Valorization of recycled steel wires from end-of-life tires as an alternative fiber reinforcement in geopolymer concrete to foster circularity : a review

Recycled tire steel fiber reinforced geopolymer concrete provides a sustainable and circular economy-based alternative to traditional steel fiber reinforced concrete, wherein steel wires derived from recycling of end-of-life tires are used as alternative fiber reinforcement, while cement is completely replaced with industrial wastes like fly ash and slag. This study presents the current state-of-knowledge on the engineering properties of recycled steel wires reinforced geopolymers wherein mechanical properties, rheology, durability, and microstructural investigations of recycled steel wires reinforced geopolymer composites were discussed and compared with industrial steel fibers reinforced geopolymers. A life cycle assessment was also performed to compare the environmental impacts of recycled steel wires reinforced geopolymers with steel and polypropylene fiber-reinforced geopolymers. The inclusion of recycled steel wires positively impacted the mechanical properties of geopolymer concrete, whereas rheology was adversely affected. Microstructural investigations indicated a compact geopolymer with strong fiber-matrix bond resulting from the presence of residual rubber on the fiber surface. There were a lot of discrepancies and limitations pertaining to durability in the literature. Life cycle assessment indicated a 40% reduction in greenhouse gas emissions of steel fiber and polypropylene fiber reinforced geopolymer by replacing them with recycled steel wires, indicating the sustainability and circular economy potential of recycled steel wires.