ASTM C1768/C1768M-12 (R2017) PDF Download

The ASTM C1768/C1768M-12 (R2017) standard outlines two procedures for making and curing cylindrical specimens of concrete under conditions that accelerate the rate of hydration at early ages.

The first procedure, called the Warm Water Method (Procedure A), involves increasing the concrete temperature to promote faster hydration and achieve a larger portion of the later-age properties of the concrete during the short curing period. This method helps estimate the later-age strength under standard-curing conditions by recording the temperature history of the specimens and calculating the maturity index at the time of testing. This index, along with the early-age strength test results, can be used to estimate the later age strength (e.g., at 28 days) under standard curing. The Warm Water Method is useful for providing an indication of the potential strength of the concrete sample at the earliest practical time and for quality control purposes.

The second procedure, called the Autogenous Curing Method (Procedure B), involves enclosing the concrete specimens in an airtight container to prevent moisture loss during curing. This method promotes self-curing of the concrete by utilizing the moisture generated from the process of hydration. Similar to Procedure A, the Autogenous Curing Method can be used to estimate the later-age strength under standard-curing conditions by determining the maturity index and using it in conjunction with the early-age strength test results.

The choice of procedure to use depends on the experience and local conditions. Both methods require a field laboratory with appropriate curing containers and testing equipment to measure compressive strength within the specified time limits. These accelerated curing procedures are practical for obtaining early-age strength information and variability of the production process, allowing adjustments in mixture proportions to be made in a timely manner.