Potential Use of Plastic Wastes for Low Thermal Conductivity Concrete

The use of plastics has increased over the years, thus resulting in a large volume of plastic waste being generated and accumulated in the environment. Due to its non-biodegradability and persistence, recycling processes have become one of the sustainable solutions for preventing environmental deterioration. Plastic wastes, including high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP), and polyethylene terephthalate (PET), were collected from industrial sector and used as additional ingredients to improve concrete properties. Prior to concrete processing, an increase in wettability of plastic fibers using nonionic surfactant, Dehydol LS-12, was investigated. At the optimal concentration of 10 times of the critical micelle concentration (CMC), an interfacial tension and a contact angle were reduced to 31⁻32 mN/m and 65°⁻68°, respectively. Properties of concrete were determined and compared to those of the mortar samples. Porosity was found to increase with higher volume fraction of plastic fibers, whereas decreases in workability, bulk density, thermal conductivity, splitting tensile strength, and compressive strength were encountered. The lowest thermal conductivity was recorded for concrete samples prepared with 30% by volume of LDPE fibers, and the rest in descending order were HDPE, PP, and PET, respectively. Furthermore, the maximal inclusions of plastic fibers were 5% for HDPE and LDPE, 10% for PP, and 50% for PET so as to satisfy the precast concrete wall requirements.