Restrained shrinkage cracking: the role of shrinkage reducing admixtures and specimen geometry: Fid-Bau Portal

Restrained shrinkage cracking: the role of shrinkage reducing admixtures and specimen geometry

Weiss, W. J. / Shah, S. P.

Abstract Early-age cracking may occur in concrete elements if shrink-age is prevented by the surrounding structure. The risk of early-age shrinkage cracking in any given structure is influenced by many factors including the magnitude of shrinkage, rate of shrinkage, degree of stress relaxation, degree of structural restraint, and rate at which material properties develop. In addition to the aforementioned factors, this paper highlights the fact that shrinkage cracking is also influenced by geometry. This paper compares two series of experiments to better understand the role of specimen geometry. In the first series ring specimens of varying size were prepared to undergo the same rate of shrink-age and maximum strain development. Although the maximum residual tensile stress that developed was nearly identical for all geometries, the age at which cracking occurred varied with specimen thickness. In the second series of experiments the combined effect of moisture gradients and specimen geometry was investigated. In these experiments specimen thickness was varied while the surface area exposed to drying was maintained constant. The age of cracking was measured, as was the development of a moisture gradient. Again the influence of specimen size/geometry was apparent with smaller specimens cracking at an earlier age. This paper provides an explanation for this geometry dependence through the use of fracture mechanics concepts.