Effects of Delayed Curing:

The concrete specimens placed in laboratory air for varying periods after casting, before being moist-cured, have indicated that the strength at 7 to 28 days decreases progressively as the period of air curing is increased. An exposure for 3 days to air at a temperature of 23°C and having a relative humidity of approximately 60% before being moist-cured at 23°C has been found to reduce the 7 days strength by 12% and the 28 days strength by about 10%. The specimens left in air at 23°C for the entire curing period have shown a reduction of 25% in the strength at 7 and 28 days as compared with standard moist-curing. The reduction under field conditions would probably have been greater. Similar adverse curing causes greater relative reduction in strength when Portland blast furnace slag cement and the cements blended with fly ash are used.