The Effect of Heat Curing on the Early-Strength Development of Low-Carbon Concrete

The production of cement clinker requires the heating of raw materials up to a temperature of 1450 ℃, making it the third largest industrial energy consumer, generating 6–7% of global CO2 emissions. The fastest alternative for reducing the environmental impact of the cement industry is the partial replacement of cement clinker with supplementary cementitious materials (SCM). Due to the high price of silica fume and the sharp decrease in fly ash, ground granulated blast furnace slag seems the most promising SCM for the latter purpose. However, the high level of cement clinker substitution with slag can delay the setting and hardening time of low-carbon concrete. In the scope of this study, heating cables are applied to investigate the effect of heat treatment on the early-strength development of low-carbon concrete. The heating cables are used to supply enough energy to the slag grains and activate their hydration. The amount of heating energy, starting time and duration of heating are tested to accelerate the hardening time of cement with 40–70% of slag to the same level as cement with around 20% of slag (CEMII/B), which is the most used in Finland. Also, the optimum curing process with the least demand for electricity is estimated. The heating system was developed to uniformly distribute the defined amount of heat inside the cast samples. The experimental methods applied to evaluate the development of compressive strength included tracking of the ultrasound pulse velocity, rebound hammer and continuous temperature measurement.