Microstructure of composite cements containing blast-furnace slag and silica nano-particles subjected to elevated thermally treatment temperature

This paper aims to study the effect of thermally treatment temperatures on composite cements containing nano-silica (NS) and blast-furnace slag (GBFS). The composite cements are composed of NS from 0, 1 and 4 mass% and GBFS from 0, 25, 50 and 65 mass%. The thermal resistance of composite cement pastes was studied after the specimens subjected to thermal treatment at 200, 400, 650, 850 and 950 degrees C, with rate of heating 5 degrees C/min for 2 h soaking time. The compressive strength, apparent density and total porosity of composite cement pastes were determined. Substitution of OPC with 25-50% GBFS in the presence of silica-nano-particles improves the fire resistance of composite cement pastes up to 650 degrees C. The relative compressive strength of unsuperplasticized mixes containing 25, 50 and 65 mass% GBFS (M25, M50 and M65 mixes) were 101.34-109.76%, 113.67-120.98%, 79.55-96.67%, 37.06-41.47% and 12.35-23.08%, whereas the relative compressive strength of superplasticized M25S, M50S and M65S mixes were 109.71-149.02%, 116.71-153.92%, 104.23-143.13%, 77.35-95.40% and 24.47-38.24% for samples thermally treated at 200, 400, 650, 850 and 950 degrees C. It can be concluded that superplasticized cement pastes made with 50 mass% in the presence of 4 mass% NS have higher thermal resistance up to 650 degrees C. (C) 2015 Elsevier Ltd. All rights reserved.