This report presents a case study on the SR-70 section with microsurface for understanding its performance; a development of a methodology for evaluating the asphalt pavement subsurface condition for applying pavement preservation treatments; and a development of a tool for identifying and quantifying the subsurface distresses.

From the case study, it was found that the main distresses on SR-70 were longitudinal cracks, fatigue cracks, and potholes. The longitudinal cracking was the most widely distributed distress with 22% of lane length in the 2-mile test section among the three distress types. Based on the water stripping test results and the core visual observations, it was confirmed that the test section on SR-70 had the water stripping problem.

In order to have a representative condition indicator for the test section, the conditions were converted into the scores scaled from 0 to 100. Layers with closer to a score of 100 have the better subsurface condition. Therefore, the 28% of the test section length with the surface distress was detected as the fair subsurface condition with a score of 56. The rest 72% of the length was estimated as the good subsurface condition with a score of 78. Similarly, 20.5% of the test section length with the problem locations determined by GPR had the fair subsurface condition with a score of 56 and the rest 79.5 % of the length had the good subsurface condition with a score of 76.

The lab test results showed poor correlations among the water stripping severities, air voids, and tensile strengths. Thus, the air voids or tensile strength cannot properly estimate the water stripping severity or vice versa. When the laboratory test results with the surface distresses or in the GPR-based problem locations were compared to that without the surface distresses or in the GPR-based non-problem locations, in general, average air voids and water stripping severities decrease and average tensile strengths increase. The observation confirms that the evaluation processes are applicable for evaluating the subsurface condition. Furthermore, the probability that a location determined to be problematic by GPR to be on one of poor conditions based on lab tests was 1.0. The same probability was obtained for a GPS-based problem location. Accordingly, it was concluded that the laboratory tests with the surface distresses survey or the GPR measurement were reliable method to evaluate the subsurface condition. The FWD results had a weak correlation with the laboratory test results possibly due to fairly long testing interval (i.e., 328 ft). The current FWD test protocol should be improved for evaluating the subsurface condition in pavement preservation application.

Guidelines of subsurface condition evaluation for pavement preservation treatment application was developed utilizing the findings from the case study. A concept of hierarchy was used in the guideline by taking project importance and available resources into consideration. A tool including guidelines, computer software (e.g., iSub and iMoisture), and its manual was also developed based on the methodology as a research product. Based on the guideline, it was concluded that the subsurface condition of the case study section on SR-70 was inadequate for the application of the pavement preservation treatments.

Report Number



subsurface condition evaluation, high air voids, low tensile strength, water stripping, digital image analysis, iSub, iMoisture, pavement preservation treatment

SPR Number


Performing Organization

Joint Transportation Research Program

Publisher Place

West Lafayette, Indiana

Date of this Version