The synergistic effect of recycled steel fibers and rubber aggregates from waste tires on the basic properties, drying shrinkage, and pore structures of cement concrete

Waste tires can be recycled to obtain rubber particles and recycled steel fibers, the two could be used in cement concrete as aggregate and reinforcement, respectively. However, the synergistic effect of these two components on the basic properties of concrete materials still needs to be clarified. In this study, the rubber aggregate treated with different modification solutions was used to replace the fine aggregate in ordinary concrete, and the waste tire steel fiber reinforced rubber concrete specimens were prepared to investigate the workability, mechanical properties, drying shrinkage characteristics, and pore structures. The results showed that the reduced workability caused by the addition of rubber and steel fiber in fresh concrete mixtures was refined after the modification treatment of waste tire rubber aggregate, with a slump increase about 3.4 cm at a 15 % rubber content. The compressive strength, splitting tensile strength, flexural strength, and ultrasonic velocity of the specimens modified with Polyvinyl alcohol (PVA) solution were higher than that of the unmodified specimens, at 15 % rubber aggregate content, with an increase of 5.8 % in compressive strength, 7.9 % in splitting tensile strength, and 4.0 % in flexural strength. In addition, the modified waste tire rubber had an enhancement effect on the drying shrinkage properties along with the recycled steel fibers, which can further inhibit the initiation of cracks in the cement matrix. The modified waste tire rubber aggregate also effectively optimized the microstructure and size distribution of pores in concrete matrix. Therefore, the reasonable use of waste tire rubber and recycled steel fibers in cement concrete materials can not only achieve the full-component utilization of waste tires considering the economic and environmental benefit, but also synergistically enhance the basic properties of cement concrete.