Comments on the interpretation of results from the restrained ring test

The restrained ring test has recently been standardized (ASTM C1581-04) as a test method to assess the restrained shrinkage cracking susceptibility of a concrete mixture. Unfortunately, there is currently a lack of published information regarding the repeatability of the test. This paper quantifies the variability of the ASTM C1581-04 ring test procedure. To determine the repeatability of the standard test, 24 restrained ring specimens were cast from the same mortar mixture and stored in carefully controlled environmental conditions. Results from the restrained ring test were assessed using the same mixture proportions. The results indicate that a standard deviation of approximately 6 ue can be expected in the strain measurements from the same mixture and 8 us from different batches of the same mixture. The total coefficient of variation observed was less than 12 % (within single mixture and between different batches). A probabilistic approach was used to describe the variability associated with the age of cracking and to provide a tool that allows cracking prediction, especially when only a fraction of the ring specimens crack.