Effect of coarse basalt aggregates on the properties of Ultra-high Performance Concrete (UHPC)

In the present research, Ultra-high Performance Concretes (UHPCs) applying coarse basalt aggregate with a maximum particle size of 16 mm are designed by using the particle packing theory and considering optimal powder proportion. The fluidity, shrinkage, strength of paste, and the compressive and tensile splitting strength of UHPC are investigated. The effect of coarse basalt aggregate size and resulting powder content change are evaluated. Furthermore, the mineral admixture effect, interaction between aggregate and steel fibre are analysed and discussed. The results show that the optimal proportion of powder is 5% of micro-silica and 20% of limestone powder by mass of the total powder. The coarse basalt aggregate has limited reducing effect on the mechanical strength of UHPC. The optimal powder content of about 800 kg/m3 and 700 kg/m3 is found for UHPC when the maximum basalt aggregate size is 8 mm and 16 mm, respectively. Furthermore, a distribution modulus q of 0.19 for the modified Andreasen and Andersen model is recommended for designing UHPC with coarse aggregates. The optimal powder contents are the same for UHPC without and with 2 vol% steel fibre, and longer fibre is suggested for UHPC with coarser aggregate.