Experimental Analysis of Thermal Conductivity and Volumetric Heat Capacity in Concrete Incorporating HDPE Waste Plastic Powder as a Function of Temperature

The objective of this study is to comprehensively investigate the influence of incorporating high-density polyethylene (HDPE) waste plastic on the thermophysical properties of ordinary concrete, by partially replacing sand with HDPE plastic powder. The samples (cement, sand, HDPE, and concrete) were characterized using advanced analytical techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray fluorescence (XRF). These analyses confirmed that the incorporation of HDPE powder does not induce significant alterations in the internal microstructure of the composite material. Thermophysical properties were measured using a CT-Meter for various plastic powder substitution rates (5–30% by weight) and at different temperatures (25°C, 30°C, 40°C, and 50°C) in a thermoregulated box. The results demonstrated a progressive decrease in thermal conductivity and thermal diffusivity with increasing HDPE content. Furthermore, the volumetric heat capacity increased as 5% of the plastic powder was added, then decreased. This phenomenon was observed for all the temperatures analysed, except 25°C. Moreover, the incorporation of plastic waste into the concrete significantly altered its thermophysical properties, leading to a reduction in thermal performance.