Search Results (157)

This study addresses the early-age brittleness and performance limitations of sustainable cement soil. While prior works optimized the baseline compressive strength using recycled sand and nanoclay, the multi-scale synergistic effects of fibers and nanomaterials on the post-peak deformation remain underexplored. To address this gap, a composite modification system incorporating recycled sand, nanoclay, polypropylene fibers, and graphene derivatives was developed. The experimental program comprised standard specimen fabrication, early-age curing, and unconfined compressive strength (UCS) testing, supplemented by RBF neural network curve fitting and quantitative ArcGIS digital image processing of scanning electron microscopy (SEM) micrographs. The results demonstrate that optimizing the fiber parameters (0.6% content with 6 mm length) successfully increases the early UCS to 2263.2 kPa, which is further elevated to a peak of 2755.0 kPa upon co-incorporation with 0.05% small-sized graphene oxide. Correspondingly, a newly introduced ductility index quantitatively confirms that the single-fiber reinforcement yields an index of 1.93, which is further enhanced to 2.02 by the graphene composite system. Microstructure tracking and digital image extraction revealed that the SEM-derived surface porosity decreased significantly, exhibiting a clear inverse relationship with the macroscopic mechanical strength. These quantitative microstructural shifts confirm that graphene effectively filled micropores and reinforced the fiber–matrix interface, establishing a dense matrix network with enhanced interfacial bonding. This multi-scale approach offers a sustainable strategy for green geotechnical applications. Full article

Recycled polypropylene (rPP) biocomposites represent a convergent strategy for plastic waste valorization and agro-industrial residue reutilization. This study quantifies tensile, flexural, and compressive performance (ASTM D638, D790, D695) of rPP biocomposites incorporating raw corn stover (Zea mays), banana pseudostem (Musa spp.), and barley residue (Hordeum vulgare) fibers at 10, 20, and 30 wt%, processed by single-screw extrusion and compression molding without compatibilizer. Two-way ANOVA with Tukey HSD post hoc analysis (α = 0.05) evaluated effects of fiber type and concentration. Tensile strength declined monotonically across all systems, from 24.9 MPa (neat rPP) to 7.9 MPa at 30 wt% banana fiber. Corn fiber exhibited exceptional tensile concentration stability (only −11% across the full range) and the best flexural retention at 10 wt% (36.6 MPa, 79% of neat rPP). A performance plateau was identified at 20 wt% under both tensile and flexural loading, beyond which further addition produced no significant reduction. Under compression, fiber type exerted its largest statistical effect (F = 81.231), all three systems were mutually distinguishable, and no plateau was observed. These results establish a loading-mode-resolved mechanical baseline for uncompatibilized rPP biocomposites, with corn fiber at 10–20 wt% as the most versatile formulation across all loading modes. Full article

This study evaluates the industrial-scale feasibility of injection moulding of a recycled polypropylene composite reinforced with recycled fibers derived from an industrial waste stream. Although previous laboratory-scale research has demonstrated the potential of natural fiber-reinforced thermoplastics, their large-scale industrial implementation remains limited due to uncertainties related to processability, reproducibility, and manufacturing robustness. In this work, the composite material is validated through injection moulding trials carried out in four independent industrial companies located in Andalusia (Spain) and three industrial case studies across different industrial sectors in Slovenia, operating under real production conditions. The extrusion process was characterized in terms of process stability, confirming continuous operation with automated dosing and stable material flow without interruptions under industrial conditions. Injection processing parameters, cycle stability, part quality, and defect formations are also considered important when assessing the manufacturing feasibility. The multi-site validation approach enables the evaluation of reproducibility across different injection moulding systems and mould geometries, providing critical insights into the scalability and technological readiness level of recycled natural fiber-reinforced polypropylene composites. Although direct energy consumption measurements were not systematically recorded, the observed processing stability and cycle repeatability indicate a consistent and energy-efficient operation under industrial processing conditions. The results contribute to bridging the gap between laboratory-scale material development and real industrial implementation. Full article

Presently, there is little to no literature that investigates the effect of electron beams on para-aramid (Kevlar^®) fiber polymer (KFRP) composites. Therefore, we assessed the effect of homogeneous low-potential electron beam irradiation (HLEBI) on Kevlar-reinforced recyclable thermoplastic (TP) polypropylene (PP) (KFRPP). Samples were assembled in an interlayered configuration of four-sized KF plies between five PP sheets [PP1-KF1-PP2-KF2-PP3-KF2-PP2-KF1-PP1] designated [PP]₅[KF]₄, which were hot-pressed at 493 K at 4 MPa for 7 min. Experimental results show when an HLEBI setting of 250 kV cathode potential (V_c) at an 86 kGy dose is applied to finished sample surfaces, the Charpy impact strength (a_uc) at median fracture probability (P_f of 0.50) is increased 59% from 72.5 kJ/m² when untreated to 115.6 kJ/m² thereafter, while a 170 kV–129 kGy setting increased a_uc about 15%, to 83.3 kJ/m², when compared to the untreated sample. Scanning electron microscopy (SEM) showed the 250 kV–86 kGy HLEBI increases KF/PP adhesion with increased consolidation and KF bundling, while the electron spin resonance (ESR) showed HLEBI generates dangling bonds (DBs) in KF and PP, which is evidence of the strengthening KF/PP interface. X-ray photoelectron spectroscopy (XPS) of the N1s spectrum of Kevlar fiber from the fracture region of the untreated sample showed a dominant peak at 399.5 eV with 82.7% area, which is characteristic of the Kevlar backbone N–(C=O)–, indicating poor adhesion with fiber pullout. However, the dominant peak was shifted in the 250 kV–86 kGy sample to that of strongly bonded imines, –C=N–, at 398.6 eV and 36.8%, indicating strong bonds generated at the KF/PP interface. Together, the N1s, C1s and O1s spectra indicate increased polar groups, reduced weak Van der Waals forces, and the generation of a strong active nitrogen-containing interphase, acting to reduce fiber pullout to increase the impact strength of the [PP]₅[KF]₄ composite system. Full article

The study of river basins is key to understanding the dynamics of microplastic (MPs) generation, transport, and accumulation in regions where various productive activities converge and waste management is limited. The objective of this study was to characterize economic activities in the Tecolutla River basin, Mexico, to identify risk factors associated with MPs generation and release throughout the production chain. A descriptive applied research study was conducted using a structured questionnaire administered to 19 economic units distributed across seven municipalities in the Tecolutla River basin, Veracruz, Mexico. The instrument allowed for the evaluation of the use of plastic materials in inputs, production processes, final products, and waste management practices. Among the economic units analyzed (n = 19), 94.7% reported the use of polymeric materials, with a predominance of thermoplastics such as polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polypropylene (PP), which have a high potential for secondary fragmentation. Within the tertiary sector, accommodation and food preparation services account for the highest proportion of units with limited separation and recycling practices. Activities in the secondary sector, especially the textile and construction industries, showed a high potential for releasing this pollutant due to the use of synthetic fibers, composite materials, and the absence of retention systems. The results provide a basis for the design of mitigation strategies targeting priority productive sectors at the watershed scale. Full article

Against the backdrop of dual-carbon goals and resource constraints, the high-value utilization of recycled fine aggregates (RFAs) remains limited, leading to inconsistent engineering performance and insufficient durability. Enzyme-induced carbonate precipitation (EICP) represents a promising low-carbon cementation method, yet its deposition uniformity and cementation efficiency are influenced by the pore structure of granular media and associated mass transfer pathways. This study employs a two-stage experimental design to investigate the synergistic effects of particle size distribution characteristics, represented primarily by d₅₀, and fiber addition on EICP-cemented RFA. Phase I (fiber-free; d₅₀ = 0.67–1.14 mm) results indicate that, across the tested gradation schemes, the CaCO₃ content generally decreased from 9.49% to 7.72% as the representative d₅₀ increased, while the dry density changed only slightly (1.637–1.617 g/cm³). However, the unconfined compressive strength (UCS) decreased from 1000 kPa to 541 kPa (45.9% reduction), indicating that strength is primarily governed by the connectivity of the cementation network rather than solely by the degree of densification. In Phase II, glass fiber (GF), polypropylene fiber (PPF), and jute fiber (JF) were incorporated into the ERFA4 gradation scheme selected for fiber modification. All three systems exhibited a unimodal optimum pattern: the peak CaCO₃ contents reached 10.71% (GF 0.5%), 10.11% (PPF 0.7%), and 11.46% (JF 0.7%), corresponding to peak UCS values of 1917, 1874, and 2450 kPa, respectively. Microscopic analysis suggested that fiber bridging coupled with CaCO₃ deposition may contribute to the formation of a “fiber-CaCO₃-particle” stress-transfer network, which is consistent with the observed enhancements in load-bearing capacity, ductility, and post-peak stability. Full article

Recycled polypropylene reinforced with glass fiber (rPP-GF) represents a promising sustainable material alternative addressing global imperatives for environmentally responsible manufacturing. This systematic literature review examines the mechanical, thermal, and sustainability performance of rPP-GF composites based on 66 peer-reviewed studies published between 2014 and 2024, following PRISMA guidelines. The evidence demonstrates that glass fiber reinforcement significantly enhances mechanical and thermal performance. Compared to virgin counterparts, rPP-GF composites reduce environmental impact. However, technical challenges, including fiber attrition during reprocessing and a lack of standardized testing protocols, remain significant barriers. Future research should prioritize unified testing frameworks, hybrid filler systems, and advanced recycling technologies for enhanced circular economy applications. Full article

Continuous unidirectional (UD) thermoplastic composite tapes are increasingly used in aerospace, automotive, and energy applications because of their high specific strength, low weight, recyclability, and compatibility with automated manufacturing. Since final component performance strongly depends on tape quality, reliable defect characterization and detection are essential. In this study, manufacturing-induced defects in polypropylene-based UD tapes reinforced with carbon and glass fibers were investigated using real images acquired directly from laboratory-scale production without synthetic data. Defects related to interfacial integrity, matrix distribution, fiber architecture, and surface irregularities were systematically analyzed, and a practical four-class defect taxonomy was established. To enable automated inspection under limited-data conditions, lightweight YOLOv8, YOLOv11, and the new YOLO26 models were comparatively evaluated using a UD tape-specific augmentation strategy combining physically constrained Albumentations and on-the-fly augmentation. Among the tested models, YOLO26-s achieved the best overall performance, reaching a mean mAP@0.5 of 0.87 ± 0.03, outperforming YOLOv11 (0.83) and YOLOv8 (0.78), with 0.90 precision and 0.85 recall. Interfacial (0.92 mAP) and matrix-related (0.90 mAP) defects were detected most reliably, whereas fiber-related (0.89 mAP) and surface defects (0.79 mAP) remained more challenging, particularly in glass-fiber-reinforced tapes due to transparency-masking effects. The results demonstrate the potential of compact deep learning models for computationally efficient and manufacturing-relevant in-line quality monitoring of UD tape production. Full article

The increasing demand for sustainable and environmentally friendly construction materials has spurred interest in biopolymer composites reinforced with agricultural waste. Rice husk (RH), a byproduct of rice milling, is abundant and rich in lignocellulosic fibers and silica, making it excellent for use in fiber-reinforced biopolymers. The novelty of this study lies in its integrated and construction-oriented evaluation of rice husk (RH)-reinforced biopolymers, combining mechanical, thermal, environmental, and economic perspectives within a single framework. The study introduces a novel comparative approach by benchmarking multiple polymer matrices-including PP, recycled HDPE, epoxy, PLA, and bio-binders-under unified quantitative performance criteria. Another key novelty is the identification of the dual functional role of silica-rich RH in simultaneously enhancing structural strength and flame retardancy while contributing to carbon emission reduction. With a high silica content (15–20%) and lignocellulosic structure, RH serves as a natural filler that enhances the performance of polymer matrices such as polypropylene (PP), epoxy, polylactic acid (PLA), and recycled polyethylene. Mechanically, RH-reinforced composites demonstrate significant improvements in tensile, flexural, and impact strength. For example, PP composites with NaOH-treated RH and coffee husks achieved tensile strengths between 27.4 MPa and 37.4 MPa, with corresponding Young’s modulus values ranging from 1656 MPa to 2247.8 MPa. Recycled HDPE-RH blends reached tensile strengths up to 74 MPa and flexural values of 39 MPa, validating their structural applicability. Epoxy matrices embedded with 0.45 wt.% RH nanofibers showed degradation thresholds of 411 °C and 678 °C, reflecting substantial thermal resistance. Flame retardancy is further improved by the presence of RH biochar, which leads to reduced peak heat release rate (PHRR) and enhanced char formation. In building insulation applications, RH-based composites exhibit low thermal conductivity values between 0.08 and 0.14 W/m·K, contributing to energy efficiency. Economically, RH reduces material costs by 30–40%, while environmentally, its integration lowers carbon emissions in PP composites by up to 10%, and promotes biodegradability. Despite challenges such as moisture absorption and interfacial adhesion, these can be mitigated through alkali treatment, compatibilizers (e.g., MAPP), or hybrid reinforcement strategies. Full article

This study investigates the properties of concrete incorporating recycled aggregates (RAs) for rigid pavement applications. A 15-point three-level experimental design was used to vary three composition factors: Portland cement substitution with fly ash (FA), and dosages of a superplasticizer (SP) and polypropylene fibers (PFs). A set of experimental–statistical models (ES models) was developed to predict the concrete strength, abrasion and frost resistance (FR), water absorption (WA), and global warming potential (GWP). This study aimed to develop a material that achieves both adequate mechanical performance for pavement applications and enhanced environmental sustainability by incorporating RAs and FA. The results demonstrate that replacing up to 13% of cement with FA does not compromise the splitting tensile strength or FR. For non-fibrous concrete, this substitution increases FR by approximately 50 freeze–thaw cycles. Application of PFs (2.4–3 kg/m³) enhances splitting tensile strength by 14–16% and improves FR by about 50 cycles. Using response surface methodology (RSM), optimal concrete compositions were identified that meet all target criteria: compressive strength ≥ 40 MPa, flexural strength ≥ 5 MPa, FR ≥ F200 (cycles), and abrasion resistance (AR) ≤ 0.5 g/cm², while simultaneously minimizing GWP. An additional optimum composition was determined by imposing a constraint on splitting tensile strength of ≥4.5 MPa. This graphical optimization approach, utilizing two-factor interaction diagrams, provides an effective and visual methodology for practical concrete mixture design. The novelty of the method lies in the discretization of the factor space, which enables efficient identification of optimal concrete mixture compositions. Full article

The demand for concrete has led to increased use of raw materials and significant waste generation. Recycled aggregate concrete (RAC) offers a viable approach to sustainable concrete; however, the use of weakly bonded mortar on aggregate leads to low strength and crack formation. Fiber reinforcement, specifically hybrid fiber reinforcement combining steel, glass, basalt, and polypropylene fibers, can increase the tensile and flexural properties of RAC. This study developed machine learning models to enable the prediction of hybrid fiber-reinforced RAC’s compressive, splitting tensile, and flexural strength performance; these new models overcome the limitations of previous research, which relied on only one fiber type and regular methods of optimization. Two models (a deep neural network (DNN) and an XGBoost model) were trained and optimized using bald eagle search (BES), particle swarm optimization (PSO), and the Bayesian optimization (BO) algorithm to improve performance. Among the three optimization analyses, PSO-XGBoost achieved the highest accuracy for compressive strength and splitting tensile strength, while BES-XGBoost achieved the highest accuracy for flexural strength. The most significant influences on the compressive strength were curing age and silica fume, while the main drivers of splitting tensile strength and flexural strength were fiber volume and fiber characteristics. The use of SHAP-based methodology with a user-friendly interface further improved the design of RAC mixtures, reducing waste from raw materials, enhancing the structural performance of RAC, and enabling data-driven decision-making in the manufacturing of eco-friendly concrete products. Full article

Ultra-high-performance concrete (UHPC) provides exceptional strength and durability; however, its high cement and silica fume contents raise cost and environmental concerns. This study investigates the direct tensile behavior of a sustainability-driven UHPC in which 52% of the solid constituents are replaced with recycled glass and tensile performance is tailored using recycled and commercial fiber systems. A previously optimized recycled-glass UHPC matrix complying with ASTM C1856 was reinforced with recycled polyethylene fibers of varying lengths, commercial polypropylene and polypropylene–polyethylene fibers, brass-coated high-strength steel microfibers, and hooked-end steel macrofibers at fiber volume fractions of 1%, 2%, and 3%. Direct tensile tests were performed under displacement control in accordance with JSCE-08, and first-crack stress, peak tensile stress, tensile strain capacity, and energy absorption were derived from the stress–strain response. The most significant finding is that stable strain-hardening and multiple cracking can still be achieved in a UHPC matrix incorporating very high recycled-glass contents when appropriate steel fiber systems are used. Hooked-end steel fibers at 3% volume fraction reached peak tensile strengths of approximately 12 MPa and toughness values close to 40 kJ/m³, demonstrating that post-cracking performance comparable to conventional UHPC can be preserved despite aggressive matrix modification. In contrast, polymeric and recycled polyethylene fibers primarily enhanced first-crack stress but did not generate sustained post-cracking hardening, indicating their suitability for crack control and serviceability rather than structural tensile strengthening. Full article

Unidirectional glass fiber-reinforced thermoplastic (UGFT) composite tapes are promising recyclable structural materials for applications such as composite pressure pipes. However, their durability under hydrothermal environments remains a critical concern. This study emphasizes metrology-driven evaluation of aging behavior in polypropylene-based UGFT tapes. Specimens were conditioned at 95 °C in a deionized-water environment for up to 4 weeks, and multiple complementary measurement techniques were applied to quantify degradation. Mass-change metrology was performed to characterize water uptake kinetics and establish diffusion-driven aging progression. Tensile testing enabled quantitative assessment of mechanical strength retention, defining a >25% reduction in strength as a threshold for significant deterioration. Acoustic emission (AE) acted as the central non-destructive monitoring method, capturing high-fidelity waveforms generated during loading. AE waveform descriptors, such as amplitude, rise time, and frequency content, served as measurable indicators of internal damage mechanisms including matrix cracking, interfacial debonding and fiber breakage. To process large AE datasets, principal component analysis was used for dimensionality reduction, followed by k-means clustering to group signals by damage type. Optical microscopy provided microstructural verification of these classifications. The integrated metrological framework demonstrates a reliable pathway to monitor, identify, and quantify damage evolution in hydrothermally aged UGFT structures. Full article

This study aims to evaluate the properties of poly(propylene) or PP composite reinforced with coconut coir fibers, and how these vary with fiber length and composition ratio. This innovative thermoplastic composite material was manufactured using a low-tech process from only PP, coconut coir fibers, and xylene (dissolution agent). Therefore, this process is widely accessible whilst both reusing/recycling waste plastic and making use of waste fiber material to produce a useful material that can fulfill demand for wood products, which has many environmental benefits. In this research, the coconut coir fibers are used as reinforcement, as well as the filler of the composite. Nine variations in composite material were produced from three length categories of fibers (2–5 mm, 10–20 mm, and 30–40 mm) and three composition ratios (60:40, 70:30, and 80:20) of predominant plastics of PP and fibers. Physical properties of the respective composite, such as density, moisture content, and thickness swelling, were fulfilled to the Japanese Industrial Standard (JIS) for particleboard. Mechanical properties of the composites showed that both modulus of elasticity (MoE) and modulus of rupture (MoR) decreased as the length of the fibers used increased. Conversely, an increase in the proportion of PP resulted in a stronger composite. However, statistically, the interaction between the amount of PP and the length of coir fibers within the biocomposite did not influence their quality. These results demonstrate that a low-cost process for manufacturing composite from waste materials can meet most industry standards and indicate that further refinement of the process, building on these findings, could achieve an innovative thermoplastic composite with widespread structural applications whilst delivering environmental benefits. Full article

The increasing environmental impact of the textile industry has led to the development of sustainable production methods. One of the effective approaches is the use of recycled fibers, which helps to save resources, reduce carbon emissions, and support the circular economy. This study investigates the feasibility of producing durable upholstery fabrics incorporating recycled polypropylene (r-PP) and virgin polypropylene (v-PP). Filament yarns with varying r-PP/v-PP blend ratios, produced by the melt spinning process, were used as weft yarns, while commercially available virgin polyester filament yarns were employed in the warp direction for all fabric samples. Performance tests in accordance with the standards were applied to the fabrics and the results were also evaluated statistically. The results show that acceptable performance is achieved in some mechanical properties if similar blend ratios and production parameters are used. In the study, an optimization model was developed to maximize the weft breaking strength using the equations obtained from the regression analyses. With the help of the mathematical model created, the values of other physical and performance properties of the fabric depending on the maximum breaking strength value could be estimated without the need for trial production. The model was solved using Lingo 18.0 optimization software. The solution of the model revealed that the optimum weft yarn blend ratio is 10/90 r-PP/v-PP, and the maximum weft breaking strength value is 562.45 N. Full article