Cement: Definition, Composition, Types, Function

Cement: The earliest known occurrence of Cement dates back to twelve million years ago. Cement was formed after oil shale adjacent to limestone burned naturally. These ancient deposits were studied in the 1960s and 1970s and identified as Cement.

Cement is abundantly used in construction as a binding material, and its applications in various fields have made it an important civil engineering material. It is even a common household name for fixing spots or cracks on walls. Let us study Cement in detail, composition, and its use these days. Let’s look at some of the frequently asked questions about Cement:

Cement: Definition

Definition: A Cement is a binder or an adhesive for different materials used for construction that sets and becomes hard by adhering to different surfaces of various building materials used in the construction. It forms a composite material strong enough to withstand the various types of loads.

Who Discovered Cement?

In the early \({\rm{19th}}\) century \(\left( {1824} \right),\) limestone was used as the binder material for buildings. This limestone was an excellent binding material that is still used but could not impart great strength and hence failed as a binding material in modern-day architecture.

At that time, Joseph Aspdin of Yorkshire, England, discovered a new building material by heating limestone and clay together in a specific proportion and then giving birth to our modern-day Cement. The Cement prepared was Hydraulic cement, one that hardens after adding water into it and is known as Ordinary portland cement.

What is the Composition of Cement?

The composition of Cement broadly consists of the following two types of constituents: a constituent in its body, which are calcareous compounds like lime, chalk, and marine shells which have a heavy amount of calcium in them, along with argillaceous compounds like clay, marl, and shale having a good amount of silica in them. So, the elemental composition of Cement is lime (obtained from calcareous compounds) and silica(obtained from argillaceous compounds) which covers a significant portion of the Cement body. Alongside vast lime and silica, there are few other constituents like Alumina, Calcium sulphate, Iron oxide, magnesia, sulphur, and alkalies.

Constituents of Ordinary Portland Cement

Function of Constitutes

Lime (\(62\% {\text{ }} – {\text{ }}67\% \))

It imparts strength and soundness to the cement, and if it is present in excess, it makes the Cement unsound and causes it to expand and disintegrate. Whereas, if it is in deficiency, then the strength imparted becomes low and causes the Cement to set quickly.

Silica (\(17\% {\text{ }} – {\text{ }}25\% \))

Silica also imparts strength to the cement, similar to that of Lime. As the amount of silica is increased in cement, the strength of Cement also increases but the setting time of Cement decreases. So, when we need Cement with an early setting, the percentages of silica and lime also have to be changed.

Alumina (\(3\% {\text{ }} – {\text{ }}8\% \))

Alumina is used for imparting quick setting property to the cement. Also, it acts like flux in reducing the clinkering temperature during the preparation of cement. If alumina is present in excess, then Cement reduces its strength as well.

Calcium Sulphate (\(3\% {\text{ }} – {\text{ }}4\% \))

Calcium sulphate in Cement is present in the form of gypsum \(\left( {{\rm{CaS}}{{\rm{O}}_4}.2{{\rm{H}}_2}{\rm{O}}} \right)\). It helps in increasing the initial setting time of the cement, so that Cement remains workable for a more extended period.

Iron Oxide (\(3\% {\text{ }} – {\text{ }}4\% \))

It imparts three essential things in cement, which are strength, hardness, and colour.

Magnesia (\(1\% {\text{ }} – {\text{ }}3\% \))

As iron oxide, magnesia also imparts strength, hardness, and colour in the cement, but excess magnesia can lead to the unsoundness of cement.

Sulphur (\(1\% {\text{ }} – {\text{ }}3\% \))

Sulphur is responsible for volume changes in the cement. A very small amount of sulphur makes the Cement sound, and an excess of Sulphur imparts unsoundness to the cement.

Alaklies (\(0.3\% {\text{ }} – {\text{ }}1\% \))

Alkalies are responsible for staining in Cement or white coloured efflorescence of the structure, which is using Cement of higher concentration. This is also considered as cancer of cement.

So when all of these constituents of Cement are mixed and burnt together with each other, it leads to the formation of some complex chemical compounds which are not formed simultaneously and are called bogues compounds. These are Tricalcium aluminate, Tetra calcium alminoferrate, tricalcium silicate, and Dicalcium silicate.

1. Tricalcium Aluminate: It undergoes the process of hydration within the first twenty-four hours after the addition of water in the cement. It also does the quick setting of Cement and also leads to the volume changes as well and hence causes cracks in the cement. The heat of hydration of tricalcium aluminate is the highest amongst all bogues compounds.
2. Tetra Calcium Aluminoferrate: It also undergoes the process of hydration within the first twenty-four hours after the addition of water in cement. It is observed to have the worst cementing property amongst all the bogues compounds and hence makes no engineering significance in cement.
3. Tricalcium Silicate: It undergoes hydration after one week of addition of water in Cement and is responsible for the development of early strength in the cement, and this is the reason as well that concentration of tricalcium silicate can be improved to attain early strength in structure to be built.
4. Dicalcium Silicate: It undergoes hydration within a year after the addition of water to the Cement and hence responsible for the progressive strength in a structure. It is also quite inert against the chemical in Cement and hence can be used to create resistance against chemicals in the cement.

Hydration of Cement

When Cement is mixed with water and aggregates, it undergoes an exothermic reaction called hydration. The chemical substance in Cement reacts with water to form hydrates products, also known as hydration products.

During the hydration process, heat is also released, called the heat of hydration, and this is maximum for Tricalcium aluminate followed by tricalcium silicate and tetra calcium alumino ferrate and the least for Dicalcium silicate.

Types of Cement

There are different types of Cement depending on the use and the composition of cement. Every type of Cement has a different way of being used and has its advantages and disadvantages.

1. Rapid Hardening Cement

This type of Cement develops early strength as it has a higher rate of gain of strength and should not be confused with quick setting Cement as it takes normal time to set but attains its strength quickly. The strength attained by rapid hardening Cement in \(3\) days is equal to the strength obtained in \(7\) days for normal cement. Also, such a type of Cement is generally used in prefabricated construction, cold weather concreting, emergency repair work, or pavement of roads where the strength needs to be achieved quickly.

2. Extra Rapid Hardening Cement

This Cement is formed by inter grinding clinkers of the rapid hardening Cement with calcium chloride. The process of mixing cement, transportation of Cement, and placing with compaction should be done within twenty minutes. The strength attained by this Cement is \(10\% {\text{ }} – {\text{ }}15\% \) more than the seven days age cement.

3. Sulphate Resisting Cement

Seawater contains sulphur in excess, and it leads to volume change. Not only the soil below seawater may have a high amount of sulphur due to sewage but also normal OPC (ordinary portland cement) reacts with sulphur and increases its volume. To avoid this, lime and alumina of Cement are reduced. 

This type of Cement has great application in marine construction, sewage treatment works, and foundation works.

4. Quick Setting Cement

The Cement is obtained by adding a small amount of alumina in finely ground Cement clinkers and reducing the proportion of gypsum. This Cement is used for grouting operations and underwater concreting as well.

5. Low Heat Cement

Low heat Cement is a special type of Cement having low heat of hydration, and this can be achieved by increasing the proportion of dicalcium silicate and reducing the proportion of tricalcium silicate and Tricalcium aluminate. This Cement also develops a slower rate of gain of strength.

This type of Cement finds its application in huge constructions where a lot of quantity of Cement is to be used like in building dams.

6. Hydrophobic Cement

The Cement is prepared by inter grinding Cement clinkers with water repellent film-forming substance like stearic acid or oleic acid. This film protects the Cement from interacting with the moisture present in the atmosphere, and the Cement remains fresh for use even after storage and long transportation.

Properties of Cement

There are many physical properties of Cement that must be checked before using it like,

1. Strength of Cement: The strength of Cement should be checked before use and must be greater than \(175\;{\rm{kg}}/{\rm{c}}{{\rm{m}}^2}\) for an ordinary portland Cement by doing a cubical test of sand and Cement mixture in a \(3:1\) ratio, respectively.
2. Fineness of Cement: A good Cement is fine in nature, and the fineness of Cement can also be checked by sieve test or by touching the Cement between the index finger and thumb.
3. Soundness of Cement: Cement is subjected to expansion or volume change due to composition, particle size, and many other factors. But a good Cement should not change its volume much.
4. Colour of Cement: The colour of Cement is greenish-grey, and the colour of Cement also shows the degree of burning as lighter colour, like yellow, shows poor burning of cement.
5. Resistance against Moisture: The Cement should be moisture resistant to prolong its life and its efficiency.
6. Plasticity: The Cement should be plastic in nature. It improves its workability in the initial time.

FAQs on Cement

Let’s look at some of the frequently asked questions about Cement:

Question-1: Which type of Cement is best?
Answer: All types of Cement are best if used according to the situation. The most commonly used Cement is Ordinary Portland cement.

Question-2: What is the chemistry of cement?
Answer: When all of the constituents of Cement are mixed and burnt together with each other, it leads to the formation of some complex chemical compounds which are not formed simultaneously and are called bogues compounds, like Tricalcium aluminate, Tetra calcium alminoferrate, tricalcium silicate, and Dicalcium silicate.

Question-3: How is Cement important?
Answer: A Cement is a binder or an adhesive for different materials used for construction that sets and becomes hard by adhering to different surfaces of various building materials used in the construction to form a composite material strong enough to withstand the various types of loads.

Question-4: What are the components of cement?
Answer: The composition of Cement broadly consists of the following two types of constituents: a constituent in its body, which are calcareous compounds like lime, chalk, and marine shells which have a heavy amount of calcium in them, along with argillaceous compounds like clay, marl, and shale having a good amount of silica in them. So, the elemental composition of Cement is lime (obtained from calcareous compounds) and silica (obtained from argillaceous compounds) which covers a significant portion of the Cement body. Alongside vast lime and silica, there are few other constituents like Alumina, Calcium sulphate, Iron oxide, magnesia, sulphur, and alkalies.

Question-5: What are the 5 types of cement?
Answer: There are different types of Cement depending on the use and the composition of cement. Every type of Cement has a different way to be used and its own advantages and disadvantages.

1. Rapid Hardening Cement
2. Extra Rapid Hardening Cement
3. Sulphate Resisting Cement
4. Quick Setting Cement
5. Low Heat Cement

Now that you are provided with all the necessary information on the Cement and we hope this article on the Cement has helped you. If you have any questions feel to post your comment below. We will get back to you at the earliest.