Stress distribution in restrained ring test due to drying and autogenous shrinkage

Cracking of concrete is crucial from point of view of both durability and mechanical properties. With the extensive use of high-performance concretes that have low water to cement ratios, cracking sensitivity of concrete becomes even more important concern. Testing of concrete shrinkage restrained by steel ring turned into a standard for evaluation of the concrete potential for cracking. The stress at cracking in concretes with w/c ratios of 0.7, 0.45, 0.33, 0.25 and 0.21 was determined by means of restrained ring test and compared with the splitting tensile strength. The results show the significant change of stress to strength ratio at cracking with the change of water to cement ratio. Analysis of stresses was performed considering two types of shrinkage: drying shrinkage and autogenous shrinkage. Because drying shrinkage is driven by external drying that causes moisture gradient across the specimen and autogenous shrinkage is driven by internal drying – self-desiccation – that is uniformly distributed, stress distribution caused by these two types of shrinkage is significantly different. The analysis of the distribution of stresses in the restrained concrete ring due to autogenous and drying shrinkage provides a good explanation of the observed experimental data.