Effect of silica fume and limestone powder on mechanical properties of ultra-high performance concrete

Abstract

This research aimed to study the effect of Portland cement replacement with silica fume and limestone powder in Ultra High Performance Concrete (UHPC). Nine mix proportions were designed with a constant amount of binder at 1200 kg per cubic meter of concrete. In these mixes, the cement was replaced with silica fume at 10%, 15% and 20% and limestone powder at 15% and 30% by weight of binder. For all mixes, the ratio of water to binder (W/B) and the steel fiber volume fraction were 0.2 and 2% respectively. After the preparation of test specimens and stream curing for 3 days, compressive strength, flexural strength, and length change due to shrinkage of the UHPC mixes were examined. The results showed that the silica fume increases the compressive and flexural strength (at the first peak load) but the limestone decreases. Without the limestone, the 20% silica fume mix provides the maximum average residual strength. However, when either 15% or 30% limestone is admixed, the optimum residual strength occurs at the 15% silica fume. Moreover, it is worth noting that the reducing amount of cement by replacing either with silica fume or limestone powder effectively reduces the shrinkage.