OPC 42.5 R
Ordinary Portland cement 42.5 is the standard grade of cement used in the majority of ordinary cement 
applications, such as pavements, residential buildings, and pipes. OPC 42.5 comes in two sub grades, OPC 42.5 R, and OPC 42.5 N.
OPC 42. 5 R develops high strength early in the curing phase, whereas OPC 42.5 N develops high strength at the normal rate. OPC 42.5 R is suitable for applications where high strength is needed relatively quickly after pouring and setting. Both types of OPC 42.5 will attain a minimum compressive strength of 42.5 MPa on the 28th day after pouring, however OPC 42.5 R will gain strength more quickly than its N rated counterpart.
The Secret of OPC 42.5 R Cement
OPC is a blend of lime, silica, iron and aluminum. These elements must be mined, extracted and crushed so that they can be mixed in the correct proportions. Though made from rough and jagged rocks, precision is the key to making OPC.
Source materials are deposited from separate silos onto a conveyor belt by computer controlled feeds, and the batch, known as ‘raw mix’, is sent to a blending chamber, where it is mixed and analyzed to ensure that the correct amounts of each material are present. This can be either a wet or a dry process, and plants differ greatly from one another as to how they manage this stage of manufacturing.
The R rating of OPC 42.5 R is conferred by blending the base ingredients in certain precise portions. An adjustment of just a few percent of any raw material can lead to large variances in strength and other qualities of the resulting product. This is why chemical analysis at the raw mix stage is carried out so very rigorously.
The bulk of OPC is made up of calcium and silicone, which together form 66% of the total mass of the product. Iron and aluminum act as flux materials, lowering formation temperatures for the calcium silicates which make up OPC.
When analysis is complete, the raw mix is sent to a kiln where it is heated gradually along its length to between 1400 and 1450 degrees Celsius at its hottest point. As the raw mix travels through it, it begins to melt and calcium silicates begin to form. The end result of this firing are small nodules of calcium silicates called ‘clinker’.
Clinker is ground down in a rotating chamber until it becomes a fine powder known as OPC. The size of the final particles determine the grade of OPC. OPC 42.5 is a relatively coarse type of OPC, with the grains of the final product being around 40 microns in diameter.
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