Study on the Design Tack Coat Rate and Interface Shear Strength of Geosynthetic Pavement Interlayers

The shear bond behavior of geosynthetic interlayers has been intensively investigated, aiming to avoid debonding between surrounding asphalt layers and geosynthetic. Different variables have shown to affect the performance of pavement interlayers, such as tack coat type and rate, surface condition, and geosynthetic properties. However, there is no clear consensus for the design tack coat rate. The present study evaluated five geosynthetic interlayers obtained from field and laboratory studies, in which interface shear strength properties were investigated. Results obtained with different tack coat rates showed an interesting behavior of interface shear strength values and the percentage of tack coat concerning index asphalt retention. An approach using a modified design tack coat rate equation is presented. Maximum results of interface shear strength were not related to the design tack coat rate proposed by the existing equation, while the proposed modified equation led to better estimation of an optimum tack coat rate.