What is Ordinary Portland Cement (OPC)?

Ordinary Portland Cement (OPC) is the foremost cement type developed at early stages that resembles a stone seen in Portland, England which is the reason for its name. It has a greenish-grey colour.

Cement can be defined as a material that possesses remarkable adhesive and cohesive properties that are capable of bonding together several types of mineral fragments to a single compact mass when mixed with water. 

The history of cement starts with the history of engineering construction. Since then, cement has been one of the prime construction materials used for structures. It was developed by “Joseph Aspdin” in the year 1824, who was a bricklayer and a builder. 

Watch Video: What is Cement?

Also Read: Top 10 Types of Cement Used in Construction

The setting and hardening of cement are by hydration, which is the chemical reaction between the cement compounds and the water. The hydration reactions give hydration products which impart strength to the final hardened mass.

Read More: Hydration of Cement

In this article, we will discuss the composition of cement, the manufacture of cement and its properties.

Composition of Cement

The two main raw materials for cement manufacture are calcareous materials and argillaceous materials. Together they are used in cement manufacture and the final products constitutes 7 main ingredients as shown in Table 2 below.

The cement is composed of mainly 7 ingredients as shown in the table below. Each ingredient contributes some properties to the cement. Excess amount of these ingredients in cement results in undesirable properties of cement which is explained in the table.

Sl.No	Ingredient	Percentage Composition	Properties	Excess Amount
1	Lime (CaO)	60-65%	Strength & Soundness- Role in formation of silicates and aluminates	Unsoundness in the form of volume change
2	Silica (SiO2)	17-25%	Strength	Increase Strength and setting Time
3	Alumina (Al2O3)	3-8%	Quick Setting Time	Weaken the Cement
4	Iron Oxide (Fe2O3)	3-4%	Act as a flux, Imparts Reddish brown tint to cement, At high temperature reacts with Al and Ca to form C4AF
5	Magnesia (MgO)	1-3%	Imparts Color & hardness	Unsoundness-more hardness result to cracks
6	Alkalies  (K2O, Na2O)	0.2 – 1.3%		Subjected to alkali-aggregate reaction result in efflorescence.
7	Sulphur Trioxide (SO3)	1-3%

Among the 7 main ingredients, Lime, silica, alumina and Iron oxides are the main ingredients that contribute to the bogues compounds present in cement. All other materials like magnesia, Alkalies and sulphur trioxides are forms of impurities present when these ingredients are naturally taken for manufacture. This is because the natural products can never exist in its pure state.

Bogues Compounds in Cement

The basic chemical composition of cement is given in table 1. For convenience, they are given in short forms as shown in the table. These compounds are together called as bogue compounds.

Bogue compounds in cement

When cement is combined with water, a hydration process occurs. In this process, the bogues compounds react with water to form certain hydration products, which is the cause of strengthening and hardening of concrete. 

Continue Reading on Bogues Compounds in Cement | Calculation of Bogues Compound

For more ideas about the hydration reaction and the hydration products along with their individual role in strength gain, please read the article:

Hydration Products of Cement | Chemical Reaction | Significance

Hydration of Cement | Heat of Hydration |Stages of Hydration of Cement

What gives Colour to Cement?

One of the important colour-giving compounds present in cement is iron oxide. Which as per theory is supposed to provide a brownish red colour to the cement. But in actual case, all the bogues compounds except C₄AF, have a white colour. C₄AF has a brown colour due to the presence of ferrite.

As mentioned above, the magnesia is present in the bogues compound C4AF. Magnesia is present in smaller amounts, which under high temperatures of manufacturing, polarizes and deforms the iron electron shells (Ferrite in C4AF). These then absorb light and provide cement with a greenish-grey colour.

Also Read:

1. 10 Top Types of Cement in Construction
2. Top 5 Physical Properties of Cement