The early construction of a school building will be done during the months of February, March and April when the weather is quite variable. Will it be right to air cure the concrete cylinders to get realistic strength data?
Concrete cylinders must be cured in accordance with ASTM C 31 "Standard Method of Making and Curing Concrete Compressive and Flexural Strength Test Specimens in the Field." This specification makes allowance for several types of curing depending on whether the cylinders are for checking the adequacy of the mix proportions, for quality control or for use as the basis for acceptance. In any case, after the initial 24 hours the specimens are cured by immersion in saturated limewater or by storage in a moist room or cabinet meeting the requirements of ASTM C 511. In the event that the cylinders are intended for determining the time for safe removal of forms or when the structure may safely be put into service the cylinders are stored so that they receive the same curing and protection as those portions of the structure that they represent. In such a case, if the structure is given no moist curing the cylinders should also be treated that way. This is the only instance under which they could justifiably be "air cured." Air curing (that is, with no attempt to retain moisture) results in far lower strength than curing by recommended methods.