Chemically treated plastic aggregates for eco-friendly cement mortars

The use of waste plastic as aggregate in cement composites can solve the problem of the disposal of waste plastics in a sustainable way, and it reduces the need for extracting traditional materials like sand and gravel, which causes erosion and environmental degradation. The reaction of plastics with certain oxidizing chemicals is believed to result in chemical or electrostatic bonding between the plastic surface and the cement matrix. The present study investigates the effect of pre-treating plastic aggregates (with sodium hydroxide and sodium hypochlorite) on certain engineering properties of cement mortars. Five types of recycled plastics are used as partial sand replacements. Two replacement levels (5 and 15% by volume of sand) and two methods of chemical treatment are investigated. The results showed a decline in the properties of mortars made with chemically treated plastic aggregates: the addition of treated plastic aggregates makes the matrix porous, thereby degrading the mechanical properties. This behaviour intensifies with increasing plastic dosage. The polyoxymethylene (POM) and acrylonitrile butadiene styrene (ABS) plastic mortars performed best, while the polyethylene terephthalate (PET) mortars achieved poor results. Water-rinsing the treated aggregates removed reactive species from the plastic surface, and neutralized the matrix alkalinity resulting in comparatively less porous structures.