Statistical Variations of Rebar Placement and Its Effect on Service Life

Abstract

Significant attention is given to the transport properties of the concrete covering the reinforcing bars (covercrete) while neglecting the statistical characteristic of its thickness resulting from variations in rebar placement. A statistics-based model was developed to evaluate the effect of variations in covercrete thickness on the equivalent service life of a structure. It was demonstrated that service life can diminish by ∼3% when the standard deviation of the covercrete thickness reaches 15 mm (.6 in.), as sometimes observed in practice. Field investigation of covercrete thickness in five infrastructure projects identified two sources of errors: (1) error in the average covercrete thickness, which indicates poor control of the specified thickness, and (2) standard deviation of thickness that ranges from 7.3 to 16.4 mm (.29 to .65 in.). As a result, the projects' equivalent service life ranged from .4 to .99, where higher values were obtained in projects in which the mean concrete cover thickness was much greater than specified.