Investigating properties of low binder ultra-high performance concretes containing nano and/or micro silica

This thesis presents the effect of using binary and ternary blends of portland cement, nano silica (NS) and/or micro silica on the mechanical, transport and physical properties of low binder ultra-high performance concretes (UHPC). For this, two concrete groups were designed with and without 10% silica fume (SF) by weight of cement with a water/binder ratio of 0.20 and total binder of 800 kg/m3. Commercially available NS was used in partial substitution of cement at 0, 0.5, 1, 2 and 3% by weight. The results show that among different NS contents at 90 days, UHPC containing 2% NS exhibited the best results for the mechanical property tests. Additionally, UHPCs containing 3% NS exhibited better results for the transport property tests. The results also proved replacing NS with cement decreased both dry and autogenous shrinkage of UHPCs. Furthermore, the group samples of UHPC containing binary cementitious materials (NS and SF) gave better results than concretes containing only NS. The test results also demonstrated the effect of 8 kg/m3 of nano silica with 1% of replacement on the most investigated test properties were almost equal to 10% replacement of micro silica.