The initial surface absorption test (ISAT): an analytical approach

An experimental research programme was carried out to investigate the effects of high-intensity prolonged triaxial stresses on the strength and stiffness properties of concrete. The specimens tested were subjected to constant stresses equal to 90 or 95% of the failure stress deviator under monotonic loading in different deviatoric planes. The stiffness properties of the specimens were evaluated at different time intervals. The decrease in shear modulus was taken as a measure of the creep-induced damage. The specimens which did not fail at constant stress within five days were unloaded and monotonically reloaded to failure. For the specimens tested at the lower stress, damage tends to stabilize after the early stage at constant load, whereas, for the tests performed at the higher stress, damage seems to keep on increasing for the entire duration of the creep test. The strength of the specimens surviving the creep tests was found to increase moderately with respect to the control samples, with the failure envelope of the material being dependent on the hydrostatic creep stress.