How SCMs improve concrete durability – A fundamental view

Abstract

The influence of supplementary cementing materials (SCMs) on the hydration and durability of blended cement has been evaluated using chemical and physical principles. Similarities and differences between various SCMs has been considered while they have been grouped into categories as latent hydraulic or pozzolanic and sub-divided into siliceous, aluminous, carbonaceous etc. For instance has the important synergy between SCMs producing calcium aluminate hydrate and calcium carbonate been elucidated showing how maximizing water binding leads to reduced porosity and thereby increased strength by forming calcium monocarboaluminate hydrate. Similarly would any magnesium content in the carbonate lead to hydrotalcite formation in the presence of aluminates. The interaction of admixtures with SCMs, like plasticizers, and the use of accelerators to speed up hydration are also treated. The influence of SCMs on durability issues like chloride ingress, carbonation, alkali aggregate reactions, sulphate resistance and freeze-thaw resistance is discussed as well. The importance of not accelerating the durability exposure too much is stressed in order avoid creation of products from the SCMs that will not occur in practice. Generally speaking SCMs improve the resistance of blended cements to most degradation mechanisms at equal w/c, with the exception of carbonation that can be improved by reducing w/c.