Effect of Temperature on the Early-age Hydration and Setting Behaviour of Mixes Containing GGBS

Over the past years there has been an increasing trend to use supplementary cementitious materials in concrete to improve its sustainability credentials and durability properties. Perhaps amongst the most popular supplementary cementitious materials is ground granulated blast -furnace slag (GGBS). While the hydration and setting characteristics of mixes with GGBS cured under standard conditions (20 degrees C) has been adequately investigated, the effect of temperature on heat of hydration and setting and the interrelation of these properties has not been evaluated for GGBS containing mixes. In this study, the heat of hydration and setting behaviour of mixes with various levels of GGBS (0, 20, 35, 50 and 70%) cured under elevated temperatures (20, 30, 40, 50 and 60 degrees C) is determined. Elevated curing temperature accelerates the hydration reactions and can significantly reduce the setting time of GGBS-containing mixes. The investigation of heat of hydration at very early ages, can provide an indication of the initial and final setting times of cementitious mixes. The "apparent" activation energy used to characterise temperature sensitivity of cementitious systems, is calculated based on heat of hydration and setting time measurements. It was found that the "apparent" activation energy increases with GGBS content for both heat of hydration and setting behaviour. The value of "apparent" activation energy differs significantly depending on the material property that is considered, such as compressive strength, heat of hydration or setting time.