FIELD EVALUATION OF DOWEL PLACEMENT IN CONCRETE PAVEMENTS

Presented in this paper are the results of a laboratory and field investigation conducted to determine the effectiveness of the radar device for evaluating dowel bar misalignment and to evaluate the effectiveness of an automatic dowel bar inserter to properly place dowel bars in rigid pavements. The investigation was sponsored by the Demonstration Projects Division of the Federal Highway Administration (FHWA). A commercially available radar system was used. The radar system is capable of locating steel embedded in concrete. The system produces a real-time graphic recording that indicates the location and the relative depth of the embedded steel. Cores are obtained to calibrate the graphic recordings to obtain the actual embedded depth of the steel bars. The laboratory study indicated that dowel bars placed about 5 in. below the concrete surface could be located reasonably accurately by the radar system. In the laboratory, the standard deviation obtained for the differences between actual and measured individual readings was 0.24 in. The field evaluation was conducted during June 1986 along a section of Interstate 86 in the state of Idaho. At this project, an inserter was used to place the dowel bars in the plastic concrete. Dowel placement along 16 transverse joints was evaluated with the radar system. Results indicate that the radar system is capable of determining the location of dowel bars placed in concrete pavements. However, the degree of accuracy is operator dependent and test results must be considered in statistical terms.