Microwave radiation treatment to improve the strength of recycled plastic aggregate concrete

Abstract

In this study, microwave radiation pre-treatment (MRP) of three recycled plastic aggregates, namely; Polyethylene Terephthalate (PET), High-Density Polyethylene (HDPE) and Polypropylene (PP), was carried out to enhance the bond strength between the plastic aggregates and the concrete matrix. Five concrete mixes were prepared, which included treated and untreated PET plastic aggregate, treated and untreated mixed plastic type aggregates and a control mix without any plastic. The replacement was 15% by volume as a partial replacement of coarse aggregate for all mixes. The modification of plastic surface was assessed before and after the microwave treatment by measuring the contact angle of a water droplet and using SEM images. The engineering characterizations of the concrete incorporating microwave treated recycled plastic aggregates were assessed through investigating physical and mechanical properties as well as water absorption. The results demonstrated that the Interfacial Transition Zone (ITZ) was improved due to PET plastic surface treatment, leading to an improvement in the strength of concrete. No improvement was seen in the strength of concrete that included treated mixed plastic types. Scanning electron microscopy (SEM) images of the treated plastic surface illustrated more roughness in the treated PET plastic surface, while the images of ITZ showed an improvement in the adhesion between the plastic and the cement paste. Despite the unexpected results of the treated mixed recycled plastic, the positive strength results of the concrete containing treated PET indicated that there is a potential for microwave treatment to be used as a method to induce surface modification.