Use of Ground-penetrating Radar for Detecting Voids Underneath a Jointed Concrete Pavement

About the report:

A survey of a jointed, reinforced concrete pavement with ground-penetrating radar indicated that the equipment provides a nondestructive inspection technique that can be used at a minimum rate of 5 lane miles of pavement per hour and with only minimal interference with traffic. The coring of some slabs and subsequent use of a devised water test revealed that the radar was very effective in detecting voids deeper than 1/8 in but considerably less effective in spotting shallow voids. The overall accuracy was approximately 68%, which indicates that the sensitivity of the equipment needs to be improved. The location component used with the radar unit showed insufficient accuracy. A regression analysis of the recorded quantities of grout used daily in subsealing portions of the pavement versus the total linear feet of voids detected underneath the slabs grouted each day yielded only a 51% correlation. However, the regression was found to be significant at a 95% probability level. It is believed that if the width and depth of each void can be conveniently estimated so that the extent of voids can be expressed in terms of volume instead of length only, an even more successful method of estimating grout quantities would be available. It has been shown that information derived from a radar survey can be very useful in developing a sound and cost-effective slab stabilization operation through the proper placement of grout holes.

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