Contents lists available at ScienceDirect Resources, Conservation & Recycling journal homepage: www.elsevier.com/locate/resconrec Review Recycling waste rubber tyres in construction materials and associated environmental considerations: A review Abbas Mohajerani a, *, Lucas Burnett a , John V. Smith a , Stefan Markovski a , Glen Rodwell a , Md Tareq Rahman a , Halenur Kurmus a , Mehdi Mirzababaei b , Arul Arulrajah c , Suksun Horpibulsuk d , Farshid Maghool c a School of Engineering, RMIT University, Melbourne, Australia b School of Engineering and Technology, CQUniversity, Melbourne, Australia c Department of Civil and Construction Engineering, Swinburne University of Technology, Victoria, Australia d School of Civil Engineering and Center of Excellence in Innovation for Sustainable Infrastructure Development, Suranaree University of Technology, Nakhon Ratchasima, Thailand ARTICLE INFO Keywords: Recycling Waste rubber Rubber tyres Construction materials Environmental sustainability Leachate ABSTRACT Waste tyres and their accumulation is a global environmental concern; they are not biodegradable, and, globally, an estimated 1.5 billion are generated annually. Waste tyres in landfill and stockpiles are renowned for leaching toxic chemicals into the surrounding environment, acting as breeding grounds for mosquitoes, and fuelling inextinguishable fires. The properties of waste tyre rubber and engineering applications have been previously reported in a range of publications with respect to the environmental, economic, and technical factors. This study compiles and reviews this research with a focus on geotechnical engineering applications, such as earthworks and infrastructure construction. The applications of waste rubber in construction materials includes cementitious concrete, asphalt concrete, and granular materials for earth structures. Crumb rubber, when used as a sand replacement in flowable concrete fill, improved ductility and strength-to-weight ratio. A 40 MPa concrete mix with 0.6% rubber crumb content exhibited optimal strength and air entrainment capabilities, displaying minimal damage after 56 freeze/thaw cycles. Rubber, as a partial replacement for aggregate in road base and sub-base layers, adversely affected the California Bearing Ratio (CBR) of the graded aggregate base course. Rubber-soil mixtures as the interface of foundation and structure yielded a 60–70 % reduction in vertical and horizontal ground accelerations when subjected to earthquake simulation modelling. There is concern re- garding the toxicity of waste rubber incorporated products due to leachates of heavy metals and other chemicals common in tyres. Further comprehensive studies in this area are needed. Leachate studies should be conducted under different pH and liquid to solid ratios. 1. Introduction It is estimated that the annual generation of waste tyres amounts to 1.5 billion whole-tyres worldwide (Mashiri et al., 2015); contributing to the huge number of tyres already found in landfill and stockpiles. In Australia, approximately 51 million tyres are disposed of annually (Mountjoy et al., 2015), and this is likely to increase proportionally with the present population expansion. Demographic statistics de- monstrate a population increase of 989.5 million people from 2015 to 2017, a 4.16% increase, suggesting, if tyred-vehicle use per capital remains unchanged, a similar growth in annual waste tyre production (AUSSTATS, 2020; ABS 2014). The growing abundance of waste tyres and lack of coordinated processing or recycling framework presents a growing concern for the management of this material. Due to recent global recognition and strong environmental aware- ness, many authorities have imposed strict rules and regulations re- garding this waste product to prevent excessive stockpiles and landfill operations. With these sanctions in place, researchers have been pre- sented with an opportunity to explore sustainable measures and alter- native uses for waste tyres. The potential for use in civil engineering has been investigated for over 30 years (Oikonomou and Mavridou, 2009), with some sources even suggesting its usage dating back as early as the 19th century, when automobiles were first invented (Shu and Huang, 2014). Diminishing natural resources that are consumed by the https://doi.org/10.1016/j.resconrec.2020.104679 Received 4 August 2019; Received in revised form 31 December 2019; Accepted 1 January 2020 ⁎ Corresponding author. E-mail address: abbas.mohajerani@rmit.edu.au (A. Mohajerani). Resources, Conservation & Recycling 155 (2020) 104679 0921-3449/ © 2020 Elsevier B.V. All rights reserved. T