Effects of air encapsulated with waste plastic straws in cement matrix on thermal insulation performance: sustainable and energy-efficient foam concrete production

Abstract

In this study, the effects of incorporating recycled polypropylene-based straws into a cement matrix in the form of foam concrete on thermal insulation performance, mechanical strength, and environmental durability were investigated. Within the experimental program, nine different plastic-reinforced mixtures and a reference mixture were prepared using three different straw lengths (0.5 cm, 1.0 cm, and 2.0 cm) and three different volume ratios (0.5%, 1.0%, and 2.0%). Density, compressive strength, thermal conductivity, water absorption rate, apparent porosity, mass loss in sulfate and acidic environments, and durability following exposure to high temperatures were used to evaluate the properties of both fresh and hardened concrete. Besides, SEM imaging was conducted to analyze the microstructure. The findings indicated that the best balance performance was obtained in the 10WS series (with 1.0 cm-long straw at a ratio of 1%). The mixture had a porosity of 6.46% and a compressive strength of 22.67 MPa. Furthermore, thermal conductivity decreased by up to 30% compared to the reference mixture. The addition of plastic straws was found to have limiting effects on environmental durability; specifically, the 20WS series experienced mass loss exceeding 5% in environments containing sulfate. In conclusion, the re-use of waste plastic straws as construction materials offers thermal insulation advantages; however, it may have adverse effects on mechanical and environmental performance if the optimal content and sizing are not achieved. This study presents significant findings on the controlled use of waste plastics in the sustainable development of materials.