The effects of elevated temperature on cement paste containing GGBFS

Fires can expose concrete to extreme temperatures. Thus, it is important to know the effect of elevated temperature on the concrete property. High performance concrete (HPC) often contains other supplemental cementitious materials besides cement, such as ground granulated blast furnace slag (GGBFS) and chemical admixtures such as superplasticizer (SP). GGBFS has been used successfully to improve concrete properties. This paper investigates the effects of GGBFS on concrete properties at elevated temperature. A total of 588 test specimens were prepared with three water-to-binder (W/B) ratios and six different GGBFS contents. The test specimens were cured for 28 days and then subjected to seven different elevated temperatures of up to 1050 °C for 4 h. It was found that at a temperature of 1050 °C, cracks appeared for all three W/B ratios when the GGBFS content was 10% or less. Cracking was significantly reduced as the GGBFS content was increased to 20% or above. It was also found that at elevated temperature (1050 °C), compressive strength greatly increased with increasing GGBFS content, especially for the W/B ratio of 0.23. Thus, the fire resistant properties of HPC are greatly improved by the addition of GGBFS. In contrast, GGBFS with a W/B ratio of 0.71 showed no significant increase in compressive strength. At a W/B ratio of 0.23, the clear trend was observed that the optimum GGBFS content for fire resistance is between 50% and 80%. The compressive strength of concrete is more susceptible than the elastic modulus to the effects of elevated temperature.