Pavement Analysis Group

The Pavement Analysis Group has primary responsibility for selecting treatment types for existing pavements. Many of our projects are Transportation Improvement Program(TIP) projects for which we design pavement rehabilitations. These may include overlays, milling, full depth repairs, partial depth patching and reconstruction. In order to select the most suitable treatment, most projects are tested using the Falling Weight Deflectometer (FWD), Dynamic Cone Penetrometer (DCP), coring and perhaps Ground Penetrating RADAR (GPR).

The FWD gives us information about how the existing pavement and the soil beneath it react to a truck load. Since it is the truck loads that cause damage to the pavement, this testing helps us design pavements that are strong enough to carry future loads. Sometimes the test results can also help us locate weak areas along a project, or weak layers that need to be improved. FWD testing is used in conjunction with DCP's to determine whether jointed concrete pavements are located on subgrade with adequate strength to allow rubblization if the pavement condition warrants this option.

In order to analyze the FWD data, you have to have good information about the existing pavement thickness. Normally this is obtained by taking cores along the length of the project and measuring the thickness of the various layers. Since many of the roads we test have been resurfaced one or more times, accurate information about layer thickness is not available in the historic records. The GPR is also used to determine layer thickness without coring.

The cores also give us a way to detect problems in the asphalt mix itself. Each core is carefully examined to see if stripping or other problems are present. The cores are taken to the M&T lab for testing if mix problems appear to be the cause of the roadway distress.

We also look at roads at the request of divisions or counties. Some of these roadways are being considered for resurfacing and we test the road to see if resurfacing will be enough to take care of the road for an adequate period of time. Our report always includes several ideas for treating the roadway, including a ten year design based on projected traffic.

Another common reason for a pavement analysis is a request to eliminate a weight restriction on a roadway. These are often associated with either a quarry or some other source of heavy trucks. We test the existing pavement, core to determine the existing thickness, and report to the person who requested the information on whether the roadway can sustain the estimated truck traffic.

The analysis group has conducted many field investigations of pavement failures at the request of divisions. These have included problems like rutting, shoving, delamination of paving layers, base course failures, and drainage problems. Depending on the cause of the problem, we work with the Construction Unit, or Materials and Tests to make sure we find the cause of the failure and to insure that the same problem does not continue to occur.

For more information on the work or analysis techniques, call Judith Corley-Lay at 919-250-4094. She can be reached by email at jlay@dot.state.nc.us. Other members of the analysis group include Tom Hearne (704-983-4019) and Josh Holland (704-876-0602).