Cement is a widely used binding material in building and civil engineering construction. They are finely grounded powders that set to a hard mass when mixed with water. This results due to a chemical reaction
Cement is a widely used binding material in building and civil engineering construction. They are finely
grounded powders that set to a hard mass when mixed with water. This results due to a chemical
reaction of the cement compounds with water, which is known as hydration. Cement is seldom used on
its own; rather it is mixed with inert material (known as aggregate), and used in the form of mortar and
concrete. Mortars are used for binding bricks, blocks and stone in walls, or as surface renderings while
concrete is used for a huge number of constructional purposes.
The origin of hydraulic cement goes back to ancient Greece and Rome. In those times, lime and volcanic
ash were used, which slowly reacted in the presence of water to form a hard mass. Cement is prepared
in cement manufacturing companies. The basic raw materials used for its production are lime and clay,
which is extracted from quarries. Lime is mixed along with bauxite, iron ore and made into a powder
form. This mixture is then preheated and fed into a rotary kiln. Coal powder is then injected to a
temperature of 1200-1500 degrees. The rotary kiln is a tube which is about 200 meters long and 6
meters in diameter, with a long flame at one end. The mixture enters the kiln at the cool end, gradually
passes down to the hot end, and then falls out of the kiln and cools down. The resulting product is
known as a clinker. After cooling, the clinker may be stored temporarily in a clinker store, or it may pass
directly to the cement mill, where it is ground to a fine powder. A small amount of gypsum is also
ground up with it to obtain what we call Ordinary Portland Cement (OPC). The gypsum is used to control
the setting properties of the cement. Depending upon the 28 day compressive strength of the product,
various grades of cements are obtained.
Cement is characterized by various properties, some of which are summarized below:
Fineness: It refers to the uniform size among the particles in the cement. High fineness is
preferred as it increases the strength build-up of cement, and also provides more area for water
Setting time: There are two important setting times – initial setting time and final setting time.
The time at which the cement paste loses its plasticity after the addition of water is known as
the initial setting time. During this time, the temperature rises rapidly and this time is required
for mixing, transporting and placing of the concrete. It usually takes about 30-45 minutes. The
final setting time is the time consumed by the paste to become a hard mass and it usually occurs
below 10 hours. The temperature reaches the peak value during the final setting time.
Comprehensive Strength: This refers to the strength of the cement which helps it to resist
Heat of hydration: The heat generated due to the hydration of cement i.e. the chemical reaction
between cement and water, is known as the heat of hydration.
Various tests, such as physical tests, field tests and laboratory tests, are available to check these
qualities and properties of cement.
Types of cement:
Cement plays a crucial role in the construction process. There are various types and grades of cement
available in the market. They must be selected carefully as it is the quality of cement that decides the
strength of your structure. The two main types are:
a) Ordinary Portland cement (OPC): It is the most common type of cement that is used generally
around the world. It usually originates from limestone and is graded according to its strength,
namely, OPC-33 grade, OPC-43 grade and OPC-53 grade. The grade indicates the strength (MPa)
that the concrete will attain after 28 days of setting.
b) Portland Pozzolana Cement (PPC): It is characterized by greater resistance to attack of chemical
agencies and production of lower heat of hydration, which makes it particularly suitable for
hydraulic works and construction in sea water. PPC contains gypsum and pozzolanic materials,
and is produced by a fully automated and dry manufacturing process. It is generally used in
constructions where strong resistivity or excellent surface finishes are required. The two grades
found in this category are PPC grade 43 and PPC grade 53.
However, various other types of cement are also used depending on the applications and as per
Rapid Hardening Cement: It gives greater strength development at an early stage than OPC as it
contains higher C 3 S content and finer grinding.
Low Heat Cement: It is widely used in mass concrete construction. It is less reactive and its initial
setting time is greater than OPC. Low heat cement is manufactured by increasing the proportion
of C 2 S and by decreasing the C 3 S and C 3 A content.
Sulfate Resisting Cement: This type of cement, which is prepared by reducing the C 3 A and C 4 AF
content, shows excellent resistance to sulfate attacks.
White cement: It is a type of OPC which is pure white in color. It is obtained by reducing the iron
oxide content in OPC and is used mainly for interior and exterior decorative work.
Colored cement: By adding 5-10% mineral pigments with Portland cement during the time of
grinding, various color combinations can be produced.
Expansive cement: This type of cement does not shrink during or after the time of hardening.
Rather, it expands slightly with time.
Other commonly used types of cement include hydrophobic cement, Portland blast furnace
cement, Portland Slag cement, air entraining cement, high alumina cement, etc.
Cement is considerably cheap, and easy to mix and adjust. The raw materials are easily available in most
places and the composition of cement in concrete can also be changed to meet almost all engineering
requirements. It is very strong, has high thermal mass and helps create large structures quickly. All this
makes it widely useful in engineering and construction. One disadvantage of cement is the
environmental issues surrounding its manufacture as it involves digging up habitat and limestone
formations. This makes it highly energy intensive, and greenhouse gas producing. But the fact that no
one has been able to come up with a better alternative solution, still makes it one of the most sought
after materials for construction works.