**3. Supplementary cementitious materials (SCMs) in concrete industry**

SCMs are increasingly used in concrete mix designs. Recently, binary and ternary concrete mixes are becoming the norm in heavy construction industries including the construction of bridges, tunnels, and culverts. Different types of SCMs are used according to the targeted characteristics of the developed mix. SCMs are available in granular shape with diameters ranging from nano-centimeters (as nano-silica) to a few millimeter diameter (as quartz flower). SCMs are used in partial replacement of cement. Cement weight up to 30% can be replaced by an equivalent volume of SCMs. Currently, different types of SCMs are available in the construction market including nano-silica, micro-silica, also known as silica fume, class C fly ash, class fly ash, quartz flour, blast furnace slag, and single and multi-walled carbon nanotubes. The characteristics of different SCMs, their impact on concrete mechanical properties, and their potential use are described in the following section.
