Effects of nanomaterials on hardening of cement-silica fume-fly ash-based ultra-high-strength concrete

In this paper, the flowability, compressive strength, hydration heat, porosity and calcium hydroxide content of cement-silica fume-fly ash-based ultra-high-strength concrete (UHSC) incorporating either nano-silica (SiO2) or nano-calcium carbonate (CaCO3) were investigated. Test results showed that the flowability of UHSC was reduced by incorporating nano-silica and nano-calcium carbonate. After incorporating nano-silica, the hydration heat flow of UHSC increased, and the hydration heat of UHSC increased at first but decreased later. For UHSC with nano-calcium carbonate, the hydration heat flow increased and the hydration heat decreased. With the increase of both nano-silica and nano-calcium carbonate content, the compressive strength of UHSC increased at first and then decreased. The porosity decreased at first and increased later with the increase of nano-silica and nano-calcium carbonate content. As regards the calcium hydroxide content, this decreased with the increase of nano-silica content, but increased with the increase of nano-calcium carbonate content.