Search Results (7,140)

With the expansion of global oil and gas resource exploration and development into deep and ultra deep layers, the efficient development of deep carbonate rock fracture cave reservoirs has become the key to ensuring energy security. However, this type of reservoir commonly faces high temperatures, high salinity, and extremely strong heterogeneity, leading to increasingly severe water content spikes caused by dominant water flow channels. Although the existing traditional inorganic plugging agent has good temperature resistance, it has the defects of great brittleness and easy cracking, while the organic polymer gel is prone to degradation failure under high temperature and high salt environments. In order to solve the above problems, a new biochar-enhanced inorganic composite gel system was constructed by using biochar prepared from agricultural and forestry waste pyrolysis as a functional enhancement component. Through rheological testing, high-temperature and high-pressure mechanical experiments, long-term thermal stability evaluation, and dynamic sealing experiments of fractured rock cores, the reinforcement and toughening laws and rheological control mechanisms of biochar on inorganic matrices were systematically studied. Research has found that a biochar content of 0.5 wt% can significantly improve the micro pore structure of the matrix. By utilizing its micro aggregate filling effect and interfacial chemical bonding, the compressive strength of the solidified body can be increased to over 2 MPa, and there is no significant decline in strength after aging at 130 °C for 30 days. More importantly, the unique “adsorption slow-release” mechanism of biochar effectively stabilizes the hydration reaction kinetics at high temperatures, extending the solidification time of the system to 15 h and solving the problem of flash condensation in deep well pumping. This system exhibits excellent shear thinning characteristics and crack sealing ability, and presents a unique “yield reconstruction” toughness sealing feature. This study elucidates the multidimensional strengthening mechanism of biochar in inorganic cementitious materials, providing technical reference for stable oil and water control in deep fractured reservoirs. Full article

To investigate the sulfate corrosion resistance of cast-in-place repair concrete incorporating recycled coarse aggregate (RCA) under partially exposed conditions, cast-in-place repair concrete specimens with different RCA contents (0%, 30%, and 50%) were immersed in Na₂SO₄ solution. The study systematically investigated the changes in apparent morphology, dimensions, mass, and mechanical properties of the specimens under sulfate corrosion. SEM, XRD, TG/DTG, and MIP were used to characterize the microstructure and mineral composition of the specimens at different corrosion ages. Results indicate that RCA cast-in-place repair concrete partially exposed to a sulfate corrosion environment undergoes coupled physical and chemical corrosion, and the interfacial zone between the recycled aggregate concrete to the base concrete represents the most vulnerable region in the composite system. Incorporating 30% RCA can effectively reduce the degradation rate of specimens under sulfate corrosion, enhance the compactness of the bonding interface, and optimize the interfacial bond strength, compressive strength, and pore structure of the specimens. Excessive RCA content disrupts the internal pore structure, accelerates sulfate ion ingress, and weakens the interfacial bond strength. The presence of RCA significantly reduces the interfacial shear strength of the specimens. After 360 days of sulfate corrosion, specimens featuring 30% and 50% RCA contents exhibit a reduction in shear strength of 15.91% and 40.0%, respectively, compared with the 0% RCA content specimen. Research findings provide a theoretical basis for the application of RCA in concrete repair engineering. Full article

Laser surface microtexturing has emerged as an effective approach for improving the performance of adhesive joints between dissimilar materials. In this study, the influence of laser-generated micrometric surface features on the mechanical behavior of hybrid adhesive joints was investigated for two material systems: structural steel bonded to polyamide (PA66) and structural steel bonded to technical ceramic (Al₂O₃). Single-lap joints were manufactured using a two-component epoxy adhesive with two nominal bond-line thicknesses (0.1 mm and 1.0 mm). Prior to bonding, selected surfaces were modified by ultrashort-pulse laser microtexturing, producing well-defined circular features with characteristic depths on the order of tens of micrometers. The resulting microstructures were characterized using optical and scanning electron microscopy, and their geometric parameters were quantified through profilometric measurements. Mechanical performance was evaluated under shear and bending loading conditions. The results demonstrate a substantial increase in joint strength for laser-microtextured surfaces compared with non-textured references for both material combinations. The effect of surface microtexturing was more pronounced than the influence of adhesive layer thickness within the investigated range. These findings confirm that laser-induced surface microtexturing is a versatile and application-oriented surface preparation method capable of enhancing the reliability of adhesive bonding in hybrid metal–polymer and metal–ceramic assemblies. Full article

In the context of the “dual-carbon” targets and the development of green building materials, lightweight mortar has attracted considerable attention, owing to its low density and excellent thermal insulation properties. However, lightweight aggregates, such as vitrified microspheres, while effectively reducing mortar density, exhibit high porosity and weak interfacial bonding, which compromise mechanical performance. To address this issue, this study introduces sugarcane bagasse fiber (SBF) as a reinforcing material, with contents of 0%, 0.4%, 0.8%, 1.2%, and 1.6%. The effects of SBF on physical properties (consistency, density, water absorption) and mechanical properties (compressive strength, flexural strength, and tensile bond strength) were systematically evaluated. Furthermore, low-field nuclear magnetic resonance (LF-NMR) and scanning electron microscopy (SEM) were employed to analyze pore structure and interfacial transition zone (ITZ) characteristics at multiple scales. The results indicate that: (1) at low contents (0.4–0.8%), SBF was uniformly dispersed, improving matrix compactness; (2) compared with the control group, the 28-day compressive, flexural, and tensile bond strengths increased by 7.1%, 13.1%, and 25%, respectively; (3) NMR analysis revealed that the incorporation of SBF significantly increased the proportion of capillary pores, reduced total porosity, and enhanced mortar compactness, thereby improving mechanical strength; (4) fractal dimension analysis showed that contents of 0.4% and 0.8% increased structural complexity while reducing pore connectivity, leading to higher compressive strength; (5) SEM observations further demonstrated that the fibers provided bridging and anchoring effects within the ITZ, promoted the deposition of hydration products, and enhanced interfacial compactness. Full article

Conventional phenolic-resin-based carbon fiber paper (CFP) typically suffers from low mechanical strength, poor toughness, insufficient pore interconnectivity, and a reliance on extreme high-temperature graphitization to attain high conductivity. This study employs a novel melamine-hexamethylenediamine (MH) thermosetting resin as the binder to fabricate MH resin-based CFP (MHCFP). Through the synergistic effects of robust interfacial bonding, triazine-ring-induced low-temperature formation of sp² carbon clusters, and nitrogen doping, the MHCFP achieves comprehensive performance superiority over the phenol-formaldehyde (PF)-based CFP (PFCFP) at moderate carbonization temperatures (500–700 °C): MHCFP exhibits superior toughness, tensile strengths of 23–45 MPa (vs. PFCFP’s 8–18 MPa), and in-plane resistivity of 24–39 mΩ·cm (vs. PFCFP’s 54–83 mΩ·cm). Furthermore, MHCFP possesses a highly open macroporous structure (porosity > 78%), ensuring excellent gas permeability and water management capability. This work presents a promising low-temperature strategy for developing high-performance CFP, showing great potential for next-generation proton exchange membrane fuel cell gas diffusion layers. Full article

In this study, rice-husk fiber (RHF) extracted via alkali hydrolysis was used as a reinforcing material (0–10 wt%) in a pectin-sodium alginate (PE/SA) matrix to develop biofilms by the casting method. These biofilms were characterized by using FTIR, XRD, TGA, and DSC. The thickness, moisture content, water solubility, swelling behavior, water-contact angle, water-vapor permeability, optical transparency, and mechanical properties of biofilms were investigated. It was observed that the PE/SA/RHF film loaded with 5% RHF had better visual attributes, and a further increase in reinforcement was not found to be as favorable. The addition of 10 wt% RHF significantly enhanced the thickness from 0.094 to 0.127 mm, water solubility from 49.25 to 56.13%, water-contact angle from 48.4 to 62.6°, and tensile strength from 4.17 to 10.23 MPa. However, decreases in water-vapor permeability from 1.94 × 10⁻⁹ to 1.32 × 10⁻⁹ g·m⁻¹·Pa⁻¹·s⁻¹ and in elongation at break from 19.24 to 2.87% were observed in the biofilms. Structurally, FTIR confirmed intermolecular hydrogen bonding between components. XRD revealed that the films remained predominantly amorphous, without significant crystalline alterations. Furthermore, thermal stability improved with the addition of RHF. Finally, these PE/SA/RHF composite films may be potential eco-friendly biodegradable packaging candidates for food industry applications. Full article

To further improve the seismic behavior of high-strength foam concrete filled cold-formed checkered steel composite wall structures, it is crucial to investigate the bond–slip behavior between the cold-formed checkered steel (CFCS) and foam concrete (FC) within the wall. Hence, six CFCSFC specimens were designed and subjected to monotonic and cyclic loading tests to study the influence of anchorage lengths on failure modes, bond strength-slip displacement curves, and characteristic bond strength. Results indicated that with the anchorage length increases, the ultimate bond strength of the specimens continuously decreases, and the specimens exhibit more severe failure under cyclic loading than monotonic loading. Compared to the specimens with a 400 mm anchorage length, the ultimate bond strength decreased by 4.8–9.6% for those with a 500 mm length, and by 10.7–16.0% for those with a 600 mm length. Strain along the inner flange of the steel section generally decreased with increasing anchorage length, with loading end strain significantly exceeding free-end strain. Finite element simulations revealed that specimen failure primarily manifested as steel section yielding when anchorage lengths ranged from 1400 mm to 1800 mm. Furthermore, a calculation formula for characteristic bond strength as a function of anchorage length was proposed. Full article

The plugging of fractured gas reservoirs with severe lost circulation during oil and gas drilling and production has long been challenged by technical issues such as low plugging strength and short effective duration. This paper reports the preparation of a high-strength supramolecular gel plugging agent via micellar copolymerization based on the synergistic effects of hydrophobic association and hydrogen bonding. Systematic optimization determined the optimal synthesis formula: acrylamide (AM) 12%, 2-acrylamido-2-methylpropanesulfonic acid (AMPS) 2%, stearyl methacrylate (SMA) 0.4%, sodium dodecyl sulfate (SDS) 1.5%, and potassium persulfate 0.3%, with a reaction temperature of 60 °C. Performance evaluations revealed that the gel possesses a controllable gelation time (120 min) and excellent viscoelastic recovery properties. At a compressive strain of 87%, the compressive stress reached 1.43 MPa while maintaining structural integrity. Swelling behavior analysis indicated that the gel follows a non-Fickian diffusion mechanism, with its swelling process governed by the synergistic interplay of water molecule diffusion and polymer network relaxation. Core plugging experiments demonstrated that the gel achieved plugging efficiencies exceeding 95% for cores with permeabilities ranging from 0.18 to 0.90 μm², with a maximum breakthrough pressure gradient of up to 11.48 MPa/m. These results highlight the gel’s efficient and broad-spectrum plugging capability for fractured lost circulation zones. This preliminary study provides experimental foundations for the material design and performance optimization of supramolecular gel-based long-lasting plugging agents for severe lost circulation gas reservoirs, and further field-scale validation is required for engineering application. Full article

This study investigates the early-age bond behavior between steel reinforcement and lightweight alkali-activated concrete (LWA-AAC) using pull-out tests and modeling. Deformed and plain steel bars with different diameters were embedded in two LWA-AAC matrices to examine the effects of curing age, matrix strength, confinement, and bar surface geometry. The bond of plain bars is governed primarily by adhesion and friction and shows weak dependence on matrix strength or confinement. In contrast, the bond strength of deformed bars increases with curing age and matrix strength, while reduced confinement promotes a transition from ductile pull-out to brittle splitting failure. This confinement-sensitive transition highlights the dominant role of matrix tensile capacity in controlling bond stability in LWA-AAC. Compared with lightweight ordinary Portland cement (OPC) concrete, LWA-AAC exhibits more brittle bond behavior, characterized by smaller peak slip, steeper post-peak softening, and lower residual bond stress. Existing OPC-based bond models show limited applicability to LWA-AAC due to differences in failure mechanisms and confinement sensitivity. New empirical models incorporating matrix tensile strength and geometric confinement are proposed to predict bond parameters and bond–slip responses, providing a mechanism-informed basis for the design of reinforced LWA-AAC structures. Full article

Reinforcement corrosion is one of the primary deterioration mechanisms affecting the long-term seismic performance of reinforced concrete (RC) structures. Although the effects of corrosion on individual RC members have been widely investigated, its influence on the cyclic behavior of RC frame systems has received limited attention. This study numerically investigates the seismic response of a single-bay reinforced concrete frame subjected to cyclic lateral loading under various corrosion scenarios. A three-dimensional nonlinear finite element model was developed in ABAQUS, incorporating corrosion-induced effects such as reinforcement cross-sectional loss, degradation of mechanical properties, bond strength deterioration, and concrete softening. The corrosion propagation rate and exposure duration were considered as key parameters, and different corrosion scenarios were comparatively evaluated. The numerical model was validated using an experimentally tested non-corroded reinforced concrete frame subjected to cyclic loading. The results demonstrate that reinforcement corrosion leads to significant degradation in the seismic performance of RC frames. Depending on corrosion severity, reductions of up to approximately 25% in lateral load capacity and up to 27% in both initial stiffness and energy dissipation capacity were observed. The findings further indicate that stiffness- and energy-based performance indicators are more sensitive to corrosion damage than strength-based indicators. The study highlights the importance of explicitly accounting for corrosion effects in the seismic performance assessment of reinforced concrete frame systems and provides a practical numerical framework for evaluating corrosion-induced performance degradation. Full article

Background: Cavity disinfection is commonly performed in pediatric restorative dentistry to reduce residual bacterial contamination. Although boric acid has been proposed as a potential antimicrobial agent, its effect on marginal integrity and adhesive performance in primary teeth remains unclear. This study evaluated the effects of 3% and 5% boric acid, compared with 2% chlorhexidine (CHX), on microleakage and microshear bond strength of composite restorations in primary teeth bonded with a two-step self-etch adhesive system. Methods: Seventy-two extracted primary second molars were allocated to four groups (n = 18) for microleakage assessment: control, 2% CHX, 3% boric acid, and 5% boric acid. Standardized Class V cavities were prepared, disinfectants were applied for 60 s, and restorations were completed using Clearfil SE Bond and resin composite. Microleakage at occlusal and gingival margins was evaluated using dye penetration. For microshear bond strength testing, 60 primary molars (n = 15 per group) were treated similarly, and shear force was applied to bonded composite microcylinders. Data were analyzed at the p < 0.05 significance level. Results: Both boric acid groups showed significantly higher occlusal and gingival microleakage than the control and CHX groups (p < 0.05). Gingival microleakage was greater than occlusal microleakage in the boric acid groups (p < 0.05). Microshear bond strength was significantly reduced in the boric acid groups compared with the control (p < 0.05), whereas CHX had no significant effect. Failure modes did not differ significantly. Conclusions: While 2% CHX did not adversely affect adhesive performance, 3% and 5% boric acid increased microleakage and reduced bond strength. Caution is advised when using boric acid with self-etch adhesive systems in primary teeth. Full article

The development of lightweight, high-strength structural systems is a persistent pursuit in modern civil engineering. This paper presents an experimental study on a novel hybrid beam concept in which a sawn timber core is fully bonded with an externally applied Carbon Fiber-Reinforced Polymer (CFRP) laminate, fabricated through a controlled hand lay-up process. The design seeks to exploit the complementary characteristics of the two materials: timber provides compressive resistance and serves as a permanent formwork, while the CFRP carries tensile stresses with high efficiency. Fourteen hybrid beams, with variations in the number of longitudinal CFRP layers (one, two or, three), the presence or absence of longitudinal CFRP layers bonded along the top and bottom surfaces, and the presence or absence of circumferential wrapping in the pure bending region, were tested under four-point bending alongside two solid timber control beams. The results demonstrate that circumferential wrapping is a critical design detail. Wrapped beams consistently failed by tensile rupture of the CFRP—the intended failure mode—and exhibited ultimate moments 15–20% higher than their unwrapped counterparts. Beams with two longitudinal CFRP layers offered the most favorable balance between strength enhancement and material efficiency; adding a third layer shifted the failure mode to crushing of the timber core, indicating a core-limited condition. All hybrid beams showed pronounced linear-elastic behavior up to sudden brittle failure, with performance variability attributable to the inherent inhomogeneity of wood and the sensitivity of the hand lay-up process. The study provides quantitative data and mechanistic insights that support the design and application of bonded CFRP–timber hybrid beams as efficient structural members. Full article

Aiming at the critical problem that recycled concrete aggregate (RCA) has more cracks and severe defects on its surface than natural aggregate, resulting in an excessively weak interfacial transition zone (ITZ) between RCA and cement paste, this paper proposes a triple synergistic modification method combining calcium ion accelerating solution treatment, dopamine polymerization treatment and nanofiber reinforcement to improve the properties of recycled aggregate. Through in-depth research on the mechanical properties of basalt fiber-reinforced fully recycled concrete after triple modification, it is found that the triple modification technology can significantly optimize the structure of the recycled aggregate-cement paste ITZ. The 28-day compressive strength of the fully recycled concrete is increased by 56% (reaching 27.7 MPa), and the splitting tensile strength is improved by 129% (reaching 5.32 MPa). Microscopic analysis shows that the modified system realizes gradient strengthening of the ITZ structure through the synergistic mechanism of “pore filling, chemical bonding and fiber bridging”. This research provides a new idea for the high-performance modification of fully recycled concrete, and has important significance for promoting the sustainable development of the construction industry. Full article

Polymer adhesive materials have been utilized across a wide range of applications, including adhesion to wood, metals, and biomaterial substrates. To meet increasing performance demands, the development of high-performance adhesive materials continues to be actively pursued by introducing advanced functions and capabilities into polymer networks. By incorporating dynamic covalent bonds into the polymer network, these materials gain self-healing and reprocessing abilities. While these materials exhibit high mechanical robustness and stability under service conditions, the bonding/rebonding reactions of dynamic covalent bonds allow the polymers to detach from target surfaces when needed. Additionally, noncovalent interactions within the network and between the polymer and the target surface significantly contribute to overall adhesive strength. Although dynamic covalent bonds and noncovalent interactions operate through different mechanisms, both contribute significantly to adhesive performance. This review manuscript presents studies on polymer networks containing dynamic covalent bonds and non-covalent interactions. Based on these studies, the respective contributions of each type of bond to the superior adhesive strength of the materials are discussed, and potential target substrates for adhesion, including wood, metal, and biomaterials, are proposed. Full article

This study investigates the interplay between Portland cement strength class (32.5, 42.5, and 52.5) and fiber/cement ratio (ranging from 1/2 to 1/5 by weight) to optimize the physical-mechanical and thermal performance of cement-bonded fiberboards. The experimental data revealed a distinct trade-off: while reducing the fiber content towards a 1/5 ratio significantly improved flexural strength and dimensional stability through matrix densification, it inevitably compromised thermal insulation. Among the binders evaluated, the 42.5 strength class emerged as the most effective option, outperforming the 32.5 class and, notably, offering a more balanced profile than the 52.5 class. The highest stiffness was recorded with the 42.5 cement at a 1/5 ratio (modulus of elasticity (MOE): 5902 ± 532 N/mm²; modulus of rupture (MOR): 12.49 ± 0.6 N/mm²), yielding performance metrics comparable to the 1/4 ratio (MOR: 12.78 N/mm²). Furthermore, this formulation demonstrated superior moisture resistance, achieving water absorption (WA) values as low as 18.9%. Thermal conductivity (TC) measurements at 20 °C confirmed that while fiber-rich mixtures (1/2 ratio) favored insulation, the 42.5 cement at a 1/4 ratio maintained a competitive conductivity value (λ = 0.1625 W/mK), lower than that of the 52.5 grade, thereby striking a critical balance between structural integrity and thermal efficiency. Statistical analyses (Two-way ANOVA, p < 0.05) corroborated the significant influence of both cement type and mix ratio. Microstructural insights from Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) suggest that the superior performance of the 42.5 cement is associated with optimized hydration kinetics and a well-graded particle size distribution (D50 = 14.80 µm), which together facilitated effective fiber encapsulation. Full article