Initial surface absorption of concrete: examination of modified test apparatus for obtaining uniaxial absorption

A modification to the initial surface absorption test (ISAT) is examined, which incorporates a water-filled guard ring. lhis produces an absorptionfiw pattern closer to the pure uniaxial situation than the conventional test apparatus. A series of laboratory specimens covering a range of concrete mixes and surface drying conditions have been examined using both the conventional and the modified ISATapparatus. A correlation between the initial 10 min absorption rate and the cumulative absorption over the 2 h test period was observed for both types of apparatus. At higher absorption rates the cumulative absorption, for a given initial su$ace absorption rate, was lower for the modified apparatus, suggesting that a more uniform absorption pattern was achieved using this modification. Althoughthe problem of compensating for the fluctuating state of saturation in concrete structures has yet to be resolved, possible relationships between the modijied ISAT test results and sorptivity are presented.