RESUMEN
The composition of 23 concrete mixtures was varied in five separate series to evaluate the influence of porosity on the ²²²Rn exhalation rate. In each series, a range in porosities is obtained by varying (1) the amount of cement, (2) type of cement (Portland or blast furnace slag cement), (3) the amount of water at a fixed cement level, (4) addition of an air entraining agent, or (5) the amount of recycled aggregates. The porosities ranged from 1% to 16%. The ²²²Rn exhalation rate is normalized to the ²²6Ra activity concentration and expressed as the ²²²Rn release factor to eliminate the effect of differences in ²²6Ra activity concentrations among the various concrete mixtures. Since most ²²²Rn originates from the cement, a ²²²Rn release factor based on the amount of ²²6Ra introduced by the cements appeared to be more adequate. Although the methods to attain the porosities in the concrete mixtures differ widely, this cement-related factor corresponds well with the capillary porosity of the mixtures. Since the water-to-cement ratio of the fresh paste is a good indicator of the capillary porosity, this is the guiding factor in the fabrication of concretes low in ²²²Rn exhalation. The lower the water-to-cement ratio, the less capillary pore area will be available from which ²²²Rn can emanate from the mineral matrix into the pore system. The good correlation between the cement-based ²²²Rn release factor and literature data on the internal capillary pore area support the results of this study.
Asunto(s)
Materiales de Construcción/análisis , Porosidad , Radón/análisis , Aire , Cinética , Radiactividad , Agua/químicaRESUMEN
The measurement of volume change, which is induced by changing the relative humidity, is performed on rice by using environmental scanning electron microscope (ESEM) and stereoscopy techniques. The typical DeltaV% approximately RH curve of rice in both sorption and desorption can be categorized into three regions: low, intermediate, and high dependence on relative humidity from low- to high-relative humidity. The volume changes faster for rice samples with lower crystallinity, which is because the amorphous component is easier to absorb moisture than the crystalline component. The volume change behavior in various relative humidity environments is comparable with rice isotherm curve in sorption process though discrepancies exist in desorption, which are thought to be the presence of small pores and microstructure changes at high relative humidity. The volume in the desorption branch is less than that in the sorption branch at the same relative humidity, which can be attributed to the collapse of interior structures, existence of small pores, surface topography loss, and amylose leach.