechanical properties of phosphogypsum cemented backfill.

Phosphogypsum (PG) stockpiles occupied a large amount of land resources, and serious environmental pollution problems have attracted the attention of countries around the world. Cemented backfill can reduce the environmental problems caused by tailings stockpiles and is an important development trend in green mine construction. To investigate the effect of binder type on the performance of PG cemented backfill, this paper used ground granulated blast furnace slag (GGBFS) to substitute part of Portland cement (PC) as binder and studied the effect of different ratios of binder on the uniaxial compressive strength (UCS), surface crack extension, acoustic emission (AE) characteristics, and microstructure of PG cemented backfill. The results show that substituting part of PC with GGBFS is beneficial to improve the mechanical properties of PG cemented backfill. When PC was substituted by 50% of GGBFS, the 28d UCS of the backfill was increased from 1.535 to 4.539 MPa. Furthermore, the UCS of the backfill gradually increased as the GGBFS substitution level increased, and more AE signals could be monitored during uniaxial compression. Compared with PC, the sulfate in PG participates in the hydration reaction of GGBFS, more hydrated calcium-aluminum-silicate-hydrate (C-A-S-H) gels and ettringite (AFt) are formed, and the microstructure of the backfill is denser, and the required strength can be obtained with less binder. Thus, substituting part PC with GGBFS as a binder can provide an economical and environmentally friendly alternative for the consumption and reuse of large quantities of PG.

Investigating the synergistic effect of graphene nanoplatelets and fly ash on the mechanical properties and microstructure of calcium aluminate cement composites

Nanomaterials like graphene nanoplatelets (GNP) have been extensively applied in various fields as reinforcing materials offering excellent mechanical properties. However, for calcium aluminate cement (CAC) composites, the investigation of the GNP reinforcing effect is lacking. The synergistic effects of GNP and fly ash (FA) in CAC composites were evaluated in this study. The GNP was initially dispersed in mixing water using a dispersant combined with ultrasonication. The CAC composites with different GNP contents were prepared and their mechanical performance was investigated. In addition, partial replacement of CAC with FA was investigated for increasing sustainability and material cost of GNP-CAC composites. Their fresh properties, mechanical properties, and microstructural performance were analyzed using different techniques involving flowability, bulk density, volume of permeable void, water absorption, compressive strength, splitting tensile strength, flexural strength, nitrogen adsorption, TGA, and SEM-EDS tests. Using FA and GNP in CAC composites offers a positive impact by significantly increasing their strengths. Optimized mix was achieved by replacing 20% of FA and adding 0.3% of GNP in CAC composites. Results revealed that the 20% FA replacement of cement with 0.3% GNP addition remarkably increased the compressive, splitting tensile and flexural strengths at 28 days by about 57.2%, 35.5%, and 21.7%, respectively. The results suggest that using FA and GNP contributes to synergistic effects to promote the formation of silica tetrahedron in calcium aluminate silicate hydrate (CASH) gel, to refine pore characteristics, and to reduce conversion effects of metastable phases of CAC such that it can ultimately produce a green rapid-set high-performance concrete system.

Enhancing the properties of alkali-activated slag through dry ice addition: Investigation of hydration products and performance characteristics

To study the effect of dry ice on the performance of alkali-activated binders, we added dry ice to an alkali-activated slag (AAS). The addition amount was set to 5%, 10%, and 15% of the slag mass, depending on the amount of CO2 emitted by the material used in the preparation process. Microscopic experiments were performed to analyze the effect of dry ice on the hydration products of the AAS paste; transmission electron microscopy and scanning electron microscopy were used to observe the morphology of the hydration products. Furthermore, experimental tests for the compressive strength, ultrasonic pulse velocity, and electrical resistivity were performed. The results showed that compared with the content of the overall reaction products, the effect of dry ice on the reaction rate was more evident. The addition of dry ice slowed the hydration of the AAS, and the production of the hydration products, such as calcium aluminum silicate hydrate (C-A-S-H) gels, was significantly reduced in the early stage (1 d). Experiments on the strength showed that adding more than 5% dry ice degraded the early mechanical properties of the AAS. However, the mechanical properties of the AAS with dry ice added in the middle (3 and 7 d) and late (28 d) stages rapidly improved because the dry ice was added to the AAS to form potassium and calcium carbonate. In the middle (3 and 7 d) and late (28 d) stages, CO32− underwent a carbonation reaction to form carbonate compounds, enhancing the mechanical properties of the AAS.