Accelerated curing is a procedure by which high early strength is achieved is concrete.This is basically used in prefabrication industries where development of high early strength enables early de-shuttering, saving cost and time for production.
Procedure:-
1.In the accelerated curing test the standard cubes are cast.
2.Those cubes are then covered with top plate and the joints are sealed with special grease to prevent drying.
3. Within 30 minutes of adding water, the cubes having sealed effectively, are placed in an air-tight oven which is then switched on. The oven temperature is brought to 93°C in about one hour time. It is kept at this temperature for 5 hours.
4.At the end of this period the cubes are removed from oven, stripped, cooled, and tested.
1.In the accelerated curing test the standard cubes are cast.
2.Those cubes are then covered with top plate and the joints are sealed with special grease to prevent drying.
3. Within 30 minutes of adding water, the cubes having sealed effectively, are placed in an air-tight oven which is then switched on. The oven temperature is brought to 93°C in about one hour time. It is kept at this temperature for 5 hours.
4.At the end of this period the cubes are removed from oven, stripped, cooled, and tested.
The time allowed for this operation is 30 minutes.
The strength of concrete is determined within 7 hours of casting and this accelerated strength shows good relationship with 7 and 28 days strengths of normally cured concrete. The fig below shows relationship between accelerated strength and normally cured concrete strength at 7 and 28 days.
Fineness of cement is one of the main factors that affects the rate of gain of strength. It has been estimated that particles of cement over 40 micron in size contribute to the compressive strength of concrete only over long periods, while those particles smaller than 25 to 30 micron contribute to the 28 days strength, those particles smaller than 20 to 25 micron contribute to the 7 days strength, and particles smaller than 5 to 7 micron contribute to the 1 or 2 days strength.
