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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Cement 42.5

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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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Cement 42.5, Portland Cement

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OPC 42.5 is a general use grade of ordinary Portland cement. Replacing the once popular OPC 33 in general cement work whilst maintaining its duties as a medium strength cement, OPC 42.5 is commonly used for both construction and pre-cast work. OPC 42.5 can therefore be found in a multitude of locations, from residential buildings to underground pipes.

OPC Grades

There are several different OPC grades, one of which is OPC 42.5. Ordinary Portland cement grades are determined by the compressive strength which is obtained on the 28th day after pouring. OPC 42.5 must have a minimum compressive strength of 42.5 MPa, or 425 kg/cm2 on the 28th day after it is poured in order to qualify as being OPC 42.5. It should be noted that the 42.5 MPa minimum requirement is just that, a minimum requirement, and that most cements exceed this strength.

The two most commonly utilized grades of OPC on the market today are OPC 42.5 and OPC 52.5. There is no chemical difference in composition between these two grades of cement, however OPC 42.5 powder is more coarse than OPC 52.5 powder.

Manufacturing OPC 42.5

OPC 42.5 is made in the same way that all Portland cement is made. First a raw mix of lime, silica, iron, and aluminum is prepared from rock sources which have been crushed and pounded to the size of small pebbles.

Rock is usually mined locally, and any components that are lacking for the making of Portland cement are then added afterwards. Though cement is essentially powdered rock, the various materials must be present in precise quantities in order for high quality Portland cement to be produced. In order to ensure that the correct mix is obtained at the beginning of the cement making process, controlled amounts of individual raw materials are fed from silos onto a conveyor belt, which takes them to the raw mill.

Once in the raw mill, the raw materials are ground up to create what is called the ‘raw mix’. Once the raw mix has been formulated, one of two manufacturing processes can follow. The raw mix is either dried by hot air if a dry process is to be used, or mixed with water to make a raw mix slurry if a wet process is to be used.

Once made, the raw mix is then blended in a blending chamber, and chemically analyzed to ensure that the precise ratios of raw materials are present. It is important that the raw mix is mixed thoroughly to form a completely homogeneous mixture, and that all elements in the mix are as close to being the same size as is possible. Calcium and silicone make up the bulk of the mix because they are the ingredients which later form the calcium silicates that comprises a 66% of Portland cement. Smaller amounts of iron and aluminum are present to act as flux during the firing process, lowering the temperature at which calcium silicates will form.

After blending, the raw mix travels to the kin, a large rotating cylinder which is heated gradually over the length of the kiln, with the temperature rising to between 1400 and 1450 degrees Celsius at its hottest point. As the raw mix grows hotter, aluminum and iron melt, and calcium silicates begin to form. By the end of the firing process, small nodules of an entirely new compound are formed. These nodules are called ‘clinker’.

The clinker is cooled after it leaves the kiln, and then ground with gypsum, an additive which controls the speed at which the cement will set. The grinding process continues until the clinker nodules are a very fine powder. If the clinker is ground relatively coarsely, (relatively coarsely being in the neighborhood of around 40 microns in diameter) the result of this grinding process is OPC 42.5

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