VARIATION OF DIFFERENTIAL STRAIN RATIO IN NORMAL-STRENGTH AND HIGH-STRENGTH CONCRETE UNDER SHORT-TERM UNIAXIAL COMPRESSION

The creep behaviour of concrete test specimens of three different mix proportions and strength levels was studied at various sustained stres s levels. The experimental results of short-term sustained loading tes ts were analysed to provide a quantitative description of the observed behaviour. The creep behaviour of normal- and high-strength concrete and the companion mortar specimens was compared. A method based on the variation of differential strain ratio (the rate of change of transve rse strain with respect to axial strain) for determining whether a con crete specimen has reached the point of creep fracture is proposed. Te st results showed that the stress-strength ratio of the creep strength of concrete increased with the strength of concrete. The transverse a nd axial strains of concrete at this critical stress-strength ratio di d not vary much with the strength of concrete, but averaged about 320- 350 and 1430-1470 microstrain respectively.