Functions and impacts of plastic/rubber wastes as eco-friendly aggregate in concrete - A review

About 6.5 billion tons of discarded plastic and rubber wastes are generated every year globally, and the disposal of these wastes poses a great threat to the environment due to their long period for degradation. Therefore, a direct recycling and reusing of these wastes as green construction material can potentially reduce the environmental burden. Considering plastic and rubber are both synthesized polymer materials containing similar basic elements with distinct structures, this paper aims to comparatively review the functions and impacts of plastic and rubber wastes used as eco-friendly aggregates on the fresh and hardened properties as well as the durability performance in mortar and concrete. The type and source of plastic and rubber wastes used as aggregate, as well as their effects in terms of aggregate size, replacement content, shape and treatment method are highlighted. In general, the presence of plastic aggregate decreases the workability of concrete, while the effect of rubber aggregate is mainly governed by the size and replacement content. Also, the smooth surface and low specific gravity of plastic/rubber aggregate compared to natural aggregate increased the pore structure which reduced the matrix density and mechanical strength. Nevertheless, chemical treatment of rubber aggregate was found to be an efficient and feasible method to compensate the mechanical strength loss of rubber incorporated concrete. Apart from improving ductility of concrete, one of the most promising characteristics of the plastic/rubber aggregate is the low thermal, acoustical and electrical conductivity and therefore these aggregates are excellent options for producing thermal and sound insulating concrete. (C) 2019 Elsevier Ltd. All rights reserved.