Novel uses of recycled rubber in civil applications

Waste tyres and their accumulation is a global environmental concern, as 1.5 billion of waste tyres are generated annually in the world. The products are not biodegradable and, if disposed of in landfills and stockpiles, are recognized for leaching toxic chemicals into the surrounding environment, acting as breeding grounds for mosquitoes, and fueling inextinguishable fires. The potential of using rubber from worn tyres in many civil engineering works has been studied for more than 30 years, and their application in construction materials comprises cementitious concrete, asphalts, and granulates for earth structures. Recycling of tyres in these field represents a suitable way of disposal for both environmental and economic reasons. Therefore, the aim of this review is to present the state of the art in tyre recycling in civil applications. In particular, the re-use of waste tyres in cement-based materials has been discussed, and then the recycling of waste tyres in bituminous mixtures and in geotechnical applications has been reviewed. This review is mainly focused on the physical properties of construction materials when recycled rubber is incorporated, trying to highlight the effects deriving from the interaction between rubber and these materials, and analyzing the proposed technological approaches from a material science perspective.