Search Results (6,094)

Construction of cement-based coastal components requires natural aggregates, while oyster farming and processing generate waste shells. This study compared mortar flow, strength, and chloride-migration screening responses across crushed waste oyster shell (CWOS) replacement levels. CWOS replaced 0%, 5%, 10%, or 15% of river sand by mass (Control = 0%), following reference sand sieve-fraction mass proportions with a fixed mixing-water amount and total fine-aggregate mass. Flow values were 280, 260, 230, and 180 mm. CWOS-10 reached 28 d flexural and compressive strengths of 9.20 ± 0.30 and 63.13 ± 0.53 MPa, or 94.8% and 95.0% of Control. Its 28 and 90 d coefficients from modified fixed-voltage rapid chloride-migration screening (30 V, 8 h) were (3.86 ± 0.04) × 10⁻¹² and (3.19 ± 0.04) × 10⁻¹² m²/s, higher than Control. CWOS-10 retained approximately 95% of both 28 d Control strengths at 10% river-sand replacement and was selected as a candidate for future cement-based prototypes. A four-panel modular wave-dissipating block concept incorporated local panel replacement, with a 3D-printed model illustrating connection and assembly features. These findings demonstrate the potential of waste oyster shells for partial sand replacement in mortar, enabling shell-waste reuse while reducing natural-sand consumption. Full article

The use of β-hemihydrate phosphogypsum (β-HPG) in building materials is limited by insufficient strength and water sensitivity. This study evaluated calcium sulfate whiskers (CSW) as a modifier at 0–4 wt% relative to β-HPG mass under a fixed water-to-gypsum ratio of 0.58. Workability, dry flexural and compressive strengths, wet compressive strength, and water resistance were assessed alongside isothermal calorimetry, X-ray diffraction, mercury intrusion porosimetry, and scanning electron microscopy. The 2 wt% mixture showed the highest mean dry flexural and compressive strengths among the tested formulations, reaching 5.95 and 22.0 MPa, respectively, approximately 49% and 23% higher than the control. Wet compressive strength after 24 h immersion increased from 7.4 to approximately 8.5 MPa at this dosage. The corresponding paste spread diameter was 155 mm. Higher dosages further reduced mercury-accessible porosity and water absorption without exceeding these mean strengths. The higher wet strengths were accompanied by lower softening-coefficient estimates. CSW advanced the hydration heat-flow peak, while dihydrate gypsum remained the dominant crystalline phase. This integrated assessment distinguishes pore-volume reduction from mechanical improvement and absolute wet strength from relative strength retention. The findings provide an experimental basis for selecting CSW-modified phosphogypsum formulations according to strength, workability, and moisture-exposure requirements. Full article

Polymer concretes with fiber reinforcement have many desirable properties when compared to cementitious concretes, including rapid development of mechanical properties, excellent bond to concrete and other substrates, high tensile strength, and resistance to abrasion and aggressive chemical environments. However, their use as a structural material has been limited, in part, by temperature-dependent mechanical properties, affecting bond and development of steel reinforcement, deformation of structural elements, and section capacity of structural members. This research investigated the development of mechanical properties for a commercially available polymer concrete with fiber reinforcement to determine the effects of temperature on compressive strength, elastic modulus, modulus of rupture, and pull-out bond strength. The compressive, flexural, and bond strengths of the tested polymer concrete with fiber reinforcement were over 70% of their 7 d values within 4 h after mixing when cured at laboratory temperature, demonstrating the rapid development of mechanical properties that is possible with polymer binders. The average 7 d compressive strength across the experimental program was 62.2 MPa at 25 °C, with the measured elastic modulus and modulus of rupture roughly half and three times that of estimated values using established code relationships and the measured compressive strength, respectively. The pull-out bond strength at 25 °C was found to be similar to non-proprietary ultra-high performance and polymethyl methacrylate concretes, and the variation in mechanical properties with temperature was roughly linear and independent of the mechanical property tested when normalized by the value at laboratory temperature. This limited test series supports the structural use of polymer concrete with fiber reinforcement, when in-service temperature is expressly considered in the design process, although further testing is needed to develop rational design procedures. Full article

This study investigates the effects of resin content, fiber architecture, and manufacturing process on the mechanical response and ballistic behavior of Aramid III/epoxy support layers used in B4C ceramic composite armor. Three plain-woven Aramid III/epoxy laminates containing 20 wt%, 30 wt%, and 38 wt% resin were fabricated and characterized in terms of density, porosity, flexural properties, interlaminar shear strength, and low-velocity impact response. In addition, unidirectional (UD) and plain-woven laminates with a fixed resin content of 30 wt% were compared to clarify the influence of fiber architecture, while autoclave and hot-press processing were compared in terms of internal porosity and structural uniformity. The results showed that the 30 wt% resin laminate exhibited the lowest measured porosity (0.3%) and the best overall balance of flexural strength, flexural modulus, and impact-energy absorption, with values of 421 MPa, 34.6 GPa, and 141.5 J, respectively. The UD laminate exhibited a 38.5% higher impact-energy absorption than the corresponding plain-woven laminate, demonstrating the influence of continuous fiber alignment on load transfer and impact deformation. The autoclave process produced lower porosity than hot pressing for the 30 wt% laminate, indicating improved consolidation and microstructural uniformity. Ballistic tests were conducted on the plain-woven support-layer configurations using 12.7 mm armor-piercing incendiary projectiles under identical nominal areal density and impact conditions. The 30 wt% configuration achieved protection in all four tests and exhibited a mean back-face signature of 11.25 mm, compared with protection success rates of 50% and 75% for the 20 wt% and 38 wt% configurations, respectively. Post-impact characterization revealed B4C fragmentation, fiber deformation, matrix cracking, interlaminar delamination, and deformation of the UHMWPE backing layer. These results indicate that an intermediate resin content provides a favorable balance between interfacial load transfer and fiber deformation within the investigated armor configuration. The effects of fiber architecture and manufacturing process are also discussed as important factors affecting the structural and mechanical response of the support layer. Full article

This study compared the physical properties and color stability of specimens fabricated from a commercial filler-containing dental 3D printing resin using printer systems equipped with 405 or 385 nm light sources. Specimens were subjected to three-point flexural strength, Vickers hardness, water sorption, solubility, and color stability tests. Color stability was evaluated under dry (A), water-immersed (B), light-shielded (C), and light-exposed (D) conditions, and color differences (ΔE₀₀) were calculated using the CIEDE2000 formula. Data were analyzed using Student’s t-test or Welch’s t-test, as appropriate (α = 0.05). Flexural strength and Vickers hardness were significantly higher, and solubility was significantly lower, in the 385 nm group than in the 405 nm group (p < 0.05), whereas water sorption did not differ significantly. The ΔE₀₀ values were below the clinically acceptable threshold of 1.77 for all comparisons except A–B in the 405 nm group. The A–B and A–C values were significantly lower in the 385 nm group, whereas the B–C value was significantly higher (p < 0.05); no significant difference was observed for C–D. These findings suggest that differences between printer systems, including light-source wavelength, should be considered when fabricating dental prostheses using 3D printing resins. Full article

Polymethyl methacrylate (PMMA) remains the material of choice for denture base fabrication; however, its limited mechanical durability and susceptibility to microbial colonization continue to compromise long-term clinical performance. This study aimed to engineer a multifunctional PMMA denture base composite through hybrid reinforcement with hemp fiber (HF), silk fibroin (SF), and phytocannabinoid-rich fractions (Frac1–Frac4) and to comprehensively evaluate its mechanical, structural, antimicrobial, and cytocompatibility properties. Twenty experimental groups were fabricated, including conventional PMMA, PMMA/HF, PMMA/SF, and hybrid PMMA/HF/SF systems with or without 1 wt% phytocannabinoid fractions. Flexural strength, elastic modulus, Charpy impact strength, and Vickers hardness were determined according to standardized protocols. Structural characterization was performed using ATR-FTIR, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Bacterial metabolic viability of Streptococcus mutans and Lactobacillus acidophilus was evaluated using the MTT assay, while cytotoxicity was assessed using the LDH assay. Mechanical outcomes were analyzed using two-way factorial ANOVA to evaluate the main effects of the material system and phytocannabinoid condition and their interaction; significant interactions were followed by Tukey-adjusted simple-effects comparisons. Biological data were analyzed using the procedures specified for those outcomes (α = 0.05). The material system and phytocannabinoid condition significantly affected all mechanical properties (all main-effect p-values ≤ 6.068 × 10⁻⁸³). Significant material system × phytocannabinoid condition interactions were observed for flexural strength, Vickers hardness, and impact strength, whereas the interaction was not significant for elastic modulus. The PMMA/HF/SF control group exhibited the highest flexural strength (138.04 ± 2.05 MPa), elastic modulus (2.519 ± 0.017 GPa), Vickers hardness (26.14 ± 0.22 VHN), and impact strength (24.22 ± 0.22 kJ/m²). Although phytocannabinoid incorporation produced a gradual reduction in mechanical performance, all hybrid-reinforced formulations remained mechanically superior to unmodified PMMA. ATR-FTIR and XRD analyses confirmed preservation of the characteristic PMMA chemical structure and amorphous polymer architecture without evidence of new crystalline phases. SEM demonstrated markedly reduced bacterial adhesion and biofilm formation on phytocannabinoid-containing composites. The PMMA/HF/SF formulations exhibited the greatest antibacterial performance, reducing bacterial viability to 14.59–19.40% for L. acidophilus and 15.21–24.13% for S. mutans, while maintaining low cytotoxicity (<5%). These findings demonstrate the feasibility of combining hybrid natural-fiber reinforcement with phytocannabinoid functionalization in PMMA and support further investigation of this approach for denture base applications. Full article

To investigate the flexural behavior of high-strength concrete beams reinforced with a hybrid configuration of GFRP bars and high-strength steel bars, four-point bending tests were conducted on five C80 high-strength concrete beams, with the reinforcement ratios of high-strength steel bars and GFRP bars taken as the main variables. Combined with finite element simulation and theoretical analysis, the failure modes, load–deflection responses, crack development, and reinforcement strain characteristics of the test beams were examined. The results show that all test beams exhibited flexural failure with an appropriate reinforcement ratio, characterized by yielding of the high-strength steel bars in the tensile zone and crushing of the concrete in the compression zone. Increasing the GFRP reinforcement ratio primarily enhanced the peak load and post-cracking stiffness, whereas increasing the HRB635 reinforcement ratio had a more pronounced influence on the yield load and sectional stiffness. The strain distribution at the midspan section generally conformed to the plane-section assumption, and the two types of reinforcement demonstrated good collaborative load-bearing behavior and deformation compatibility. The established finite element model accurately simulated the load–deflection responses, crack evolution, and failure patterns of the test beams. A distinct post-yield load-carrying stage was observed: after yielding of the HRB635 steel reinforcement, the GFRP bars remained in the linear–elastic range and continued to carry increasing tensile force until crushing of the C80 concrete in compression. Based on this experimentally identified failure sequence, a normal-section flexural capacity model was developed in which the HRB635 reinforcement is taken as yielded while the GFRP stress is determined from sectional strain compatibility rather than directly assigned its tensile design strength. The predicted capacities agreed well with both the experimental and finite element results. Full article

Softening impact-resistant polypropylene (PP) copolymers (ICPs) may be accompanied by reduced breakdown performance; coordinating mechanical and electrical properties is closely related to crystalline-framework and rubber-rich-phase organization. Homopolymer PP matrix HICP and random copolymer PP matrix RICP formed the primary comparison, with high-phase-continuity CICP as a reference, through composition, fractionation, crystalline structure, morphology, viscoelasticity, and charge analyses. Relative to HICP, RICP matrix randomization extended crystallizability distributions toward lower temperatures, refined the crystalline framework, and expanded interphase regions. Tensile and flexural moduli decreased by 38.8% and 38.7%, respectively, while Weibull characteristic breakdown strength increased from 226.2 to 310.8 kV/mm. CICP, containing 23.3 wt% ethylene, comprised a continuous low-crystallinity/rubber-rich phase with dispersed PP crystalline domains. Its tensile modulus was 89.4 ± 4.9 MPa; it retained partial break in notched impact testing at −20 °C and a characteristic breakdown strength of 384.4 kV/mm. Thermally stimulated depolarization current, conduction, and space-charge results indicated that local trapping environments and multiphase transport pathways jointly regulate charge migration and accumulation, providing a charge-behavior basis for maintaining high insulation performance as flexibility increases. The relationships linking molecular sequences, crystalline organization, phase connectivity, and mechanical–electrical responses provide a basis for designing multiphase PP-based DC cable insulation. Full article

To further enhance the mechanical performance and early-age crack resistance of engineered cementitious composites (ECC), an ECC-based multiscale hybrid-fiber system was investigated. The system used carbon nanotube-modified polyethylene (M-PE) fibers as the primary reinforcement together with polypropylene (PP) and basalt (BF) fibers. The effects of fiber hybridization on compressive strength, uniaxial tensile behavior, flexural performance, early-age crack resistance, and microstructure were systematically evaluated. Mixtures retaining at least 60% M-PE exhibited a clear post-cracking strain-hardening response, whereas lower M-PE fractions led to crack localization and loss of strain hardening. At 28 days, BF-0 (1.5 vol.% M-PE + 0.3 vol.% BF) reached compressive, tensile, and flexural strengths of 85.3, 7.35, and 36.38 MPa, respectively. A six-indicator entropy-weighted TOPSIS evaluation identified BF-0 as the best-balanced mixture among the investigated groups. Increasing PP or BF content improved early-age plate crack resistance; BF-5 (1.5 vol.% BF) achieved the highest crack reduction coefficient of 67.98%, with a nominal total crack area of 27.6 mm². Scanning electron microscopy (SEM) observations were used only as qualitative morphological evidence, whereas mercury intrusion porosimetry (MIP) revealed quantitative pore-structure trends and X-ray diffraction (XRD) indicated that fiber hybridization did not generate new detectable crystalline phases. The results reveal the performance trade-offs among strength, ductility, and early-age crack control in multiscale hybrid-fiber cementitious composites. Full article

Additive manufacturing technologies in construction, particularly concrete 3D printing, offer new opportunities to automate building processes and improve material efficiency. However, the use of agricultural waste in cement-based composites for 3D printing remains limited, and the combined effects of such waste on rheology, interlayer bonding, mechanical performance, and thermal insulation are still insufficiently studied. This study aims to develop 3D-printable cement-based composites incorporating ground rice husk (GRH) as a multifunctional filler. GRH was introduced at dosages of 0–40% by mass of cement while maintaining constant workability. Because GRH is hydrophilic and water-absorbing, increasing its content required progressively higher amounts of added mixing water. Consequently, GRH dosage and water adjustment were not independent variables, and the reported effects represent the combined response of the composite to GRH incorporation and the associated water adjustment required to preserve printability. Under these conditions, increasing the GRH content reduced the compressive strength from 45.6 to 5.2 MPa, the flexural strength from 8.0 to 1.9 MPa, and the interlayer bond strength from 0.56 to 0.13 MPa, while thermal conductivity decreased from 0.85 to 0.35 W/(m·K) and water absorption increased by 98%. SEM confirmed the transition from a dense cementitious matrix to a highly porous structure, with filler particles connected by thin films of cement paste. The study demonstrates the potential of using rice husk in 3D-printable cement-based composites and highlights the trade-off between mechanical performance and thermal insulation as GRH content increases. Full article

A paradigm change in the construction sector is represented by the switch from traditional concrete construction to extrusion-based 3D concrete printing (3DCP), which is motivated by the need for automation, geometric freedom, material efficiency, and less environmental impact. However, because of its anisotropic behaviour, which results from the multilayer deposition method and the quality of interlayer bonding, 3D-printed concrete’s structural use is still difficult. In the present research, compressive and flexural tests were used to characterise the mechanical characteristics of both binders before and after printing. This allowed for the evaluation of the impacts of extrusion and layer orientation on strength development. A 3D-printed arch beam made entirely of CEM I 52.5 R was evaluated under three-point bending at the structural level. In order to minimise tensile demands and lessen the impact of anisotropic flaws, the arch design was chosen to align internal force flow primarily in compression. Extrusion can improve mechanical performance in high-clinker systems; however, anisotropy has a considerable impact on flexural performance depending on loading direction and layer orientation, according to the results. When anisotropy is appropriately taken into consideration, low-carbon binders’ behaviour remained within acceptable ranges for structural applications, despite their decreased early-age strength. This study also shows an application in the structural design of 3D-printed concrete arches, using classical finite element tools, normally used by structural designers. Full article

Additive manufacturing technologies using extrusion of plastic material (MEX) stand out due to the accessibility of equipment and raw materials (filaments, granular materials), the variety of equipment and materials, low operating costs and the potential for use in non-industrial environments. However, additive manufacturing using extrusion of plastic material (MEX) faces a number of factors that reduce the mechanical characteristics of parts and the productivity of the manufacturing process, preventing the adoption of this manufacturing technology on a large scale. Post-processing is a crucial step in additive manufacturing using plastic extrusion, which has a significant impact on the finished product. In this sense, in this paper, the influence of the annealing heat treatment (temperature, t = 75 °C and duration, d = 180 min) on the mechanical characteristics during three-point bending of the specimens manufactured additively by extrusion of filaments made of PETG and recycled PETG 100 (rPETG 100, where 100 represents the amount of recycled material) is studied using the layer height deposited in one pass, L_h = (0.10/0.15/0.20) mm, and the percentage fill density, I_d = (50/75/100)%. The annealing heat treatment generated a 14.24% increase in flexural strength of the additively manufactured PETG specimens and a 2.48% increase in the flexural strength of the additively manufactured rPETG specimens. Full article

This study explores the quasi-static and dynamic responses of irregular, honeycomb-like topologies made from glycol polyethylene terephthalate (PETG) with various sparse infill densities, using fused filament fabrication (FFF) manufacturing technology. Both tensile and flexural tests revealed a linear increase in Young’s modulus and sample strength as infill density increased, under constant printing and testing conditions. Below 50% infill, this trend remained unchanged, despite cells being irregular and fracture mechanics differing. Low-velocity impact tests were conducted at a velocity of 1.5 m/s, equivalent to an incident energy of 6.2 J. Regarding dynamic responses, irregular honeycomb-like structures use 12.5–25% of the nominal pendulum energy during complete fracture in Charpy tests, and 74.3–98.3% of total available energy during low-impact crushing. Samples with infill densities of 15% and 25% revealed higher absorbed energy values of around 6.5 and 6.1 J, respectively, compared with denser samples. Although they exhibit more favorable mass-specific energy absorption, these samples collapse more quickly than their stiffer 50–100% counterparts. The findings provide valuable insights into irregular, honeycomb-like structures and open up perspectives for optimization and component-level assessment, with potential applications as impact-resistant, secondary/non-structural components for the automotive industry. Full article

The growing demand for sustainable binder systems in 3D-printed concrete (3DPC), together with the declining availability of fly ash (FA), has increased the need for alternative supplementary cementitious materials. This study investigates the feasibility of using basaltic rock dust (BRD) as a high-volume replacement of FA in 3DPC through a two-stage experimental programme involving mix optimisation followed by evaluation under printing conditions. Five mortar mixes incorporating BRD at FA replacement levels of 0%, 25%, 50%, 75%, and 100% by mass were first evaluated to identify the optimum replacement level within the investigated range, after which the optimum mix was comprehensively characterised in terms of its fresh properties, rheological behaviour, hydration characteristics, mechanical performance, anisotropy, and microstructure. The results showed that 75% FA replacement by BRD achieved the optimum overall performance among the investigated BRD-containing mixes, based on the combined consideration of high BRD utilisation, flowability, hydration behaviour, and compressive strength. Although its 28-day compressive strength under conventionally cast conditions remained slightly lower than that of the control mix, under printing conditions, the C75 mix increased the flow diameter from 165 mm to 176 mm and the maximum printable layers from 14 to 16 while reducing the shape retention spread diameter from 96 mm to 89 mm. Compared with the control mix, the BRD-incorporated mix also increased the compressive strength by 10.9% in the Y- direction and 22.9% in the Z-direction, respectively, while reducing the compressive anisotropy from 20.97% to 12.39%. Although the flexural strength decreased from 7.66 to 5.02 MPa in the Y-direction and from 7.29 to 5.19 MPa in the Z-direction, the directional dependence decreased from 4.83% to 3.34%. SEM observations revealed a more compact cementitious matrix with fewer visible large pores in C75 than in the control mix. These findings demonstrate that BRD has strong potential as a high-volume replacement for FA in 3D-printed concrete, reducing reliance on fly ash while achieving favourable printability, compressive performance, and structural uniformity. Full article

Fiber-reinforced polymer composites are attractive multifunctional material systems for aerospace, defense, and transportation because of their low density, high specific mechanical properties, and tailorable electromagnetic response. This study comparatively evaluated the effects of fiber system, thermoset matrix, and hybridization on the mechanical, thermomechanical, and electromagnetic behavior of Coremat interlayered sandwich composites containing carbon, glass, and aramid fabrics with polyester, vinylester, and epoxy matrices. Eighteen configurations were fabricated by hand lay-up and evaluated by tensile, three-point bending, heat deflection temperature (HDT), Vicat softening temperature (VST), and two-port S-parameter measurements over 4–40 GHz. The carbon/epoxy configuration exhibited the highest tensile strength (231.2 MPa), whereas the glass/vinylester configuration showed the highest flexural strength (160.5 MPa), HDT (128.0 °C), and VST (132.7 °C). The relatively low standard deviations across the tested configurations indicated consistent experimental repeatability and limited within-configuration dispersion. Carbon-containing systems strongly suppressed electromagnetic transmission; however, the single carbon systems were predominantly reflection driven. The carbon/glass polyester hybrid S10 provided the highest total shielding effectiveness (38.45 dB) at an overall laminate thickness of 3.30 mm, corresponding to a normalized shielding effectiveness of 11.65 dB/mm, while the carbon/aramid epoxy hybrid exhibited the highest incident-power absorption ratio (22.4%) together with very low transmission (0.22%). Overall, the results show that fiber system, matrix type, and hybrid architecture should be selected jointly when balancing structural, thermomechanical, and electromagnetic requirements. Full article