Search Results (1,428)

Refractory geopolymers derived from aluminosilicate sources and alkaline activation are a promising alternative to traditional fired bricks, particularly when low-cost, waste-derived raw materials are used. This study improves the workability of a refractory brick formulated with clays (Kaolin and Tepozan–Bauwer), seashell waste, sodium silicate, potassium hydroxide, and water by incorporating sodium lignosulfonate (LS) and polycarboxylate (PC) plasticizers. Clays from Comonfort, Guanajuato, Mexico, and seashells were ground and sieved to pass a 100 Tyler mesh. A base mixture was prepared and evaluated using the Mini Slump Test, varying plasticizer content from 0 to 2% relative to the solid fraction. Based on workability, 0.5% LS and 1% PC (by solids) increased the slump, and a blended plasticizer formulation (1.5% by solids, 80%PC+20%LS) produced the highest workability. These additives act through different mechanisms, with LS primarily promoting electrostatic repulsion and PC steric repulsion. Bricks with and without plasticizers exhibited thermal resistance up to 1200 °C. After four calcination cycles, compressive strength values were 354.74 kg_f/cm² for the brick without plasticizer, 597.25 kg_f/cm² for 1% PC, 433.63 kg_f/cm² for 0.5% LS, and 519.05 kg_f/cm² for 1.5% of the 80%PC+20%LS blend. Strength was consistent with changes in porosity and apparent density, and 1% PC provided a favorable combination of high workability and high compressive strength after cycling. Because the cost of clays and seashells is negligible, formulation selection was based on plasticizer cost per brick. Although 1% PC and the 1.5% of 80%PC+20%LS blend showed statistically comparable strength after cycling, 1% PC was selected as the preferred option due to its lower additive cost ($0.0449 per brick) compared with the blend ($0.0633 per brick). Stereoscopic microscopy indicated pore closure after calcination with no visible cracking, and SEM–EDS identified O, Si, and Al as the significant elements, with traces of S and K. Overall, the study provides an integrated assessment of workability, multi-cycle calcination, microstructure, and performance for refractory bricks produced from readily available clays and seashell waste. Full article

This study investigates the effects of agro-waste-based capsules made from grape seeds and cherry pits on the physical, mechanical, thermal and self-healing properties of concrete. Capsule-containing mixtures were compared with a reference concrete after 28 days of water curing using both standardized and non-standardized testing methods. Capsule incorporation reduced workability by up to 91% and altered air content depending on capsule type, increasing it by 47% for grape seed capsules and decreasing it by 65% for cherry pit capsules. Fresh concrete density was reduced by 5.5% and 6.8% for grape seed and cherry pit capsules, respectively, while hardened concrete density decreased by 11% and 9%, implying lighter structures with improved seismic resistance. Compressive strength decreased by 49% for grape seed capsules and 27% for cherry pit capsules. Thermal conductivity was reduced by 32% and 22%, respectively, indicating improved energy efficiency. Concrete with grape seed capsules showed freeze–thaw performance comparable to the reference concrete after 112 cycles, whereas concrete with cherry pit capsules exhibited superior dynamic modulus behavior, suggesting continuous crack healing, despite significant mass loss due to poor capsule–matrix bonding. SEM analysis showed no significant crack reduction, while EDS revealed calcium-rich areas in grape seed capsule concrete, indicating possible crack healing. Overall, agro-waste capsule concrete shows potential for improving seismic resistance and energy efficiency, although further research is required to clarify the self-healing effect. Full article

To improve the fatigue life of high-strength bolts, this study builds upon conventional thread rolling by introducing a localized rolling reinforcement process specifically at the thread root. Experimental specimens were prepared from 42CrMo high-strength bolts using a combined manufacturing technique that integrates thread forming and root rolling. A comparative analysis was conducted to evaluate the fatigue performance of bolts with and without the root rolling reinforcement. The experimental results demonstrated that the thread root rolling treatment further refines the surface grains beyond the effects of standard thread rolling. At a rolling force of 2.5 kN, the surface microhardness increased from the original 500 HV0.2 to 540 HV0.2. The process also improved surface finish, reduced grain size, and increased dislocation density. The optimal enhancement was achieved at a rolling force of 3.5 kN, resulting in an approximately 11-fold improvement in fatigue life. Fractographic analysis via Scanning Electron Microscopy (SEM) indicated a reduced number of crack initiation sites. This study confirms the effectiveness of the proposed rolling reinforcement process, offering a viable technical pathway for optimizing the anti-fatigue manufacturing of high-strength bolts. Full article

Early-age cracking limits the structural use of steel fiber-reinforced lightweight aggregate concrete (SFLWAC), and robust experimental evaluation methods are still needed. This study examines the influence of steel fiber volume fractions (i.e., 0%, 0.5%, 1.0%, and 2.0%) on the cracking performance of SFLWAC through mechanical testing, autogenous shrinkage measurements, and two types of partially restrained ring tests, with and without a clapboard. The performance of three crack resistance indices is compared: the strain-based ASTM C1581 index, a stress-based area index, and a newly proposed energy-based index defined as the strain energy accumulation degree (SEAD), i.e., the ratio between the accumulated and critical strain energy density. The 28-day splitting tensile strength was improved by 77.9% and autogenous shrinkage was diminished by 30.7% as steel fiber volume content increased from 0 to 2.0%, thereby improving the resistance to shrinkage-induced cracking. In the partially restrained ring tests, SEAD decreased with increasing fiber content, and crack initiation occurred when SEAD reached an approximately constant threshold, whereas ASTM C1581 and the area index could not consistently rank mixtures when some rings cracked and others remained intact. These results demonstrate that SEAD provides a physically meaningful and unified measure of cracking risk for SFLWAC under partially restrained shrinkage and has the potential to be extended to other fiber-reinforced concretes and shrinkage-related cracking problems. Full article

This study examines how the Alkali–Silica Reaction (ASR) modifies chloride transport and chloride-induced corrosion (CIC) in reinforced concrete beams. Non-reactive and reactive concrete beams were cast with blue metal and dacite aggregates and subjected to a two-stage exposure: (i) alkali-rich immersion at 38 °C to induce ASR, and (ii) impressed-current CIC and NT BUILD 492 chloride migration testing. Microstructural changes were characterized using SEM–EDS and TGA. The reactive specimens developed extensive surface cracking, but after one year of ASR exposure, exhibited 47–53% lower non-steady-state migration coefficients (Dnssm: 7.03–8.02 × 10⁻¹² m²/s) than the non-reactive beam (15.09 × 10⁻¹² m²/s). After two years, Dnssm was reduced by approximately 37–56% (4.78–6.93 vs. 10.92 × 10⁻¹² m²/s). Crack mapping confirmed higher crack density and width in reactive beams, while SEM–EDS and TGA evidenced Ca depletion and the formation of C–(N,K)–S–H gels, which fill cracks and refine the pore structure. Electrical resistance monitoring showed earlier corrosion initiation in ASR-damaged beams but less pronounced resistance loss during the propagation phase. Overall, the results indicate that ASR can initially accelerate corrosion initiation through microcracking and reduced resistivity, but long-term gel deposition can partially seal transport paths and lower chloride migration under the specific conditions of this study. Full article

Plastic streams dominated by polyethylene (PE) including PE HD/MD (High Density/Medium Density) and PE LD/LLD (Low Density/Linear Low Density), polypropylene (PP), and polyvinyl chloride (PVC) across Europe demand a design framework that links synthesis with end of life reactivity, supporting circular economic goals and European Union waste management targets. This work integrates polymerization derived chain architecture and depolymerization mechanisms to guide selective valorization of commercial plastic wastes in the European context. Catalytic topologies such as Bronsted or Lewis acidity, framework aluminum siting, micro and mesoporosity, initiators, and strategies for process termination are evaluated under relevant variables including temperature, heating rate, vapor residence time, and pressure as encountered in industrial practice throughout Europe. The analysis demonstrates that polymer chain architecture constrains reaction pathways and attainable product profiles, while additives, catalyst residues, and contaminants in real waste streams can shift radical populations and observed selectivity under otherwise similar operating windows. For example, strong Bronsted acidity and shape selective micropores favor the formation of C₂ to C₄ olefins and Benzene, Toluene, and Xylene (BTX) aromatics, while weaker acidity and hierarchical porosity help preserve chain length, resulting in paraffinic oils and waxes. Increasing mesopore content shortens contact times and limits undesired secondary cracking. The use of suitable initiators lowers the energy threshold and broadens processing options, whereas diffusion management and surface passivation help reduce catalyst deactivation. In the case of PVC, continuous hydrogen chloride removal and the use of basic or redox co catalysts or ionic liquids reduce the dehydrochlorination temperature and improve fraction purity. Staged dechlorination followed by subsequent residue cracking is essential to obtain high quality output and prevent the release of harmful by products within European Union approved processes. Framing process design as a sequence that connects chain architecture, degradation chemistry, and operating windows supports mechanistically informed selection of catalysts, severity, and residence time, while recognizing that reported selectivity varies strongly with reactor configuration and feed heterogeneity and that focused comparative studies are required to validate quantitative structure to selectivity links. In European post consumer sorting chains, PS and PC are frequently handled as separate fractions or appear in residues with distinct processing routes, therefore they are not included in the polymer set analyzed here. Polystyrene and polycarbonate are outside the scope of this review because they are commonly handled as separate fractions and are typically optimized toward different product slates than the gas, oil, and wax focused pathways emphasized here. Full article

This study systematically investigates the tensile property degradation of Carbon Fabric-Reinforced Cementitious Matrix (CFRCM) composites under anodic polarization, explicitly comparing the effects of three standard-required electrolyte environments (NACE/ISO). CFRCM specimens were polarized for 20 days at current densities of 200 and 400 mA/m² in NaCl, NaOH, and simulated concrete pore solutions. Results reveal that anodic polarization significantly reduces peak tensile strength and post-cracking stiffness, with degradation severity dependent on the electrolyte type (NaCl > NaOH > Pore Solution). Crucially, comparative analysis demonstrates that the strength degradation of carbon fiber bundles embedded in the mortar matrix is more pronounced than that of bare bundles. This work provides essential durability data for CFRCM composites for integrated ICCP-Structural Strengthening systems. Full article

Hot stamping dies fabricated from Mo–W hot-work steels are exposed to severe thermo-mechanical fatigue (TMF), high-temperature oxidation, and complex tribological loading, which collectively accelerate die degradation and reduce production stability. Although individual failure modes have been reported, an integrated understanding linking microstructural evolution, interfacial reactions, and wear mechanisms remains limited. A failed Mo–W hot-work steel die removed from an industrial B-pillar hot stamping line was examined using Rockwell hardness mapping, optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) with Williamson–Hall (W–H) microstrain analysis. Surface (0–2 mm) and subsurface (~8 mm) regions of 10 × 10 × 10 mm samples were compared. Pits, cracks, reaction layers, and debris were quantified from calibrated SEM images. A 17% hardness reduction from surface (46.2 HRC) to subsurface (37.6 HRC) revealed pronounced TMF-induced softening. W–H analysis indicated microstrain of ~0.0021 and crystallite sizes of 50–80 nm in the surface region, reflecting high dislocation density. SEM/EDS showed pit diameters of 150–600 μm, reaction-layer thicknesses of 15–40 μm, and crack lengths of 40–150 μm. Fe–O oxides, Fe–Al intermetallics, and FeSiAl4 reaction phases were identified as major constituents of brittle surface layers and debris. Wear morphology confirmed a mixed mode of adhesive galling and oxide-assisted abrasive plowing. Full article

This study systematically investigates the composition–structure–property relationships in electrospark-deposited Cr-Ta coatings (10, 25, and 40 at.%) on CrNi₃MoVA steel for wear resistance applications. Microstructural characterization reveals that the Cr-10Ta coating exhibits a dense microstructure with excellent metallurgical bonding to the substrate, consisting of a reinforcing Cr₂Ta Laves phase and Fe-Cr solid solution. In contrast, higher Ta content (25–40 at.%) results in the formation of brittle Ta oxides and the development of cracks. Mechanical testing indicates that the Cr-10Ta coating exhibits superior hardness (6.35 GPa) and elastic–plastic deformation resistance (H/E = 0.041, H³/E² = 0.0109), outperforming both higher-Ta coatings and the substrate material. Corresponding tribological assessments reveal that the Cr-10Ta coating achieves the lowest friction coefficient (~0.4) along with a minimal wear rate, which can be attributed to its synergistic combination of fine-grained structure, high dislocation density, and Laves phase reinforcement. The findings underscore that precise control over Ta content serves as an effective strategy for optimizing the wear resistance of Cr-Ta coatings through microstructural engineering. Full article

Traditional exterior walls are heavy, offer insufficient insulation, and have poor durability, making it challenging to meet the combined requirements of energy efficiency and structural enclosure performance. To address the issues of excessive weight and inadequate insulation in conventional concrete exterior wall panels, alternative materials and designs are being adopted. A novel double-layer composite wall panel structure is proposed, arranging normal concrete (NC) on the exterior side to ensure the panel’s durability and ceramsite foam concrete (CFC) on the interior side to enhance thermal insulation and reduce thermal bridging effects. To address the scenario where the wall panel is subjected to out-of-plane loads during service, causing stress in the CFC layer, bending performance tests were conducted on CFC-NC double-layer composite panels under load applied on the CFC side. Research shows that CFC-NC double-layer composite wall panels exhibit bending performance under four-point bending conditions that is basically consistent with that of monolithic wall panels. As the thickness of the CFC layer increases, cracks may appear near the interface in the CFC layer that do not extend from NC cracking, and may even occur earlier than NC cracking. As the density grade of CFC decreases, the compressive deformation of CFC becomes more pronounced; however, no crushing of the CFC occurs at the ultimate bearing capacity stage. Under four-point bending conditions, the strain at the mid-span section of the composite wall panel along the thickness direction is basically linearly distributed. Under the same conditions of wall panel thickness, reinforcement ratio, and shear span ratio, the flexural bearing capacity of CFC-NC double-layer composite wall panels with CFC density grades A8, A6, and A4 is approximately 12.5%, 25.03%, and 18.29% lower, respectively, compared to C30 cast-in-place wall panels. The flexural bearing capacity of the composite panels increases correspondingly with the increase in CFC layer thickness and reinforcement ratio. Specimens with smaller shear span ratios exhibit more pronounced shear effects. Based on the stress–strain relationship of CFC, a modified calculation method for the flexural capacity of ordinary concrete sections is presented. Referring to the ACI 318-14 code, a calculation method for the bending deformation of composite wall panels is provided. The research results can offer a theoretical basis for the design and application of CFC-NC double-layer composite wall panels. Full article

This study quantitatively investigates the corrosion behavior of aluminum (Al1070) under salt water acetic acid test (SWAAT) conditions, focusing on the effects of chloride ions (Cl⁻) and acetic acid (CH₃COOH) concentration on the pitting corrosion. Potentiodynamic polarization tests showed that increasing Cl⁻ concentration caused a negative shift in corrosion potential (E_corr) and an increase in corrosion current density (i_corr), indicating accelerated passive film breakdown and enhanced pitting susceptibility. Immersion tests and SEM analysis revealed intensified surface discoloration, oxide formation, and crack propagation at higher Cl⁻ levels, confirming localized dissolution. The effect of acetic acid was evaluated for concentrations ranging from 0 to 2000 µL L⁻¹. Higher acetic acid levels lowered solution pH and slightly increased E_corr and elevated i_corr while reducing ΔE(E_pit − E_corr), indicating increased localized corrosion susceptibility. SEM and 3D XCT analyses showed increased pit density, corrosion loss, and pitting showed temporary pit coalescence at intermediate concentrations. Mechanistically, the acidic SWAAT environment (pH 2.8–3.0) positions aluminum in the active corrosion region. Cl⁻ destabilizes the passive oxide layer, initiating pitting, while acetic acid promotes metal dissolution via hydrogen evolution reactions. Their combined action exerts a specific effect, accelerating localized corrosion through chemical oxide layer degradation. These results provide quantitative insights into aluminum corrosion under SWAAT conditions. They could inform the design of corrosion resistant materials and reliability assessments in industrial applications. Full article

This work contributes to reinforcing cork-based mortar, with the potential of developing a new eco-friendly lightweight mortar for specific structural applications. Thirteen lightweight mortars were produced by adding cork aggregates (CAs) at fractions of 0.30%, 0.60%, and 0.90% of mortar weight. For each level of CA content, three volume fractions of polyethylene fibers (PFs) were added: 0.25%, 0.50%, and 0.75%. The results indicate that lightening mortar with CA considerably reduces its workability, density, mechanical strengths, and thermal conductivity, as well as increasing its porosity. However, adding PFs to the matrix significantly improves the mortar’s flexural strength by up to 26% and reduces its cracking and brittleness. The 28-day compressive strengths of all mortars remain higher than 15 MPa and can be used in the production of structural elements, according to the RILEM recommendations. The thermal conductivity and dry density decreased, respectively, from 1.73 W/m·K and 2050 kg/m³ for the control mixture to 0.73 W/m·K and 1583 kg/m³ for mortar with 0.90% CA and 0.75% PF. The combination of up to 0.90% CA with 0.75% PF demonstrates satisfactory mechanical and thermal properties and is strongly recommended for use in construction across numerous types of mortar, such as screed mortar for repair and flooring. Full article

Cellulose nanofibril (CNF), as a renewable biomass material, has the characteristics of low density, high strength, and high hydrophilicity. It can also overcome shortcomings of traditional inorganic nano materials, such as difficult dispersion, high cost, and high health risks. In this work, CNF was modified with a cationic surfactant to further enhance the compatibility with hydrating cement. The effects on cement paste were assessed via compressive and flexural strength, heat of hydration, and restrained ring cracking. The reinforcing mechanisms were analyzed by microhardness test, XRD, and BSE-SEM/EDS. Results showed that cation-modified CNF improved mechanical performance, with an optimal dosage of 0.15 wt.% (by binder). Restrained ring test showed that cation-modified CNF–cement composite delayed crack initiation. An isothermal calorimetry test revealed that cation-modified CNF can increase hydration rate in early age. Microstructural analysis confirmed promotion of denser hydration products. A comprehensive consideration of experimental results indicates internal curing and “short-circuit diffusion” are likely the enhancing mechanism. Full article

To address the issue of inefficient interfacial diffusion between virgin asphalt and the aged asphalt in Reclaimed Asphalt Pavement (RAP), this study investigates how a rejuvenator improves the interfacial blending behavior and restores the functional properties of aged asphalt. Molecular dynamics (MD) simulations were employed to construct aged asphalt–rejuvenator models with varying rejuvenator contents and to establish a bilayer dynamic model of the virgin-aged asphalt–rejuvenator diffusion system. The kinetic characteristics of the diffusion process were analyzed based on system density and relative concentration profiles, while the mean square displacement (MSD) and diffusion coefficients were calculated to elucidate the diffusion mechanism. The accuracy of the MD simulation results was validated using Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC), and the regulatory mechanism of the rejuvenator on the interfacial diffusion between virgin and aged asphalt was revealed at the microscopic scale. The results demonstrated that the addition of the rejuvenator effectively promotes the blending and diffusion at the virgin-aged asphalt interface. Specifically, a 6% rejuvenator significantly improved the diffusion efficiency at elevated temperatures, optimized system density toward virgin asphalt properties, and achieved the most uniform molecular distribution, thereby facilitating balanced intermolecular interactions. Meanwhile, the regenerant effectively restored the aromatic fraction content, reduced polar functional groups such as sulfoxide, and significantly lowered the glass transition temperature (Tg), thereby enhancing the low-temperature crack resistance and overall mechanical performance of RAP. Full article

This study investigates the evolution characteristics of fissure networks in cohesive soils under wetting–drying cycle conditions with varying guar gum content. Four wetting–drying cycles were conducted under outdoor natural conditions, with real-time monitoring of changes in the surface crack network during drying and wetting. Geometric parameters—including surface crack density, width, connectivity coefficient, shape coefficient, and crack depth ratio—were quantitatively analyzed using digital image processing software. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to reveal the mechanisms of microstructural improvement. Results indicate that as wetting–drying cycles increase, the fracture network progressively simplifies, with fracture density and fractal dimension decreasing while fracture width increases. The incorporation of guar gum reduced the crack depth ratio to approximately 0.62 times that of undamaged soil. The average crack width decreased from 2.69 mm to 2.16 mm during the fourth wet-dry cycle, whilst the connectivity coefficient and shape coefficient stabilized. SEM analysis indicated that guar gum promoted “bonded bridging” structures between soil particles, while XRD results confirmed no alteration in the mineral composition of the soil. The study demonstrates that the addition of guar gum enhances soil crack resistance and stability, providing theoretical support for the ecological protection of clayey slopes. Full article