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Experimental methodology to study plastic shrinkage cracks in high strength concrete
Date Issued
2006
Author(s)
Sivakumar, A
Santhanam, A
Abstract
Plastic shrinkage cracks occur primarily in concrete elements having large surface to volume ratios. These cracks develop at early ages of concrete due to the rapid loss of water from the surface of concrete before it is set and has still not attained sufficient tensile strength. High strength concrete incorporating silica fume is more susceptible to plastic shrinkage cracks because of the minuteness of the capillary pores, which causes higher strains on drying. Often, the cracks that develop are so fine that they cannot easily be distinguished from the surface; this is especially true in the case of fibre concretes. This paper describes an experimental methodology to monitor cracking due to plastic shrinkage using a simple and reproducible technique. Rectangular concrete slabs, with a stress riser in the center, and adequate base and end restraints, are subjected to drying in adverse conditions in an environmental chamber. Cracking along the tip of the riser is then studied using a combination of photographs and hand-held microscope. The various crack measurements are then made using image analysis software. A statistically accurate measure of the crack area is then obtained. This parameter is used to compare different types of concrete. This methodology was found to be successful even for the characterization of very fine cracks in hybrid fibre concrete systems.