Abstract
Many studies have recently been conducted to reduce the environmental influences of construction in industrial sectors. Recycling rubber as aggregate in concrete helps to reduce the environmental effects of waste automobile tires, and enhances the deformability of the concrete in structural applications such as slabs on grade and concrete pavements. This study aims at examining the reinforcement of rubberized concrete by a hybrid system of fibers comprising industrial steel fibers and steel fibers from waste tires. Six concrete mixtures with/without steel fibers were investigated, using 0, 20% and 40% by volume of waste tire rubber (WTR) particles as a substitute for natural aggregates. The fresh properties of these concrete mixes were evaluated using concrete slump and air content tests, as well as unit weight. Compressive and splitting tensile strengths at 7 and 28 days and flexural strength at 28 days were used to evaluate the hardened concrete properties. Concrete porosity and rapid chloride permeability tests were conducted to evaluate the concrete's permeability, and its volume stability was assessed by examining free-drying shrinkage and restrained shrinkage. The results showed that, although the mechanical properties of the concrete were negatively impacted when a portion of the crushed rock and sand aggregates were replaced by rubber particles, it was possible to produce rubberized concrete with comparable mechanical properties and durability to conventional concrete when 40 kg/m(3) of steel fibers was used in conjunction with 20% rubber. The flexural strain capacity and post-peak properties of the rubberized concrete containing 20% rubber and 40 kg/m3 steel fibers were substantially better than conventional concrete. In addition, the free drying shrinkage strain after 56 days for all mixes was low, below 457 micro-strain or 0.046%, and the presence of high quantities of rubber particles and/or steel fibers in the concrete ring specimens subjected to restrained shrinkage testing prevented the initiation and propagation of cracks. The outcome of this study highlights the potential of these combinations for use in concrete pavement and slab on grade applications.