Variation of differential strain ratio in normal-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 stress levels. The experimental results of short-term sustained loading tests 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 transverse strain with respect to axial strain) for determining whether a concrete specimen has reached the point of creep fracture is proposed. Test results showed that the stress–strength ratio of the creep strength of concrete increased with the strength of concrete. The transverse and axial strains of concrete at this critical stress–strength ratio did not vary much with the strength of concrete, but averaged about 320–350 and 1430–1470 microstrain respectively.