Rendering mortars with crumb rubber: Mechanical strength, thermal and fire properties and durability behaviour

Abstract

The difficulties related to waste tire disposal encourage the use of crumb rubber in civil construction as a component of cement composites. In this study, crumb rubber is evaluated as a partial replacement of the aggregate in rendering mortars, in quantities of 0%, 2%, 4% and 6%, using a systemic approach. A wide range of characteristics were analyzed, related to the fresh and hardened mortar, thermal and fire properties, along with the durability of the composites used as rendering mortar. Crumb rubber mortars require a higher water content to achieve the same workability of the control mixture, decrease the bulk density and increase the water retention and air content of the mortar. The flexural strength is maintained for hardened mortars with up to 4% crumb rubber, the compressive strength and dynamic modulus of elasticity are maintained only up to 2% rubber, with the decrease of these properties at higher contents of the residue. Generally, water absorption raises with the increment of rubber, but capillary water absorption decreases. The mortars do not propagate flame and they are non-combustible. The addition of crumb rubber leads to a reduction in thermal conductivity of up to 32% for the mortar with 6% of crumb rubber, which enhances their behaviour as a thermal insulator. The durability of rendering mortars with crumb rubber is increased, reducing cracking and maintaining their tensile bond strength at the same level of the reference mortar, even after thermal cycles of accelerated aging. The rendering mortars with 2% and 4% of crumb rubber content presented the best set of properties related to deformation capacity, thermal insulation and lower cracking, with tensile bond strength above the minimum required at standards.