Effect of in situ temperature on the early age strength development of concretes with supplementary cementitious materials

• In-situ temperature histories from blocks, walls and slabs cast during winter and summer.
• Temperature sensitivity of supplementary cementitious materials.
• Effect of supplementary cementitious materials on the peak temperature of structural members.
• Early age in-situ strength development as affected by geometry, size, ambient conditions and type of binder.
• Accuracy of maturity functions, Nurse–Saul and Arrhenius based, in estimating in-situ strength development.

A UK based project which involved casting of blocks, walls and slabs, during winter and summer, provided in situ temperature histories that could be simulated in the laboratory using a computer controlled temperature match curing tank. The concretes which were of 28-day target mean strengths of 50 and 30 MPa also had partial cement replacement with supplementary cementitious materials (SCMs) such as ground granulated blast-furnace slag (GGBS) and pulverised fuel ash (PFA). The SCMs were effective in reducing the peak temperature especially when there was heat dissipation. The contribution to early age strength by SCMs increased with the high in situ temperatures especially in blocks cast during summer. The accuracy of strength estimates obtained from maturity functions was examined. The temperature dependence of the Nurse–Saul function was not sufficient to account for the improvement in early age strengths resulting from the high temperatures in blocks cast during summer. The Arrhenius based function, was better at estimating the early age strengths as it assumes that the concrete strength gain rate varies exponentially with temperature.