Transient plane source measurements of the thermal properties of hydrating cement pastes

A transient plane source measurement technique is applied to assessing the heat capacity and thermal conductivity of hydrating cement pastes in their fresh state and during the course of 28 d of hydration at 20°C. Variables investigated include water-to-cement mass ratio (w/c – 0.3 or 0.4) and curing conditions (sealed or saturated curing). The heat capacity data for the fresh cement pastes are compared to a simple law of mixtures, and analytical expressions are developed to estimate the heat capacity as a function of degree of hydration for the two curing conditions. The measured thermal conductivities of the fresh pastes along with the known thermal conductivity of water are used to estimate the thermal conductivity of the original cement powder via application of the Hashin-Shtrikman (H-S) bounds. Hydration is seen to have only a minor influence on the measured thermal conductivity. Extension of the law of mixtures for heat capacity and the H-S bounds for thermal conductivity to predicting the corresponding properties of concretes are discussed. RésuméUne technique basée sur une source de chaleur pulsée est utilisée pour déterminer la capacité calorifique et la conductivité thermique de pâtes de ciment à l’état frais et pendant les 28 premiers jours d’hydratation à 20°C. Les variables étudiées sont le rapport eau-ciment en masse (e/c 0.3 ou 0.4) et les conditions de cure (éprouvettes scellées ou dans l’eau). Les mesures de capacité calorifique des pâtes de ciment fraîches sont comparées avec la simple loi des mélanges. Des expressions analytiques ont été développées pour estimer la capacité calorifique en fonction du degré d’hydratation pour les deux conditions de cure. La conductivité thermique de la poudre de ciment utilisée est estimée à l’aide des valeurs de conductivité thermique mesurées et de la conductivité thermique de l’eau par la méthode des limites Hashin-Shtrikman. Le degré d’hydratation semble avoir une influence mineure sur la valeur de la conductivité thermique mesurée. L’utilisation de l’extension de la loi des mélanges pour la capacité calorifique et des limites H-S pour la conductivité thermique afin de prédire les propriétés correspondantes du béton est discutée.

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