CONCRETE MATURITY, WHAT IS IT?
The strength developed by a concrete mixtur's depends on the temperature history and the curing time. Long curing times and increases in the curing temperatures lead to increases in strength development. The maturity method of testing recognizes this combined effect of time and temperature and provides a basis for estimating the in situ strength gain of concrete by monitoring its temperature over time.
The concept of maturity was first developed in the late 1950 when the first publication was released. As a result of this research the “American Society for Testing and Materials” (ASTM) publishes in 1987 its first standard practice for maturity.
The Maturity Method foundation is very simple: exposing the concrete to higher temperatures results in a higher hydration rate (thus, a fast strength development). If, on the contrary, the concrete is exposed to lower temperatures, hydrates slowly.
In brief: two concrete samples with the same maturity will have the same strength, even though each may have been exposed to different curing conditions.
Calculating the Maturity Index can be achieved trough one of two available and commonly accepted methods:
Time-Temperature Factor (Nurse-Saul): is the accumulated product of time and temperature.
Equivalent Age (Arrhenius Equation): besides those factors also accounts for non-linearity in the rate of cement hydration.