Mechanical Properties of Green Concrete Containing Polypropylene Plastic Waste

Plastic aggregate concrete (PAC) can result in reducing natural resource extraction while reducing the cost and energy consumption of the plastic recycling process. According to previous studies, polypropylene is the plastic type, having the highest demand but the lowest recycling percentage. Therefore, this study investigates the performance of incorporation of recycled polypropylene (PP) waste plastic as a partial replacement of natural coarse aggregate (NCA) in normal-strength concrete. This study aims to evaluate the fresh and hardened properties of PAC including workability, fresh density, compressive strength, hardened density, and splitting tensile strength. The experimental work consists of varying percentages of PP aggregate (PPA) as volumetric replacement levels of 0%, 10%, 20%, and 30% of the NCA. The results revealed that the workability and strength properties of concrete were negatively affected by PPA incorporation, while a positive impact of 2%, 5%, and 7.5% reduction in concrete density was achieved with 10%, 20%, and 30% PP content, respectively. The microstructural analysis was carried out to authenticate the strength reduction in PAC. It clearly showed that the Interfacial transition zone (ITZ) between PPA and cement paste was weaker than that of NCA. The enhancement of workability in PAC was possible with the addition of a high-range water-reducing superplasticizer (Plastobuild ES), whereas minor strength reduction was observed with the increasing admixture dosage levels. However, the concrete mix design satisfied the expected compressive strength limits of normal strength structural concrete up to 30% PP replacement level. Thus, it is suggested to use PPA up to 30% for structural concrete with further inspection of the influences of the various types of admixtures on the performance of PAC, structural performance, and durability properties.