**7. Conclusion**

Supplementary cementitious materials (SCMs) are increasingly used in the construction industry to develop mixes with superior mechanical properties and improved long-term performance (durability). Different types of SCMs are available in the global market including micro-silica, class C fly ash, class F fly ash, quartz flour, and blast furnace slag. SCMs are incorporated in mix designs in partial replacement of Portland cement, with percentages ranging from 10% up to 40%. SCMs are used in proprietary UHPC mixes as Ductal, Cemtec, CRC, and Cor-Tuf, with percentages ranging from 20–40%. In non-proprietary HPC mixes, SCMs would have similar percentages; however, final strength is reduced due to the absence of steel fibers. SCMs improves the concrete properties through three techniques: 1) increase the amount of binder resulting from the hydration process, which increases the concrete final strength, 2) react with calcium hydroxide, which stops the efflorescence phenomenon, and 3) increase the packing order (density) of the cement matrix, which reduces concrete permeability, and its susceptibility to environmental attacks, de-icing salt effect, and protect reinforcing steel against corrosion. The reduction of cement consumption, being partially replaced by SCMs, reduces the carbon footprint of the construction industry.

The advantages of SCMs are partially offset with challenges including the scarcity of specific types of SCMs in some parts of the world. Specific types of SCMs are expensive compared to cement. Also, a special mixing regimen is required to avoid losing mix-flowing ability. Currently, SCMs are successfully used in concrete mix designs for high-rise residential construction, precast/prestressed girder bridge construction, and in architecture applications. The continuous research in concrete mix development using alternative SCMs will result in increased market share in global construction markets.
