Applicability of fib model code's maturity function for estimating the strength development of GGBS concretes

The early age compressive strength of concrete can, according to the fib Model Code, be estimated from its 28-day strength using an exponential function. This requires an “s” value which depends on the strength class of the cement. This has recently been extended to include supplementary cementitious materials (SCMs), or otherwise known as additions, by providing a way of determining an appropriate “s” value based, in addition to cement strength class, on the water/binder and SCM/binder ratio. The applicability of this relationship for four concrete grades (C30/37, C35/45, C50/60 and C60/75) with up to 70% ground granulated blast-furnace slag (GGBS) has been investigated and shown to be satisfactory. This increased confidence in its use for predicting the strength development of other curing regimes, i.e. adiabatically cured concrete cubes, using the maturity function in the fib Model Code. Predictions/estimates of the effect of the adiabatic temperature history on the compressive strength development using the maturity function in the fib Model Code have been compared to those of the Arrhenius function that uses a strength-time relationship and “apparent” activation energy determined from experimental data. The fib Model Code's strength estimates were not significantly affected by the use of one value of “apparent” activation energy for all concrete mixes, i.e. the “apparent” activation energy was not specific to the concrete mix.