Effect of Oil Palm Broom Fiber on the Mechanical Properties of Rice Husk Ash–Blended Concrete

The high carbon footprint of cement production and the cost and environmental impact of steel reinforcement make conventional concrete unsustainable for long-term use. Reducing cement consumption and identifying sustainable, cost-effective alternatives to steel are critical for lowering construction’s ecological and economic burden. Bio-based supplementary cementitious materials (SCMs), such as rice husk ash (RHA), and natural plant fibers show promise, but prior studies have mostly tested them separately or with varying combinations, leaving the specific effect of fiber dosage at fixed SCM levels remain unclear. Therefore, this study addresses this gap by systematically investigating the effect of oil palm broom fiber (OPBF) content (0–5% by weight, in 0.5% increments) on the fresh and hardened properties of concrete containing a fixed 10% RHA replacement of cement. The physical, fresh and mechanical properties of OPBF were evaluated, and statistical analyses (ANOVA, Tukey’s HSD) were conducted to identify significant performance differences and determine the optimal fiber content. Experimental results indicate that increasing OPBF content reduced workability by up to 62.5% observed at 5% OPBF, while compressive and flexural strengths peaked at 2.5% (27.8 MPa) and 3.0% OPBF (5.8 MPa), respectively. The results go beyond previous efforts by providing the first systematic dataset on OPBF reinforced RHA–blended concrete performance, establishing optimum fiber dosages, and demonstrating the potential of agricultural residues to produce sustainable, performance-optimized concrete for low-load-bearing applications.