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1.1 This practice covers two procedures for making and curing cylindrical specimens of concrete under conditions that increase the rate of hydration at early ages. The procedures are: A—Warm Water Method and B—Autogenous Curing Method.

1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. (Warning—Fresh hydraulic cementitious mixtures are caustic and may cause chemical burns to skin and tissue upon prolonged exposure.2)

1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

5.1 By increasing the concrete temperature, the rate of hydration increases and a larger portion of the later-age properties of the concrete can be attained during the short curing period compared with standard temperature curing as described in Practice C31/C31M and Practice C192/C192M.

5.2 Specimens subjected to accelerated curing can be used to estimate the later-age strength under standard-curing conditions by using this practice in conjunction with Test Method C918/C918M. The temperature history of the test specimens is recorded and the maturity index at the time of testing is calculated. Based on the measured maturity index and the early-age strength test results, the later age strength (such as at 28 days) under standard curing can be estimated from a previously established strength-maturity relationship for that concrete mixture. Thus accelerated curing procedures can provide, at the earliest practical time, an indication of the potential strength of the concrete sample. These early-age strength tests also provide information on the variability of the production process for use in quality control, so that necessary adjustments in mixture proportions can be made in a timely manner.

5.3 The user shall select the procedure to use on the basis of experience and local conditions. These procedures, in general, will be practical if a field laboratory is available to house the curing containers and the testing equipment to measure compressive strength within the specified time limits.