Prediction model on creep of recycled aggregate concrete filled steel tube

This paper intends to propose the creep model for recycled aggregate concrete filled tube (RACFST), which is based on the concrete model with the capability of well predicting the time-dependent behavior of recycled aggregate concrete (RAC). Existing concrete models for RAC only consider the influence of the amount of residual cement mortar attached on the recycled aggregate on the creep of concrete, without considering the effect of the water-cement ratio of the origin concrete. Based on the analytical results, the important factor which influences time effects of RAC was specified to propose a modified model considering the water-cement ratio of the original concrete. All the concrete models for RAC were benchmarked against 39 available creep tests to evaluate the reliability of those models in predicting the creep of RAC. It is indicated that the modified model proposed in this paper has the best performance in estimating the creep of RAC members whose water-cement ratios are different from those of original concrete. In order to verify the reliability of the proposed model in predicting the long-term responses of RACFST, the creep models were benchmarked against the long-term tests on eight RACFST stub columns under axial loading with different loading ages. The strength of RAC core in the experiments was higher than that of original concrete. When predicting the test results, the age-adjusted effective modulus method was employed by adopting an infinite notional size for the concrete component to eliminate the effects of relative humidity. It can be noted that the modified model proposed in this paper also has the best accuracy in predicting the creep of RACFST with the maximum deviation within 8%, which can be applied in the analysis of long-term responses for such member in the practical engineering.