Rapid Hardening Cement – Manufacture, Properties and Uses

Table of Contents

What is cement?

Cement is a binding materials, which binds aggregates and reinforcing materials together. There are different types of cement for different works. cement is classified mainly into two categories on the hardening mechanism.
1. Hydraulic Cement
2. Non-hydraulic Cement

In addition to these main types, based on the composition and characteristics there are many types of cement. They are
1. Ordinary Portland Cement (OPC)
2. Portland Pozzolana Cement (PPC)
3. Rapid Hardening Cement (RHC)
4. Quick Setting Cement
5. Low Heat Cement
6. Sulphate Resisting Cement
7. Blast Furnace cement
8. High Alumina Cement
9. White Cement
10. Colored Cement
11. Air Entraining Cement
12. Expansive Cement
13. Hydrophobic Cement

Rapid cement hardening Cement is a special type of cement which in less time achieves high strength. Normally, the strength of conventional types of cement in 7 days is the same as the strength of 3 days. This type of cement is also known as Portland Cement High-Early Strength.

Composition of Rapid Hardening Cement

We know that in general cement is a mixture of calcareous (calcite), siliceous (silicate), argillaceous (clay) and other substances. Rapid hardening cement is a composition of the following ingredients
60% Tricalcium silicate
15% Dicalcium silicate
10% Tricalcium aluminate
8% Tetracalcium aluminoferrite
It is observed that Rapid Hardening cement contains a higher percentage of Tricalcium silicate than Ordinary Portland Cement.

Manufacture of Rapid Hardening Cement

The manufacture of rapid cement hardening is a dry cement manufacturing process. Limestone and shale are used as a raw material in this cement and heated to form clinkers at extremely high temperatures. The lime and shale clinker are then mixed with a small amount of gypsum and ground to form rapidly hardening cement very finely.

All the difference between fast hardening cement and ordinary portland cement is the amount of limestone (tri-calcium silicate) used as raw material, which gives the cement the high early strength.

Properties of Rapid Hardening Cement

Even though it is similar to Ordinary Portland Cement, Rapid Hardening cement has some special properties. They are

Strength
Rapid cement achieves double strength in the first 24 hours than ordinary portland cement. It develops strength rapidly because

It contains a higher percentage of Tricalcium silicate which helps in quick hydration and hardening of cement. So this tricalcium silicate affects the initial development of high strength.
Cement clinkers are grinded into a fine manner than ordinary cement, which increases the surface area of the cement particles and provides better rate of hydration,so the cement attains early strength.
Tricalcium aluminate helps in process of hydration and hardening, causes high amount of heat emission.

For the same ratio of water and cement, RHC develops same amount of strength in 3 days that OPC develops in 7 days.

Know also: What is portland cement? and its uses

Fineness
The cement clinkers in Rapid hardening cement are grounded in a finer (min 3250 sqcm/gm) manner than OPC (2250 sqcm/gm).

Setting Time
Initial time = not less than 30 minutes, solidification begins within this time period.
Final setting time = not more than 600 minutes, the mixture attains sufficient hardness during this time period.

Weight
Rapid hardening cement is lighter than ordinary Portland cement.

Resistance
Rapid cement has higher resistance against chemical attacks. Eg: sulfate

Curing Time
RHC requires less time for curing when compared to OPC it develops strength quickly.

Heat of Hydration
RHC produces high amounts of heat during the setting process as it undergoes quick hydration reactions for its high tricalcium silicate and finer grind composition.

Storage of Cement

Storing cement in fields is a great task. Rapid hardening cement has to be kept in a dry and cool place. Otherwise, the moisture content will damage the texture and the ability of the cement easily by causing untimely hydration and carbonation.

Uses of Rapid Hardening Cement

It is used where it is necessary to remove the formwork as soon as possible and recycle it.
It is used where it requires high early intensity.
It is usually used to build roads, where it is necessary to rapidly open the path for traffic.
It is used in the manufacturing of concrete goods such as slabs, columns, electric poles, block fences, etc. so molds can be quickly released.
It is used to cement the cold weather as accelerated energy development during hydration prevents the concrete from freezing.

Advantages of Rapid Hardening Cement

This needs a fast recovery time.
It is resistant to attacks on sulphates.
Shrinkage is minimized as concrete is cured and hardened.
For fields such as road pavements, accelerated hardening concrete is used so that roads can be opened early. It is also used in the manufacturing of prefabricated slabs, posts, electric poles, in cold countries concreting.
This achieves high strength in the early days and in contrast with other forms of concrete, the structure-function can be removed earlier.
It is a very long-lasting cement that suits the pace of building and resources needed to make projects work.

Know also: Advantages and Disadvantages of Hydraulic cement

Disadvantages of Rapid Hardening cement

Even though Rapid Hardening Cement has many advantages over Ordinary portland cement, it has some disadvantages also.

For underwater structures like dams, RHC should not be used. It is a hydraulic cement that exerts high amount of heat for hydration process. The rapid hydration process, when in contact with an high amount of water can cause shrinkage cracks. After long time, it can cause rust in reinforcement and reduces the lifespan of the concrete structure.
In large concrete structures, Rapid cement should not be used as it creates large amount of heat. This causes cracks because of the heat difference in the internal and external parts of the structure.
Rapid cement is 10% costlier than ordinary portland cement. it is expensive.

Conclusion:

Rapid Hardening Cement has more advantages when compared to normal portland cement, it requires less hardening time and has long shelf life. Even though the cost of RHC is little expensive than other types of cement, it is less prone to shrinkage and cracks in the structures.