Evaluation of Bond Strength Between Old and New Pavement Overlays

The main objective of this research was to study the factors that affect the bond strength between old pavement and new overlay. The secondary objective was to find the best tack coat material and its application rate which could be used in Jordan. A procedure was developed for determining the bond strength between pavement layers. An easy to use procedure was selected to provide a good indication of the quality of the bond. The direct shear box device normally used to test the shear in soils was developed to test asphalt pavement concrete slabs. The experiment included two types of cutback asphalts (RC250 and RC800) and an asphalt cement binder (AC) of 60/70 penetration. Bond strength was measured with a shear type device at two testing temperatures and three levels of normal pressure. Three application rates that encompassed the specification range were investigated for each tack coat type. The effects of tack coat type, application rate, testing temperature and normal pressure on the bond strength were evaluated. It was found that all of the main variables used in the test plan affected bond strength. The bond strength increases with the decreasing in testing temperature, and it increases with the increasing in normal pressure. The AC60/70 had higher bond strength than the other two cutbacks (RC800 and RC250) and the optimum application rate is (0.4 -0.6) kgmlm2