Search Results (99)

Coal-based humic acid waste residue is a solid waste generated during the production of humic acid products. The extraction of coal-based humin (NHM) from such residues presents an effective approach for solid waste resource recovery. In this study, a novel calcium-based humin (Ca-NHM) was synthesized via a low-temperature-assisted method. The material was characterized and its cadmium passivation mechanism was investigated using scanning electron microscopy (SEM), zeta potential analysis (Zeta), carbon nuclear magnetic resonance (¹³C-CPMAS-NMR), and X-ray photoelectron spectroscopy (XPS). Soil incubation experiments were conducted to determine the actual cadmium adsorption capacity of coal-based humin in soils and to evaluate the stability of cadmium passivation. Plant cultivation experiments were carried out to verify the effects of coal-based humin on migration and transformation in soil, as well as on cadmium bioefficiency. The results showed that Ca-NHM passivated soil cadmium through multiple mechanisms such as ion exchange, electrostatic adsorption, complexation reactions, and physical adsorption. Compared with NHM, Ca-NHM exhibited a 69.71% increase in passivation efficiency, and a 2.44% reduction in cadmium leaching concentration. In Ca-NHM treatments, the above- and below-ground biomass of pakchoi increased by 18.06%, and 80.95%, respectively, relative to the control group. Furthermore, Ca-NHM enhanced the cadmium resistance of pakchoi, reduced the enrichment coefficient, activity coefficient, and activity-to-stability ratio in the above-ground portion of pakchoi, and maintained a transfer coefficient below 1, thereby alleviating cadmium toxicity. In summary, this study provides a theoretical foundation for understanding the mechanisms by which coal-based humin mitigates cadmium toxicity in pakchoi. Full article

Phosphogypsum (PG) and Carbide Slag (CS) are two industrial byproducts that can be used as cementitious materials, and their synergistic effect provides excellent activation of ground granulated blast furnace slag (GGBS), which is traditionally activated by lime (LM). However, the behavior of PG-GGBS-CS ternary blended cement remains largely unexplored. In this study, the mechanical performance, hydration mechanisms, and environmental profile of PG–GGBS–CS binders in comparison with PG–GGBS–LM were evaluated by unconfined compressive strength (UCS), XRD, SEM, and TGA analyses. The optimum formulation containing 30% PG achieved 24.88 ± 1.24 MPa at 28 d, statistically comparable to 25.6 ± 1.28 MPa for PG–GGBS–LM. The synergistic activation of PG and CS/LM on GGBS has been identified as a crucial factor in the strengthening of UCS in ternary blended cement. Hydration products consisted mainly of calcium silicate hydrate (C–S–H) gels and Ettringite (AFt). Importantly, the CO₂ footprint of PG–GGBS–CS was reduced by 3.2% compared to that of PG–GGBS–LM. These findings establish CS as an effective substitute for lime in eco-binders, combining technical efficiency with carbon mitigation and offering a viable pathway for large-scale valorization of hazardous industrial residues. Full article

The environmental impact of traditional construction materials has led to increasing interest in developing more sustainable alternatives. This study addresses the development of low-carbon autoclaved aerated concrete (AAC) through the complete replacement of ordinary Portland cement (OPC) with ground granulated blast furnace slag (BFS), activated with lime and, in some formulations, supplemented with calcium carbide slag (CCS). Five different AAC mixtures were prepared and evaluated in terms of workability, foaming behavior, compressive strength, phase composition, density, thermal conductivity, and life cycle assessment (LCA). The BFS-based mixtures activated with lime exhibited good workability and foaming stability. After pre-curing, the addition of CCS significantly improved the formation of tobermorite during autoclaving. As a result, the BFS–CCS formulations achieved compressive strengths comparable to the reference OPC-based mix while maintaining low densities (420–441 kg/m³) and thermal conductivities in the range of 0.111–0.119 W/(m·K). These results confirm the technical feasibility of producing structural-grade AAC with a lower environmental footprint. Full article

This study advances alkali-activated cementitious materials (AACMs) by developing a ground-granulated blast furnace slag/high-calcium fly ash (GGBS/HCFA) composite that incorporates Tuokexun desert sand and by establishing a clear linkage between activator chemistry, mix proportions, curing regimen, and microstructural mechanisms. The innovation lies in valorizing industrial by-products and desert sand while systematically optimizing the aqueous glass modulus, alkali equivalent, HCFA dosage, and curing temperature/time, and coupling mechanical testing with XRD/FTIR/SEM to reveal performance–structure relationships under thermal and chemical attacks. The optimized binder (aqueous glass modulus 1.2, alkali equivalent 6%, and HCFA 20%) achieved 28-day compressive and flexural strengths of 52.8 MPa and 9.5 MPa, respectively; increasing HCFA beyond 20% reduced compressive strength, while flexural strength peaked at 20%. The preferred curing condition was 70 °C for 12 h. Characterization showed C-(A)-S-H as the dominant gel; elevated temperature led to its decomposition, acid exposure produced abundant CaSO₄, and NaOH exposure formed N-A-S-H, each correlating with strength loss. Quantitatively, acid resistance was weaker than alkali resistance and both deteriorated with concentration: in H₂SO₄, 28-day mass loss rose from 1.22% to 4.16%, with compressive/flexural strength retention dropping to 75.2%, 71.2%, 63.4%, and 57.4% and 65.3%, 61.6%, 58.9%, and 49.5%, respectively; in NaOH (0.2/0.5/0.8/1.0 mol/L), 28-day mass change was +0.74%, +0.88%, −1.85%, and −2.06%, compressive strength declined in all cases (smallest drop 7.77% at 0.2 mol/L), and flexural strength increased at lower alkalinity, consistent with a pore-filling micro-densification effect before gel dissolution/cracking dominates. Practically, the recommended mix and curing window deliver structural-grade performance while improving high-temperature and acid/alkali resistance relative to non-optimized formulations, offering a scalable, lower-carbon route to utilize regional desert sand and industrial wastes in durable cementitious applications. Full article

The efficient resource utilization of industrial solid wastes, such as ground granulated blast-furnace slag (GGBS) and coal gangue (CG), is essential for sustainable development. However, their activation commonly depends on expensive and corrosive chemical alkalis. This study proposes a solution by developing a fully waste-based cementitious material using calcium carbide slag (CS), another industrial residue, as an eco-friendly alkaline activator for the GGBS-CG system. The influence of CS dosage (0–20 wt%) on hydration evolution and mechanical properties was examined using uniaxial compression testing, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The results indicated that a CS dosage of 10 wt% yielded the highest compressive strength, reaching 10.13 MPa—a 16.5% improvement compared to the 20 wt% group. This enhancement is ascribed to the formation of hydrotalcite (HT) and calcium silicate hydrate (C-(A)-S-H) gel, which densify the microstructure. In contrast, higher CS contents led to a passivation effect that restrained further reaction. This work offers a practical and theoretical basis for the development of low-carbon, multi-waste cementitious materials and presents a promising strategy for large-scale valorization of industrial solid wastes. Full article

In the context of the current global transition toward low-carbon energy, the issue of $C{O}_2$ utilization has become increasingly important. One of the most promising natural targets for $C{O}_2$ sequestration is the terrigenous sedimentary formations found in oil, gas, and coal basins. It is generally assumed that $C{O}_2$ injected into such formations can be stored indefinitely in a stable form. However, the dissolution of $C{O}_2$ into subsurface water leads to a reduction in pH, which may cause partial dissolution of the host formation, altering the structure of the subsurface in the injection zone. This process is relatively slow, potentially unfolding over decades or even centuries, and its long-term consequences require careful investigation through mathematical modeling. The geological formation is treated as a partially soluble porous medium, where the dissolution rate is governed by surface chemical reactions occurring at the pore boundaries. In this study, we present an applied mathematical model that captures the coupled processes of mass transport, surface chemical reactions, and the resulting microscopic changes in the pore structure of the formation. To ensure the model remains grounded in realistic geological conditions, we based it on exploration data characterizing the composition and microstructure of the pore space typical of the Cenomanian suite in northern Western Siberia. The model incorporates the dominant geochemical reactions involving calcium carbonate (calcite, $CaC{O}_3$), characteristic of Cenomanian reservoir rocks. It describes the dissolution of $C{O}_2$ in the pore fluid and the associated evolution of ion concentrations, specifically $H^{+}$, $C{a}^{2+}$, and $HC{O}_3^{-}$. The input parameters are derived from experimental data. While the model focuses on calcite-based formations, the algorithm can be adapted to other mineralogies with appropriate modifications to the reaction terms. The simulation domain is defined as a cubic region with a side length of 1 $\mathsf{\mu }$m, representing a fragment of the geological formation with a porosity of 0.33. The pore space is initially filled with a mixture of liquid $C{O}_2$ and water at known saturation levels. The mathematical framework consists of a system of diffusion–reaction equations describing the dissolution of $C{O}_2$ in water and the subsequent mineral dissolution, coupled with a model for surface evolution of the solid phase. This model enables calculation of surface reaction rates within the porous medium and estimates the timescales over which significant changes in pore structure may occur, depending on the relative saturations of water and liquid $C{O}_2$. Full article

The salinization of agricultural soils is a serious threat to farming and ecological balance in arid and semi-arid regions. Accurate estimation of soil water-soluble ions (calcium, carbonate, magnesium, and sulfate) is necessary for correct monitoring of soil salinization and sustainable land management. Hyperspectral ground-based data are valuable in soil salinization monitoring, but the acquisition cost is high, and the coverage is small. Therefore, this study proposes a two-stage deep learning framework with multispectral remote-sensing images. First, the wavelet transform is used to enhance the Transformer and extract fine-grained spectral features to reconstruct the ground-based hyperspectral data. A comparison of ground-based hyperspectral data shows that the reconstructed spectra match the measured data in the 450–998 nm range, with R² up to 0.98 and MSE = 0.31. This high similarity compensates for the low spectral resolution and weak feature expression of multispectral remote-sensing data. Subsequently, this enhanced spectral information was integrated and fed into a novel multiscale self-attentive Transformer model (MSATransformer) to invert four water-soluble ions. Compared with BPANN, MLP, and the standard Transformer model, our model remains robust across different spectra, achieving an R² of up to 0.95 and reducing the average relative error by more than 30%. Among them, for the strongly responsive ions magnesium and sulfate, R² reaches 0.92 and 0.95 (with RMSE of 0.13 and 0.29 g/kg, respectively). For the weakly responsive ions calcium and carbonate, R² stays above 0.80 (RMSE is below 0.40 g/kg). The MSATransformer framework provides a low-cost and high-accuracy solution to monitor soil salinization at large scales and supports precision farmland management. Full article

This study focuses on the development of high-performance composite cementitious materials for offshore engineering applications, addressing the critical challenges of durability, environmental degradation, and carbon emissions. By incorporating polycarboxylate superplasticizers (PCE) and combining fly ash (FA), ground granulated blast furnace slag (GGBS), and silica fume (SF) in various proportions, composite mortars were designed and evaluated. A series of laboratory tests were conducted to assess workability, mechanical properties, volume stability, and durability under simulated marine conditions. The results demonstrate that the optimized composite exhibits superior performance in terms of strength development, shrinkage control, and resistance to chloride penetration and freeze–thaw cycles. Microstructural analysis further reveals that the enhanced performance is attributed to the formation of additional calcium silicate hydrate (C–S–H) gel and a denser internal matrix resulting from secondary hydration. These findings suggest that the proposed material holds significant potential for enhancing the long-term durability and sustainability of marine infrastructure. Full article

The utilization of steel slag (SS), fly ash (FA), and ground granulated blast furnace slag (GGBFS) as soil additives in construction represents a critical approach to achieving resource recycling of these industrial by-products. This study aims to activate the SS-FA-GGBFS composite with a NaOH solution and Na₂CO₃ and employ the activated solid waste blend as an admixture for lateritic clay modification. By varying the concentration of the NaOH solution and the dosage of Na₂CO₃ relative to the SS-FA-GGBFS composite, the effects of these parameters on the activation efficiency of the composite as a lateritic clay additive were investigated. Results indicate that the NaOH solution activates the SS-FA-GGBFS composite more effectively than Na₂CO₃. The NaOH solution significantly promotes the depolymerization of aluminosilicates in the solid waste materials and the generation of Calcium-Silicate-Hydrate and Calcium-Aluminate-Hydrate gels. In contrast, Na₂CO₃ relies on its carbonate ions to react with calcium ions in the materials, forming calcium carbonate precipitates. As a rigid cementing phase, calcium carbonate exhibits a weaker cementing effect on soil compared to Calcium-Silicate-Hydrate and Calcium-Aluminate-Hydrate gels. However, excessive NaOH leads to inefficient dissolution of the solid waste and induces a transformation of hydration products in the modified lateritic clay from Calcium-Silicate-Hydrate and Calcium-Aluminate-Hydrate to Sodium-Silicate-Hydrate and Sodium-Aluminate-Hydrate, which negatively impacts the strength and microstructural compactness of the alkali-activated solid waste composite-modified lateritic clay. Full article

Predicting the flexural behavior of fiber-reinforced ultra-high-performance concrete (UHPC) remains a significant challenge due to the complex interactions among numerous mix design parameters. This study presents a machine learning-based framework aimed at accurately estimating the modulus of rupture (MOR) of UHPC. A comprehensive dataset comprising 566 distinct mixtures, characterized by 41 compositional and fiber-related variables, was compiled. Seven regression models were trained and evaluated, with Random Forest, Extremely Randomized Trees, and XGBoost yielding coefficients of determination (R²) exceeding 0.84 on the test set. Feature importance was quantified using Shapley values, while partial dependence plots (PDPs) were employed to visualize both individual parameter effects and key interactions, notably between fiber factor, water-to-binder ratio, maximum aggregate size, and matrix compressive strength. To validate the predictive performance of the machine learning models, an independent experimental campaign was carried out comprising 26 UHPC mixtures designed with varying binder compositions—including supplementary cementitious materials such as fly ash, ground recycled glass, and calcium carbonate—and reinforced with mono-fiber (straight steel, hooked steel, and PVA) and hybrid-fiber systems. The best-performing models were integrated into a hybrid neural network, which achieved a validation accuracy of R² = 0.951 against this diverse experimental dataset, demonstrating robust generalizability across both material and reinforcement variations. The proposed framework offers a robust predictive tool to support the design of more sustainable UHPC formulations incorporating supplementary cementitious materials without compromising flexural performance. Full article

Alkali-activated slag-like powder (AASP) materials are a novel type of binder prepared by activating slag-like powder (SP) with alkaline activators, providing a sustainable alternative to traditional cement for construction in remote mountainous regions, as well as on islands and reefs far from the inland, reducing transportation costs, shortening construction timelines, and minimizing energy consumption. SP is locally produced from siliceous and calcareous materials through calcining, water quenching, and grinding, exhibiting reactivity similar to that of ground granulated blast-furnace slag. In this study, siliceous sand and ground calcium carbonate powder were utilized to produce SP, with sodium carbonate (Na₂CO₃), sodium hydroxide (NaOH), and their mixture serving as activators. The results indicated that the Ca/Si ratio in SP, along with the dosage of Na₂CO₃ (D_sc) and Na₂O content (N_c) in the activator, significantly affected the compressive strength of AASP materials at both early and late stages. The 28-day compressive strength reached up to 78.95 MPa, comparable to that of alkali-activated slag (AAS) materials. The optimum mix ratio for Na₂CO₃-NaOH based AASP materials was also determined to be 80% D_sc and 8% N_c (C8N2-8). Microscopic analyses were employed to investigate the changes in the macroscopic properties of AASP materials driven by hydration products, chemical group composition, and microstructure. Full article

The significant anthropogenic carbon dioxide (CO₂) emissions from cement production and the disposal of the majority of post-consumer waste glass into landfill sites have increased environmental pollution. In order to reduce the environmental impact, ground glass pozzolan (GGP) as a partial cement replacement has drawn interest from the concrete industry. This review examines the potential of GGP as a supplementary cementitious material (SCM), exploring the chemical composition of pozzolans, the different types of glass used for GGP, and the impact of glass color on pozzolanic reactivity. In addition, this study gathers the most recent research articles on the fresh and mechanical properties of concrete incorporating GGP. Key findings show that the incorporation of GGP in concrete improves the modulus of elasticity and the compressive, tensile, flexural, and punching strengths due to the pozzolanic reactions. The results indicate that GGP, made from waste glass, has pozzolanic properties that form additional strength-enhancing calcium silicate hydrate (C-S-H) gel and densify the concrete matrix. Additionally, the life cycle assessments of GGP-incorporated concrete demonstrate reductions in energy consumption and CO₂ emissions compared to conventional concrete, supporting a circular economy and sustainable construction practices. Full article

This study evaluates the influence of multiwall carbon nanotubes (MWCNTs), reduced graphene oxide (rGO), and magnesium oxide (MgO) on the thermal conductivity of alkali-activated engineered composites (AAECs). Thirty-two ambient-cured AAECs consisting of two types of powdered-form reagents/activators (type 1—calcium hydroxide: sodium meta silicate = 1:2.5; type 2—calcium hydroxide: sodium sulfate 2.5:1), two dosages of MgO (0 and 0.5%) of MgO, three percentages (0, 0.3%, and 0.6%) of MWCNTs/rGO, and binary (45% ground granulated blast furnace slag ‘GGBFS’ and 55% Class C fly ash ‘FA-C’) and ternary combinations (40% GGBFS, 25% FA-C and 35% class F fly ash ‘FA-F’) of industrial-waste-based source materials, silica sand, and polyvinyl alcohol (PVA) fiber were developed using the ‘one-part dry mix’ technique. Problems associated with the dispersion and agglomeration of nanomaterials during production were avoided through the use of defined ultra-sonication with a high-shear mixing protocol. The impact of the combination of source materials, activators, and MgO/MWCNT/rGO dosages and their combinations on the thermal properties of AAECs is evaluated and discussed based on temperature–time history and thermal conductivity/diffusivity properties along with micro-structural characteristics. It was found that the change in temperature of the AAECs decreased during testing with the addition of MWCNTs/rGO/MgO. The thermal conductivity and diffusivity of AAECs increased with the increase in MWCNT/rGO/MgO contents due to the formation of additional crystalline reaction products, improved matrix connectivity, and high conductivity of nanomaterials. MWCNT AAECs showed the highest thermal conductivity of 0.91–1.26 W/mK with 49% enhancement compared to control AAECs followed by rGO AAECs. The study confirmed the viability of producing MgO/MWCNT/rGO-incorporated AAECs with enhanced thermal properties. Full article

The paper examines the use of waste eggshells as a valuable biofiller for modifying plasticized poly(vinyl chloride) (PVC). The raw ES was characterized using TGA, FTIR, particle size analysis, and XRD. The effects of ES on the processing, mechanical and thermal properties, density, porosity, and colour of PVC matrix composites were evaluated compared to pPVC/CC produced using the same methodology. It was found that pPVC/ES exhibits different processing properties to pPVC/CC. The mechanical properties of PVC/ES are slightly lower than those of pPVC/CC at concentrations up to 20 phr. However, at 30 phr and 40 phr, the differences in the mechanical properties of composites with both CC and ES are very similar, and the values are within the designated standard deviation of the measurement. The mechanical properties of PVC/ES do not limit their potential applications. When using eggshell (ES) as a filler, improvements in tensile strength (t_ts) were observed, ranging from 38% to 61% compared to the unfilled matrix and from 35% to 54% compared to pPVC/CC with an equivalent amount of filler. Although ground eggshells have similar insulating properties to calcium carbonate (CC), they are more effective at scavenging chlorine (Cl•) released during the initial stages of decomposition. This effectiveness helps to slow down the breakdown of PVC, as the eggshells maintain their porous, sponge-like structure when used as a filler. Full article

Microbially induced calcium carbonate precipitation (MICP) is a biomediated ground improvement technology that uses ureolytic bacteria to precipitate calcium carbonate minerals to improve the strength and stiffness of soils. MICP can be mediated by either augmented non-native or stimulated indigenous microorganisms, resulting in biocemented soils and generated aqueous ammonium (NH₄⁺) byproducts. Although the process has been extensively investigated, the fate and transport of generated NH₄⁺ byproducts has posed an environmental challenge and to date, their associated environmental impacts have remained poorly understood. In an effort to better quantify process impacts, a large-scale experiment was conducted involving three 3.7 m long soil columns, wherein three different ureolytic biocementation treatment approaches were employed. A life cycle sustainability assessment (LCSA) was performed to compare the environmental impacts and costs of these different MICP treatment approaches as well as evaluate the potential environmental benefits of NH₄⁺ byproduct removal using post-treatment rinsing. The objective of this paper is to present the results of the LCSA study. LCSA results suggest that when treatments are consistent with those performed in this study, stimulation can be more sustainable than augmentation, and the use of lower ureolytic rates can further reduce process environmental impacts by achieving greater spatial uniformity and extent of biocementation. The LCSA outcomes also illustrate tension between the environmental benefits afforded by NH₄⁺ byproduct removal and the life cycle impacts and costs associated with this removal. For the specific testing conditions, the injection of 1.8 pore volumes of rinse solutions to remove generated NH₄⁺ byproducts following biocementation was found to minimize environmental impacts; however, further refinement of such approaches will likely result from future field-scale applications. Full article