What is a Cement? Raw Materials of Cement || Role of Ingredients in Cement Properties || What give Colour to Cement?

The history of cement starts with the history of engineering construction. From then, cement is one of the prime most construction material used for structures. It was developed by “Joseph Aspdin” in the year 1824, who was a bricklayer and a builder. Ordinary Portland Cement (OPC) is the most common cement developed at early stages that resembles like a stone seen in Portland, England which is the reason for its name. It has a greenish grey colour.

Watch Video: What is Cement ?


Also Read: Top 10 Types of Cement Used in Construction

Cement can be defined as a material that possess remarkable adhesive and cohesive properties that is capable to bond together several types mineral fragments to a single compact mass when mixed with water. 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 imparts 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 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.

Bogues compounds in cement
Bogues compounds in cement

When cement is combined with water, 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. For more idea about the hydration reaction and the hydration products along with their individual role in strength gain, please read the article:

HydrationProducts of Cement | Chemical Reaction | Significance

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


Raw Materials Used for Cement Making

 

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 the 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 contributes to the bogues compounds present in cement. All other materials like magnesia, Alkalies and sulphur trioxides are form of impurities present when these ingredients are naturally taken for manufacture. This is because, the natural products can never exist in its pure state.


What give Colour to Cement?

 

One of important colour giving compound 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 temperature of manufacturing, polarizes and deforms the iron electron shells (Ferrite in C4AF). These then absorbs light and provide cement a greenish grey colour.

Watch Video: What is Cement ?

Also Read: Calculate Cement Required for Floor Tiling


Anre A

I am a structural engineering professional who is passionate about researching new content in the construction industry and bringing to people around the world.

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