Compressive Strength Analysis of 20,5 MPa Concrete with Polyethylene Terephthalate (PET) Plastic and Palm Kernel Shell

Concrete production relies heavily on natural aggregates, and their continuous extraction contributes to environmental degradation. Recent research has increasingly focused on the integration of waste materials into concrete mixtures as a means of enhancing sustainability while maintaining acceptable mechanical performance. This study investigates the partial replacement of fine aggregate with polyethylene terephthalate (PET) plastic waste and coarse aggregate with palm kernel shell (PKS), aiming to evaluate their combined influence on the compressive strength of 20.5 MPa design concrete. PET was substituted at 0%, 1%, and 2% of the fine aggregate mass, while PKS was used at 0%, 10%, and 20% of the coarse aggregate mass, resulting in three mix variations (0%-0%, 1%-10%, and 2%-20%). Compressive strength tests were performed on cylindrical specimens at curing ages of 7, 14, and 28 days. The results revealed that increasing PET and PKS content led to a decline in compressive strength due to weakened interfacial bonding and higher porosity. Although the mixed waste substitutions did not meet the target design strength, limited substitution levels show potential for sustainable non-structural concrete applications. These findings highlight the importance of optimizing PET and PKS proportions to balance mechanical properties with environmental benefits.