Determination of coefficient "s" and apparent activation energy for fib model code's maturity-based strength function when applied to fly ash concrete

The maturity-based strength function recommended by fib model code 2010 can be easily utilized to estimate the compressive strength of normal-strength or high-strength cement concrete. However, the lack of calculation approaches and guidelines for determining the coefficient "s" and the apparent activation energy Ea in the fib model code's maturity method have limited its further application to fly ash (FA) concrete. In this study, with reference to ASTM C1074, this limitation is addressed by adopting the equivalent mortar method to determine the coefficient "s" for the concrete under investigation. The feasibility and superiority of the equivalent mortar method were validated through two cases. Moreover, the original strength function in fib model code is modified to incorporate the reaction rate constant, allowing the use of Arrhenius equation to determine the mixture-specific Ea value. The iterative searching method is also supplemented to find the best-fit Ea value. The results demonstrated that the Ea value, obtained either through the linear Arrhenius plot or the iterative searching method, does not match the default Ea value (33.33 kJ/mol) provided by the fib model code, and can achieve relatively lower standard error for strength estimation of FA concrete.