Test method to evaluate shrinkage cracking of concrete

The possibility of shrinkage for a given drying environment depends on the following factors: free shrinkage, creep, and age-dependent properties of concrete. A common way to account for shrinkage cracking is to provide so-called secondary reinforcement. Recently, shrinkage reducing admixtures have been introduced. These admixtures can also reduce the possibility of shrinkage cracking. However, there is no standard test to assess cracking due to restrained shrinkage. It is also difficult to produce controlled cracking in linear specimens. Therefore, a ring type of specimen is used in this study. With the dimensions of specimen, it can be shown that the concrete ring is subjected to approximately uniaxial tensile stresses. Crack development is measured with an internally illuminated microscope. Effects of type and volume of fibers, conventional mesh reinforcement and of a shrinkage reducing admixture are being studied.