Search Results (1,381)

This study demonstrates a high-value pathway for fabricating porous ceramics by utilizing gold tailings (GT) as the principal raw material, with silicon carbide (SiC) as a high-temperature foaming agent. The microstructure, mechanical strength, and thermal conductivity were tailored by adjusting GT content, sintering temperature, raw material particle size, and foaming agent dosage. The optimized ceramics exhibit a total porosity of 60.1–83.7%, a compressive strength of 3.25–7.18 MPa, and a thermal conductivity of 0.15–0.32 W·m⁻¹·K⁻¹. These properties not only meet, but in fact exceed the key requirements specified in the Chinese National Standard GB/T 16533-1996 for porous thermal insulation ceramics. Notably, the materials achieve an optimal balance between high porosity and adequate mechanical strength. The findings confirm that gold tailings can be effectively valorized to produce standardized, porous ceramics suitable for industrial thermal insulation applications. Full article

In this article, a Nd₂Fe₁₄B_p/2024Al composite was prepared using high-energy ball milling, magnetic field cold isostatic pressing, and microwave sintering. The influence of powder particle size on microstructure and mechanical properties was discussed. The experimental results demonstrated that a ball milling duration of 10 h yielded powders with an average particle size of 5 μm, resulting in a refined and homogeneous microstructure, with a hardness value of 115 HV. Additionally, the densification process of the microwave-sintered sample was analyzed. When the sintering temperature was 490 °C, in-depth analysis was conducted on the effect of Nd₂Fe₁₄B addition on the microstructure and properties of the composite. The results showed that when the addition of Nd₂Fe₁₄B was 15 wt.%, the microstructure of the composite was uniform with fewer pores, and the Nd₂Fe₁₄B phase was evenly distributed on the matrix. At the same time, the compactness, microhardness, yield strength, and compressive strength of the composite also reached their optimal values, which were 94.3%, 136 HV, 190.5 MPa, and 248.9 MPa, respectively. When the addition of Nd₂Fe₁₄B reached 20 wt.%, the magnetic properties of the composite were slightly better than those of 15 wt.% Nd₂Fe₁₄B addition. However, based on the goal of preparing a high-magnetic and high-performance aluminum-based composite, considering the microstructure, mechanical properties, and magnetic properties comprehensively, it is believed that 15 wt.% is the optimal addition amount of Nd₂Fe₁₄B. Full article

Urbanization generates large quantities of arsenic-contaminated excavated soils that pose environmental risks due to arsenic volatilization during high-temperature sintering processes. While these soils have potential for recycling into construction materials, their reuse is hindered by arsenic release. This study demonstrated calcium hydroxide (Ca(OH)₂) as a highly effective additive for suppressing arsenic volatilization during soil sintering, while simultaneously improving material properties. Through comprehensive characterization using inductively coupled plasma-mass spectrometry (ICP-MS), scanning electron microscopy (SEM) and X-ray microtomography (μCT), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), results demonstrated that Ca(OH)₂ addition (0.5–2 wt.%) reduces arsenic volatilization by 57% through formation of thermally stable calcium arsenate (Ca₃(AsO₄)₂). Ca(OH)₂ acted via two mechanisms: (a) chemical immobilization through Ca-As-O compound formation, (b) physical encapsulation in a calcium-aluminosilicate matrix during liquid-phase sintering, and (c) pH buffering that maintains arsenic in less volatile forms. Optimal performance was achieved at 0.5% Ca(OH)₂, yielding 9.14 MPa compressive strength (29% increase) with minimal arsenic leaching (<110 ppb). Microstructural analysis showed Ca(OH)₂ promoted densification while higher doses increased porosity. This work provides a practical solution for safe reuse of arsenic-contaminated soils, addressing both environmental concerns and material performance requirements for construction applications. Full article

The significant negative thermal expansion (NTE) that occurs in La(Fe,Si)₁₃-based alloys during magnetic transition make them promising to combine with positive thermal expansion (PTE) materials to obtain near-zero thermal expansion (NZTE) materials. However, La(Fe,Si)₁₃-based alloys with NTE generally show intrinsic poor mechanical properties. Here, thermal expansion properties are optimized by adding Ag in La_0.6Ce_0.4(Fe_0.91Co_0.09)_11.9Si_1.1 to form a multi-phase structure exhibiting enhanced compressive strength. Through spark plasma sintering (SPS) and annealing, the samples consisted of α-Fe(Co,Si), NaZn₁₃-type, and LaAg₂ phases. When the annealing temperature reaches 1323 K, LaAg₂ disappears and is replaced by La₂O₃. The LaAg₂ phase and α-Fe(Co,Si) phase contribute as PTE materials to compensate for the NTE of the NaZn₁₃-type phase. Near-zero thermal expansion was achieved in the temperature range of 240–294 K, with a coefficient of thermal expansion (CTE) of 3.5 ppm/K at a 9.581 at.% Ag content. Benefiting from the uniform phase distribution and coordinated deformation, the samples obtained high mechanical strengths, with fracture stresses of 1481.1 MPa for the 15 wt.% Ag sample. This work provides a promising route for high-strength and near-zero thermal expansion Ag/La(Fe,Si)₁₃ composites. Full article

Clarifying the differential effects of temperature gradient and temperature change rate on the evolution of rock fractures and damage mechanism under thermal shock is of great significance for the development and utilization of deep geothermal resources. In this study, granite samples at different temperatures (20 °C, 150 °C, 300 °C, 450 °C, 600 °C, and 750 °C) were subjected to rapid cooling treatment with liquid nitrogen. After the thermal treatment, a series of tests were conducted on the granite, including wave velocity test, uniaxial compression experiment, computed tomography scanning, and scanning electron microscopy test, to explore the influence of thermal shock on the physical and mechanical parameters as well as the meso-structural damage of granite. The results show that with the increase in heat treatment temperature, the P-wave velocity, compressive strength, and elastic modulus of granite gradually decrease, while the peak strain gradually increases. Additionally, the failure mode of granite gradually transitions from brittle failure to ductile failure. Through CT scanning experiments, the spatial distribution characteristics of the pore–fracture structure of granite under the influence of different temperature gradients and temperature change rates were obtained, which can directly reflect the damage degree of the rock structure. When the heat treatment temperature is 450 °C or lower, the number of thermally induced cracks in the scanned sections of granite is relatively small, and the connectivity of the cracks is poor. When the temperature exceeds 450 °C, the micro-cracks inside the granite develop and expand rapidly, and there is a gradual tendency to form a fracture network, resulting in a more significant effect of fracture initiation and permeability enhancement of the rock. The research results are of great significance for the development and utilization of hot dry rock and the evaluation of thermal reservoir connectivity and can provide useful references for rock engineering involving high-temperature thermal fracturing. Full article

Concrete materials undergo a series of physical and chemical changes under high temperature, leading to the degradation of mechanical properties. This study investigates basalt fiber-reinforced concrete (BFRC) through high-temperature testing using the split Hopkinson pressure bar (SHPB) apparatus. Impact compression tests were conducted on specimens after exposure to elevated temperatures to analyze the effects of varying fiber content, temperature levels, and impact rates on the mechanical behaviors of BFRC. Based on fractional calculus theory, a dynamic constitutive equation was established to characterize the viscoelastic properties and high-temperature damage of BFRC. The results indicate that the dynamic compressive strength of BFRC decreases significantly with increasing temperature but increases gradually with higher impact rates, demonstrating fiber-toughening effects, thermal degradation effects, and strain rate strengthening effects. The proposed constitutive model aligns well with the experimental data, effectively capturing the dynamic mechanical behaviors of BFRC after high-temperature exposure, including its transitional mechanical characteristics across elastic, viscoelastic, and viscous states. The viscoelastic behaviors of BFRC are fundamentally attributed to the synergistic response of its multi-phase composite system across different scales. Basalt fibers enhance the material’s elastic properties by improving the stress transfer mechanism, while high-temperature exposure amplifies its viscous characteristics through microstructural deterioration, chemical transformations, and associated thermal damage. Full article

Paulownia wood, as a fast-growing natural material, exhibits inherently low axial compressive strength. To improve the axial structural performance of Paulownia wood, wood-cored glass fiber-reinforced polymer (GFRP) sandwich Paulownia wood columns were developed in this study. Nevertheless, the behavior of such columns remained largely unexplored—particularly under elevated temperatures and upon subsequent cooling. Consequently, an experimental program was conducted to characterize the influences of GFRP wrapping layers, steel hoop end confinement, high temperature, post-cooling strength recovery, and chamfer radius on the axial compressive performance of the columns. End crushing occurred in the absence of steel hoops, whereas mid-height fracture dominated when end confinement was provided. As the temperature rose from room temperature to 100 °C and 200 °C, the load-bearing capacity of the columns decreased by 38.26% and 54.05%, respectively, due to the softening of the GFRP composites. After cooling back to room temperature, the post-high-temperature specimens recovered approximately 95% of their original capacity, confirming that no significant thermal decomposition had been initiated. The load-bearing capacity also increased significantly with the number of GFRP layers, as the additional thickness provided both higher axial load capacity and enhanced lateral confinement of the wood core. Relative to a 4.76 mm chamfer, a 9.52 mm radius increased axial capacity by 14.07% by mitigating stress concentration. A theoretical model accounting for lateral confinement was successfully developed to predict the axial load-bearing capacity of the wood-cored GFRP sandwich columns. Full article

During deep coalbed methane (CBM) drilling, wellbore stability is significantly influenced by the interaction between drilling fluid and coal rock. However, quantitative data on mechanical degradation under long-term high-temperature and high-pressure conditions are lacking. This study subjected coal cores to immersion in field-formula drilling fluid at 60 °C and 10.5 MPa for 0–30 days, followed by uniaxial and triaxial compression tests under confining pressures of 0/5/10/20 MPa. The fracture evolution was tracked using micro-indentation (µ-indentation), nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM), establishing a relationship between water absorption and strength. The results indicate a sharp decline in mechanical parameters within the first 5 days, after which they stabilized. Uniaxial compressive strength decreased from 36.85 MPa to 22.0 MPa (−40%), elastic modulus from 1.93 GPa to 1.07 GPa (−44%), cohesion from 14.5 MPa to 5.9 MPa (−59%), and internal friction angle from 24.9° to 19.8° (−20%). Even under 20 MPa confining pressure after 30 days, the strength loss reached 43%. Water absorption increased from 6.1% to 7.9%, showing a linear negative correlation with strength, with the slope increasing from −171 MPa/% (no confining pressure) to −808 MPa/% (20 MPa confining pressure). The matrix elastic modulus remained stable at 3.5–3.9 GPa, and mineral composition remained unchanged, confirming that the degradation was due to hydraulic wedging and lubrication of fractures rather than matrix damage. These quantitative thresholds provide direct evidence for predicting wellbore stability in deep CBM drilling. Full article

High-entropy alloys (HEAs) of the Cantor type (CoCrFeMnNi) are widely recognized as model systems for studying the relationships between composition, microstructure, and functional performance. In this study, atomized Cantor alloy powders were consolidated using spark plasma sintering (SPS) under systematically varied process parameters (temperature and dwell time). The densification behavior, microstructural evolution, and mechanical response were investigated using Archimedes’ density measurements, Vickers hardness testing, compression tests, scanning electron microscopy, and EDS mapping. The results reveal a non-linear relationship between sintering temperature and densification, with maximum relative densities obtained at 1050 °C and 1100 °C for short dwell times. Despite the ultrafast nature of SPS, grain growth was observed, particularly at elevated temperatures and extended dwell times, challenging the assumption that SPS inherently limits grain coarsening. All sintered samples retained a single-phase FCC structure with homogeneous elemental distribution, and no phase segregation or secondary precipitates were detected. Compression testing showed that samples sintered at 1050 °C and 1070 °C exhibited the highest strength, demonstrating the strong interplay between sintering kinetics and grain cohesion. Full article

The long-term stability of grout-reinforced fractured rock masses in acidic groundwater environments after tunnel fires is critical for the safe operation of underground engineering. In this study, grouting reinforcement tests were performed on fractured diorite specimens using a high-strength fast-anchoring agent (HSFAA), and their mechanical degradation and microstructural evolution mechanisms were investigated under coupled high-temperature (25–1000 °C) and acidic corrosion (pH = 2) conditions. Multi-scale characterization techniques, including uniaxial compression strength (UCS) tests, X-ray computed tomography (CT), scanning electron microscopy (SEM), three-dimensional (3D) topographic scanning, and X-ray diffraction (XRD), were employed systematically. The results indicated that the synergistic thermo-acid interaction accelerated mineral dissolution and induced structural reorganization, resulting in surface whitening of specimens and decomposition of HSFAA hydration products. Increasing the prefabricated fracture angles (0–60°) amplified stress concentration at the grout–rock interface, resulting in a reduction of up to 69.46% in the peak strength of the specimens subjected to acid corrosion at 1000 °C. Acidic corrosion suppressed brittle disintegration observed in the uncorroded specimens at lower temperature (25–600 °C) by promoting energy dissipation through non-uniform notch formation, thereby shifting the failure modes from shear-dominated to tensile-shear hybrid modes. Quantitative CT analysis revealed a 34.64% reduction in crack volume (V_ca) for 1000 °C acid-corroded specimens compared to the control specimens at 25 °C. This reduction was attributed to high-temperature-induced ductility, which transformed macroscale crack propagation into microscale coalescence. These findings provide critical insights for assessing the durability of grouting reinforcement in post-fire tunnel rehabilitation and predicting the long-term stability of underground structures in chemically aggressive environments. Full article

In this article, composite binders based on industrial waste—phosphogypsum, granular phosphoric slag, and burnt barium carbonate tailings––are investigated. It was found that the optimal composition (65% slag, 20% phosphogypsum, 15% tailings) provides compressive strength up to 31.1 MPa after steaming, which corresponds to grade M300 cement. Replacing natural gypsum with phosphogypsum increases strength by 5–10%, and using waste reduces cost by 20–25% compared to traditional binders. This technology eliminates the need for high-temperature firing, reducing energy consumption by 40–50%. Neutralization of harmful impurities of phosphogypsum with oxides of MgO and CaO reduces the ecotoxicity of the material by 70–80%. It is shown that hydrothermal treatment accelerates hardening, providing 90% of brand strength in 28 days. The developed binders are promising for the production of building blocks, road surfaces, and land reclamation. Full article

The applicability of biochar as a coarse aggregate substitute in concrete to increase sustainability and multifunctionality was investigated. Biochar, a porous carbon-rich byproduct from biomass pyrolysis, was incorporated at various replacement ratios (5–20%) under four water-to-binder (w/b) conditions (0.25–0.40). The key physical, mechanical, thermal, and microstructural properties, including the unit weight, porosity, compressive strength, flexural strength, and thermal conductivity, were evaluated via SEM and EDS analyses. The results revealed that although increasing the biochar content reduced the mechanical strength, it significantly improved the thermal insulation performance because of the porous structure of the biochar. At low w/b ratios and 5–10% biochar content, sufficient mechanical properties were retained, indicating a viable design range. Higher replacement ratios (>15%) led to excessive porosity, reduced hydration, and impaired durability. This study quantitatively analyzed the interproperty correlations, confirming that the strength and thermal performance are closely linked to the internal matrix density and porosity. These findings suggest that biochar-based concrete has potential for use in thermal energy storage systems, high-temperature insulation, and low-carbon construction. The low-carbon effect is achieved both by sequestering stable carbon within the concrete matrix and by partially replacing cement, thereby reducing CO₂ emissions from cement production. Moreover, the results highlight a strong correlation between increased porosity, enhanced thermal insulation, and reduced strength, thereby offering a solid foundation for sustainable material design. In particular, the term ‘high temperature’ in this context refers to exposure conditions above approximately 200~400 °C, as reported in previous studies. However, this should be considered as a potential application to be validated in future experiments rather than a confirmed outcome of this study. Full article

This study elucidated the evolution and catastrophic failure mechanisms of concrete’s mechanical properties under high-temperature and moisture-coupled environments. Specimens underwent hygrothermal shock simulation via constant-temperature drying (100 °C/200 °C, 4 h) followed by water quenching (20 °C, 30 min). Uniaxial compression tests were performed using a uniaxial compression test machine with synchronized multi-scale damage monitoring that integrated digital image correlation (DIC), acoustic emission (AE), and infrared thermography. The results demonstrated that hygrothermal coupling reduced concrete ductility significantly, in which the peak strain decreased from 0.36% (ambient) to 0.25% for both the 100 °C and 200 °C groups, while compressive strength declined to 42.8 MPa (−2.9%) and 40.3 MPa (−8.6%), respectively, with elevated elastic modulus. DIC analysis revealed the temperature-dependent failure mode reconstruction: progressive end cracking (max strain 0.48%) at ambient temperature transitioned to coordinated dual-end cracking with jump-type damage (abrupt principal strain to 0.1%) at 100 °C and degenerated to brittle fracture oriented along a singular path (principal strain band 0.015%) at 200 °C. AE monitoring indicated drastically reduced micro-damage energy barriers at 200 °C, where cumulative energy (4000 mV·ms) plummeted to merely 2% of the ambient group (200,000 mV·ms). Infrared thermography showed that energy aggregation shifted from “centralized” (ambient) to “edge-to-center migration” (200 °C), with intensified thermal shock effects in fracture zones (ΔT ≈ −7.2 °C). The study established that hygrothermal coupling weakens the aggregate-paste interfacial transition zone (ITZ) by concentrating the strain energy along singular weak paths and inducing brittle failure mode degeneration, which thereby provides theoretical foundations for fire-resistant design and catastrophic failure warning systems in concrete structures exposed to coupled environmental stressors. Full article

This study investigates the early-age compressive strength development of concrete incorporating ground granulated blast-furnace slag (GGBFS) under varying water-to-binder (W/B) ratios (35%, 45%, and 55%) and curing temperatures (5 °C, 20 °C, and 35 °C). Concrete mixtures were prepared with 0%, 20%, and 40% GGBFS replacement levels, maintaining a constant slump of 180 mm. The influence of GGBFS on fresh properties was evident, as higher GGBFS content reduced the demand for high-performance air-entraining water-reducing admixture (AEWR) by up to 72% at 40% GGBFS and W/B of 35%. All mixtures maintained target air content within 4.5 ± 1.5%. The Nurse–Saul maturity method was applied to determine the datum temperature $T_0$ (The minimum temperature required for the degree of maturity to increase) for early-age strength prediction. The optimal $T_0$ was found to be −3 °C for both OPC and GGBFS-blended concretes, replacing the conventional −10 °C value. Compressive strength predictions were conducted using Plowman, Logistic, and Gompertz models within the 5–10 MPa range. The Plowman and Gompertz models predicted early-age compressive strength with an error of approximately 10% in the 5–10 MPa range. In the lower strength range of 3–5 MPa, the Gompertz model exhibited superior predictive performance, with prediction errors 0.5–1 MPa lower than those obtained using the Plowman model. These findings will help in enhancing the maturity method’s reliability for low-temperature or time-constrained construction and support the use of GGBFS as a sustainable cement replacement. The study offers practical insights into optimizing early-age performance in blended cementitious systems. Full article

In this study, cement, short-cut carbon fibers, and polymer water-absorbing resin were used as the main materials, with high-performance water-reducing polycarboxylic acid agent as the modified material. A new conductive cement-based grouting material was developed by incorporating functional additives. Its mix design was optimized based on initial setting time, fluidity, bleeding rate, and compressive strength. The optimal ratio of the grouting material was determined as follows: 0.4 wt% of high water-absorbent resin, 0.25 wt% of high-efficiency water reducer, 0.8 wt% of short-cut carbon fibers, and a water–cement ratio of 0.8:1. The electrical conductivity of the grouting material was studied in depth under different dosages of short-cut carbon fibers, considering factors such as curing age, temperature, and pressure conditions. The results show that with the increase in curing age, the volume resistivity of the specimen gradually increases; the resistivity of the conductive cementitious grouting material decreases with the rise in temperature, showing a negative temperature coefficient effect; additionally, the doping of an appropriate amount of short-cut carbon fibers enables the conductive cementitious grouting specimen to exhibit good pressure-sensitive properties. Field test verification indicates that the new cementitious conductive grouting material has excellent conductive properties, and the grouting quality can be effectively evaluated via high-density electrical testing. Full article