Wisconsin Method for Probing Portland Cement Concrete Pavement for Thickness

Abstract

Since 1998 the Wisconsin Department of Transportation (DOT) has used contractors' probing measurements instead of coring to determine aportland cement concrete (PCC) pavement thickness. This study compares core depths with probe depths for 13 projects constructed in 2008 and 2009 across the state of Wisconsin. A statistical comparison of sample means, estimates of differences, and an analysis at 95% confidence interval were completed. The results of this study were compared with results of a 1998 study by Wisconsin DOT and a 2008 follow-up study by the Construction and Materials Support Center (CMSC) at the University of Wisconsin–Madison. Approximately 69% of the projects studied met the criterion of equal means. In comparison, 25% met the criterion in the 1998 Wisconsin DOT study and 50% in the 2008 CMSC follow-up study. In addition, this study determined the preferred number of cores needed to perform a t-test for future quality verification studies by Wisconsin DOT. The study showed that five to 10 cores are required, depending on the pavement area. When the t-test was done with the ideal number of cores, 100% of the projects studied met the criterion of equal means. The study also compared probing for projects built on granular base versus those on hot-mix asphalt (HMA) base. The results showed that projects built on HMA base had a higher degree of comparison. This study also compared productivity and accuracy of probing with coring and other nondestructive measurement techniques. The study demonstrates that probing is an accurate and efficient method of determining depths of PCC pavement and can replace coring.