Cement is one of the most important base products of construction industry and Ordinary Portland cement or OPC is by far the most important type of cement. Prior to 1987, there was only one grade of OPC [which was governed by IS 269-1976]. After 1987 higher grade cements were introduced. The OPC was classified into three grades, namely..
1. OPC-33 Grade
2. OPC-43 Grade
3. OPC-53 Grade
These classifications are based on the strength of the cement at 28 days when tested as per IS 4031- 1988. If the 28 days strength is not less than 33N/mm2, it is called 33 grade cement, if the strength is not less than 43N/mm2, it is called 43 grade cement, and if the strength is not less then 53 N/mm2, it is called 53 grade cement. But the actual strength obtained by these cements at the factory are much higher than the BIS specifications.
The physical and chemical properties of different types of OPC are shown in Table below.
It has been possible to upgrade the qualities of cement by using high quality limestone, modern equipments, closer on line control of constituents, maintaining better particle size distribution, finer grinding and better packing. Generally use of high grade cements offer many advantages for making stronger concrete. Although they are little costlier than low grade cement, they offer 10-20% savings in cement consumption and also they offer many other hidden benefits. One of the most important benefits is the faster rate of development of strength. In the modern construction activities, higher grade cements have become so popular that 33 grade cement is almost out of the market. Table shows the grades of cement manufactured in various countries of the world.
The manufacture of OPC is decreasing all over the world in view of the popularity of blended cement on account of lower energy consumption, environmental pollution, economic and other technical reasons. In advanced western countries the use of OPC has come down to about 40 per cent of the total cement production. In India for the year 1998-99 out of the total cement production i.e., 79 million tons, the production of OPC in 57.00 million tons i.e., 70%. The production of PPC is 16 million tone i.e., 19% and slag cement is 8 million tons i.e., 10%. In the years to come the use of OPC may still come down, but all the same the OPC will remain as an important type for general construction.
