Advanced Materials Research Vol. 1190

Abstract: This study evaluates hydrothermally synthesized Ni–zirconia sulfate catalysts in comparison with natural mineral–based catalysts (Cu-Bentonite and Cu-Zeolite) for waste cooking oil upgrading toward sustainable aviation fuel (SAF). Catalyst properties were characterized using XRD, BET, and SEM–EDS, while catalytic cracking performance was assessed based on oil liquid product (OLP) yield and C₁₂–C₁₆ selectivity. XRD confirms the formation of a stable monoclinic ZrO₂ phase with enhanced crystallinity after Ni incorporation, whereas Cu-Bentonite and Cu-Zeolite preserve their layered and FAU-type structures. BET and SEM–EDS analyses indicate that Ni–zirconia sulfate exhibits favorable mesoporosity and more homogeneous metal dispersion. Catalytic tests show that SZ–Ni 1% delivers the highest performance, achieving a C₁₂–C₁₆ selectivity of 77.37% and an OLP yield of 53.62%, outperforming Cu-based catalysts. The enhanced performance is attributed to a bifunctional acid–metal mechanism, where strong Brønsted–Lewis acidity and Ni hydrogenation sites synergistically promote cracking and hydrodeoxygenation. These findings demonstrate that Ni–zirconia sulfate is an effective catalyst for SAF-range hydrocarbon production, while natural mineral catalysts offer lower-cost but less efficient alternatives.

Abstract: This systematic literature review evaluates the potential of eggshell powder (ESP) as a sustainable soil stabilization material, synthesizing evidence from 22 peer-reviewed studies published between 2015 and 2025. This review tries to comprehensively assess its effects across multiple geotechnical properties and multiple soil types, covering standalone, blended, and bio-stabilization systems. The screening was done from a major database, extracting data on soil type, additive content, and mechanical performance. Findings reveal that ESP consistently enhances unconfined compressive strength (UCS) by 70 - 200%, increases California Bearing Ratio (CBR) by 100 - 200%, and reduces plasticity index (PI) sufficiently to improve soil classification from high to low plasticity categories. Optimal ESP contents range from 4–10% for standalone application to 3–15% in blended systems, with 10% recommended for bio-stabilization. Improvements are driven by pozzolanic reaction, cation exchange, flocculation, void filling, and calcite precipitation. ESP offers significant environmental benefits through waste valorization and reduced carbon footprint compared to cement and lime. However, challenges remain in scaling laboratory successes to field application and assessing long-term durability. This review supports the integration of ESP into sustainable geotechnical practice while highlighting the need for further applied research.

Abstract: The increasing use of carbon fiber reinforced polymers (CFRPs) in aerospace and automotive has led to a growing volume of prepreg waste, creating economic and environmental challenges. This study investigates the feasibility of repurposing expired carbon fiber prepreg waste into Forged Carbon Fiber (FCF) composites through compression molding. Chopped fibers recovered from ambient-aged unidirectional T700 prepreg were used to manufacture waste forged carbon fiber composites (WFCF) and were compared with forged composites made from new chopped fibers (NFCF) and from mixed WFCF/NFCF formulations. Thermal analysis by differential scanning calorimetry confirmed that the waste prepreg fibers had undergone partial curing during storage, resulting in a modified resin structure before reprocessing. Mechanical performance was evaluated using tensile, three-point bending, and Charpy impact tests. The WFCF composites exhibited low tensile strength and modulus, but a relatively high flexural modulus, highlighting a strong dependence on loading mode. In contrast, NFCF composites reached higher tensile strengths. These results demonstrate that although 100% waste prepreg fibers are unsuitable for structural applications, their use in forged carbon composites becomes viable when blended with virgin fibers. This approach offers a practical pathway to valorize prepreg waste and support a more sustainable circular economy for advanced composite materials.

Abstract: The environmental impact associated with cement production has intensified the search for sustainable alternatives for cementitious composites. Coconut fiber, a renewable and low-cost material widely available in tropical regions, has attracted attention as a natural reinforcement for concrete applications. This study evaluated the mechanical behavior of cementitious composites reinforced with low contents of coconut fiber (0.10%, 0.20%, and 0.30% w/w). The reference mixture presented an average axial compressive strength of approximately 15.8 MPa and an average diametral tensile strength of approximately 8.0 MPa. The incorporation of 0.10% coconut fiber resulted in the highest average mechanical performance among the evaluated mixtures. Axial compressive strength showed a slight increase to approximately 15.9 MPa, while diametral tensile strength increased to approximately 9.4 MPa. Higher fiber contents (0.20% and 0.30%) resulted in reductions in compressive strength, with no substantial additional gains in diametral tensile strength. The incorporation of coconut fibers also modified the fracture behavior of the composites, indicating reduced brittleness and possible crack-bridging action. Overall, the results suggest that low fiber incorporation may contribute to improved tensile-related performance without significantly compromising compressive strength. Among the investigated compositions, 0.10% (w/w) presented the most balanced mechanical behavior, demonstrating the potential of coconut fiber as a sustainable reinforcement material for cementitious composites in civil construction.