Restrained Shrinkage Cracking in Concrete Elements: Role of Substrate Bond on Crack Development

Abstract

Several specimen geometries have been used to assess restrained shrinkage-cracking behavior of concrete materials. This paper used a series of restrained slab tests to illustrate the importance of specimen geometry on the restrained shrinkage cracking behavior. While restraint was provided along the base of the slab, a portion of the slab was left unbonded to the base in the center of the specimen. The length of this unbonded portion was varied to demonstrate its impact on the age of cracking and crack width that occurred. The age of cracking was measured using visual analysis, image analysis, conductive surface coating, and acoustic emission. Whereas image analysis and conductive paint detect cracks only after they appear on the surface, acoustic emission also provides information on damage development before the cracks were visible. Cracking occurred in a less stable fashion in slabs with a larger unbonded region. The larger unbonded length in a slab caused wider cracks to appear at an earlier age than in a slab with a smaller unbonded region.