Search Results (1,877)

To investigate the impact of underground multiple stress disturbances on the long-term stability of cemented tailings backfill (CTB), this study conducted experiments under different disturbance levels (20–80% of static strength) and frequencies (1–4 times). By comprehensively utilizing mechanical testing, wave velocity monitoring, digital image correlation (DIC), and scanning electron microscopy (SEM), the “heterogeneous” evolution mechanism of macro-micro damage was revealed. The results indicate that disturbance level and frequency exert distinctly different driving effects on the deterioration of CTB, rather than a simple linear superposition. Specifically, low-frequency disturbance produces a compaction strengthening effect, microscopically promoting the generation of Ca(OH)₂ and ettringite (increased Ca/Si ratio). In contrast, the combination of high disturbance and high frequency induces free water extrusion and inhibits hydration, leading to an advanced damage threshold based on energy evolution and the accelerated coalescence of microcracks, which favors the formation of C-S-H gel (decreased Ca/Si ratio). Within this heterogeneous mechanism, the disturbance level acts as the dominant controlling factor. This study clarifies the nonlinear mechanical and chemical evolution paths under composite disturbances, providing theoretical support for the dynamic stability control of backfill in deep multi-step mining. Full article

Magnesium–rich environments are frequently encountered in cementitious systems, including the use of high–Mg raw materials in clinker production, cement–clay interfaces relevant to nuclear waste disposal, and exposure of cement–based materials to seawater, where progressive decalcification can substantially alter the structure and durability of calcium aluminosilicate hydrate (C–A–S–H) phases. In this study, density functional theory (DFT) calculations were employed to investigate the combined effects of interlayer and intralayer partial decalcification, Mg²⁺ substitution, and reinforcement with epoxy– and hydroxyl–functionalized reduced graphene oxide (rGO) on the structural stability and elastic properties of alkali charge–balanced C–A–S–H under dry and hydrated conditions. Adsorption–energy calculations reveal thermodynamically favorable interactions between functionalized rGO and silicate hydrate species in the presence of Mg²⁺, with hydroxyl/rGO promoting stronger interfacial stabilization and epoxy/rGO preserving greater graphene lattice integrity. The results demonstrate that Mg²⁺ substitution together with rGO intercalation generally enhances the mechanical response of partially decalcified structures through structural densification and interfacial cohesion. Relative to dry systems, hydration further improves elastic performance, increasing Young’s modulus and bulk modulus by 1–11% and 4–19%, respectively, for interlayer decalcified nanocomposites, while intralayer configurations exhibit stronger but model–dependent enhancements of up to ≈22% and ≈33%. Compared with untreated systems, rGO–treated nan–composites exhibit enhanced stiffness, with Young’s modulus and bulk modulus increasing by up to ≈22% and ≈15%, respectively. Overall, these findings provide atomistic insights into stabilization mechanisms in partially decalcified alkali charge–balanced C–A–S–H systems and identify Mg²⁺–rGO incorporation as a promising strategy for mitigating decalcification–induced degradation in durable low–carbon cementitious nanocomposites. Full article

Modern prosthetic dentistry has been significantly reshaped by adhesive dentistry, CAD/CAM technologies, and advanced ceramic materials, leading to the development of minimally invasive all-ceramic restorative approaches. However, the longevity of the adhesive interface is fundamental to the long-term effectiveness of these restorations. With a focus on bond durability and clinical performance, this narrative review aims to evaluate modern adhesive strategies, tooth preparation requirements, and cementation techniques in all-ceramic minimally invasive restorations. Methods: A narrative review of the literature was performed using Google Scholar, Web of Science, and PubMed/MEDLINE databases. Publications from 2000 to 2026 were analysed. In vitro research, narrative reviews, and systematic reviews related to adhesive systems, resin cements, CAD/CAM materials, and minimally invasive prosthodontic principles were the core subjects of the research. Results: The findings indicate that material selection, surface conditioning techniques, and cementation methods have a significant impact on the clinical effectiveness of all-ceramic restorations. Retention and marginal sealing are greatly enhanced by resin-based adhesive systems. Nevertheless, hydrolytic degradation, procedure sensitivity, and substrate-related factors remain a challenge to the adhesive interface. Advances in CAD/CAM and ultra-conservative designs, like occlusal veneers and partial-coverage restorations, have increased treatment alternatives while ensuring acceptable functional and aesthetic results. Conclusions: Minimally invasive all-ceramic restorations represent a conservative and clinically effective treatment approach in modern prosthodontics. Their long-term performance is primarily dependent on adhesive interface stability and adherence to evidence-based clinical protocols. Continued developments in adhesive materials and ceramic systems are expected to improve bond durability and broaden clinical indications. Full article

Residual mud cake on the wellbore significantly compromises the cement–formation interfacial cementation quality. However, the research on the weak cementation mechanism of the cementing interface caused by mud cake properties is insufficient. In this paper, laboratory experiments and theoretical analysis were conducted to investigate the influence of mud cake properties on interfacial cementation strength. The results show that the main mechanism of weak cementation of the cement–formation interface caused by mud cake has three aspects: the thickness of mud cake is large, the structure is loose, the strength is low, the bearing capacity is insufficient, and the deformation–compression behavior is small and easily sheared. Based on this, three interfacial strengthening methods, chemical thinning by anhydrous sodium silicate, density enhancement by wollastonite and deformation–compression regulation using sepiolite fibers, were proposed to improve the cementation strength. The addition of anhydrous sodium silicate reduced mud cake thickness by up to 93.5% and increased interfacial cementation strength by 2.43 times. Wollastonite increased mud cake structural stability from 69 to 284 s·mm⁻¹ and improved interfacial cementation strength by up to 2.27 times. Sepiolite fibers increased the deformation–compression coefficient from 1.26 to 1.83, and the maximum interfacial cementation strength was achieved at R ≈ 1.64. In addition, the proposed additives improve the performance of mud cake and have good compatibility with drilling fluid. This study provides a theoretical basis for improving the cementing quality of the cementing interface. Full article

Freeze–thaw cycles cause mechanical deterioration and instability of slope rock masses in open-pit coal mines located in the cold regions of Northwest China. In this study, the research object is fine-grained sandstone from the Yan’an Formation in the Tarangole mining area of the Ordos Basin. Here, indoor freeze–thaw cycling, uniaxial compression, and triaxial compression tests were conducted to systematically analyze the deformation behavior, strength evolution, and failure modes of the sandstone under varying numbers of freeze–thaw cycles, freezing temperatures, and confining pressures, thereby revealing its freeze–thaw damage mechanism. The results show that the number of freeze–thaw cycles is the dominant factor affecting the elastic modulus. Freezing temperatures (especially between −5 °C and −15 °C) and the number of freeze–thaw cycles (particularly the first 10 cycles) significantly reduce peak strength. In addition, confining pressure can significantly enhance the resistance to deformation (under 15 freeze–thaw cycles, the elastic modulus increases by 181.8% as confining pressure rises from 0 to 2 MPa). Within the low confining pressure range (0–1.5 MPa), peak strain decreases monotonically with increasing confining pressure and is independent of the number of freeze–thaw cycles. Finally, the increase in the number of freeze–thaw cycles and the decrease in temperature jointly promote crack development, and the failure mode shifts from pure shear to a shear-tension composite mode. The underlying cause lies in the evolution of interparticle cementation within the soil skeleton and in the associated pore–crack structure. In addition, based on fracture damage mechanics and the modified Weibull distribution, a damage evolution equation and a constitutive model for sandstone considering freeze–thaw cycles and temperature effects were established and validated. Therefore, the research findings can provide a theoretical basis for slope support, freeze–thaw disaster prevention and mitigation, and stability assessment in the Tarangole mining area and other cold regions. Full article

An anti-contamination agent (Zn/Al–ATMP–LDH) was synthesized by intercalation and used to correct the abnormal thickening and related operational risks caused by contact contamination between drilling fluids and cement slurries during high-temperature/high-pressure cementing. The experimental results show that the agent is chemically stable and exhibits good compatibility with conventional spacer fluid additives. When compared with the direct addition of amino tris(methylenephosphonic acid) (ATMP), confining ATMP within a layered double hydroxide (LDH) markedly mitigates the retarding effect. At a dosage exceeding 0.3 wt%, the compressive strength of cement stone increased from 0 to 32.84 MPa following curing at 90 °C for 1 day and continued to develop steadily after 7 days. Following conditioning at 187 °C and 145 MPa for 120 min, the spacer system formulated using the proposed agent as the core component served to enhance the rheology of the mixed slurry via synergistic adsorption–regulation–dispersion stabilization-controlled release. The mixed slurry maintained stable rheological properties before and after aging with no uncontrolled thickening. When mixing the cement slurry and drilling fluid at a 7:3 volume ratio, the slurry consistency exceeded 60 Bc within 1 h, failing to meet operational requirements. In contrast, the mixed slurry containing the anti-contamination spacer (cement slurry–drilling fluid–spacer = 7:2:1) exhibited a thickening time greater than 300 min and was successfully applied in field-cementing operations in a well in the Gaomo area. Full article

Accelerated carbonation of cement-based materials offers a promising route for CO₂ sequestration driven by waste heat co-emitted from cement and power plants; however, existing kinetic models typically describe the low-temperature gas–liquid–solid regime near 100 °C and the high-temperature gas–solid regime near 600 °C in isolation, limiting their applicability to plant-scale reactor design. This study proposes a unified dual-regime kinetic framework spanning 20–700 °C. The low-temperature branch couples Henry’s-law CO₂ solubility, a sigmoidal water-film stability function, and an Arrhenius ionic reaction term, whereas the high-temperature branch integrates shrinking-core surface reaction and product-layer diffusion with an attenuation term near the CaCO₃ decomposition onset. Seven parameters were calibrated by bounded least squares against a 51-point temperature dataset compiled from the author’s previously published carbonation experiments. The calibrated model reproduced the bimodal temperature dependence of the carbonation degree (R² = 0.62; RMSE = 0.083), with peaks near 100 °C and 640 °C, and predicted reactor volumes of order-of-magnitude 150–200 m³ for a 1 Mt/y cement plant under three waste-heat operating points. The framework bridges particle-scale kinetic and plant-scale design, and identifies mixing as the dominant operational sensitivity at the clinker-cooler condition. Full article

Road engineers still face a critical challenge in improving the crack resistance of cement-stabilized macadam (CSM) base courses. This study employs the discrete element method (DEM) with realistic aggregate morphologies from X-ray computed tomography to model normally bonded and weakly bonded CSM. The mesoscopic parameters of normally bonded models were calibrated against laboratory unconfined compressive strength (UCS) tests, and a weakening ratio of bond strength (Wr_bs) was introduced to define the weakly bonded model. The results show that UCS decreases monotonically with the reduction in Wr_bs and the increase in Rr_ca. The maximum strength reduction reaches 26.3% at the extreme condition of Rr_ca = 100% and Wr_bs = 50%. Despite this reduction, the UCS of weakly bonded specimens remains compliant with Chinese specifications for base course materials when designed with appropriate parameters. Notably, weakly bonded specimens exhibit a more dispersed crack distribution and a more gradual energy dissipation process. This mechanism is associated with a reduced tendency for macroscopic crack initiation and propagation, suggesting the potential of weakly bonded CSM to enhance crack resistance. This work provides a mesoscopic theoretical foundation for the engineering application and sustainable development of weakly bonded CSM in pavement base courses. Full article

Land-use changes and unsustainable agricultural practices can alter soil properties, thereby increasing soil erodibility and the risk of land degradation. This study assessed the impact of converting forest to grassland and cropland on soil erodibility in the Kolubara watershed (western Serbia) using soil samples collected at two depths (0–15 and 15–30 cm). Soil erodibility was determined using the following indicators: clay ratio (CR), soil structure stability index (SSI), mean weight diameter (MWD), soil organic carbon cementing agent index (SCAI), saturated hydraulic conductivity (Ks), the K-factor, and a comprehensive soil erodibility index (CSEI) calculated by a weighted summation method. Most soil indicators differed significantly among land uses. Forest soils exhibited the highest MWD (2.94 mm), Ks (1119.15 mm h⁻¹), and SSI (5.86), whereas the lowest values were recorded in cropland soils (1.64 mm, 29.68 mm h⁻¹, and 3.07, respectively). In contrast, cropland soils showed the highest CR (0.005) and K-factor (0.038 t ha h ha⁻¹ MJ⁻¹ mm⁻¹), while the lowest values occurred in forest soils (0.003 and 0.032 t ha h ha⁻¹ MJ⁻¹ mm⁻¹). The significantly higher CSEI in cropland (0.75) compared with forest soils (0.62) corresponded to reduced soil structural stability and lower organic matter–related indicators. Grassland soils generally showed intermediate values for most indicators. Soil depth significantly influenced only SSI and Ks. Differences in soil erodibility among land uses are closely related to soil physical and chemical properties, particularly soil organic carbon and soil structure-related properties (total porosity and bulk density). These findings emphasize the substantial impact of land-use change on soil erodibility and highlight the need to implement effective soil conservation practices to improve soil stability and mitigate erosion. Full article

Cement clinker production is a thermal- and emissions-intensive process requiring high-temperature heat for drying, calcination, and sintering. This review provides a process-based assessment of refuse-derived fuel (RDF), solid recovered fuel (SRF), tire-derived fuel (TDF), and biomass as partial substitutes for coal and petcoke in modern dry-process cement kilns. The study synthesized the evidence from plant-scale trials, pilot and laboratory experiments, process modeling, computational fluid dynamics, emissions studies, life-cycle assessment (LCA), techno-economic analysis (TEA), and regional case studies to evaluate alternative fuels across fuel properties, kiln-zone suitability, process stability, clinker quality, emissions performance, and environmental outcomes. The review shows that stable co-processing generally requires fuels with net calorific values above 14 MJ kg⁻¹ and moisture contents below 15%, although TDF can provide 26–33 MJ kg⁻¹ and sustain high-energy kiln duty when sulfur, zinc, and steel residues are controlled. RDF, SRF, and biomass require pre-processing, homogenization, calibrated dosing, and continuous fuel-quality monitoring to limit incomplete burnout, deposit formation, volatile circulation, and clinker-quality variation. LCA studies show that 20% RDF thermal substitution can reduce global warming potential by about 3.3–4.2%, increasing to approximately 6.7% when avoided landfill methane credits are included. Modern abatement systems can maintain particulate matter at about 10–30 mg Nm⁻³ and PCDD/F below 0.1 ng TEQ Nm⁻³ under stable operation. The review concludes that alternative fuels are quality-dependent co-processing options whose mitigation role is complementary to clinker-factor reduction, energy-efficiency improvement, low-clinker binders, electrified heating, oxy-fuel calcination, and carbon capture. Full article

Red clay in humid-hot environments suffers from severe water sensitivity and rainfall-induced slope instability, while traditional cement/lime stabilization faces high carbon emission challenges. Existing studies on plant ash-modified red clay mainly focus on basic mechanical properties, while systematic research on water retention characteristics and slope stability under extreme rainfall in humid-hot climates remains insufficient. To address this gap, this study proposes a sustainable stabilization method using agricultural waste-derived plant ash for red clay modification in humid-hot regions. Red clay exhibits distinct engineering behaviors owing to its unique physicochemical properties, leading to compromised slope stability and reduced resistance to rainwater infiltration. In this study, red clay was stabilized with 5%, 10%, 15%, and 20% plant ash. Laboratory tests evaluated compaction characteristics, shear strength, and water retention, supported by microstructural analysis via scanning electron microscopy (SEM). Slope stability under rainfall conditions was further simulated using ABAQUS 2022 software. Key findings include: (1) The addition of plant ash significantly altered the compaction properties. As the plant ash content increased from 0% to 20%, the maximum dry density of the modified red clay decreased linearly from 1.68 g/cm³ (unmodified soil) to 1.53 g/cm³, while the optimum moisture content rose from 21.86% to 23.85%. (2) The mechanical properties exhibited a non-linear response, peaking at 10% ash content. At this optimum dosage, the unconfined compressive strength, cohesion, and internal friction angle increased by 70.4%, 83.0%, and 37.1%, respectively, compared to untreated soil. (3) Plant ash enhanced water retention capacity, shifting the soil-water characteristic curve (SWCC). The modified soil demonstrated faster dehydration at low suction but improved water retention at high suction. The permeability coefficient decreased by an order of magnitude. Microstructural analysis revealed reduced porosity and fracture infilling by cementitious gels. (4) Numerical simulations confirmed that 10% plant ash reduced maximum slope displacement from 0.96 m to 0.61 m under heavy rainfall (90 mm total precipitation over 36 h, peak intensity 90 mm/day), elevating the safety factor from 0.85 to 1.45. Failure modes transitioned from deep-seated slip to localized shallow erosion. These results demonstrate that plant ash is a sustainable and effective additive for red clay slope stabilization in tropical climates. Full article

To enhance the strength and water stability of stabilized expansive soil, this study investigates the use of cement, montmorillonite adsorption modifier (MAM), and their composite system. Laboratory tests evaluated compaction characteristics, swell–shrink behavior, and mechanical performance. The results show that MAM more effectively regulates compaction by reducing optimum water content and increasing maximum dry density; 6% MAM increases maximum dry density by ≈0.04 g/cm³ and reduces optimum water content by ≈2%. In terms of swell–shrink behavior, MAM reduces both swelling and linear shrinkage more effectively than cement. The incorporation of 5% MAM reduces the free swelling ratio by 40% and the equilibrium moisture absorption by 2.7%, lowering the swelling classification to non-expansive. Furthermore, 5% MAM decreases the unloaded and loaded swelling ratio by 14.7% and 5%, respectively, while increasing MAM from 2% to 6% further reduces linear shrinkage by 1.12%. Cement significantly enhances compressive strength, with 7–28 d values reaching 2.2–2.7 times those of untreated soil at 9% content; however, its water stability under wet–dry cycles is limited. In contrast, the cement–MAM composite system achieves balanced improvement by simultaneously suppressing swelling and enhancing both strength and water stability. These findings provide a reference for the treatment and engineering application of expansive soils. Full article

The development of sustainable grouting materials is essential for enhancing underground strata stability while reducing the environmental impact associated with ordinary Portland cement (OPC). This review summarizes previously published studies on alkali-activated grouting materials (AAGMs) prepared using fly ash (FA) and ground granulated blast furnace slag (GGBFS), activated by sodium hydroxide and sodium silicate solutions. A comprehensive literature-based analysis was conducted to evaluate both fresh and hardened properties, including fluidity, setting time, yield stress, compressive strength, and durability-related performance. Particular attention was given to the influence of FA-GGBFS proportions and activator composition on rheological behaviour, mechanical performance, and engineering applicability. The reviewed studies indicate that increasing GGBFS content significantly accelerates geo-polymerization and setting behaviour and enhances early-age strength development due to its higher calcium reactivity. In contrast, FA contributes to improved workability and flowability, attributed owing to its spherical particle morphology and slower reaction kinetics. The reviewed literature further suggests that balanced FA–GGBFS alkali-activated systems can provide a favourable combination of fluidity, injectability, setting behaviour, and mechanical performance, making them particularly suitable for underground grouting and rock mass reinforcement applications. Compared with conventional OPC-based grouts, AAGMs demonstrate superior mechanical performance together reduced environmental impact through the utilization of industrial by-products and reduced clinker consumption. However, several critical challenges still hinder the large-scale implementation of alkali-activated grouting materials in underground mining, particularly with respect to field-scale validation, shrinkage mitigation, safe handling of alkaline activators, and the current lack of standardized specifications and design guidelines for underground grouting applications. These findings provide a robust scientific basis for the design and application of eco-efficient grouting materials in deep underground mining environments and support the advancement of sustainable practices in underground engineering. Full article

With the advancement of China’s carbon peaking and carbon neutrality targets and the low-carbon upgrading of the construction industry, steel fiber recycled aggregate concrete (SFRAC) has attracted increasing attention as a sustainable construction material due to its advantages in resource recycling and enhanced mechanical performance. However, its compressive strength is influenced by multiple interacting factors, making accurate prediction challenging when using conventional empirical or regression-based methods. To enhance predictive performance, a compressive strength database was established based on published experimental data. The input layer included seven mixture parameters: water content, cement content, fine aggregate content, natural coarse aggregate content, recycled coarse aggregate content, steel fiber content, and superplasticizer dosage, with the 28-day compressive strength serving as the output variable. Using this database, four prediction models were developed, including a back-propagation (BP) neural network and three optimized variants—GA–BP, PSO–BP, and GA–PSO–BP, optimized by genetic algorithm (GA) and particle swarm optimization (PSO)—were developed. Their performance was evaluated using the coefficient of determination (R²), root mean square error (RMSE), and mean absolute error (MAE). Among the four models, GA–PSO–BP produced the best predictive performance, with a best-run R² of 0.9308 on the validation set, exceeding the BP, GA–BP, and PSO–BP neural networks by 0.0642, 0.0326, and 0.0512, respectively. Over 10 independent runs, it attained an average R² of 0.8822 and consistently delivered the lowest RMSE and MAE with small standard deviations, confirming its superior predictive accuracy and stability. These findings suggest that integrating GA and PSO can effectively enhance the predictive accuracy and stability of the BP neural network, thereby providing a dependable reference for compressive strength prediction and mix proportion optimization of steel fiber recycled aggregate concrete. Full article

Geopolymer grouting material incorporating solid wastes show considerable potential for subgrade rehabilitation in roadway engineering. This study investigates the effects of alkali dosage and silicate modulus on the setting time, flowability, compressive strength, autogenous shrinkage, chemical shrinkage, and drying shrinkage of such materials prepared with a water-to-binder ratio of 0.45. Mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) were employed to elucidate the microstructural mechanisms underlying the observed macroscopic behaviors. The results show that the flowability, expressed in terms of flow time, first increases and then decreases with increasing silicate modulus. Higher alkali dosage and silicate modulus enhance compressive strength and accelerate setting and hardening, but also substantially intensify autogenous, chemical, and drying shrinkage. The impact of silicate modulus is greater than that of alkali dosage, since a higher silicate modulus produces a more significant reduction in setting time and a more pronounced improvement in compressive strength, while also causing a much larger rise in autogenous and drying shrinkage. At 6% alkali dosage and a silicate modulus of 2.0, the grouting material attains a compressive strength over 70 MPa, but its chemical shrinkage reaches 0.04464 mL/g, autogenous shrinkage rises to 6267 µε, and drying shrinkage exceeds 3.45%, all severely impairing its volumetric stability. SEM observations show that higher alkali dosage and silicate modulus yield a denser microstructure, explaining the enhanced compressive strength, and the simultaneous growth of microcracks confirms the observed shrinkage increases. The MIP results demonstrate that increasing silicate modulus is more effective than increasing the alkali dosage in reducing porosity and refining the pore structure. However, no direct correlation was observed between the mesopore content and shrinkage in the geopolymer systems investigated in this study. Nevertheless, the fact that mesopores account for more than 85% of the total pore volume may provide a possible mechanistic explanation for why geopolymers generally exhibit substantially higher shrinkage than conventional cement-based materials. Full article