A testing and analysis procedure is outlined to quantify the behavior of concrete under restrained shrinkage using ring specimens. Cracking resistance is found to depend not only on shrinkage potential and tensile strength, but also on shrinkage rate and tensile creep characteristics of the concrete. The creep strain obtained for the ring specimens can be as high as 50% of the free shrinkage strain, indicating that tensile creep is significant and must be considered in evaluating the risk of cracking under restrained conditions. Shrinkage-reducing admixtures significantly enhance the cracking resistance of concrete by reducing both the shrinkage potential and the shrinkage rate. A separate study was carried out on the concrete mixtures to determine the tensile creep characteristics under a constant stress. The results from the two studies are compared. The comparison shows that tensile creep of concrete is lower under restrained shrinkage than under a constant stress. This suggests that use of tensile creep properties obtained under a classical constant load test, for analysis or modeling of restrained concrete elements subjected to drying, would lead to unconservative predictions of performance.
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