Accelerated Curing Methods of Concrete

Abstract

Concrete is usually placed in a structure in stages or lifts, one on top of another. thus by the time the results of the 28-day test, or even the 7 day test, are available a considerable amount of concrete may overlay that represented by the test specimens in question. It is then rather late for remedial measures if the concrete is too weak, if it is too strong this indicates that the mix was uneconomical. It is clear that it would be a tremendous advantage to be able to predict the 28 day strength within a few hours of casting. the strength of concrete at 24 hours is an unreliable guide in this respect, not only because different cements gain strength at varying rates, but also because even small variations in temperature during the first few hours after casting have a considerable effect on early strength. It is, therefore necessary for the concrete to have achieved a greater proportion of its potential strength before testing. A Major disadvantage of the standard compression test is the length of time needed before the results are known, i.e. 28 days or even 7 days, by which time a considerable quantity of additional concrete may have been placed in the structure. Consequently, it is rather late for remedial action if the concrete is too weak; if it is too strong then the mix was probably uneconomical. Clearly, it would be advantageous to be able to predict the 28-day strength within a few hours of casting. Unfortunately, the 1- to 3-day strength of a given mix cured under normal conditions is not reliable in this respect because it is very sensitive to small variations in temperature during the first few hours of casting and to variation in the fineness of cement. To predict the 28-day strength it is, therefore, necessary for the concrete to have achieved, within a few hours of casting, a greater proportion of its 28-day strength. This can be done by tests based on accelerating curing methods