Search Results (872)

Grouting materials are essential for trenchless road repair. However, conventional cement-based grouting materials suffer from considerable shrinkage and low early-age strength. To address these challenges, this study utilizes industrial solid wastes (phosphogypsum and slag) for the synergistic synthesis of a phosphogypsum–slag-based geopolymer (PBG). Using PBG as a binder and fine sand as an aggregate, a sustainable grouting material was developed. The influence of binder-to-sand and water-to-solid ratios on PBG workability was systematically evaluated, identifying the optimal water-to-solid ratio. Based on this, the effects of the binder-to-sand ratio on mechanical strength at various curing ages, durability, and leaching of toxic substances were analyzed. The mechanism of strength development mechanism and immobilization behavior of toxic substances were revealed through SEM. The results indicate that the material exhibits excellent performance when the water-to-solid ratio is 0.28 and the binder-to-sand ratio ranges from 0.70 to 0.75. The material exhibits fluidity of 160–240 mm, initial setting time > 30 min, and final setting time <400 min, a bleeding rate < 0.4%, and 28-day compressive strength ≥ 9.0 MPa. Both the impermeability and freeze–thaw resistance of PBG grouting material improve with a higher binder-to-sand ratio. Toxic substance leaching complies with Class III groundwater quality standards. Carbon footprint analysis indicates that the material significantly reduces carbon emissions. Full article

For optimizing the operational efficiency and productivity within blast furnace processes, a profound understanding of the viscous flow characteristics of CaO–SiO₂–MgO–Al₂O₃–B₂O₃ slag systems is of paramount importance. In this study, we conducted a comprehensive investigation into the influence of the CaO/SiO₂ and MgO/Al₂O₃ ratios on the viscosity, break point temperature (T_Br), and activation energy (E_η) of low boron-bearing high-alumina slag. Concurrently, we elucidated the underlying mechanisms through which these ratios affect the viscous behavior of the slag by employing a combination of analytical techniques, including X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and thermodynamic modeling using the Factsage software. The experimental findings reveal that, as the CaO/SiO₂ ratio increases from 1.10 to 1.30, the slag viscosity at 1773 K decreases from 0.316 Pa·s to 0.227 Pa·s, while both the T_Br and E_η exhibit an upward trend, rising from 1534 K and 117.01 kJ·mol⁻¹ to 1583 K and 182.86 kJ·mol⁻¹, respectively. Conversely, an elevation in the MgO/Al₂O₃ ratio from 0.40 to 0.65 results in a reduction in slag viscosity at 1773 K from 0.290 Pa·s to 0.208 Pa·s, accompanied by a decrease in T_Br from 1567 K to 1542 K. The observed deterioration in slag flow properties can be attributed to an enhanced polymerization degree of complex viscous structural units within the slag matrix. Ultimately, our study identifies that an optimal viscous performance of the slag is achieved when the CaO/SiO₂ ratio is maintained at 1.25 and the MgO/Al₂O₃ ratio is maintained at 0.55, providing valuable insights for the rational design and control of blast furnace slag systems. Full article

It is known that geopolymer mortar exhibits high compressive strength but relatively low flexural strength, high brittleness, and poor toughness. Engineering practices for cement-based materials have demonstrated that incorporating fibers can effectively prevent the expansion of existing cracks and the formation of new ones in the materials. Adding polypropylene fibers to geopolymer mortar can, on the one hand, improve the crack resistance of the mortar, and on the other hand, enhance the impact resistance of the geopolymer mortar. In this paper, slag, metakaolin, and fly ash are utilized as silico-aluminous raw materials, standard sand is employed as aggregate, and a mixture of water glass and NaOH in a specific proportion is used as the alkali activator to prepare geopolymer mortar. Polypropylene fibers are incorporated to improve its mechanical properties. The effects of fiber length and mixing method on the mechanical properties of geopolymer mortar are studied to determine the optimal fiber length and mixing method. The mechanism of the mechanical properties of fiber-reinforced geopolymer mortar is analyzed by combining SEM. The research results indicate that the geopolymer mortar with 15 mm single-doped fibers exhibits the best flexural strength and toughness. In contrast, the geopolymer mortar with 12 mm single-doped fibers demonstrates the best compressive strength. The geopolymer with 9 mm and 18 mm hybrid-doped fibers has the best mechanical properties and is superior to the geopolymer mortar with single-doped fibers. Full article

This article uses a water model with a ratio of 1:5.75 to study the influence of factors such as the position and flow rate of top and bottom composite argon blowing on the mixing time of molten steel in a 300t ladle at a certain factory. Using engine oil to simulate steel slag, the mass transfer velocity of molten steel under different bottom and top blowing positions and flow rates of the ladle was compared. At the same time, numerical simulation was used to analyze the changes in the flow field of molten steel under different ladle blowing modes. The optimal ladle composite bottom argon process was proposed and industrial experiments were conducted on site. The research results show that the stirring effect of top–bottom composite argon blowing in the ladle is significantly better than that of the pure bottom blowing mode. When the top blowing gun is located 300 mm at the bottom of the ladle, the mixing time of the molten steel is shortest and the stirring efficiency is highest. The higher the insertion depth of the top blowing gun, the faster the flow rate of the molten steel, and the smaller the proportion of dead zones. Top and bottom blowing can improve the mass transfer rate between steel slag and promote the formation of refined slag. Through industrial experiments, it was found that the S content in the molten steel decreased by approximately 22.3% and the total oxygen content decreased by 25% before and after 10 min of composite argon blowing at the top and bottom of the ladle. Full article

This study investigates the fact that reinforcing geopolymers with natural fibers provides a practical way to improve their strength and durability. Offering environmental benefits compared to Portland cement, their mechanical performance still presents challenges. The particularity of this study lies in the pretreatment of natural fibers to limit their degradation within the alkaline geopolymer matrix. It also explores the effect of their length and content on matrix geopolymer. XRD (X-ray diffraction) analysis confirmed the crystalline structure of the geopolymer gels, unaffected by fiber inclusion. SEM (Scanning Electron Microscopy) observations showed a decrease or even disappearance of mineralization in treated sisal and palm fibers within the matrix, along with some partial detachment of the fibers. Optimal compressive strength was achieved using metakaolin and GGBS (Ground Granulated Blast-furnace slag). Incorporating 4% short palm fibers enhanced flexural strength, while long sisal fibers led to a 30% increase in flexural strength compared to short fibers, representing a 10.7% overall improvement. However, current geopolymer systems still face challenges such as low flexural strength and brittleness, which this study overcomes by incorporating processed natural fibers as sustainable reinforcements with optimal content. Full article

This study focuses on the performance evolution of Engineering Geopolymer Composites (EGCs) in long-term thermal environments, investigating the mechanical properties and microstructural evolution of alkali-activated fly ash–slag composites under sustained 60 °C thermal conditions. The research results indicate that sustained exposure to 60 °C significantly enhances the static and impact loading compressive strength of EGCs; however, single-slag or high-alkalinity systems exhibit strength retrogression due to insufficient long-term thermal stability. After exposure to elevated temperatures, the tensile strain-hardening curve of EGCs becomes smoother, with a reduced number of cracks but increased crack width, leading to a transition from a distributed multicrack propagation pattern to rapid widening of primary cracks. Due to the bridging effect of PVA fibers, sustained elevated temperature significantly enhances the peak impact load stress of the S50-6 sample. Microscopic analysis attributes this improvement to the matrix-strengthening effect caused by accelerated C-(A)-S-H gel polymerization and refined pore structure under continuous heat, as well as the energy dissipation role of the fiber system. The study recommends an optimal EGC system formulation with a fly ash–slag mass ratio of 1:1 and a Na₂O concentration of 4–6%. This research provides a theoretical foundation for understanding the performance evolution and strength stability of EGC materials under sustained elevated temperature. Full article

Given the significant impact of concrete’s compressive strength on structural service life, the development of accurate and efficient prediction methods is critically important. A hybrid machine learning modeling method based on the Whale Optimization Algorithm (WOA)-optimized XGBoost algorithm is proposed. Using 1030 sets of concrete mix proportion data covering eight key parameters—cement, blast furnace slag, fly ash, water, superplasticizer, coarse aggregate, fine aggregate, and curing age—the predictive performance of four models (linear regression, random forest, XGBoost, and WOA-XGBoost) was systematically compared. The results demonstrate that the WOA-XGBoost model achieved the highest goodness of fit (R² = 0.9208, MSE = 4.5546), significantly outperforming the other models, and exhibited excellent generalization capability and robustness. Feature importance and SHAP analysis further revealed that curing age, cement content, and water content are the key variables affecting compressive strength, with blast furnace slag showing a significant marginal diminishing effect. This study provides a high-precision data-driven tool for optimizing mix proportions and predicting the strength of complex-component concrete, offering significant application value in promoting the resource utilization of industrial waste and advancing the development of green concrete. Full article

Lithium slag (LS), a solid waste generated during lithium smelting, exhibits significant potential for geopolymer preparation. However, the high shrinkage of lithium slag geopolymer mortar (LSGM) severely restricts its engineering application. Currently, research on the effects of mix proportions (GBFS-LS mass ratio, water–binder ratio, and binder–sand ratio) on LSGM’s shrinkage, and the correlation between shrinkage behavior and microstructures (pore structure and thermal behavior), remains insufficient. Additionally, there is a lack of targeted shrinkage prediction models for LSGM. To address these research gaps, this study systematically investigates the shrinkage characteristics of LSGM and develops a modified prediction model. Thermogravimetric analysis–differential thermal gravimetric analysis (TG-DTG) results show that a lower GBFS-LS ratio promotes the formation of dense sodium-alumino-silicate hydrate (N-A-S-H) gels. Meanwhile, mercury intrusion porosimetry (MIP) tests demonstrate that optimizing the water–binder ratio and binder–sand ratio refines the pore structure of LSGM, where the average pore size is reduced from 53.5 nm at a GBFS-LS ratio of 3 to 28.75 nm at a GBFS-LS ratio of 1.5.Quantitatively; compared with the group with a GBFS-LS ratio of 3, the 90-day shrinkage strain of the group with a GBFS-LS ratio of 1.5 decreases by 25.8%. When the water–binder ratio decreases from 0.57 to 0.27, the 90-day shrinkage strain reduces by 36.7%; in contrast, increasing the binder–sand ratio from 0.21 to 0.39 leads to a 39.8% increase in 90-day shrinkage strain. Based on the experimental data and the fundamental framework of the American Concrete Institute (ACI) model, this study introduces mix proportion influence coefficients and constructs a novel shrinkage prediction model tailored to LSGM. The coefficient of determination (R²) of the proposed model exceeds 0.98. This model provides a reliable quantitative tool for the mix proportion optimization and engineering application of LSGM. Full article

In this study, the effects of waste steel fiber and high volume blast furnace slag (BFS) substitution on rheological properties, thixotropic behavior and carbon emission were investigated in order to increase the sustainability of three-dimensional (3D) printable concrete (3DPC). Cement was replaced with BFS at 0%, 25%, 50% and 75% by volume, while waste steel fibers were added to the mixtures at three different lengths (5, 10, 15 mm) and volumetric ratios (0.5% and 1.0%). A total of 39 mixtures were optimized with respect to extrudability, buildability and shape stability criteria, and their rheological and thixotropic properties were characterized by a modified rheometer procedure. Results showed that 50% BFS substitution reduced dynamic yield stress and viscosity by 69% and 52%, respectively, and eliminated the need for a water-reducing admixture. 75% BFS substitution improved structural build-up (A_thix) but required 6% silica fume. The fiber effect interacted with length and BFS content, with short fibers increasing rheological resistance, while the effect of long fibers decreased in mixtures with high BFS. The carbon emission assessment revealed that 75% BFS substitution provided an outstanding CO₂ reduction of up to 71% compared to the control mix. These findings prove that high-volume BFS and waste fibers are an effective strategy to optimize rheological performance and environmental impact for sustainable 3D concrete printing. Full article

Taking municipal solid waste incineration bottom ash (MSWIBA) and natural soil as raw materials, this study incorporated steel slag to prepare MSWIBA mixed soil for pavement base courses. The modified soil was subjected to a 7-day unconfined compressive strength (UCS) test, California Bearing Ratio (CBR) test, water stability test, and freeze–thaw cycle test. The results demonstrate that the incorporation of steel slag and MSWIBA greatly boosts the modified soil’s performance. The 7-day UCS and CBR first increase and then decrease with the increase in steel slag content and MSWIBA proportion. Based on this, the optimal mix ratio of MSWIBA mixed soil was determined as 50% MSWIBA + 50% natural soil (mass ratio) with an additional 15% steel slag (relative to the total mass of MSWIBA and soil). Under this optimal ratio, the 7-day UCS of the mixed soil reaches 0.82 MPa, the 5-day water stability coefficient is 0.91, and the strength retention rate after 11 freeze–thaw cycles is 65.3%, all meeting the technical requirements for pavement base course materials. A freeze–thaw resistance study based on the optimal ratio revealed that the sample with the optimal mix ratio exhibits better freeze–thaw resistance than other ratios; its strength first decreases and then tends to stabilize with increasing freeze–thaw cycles. It was found through XRD and SEM experiments that the incorporation of steel slag promoted the progress of the hydration reaction and generated gelation products. The stacking and friction between MSWIBA and soil particles enhance the structural stability. Meanwhile, in the alkaline environment produced by the hydration of steel slag, MSWIBA further promotes hydration, increasing the total amount of cementitious substances. The C-S-H and other gels generated by hydration fill the pores, resulting in fewer cracks between the matrices and a denser matrix. It should be noted that this study focuses on short-term performance and microscopic mechanisms, and discussions on long-term heavy metal leaching behavior remain hypothetical—long-term leaching experiments have not been conducted, and the long-term environmental safety of the mixture still needs to be verified by subsequent experimental data. Full article

In response to the pressing environmental challenges posed by electrolytic manganese residue (EMR) and red mud (RM), this study proposes an innovative cementitious material technology for the synergistic co-utilization of these industrial wastes. By employing steel slag (SS) as a calcium-rich skeleton, the system effectively immobilizes sulfates from EMR and alkalinity from RM, converting hazardous wastes into value-added construction materials. Through orthogonal experimentation, an optimal mix proportion was established—30% RM, 20% EMR, and 50% SS at a water-to-binder ratio of 0.28—which achieved a 28-day compressive strength of 20.40 MPa, meeting relevant industry standards for auxiliary cementitious materials. Microstructural analysis unveiled a multi-stage alkali-sulfate synergistic activation mechanism: (1) the high alkalinity derived from RM rapidly activates the dissolution of aluminosilicate phases in both SS and EMR; (2) sulfate ions released from EMR promote extensive formation of ettringite (AFt), enhancing early-age structural integrity; and (3) calcium ions from SS facilitate the development of a dense C-S-H gel matrix, which serves as the primary binding phase. More profoundly, this process exemplifies a self-stabilizing waste-to-resource conversion mechanism, whereby harmful constituents (sulfates and free alkalis) are constructively incorporated into stable hydration products. This work not only elucidates a coherent scientific framework for the safe and efficient reclamation of multi-source solid wastes, but also demonstrates a scalable and ecologically viable pathway for million-ton-scale valorization of EMR and RM. Furthermore, it presents feasibility insights for the application of high-dosage steel slag-based material systems, thereby unifying significant environmental and economic advantages. Full article

The synergistic preparation of geopolymer from lithium slag, fly ash, and slag for underground construction can facilitate the extensive recycling of lithium slag. The effects of different activator moduli and water–binder ratios on the mechanical properties and damage mechanisms of the lithium-slag-based geopolymer were investigated by uniaxial compression tests and acoustic emission (AE) monitoring. The results show that, based on a comprehensive evaluation of peak stress, crack closure stress, plastic deformation stress, and elastic modulus, the optimal activator modulus is determined to be 1.0, and the optimal water-to-binder ratio is 0.42. At low modulus values (0.8 and 1.0) and low water–binder ratio (0.42), the AE events exhibit a steady pattern, indicating slow crack initiation and propagation within the geopolymer; with the increasing activator modulus and water-to-binder ratios, the frequency of AE events increases significantly, indicating more-frequent crack propagation and stress mutation within the geopolymer. Similarly, when the modulus is 0.8 or 1.0 and the water–binder ratio is 0.42, the sample presents a macroscopic tensile failure mode; as the modulus and water–binder ratio increase, the sample presents a tensile–shear composite failure mode. The energy evolution laws of geopolymer specimens with different activator moduli and water-to-binder ratios were analyzed, and a damage constitutive model was established. The results indicate that, with optimized mix proportions, the material can be used as a supporting material for underground spaces. Full article

The main objective of this study was to evaluate the long-term mechanical performance and shrinkage behavior of ultrahigh-performance concrete (UHPC) in which the granulated ground blast-furnace slag (GGBFS), used as part of the binder, is replaced partially or fully with ferronickel slag (FNS). The aim was to identify potential strength reduction and expansion problems associated with the use of FNS powder. For steam-cured UHPC, the compressive strength of the FNS100 (124.8 MPa) was comparable to that of the control case (FNS0, 125.1 MPa), and the tensile strength showed only a 0.3 MPa difference. Under constant-temperature and constant-humidity conditions, all mixtures satisfied the design strength standard of 120 MPa by the end of the curing period. Considering constant-temperature and constant-humidity conditions, shrinkage evaluation revealed that the FNS100_NON_AD (no shrinkage-reducing and expansive agents) exhibited 3.8 times greater shrinkage compared to FNS0, while other mixtures remained within a narrow range. These results indicate that shrinkage was governed more by the presence and type of admixtures than by the FNS replacement rate itself. This study demonstrated that FNS has sufficient potential for use as a binder in UHPC and encourages further research to optimize admixture use for long-term durability and shrinkage control. Full article

One-part geopolymers (OPG) offer a low-carbon alternative to Portland cement, yet mix design remains largely empirical. This study couples machine learning with SHAP (Shapley Additive Explanations) to quantify how mix and curing factors govern performance in Ca-containing OPG. We trained six regressors—Random Forest, ExtraTrees, SVR, Ridge, KNN, and XGBoost—on a compiled dataset and selected XGBoost as the primary model based on prediction accuracy. Models were built separately for four targets: compressive strength at 3, 7, 14, and 28 days. SHAP analysis reveals four dominant variables across targets—Slag, Na₂O, Ms, and the water-to-binder ratio (w/b)—while the sand-to-binder ratio (s/b), temperature, and humidity are secondary within the tested ranges. Strength evolution follows a reaction–densification logic: at 3 days, Slag dominates as Ca accelerates C–(N)–A–S–H formation; at 7–14 days, Na₂O leads as alkalinity/soluble silicate controls dissolution–gelation; by 28 days, Slag and Na₂O jointly set the strength ceiling, with w/b continuously regulating porosity. Interactions are strongest for Slag × Na₂O (Ca–alkalinity synergy). These results provide actionable guidance: prioritize Slag and Na₂O while controlling w/b for strength. The XGBoost+SHAP workflow offers transparent, data-driven decision support for OPG mix optimization and can be extended with broader datasets and formal validation to enhance generalization. Full article

The rapid rise in atmospheric CO₂ concentrations has intensified the need for scalable, sustainable, and economically viable carbon sequestration technologies. This study introduces a cost-effective CaO/Ca(OH)₂-based mineralization process that not only enables efficient CO₂ removal but also allows the simultaneous recovery of high-purity calcite nanoparticles as value-added products. The process involves hydrating CaO, followed by controlled carbonation under optimized CO₂ flow rates, temperature conditions, and and additive use, yielding nanocrystalline calcite with an average particle size of approximately 100 nm. Comprehensive characterization using X-ray diffraction, transmission electron microscopy, and energy-dispersive X-ray spectroscopy confirmed a polycrystalline structure with exceptional chemical purity (99.9%) and rhombohedral morphology. Techno-economic analysis further demonstrated that coupling CO₂ sequestration with nanoparticle production can markedly improve profitability, particularly when utilizing CaO/Ca(OH)₂-rich industrial residues such as steel slags or lime sludge as feedstock. This hybrid, multi-revenue strategy—integrating carbon credits, nanoparticle sales, and waste valorization—offers a scalable pathway aligned with circular economy principles, enhancing both environmental and economic performance. Moreover, the proposed system can be applied to CO₂-emitting plants and facilities, enabling not only effective carbon dioxide removal and the generation of carbon credits, but also the production of calcite nanoparticles for diverse applications in agriculture, manufacturing, and environmental remediation. These findings highlight the potential of CaO/Ca(OH)₂-based mineralization to evolve from a carbon management technology into a platform for advanced materials manufacturing, thereby contributing to global decarbonization efforts. Full article