investigating the compressive and tensile strength of concrete containing recycled aggregate with polypropylene fibers

In this research, recycled concrete aggregates were used instead of natural aggregates in concrete, and then the recycled concrete was reinforced with polypropylene fibers.the purpose of this study is to first investigate the effect of replacing recycled aggregates with natural aggregates on the mechanical resistance of concrete and then to investigate the effect of adding polypropylene and micro silica fibers on concrete containing natural and recycled aggregates in two water-to-cement ratios of 0.4 and 0.55. the results of this research show that by replacing recycled aggregates with natural aggregates, the compressive and tensile strengths of concrete have decreased significantly. also, the results show that the addition of polypropylene fibers with a weight ratio of 1.5% had a significant effect in compensating the reduction of compressive and tensile strengths in recycled concrete. it should be mentioned that the samples containing microsilica and polypropylene fibers in all mixing designs (natural and recycled aggregates) had higher resistance values (tension and pressure) than the samples without microsilica. also, concrete samples with a water-cement ratio of 0.4 had higher compressive strengths than concrete samples with a water-cement ratio of 0.55.