Blended cement is obtained by mixing OPC with mineral admixtures or additives like fly ash, slag or silica fumes. Blended cements are now being considered superior as compared to conventional OPC category of cements.
Advantages of Blended Cement
The advantages of using blended cement can be broadly be divided in two categories i.e.
Technical advantages and
1. Technical Advantages
It reduces water demand and therefore water-cement ratio can be reduced.
It improves workability for the same water content.
The blended cements are finer as compared to OPC, therefore the permeability of concrete is less. This results into improved durability.
2. Environmental Advantages
Energy saving: Blended cements are obtained by adding mineral admixtures with OPC. The energy, which would have otherwise been utilized for production of OPC, is thus saved. This saving is to the tune of 0.8 to 1.2 MWH/ton of cement.
Conservation of natural resources: The used mineral admixtures are the waste products of thermal and steel plants. By using these products, we are conserving the precious minerals like lime stone, clay and silica etc.
Pollution control: By reducing the production of cement, pollution is also controlled as cement is an energy intensive product. It has been estimated that 7% of total pollution is only due to cement production which can proportionately be reduced if more blended cement is used.
Note: Presently in India about 30% of the total production is blended cement. This figure is likely to increase sharply with the increase in awareness of use of blended cement. In UK & USA, the usage of blended cement is nearly 90% of the total production. Durability problem can be effectively tackled by reducing the permeability of the concrete using blended cement.