Effect of sample conditioning on the water absorption of concrete

ASTM C1585 is commonly used to determine the absorption and rate of absorption of water in unsaturated hydraulic cement concretes. Unfortunately, a wide range of relative humidities can exist in the samples after this relatively short conditioning period and such variation may considerably influence the test results. Three main variables were studied in this program: the water to cement ratio, the paste volume fraction, and the effect of sample conditioning. The results confirm that water absorption testing is considerably influenced by sample preparation. Samples conditioned at 50% relative humidity can show up to six times greater total absorption than similar samples conditioned at 80% relative humidity. Samples that were conditioned in the oven at 105 °C do not appear to follow a similar trend when compared with specimens conditioned in chambers at lower temperatures for a longer duration. The absorption is also influenced by the volume of paste in the samples. The experiments show that a lack of control on moisture content or lack of consideration of the material composition may lead to a misunderstanding of the actual absorption behavior.

► Water absorption tests are influenced considerably by the moisture content of the samples before starting the test.
► The conditioning procedure described in ASTM C1585-04 is not able to eliminate the “moisture history” of the samples.
► It is recommended that field samples be pre-saturated prior to being exposed to the conditioning regimen of ASTM C1585.
► Conditioning samples in an oven at 105 °C is not recommended, as it can adversely affect the microstructure of samples.