Search Results (1,420)

Crumb rubber (CR), a recycled elastomeric polymer derived from scrap tyres, has been used as a partial replacement for fine aggregates in concrete to manage non-biodegradable waste tyre piling, which fills landfills and harms the environment. Polymer-modified rubber improves the concrete’s flexibility, toughness, and impact resistance, but reduces its strength and modulus of elasticity. Multi-walled carbon nanotubes (MWCNTs) are being used to mitigate these issues. The purpose of this study is to investigate the impact of CR% (1% to 5%) as a partial replacement for sand by volume and MWCNTs (at a percentage of 0.05% to 0.08%) as additives by weight of cement as input parameters for determining the mechanical strength (compressive, tensile, and flexural) and deformation properties (modulus of elasticity and Poisson’s ratio) of MWCNT- and polymer-modified CR concrete using response surface methodology (RSM). The results show that 0.05% MWCNT and 1% CR content led to increases in compressive strength, flexural strength, and tensile strength by 14.12%, 11%, and 13.68%, respectively. In addition, models to predict those properties have been developed using RSM with a 95% reliability level. It has been observed that the notable development in the mechanical characteristics of CR concrete with the accumulation of MWCNTs and the models constructed using RSM were deemed satisfactory, with a variation of 0.05% to 0.065% of MWCNTs along with 2% CR. Full article

Coral aggregate concrete (CAC) is a promising sustainable material for construction on remote islands, but it is often limited by relatively low strength and durability. Fiber reinforcement has therefore been introduced as an effective modification strategy. This review focuses on fiber-reinforced coral aggregate concrete (FRCAC), highlighting the roles of different synthetic and natural fibers in improving its performance. Firstly, the characteristics of coral aggregates and the effects of seawater mixing are summarized. Then, the influence of fiber incorporation on the mechanical behavior of CAC under static loading, including compressive, tensile, and flexural responses, is reviewed. In addition, the performance of FRCAC under dynamic and complex loading conditions, such as impact, cyclic, and triaxial loading, is discussed. Overall, fiber reinforcement significantly enhances the tensile strength, ductility, and energy dissipation capacity of CAC, particularly at high strain rates. The maximum reported improvements in splitting tensile strength and flexural strength can reach up to approximately 58% and 68%, respectively, depending on fiber type and dosage. However, the enhancements in compressive strength and elastic modulus are generally limited, with maximum reported increases of about 23% and 7%, respectively. Under multiaxial stress states, fibers mainly contribute to crack control and damage mitigation rather than substantial strength enhancement. Durability and environmental aspects are also addressed. Fiber addition may reduce chloride ingress in CAC, although long-term durability data remain limited. The use of coral aggregate must be balanced with the need to protect coral reefs. Finally, key knowledge gaps and future research directions are identified to support the sustainable application of FRCAC in marine infrastructure. Full article

Background/Objectives: Bulk-fill (BF) resin-based composites (RBCs) have become increasingly popular due to their efficient placement. However, there is a lack of comprehensive performance comparisons among commercially available BF RBCs. In standardized curing conditions, this study aimed to compare the mechanical performance, water sorption and solubility, surface roughness, and color stability of commercially available BF RBCs with different consistencies (flowable and packable). Methods: Ten BF RBCs, along with a conventional RBC (control), were evaluated. Flexural strength and elastic modulus were measured using a three-point bending test. Water sorption and solubility were assessed after 28-day water storage. Color (ΔE₀₀) and surface roughness (ΔRa) changes were measured after 28-day immersion in water, Pepsi, or coffee. One-way ANOVA and Tukey’s tests analyzed the data. Results: 3M Flow, Shofu Bulk, and Ivoclar Flow revealed lower strength (p < 0.001) compared to 3M Bulk (132.17 ± 12.54 MPa) and the control (124.56 ± 15.60 MPa). Shofu Bulk (24.68 ± 12.55 µg/mm³) and Ivoclar Flow (27.11 ± 6.27 µg/mm³) were the least affected by water sorption. While Shofu Bulk (13.98 ± 11.39 µg/mm³), Ivoclar Flow (20.28 ± 6.64 µg/mm³), and SDR (20.84 ± 9.74 µg/mm³) exhibited the lowest solubility (p < 0.01). After water and Pepsi immersion, FGM Bulk showed a significant color change compared to 3M Bulk and Ivoclar Bulk (p < 0.05). Following coffee immersion, Shofu Bulk (17.38 ± 1.82) revealed significant color changes (p < 0.001). Increased surface roughness was observed in 3M Bulk and Ivoclar Bulk after water immersion, Shofu Bulk after Pepsi immersion, and FGM Bulk after coffee immersion. Conclusions: BF RBCs exhibit notable variability in their intrinsic properties. 3M Bulk and Control showed the highest strength, while Shofu Bulk had significant color changes. Full article

The use of monolithic alumina is limited by its intrinsic brittleness, which is commonly addressed through second-phase reinforcement. Silicon carbide (SiC) is an attractive reinforcement due to its high-temperature stability; however, its oxidation behavior strongly influences composite processing and properties. In this study, alumina/SiC composites containing 1, 5, and 10 wt.% SiC were prepared by conventional powder mixing, calcined at 800 °C for 1 h, and pressureless sintered at 1400 °C in air. Phase evolution, microstructure, densification, and mechanical properties were investigated using XRD, SEM/EDS, density–porosity measurements, and flexural testing. Air sintering led to SiC oxidation and the formation of silica-rich glassy phase and mullite, which significantly affected densification. The composite containing 1 wt.% SiC exhibited the best performance, with a flexural strength of 248.7 MPa, a Weibull modulus of 5.7, an average grain size of 1.86 µm, and a porosity of 11.08%. Higher SiC contents resulted in excessive porosity and severe degradation of mechanical properties. Full article

The mechanical behavior of lime-stabilized layers is essential for mechanistic–empirical pavement design, particularly in tropical regions where soil behavior differs from that of temperate residual soils. This study investigated three tropical soils (Argisol, Luvisol, and Latosol) stabilized with two hydrated lime sources (calcitic and dolomitic) at contents of 3% and 5%, compacted at standard or modified effort. Unconfined compressive strength (UCS) was measured at 7, 28, and 90 days, while flexural tensile strength (FTS) was obtained at 28 days, from which the flexural static modulus (FSM) and strain at break (ε_b) were derived. The results showed a strong soil-dependent response to lime treatment, with Argisol and Latosol behaving as lime-stabilized materials, whereas Luvisol exhibited more moderate improvements typical of soil modification. Compactive effort, lime type, and lime content significantly influenced UCS, FTS, and FSM, with compactive effort being the dominant and operationally achievable factor. Higher compactive effort, calcitic lime, and a 5% lime content consistently resulted in improved mechanical behavior, while curing time strongly influenced compressive strength due to progressive pozzolanic reaction. In contrast, strain at break was not significantly affected by the studied controllable factors and converged toward approximately 200 microstrain for soil–lime mixtures with UCS > 1 MPa, indicating a less brittle behavior relative to cement-stabilized materials and providing a representative input for preliminary design. Finally, significant correlations were established between UCS and FTS and between UCS and FSM, enabling the estimation of flexural parameters directly from compressive strength and supporting design simplifications when flexural testing is unavailable. Full article

Polymer-based composites have emerged as viable alternatives to metals for applications requiring reduced weight, corrosion resistance, and cost-effectiveness; however, their relatively low mechanical strength remains a significant limitation. This study evaluates the flexural performance of unsaturated polyester composites reinforced with coconut shell charcoal (CC) powder at filler contents of 0%, 10%, 20%, and 30% by weight, in accordance with ASTM D790. The incorporation of 20 wt% CC yielded the highest flexural strength of 132.43 MPa, representing a 153% improvement compared to pure polyester (52.10 MPa). Flexural modulus also increased substantially at this composition, indicating enhanced stiffness resulting from improved interfacial bonding and efficient stress transfer. In contrast, increasing the filler content beyond 20 wt% resulted in a reduction of up to 32% in strength, attributed to particle agglomeration and void formation. Overall, the results identify 20 wt% CC as the optimal reinforcement level, significantly improving energy absorption and bending resistance, thereby positioning this composite as a promising candidate for lightweight structural applications. Full article

The pursuit of alternatives to nonrenewable materials has stimulated the development of sustainable materials with improved performance, particularly polymer composites reinforced with plant-based fibers. In this study, eucalyptus fibers were thermally treated and evaluated as eco-friendly reinforcements for polyester composites, aiming to enhance their physical and mechanical properties. The fibers were subjected to heat treatments between 140 and 230 °C in a Macro-ATG oven, followed by analyses of anatomical characteristics and chemical composition. Composites containing 25% fiber reinforcement were produced using an orthophthalic unsaturated polyester matrix catalyzed with methyl ethyl ketone peroxide, with untreated fibers used as references. Thermal treatment induced significant modifications in fiber morphology and composition, including increases in cell wall fraction at 170 and 200 °C and higher cellulose contents at 140 and 170 °C. Mechanical performance was assessed through tensile, flexural (modulus of rupture—MOR), modulus of elasticity (E_B), and impact tests. Composites reinforced with heat-treated fibers exhibited lower apparent density and, notably, those treated at 230 °C showed markedly reduced water absorption and enhanced tensile strength compared with the control. Overall, treatment at 230 °C proved most effective, highlighting the potential of thermally modified eucalyptus fibers as viable reinforcements for high-performance, bio-based polymer composites. Full article

Background/Objectives: Light-curing dental resin composites remain limited by high polymerization shrinkage, inadequate wear resistance, and elevated water sorption. The combined influence of filler shape, size, and loading level on mechanical performance and hydrolytic stability remains insufficiently understood. This study aimed to systematically investigate the effects of filler morphology and particle size distribution on the key properties of dental composites. Methods: Spherical silica (SiO₂) nanoparticles (D50 = 0.50 μm) were synthesized via the Stöber method, while irregular aluminosilicate glass was used in coarse (D50 = 3.71 μm) and fine (D50 = 1.98 μm) fractions. Three composite groups were formulated: Group 1 (72 wt.% filler with 0–30% SiO₂), Group 2 (maximum filler loading 76–80 wt.% with 10–30% SiO₂), and Group 3 (74.5 wt.% filler with varying coarse/fine glass ratios). Flexural strength, flexural modulus, Vickers microhardness, depth of cure, water sorption, and solubility were evaluated according to ISO 4049:2019. Results: Incorporation of spherical SiO₂ nanoparticles significantly reduced composite viscosity, enabling maximum filler loading to increase from 72 to 80 wt.%. All composites exceeded ISO requirements for flexural strength (80.54–118.11 MPa), depth of cure (3.01–5.65 mm), water sorption (14.61–22.87 μg/mm³), and solubility (1.20–5.90 μg/mm³). The highest flexural strength (118.11 ± 10.54 MPa) and modulus (9.26 ± 1.12 GPa) were achieved at 78 wt.% filler loading. Bimodal glass systems (50/50 ratio) demonstrated optimal mechanical properties, while higher fine fractions reduced strength. Conclusions: Spherical SiO₂ nanoparticles effectively reduce viscosity and enable higher filler loading. The optimal balance between filler loading, particle shape, and size distribution should be tailored to clinical requirements, with high-strength formulations suited for posterior restorations and bimodal formulations for universal applications. Full article

Biobased composites from fast growing hemp have drawn significant attention because they are inexpensive, biodegradable, sustainable, promote the circular economy, and have good mechanical properties. This proof-of concept study focused on utilizing low value hemp hurd (H), a byproduct of hemp fiber production, as a reinforcement for use in biocomposite materials. The H was characterized by particle size, surface area and chemical composition. Mixtures of 30–50% H and 70–50% phenol-resorcinol-formaldehyde (PRF) resin were blended and subsequently extruded on a single screw extruder. The uncured (wet) blends were evaluated for their rheological properties and showed pseudoplastic behavior. The extruded biocomposites were cured and their water absorption, flexural strength/modulus, and thermal properties were determined. The water absorption properties increased with H content 17% after 12 days for 30 H to 44% for 50 H. The biocomposites containing 40% H had a flexural strength of 41 MPa, while lower values were obtained at 50% and 30% H. These results show that underutilized H can be valorized in extrudable biocomposites. Full article

In order to clarify the road performance and load response behavior of polyurethane mixtures, a low-temperature bending test, dynamic modulus test, rutting test, Hamburg rutting test, and four-point bending fatigue test were conducted on multi-crushed stone polyurethane concrete (SPC-16) and polyurethane concrete (PC-20) as the test objects, and the results were compared with the road performance of an asphalt mastic crushed stone mixture (SMA-13). The differences in the load response between two typical polyurethane mixture pavement structures and a typical asphalt pavement structure were analyzed under four working conditions: a normal-temperature standard load, normal-temperature heavy load, high-temperature standard load, and high-temperature heavy load. The results showed that the low-temperature flexural tensile strength of the polyurethane mixture was 1.3–1.7-times that of SMA-13, the maximum flexural tensile strain was 1.1–1.8-times that of SMA-13, the dynamic stability of the polyurethane mixture was more than 15-times that of SMA-13, and the fatigue life of the polyurethane mixture was 8–12-times that of SMA-13. The surface deflection, base stress, and surface strain of the typical asphalt pavement structures and two typical polyurethane mixture pavement structures at the same temperature all increased with an increase in the load. The load response of the polyurethane mixture pavement structures under high-temperature conditions was relatively stable. Full article

Unlike typical fiber-reinforced polymers, aerospace composites consist of 90% carbon and 10% glass fabrics impregnated with thermosetting resin. Due to the strong bonding between fibers and the thermoset nature of the matrix, recycling these materials is particularly challenging. This study evaluates mechanical recycling of aircraft composite waste via industrial grinding and chemical recycling through a solvolysis process. Recovered fibrous fractions were integrated into an epoxy matrix at 50 wt% loading using hot-pressing and into polyamide 12 at 15 wt% via a twin-screw extrusion process. The mechanical results showed that chemically recycled fibers in epoxy reached a flexural modulus of 9.9 GPa and strength of 112 MPa, significantly outperforming mechanically recycled fillers (6.1 GPa and 98.0 MPa) compared to virgin carbon fibers (11.3 GPa and 132 MPa). In PA12, the addition of chemically recycled fibers yielded a 2.14 GPa modulus and a 67.7 MPa strength. Furthermore, life cycle assessment confirmed that both recycling routes drastically reduce global warming potential and aquatic ecotoxicity compared to landfilling. These findings indicate that while mechanical recycling is simpler, chemical solvolysis provides a superior pathway for the high-value circular reuse of complex aerospace waste in new thermoplastic and thermoset applications. Full article

Powder Injection Molding (PIM) is a versatile manufacturing technology widely used for fabricating components with complex geometries from metals and ceramics, yet its application to high-performance thermoplastics remains underutilized. This study explores the feasibility of manufacturing products from Polyphenylene Sulfide (PPS)—a promising linear aromatic polymer synthesized in powder form—using PIM technology and investigates the development of PE-based feedstocks with PPS and solid fillers. Regarding the matrix formulation, it was found that using pure paraffin as a binder limited the maximum PPS content to 20%. Consequently, a modified binder system consisting of Low-Density Polyethylene (LDPE) and paraffin in a 70:30 wt.% ratio was utilized, which successfully increased the PPS loading in the feedstock to 50% and enabled stable molding. Following matrix optimization, the study examined composites incorporating various fillers, including chalk, talc, and carbon fibers. Systematic rheological analysis confirmed that these composite suspensions possess characteristics necessary for molding products with complex geometries. Key results indicate that optimal sintering conditions were established to achieve the required mechanical properties. Among the tested fillers, carbon fibers were the most effective reinforcement, increasing the elastic modulus by 33% and flexural strength by 20%. Representative examples of samples successfully manufactured via this approach are presented. Full article

Metformin is a promising small molecule for dentin regeneration, but an effective local delivery system for pulp applications has been underexplored. This study encapsulated metformin in poly(lactic-co-glycolic acid) (PLGA) microspheres and incorporated them into calcium phosphate–chitosan cement (CPCC) as a direct pulp-capping material (DPC). Metformin-PLGA microspheres were prepared by double emulsion and mixed with CPCC at a concentration of 0% to 20% by weight. Microsphere morphology, encapsulation efficiency, chemical composition, and physico-mechanical properties were characterized, and compatibility with human dental pulp stem cells (hDPSCs) was evaluated by live/dead assay and SEM. The microspheres were spherical (5.43 ± 0.17 µm) with (51 ± 3.69%) encapsulation efficiency, and FTIR confirmed metformin incorporation. The 15% Met-PLGA-CPCC group showed flexural strength (15.22 ± 1.98 MPa), elastic modulus (4.60 ± 0.73 GPa), and work of fracture (104.96 ± 12.48 J/m²) comparable to or higher than CPCC and MTA, while all Met-PLGA-CPCC groups had shorter setting times ranging from 18 min to 27 min than CPCC (39.15 ± 2.10 min) and MTA (123 ± 4.2 min). Metformin release increased proportionally with Met-PLGA content. hDPSCs exhibited good attachment and high viability on all materials over the evaluated period. In conclusion, Met-PLGA-CPCC provides fast-setting and favorable physico-mechanical properties, sustained metformin delivery, and excellent hDPSC compatibility. These properties support its potential as a bioactive direct pulp-capping material and as a versatile platform for regenerative applications. Full article

This study addresses a key limitation in meso-scale discrete element modeling (DEM) of ultra-high performance concrete (UHPC). Most existing DEM frameworks rely on extensive macroscopic calibration and do not provide a clear, transferable pathway to derive contact law parameters from measurable micro-scale properties, limiting reproducibility and physical interpretability. To bridge this gap, we develop and validate a micro-indentation-informed, poromechanics-consistent calibration framework that links UHPC phase-level micromechanical measurements to a flat-joint DEM contact model for predicting uniaxial compression, direct tension, and flexural response. Elastic moduli and Poisson’s ratios of the constituent phases are obtained from micro-indentation and homogenization relations, while cohesion (c) and friction angle (α) are inferred through a statistical treatment of the indentation modulus and hardness distributions. The tensile strength limit (σₜ) is identified by matching the simulated flexural stress–strain peak and post-peak trends using a parametric set of (c, α, σₜ) combinations. The resulting DEM model reproduces the measured UHPC responses with strong agreement, capturing (i) compressive stress–strain response, (ii) flexural stress–strain response, and (iii) tensile stress–strain response, while also recovering the experimentally observed failure modes and damage localization patterns. These results demonstrate that physically grounded micro-scale measurements can be systematically upscaled to meso-scale DEM parameters, providing a more efficient and interpretable route for simulating UHPC and other porous cementitious composites from indentation-based inputs. Full article

The disposal of phosphogypsum has emerged as a significant challenge for the phosphorus chemical industry in China in recent years. Utilizing phosphogypsum in alkali-activated materials represents an effective approach to valorize this byproduct. The alkali modulus is a critical parameter affecting the performance characteristics of phosphogypsum-based alkali-activated materials. This study aims to investigate the effects of the alkali modulus on the early-age properties (setting time, fluidity, flexural strength, and compressive strength) and hydration mechanisms of slag–phosphogypsum composite alkali-activated materials (HSFP) across various slag–phosphogypsum–fly ash systems, thereby identifying the optimal alkali modulus. The findings demonstrate that an alkali modulus of 1.35 optimally enhances the mechanical performance of HSFP. At this specific modulus, the equilibrium between alkalinity and soluble silica availability facilitates complete hydration, resulting in a dense gel-crystal microstructure characterized by the highest C-(A)-S-H gel content (58.2%) after 28 days. The effect of the alkali modulus on mechanical properties is contingent upon the fly ash-to-phosphogypsum (FA:PG) ratio, whereas its effect on fluidity and setting time is negligible. The effect of alkali modulus on the strength of HSFP is significantly affected by the fly ash-to-phosphogypsum (FA:PG) ratio. At an FA:PG ratio of 4:6, the flexural strength initially decreases and then increases as the alkali modulus values increase, while the compressive strength shows a consistent upward trend. At FA:PG ratios of 1:5 and 1:9, the flexural strength increases linearly with the alkali modulus, whereas the compressive strength first rises and then experiences a slight decline. These results offer both theoretical insights and practical guidance for the optimization of phosphogypsum-based cementitious material formulations, thereby supporting their potential for large-scale application. Full article