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A B S T R A C T R I~ S U M I{Three-dimensional X-ray microtomography is used to obtain three-dimensional images of the microstructure of two types of brick. The images are processed to remove the noise (random and circular pattern) and then thresholded to match the porosity determined experimentally. The 3-D binary images are then analyzed to estimate their vapor diffusivity and air permeability to compare to experimental data published in part one of this report. Care must be taken in obtaining the tomographic images at a resolution that both enables isolation and quantification of the pores of interest and provides a representative elementary volume for the transport property calculations. In general, the agreement between computed and measured properties is reasonable, suggesting that X-ray microtomography can provide valuable information on the characteristics and properties of the pore networks developed in these porous building materials. A preliminary evaluation indicates that the Katz-Thompson relationship between permeability, diffusivity, and pore size is valid for these materials. La microtomographie a rayons X synchrotron est utilis& pour obtenir des images tridimensionnelles de la m#rostructure de deux types de briques. Les images sont tout d'abord trait&s pour Oliminer le bruit (anneaux al&toires) et ensuite seuill&s par ajustement avec la porosit~ d~termin& exp&imentalement. A part# des images binaires 3D, on estime num&iquement la diffusivit~ a la vapeur et la permdabilit~ a I'air, les valeurs obtenues sont ensuite compar&s avec les donn&s exp&imen-tales publi&s dam la part# I de cette communication. Dam le cadre d'une telle procedure, la r&olution des images doit a la fois rendre possible la discrimination et la quantification de tous les pores importants vis-a-vis du ph&omkne ~tudid et foumir

RESUMEMassive walls exposed to the natural climate without special rain protection show a dynamic moisture equilibrium governed by the alternating events of rain and sunshine. The moisture further reduces the rather low insulation level of the walls. Therefore, thermal insulation measures have to be taken in order to improve the hygienic conditions and the thermal performance of the building. The influence of interior and exterior insulations on the hygrothermal behaviour of such walls can be determined with the aid of a recently developed computer program which has been experimentally validated by comparison with field tests. The results show that an exterior insulation leads to the drying of the wall, with the drying rate depending on the vapour permeability of the insulation system. An interior insulation, however, results in a rising water content of the wall due to the decreasing masonry temperature. This effect is almost independent of the vapour permeability of the insulating material. While an exterior insulation also improves the thermal resistance of the masonry, an interior insulation has the opposite effect and increases the frost damage risk. Therefore, the interior insulation of exposed wails should be combined with rain protection measures at the facade. Des tours massifs expos& au climat natuwl sans pw-

The moisture behaviour of building materials exposed to the natural climate is largely dependent on their water absorption. In contrast to most building stones, cementitious materials like concrete do not exhibit a water absorption that is proportional to the square root of time. There must be a slowing-down effect which is related to water because the absorption of organic liquids, such as hexane, is quite normal. Measurements of the porosity of hardened cement paste determined by helium pycnometry and water saturation show that water molecules can enter spaces in the microstructure which are not accessible to the smaller helium atoms. Considering the results of dilatation tests both before and after water and hexane saturation, it seems possible that a contraction of capillary pores due to moisture-related swelling of the cement gel leads to the non-linear water absorption over the square root of time. RESUM