Engineering properties of crumb rubber alkali-activated mortar reinforced with recycled steel fibres

Abstract

To mitigate the potential problems of waste tyres and Portland cement greenhouse gas emissions while further promote the sustainable development of construction industry, this paper, for the first time, explores the workability and mechanical properties of crumb rubber alkali-activated fly ash-slag mortar reinforced with recycled tyre steel fibre (RSFRAM) considering different contents of crumb rubber (CR, i.e. 5%, 10% and 15% replacement by volume of fine aggregate) and recycled tyre steel fibre (RTSF, i.e. 0.5% and 1.0% by volume). The results indicate that the inclusion of CR led to a 4.7%–26.7% improvement in workability of RSFRAM when the RTSF content was low, while the addition of RTSF compensated the strength loss caused by the addition of CR. The combination of CR and RTSF created a synergistic effect on the flexural behaviour of RSFRAM. The optimal mixture was regarded as R5F1.0 (5% CR replacement and 1.0 vol% RTSF) exhibiting comparable compressive strength, and superior flexural strength (around 171.1% higher), toughness indices (highest among all RSFRAMs) and residual strength factors (higher than 100) compared to the reference mixture without CR and RTSF. In addition, R5F1.0 can meet the strength requirement of concrete (i.e. 28 MPa for basic construction application) and thus suitable for structural applications as a sustainable material.