The measurements of thermal conductivity of a cement-based composite material are performed in dependence on moisture content from dry state to fully water saturated state using an impulse technique. Then, the obtained data are analyzed using Brugemann and Wiener homogenization formulas. The validity of applied homogenization techniques is assessed comparing the measured and calculated results. On the basis of the experimental data and the homogenization analyses, the effects of total pore volume, pore distribution and moisture content on the thermal conductivity are discussed. Key words:Thermal conductivity, moisture content, cementitious composites, homogenization IntroductionCementitious composites contain a significant amount of pores of different size. As the thermal conductivity of the air is 0.026 W/mK [1] and the thermal conductivity of cement stone is (depending on the amount and the type of aggregates) in the range of 1-3 W/mK [2], both the total pore volume and the distribution of pores can affect the thermal conductivity of a cementitious material in a very significant way. In usual service conditions, cementitious composites always contain certain amount of water. The thermal conductivity of water is 0.60 W/mK [1], which is more than 20 times higher than of the air. Therefore, if water is present in the pore space, its effect competes with the effect of air, and the thermal conductivity of a composite material can be considered as a result of this competition together with the effect of the cement matrix.

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The basic thermal and hygric parameters of two different types of carbon-fiber-reinforced cement composites are analyzed in this article. The thermal conductivity, specific heat capacity, moisture diffusivity, and water vapor diffusion resistance factor are determined as functions of thermal load and tensile load applied before the measurement as well as of the combination of both types of load. The tensile load up to failure is found to be not a very significant factor for all material properties analyzed except for the moisture diffusivity. On the other hand, the thermal load is observed to result already at 600 C in considerable changes in all investigated thermal and hygric properties except for the specific heat capacity. The combinations of thermal and tensile loads lead to similar results as the effect of the thermal load alone so that the domination of the thermal load is apparent. This is supposed to be due to the positive effect of randomly distributed carbon fibers that can reduce the damage of the pore structure by the tensile stress. The resistance of the materials studied to high temperatures expressed by the change of hygric and thermal properties after thermal load is found to be positively affected by the application of the high alumina cement and in the case of the Portland cement-based composite also by using the autoclaving procedure in the production process.

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