concretebasics.org: your guide to cement & concrete

Types of Cement

Extra Rapid Hardening Cement

These are produced by intergrinding calcium chloride (not greater than 2% by weight of Rapid Hardening Cement) with Rapid Hardening Cement.

Because calcium chloride is deliquescent the Extra Rapid Hardening Cements should be stored in dry conditions. This cement should not be stored for more than 1 month & concrete made by this cement should reach the finishing stage within 20min.

There is problem of small amount of initial corrosion of reinforcement when this cement is used. But the effect is not progressive & the cement can be used for RCC works. However, its use is not allowed for prestressed concrete construction.

This concrete is suitable for cold weather concreting or when a very high early strength is required.

The strength of Extra Rapid Hardening Cement is about 25% higher than that of Rapid Hardening Cement at 1 or 2 days and 10-20% higher at 7 days.

The setting time of Extra Rapid Hardening Cement is short (5-30min, depending on temperature), as such, early placing is essential. Shrinkage is higher than when Rapid Hardening Cements is used.