We also examined how boundary conditions affect water absorption. In Figure 4, we show the sorption versus time of bench dried samples for the following boundary conditions. Samples were either exposed to air, taped on the sides (with a vinyl tape), or placed in a closed container without taping the sides. Note that the sample exposed to air actually decreased in weight after an initial rise. Since theses samples had been bench dried for a specified time and not to a constant weight they were partially saturated at the start of the capillary sorption measurements. As a result, an observed rapid decrease in the rate of capillary suction coupled with the evaporation of moisture from the samples sides led to a reduction of the samples moisture content after the initial increase. In the other extreme, samples exposed to air but placed in a closed container had the greatest amount of sorption since there was little or no evaporation and moisture could enter from the sides due to the high humidity in the container. We also examined the case of the specimens taped on the sides only versus the case of taping sides and top. We saw only a small difference in the sorption here. However, some of this difference could be due to sample variation. Also, while the vinyl tape was essentially impermeable, the taping procedure did not necessarily produce an air-tight seal since some air could leak along the sides. For the rest of this paper we will only present results of the capillary sorption studied for samples taped on the sides.
FIG. 4. The influence of the method of exposure of the specimen to water is shown by the rate of absorption versus time. Container: specimen placed in a box; Taped: sides were covered with tape; Untaped: no protection on the sides and not in a container. All specimens were bench dried before exposure to the water.