OPC cement is Ordinary Portland Cement and in general concrete construction when there is no exposure to sulfates in the soil or groundwater OPC is the most common cement which is used.
For almost all structural work including all kinds of concrete construction, OPC is an ideal building material and is one of the most commonly and widely used types of cement in the whole world.
The name as Portland cement is given in 1824 by Joseph Aspdin because it has similarity in color and quality as found in Portland stone which is a white-grey limestone on the island of Portland.
Components of Ordinary Portland cement: (OPC cement)
The raw materials used in the manufacturing of OPC are;
- In the form of clays and shales, Argillaceous or Silicates of Alumina.
- In the form of limestone, chalk, and marl, Calcareous or Calcium carbonate which is a mixture of calcium carbonate and clay.
In the proportion of about two parts of calcareous materials to one part of argillaceous materials, the ingredients are mixed and then in a dry state or mixed in wet state crushed and ground in ball mills.
Then in a rotary kiln at a temperature between 1400 degrees C to 1500 degree C the dry powder or the wet slurry is burnt and the kiln is first cooled and the clinker is obtained. Then according to the class of product gypsum is added and it is ground to the requisite fineness.
Manufacturing of OPC Cement:
There are four steps in the manufacturing process of OPC cement as given below;
- Crushing and Grinding of Raw Material
- Mixing or Blending
Crushing and Grinding of Raw Material:
The raw materials are crushed and grinded into small suitable size particles in the first step of the manufacture of cement and there are three types of the manufacturing process;
- Dry Process
- Wet Process
- Semi Wet Process.
Depending upon the type of manufacturing process, the crushing and grinding process varies and the raw materials are dried up before crushing for dry process.
Mixing or Blending:
In this step with clay in the desired proportion, the grinded raw material like limestone is blended or mixed, and to get a homogeneous mix, it is mixed well by the help of compressed air.
These mixes are stored in silos in the dry process and in the wet process slurry tanks are used and there is 35 to 40% water in slurry.
In the manufacture of OPC cement, heating is the main important step. In this step, with the help of conveyor belts, the product obtained from the mixing is passed into the Kiln.
Firstly, to 550C the mix is preheated and all the moisture content is evaporated and clay is broken into silica, iron oxide, and aluminum oxide. Then the temperature is rise to 1500 degree Celsius where the oxides form silicate, ferrite, and aluminate.
Then the product is cooled down to 200C and in the kiln, the end product is obtained which is in the form of greenish-black or grey colored balls and called cement Clinkers.
In the final step of grinding the cement clinkers and the required amount of gypsum is mixed and into very fine particles it is grinded. Then stored in the silos and later packed in cement bags.
Types of Ordinary Portland Cement: (OPC)
Based on the different codes of the different countries there are the following types of OPC;
AS per ASTM 150: (American Standards)
- Type I; As common or general-purpose cement Portland cement is used.
- Type II; This type gives less heat during hydration and provides moderate sulfate resistance.
- Type III; This type has high early strength and this cement is ground finer.
- Type IV; for its low heat of hydration this type is used.
- Type V; Where sulfate resistance is important this type is used and for its high sulfate resistance this cement has a very low C3A composition.
As per EN 197 norm: ( European norm)
- CEM I; This type of cement is up to 5% of minor additional constituents and comprising Portland cement.
- CEM II; This type of Portland cement is up to 35% of other single constituents.
- CEM III; The percentage of blast-furnace slag is higher in this type of cement.
- CEM IV; Up to 55% of pozzolanic constituents and is a Portland cement.
- CEM V; Blast-furnace slag or fly ash and pozzolana and is a Portland cement.
As per CSA A3000-08: ( Canadian standards)
- GU; General used cement.
- MS; Moderate sulfate resistant cement.
- HE, HEL; Cement with high early strength.
- LH, LHL; Cement wit low heat.
Uses of OPC cement:
- For general construction purposes where special properties are not required such as reinforced pavements, concrete buildings, bridges, and where soil conditions are normal, it is used.
- For most of the concrete masonry units, OPC cement is used.
Properties of OPC cement:
There are the following properties of OPC cement as shown in the table below;
Final Setting time
|Final Setting time
|830 to 1650 kg/m3
Advantages of Ordinary Portland cement (OPC)
There are the following advantages of OPC cement such as;
- To cracking and shrinkage, it has great resistance but to chemical attacks, it has less resistance.
- It is recommended in projects where props are to be removed early because the initial setting time of OPC cement is faster.
- There is less period in the Curing of OPC cement and reduces curing cost.
Disadvantages of OPC cement:
There are also some disadvantages of OPC Cement such as;
- For mass concreting, it cannot be used because it has a high heat of hydration.
- OPC cement produces comparatively less cohesive concrete and difficulty occurs in concrete pumping.
- OPC cement is costly.