The text book provides detailed information on the use of supplementary cementing materials (SCM), such as fly ash, slag, silica fume and natural pozzolans, in concrete. It presents the provenance of these materials and their chemical, physical, and mineralogical properties. By providing an understanding of the chemical reactions involving these materials and the resulting changes in the microstructure of the concrete, the book explains how SCM's influence the mechanical properties of concrete and can improve its durability in aggressive environments. It includes a number of case histories where SCMs have been used in important concrete structures.