4.3.3
EFFECT OF MOISTURE UPON WATER ABSORPTION
Hall, in his review of water absorption in concrete [4.43], emphasized the importance of having a uniform moisture condition
at the start of a test. If this is not achieved then a square root time function for absorption will not be observed. In a theoretical
analysis Hall suggested that the sorptivity Si measured on a sample with an initial uniform degree of saturation M1 is given by
Si=So (1−1.08M1)0.5 where So is the sorptivity measured on a dry sample.
Millard [4.61] reported initial surface absorption (ISAT) data for a concrete dried to different levels of saturation and tested
at different temperatures (Fig. 4.46). It is evident that absorption increases with drying throughout the moisture content range
and at each temperature. The results of Hudd [4.62] in Fig. 4.47 are similar to those of Millard but they are more detailed in
the low moisture content range. For water/cement ratios 0.3–0.6 a maximum absorption is observed not for dry concrete, but