Experimental Validation of Relaxation Prediction Models in Concrete

Abstract

Concrete undergoing volumetric changes is likely to be met with sustained restraint. This restraint leads to stresses which are reduced by tensile relaxation, in turn enabling the mitigation of cracks. Although creep and relaxation are said to be related, creep is well understood, while relaxation is not. In addition, relaxation is predicted from creep values because of the difficulty involved in performing relaxation experiments. This study validates approximate relaxation prediction models by comparing predicted values with experimental results. Two related methods are used: the effective modulus method and the age-adjusted effective modulus method (AAEM). Results indicate that using approximate relaxation models to predict early-age relaxation is valid. The accuracy of prediction increases as ultimate relaxation is reached, i.e., after 72 h for both the effective modulus method and the AAEM. No improvements in predictions are observed when the AAEM is used. The nature of load application does not seem to influence predictions.