Measurements and Predictions of Heat of Hydration of Portland Cement Using Isothermal Conduction Calorimetry

Two industrial ASTM Portland cements were carefully tested for heat of hydration (HOH) continuously up to 7 days at 23o C using isothermal conduction calorimetry in accordance to ASTM C1702. Internal and external mixing procedures were implemented. The results for HOH measurements at 7 days using isothermal calorimetry were compared to those obtained through heat of solution method (ASTM C186). The results indicate that for a given Portland cement, the shape of the HOH curve can be predicted with sufficient accuracy by measuring the heat of hydration to an age corresponding to an approximately ten times the age at maximum heat flow or main hydration peak. The heat of hydration at ages up to 7 days can be predicted by fitting an analytical function similar to functions used in Maturity calculations. The suggested approach would eliminate the need for measuring data at ages when the heat flow has decreased substantially well past its maximum where the signal to noise ratio is low. This approach effectively proposes a method for predicting accurately the total heat generated at 7 days by Portland cement based on 3 days heat flow measurements.