Variation of creep Poisson's ratio with stress in concrete under short-term uniaxial compression

Abstract

An experimental study of creep Poisson’s ratio, the ratio of transverse creep to axial creep, for sustained load durations of up to 31 min, revealed that its variation with stress occurred in three stages. It was found that creep Poisson’s ratio remained fairly constant and close to the elastic Poisson’s ratio at stresses below 50% of the compressive strength. Above this stress level, creep Poisson’s ratio generally increased with stress but decreased with time under sustained loading, until a threshold stress was exceeded. Beyond this threshold stress, creep Poisson’s ratio was found to be greater than 0·5 and increasing with time. At this third stage, it was shown that the volume of concrete increased with time at increasing rates. This third stage is therefore the stage of dilating creep which will inevitably lead to eventual creep fracture. The threshold stress, which was found to be about 79 to 89% of the compressive strength in this study, was therefore established as the strength of concrete under sustained loading, or simply, the creep strength.