Mechanical properties and pore structure of recycled aggregate concrete made with iron ore tailings and polypropylene fibers

The purpose of this study was to assess the performance of introducing polypropylene (PP) fibers into recycled aggregate concrete containing iron ore tailings (TRAC). Thus, we prepared four different concretes, including natural aggregate concrete (NAC), recycled aggregate concrete (RAC), TRAC and fiber-reinforced tailings recycled aggregate concrete (TRAC-PP) series. PP fibers were used as supplementary material at different percentages (0.3%, 0.6%, 0.9% and 1.2%) and compared with NAC, RAC and TRAC. The cubic compressive strength, axial compressive strength and splitting tensile strength were analysed. The digital image correlation technique was used to monitor the strain development of concrete under compressive loading. Besides, the nuclear magnetic resonance technique was applied to evaluate the pore structure. The testing results showed that the use of recycled coarse aggregate (RCA) led to the reduction of strength of concrete, but this strength loss can be compensated by adding iron ore tailings (IOTs) to concrete. The addition of PP fibers to TRAC was significantly in the splitting tensile strength, but not obvious in the compressive strength when the supplementary percentage of PP fibers was lower than 0.6%. The failure pattern of TRAC-PP1.2 was relatively ductile and its cracks were relatively tortuous and fine. RAC had the highest total pore contents. Addition with IOTs and PP fibers to RAC significantly decreased the total pore contents. Recycling of RCA and IOTs would reduce the environmental impact and economic cost. Finally, the concrete with 30% RCA, 30% IOTs and 0.6% PP fibers can be considered as the most appropriate concrete.