There are alternative materials that can supplement clinker without compromising the performance of cement as a construction material. These materials have inherent cementitious qualities and are classified into two types: mineral additions and supplementary cementitious materials. The advantage of using these alternatives to clinker is that it reduces the amount of clinker produced, with consequent savings in raw materials, electricity, fuel, and emissions. Cements using these materials are called blended cements.
Mineral additions such as ground limestone can be added in small amounts at the final grinding stage of cement manufacturing.
Supplementary cementitious materials include fly ash (from coal-burning power stations), ground granulated blast-furnace slag (from the steel industry) and silica fume. The use of SCMs reduces the quantity of clinker or cement required. They are added to cement either at the grinding stage or by blending with cement after grinding; or can be added during concrete batching to supplement the cement. Because of differences in chemistry, SCMs affect the performance of cement in concrete to suit different applications.
The use of SCMs allows the industry to maintain the performance expected of cement while reducing the amount of clinker required in cement. As a result, this reduces the emissions of greenhouse gases, a key measure in the industry of environmental performance.