Objective
Normally, the strength of concrete is found out after 7 days and 28 days. For some construction activities, it may be too late and need to know the strength earlier.
Reference Standards
IS: 9013-1978-Method of making, curing and determining compressive strength of accelerated cured concrete test specimen.
Equipment & Apparatus
- Accelerated curing tank
- Compression Testing Machine
Procedure
- Prepare the specimen and store it in moist air of at least 90% relative humidity and at a temperature of 27+2 o C for 23 hrs + 15 minutes.
- Lower the specimen, into a curing tank with water at 100 0 C and keep it totally immersed for 3 ½ hours + 5 minutes
- The temperature of water shall not drop more than 3oC after the specimens are placed and should return to boiling within 15 minutes.
- After curing for 3 ½ hours + 5 minutes in the curing tank, the specimen shall be removed from the moulds and cooled by immersing in cooling water 27+2 o C for a period of at least one hour.
- Read my post compressive strength test of concrete for further steps.
Calculation
The corresponding strength at 28 days can be found out from the following correlation. (It is however suggested that a new specific correlation should be developed for the specific concrete used at site.)
R28 (Strength at 28 days) = 8.09 + 1.64 Ra
Ra = Accelerated Curing Strength in MPa.
Safety & Precautions
- Use hand gloves, safety shoes, while removing containers from curing tank after switching off the curing tank & place sample in machine properly.
- Equipment should be cleaned thoroughly before testing & after testing.
