Moisture transport and fixation in porous materials at high moisture levels
Abstract: The work presented in this thesis focuses on developing methods of measuring moisture properties at high moisture levels. Paper I deal with a new method of measuring moisture diffusivity at high moisture levels. Papers II to IV present methods of measuring moisture storage capacity as well as results from such measurements. Paper V evaluates the use of thermal imaging to measure transient moisture profiles. Paper VI shows how the measured moisture properties can be used in calculations The contents of the six papers are as follows: This paper presents measured moisture diffusivities for several different porous building materials. The diffusivities were calculated from the relation between the water sorption coefficients and the initial water content. The method is based on Boltzmann transformation. Knowledge of moisture storage capacity over the hygroscopic range is essential when calculating the moisture content. Generally storage capacity is represented by water retention curves, in which suction is plotted against moisture content. The pressure plate and pressure membrane technique is often used to measure water retention curves. There are, however, various ways of carrying out such measurements. This paper compares two different methods of presaturating the specimens before testing, namely capillary and vacuum saturation. It also examines the effect of different beddings between the specimen and the ceramic plate. Sorption properties, i.e. information about how much water a porous material holds in different environments, are of interest in many applications. This paper reports on the use of four different methods to measure the sorption isotherm of sandstone. The first method involved equilibrating samples over saturated salt solutions. The second involved weighing small samples in a sorption balance as they were exposed to different relative humidity. The third method was the pressure membrane and pressure plate technique. In the fourth method a newly developed micro-calorimetric technique was used. Despite the differences in the methods, satisfactory agreement was found in the measured sorption isotherm. This paper presents measurements of the moisture storage capacity of several different porous building materials. The storage capacity was measured with a sorption balance in the hygroscopic range and with pressure plate and pressure membrane extractors in the superhygroscopic range. Moisture profiles reveal much about the moisture behavior of a material or combination of materials. One possible method of measuring these profiles is thermal imaging. This paper evaluates this technique on bricks with and without cement-lime mortar attached. Degradation of historical buildings and monuments is an increasing problem in most countries around the world. In order to take the correct measures to preserve the buildings, the process causing the degradation must be identified. One technique for excluding or identifying probable causes of damage to porous materials is demonstrated in this paper. The technique is based on moisture transport calculations and is exemplified using sedimentary calcareous sandstone. The calculations were made at very high moisture levels, both under and over capillary saturation.
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