ASTM C1585 is commonly used to determine the absorption and rate of absorption of water in unsaturated hydraulic cement concretes. ASTM C1585 preconditions the samples for a total of 18 days. Unfortunately however, the range of relative humidities that can exist in the samples after this relatively short conditioning period may provide a wide enough variation to considerably influence the results of the test. Three main variables were studied in this program to assess the effect of preconditioning. First, the role of water to cement ratio was investigated by testing mortar samples with 55 % aggregate by volume with four different water-to-cement ratios (w/c of 0.35, 0.40, 0.45 and 0.50). Second, the role of paste volume was investigated by considering samples with 55 %, 45 %, and 35 % aggregate by volume with a w/c = 0.50. Finally, the effect of conditioning was assessed by exposing all the samples in three different relative humidities (50 %, 65 % and 80 %) until they reached mass equilibrium (defined as a change of mass less than 0.02 % over 15 days), taking approximately 14 months. Oven dry samples were also prepared and tested for comparison. 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 for the 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.
Citation: Cement and Concrete Composites
Pub Type: Journals
Aggregate content, concrete, conditioning, sorptivity, water absorption.