Effect of fiber size difference on acoustic and mechanical properties of natural fiber reinforced concrete containing oil palm mesocarp fiber

To mitigate environmental noise pollution, this study investigated the acoustic absorption and mechanical properties of concrete incorporating raw oil palm mesocarp fiber (OPMF). Fine and coarse OPMF fractions were evaluated as partial fine aggregate replacements at volume substitution levels of 0.0 to 10.0%. Acoustic performance was characterized across a frequency range of 50–5000 Hz using an impedance tube, while compressive, flexural, and splitting tensile strengths were determined per standard testing specifications. The incorporation of untreated OPMF significantly improved acoustic absorption, yielding sound absorption coefficients (SAC) of 0.003–0.43, sound absorption averages (SAA) of 0.087–0.14, and noise reduction coefficients (NRC) of 0.074–0.13, markedly outperforming plain concrete (SAC: 0.005–0.22, SAA: 0.06, NRC: 0.058). Mechanical properties exhibited dosage-dependent reductions relative to control: 12.48–44.89% for compressive strength, 2.34–18.07% for flexural strength, and 0.86–29.17% for splitting tensile strength. Notably, fine OPMF mixtures retained 28-day compressive strengths between 43.47 and 36.13 MPa across 2.0–10.0% loading, satisfying the minimum structural material strength thresholds specified by Eurocode 2 (C25/30–C30/37). Multi-Criteria Decision-Making (MCDM) evaluation via a Normalized Weighted Performance Index confirmed that 4% fiber loadings establish an optimal balance between acoustic attenuation and structural capacity. While full structural element design analysis was beyond the scope of this study, the findings demonstrate strong material-level feasibility for semi-structural and acoustic envelope applications.