Macro- and micro- mechanisms associated with valorization of waste rubber in cement-based concrete and thermoplastic polymer composites: A critical review

An increasing number of automobile vehicles generates an enormous quantity of waste rubber tires, WRTs, at the end of their service life. When disposed of in landfills and dumpsites, the WRTs create several well-known health and geoenvironmental issues in the nearby vicinity, apart from occupying a lot of landfill space. To come out of these unwanted situations, one of the several pathways to utilize the waste rubber, WasRub, that is obtained after shredding of WRTs could be its utilization in cement-and polymer-composites as a filler. Though several re-searchers have investigated intricacies associated with rubberized concrete, to the authors' best knowledge, in-depth efforts have not been made to investigate the pros-and cons-of utilizing WasRub with cement and polymers (like HDPE, LDPE, LLDPE, etc.), to create composites. With this in view, a critical review of the studies conducted by earlier researchers, with a special focus on the parameters and the micro-mechanisms that control the overall characteristics of the end product, has been undertaken. Based on this exercise, it has been realized that WasRub has the potential to be used as a filler material, and its bulk utilization can be achieved, a philosophy that is in line with the vision of sustainable development goals, SDGs, and circular economy, CE. However, it should be noted that most of such studies are confined to the laboratory scale, and their scaling up has not materialized so far. The reasons behind this gap has been investigated and a brief account of the same has been presented in this paper.