Search Results (2,014)

Geopolymer EPS concrete (GEPSC) is a promising low-carbon lightweight material for building envelope and thermal insulation applications. In order to investigate the effects of expanded polystyrene (EPS) content on the lightweight characteristics and mechanical properties of geopolymer EPS concrete (GEPSC), specimens with EPS volume contents of 30%, 35%, 40%, 45%, 50%, and 55% were prepared. Dry density, cube compressive strength, axial compressive strength, splitting tensile strength, flexural strength, and elastic modulus were tested, and empirical relationships among the main mechanical parameters were established. The results show that dry density, cube compressive strength, axial compressive strength, splitting tensile strength, and elastic modulus decrease with increasing EPS content, indicating a clear lightweighting–strength reduction effect. The low strength and low stiffness of EPS particles weaken the continuity and load-bearing skeleton of the geopolymer matrix, while promoting more dispersed crack propagation and a more gradual failure process. The correlation coefficients of the proposed empirical models are all greater than 0.90. Lightweighting efficiency analysis indicates that an EPS content of 40–45% provides a favorable balance among weight reduction, strength retention, and stiffness retention. Compared with EPS concrete, GEPSC exhibited 23.5–49.5% higher strength at the same density grade, indicating its good strength retention capacity and potential engineering applicability. These findings support mix optimization, mechanical parameter selection, and engineering application of low-carbon lightweight envelope materials. Full article

Bisphenol A type epoxy resin has the problem of relatively high brittleness after curing. Although traditional polysiloxane toughening methods can improve toughness, they often come at the expense of strength. In this paper, methylphenyl dimethoxysilane (MPS) was used as a monomer to synthesize end-hydroxyl poly(methylphenyl)siloxane (PMPS), which was then used to modify E51 epoxy resin. The structure and reaction degree were characterized by infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry and viscosity tests. The mechanical test results show that when the PMPS content is 20 wt%, the tensile, flexural, compressive and impact strengths of the modified resin increase by 31.26%, 26.16%, 18.53% and 98.66%, respectively, compared with the unmodified resin, and the tensile and flexural elastic moduli increase by 38.36% and 32.25%, respectively. The fracture toughness increases by 60.29%, indicating that the strength, stiffness and toughness of the material have all been improved. Dynamic mechanical analysis shows that the glass transition temperature and crosslinking density of the system gradually decrease with increasing PMPS content. Thermogravimetric analysis shows that the introduction of PMPS increases the char yield and decreases the maximum thermal decomposition rate, thereby enhancing the thermal stability of the system. Microscopic morphology analysis by optical microscopy, scanning electron microscopy and atomic force microscopy shows that the system has good compatibility, and the internal different modulus phases are distributed in a network-like manner, forming a uniform co-continuous or bicontinuous phase structure. This structure effectively promotes stress transfer and energy dissipation, alleviates local stress concentration, and thus comprehensively improves the mechanical properties of the resin system. Full article

FDM-printed polylactic acid (PLA) composites containing 5 and 10 wt% obsidian powder sourced from the Kars region of Eastern Anatolia (Turkey) were produced via twin-screw masterbatch extrusion and subsequent single-screw filament dilution. Mechanical (tensile, three-point flexure, notched Charpy impact, Shore D), physical (density), thermal (simultaneous TGA/DSC) and microstructural (macroscopic fractography and SEM at 100×–1000×) characterizations were performed on FDM-printed specimens. Young’s modulus rose monotonically by +9.0% at 5 wt% and +18.2% at 10 wt%, while ultimate tensile strength decreased by 12.4% and 17.3%, respectively. The flexural modulus increased by +15.2% at 5 wt% and plateaued at 10 wt% (+16.7%), whereas the flexural strength decreased by only 3.5% at 10 wt%, indicating that flexure-mode loading is markedly more tolerant of obsidian filler than axial tension. Shore D hardness rose by +2.11 points from 0 to 5 wt% with saturation thereafter. TGA showed a dual thermal effect: T₅ and T₁₀ dropped by 5–6 °C from 5 to 10 wt%, while the main decomposition rate decreased by ~46% and the decomposition interval widened from 9.7 to 23.5 °C, indicating a barrier/heat-shielding effect of dispersed silicate particles. SEM revealed a continuous ductile → transitional → brittle progression with increasing obsidian content; extended interfacial debonding lines at 10 wt% identified weak unmodified filler/matrix coupling as the principal performance-ceiling factor. Density measurements indicated a ~3–6% residual void fraction consistent with the inter-bead voids observed by SEM. To the authors’ knowledge, this is the first systematic study of obsidian as a reinforcing filler in PLA; the 5 wt% composition is identified as a strong candidate for esthetic, flexure-dominant, and low-load structural applications. Full article

The rapidly increasing global demand for high-performance thermal insulation materials necessitates a significant shift towards more sustainable and cost-effective solutions. This study unveils a novel and efficient pathway to synthesize engineered cordierite, a highly coveted magnesium aluminosilicate ceramic, by intelligently harnessing biogenic silica extracted directly from rice husk. Rice husk, an abundant agricultural by-product, represents a readily available and often underutilized resource. The methodology involved a precise precipitation method to successfully yield high-purity silica from rice husk ash. This extracted silica was then meticulously combined with commercial magnesium oxide (MgO) and aluminum oxide (Al₂O₃) through a solid-state reaction to synthesize the desired cordierite. The study systematically investigated the profound impact of various sintering temperatures, ranging from 850 °C to 1100 °C, on both the cordierite yield and its crucial physicochemical properties. Our experiments revealed that a sintering temperature of 1100 °C achieved a remarkable 66.5% cordierite yield. Beyond yield, the material processed at 1100 °C exhibited exceptional mechanical and thermal characteristics: a compressive strength of 65 kN/m², a flexural strength of 44 kN/m², a tensile strength of 17.5 kN/m², and a remarkably low thermal conductivity of just 3.2 W/m·K. These attributes match the mechanical requirements for structural insulation, with a thermal conductivity of 3.2 W/m·K. While higher than some high-porosity commercial cordierites (typically 1.2–2.0 W/m·K), the biogenic version offers a 40% reduction in production energy and utilizes 100% recycled silica, balancing thermal performance with superior sustainability. By utilizing agricultural waste, this method reduces CO₂ emissions associated with mineral extraction and minimizes reliance on non-renewable raw materials, providing a practical pathway for the circular economy. Full article

The mechanical properties and real-time damage evolution of sustainable concrete (SC) containing 100% recycled concrete aggregate (RCA) under the combined action of hybrid steel and polyolefin fibers were studied. Inspired by solving the massive effects on the environment from construction waste, as well as to improve the lower mechanical performance of lower-grade RCA, the effect of combining high-stiffness hooked-end steel fibers and flexible macro-polyolefin fibers within RCA was investigated. Six different mix designs were considered: plain, single-fiber (100% steel and 100% polyolefin) and three hybrid composites with varying fractions of the steel/polyolefin fibers (25/75, 50/50, and 75/25). Compressive, tensile and flexural strengths were determined by mechanical testing. During compressive testing, the damage evolution was monitored using low-cost acoustic emission (AE) as a non-destructive technique. Cumulative hits analysis, amplitude distributions, and the statistical b-value parameter were used for damage characterization. The results show that steel fiber significantly increased compressive strength (an increase of up to 13.8%), and the 50/50 hybrid mix showed a high synergistic effect, yielding the highest tensile (4.86 MPa) and flexural (25.54 MPa) strengths. AE analysis identified different damage fingerprints: Based on amplitude analysis, steel-fiber composites exhibited high-amplitude events (which may be attributable to fiber pull-out); polyolefin-fiber composites generated medium-amplitude events (may have resulted from distributed microcracking); and hybrid mixes displayed a mixed amplitude distribution. The b-value analysis provided insight into progressive damage and revealed that the hybrid fibers induce stable, diffuse damage that prevents the brittle failure of plain recycled aggregate concrete (RAC). The results show that hybrid fiber reinforcement can be a reliable approach to enhance the mechanical performance and crack resistance of RAC. Furthermore, low-cost acoustic emission (AE) serves as an effective non-destructive method for monitoring damage progression within the material. Full article

Ultra-high-performance concrete (UHPC) is known for its exceptional compressive strength and durability; however, its brittle nature requires fiber reinforcement to improve toughness and tensile performance. This study investigates the synergistic effects of triple fiber reinforcement, including desized and sized carbon fibers (0.2–1.0 vol%), steel fibers (1.0 vol%), and polypropylene fibers (0.2 vol%) on the fresh, mechanical, durability, microstructure, and fire resistance properties of UHPC. The experimental program included workability, compressive and flexural strength, load-deflection behavior, electrical resistivity, dynamic modulus of elasticity, SEM analysis, and fire resistance at elevated temperatures (425 and 900 °C). The results showed that desized carbon fibers performed better than sized fibers by improving workability, fiber dispersion, flexural behavior, and fiber–matrix bonding. The optimal triple-fiber composition, DC1.0P0.2S1.0, achieved the highest flexural strength of 24 MPa while maintaining compressive strength above 141 MPa. The triple-fiber system provided effective multi-scale crack control, where PP fibers prevented explosive spalling, carbon fibers bridged meso-crack control, and steel fibers enhanced macro-crack load transfer and ductility. SEM analysis further confirmed better dispersion and stronger interfacial bonding of desized carbon fibers. Overall, the optimized triple-fiber system significantly improved flexural performance, toughness, workability, and fire resistance without notably reducing compressive strength, demonstrating strong potential for advanced structural applications. Full article

Repair mortars containing recycled concrete powder (RCP) and ground granulated blast-furnace slag (GGBFS) are promising low-carbon materials for the rapid repair of concrete structures and pavements. However, their practical use is often limited by slow early hydration, insufficient early strength, and weak bonding with existing concrete substrates. In this study, four early-strength admixtures, namely calcium formate, anhydrous sodium sulfate, calcium acetate, and triethanolamine, were incorporated into a P·I 42.5 cement-based repair mortar containing RCP and a low dosage of GGBFS. Their effects on fluidity, flexural and compressive strength, tensile bond strength, drying shrinkage, and hydration characteristics were investigated. The results showed that the suitable dosages of calcium formate, anhydrous sodium sulfate, calcium acetate, and triethanolamine were 1.5%, 1.0%, 0.8%, and 0.05% by mass of total cementitious materials, respectively. Among the four admixtures, calcium formate provided the best balance among strength enhancement, bond performance, workability retention, and dosage tolerance. Compared with the control group, the 3 d and 28 d flexural strengths of the 1.5% calcium formate group increased by 37.0% and 20.3%, respectively. Anhydrous sodium sulfate gave the highest tensile bond strength, with the 14 d value increasing by 33.15% to 1.052 MPa, but its effective dosage range was relatively narrow. Calcium acetate was more effective in reducing drying shrinkage, with a 28 d shrinkage value of 695.14 × 10⁻⁶. SEM and XRD results suggested that the admixtures mainly accelerated early hydration, while no new major crystalline phases were detected. Excessive dosages caused strength loss, bond deterioration, or increased drying shrinkage. These findings are applicable to the specific RCP–GGBFS repair mortar formulation and dosage ranges investigated here. They provide a practical basis for selecting early-strength admixtures for RCP-containing repair mortars used in concrete structure and pavement repair. Full article

This study presents an experimental characterization and numerical assessment of Cu–Al–Be (CAB) shape memory alloys (SMAs) for potential applications in U-shaped flexural plate (UFP) seismic dampers. Six alloy compositions were evaluated through monotonic tensile tests, ASTM F2516 superelastic protocols, and increasing-amplitude cyclic loading to identify the material exhibiting stable superelastic behavior at room temperature. Among the tested materials, alloy CAB4.76-A showed the most favorable response, with high transformation stress, stable pseudoelastic behavior, and strain recovery exceeding 95% for strains up to 2.5%. A phenomenological finite element model based on the Auricchio constitutive formulation was calibrated using experimental data within the validated strain range (ε ≤ 0.025), showing good agreement in stiffness and stress prediction. The calibrated model was subsequently applied to simulate the response of a UFP device under orthogonal cyclic loading. The results indicate a strong dependence on loading orientation due to coupled bending–torsion effects, with the 90° direction exhibiting significantly higher strength and energy dissipation capacity. Comparison with analytical formulations originally developed for steel UFPs showed that these expressions provide approximate estimates when applied to SMA-based devices. The results suggest that Cu–Al–Be alloys are a promising alternative for UFP applications, while highlighting the importance of loading orientation and the need for future experimental validation at a device scale. Full article

The reprocessing of wood–plastic composites (WPCs) significantly affects their structural integrity and thermal behavior. Despite this, the effect of reprocessing on PVC-based WPCs has not been extensively investigated, and the mechanism is not well understood. This study evaluated the effect of reprocessing on the properties of a PVC-based WPC. Small pieces of extruded WPC boards (2–4 mesh) were first milled to a granulation of 50 mesh, and then the material was reprocessed by compression molding, with part of the samples reinforced with glass- and carbon-fiber fabric. The physical and mechanical properties of the reprocessed material were analyzed, and the chemical and thermal characteristics of the reprocessed WPC were compared with the virgin WPC. The results of the mechanical and physical property tests showed that the reprocessed WPC had satisfactory properties compared with the virgin WPC. Samples reinforced with carbon-fiber fabric showed a statistically significant increase in tensile and flexural strength in comparison with unreinforced reprocessed WPC samples. Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) showed that partial dehydrochlorination, thermal degradation and a decrease in thermal stability occurred. Overall, the results of this study show that although chemical degradation and a decrease in thermal stability were present in the reprocessed WPC, it retained satisfactory mechanical and physical properties that could be improved by reinforcing it with carbon-fiber fabric. Full article

The increasing demand for high-performance and multifunctional polymer materials has driven interest in improving the mechanical properties of polymer components produced through additive manufacturing. This study aims to systematically investigate and comparatively evaluate the effects of low-content nanofiller incorporation on the structural, thermal, and mechanical performance of PLA-based materials produced via fused deposition modeling (FDM), with a focus on identifying filler-dependent behavior under different loading conditions. In this study, polylactic acid (PLA) composites reinforced with 0.5 wt.% graphene (Gr) and 0.5 wt.% silver (Ag) nanoparticles, added separately, were produced using fused deposition modeling (FDM) and comparatively investigated. Each nanofiller was incorporated individually into PLA-based filaments, and standard test specimens were fabricated via 3D printing. Structural, thermal, and mechanical properties were evaluated using tensile, compressive, and three-point bending tests, along with SEM, EDS, XRD, FTIR, DSC, and TGA analyses. The results showed that pure PLA exhibited typical brittle behavior and a single-stage thermal degradation profile. The tensile strength of pure PLA was 41.93 MPa, and the flexural strength was 70.76 MPa. The addition of 0.5 wt.% graphene led to noticeable improvements, particularly in flexural properties, while only a minimal (almost negligible) increase was observed in tensile strength, with tensile strength increasing to 42.24 MPa (+0.74%) and flexural strength increasing to 110.78 MPa (+56.6%). In contrast, 0.5 wt.% Ag exhibited mixed and load-dependent mechanical behavior, with slight improvements in flexural strength but reductions in tensile and compressive properties, where tensile strength decreased to 22.13 MPa (−47.2%) while flexural strength increased to 112.06 MPa (+58.3%). Structural and thermal analyses indicated that both nanofillers did not significantly alter the PLA matrix chemically, while contributing to controlled changes in material properties primarily through physical interactions. The novelty of this work lies in the comparative evaluation of graphene and silver nanoparticle reinforcement at a fixed low loading level within FDM-processed PLA, combined with a comprehensive and correlated analysis of mechanical, structural, and thermal behavior on the same specimen sets, enabling a clearer understanding of filler-dependent performance mechanisms in additively manufactured nanocomposites. Overall, it was concluded that low-rate nanofiller additions, when properly dispersed, may lead to selective improvements in the performance of PLA-based composites depending on filler type and loading mode, and show potential for advanced engineering applications such as lightweight structural components, functional sensors, and additive-manufactured parts requiring tailored mechanical performance and multifunctionality. Full article

The application of continuous carbon fiber (CCF) can reinforce the mechanical properties of 3D-printed parts, but the effect of reinforcement layer distribution on composite performance remains unclear. This study investigates the effect of concentrated and separated distributions of CCF layers with different numbers of reinforcement layers. Tensile and flexural tests are conducted in accordance with ASTM D5083 and ASTM D790, respectively. Under the conditions of a solid-filled matrix (Onyx) and 0° CCF deposition, both concentrated and separated CCF layers improve several mechanical properties. Compared with pure Onyx, one-layer CCF increases the tensile modulus by about six times and more than doubles the tensile strength. Increasing the CCF volume leads to further increases in these properties. With concentrated three-layer CCF, the tensile modulus and tensile strength reach 7.153 ± 0.090 GPa and 109.045 ± 5.124 MPa, respectively. For flexural properties, separated two- and three-layer CCFs significantly improve the tangent modulus of elasticity from 0.467 ± 0.106 GPa for pure Onyx to 2.246 ± 0.333 GPa and 3.394 ± 0.081 GPa, respectively. This study also compares the tensile and flexural strength-to-weight ratio of all specimen groups and analyzes the failure mechanisms based on macroscopic fracture appearance. The results can provide guidance for selecting appropriate CCF layer distribution strategies to reinforce composites in different applications. Full article

Driven by the global demand for sustainable construction resources, Recycled High Ductility Cementitious Composites (R-HDCC) exhibit high ductility and cracking resistance, demonstrating significant potential for enhancing structural durability. However, fire resistance remains a critical constraint on its engineering application. To investigate the performance evolution mechanism of R-HDCC after high-temperature exposure, this study examined the effects of different temperatures (200 °C, 400 °C, 600 °C, and 800 °C) and cooling regimes (self-cooling and water-cooling) on R-HDCC. The results indicate that when the temperature exceeded 200 °C, the compressive strength of R-HDCC decreased significantly. At 800 °C, the residual compressive and flexural strengths dropped to below 20% of their initial values. However, water-cooling treatment mitigated the adverse effects on compressive and flexural strength to some extent. In terms of tensile performance, R-HDCC completely lost its functionality at temperatures of 600 °C and above, and the cooling method had minimal influence on tensile behavior. Compared with natural cooling, water-cooling specimens developed fewer microcracks and less interfacial damage, indicating that water-cooling alleviates high-temperature-induced deterioration of the material’s microstructure to a certain degree. These findings provide important insights for the scientific evaluation of the fire resistance of R-HDCC and offer valuable guidance for its practical application. Full article

The scarcity of natural aggregates and the accumulation of oil sludge in desert regions pose critical challenges for highway construction. Although aeolian sand and oil sludge pyrolysis residue have been studied individually as construction materials, their combined use in foamed lightweight soil remains unexplored. This study addresses this gap by developing a novel foamed lightweight soil termed SOFS, which is created through the synergistic modification of aeolian sand and oil sludge pyrolysis residue. A six-factor, five-level orthogonal array (L25) was employed to systematically investigate the effects of residue content, sand content, foam-to-slurry ratio, foaming agent dilution, water-to-solid ratio, and mixing time. The evaluated properties included physical properties (fluidity and wet density), mechanical properties (compressive, splitting tensile, and flexural strength), and durability (wet–dry and freeze–thaw resistance). Scanning electron microscopy was used to examine the microstructural mechanisms. Variance and range analysis identified the optimal mixture, designated H14, which achieved 28-day compressive, splitting tensile, and flexural strengths of 3.75 MPa, 2.21 MPa, and 0.9 MPa, respectively, thereby meeting desert roadbed requirements. Compared with conventional materials, H14 exhibited superior durability, with strength losses of only 16.3% in compressive strength and 19.1% in splitting tensile strength after 25 cycles. Microstructural analysis revealed a dense C-S-H gel network encapsulating the solid waste particles, with nanoscale Al- and Cl-rich crystalline phases observed at interfacial pores—a phenomenon that has rarely been documented in previous studies. These findings provide a theoretical and technical foundation for solid waste valorization and the development of sustainable desert infrastructure. Full article

Infrastructure expansion in Indonesia has increased demand for paving blocks, raising concerns over cement production costs and environmental impact. This study investigates the comparative effectiveness of pineapple leaf fiber (PALF, Ananas comosus) and sisal fiber (Agave sisalana) as reinforcements in paving blocks, evaluating water absorption and 28-day compressive strength at fiber contents of 0%, 1%, 3%, 5%, and 7% by cement volume. A full-factorial two-way ANOVA with post-hoc Tukey HSD was employed. A dosage of 3% for both fiber types resulted in compressive strengths of 14.5 MPa (PALF, +59% vs. control) and 15.2 MPa (sisal, +67% vs. control), both of which met the requirements of SNI 03-0691-1996 Class B. Sisal fiber demonstrated superior compressive performance, consistent with its higher stiffness and tensile strength as reported in the literature. Water absorption increased monotonically with fiber content for both types, with SNI Class D compliance (≤10%) maintained only at 0% for PALF and 0–1% for sisal, a known consequence of the inherently hydrophilic nature of plant-based natural fibers. A statistically significant interaction term (F = 3.697, p = 0.012) confirmed that the two fibers respond differently to dosage increases, providing nuanced practical guidance beyond what single-factor studies can offer. These findings demonstrate the promising compressive strength of agricultural waste fiber-reinforced paving blocks, warranting further investigation of abrasion resistance, flexural strength, and long-term durability before practical deployment. Such utilization supports circular economy principles in the construction industry. Full article

In this study, spent coffee grounds (SCGs) were incorporated into polylactic acid (PLA) filaments and 3D-printed parts to investigate their effects on thermal, physical, and mechanical properties. Differential scanning calorimetry showed that SCG addition slightly reduced the glass transition temperature of PLA while markedly increasing its crystallinity, whereas thermogravimetric analysis revealed a moderate decrease in degradation onset temperature that remained well above the processing and printing temperatures, ensuring safe fabrication. Tensile testing indicated that SCG incorporation led to noticeable reductions in filament strength and stiffness, whereas the elongation at break was only weakly affected because of counteracting plasticization effects. For the printed parts, SCGs imparted a dark brown coloration, decreased density, and increased moisture uptake due to their porous and hydrophilic nature, while tensile, flexural, and impact strengths were reduced and the tensile modulus and elongation at break remained statistically similar across the 0–20 wt% range. These findings indicate that SCGs can be effectively incorporated to tailor the crystallinity, color, and density of PLA-based 3D-printed composites, albeit with trade-offs in strength and impact performance. Full article