3 - Supplementary cementing materials

Abstract

Supplementary cementing materials (SCMs) exhibit pozzolanic and/or cementitious properties and are used in concrete to partially replace the Portland cement component. SCMs differ in source, physical properties, and chemical composition. This chapter discusses four types of SCMs, namely, (1) fly ash, a by-product from coal combustion, (2) slag cement, a by-product of the steel industry, (3) silica fume, a by-product from elemental silicon production, and (4) metakaolin, produced from the calcination of kaolinite clay. Part of the motivation to incorporate SCMs in concrete stems from their potential to reduce greenhouse gas emissions, energy use, and waste disposal to landfill sites. Beyond the environmental benefits, the use of SCMs as a partial cement replacement can achieve similar or improved fresh, mechanical, and transport properties compared to concrete without SCMs. Concrete containing fly ash, slag cement, silica fume, or metakaolin can improve the resistance to chloride ingress, alkali–silica reaction, freeze–thaw damage, and sulfate attack, compared to concrete without SCMs. However, concrete containing SCMs are typically more vulnerable to carbonation processes and can exhibit greater de-icer salt scaling mass loss than concrete without SCMs.