Volume 2, Issue 7 (July 2005)
Statistical Significance of the Restrained Slab Test for Quantifying Plastic Cracking in Fiber Reinforced Concrete
Fiber reinforcement has been shown to reduce the detrimental aspects of plastic shrinkage cracking in concrete. However, no standard test method currently exists to quantify the efficiency of various types or volumes of fiber reinforcement. This study was performed to evaluate the effectiveness of the restrained slab test for assessing plastic shrinkage cracking. Plastic cracking was initiated in a drying environment, and the cracks that developed in the restrained slab were analyzed using both optical microscopy and automated image analysis. The crack width data were analyzed to determine the number of measurements that are required to provide reasonable statistical significance. Statistical analysis was used to establish the variability that can be expected with this test method. The crack reduction ratio (CRR) was assessed to determine the number of replicate specimens required for a given level of statistical significance. In addition, a modified Weibull approach was used to quantify the variable nature of crack width measurements using three parameters that are related to physical features of the crack.