ACCELERATED CURING METHOD is used to get early high compressive strength in concrete. This method is also used to find out 28 days compressive strength of concrete in 28 hours. (As per IS 9013-1978-Method of making, curing and determining compressive strength of accelerated cured concrete test specimens).
Accelerated curing is useful in the prefabrication industry wherein high early age strength enables the removal of the formwork within 24 hours thereby reducing the cycle time resulting in cost saving benefits.The most commonly adopted curing techniques are steam curing at atmospheric pressure, warm water curing, boiling water curing and autoclaving.
Compressive strength test using Accelerated curing method:
1. After the test specimens (whose 28 days strength to be determined) have been made, store it in moist air of at least 90 percent humidity for 23 hours + 15 min.
2. Cover the specimens with flat steel cover plate to avoid distortion during the use.
3. Carefully and gently lower the specimens into the curing tank and shall remain totally immersed for a period of 3½
Hours + 15 min.
4. The temperature of water in the curing tank shall be at boiling (100 oC) when the specimens are placed.
5. After curing for 3 ½ hours in boil water, the specimen shall be carefully removed from the boiling water and cooled by immersing in cooling tank at 27 +2oC for 2 hrs.
6. After cooling remove the specimens from the mould and tested for its accelerated compressive strength (Ra) in N/mm2.
7. The 28 days can be found out using following formula.
Predicted 28 days compressive strength = R28 = 8.09 + 1.64 Ra, where Ra is accelerated compressive strength and R28 is predicted compressive strength at 28 days.