INTRODUCTION

                As cement hydrates and concrete cures in the field or in a pre-cast plant, there is always a risk of early-age cracking that might compromise the longer term performance of the in-place product.  Of the various sources of stresses that can influence such cracking, thermal stresses can be one of the more significant contributors.  For this reason, various models to predict the distributions of temperature [1-3] and stress [4] in hardening concrete have been developed in recent years.  Whether a simplified one-dimensional or a fully developed three-dimensional heat transfer model is utilized, critical inputs for these computations are the thermophysical properties of the concrete as a function of time, including its density, heat capacity, and thermal conductivity.  These properties will be determined by the concrete’s mixture proportions, the thermophysical properties of the aggregates that it contains, and those of its hydrating cement (binder) paste component.  While the necessary densities are generally either well known or easily measured, less information is readily available on the heat capacities and thermal conductivities, particularly those of the hydrating cement paste.  In this paper, a transient plane source (TPS) method is applied to measuring heat capacities and thermal conductivities of hydrating cement pastes cured under both saturated and sealed conditions at room temperature.

                Previous measurements of heat capacity (specific heat) and thermal conductivity (thermal diffusivity) for cement-based materials were conveniently summarized by De Schutter and Taerwe in 1995 [5].  Since that time, several additional studies have been published [6-14].  However, while most of these recent studies have focused on thermal conductivity, the obtained values for this property for hydrated cement paste still exhibit considerable scatter, as illustrated in Table 1.  For the heat capacity of hydrating cement pastes, two previous studies [5, 15] have measured the heat capacity of water-to-cement mass ratio (w/c=0.5) cement pastes of two different cement types during hydration, obtaining values in good agreement with one another.  In addition, in [13], a heat capacity of 1.6 J/(g·K) is reported for a hardened w/c=0.4 cement paste.  The current study will supplement these previous data by performing measurements on hydrating cement pastes with w/c=0.3 and w/c=0.4, using the TPS technique.

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