Estudo da estrutura de poros de um compósito de matriz cimentícia por meio da microtomografia de raios x

Abstract

The composites with Portland cement matrix have an internal pore network, which distribution system is strongly influenced by production factors, as strength, molding and curing. The pore structure has a directly impact on the physical properties of materials, such as compressive strength. Although exist many techniques for measurement and characterization of pore structures, the X-ray microtomography has shown promise for this kind of investigations, because it allows to obtain informations of the materials internal microstructure without requiring special preparation of the samples. However, in order to obtain a good spatial resolution, the technique demands small size samples, which opposes the issue of representativeness, once Brazilian standards have specimens with dimensions with (5x10) cm, that exceeds the reading capacity of the equipment used in this research. In order to facilitate the X-ray microtomography test, and in order to avoid recurring problems of sampling, were produced specimens with dimensions of (2x4) cm, molded with mortar produced according to the parameters specified in the NBR 7215 (ABNT, 1996), using Portland cement high early strength. Compression tests were performed and the percentage of total porosity has also been calculated, for the two dimensions of specimens, from the relationship between true density and bulk density, got by techniques helium pycnometry and mercury pycnometry, respectively. The results indicated a slightly higher compressive strength and slightly lower percentage of porosity for the specimens of (2x4) cm. In the pore structure analysis, it was observed a good approximation between the total porosity values, obtained by the two methods adopted. The calculations of porosity and other morphological parameters, made from the readings with microtomography equipment in the specimen of (2x4) cm, were performed considering its different regions, in order to simulate the process of sampling. The results indicated that the pore structure varies along the section of the specimen.