Recycled polypropylene-based waste as fine aggregate in cement-based composites: Engineering and microstructural properties

Abstract

Repurposing plastic-based waste materials offers a promising solution to reduce the consumption of natural resources in construction and mitigate environmental risks. This study explored the potential use of polypropylene-based fine aggregate derived from the crushing of waste chairs as a substitute for natural sand in cement-based composites. A series of physical mechanical and microstructural investigations were conducted on specimens where natural sand was partially replaced with polypropylene-based waste chair (PpWC) sand up to 100 %. Besides a sensitive statistical analysis was performed by establishing a relationship between the experimental results and constructing a Pearson correlation matrix to identify the effect of variables on the measured properties. The test results revealed that increasing the PpWC sand content resulted in lighter mixtures and reduced flowability. Additionally a corresponding increase in both water absorption and void content was observed. The incorporation of PpWC sand into the cement-based composites negatively affected its strength properties. Complete replacement of natural sand with PpWC sand reduced the ultrasonic pulse velocity and thermal conductivity values by approximately 50 % and 80 % respectively resulting in a cement-based composite with enhanced acoustic and thermal insulation properties. SEM analyses revealed that higher PpWC sand content led to more porous less dense and cracked interfacial transition zones which negatively affected the mechanical properties of the composites. Despite its relatively low strength performance PpWC demonstrates significant potential for use in cement-based composites for construction applications primarily due to its favorable unit weight and superior acoustic and thermal insulation properties. © 2025 Elsevier B.V. All rights reserved.