The pozzolanic activity of different materials, its influence on the hydration heat in mortars

This work presents the relationship that exists between pozzolanic activity in certain materials (opaline rocks, fly ash and silica fume) and hydration heat, measured using the Langavant calorimeter method. Pozzolanic activity is evaluated using an accelerated method that establishes the reaction speed of the different materials considered. While replacement of part of the cement in a mortar or concrete typically reduces the overall heat of hydration, it is shown that, compared to a control cement, silica fume and opaline rock mixes with cement give increased heat output during early hydration. This is due to their rapid and strong lime-pozzolanic reaction. The much less reactive fly ash decreased early heat output, compared to the control cement. a good correlation of between pozzolanic activity and hydration heat found.