5.2 Curing of the specimen
Curing is the name given to the procedure used for promoting the hydration of cement and consists of control of temperature and of the moisture movement from and into the concrete. Immediately after finishing, precautions shall be taken to prevent evaporation and loss of water from the specimens.
Upon completion of initial curing and within 30 min after removing the molds, store specimens in moist conditions with free water maintained on their surfaces at all times at a temperature of 73.4 ± 3 0F. Temperature between 68 and 86 0F are permitted for a period not to exceed 3 hrs immediately prior to test, if moisture is maintained on the surfaces of the specimen at all times, except when capping with sulfur.
Fresh concrete grains strength most rapidly during the first days and weeks. Structural design is generally based on 28 days strength and 70 percent of which is reached at the end of the first week after placing.
5.3 Capping of cylindrical specimen
Capping is applicable to cylindrical specimens . A cap shall be at least as strong as the concrete. The ends of all cylindrical test specimens that are not plane within 0.05 mm are capped. The capped surfaces are not departed from a plane by more than 0.05 mm and shall be nearly at right angle to the axis of the specimens. The planeness of the cap is required to be checked by means of a straight edge and feeler gauge. Caps are made as this as practicable and care should be taken so that flow or fracture does not take place, when specimen is tested. Capping can be done on completion of casting or a few hours prior to testing to specimen.
Just prior to testing, the cylindrical specimen are capped with a sulfur mixture consisting of 1 part of sulfur to 2 or 3 parts of inner filler, such as fire-clay. The specimens are securely held in a special jig so that the caps formed have a true plane surface.