Search Results (510)

To promote the resource recovery and utilization of construction spoil and to prepare flowable solidified soil with tunable properties and excellent construction adaptability, locally sourced construction spoil from Jinan was used as the primary raw material. A slag-based solidifying agent composed of cement, slag, fly ash, and desulfurized gypsum was prepared, together with a composite alkaline activation system consisting of calcium hydroxide and anhydrous sodium sulfate. The effects of solidifying-agent content, alkaline activator dosage, and slag-to-fly ash proportion on the workability, mechanical properties, and permeability of the flowable solidified soil were systematically investigated. The results show that solidifying-agent content significantly affects the material properties. As the content increased from 10% to 30%, the 28-day compressive strength increased from 0.94 MPa to 5.43 MPa, while the permeability coefficient decreased substantially; the best flowability occurred at intermediate contents. As the alkaline activator dosage increased from 1.8% to 4.8%, the slurry flow spread decreased from 214 mm to 193 mm and the bleeding rate decreased from 2.4% to 0.3%, while the 28-day compressive strength increased from 0.68 MPa to 0.92 MPa, indicating that alkaline activation markedly improves the water-retention capacity and mechanical properties of the solidified system. The slag-to-fly ash proportion regulates material performance through the synergistic effects of physical filling and chemical reactivity. Increasing the fly ash content improves slurry flowability but adversely affects strength development. These results provide experimental evidence and a theoretical basis for mix-proportion optimization and subsequent engineering application of alkali-activated slag-based flowable solidified soil. Full article

Converting waste slurry from underground construction into foamed lightweight soil (FLS) offers a route to waste valorization, but its durability under repeated moisture changes requires evaluation. This study compared FLS prepared with ordinary Portland cement (OPC), alkali-activated slag–fly ash (AASF), and hybrid OPC-AASF. Engineering properties and resistance to 18 wetting and drying (W-D) cycles were evaluated alongside pore structure evolution, microstructural changes, and environmental and economic indicators. Increasing soil content reduced unconfined compressive strength (UCS), with OPC-AASF showing a more gradual decline than OPC. All systems exhibited non-monotonic strength evolution during cycling. After 18 cycles, the UCS losses relative to the 28 d baseline were 1.9%–5.8% for OPC-AASF and 12.3%–17.6% for AASF. In selected specimens, X-ray computed tomography showed that lower macroporosity did not necessarily correspond to better strength retention. The greater strength loss in AASF was accompanied by spatial pore enrichment, coarse low-sphericity pores, and local interfacial damage. X-ray diffraction indicated retention of the main crystalline phases, while scanning electron microscopy showed better local pore wall and interfacial continuity in OPC-AASF. On a common dry-solids mass basis, the hybrid mixture containing 40% soil required 76.0% less OPC than a theoretical OPC foam concrete without waste soil. The estimated carbon emissions, energy intensity, and material cost associated with raw material inputs were 72.2%, 68.0%, and 48.1% lower, respectively. These findings support OPC-AASF as a cement-reduced stabilization system for lightweight backfill, combining waste slurry reuse with strength retention under repeated moisture fluctuations. Full article

Severe environmental contamination from accumulated phosphorus tailings and their low recycling rate remain critical bottlenecks in solid waste treatment. Furthermore, geopolymers fabricated using single or binary solid wastes generally suffer from insufficient mechanical properties and poor durability, while their synergistic activation mechanisms have not been fully clarified. To address these issues, this study developed a binary geopolymers composite using phosphorus tailings and ground granulated blast furnace slag (GGBS) as raw materials through alkali activation (sodium hydroxide and water-glass), and prepared a ternary geopolymers composite incorporating fly ash. The effects of solid waste blending ratios on flowability, compressive strength, drying–wetting and freeze–thaw resistance as well as drying shrinkage were systematically investigated, and the synergistic geopolymerization mechanism was characterized by SEM-EDS, XRD and FTIR. Experimental results show that the binary system achieves optimal performance at 40% GGBS substitution, yielding a 28-day compressive strength of 23.4 MPa with lower shrinkage and better anti-damage capacity than pure phosphorus tailings specimens. Introducing 20% fly ash into the optimized binary system forms a ternary geopolymer with a 28-day strength of 37.8 MPa, rising by 61.5%. Its drying shrinkage, mass loss from drying–wetting cycles and freeze–thaw erosion are separately reduced by 33.3%, 39.5% and 40.0%. Microscopic analyses verify that GGBS and fly ash collaboratively provide active Ca, Si and Al species to stimulate abundant C-S-H gel formation and compact the matrix microstructure. This ternary geopolymer realizes efficient collaborative utilization of three industrial solid wastes, providing theoretical support and technical guidance for large-scale resource utilization of phosphorus tailings and the fabrication of geopolymer construction materials. Full article

Water-based drilling cuttings (WBDCs) are a large-volume solid waste generated during oil and gas drilling. Their weak cementation and loose particle structure limit their direct engineering utilization. In this study, a multi-source solid-waste binder mainly composed of ground granulated blast furnace slag (GGBS) and fly ash (FA) was used to stabilize WBDCs. Portland cement was used as an auxiliary binder, and sodium silicate was used as the alkaline activator. The effects of sodium silicate modulus, sodium silicate dosage, cement dosage, and GGBS-to-FA mass ratio on strength development were investigated. XRD, FTIR, TG, MIP, and SEM-EDS were further employed to clarify the stabilization mechanism. The results showed that binder composition strongly affected the strength level and strength development rate of stabilized WBDCs. At a total binder dosage of 15%, the mixture with a sodium silicate modulus of 1.4, a sodium silicate dosage of 4%, a cement dosage of 10%, and a GGBS-to-FA mass ratio of 6:1 exhibited the best mechanical performance. Its unconfined compressive strengths reached 6.87, 9.74, and 10.17 MPa at 7, 14, and 28 d, respectively. Microstructural analyses indicated that the strength development of stabilized WBDCs was mainly associated with the formation and continued development of poorly crystalline C-S-H/C-(A)-S-H-type gels and a small amount of AFt. From 7 to 28 d, the porosity and total pore volume decreased by 9.5% and 11.0%, respectively, while the average pore diameter decreased by 31.2%. This study provides a basis for the resource utilization of WBDCs and the design of low-cement binders containing multiple industrial solid wastes. Full article

The development of carbon-neutral construction materials has stimulated interest in alkali-activated systems for the valorization of industrial non-hazardous waste. This study proposes an original comparative approach to assess the cementing reactivity of several wastes, including black and white fly ash, bottom ash, fine glass dust, and float-glass polishing sludge, through their use as partial replacements for metakaolin (MK). Formulations containing 5–50 wt% of fine waste powders (<45 μm) were prepared and mechanically compared with a reference MK-based geopolymer. Formulations containing waste additions to the reference geopolymeric paste were also evaluated to investigate their role as aggregates/fillers. Mechanical testing identified float-glass polishing sludge as the most reactive precursor, achieving a compressive strength of 25 MPa at 10 w% addition, compared with 16 MPa for the reference material. Bottom ash and black and white fly ash reached approximately 19–21 MPa at 5–10% replacement or addition. Conversely, bottom ash at substitution levels above 5% reduced mechanical performance owing to its high crystallinity and unfavorable Si/Al molar ratio. Microstructural characterization by XRD, FT-IR, density measurements, and SEM was correlated with the observed cementing activity. These results provide a basis for performance-based design criteria aimed at the sustainable valorization of locally available industrial by-products in alkali-activated materials. Full article

Alkali-activated materials are a sustainable alternative to Portland cement, yet the relative importance of activator and precursor parameters under ambient curing is unquantified, and literature-trained models are rarely validated against independent mixtures. Twelve fly ash–GGBS mortars were prepared in a 2 × 2 × 3 factorial design varying Na₂O dosage (4% and 5%), silica modulus (1.0 and 1.5) and fly ash/GGBS ratio (70:30, 50:50 and 30:70) at constant water to binder (0.50) and binder to sand (0.33) ratios, then characterized by flow, compressive strength at 7, 14 and 28 days, water absorption and scanning electron microscopy. Four ensemble models trained on 361 published records were tested on the withheld mixtures. Ambient cured strengths of 31.83–57.91 MPa were obtained, 95% developing by 14 days. Factorial analysis ranked the fly ash/GGBS ratio first (∆ = 18.83 MPa), followed by Na₂O dosage (∆ = 3.83 MPa) and silica modulus (∆ = 0.31 MPa), higher GGBS fractions giving lower water absorption and denser matrices under SEM. LightGBM gave the highest cross-validated accuracy (R² = 0.793; range 0.738–0.793). Precursor calcium content governs strength in ambient cured systems, allowing sodium silicate to be reduced without mechanical penalty and establishing data-driven design as a screening tool that condenses and improves the selection of experimental work towards the application level. Full article

Problematic fine-grained soils exhibit low strength and inadequate durability, highlighting the need for sustainable stabilization using eco-friendly binders. This study examined the strength development and durability of a natural CH soil (NSs) stabilized with fly ash (FA) based geopolymer exposed to sulfate attack and freeze–thaw (F–T) cycles. The effects of FA content (0–40%) and NaOH molarity (0–10 M) on unconfined compressive strength (UCS) were evaluated after 1, 7, 28 and 56 days of curing. Durability was assessed separately under accelerated laboratory conditions after 1, 3, 5, 7 and 11 F–T cycles and 7, 28 and 56 days of sulfate exposure. In non-activated specimens, FA contents of up to 30% enhanced the UCS primarily through the microfiller effect and possible time-dependent pozzolanic reactions. Alkali activation promoted the development of a compact binding matrix through the dissolution and polycondensation of aluminosilicate precursors, with the microstructural and chemical observations being consistent with the possible formation of C-(A)-S-H and/or N-A-S-H-type reaction products. F30M8 exhibited the highest strength, reaching a 56-day UCS of 1488.58 kPa compared with 282.46 kPa for untreated NSs. F30M8 retained approximately 94% of its UCS after 11 F–T cycles and 92% after 56 days of sulfate exposure. XRD, FTIR, and SEM-EDX analyses provided evidence of aluminosilicate restructuring and the development of a dense microstructure under alkaline activation. This refined matrix may have contributed to limiting sulfate- and ice-crystal-induced deterioration, thereby helping to preserve the structural integrity of the FA-based geopolymer-stabilized NS specimens, whereas untreated and non-activated FA-stabilized specimens disintegrated under sulfate exposure. These findings indicate that FA-based geopolymer stabilization has considerable potential for natural CH soil under the laboratory exposure conditions investigated in this study. Full article

This study investigates the influence of biomass fly ash (BFA) produced from high-temperature combustion of woody biomass fuels typical of Lithuanian energy plants on the mechanical performance, microstructure, and reactivity of alkali-activated binders based on diatomite and iron dust. Diatomite was used as a reactive silica source, while iron dust served as a matrix-modifying component enhancing binder density and strength. The role of BFA (10–30%) was evaluated in terms of compressive strength, softening factor, water resistance, and structural development using XRD and FTIR analyses. The results show that the formation of a compact geopolymer gel is the key factor controlling strength development. The highest compressive strength (53 MPa) was obtained at 10% BFA; however, it decreased to 33 MPa after thermal treatment at 200 °C, indicating limited structural stability. Increasing the BFA content to 20% and 30% improved the softening factor and water resistance but significantly reduced compressive strength to below 20 MPa and 10 MPa, respectively, demonstrating a trade-off between strength and durability. XRD analysis confirmed similar mineralogical compositions in all samples, dominated by largely unreacted quartz and magnetite, while minor amounts of andradite formed after thermal treatment. FTIR results revealed increased polymerisation with higher BFA content, reflected by the shift of the Si–O–T band (~966–985 cm⁻¹ to ~988–995 cm⁻¹), although the presence of Ca-rich and partially unreacted phases led to a less efficient geopolymeric network. Overall, the performance of the studied systems is governed by the balance between gel formation, phase composition, and microstructural integrity, with optimal properties achieved at moderate BFA content rather than at extreme compositions. Full article

Municipal solid waste incineration fly ash (MSWIFA) poses environmental risks due to high chloride and heavy metal contents. This study solidified MSWIFA via geopolymerization with coal fly ash (CFA), using low-temperature calcination and water washing to remove dioxins and chlorides, respectively. All formulations effectively immobilized heavy metals below regulatory limits. Increasing addition of calcined-washed fly ash (CWFA) from 0% to 25% reduced the 28 d compressive strength from 32.5 MPa to 4.8 MPa and fluidity from 185 mm to 128 mm, while increasing the content and modulus of alkali activator both enhanced these properties. The incorporation of moderate Ca(OH)₂ promoted the substitution of Na⁺ by Ca²⁺ within the gel framework under the combined action of the alkaline activator, thereby favoring the formation of gel network. When the dosage of Ca(OH)₂ increased to 7.5%, the 28 d compressive strength increased from 45.75 MPa to 53.33 MPa. However, excessive Ca(OH)₂ resulted in more unreacted residues and accelerated carbonation, which occupied active sites and disrupted gel continuity, leading to a slight decrease in strength to 49.85 MPa. This work provided a viable pathway for the utilization of MSWIFA into geopolymer, especially for optimizing Ca regulation to modify compressive strength, fluidity, and heavy metals toxicity. Full article

Machine learning (ML) models for alkali-activated concrete (AAC) are almost universally evaluated with random train–test splits, yet the literature-compiled datasets are strongly clustered by source study, and the reliability of such evaluations has rarely been quantified. The novelty of this study is a systematic quantification of out-of-campaign generalisation—via Leave-One-Study-Out (LOSO) cross-validation—for ML models trained on the largest curated public AAC dataset (1630 mixtures compiled from 106 published sources), together with model interpretation and an exploratory strength–carbon analysis. Four models (Linear Regression, Random Forest, Gradient Boosting, and optimised extreme gradient boosting, XGBoost) were benchmarked for predicting 28-day compressive strength (CS₂₈). XGBoost performed best under conventional random splitting, with test-set coefficient of determination R² = 0.801 and root-mean-square error (RMSE) = 7.21 MPa (5-fold cross-validation R² = 0.758 ± 0.050). Under LOSO validation across 85 study folds, however, the median R² collapsed to −0.328, with 49 of 85 folds negative: random-split metrics on literature-compiled AAC datasets are substantially inflated by within-study clustering, and study-stratified evaluation should become standard practice in this field. Within these limits, SHapley Additive exPlanations (SHAP) identified ground granulated blast-furnace slag (GGBFS) content, specimen geometry, CaO fraction, curing time, and sodium silicate (Na₂SiO₃) content as the five most influential predictors; because the oxide descriptors are derived from the declared binder proportions and the carbon-footprint values are inherited estimates from the source dataset, these attributions are associational rather than causal. No practically meaningful overall linear association was observed between estimated CO₂ footprint and CS₂₈ (Pearson r = −0.113, 95% CI [−0.175, −0.050], R² = 0.013), and a Pareto analysis identified 14 candidate low-carbon, high-strength formulations for further experimental and life-cycle assessment. The developed models are suitable for within-dataset feature attribution and exploratory screening restricted to the represented feature domain; they should not be used as external mix-design tools without validation on independent experimental campaigns. Full article

This preliminary experimental study investigates mortars with partial replacement of natural sand by recycled tyre rubber (RTR) and alkali-activated fly ash as an alternative binder to Portland cement. An experimental programme was carried out on 14 mortar mixes, including cementitious mortars (CM) and alkali-activated mortars (AAM), with 5%, 10% and 20% RTR incorporation and with/without NaOH pre-treatment of rubber (saturated solution for 30 min). Fresh behaviour was assessed through flow and fresh density, while mechanical-related performance was evaluated at 28 and 56 days through compressive and flexural strength, modulus of elasticity and ultrasonic pulse velocity. Physical properties included open porosity, dry density, water absorption by immersion and capillarity. The alkali-activated reference mix achieved higher compressive strengths (46.1–53.0 MPa) than the cement reference (28.4–30.6 MPa) under the adopted mix-design and curing conditions. RTR incorporation reduced stiffness and strength in all specimens, with 20% RTR decreasing flexural strength by 26.6–51.4%, although losses were generally smaller in AAM than in CM. Under the treatment condition investigated, NaOH pre-treatment did not consistently improve mechanical-related performance, except for limited gains at 5% RTR. Overall, AAM with 5–10% RTR showed a better balance between density reduction and mechanical-related performance than CM. Full article

This research addresses the critical challenge of “strength regression” observed in alkali-activated binders synthesized from glass wool wastes. In our preliminary studies, while sodium-based activation provided impressive initial strength, the specimens suffered a systematic and significant decline in mechanical performance at 3, 7 and 28 days, exhibiting a 74.3% strength reduction down to 24.61 MPa. Investigative analysis revealed that this instability is closely correlated with the physical degradation and micro-cracking observed in SEM micrographs, which is consistent with the literature regarding high silica-to-alumina network imbalances. To resolve these structural flaws, the precursor blend was modified by incorporating Class F fly ash and metakaolin to rebalance the Si/Al ratio. The addition of these aluminosilicate sources facilitated the consumption of excess sodium ions through enhanced geopolymerization and provided a micro-filling effect that refined the pore structure. Our findings demonstrate that this optimization not only prevents the subsequent loss of strength but also ensures stable compressive strength development up to 28 days without subsequent regression, reaching an ultimate average strength of 110.81 MPa. This approach provides a viable pathway for transforming insulation glass wool waste into high-performance, durable construction materials. Full article

Construction on very soft peaty clay remains a major geotechnical challenge due to its high compressibility and low-bearing capacity. The deep mixing method (DMM) is widely adopted for in situ stabilization using cement; however, environmental concerns associated with cement production have driven the search for sustainable alternatives such as geopolymers using low-carbon materials. Existing studies predominantly rely on dried peat, processed precursors such as fly ash or calcined ground rice husk ash (RHA), and high concentrations of alkali activators such as sodium silicate (Na₂SiO₃) and sodium hydroxide (NaOH), which increase both environmental and economic burdens. This study develops a novel waste-based geopolymer incorporating untreated brick kiln-derived RHA, activated solely with low-concentration NaOH, while completely eliminating Na₂SiO₃. The avoidance of precursor pre-treatment and Na₂SiO₃ significantly reduces processing energy, cost, and associated environmental emissions. A systematic investigation was conducted to determine the optimum mixing time for maximizing strength under field-relevant conditions. Mechanical performance was evaluated using unconfined compressive strength tests considering variations in binder content, curing duration (7, 28 days), alkali concentration (6, 3 M), and alkali-to-binder ratio (0.3, 0.5, 0.7). Failure characteristics were examined, and an integrated framework combining cost analysis, life cycle assessment, and grey relation analysis was employed to optimize mix design. The optimized geopolymer achieved 2.2 times higher strength than cement-treated soil, with 25% cost reduction and more than 85% reduction in environmental impact. These findings demonstrate a scalable and sustainable solution for stabilizing highly organic soils, while promoting the valorization of supplementary cementitious materials without energy-intensive preprocessing. Full article

The durability of alkali-activated materials (AAMs) in acidic environments is a key factor governing their suitability as sustainable alternatives to ordinary Portland cement (OPC). This study investigates the acid resistance of fly ash–slag alkali-activated mortars prepared with either seawater-based or distilled water-based activator solutions, thereby addressing the feasibility of substituting potable water in activator preparation. Eleven binder blends were tested, ranging from 100% fly ash (F100G0) to 100% ground granulated blast furnace slag (GGBS, F0G100) in 10% replacement increments, each prepared with both distilled-water (D-series) and seawater-based (M-series) activator solutions. Mortar cubes were exposed to hydrochloric acid (HCl) and sulphuric acid (H₂SO₄) after curing for 28, 60, 90, and 180 days. Durability was assessed through mass change, compressive strength retention, and ultrasonic pulse velocity (UPV), complemented by X-ray diffraction (XRD) analysis to elucidate mineralogical transformations. Results showed that acid resistance was governed primarily by binder composition: calcium-rich slag (C–A–S–H) systems deteriorated mainly by decalcification under acid exposure, whereas low-calcium fly ash (N–A–S–H) systems degraded more slowly by dealumination. Seawater activation did not significantly compromise acid resistance relative to distilled-water systems, with the two-activator series performing comparably under both HCl and H₂SO₄. Paired comparisons of the reported blend values showed small, age-dependent differences between the two-activator series: seawater activation modestly delayed strength loss under HCl at intermediate ages, while under H₂SO₄ it carried a small late-age penalty attributable to reaction of activator-derived chloride compounds with the acid; at most ages, the two series were statistically indistinguishable. X-ray diffraction showed essentially identical phase assemblages in the two series: no crystalline products formed under HCl, where an amorphous silica-rich residue accumulates on fly-ash-rich blends, whereas gypsum was the sole crystalline product under H₂SO₄, enhanced in seawater-activated fly-ash-rich blends. The findings clarify the role of marine ions in influencing acid degradation and provide guidance for designing sustainable binder systems for chloride- and sulphate-rich service environments. Overall, seawater is shown to be a viable substitute for potable water in activator preparation, retaining acid resistance comparable to distilled-water systems and supporting the development of more sustainable alkali-activated binders. Full article