Synopsis
Simulated large pour studies in which ground granulated blast furnace slags from three European sources were blended with OPC have shown that both the peak temperature and the time to reach this temperature are strongly injhenced by slag source. With a reactive slag and a moderate level of OPC replacement (20–40%) the temperature rise at the centre of a large pour may be higher than that at the centre of an equivalent OPC pour.
Five levels of slag replacement were investigated in concrete with a cement content of 315 kg/m3. The compressive strengths of concrete cubes cast from the same mix and stored under matched curing conditions were also determined.
Results obtained with concrete under variable loss, semi-adiabatic conditions were compared with those obtained with pastes under isothermal conditions at a single temperature of 20°C. The isothermal results are of little value in predicting behaviour in large pours and can be quite misleading.
It therefore follows that care should be taken when selecting a slag source and a slag level for large concrete pours. Reliance should not be placed on published results obtained with other slags or on isothermal calorimetry carried out at 20°C only.
