No abstract

A broad experimental program was carried out on cubes, cylinders and prisms (loaded transversally or longitudinally) of sizes usually used in laboratory testing. For casting, concrete mixes of various compositions were used. The 1600 results obtained were evaluated by mathematical statistical methods. The volume of test specimens was substituted either by the size of the corresponding fracture area or by the size of the highly stressed volume (HSV) in their loaded cross-section; The absolute values of the tensile splitting strength were converted to relative values (depending on the basic size of the fracture area or on the highly stressed volume). For mathematical expression of the relationships between these quantities, an exponential function was used. This relation enables to convert the test results obtained on specimens of different sizes and shapes to the strength of the basic size specimen. This is important for the test results obtained on samples taken from finished structures, as these samples are usually of different sizes. RgSUME

This paper presents various techniques for materials characterisation in relation with the question of microbial impact. Applications examples of some of these techniques are described as well as the respective results obtained by researchers working in this field. Additional readings are also reported.1359-5997 © 2005 RILEM. All rights reserved. RÉSUMÉ Cet article présente diverses techniques de caractérisation des matériaux vues sous l'angle de l'étude des impacts microbiens. Des exemples d'application de certaines d'entre elles sont décrits ainsi que les résultats obtenus par des chercheurs travaillant dans ce domaine. Une bibliographie complémentaire est également fournie.

HE mineralogical composition, size distribution, and T morphology of particles of clay minerals are important in the production and firing of ceramics. MorBvek' found that the distribution of pores in clays also influences their behavior at high temperatures. In dried clays, the porosity and distribution of pores depend on the size and shape of the particles and on texture. The object of the present work was to determine the spatial distribution of clay particles of the same shape and of approximately the same size distribution. Homoionic sediments of kaolin from Sedlec at Karlovy Vary (Karlsbad), Western Bohemia?3 were prepared from pulverized kaolin with Li, Na, Mg, and Ca chloride solutions: These compacts were dried and divided into samples for porosimetry.The distribution of pore sizes and porosity for pore radii from 7 . 5~1 0 -~ to 7.5 pm were determined6 with a mercury porosimeter" ( Table I). The porosity of the homoionic sediments decreases in the series MgZt>Ca2+>Na+>Li+. The porosity values agree with those obtained by imbibometric water tests using a pipette and by sorption of water by the pulverized homoionic kaolinites after 24 hP The mean pore size of homoionic sediments decreases with decreasing porosity, as shown by the shift of the curves of integral porosity toward smaller values of pore radii (Fig. 1). The differences in the porosity and mean pore size may be explained by a simplified texture model with different degrees of orientation.' For Li kaolinite, a high degree of orientation of particles resulting from the slow sedimentation of nonaggregated particles in contrast to Mg kaolinite is assumed. The increasing degree of preferred orientation of the particles depends on the nature of the sorbed ion in the series Mgzc to Li+; this was verified by X-ray texture analysis of samples prepared from specimens cut from a plane perpendicular to the direction of sedimentation.The diffraction traces of the specimens (Fig. 2) show large differences in basal reflection intensities. Also, in the transition from Mg to Li kaolinite, there are significant decreases in the intensities of hkO and hkl reflections. Comparing the intensities of the (002) and (020) reflections by the method of Martin' gave peak ratios (Table I) which indicate that porosity decreases with increase in particle orientation; simultaneously, the mean size of the pores (Fig. 1) decreases. These results indicate that the cations adsorbed on the surface of kaolinite influence the orientation of the crystals and thus the porosity of the samples.