OPC 42.5N is ordinary Portland cement with standard strength development. The most popularly used 
cement on the market today, OPC 42.5 comes in two sub grades. There is OPC 42.5 R, which attains strength quickly, and OPC 42.5 N, which attains it at the normal rate. With the exception of applications which require high strength quickly after pouring, OPC 42.5 N is the recommended type of cement for general applications, including construction applications and pre-cast applications.
OPC 42.5 is characterized by the fact that it attains a minimum strength of 42.5 MPa 28 days after pouring. It is not a chemical difference that separates OPC 42.5 from other popular grades of OPC, such as OPC 52.5, which attains a minimum strength of 52.5 MPa after 28 days, but a size difference. OPC 42.5 is a more coarsely ground product than OPC 52.5, and as a result possesses less strength.
Manufacturing OPC 42.5 N
OPC 42.5 N is manufactured from lime, silica, aluminum and iron. During the manufacturing of OPC these raw materials must be combined in precise quantities. If any of the ingredients is out of proportion, the entire mix is useless. To facilitate correct mix proportions, the raw ingredients are released a little at a time onto a conveyor belt from computer controlled silos, and once mixed together, subjected to extreme analysis.
Once the raw mix has been blended and analyzed to the manufacturer’s satisfaction it is sent into a kiln. Here it is heated to between1400 – 1450 degrees Celsius, which causes melting to take place. As the materials melt, calcium silicates are formed from the lime and silica. Aluminum and iron act as fluxing agents, lowering the temperature at which silicate formation can take place. Without the presence of iron and aluminum, the kiln would have to be heated much higher than 1450 degrees Celsius.
Ultimately, the end result of this firing process are a plethora of hard nodules known as ‘clinker’. Too large to be useful in itself, this clinker is then ground down in a rotating chamber until it attains the correct size, which in the case of OPC 42.5 N is around 40 microns per particle.
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