This article presents the thermal constants of hydrated cement paste, which constitute the air-void wall of cement-based foam microstructure, and examines its influence on moisture, age, pozzolanic admixture type, and content. Along with the reference mix, containing portland cement only, six other mixes were prepared by replacing cement with fly ash, silica fume, and metakaolin, up to 20 % by mass in the binder. The Transient Plane Source, a thermal analyzer that conforms to ISO test standards, was employed to evaluate the thermal constants. Here, the measurements were made at 60, 120, 210, and 300 days. The results revealed that the drop in thermal conductivity for the cement paste was significant in the earlier age but progressively became insignificant as the hydration advanced. It was also found that adding fly ash and silica fume in higher dosages resulted in reducing the conductivity, while metakaolin exhibits a reverse trend. Furthermore, the reduction in the moisture content due to pozzolanic admixture was also noticed. Finally, an empirical formulation was developed to predict the thermal conductivity of the hydrated cement paste, which was also validated against the results of past research.

This study quantifies the pore wall spacing and shape factor of lightweight cement-based foam pore structure and investigates its correlation with density, pozzolan, compressive strength, and thermal conductivity. The lightweight cement-based foam mixtures were prepared for the densities of 800–400 kg/m³ and by replacing cement with fly ash, silica fume, and metakaolin up to 20 % by mass. The nondestructive technique of X-ray microtomography was used for quantifying the pore structure parameters. In addition, the transient plane heat source technique was used to evaluate the thermal conductivity of these mixtures. The results show that the optimal pore wall spacing increases from 0.28 to 0.55 mm as the density rises from 400 to 800 kg/m³. It was observed that the median pore wall spacing (SP50) values increases as the cast density get higher. While the reduction in thermal conductivity was noticed for lower SP50 values. Furthermore, incorporating pozzolanic admixtures at higher cement replacement ratios affects the pore wall spacing. Moreover, spherically shaped pores were found in all mixtures.