Rapid Hardening Cement

Rapid Hardening Cement (RHC) are also called high early strength cement. The prime difference between the rapid hardening cement and ordinary Portland cement is the lime content. Large proportion of lime is the distinguishing feature of rapid hardening cement.

Manufacturing

Rapid hardening cement is burnt at a higher temperature than that of the OPC under more controlled conditions.

Strength

The 3 days strength of rapid hardening cement is equivalent to the 7 days strength of OPC when the water-cement ratio for both the cement is taken to be same. The increased rate of strength is due to the fact that higher proportion of tri-calcium silicate (C₃S) is contained in RHC along with finer grinding of the cement clinker. Though, the rate at which RHC gains strength is higher than the rate at which OPC gains strength, the ultimate strength is only a bit higher for RHC.

Properties

• Initial Setting Time: 30 minutes
• Final Setting Time: 600 minutes
• The specific surface is greater than 3250 cm²/gm.
• RHC is lighter than OPC.
• The curing period for RHC is less.

Uses

Rapid hardening cement is mostly used in construction of road where the traffic cannot be halted for long period of time. Besides, RHC is used where the formwork need to be removed early for reuse. It is also used on those circumstances where sufficient strength for further construction is wanted as quickly as practicable. These are also used in manufacturing precast slabs, posts, electric poles.

Advantages

• As the curing period for rapid hardening cement is less, it turns out to be economical.
• Shrinkage during curing and hardening of cement is less in case of RHC.
• RHC are good at Sulphur resistance.
• Good speed of construction can be achieved as the strength is gained in relatively shorter time.

Disadvantages

• It is expensive than Ordinary Portland Cement.

Extra Rapid Hardening Cement

Manufacturing: Intergrinding Calcium Chloride (CaCl₂) with RHC, Extra RHC can be obtained. The percentage of Calcium Chloride during the manufacturing process should not exceed 3%.

Strength: Strength of Extra RHC is about 25 % higher than that of the RHC at 1-2 days whereas the strength exceeds by only 10-20 % after 7 days.

Uses: Extra rapid hardening cement is used for cold weather concreting.