Abstract
•Composite cement paste containing 25–50mass% GBFS gives higher compressive strength.•The compressive strength increases with thermally treated OPC-NS cement pastes up to 400°C.•25–50% GBFS in the presence of silica-nanoparticles improve the fire resistance up to 650°C.•SEM shows a massive nanocrystalline C–S–H deposits without micro-cracks at 650°C.•The total porosity of M25S and M50S mixes has lower values of total porosity up to 950°C.
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 4mass% and GBFS from 0, 25, 50 and 65mass%. The thermal resistance of composite cement pastes was studied after the specimens subjected to thermal treatment at 200, 400, 650, 850 and 950°C, with rate of heating 5°C/min for 2h 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°C. The relative compressive strength of unsuperplasticized mixes containing 25, 50 and 65mass% 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°C. It can be concluded that superplasticized cement pastes made with 50mass% in the presence of 4mass% NS have higher thermal resistance up to 650°C.