Influence of the water/cement ratio (w/c) on the mechanical properties of rubberized cementitious composites

The recycling of waste tire rubber is characterized by the lack of proper techniques due to its cross-linked and complex chemical nature. Rubber has a slow rate of degradation due to its cross-linked structure. This causes environmental pollution and health risks (zika, dengue and chikungunya). One way of recycling waste tires is their crushing, generating crumbs and rubber powder, which can later be inserted with or without prior treatment into polymeric or cementitious matrices as recycled aggregate. Rubber as recycled aggregate can add to cement-based mixtures new properties derived from it, such as improving ductility, damping ratio and energy dissipation within the mixture. This work aims to study the influence of the water/cement ratio on the mechanical properties of cementitious composites with 15% tire rubber powder, through volumetric replacements by fine aggregate. Three w/c ratios were applied for the rubber and control mixtures, 0.52, 0.48 and 0.44. In case of conventional mortar, the compressive strength tends to increase with the reduction of the amount of water in the mixture due to the greater amount of cement to be added and greater packing of hydrated particles. The control mixture with a/ c = 0.44 achieved an average strength 8.6% greater than that of a/c = 0.52. On the other hand, in case of rubberized mortar, by decreasing the w/c ratio in the presence of hydrophobic rubber, water does not easily migrate into the mixture, having as an obstacle the rubber particles, which, in turn, end up covering the anhydrous cement grains, decreasing the resistance. In addition to the ductile nature of rubber itself, which behaves as a void within the mixture nor transferring the load from one point to another, leading to faster cracking. The mixture "0.52 with rubber" is highlighted for achieving greater compressive strength, when compared to its category of rubberized mortar studied in this work, and also for presenting a drop in the dynamic modulus of elasticity by 48% compared to the respective mixture of control "0.52 without rubber". Thus, the mixture "0.52 with rubber" was considered the most resistant in terms of mechanical behavior. Copyright (C) 2022 Elsevier Ltd. All rights reserved.