Hemp shives vs. plastic waste vs. polypropylene fibers in perlite concrete: An experimental comparative study of mechanical performance

The replacement of conventional aggregate in concrete with alternative and waste-based materials has attracted increasing attention due to growing sustainability and waste management concerns. In this study, the combined effects of natural perlite aggregate replacement and fiber reinforcement on the mechanical and microstructural performance of concrete were experimentally investigated. Accordingly, natural perlite aggregate was used to replace conventional stone aggregate at replacement levels of 0%, 30%, 70%, and 100%. In addition, hemp shives and recycled plastic waste, together with commercially available polypropylene (PP) fibers were incorporated at volume fractions of 0.0%, 0.5%, 1.0%, and 1.5% to evaluate the effects of perlite aggregate replacement and fiber reinforcement on the mechanical performance of concrete. After 28 days of curing, compressive strength, elastic modulus, flexural strength, splitting tensile strength, ultrasonic pulse velocity (UPV), stress-strain behavior and scanning electron microscopy (SEM) analyses were conducted. The results showed that compared with the reference mix, 30% fine perlite replacement increased compressive strength and elastic modulus by ∼6.67% and ∼4.08%, respectively, whereas higher replacement levels (70% and 100%) led to strength reductions of ∼3.51% and ∼9.71% due to the porous structure of perlite and the formation of a weaker interfacial transition zone (ITZ). The optimum ratio for fiber reinforcements was 1.0%, and in terms of fiber type, the highest performance in crack bridging and energy absorption was observed in the PP-fiber-reinforced samples. At higher fiber contents, particularly 1.5%, performance losses were observed due to reduced workability, increased void formation, and the resulting deterioration in matrix continuity. Damage images revealed that, with PP fiber use, a widespread crack pattern containing numerous hairline cracks replaced single and wide cracks. Overall, the findings indicate that using natural perlite aggregate at a 30% replacement level in combination with 1.0% PP fiber reinforcement provides an effective and practical solution for producing low-carbon concrete with balanced mechanical performance. © 2026 Elsevier Ltd.