Mechanical characterisation of cement-based mortar incorporating rubber aggregates from recycled worn tyres

Cement-based materials are brittle and highly sensitive to cracking, particularly shrinkage cracking. It is well documented that a fibre reinforcement restrains crack opening and thus limits their detrimental effects on the durability and serviceability of structures. However, a better solution to limit brittleness and prevent shrinkage cracking is to design a cimentitious composite exhibiting a high level of deformation before macrocracks appear. The present paper focuses on this challenge. It is based on the use of low-deformation-modulus aggregates, actually rubber aggregates. The results given here concern mortars. A conventional mortar was compared with ones incorporating rubber tyre particles, partly replacing the natural sand aggregates. In all cases, the size of the particles was smaller than 4mm, and two ratios of sand replacement by rubber aggregates were considered: 20% and 30% by volume. The compressive and tensile properties of these cement composites were investigated. The first results show that incorporating rubber particles as aggregates is detrimental to compressive and to tensile strengths. On the other hand, it induces a significant decrease of the modulus of elasticity and is beneficial in terms of strain capacity. Tensile tests on notched specimens show that the pseudo-strain corresponding to the peak load is significantly increased and that the benefit of fibre reinforcement remains unaltered in the case of rubber incorporation. Thus, both fibre reinforcement and rubber incorporation benefits can be drawn simultaneously. It is a promising solution to improve the durability of cement-based structures. Finally, the use of rubber particles obtained from shredded non-reusable tires adds obvious environmental interest to this research programme. (C) 2004 Elsevier Ltd. All rights reserved.