The Effect of Temperature on the Rate of Strength Development of Slag Cement

This paper will investigate the early age strength development of concretes containing slag cement (ggbs) at levels of up to 70% of the total binder to give guidance for their use in fast track construction. 28-day target mean strength for all concrete specimens was 70 MPa (10,150 psi). Although supplementary cementitious materials such as slag cement (ggbs) are economical, their use has not gained popularity in fast track construction because of their slower strength development at early ages and at standard cube curing temperatures. There are however indications that supplementary cementitious materials are heavily penalised by the standard cube curing regimes. Measurements of temperature rise under adiabatic conditions have shown that high levels of cement replacement by ground granulated blast furnace slag (GGBS), e.g. 70% are required to obtain a significant reduction in the peak temperature rise. Even though the temperature rise using slag cement is lower than from using portland cement, it is still sufficient to provide the activation energy needed for a significant reaction acceleration. Maturity measurements are needed to take advantage of the enhanced in-situ early age strength development of ggbs concrete. The contractor should confirm that the actual compressive strength of the concrete in the structure at the time of formwork removal exceeds the required strength. Maturity functions like the one proposed by Freiesleben Hansen and Pedersen (FHP), which is based on the Arrhenius equation, have been examined for their applicability to ggbs concrete. Activation energies, required as input for the FHP equation, have been determined according to ASTM C1074-98.