Effect of crushed and uncrushed aggregate ratios on the mechanical properties of polypropylene fiber-reinforced concrete

In recent years, polypropylene fibers (PPF) have been extensively used in structural concrete components due to their capacity to enhance various concrete properties. This research aims to analyze the varying ratios of crushed and uncrushed aggregate in fiber-reinforced concrete. This research study seeks to evaluate the varying proportions of crushed and uncrushed aggregate, both with and without polypropylene fiber (PPF), to examine the performance and mechanical properties of concrete. This study aims to develop a standardized normal strength concrete exhibiting rapid strength development post-casting, achieved through the strategic incorporation of both crushed and uncrushed coarse aggregates, alongside selective inclusion of polypropylene fibers (PPF). To enhance the mechanical performance of the concrete, eight distinct mix designs were formulated, varying in aggregate composition and fiber content. The first four mixtures were prepared without PPF, employing crushed-to-uncrushed aggregate ratios of 0%, 35%, 65%, and 100%, respectively. The subsequent four mixtures replicated these aggregate proportions with the addition of 1% PPF by volume. This experimental framework facilitates a systematic evaluation of the influence of aggregate type and fiber reinforcement on the mechanical properties of normal concrete. The incorporation of 1% polypropylene fiber (PPF) into concrete mixtures significantly enhances mechanical performance across multiple metrics. Specifically, the mix comprising 35% crushed and 65% uncrushed aggregates demonstrated a notable increase of 5 MPa in compressive strength upon fiber addition. Comparative analysis further reveals that flexural strength consistently improves in fiber-reinforced specimens relative to their non-fiber counterparts. Among all fiber-reinforced configurations, the mixture containing 65% crushed aggregate and 1% PPF exhibited superior mechanical behavior, outperforming other PPF-enhanced mixes in both flexural and tensile strength. This trend underscores the synergistic effect of optimal aggregate gradation and fiber reinforcement. Notably, tensile strength gains mirrored those observed in flexural performance, with the 65% crushed aggregate mix achieving higher values than those with 35% and 100% crushed aggregate under identical fiber dosage. These findings affirm the efficacy of polypropylene fiber in enhancing ductility and strength, particularly when paired with a balanced aggregate composition. The inclusion of polypropylene (PP) fiber in concrete mixtures with elevated fine aggregate content demonstrably increases the load threshold required to initiate the first crack. This enhancement in crack resistance is attributed to the fiber’s ability to bridge microcracks and distribute tensile stresses more uniformly across the matrix. Furthermore, the integration of PP fiber into conventional concrete significantly elevates the ultimate load-bearing capacity of structural elements. In addition to strength improvements, fiber-reinforced concrete beams exhibit increased displacement capacity and enhanced ductility, indicating a more favorable post-cracking behavior and energy absorption potential. These characteristics collectively contribute to improved structural resilience and serviceability under flexural loading conditions.