MATURITY METHOD

In the real world, concrete is rarely produced under isothermal conditions. The maturity method has been developed to provide a quantitative technique for predicting the in-place compressive strength development of a concrete, based on its insitu thermal history [34,35]. The Arrhenius temperature dependence and time-temperature transformation used for compressive strength can also be applied to describing the degree of hydration as a function of time and temperature. In both cases, the dispersion models of Knudsen [36] can be employed to describe the time evolution of the property of interest. The parabolic form of this model takes the form:

$$A=A_u\frac{k\sqrt{(t-t_0)}}{1+k\sqrt{(t-t_0)}}$$ (1)

where A_u is the ultimate achievable value of the property, t₀ is an induction time, and k is a rate constant that typically follows an Arrhenius function with temperature. Assuming this functional form, model properties predicted in terms of number of cycles can be calibrated to experimental properties measured as a function of time. In addition, knowing the heats of reaction and heat capacities of the concrete materials [37], the adiabatic heat signature curve of a model concrete may be readily computed. This approach assumes that all of the cement reactions can be considered to have the same activation energy and underlying rate-controlling processes.