Mineral admixtures are those admixtures which are obtain from industries. Mostly mineral admixtures are residue of some industries and are used to replace cement and make concrete cheaper. These waste products are used as mineral admixtures so that maximum utilization of wastes is possible. Some waste products also increase workability (ease of handling) of concrete. Mineral admixtures not only reduce cement costs, but also enhance serviceability/durability of concrete.
When more cement will be used in concrete than due to high early heat of hydration, there is a possibility of thermal cracking inside the concrete, but with the use of mineral admixtures probability of thermal cracking can be reduced by reducing heat of hydration.
There are many waste products that can be used as mineral admixtures. Classifications that are most commonly and widely used in the world. These are:
- Pozzolanic materials
- Fly ash
- Silica fume
- Cement containing materials(slag)
Fly ash is the cheapest mineral admixture. By using this more amount of cement would be replaced and concrete becomes economical. Silica fume is costly than cement, so it is used only where it is easily available. If special arrangement will be make than silica fume become more expansive due to which concrete cost rises to peak. Slag is comparable to cement.
Pozzolanic materials are rich in amount of aluminosilicate; these are the highly reactive materials which are obtained from industries. Pozzolanic materials are mostly used for the construction of hydraulic structures like Golden Gate Bridge….
As pozzolans are mostly contains fly ash and silica fume. So as fly ash is cheaper than silica fume, therefore mostly when there is need of these materials than mostly fly ash is used, due of easy availability and even not costly too.
Fly ash also not takes fire, because it is non-combustible as it is obtained from the remains of burn coal in power plants. Silica fume is costly and also not easily available compare to fly ash. It is also a byproduct, which is clear from its name i. e silicon and some other fumes.
Cement containing materials (slag)
Slag price is comparable to cement. When slag is using as a replacement than this mean slag is not saving any money. Slag is also a byproduct, which is obtained from iron ores. It has small grains of silica, lime and alumina. Slag has little effect on properties of concrete as compare to Pozzolanic materials.