This video visually explains the process for Standard Practice for Estimating Concrete Strength by the Maturity Method.
The maturity method is a technique to account for the combined effects of time and temperature on the strength development of concrete. The method provides a relatively simple approach for making reliable estimates of in-place strength during construction. The origin of the method can be traced to work on steam curing of concrete carried out in England in the late 1940s and early 1950s. As a result of technology transfer efforts by the Federal Highway Administration, there is renewed interest in the method within the United States.
WHAT is Concrete Maturity?
The maturity concept uses the principle that concrete strength (and other properties) is directly related to both age and its temperature history. Maturity methods provide a relatively simple approach for reliably estimating the in-place early-age compressive (and flexural) strength of concrete (14 days or less) during construction. The maturity concept assumes that samples of a concrete mixture of the same maturity will have similar strengths, regardless of the combination of time and temperature yielding the maturity. The measured maturity index of in-place concrete, a function of temperature history and age, is used to estimate its strength development based on a pre-determined calibration of the time-temperature-strength relationship developed from laboratory tests for that mixture.
WHY use Maturity Methods?
Maturity methods are used as a more reliable indicator of the in-place strength of concrete during construction in lieu of testing field-cured cylinders. The traditional approach of
measuring the strength of field-cured cylinders, cured in the same conditions as the structure, are used to schedule construction activities such as removal of forms or restoring, backfilling walls, schedule prestressing and post-tensioning operations, determining the time for opening the pavements or bridges to traffic, sawing joints, and to determine when protection measures can be terminated in cold weather.
Maturity methods use the fundamental concept that concrete properties develop with time as the cement hydrates and releases heat. The rate of strength development at early ages is related to the rate of hydration of cement. The heat generated from the hydration reaction will be recorded as a temperature rise in the concrete. The main advantage of the maturity method is that it uses the actual temperature profile of the concrete in the structure to estimate its in-place strength. The traditional approach of using field-cured cylinders does not replicate the same temperature profile of the in-place concrete and likely does not estimate its in-place strength as accurately. With maturity methods, strength information is provided in real-time since maturity measurements are made on-site at any time. As a result, construction workflow is optimized, and construction activity timing can be based on more accurate in-place strength information.
HOW are Maturity Methods Used?
The procedure for estimating concrete strength using maturity concepts is described in ASTM C 1074, Standard Practice for Estimating Concrete Strength by the Maturity Method. The temperature-time-strength relationship of a concrete mixture is developed in laboratory tests. This establishes one of two maturity functions (explained below) for that mixture. During construction, a maturity index is determined from measured temperature and age. The maturity
index is used to estimate the in-place strength from the re-established maturity-strength relationship.
The maturity concept is governed by the underlying assumption that concrete samples of a given mixture will have the same strength when they have the same maturity index. For example, concrete cured at a temperature of 50°F (10°C) for 7 days may have the same maturity index as the concrete cured at 80°F (27°C) for 3 days and therefore would have similar strengths.