The effect of nanosilica on the mechanical properties of cementitious composites containing polypropylene fibers

The purpose of this study is to investigate the effects of adding nanosilica and microsilica on the mechanical properties of cementitious composites containing polypropylene fibers. For this purpose, 13 composite mixes with the water to cement ratio of 0.28 were considered. One mix without microsilica and nanosilica, 4 mixtures with 0.5%, 1%, 3% and 5% nanosilica replacement levels, 4 mixes with 5%, 7%, 10%, 15% of microsilica, and 4 mixtures with the combination of microsilica and nanosilica were investigated. According to the results of the experiments, the composite samples containing microsilica and nanosilica had better results than the samples containing only one of these particles. In fact, the results of 28-day tests showed that the combination of 10% microsilica and 1% nanosilica produced the best cementitious composite according to compressive, tensile and flexural tests.The compressive strength was 61.32 MPa, which was 44.69 percent higher than the control mix, the tensile strength was 4.319 MPa with 34.88 percent improvement, and the flexural strength was 6.971 MPa with 30.37 percent improvement from the control mix. Using more than 3 percent of microsilica had negative effects in all circumstances comparing to the control mix. For example, the ones containing 5 percent of nanosilica and without microsilica had the compressive strength of 37.41 MPa, which was 11.72 percent lower than the control mix.