a Methodology for Thermal Characterization of Cementitious Materials.

This study was an attempt to develop and utilize a method to measure thermal conductivity of cementitious materials without affecting the state of equilibrium of the sample. The thermal comparator method employed and developed here was proved to be suitable for this kind of material. The method was used to measure thermal conductivity of neat cement and cement plus additives. An attempt was also made to study other thermal properties of cementitious materials, such as thermal expansion and early heat of hydration. Class C portland cement was used in this study, mixed with different water to cement ratios and with additives and admixtures (fine quartz, fly ash, and quartz and basalt sands); and the thermal properties were measured at curing times up to three months. Thermal conductivity and thermal expansion were found to be dependent upon curing times, moisture contents, and concentrations and types of admixed phases. Mathematical relations of thermal conductivity as a function of additive contents were obtained at different curing times for the additives used in this study. Both thermal conductivity and thermal expansion were found to reach constant values when cementitious materials approach maturity. It was shown that thermal conductivity of mature hydrated additives can be estimated using the experimental results from measurements on composites. The hydration rate was also studied and the effect of additives as accelerators or retarders was explored using the rate of heat evolution curves. Results indicate that inert additives like quartz have no significant effect on the hydration rate, and reactive additives like fly ash tend, in general, to accelerate the reaction. Applications of the methods to the determination of properties of seal materials for geologic repositories for nuclear waste are discussed.