Thermomechanical Behavior of Phosphogypsum Composites Reinforced with Olive and Eucalyptus Wood Chips

This study explores the development of sustainable composite materials based on phosphogypsum (PG), an abundant industrial by-product, reinforced with olive and eucalyptus wood chips. The objective is to valorize waste streams while enhancing the mechanical, thermal, and acoustic performance of the base material for eco-efficient construction applications. Composites were prepared with fiber contents of 5%, 10%, 15%, and 20% and evaluated through standardized experimental tests. Mechanical behavior was assessed via three-point bending tests, revealing a 26% improvement in flexural strength at 15% eucalyptus content. Water absorption increased with fiber content but remained lower in eucalyptus-reinforced composites due to better fiber–matrix cohesion. Thermal conductivity decreased significantly from 5% to 20% fiber content, reaching 0.60 W/m·K at 20% eucalyptus content, indicating enhanced insulation potential. Acoustic tests, performed using an impedance tube in accordance with ISO 10534-2, showed strong frequency-dependent absorption. The 20% olive composite achieved a peak absorption coefficient of 0.78 and an NRC of 0.68, demonstrating excellent sound-damping characteristics. This work introduces a novel integration of two underutilized Mediterranean biomasses into PG matrices and highlights their multifunctional benefits. The resulting composites offer a low-cost, low-carbon solution for thermally and acoustically optimized building components, advancing circular economy principles in the construction sector.