Creep-recovery of normal strength and high strength concrete

The creep-recovery behavior of both normal and high strength concrete (HSC) under various load conditions has not been studied thoroughly. Although the use of HSC is long-established, rational creep-recovery prediction of HSC is still unavailable since current study just regards recovery deformation as a secondary result of creep experiments. In this paper, a new prediction model for creep-recovery of normal strength concrete (NSC) with considering the influence of stress level and load history was proposed at first. Then, a model for HSC creep-recovery was established according to creep-recovery data of NSC and HSC in literatures and the influence of compressive strength of concrete. To validate the HSC model, an experimental study of the creep behavior of C80 concrete was conducted. Creep and residual strain after unloading of specimens at various compression stress levels (30% and 50% of the compression strength) were compared with the HSC creep-recovery model. Although the HSC model tends to underestimate the first 7 days' creep-recovery value, the results show high overall prediction accuracy. Moreover, parametric analysis results indicate that the recoverable creep of HSC reduces significantly than that of NSC. The effect becomes stronger with the increase of loading age and weaker with a prolongation of load duration.