Autogenous Accelerated Curing of Concrete Cylinders

About the report:

Concomitant with the Research Council's studies of accelerated curing for strength testing, Subcommittee II-i of ASTM Committee C-9 was developing and refining accelerated methods for standardization. This development included a cooperative testing program in which nine U. S. and Canadian laboratories, including the Research Council, applied various methods to their mixtures and materials. The Council's work was conducted as a part of two different projects. Procedures employing water bath curing were evaluated and subsequently the autogenous procedure was studied. This report combines the information from these two investigations with data from limited scope studies of containers and storage conditions. The curing procedures evaluated were: (1) 95°F water bath immediately for 24 hours (Procedure A); (2) 212°F water bath after 23 hours for 3 1/2 hours (Procedure B); (3) 212°F water bath after initial set (approximately 4 6 hours) for ±15 hours (Procedure C); (4) Autogenous curing immediately in special containers (Procedure D). Based upon the data developed, the following conclusions are drawn. (1) Each of the four accelerated procedures is capable of predicting strengths at later ages with accuracy equivalent to that currently achieved with moist curing. (2) Procedure A gives the lowest strength ratios (i.e., accelerated strength to that at later ages) while Procedures C and D give the highest ratios. Procedure B is intermediate. (3) The variability of test results from accelerated tests is of the same order as that from conventional procedures. (4) The four procedures are comparatively insensitive to the presence of retarding admixtures at normal dosages. Procedure C appeared to be affected by the presence of the admixture more than by changes in cement type. (5) Differences in results among the procedures and the influence of other factors such as initial mixture temperatures are greatest for mixtures at lower initial temperatures and with a low potential for heat evolution. (6) Variations of initial mixture temperatures above 60°F do not significantly influence results. Temperatures below 60°F may give slightly lower strength ratios than do higher temperature mixtures. (7) For the Autogenous Procedure, D, a fairly wide range of heat retention characteristics between container types (±25°F at 48 hours) had no significant influence on strength ratios. It is postulated that a minimum heat retention value is necessary but that limits on maximum values are not necessary. (8) Minor variations in storage conditions and/or lengths of curing do not significantly affect results for either Procedure B or D although Procedure B is slightly more influenced than Procedure D.

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