Long term durability performance and mechanical properties of high performance concretes with combined use of supplementary cementing materials

Supplementary cementing materials (SCMs) contribute to the hydration of Portland cement by physical phenomena (e.g. nucleation effect) or by chemical reactions (e.g. pozzolanic activity). The partial substitution of Portland cement with SCMs can significantly reduce the CO2 emission during the production of concrete and, therefore, can make concrete a more sustainable and environmental-friendly material. Durability of concrete is considerably improved by the incorporation of SCMs. Due to the pozzolanic activity and the filling effect, use of SCMs can result high performance concrete having both enhanced mechanical characteristics and reduced permeability that leads to improved durability. Combined use of SCMs of ternary composition of SiO2-Al2O3-CaO (e.g. blastfurnace slag and fly ash) can lead to extraordinarily favourable durability performance of concretes at even large cement substitution ratios, however, very few experimental data exist on the combined use of silica dominated and alumino-silicate dominated SCMs (e.g. silica fume combined with metakaolin) at increased cement substitution ratios. Most important aim of the present research was to reveal if there is any advantage of the combined use of silica fume and metakaolin.