The effects of silica fume and nano-silica on the workability and mechanical properties of self-compacting concrete containing polypropylene fibers

Due to the widespread usage of self-compacting concrete and the need to reduce the level of cement and increase the strength of concrete, this study investigates the effects of silica fume, nano-silica and polypropylene fibers on self-compacting concrete. For this purpose, 23 mixes were made. In order to study the self-compacting properties of concrete, J-ring, V-funnel, slump flow and T50 tests were performed. Compressive, tensile and flexural strength tests were also performed on the hardened concrete at the age of 28 days. The experimental results showed that silica fume and nano-silica, in addition to reducing the workability of self-compacting concrete, increased its compressive, tensile and flexural strengths. Polypropylene fibers increased mechanical properties, especially tensile and flexural strengths. Also, with the simultaneous addition of silica fume, nano-silica and fibers, the mechanical properties of self-compacting concrete were doubled. In the mix with the highest compressive strength, the sample had 5% silica fume, 0.75% nano-silica and 1.5% fibers. The compressive strength of this mix design increased by 40% compared to the control mix. Also, the best mix in tensile and flexural strengths had 5% silica fume, 0.75% nano-silica and 1% fibers. tensile and flexural strengths of this mix design increased by 26% and 28% compared to the control mix, respectively.