Determination of the relationship between parameters of the stripping in different depths of asphalt using GPR; A case study: District 22 of Tehran

Summary Stripping is a common distress occurring on asphalt pavements. The source of this stress comes from moisture, thus, stripping and moisture damage are often used interchangeably. A common way to identify these failures is drilling and coring from road surfaces, and doing destructive tests. The most commonly used tests are bulk density, comparing indirect tensile stress in saturated to dry condition (TSR) , and finding air void percentage .These tests are destructive, and take time more than usual. In addition, we must repair and patch the asphalt pavements where drilled and cored. Ground penetrating radar (GPR) is a method, which is not only a non-destructive method but it also evaluates the roads continuously and provides us with results much quicker than the common destructive tests. In this study, parts of the road networks in Tehran are evaluated using GPR, then several points of the road surface are drilled and cored. Finally, the results of the GPR measurements and destructive tests are analyzed and compared with each other.
Introduction Moisture damage is a common distress that occurs in asphalt pavements. In this phenomenon, adhesion between bitumen and aggregates is ruined. It usually happens where the level of underground water is high, and it is seen along the wheel paths. Stripping starts at the sub base layer, and moves to the upper layer until it appears on the surface. This problem often occurs in the moisture condition when the pavement temperature increases. Cracks appear where traffic is heavier. Finally, it causes holing and showing.
Methodology and Approaches In this study, parts of the road network in Tehran (namely,Amir Kabir Boulevard) were evaluated using GPR, and then, several points of the road surface were drilled and cored. The cores were tested, and as a result, bulk density, TSR, and air void percentage were obtained. Finally, the analysis results of the GPR and destructive tests in different depths were compared.
Results and Conclusions As the amount of asphalt bulk density increases, the air void percentage decreases to less than 7%, and the TSR reaches over 0.8. Stripping is observed where dielectric constant becomes less than 5.10 in the upper 5 centimeters of asphalt depth, and also, stripping happens in the upper 10 centimeters of asphalt depth where dielectric constant reduces to less than 5.40.