Important Information About Cement
What is Portland Cement (PC)?
Portland cement is a finely ground mixture of calcium aluminates and silicates which
is capable of setting and hardening by reacting chemically with water. It is a binding
material used in engineering constructions and is obtained by the calcinations of calcareous
and argillaceous materials. The calcined product called clinker is then finely pulverized by
grinding into a very fine powder and is finally mixed with gypsum to obtain cement.
What is Portland Composite Cement (PCC)?
When secondary cementations materials are added to Portland cement, it is known as Portland Composite Cement.
What causes hardening of Portland cement?
The compounds present in Portland cement react with water to form a cementitious crystalline structure
which adheres to the sand and aggregate. This helps in binding the mass together and increases its strength
until it becomes very hard.
Why is gypsum needed in cement?
Gypsum plays the important role of controlling the rate at which hardening of the cement occurs.
It is vital to keep the rate within limits in order to make the cement a useful product in construction.
A small amount of gypsum is added to clinker during the grinding period.
What is setting of cement?
When water is mixed with cement, a smooth paste is produced that remains plastic for a short period of time. During this period,
the paste can be disturbed and remixed without injury. As the reaction between water and cement continues, the plasticity
of the cement paste is lost. This early period in the hardening of cement is known as “Setting of Cement”.
What does 28-days strength mean?
When concrete hydrates, it hardens and gains strength. This hydration process continues over a very long period
of time. It occurs quickly at the outset and slows down as time passes. The entire process of hardening would
require several years.
Since this is impractical to wait for so long to measure the strength of concrete, a time period of 28 days was
introduced by specification-writing authorities as the time where all concrete should be tested. In this period, a
substantial amount of hydration has already taken place and this strength is taken as the design strength of the structure.