Investigation of bond between asphalt layers in flexible pavement

Abstract

Poor bond between two asphalt layers is one of the main causes of premature failure of pavement surface layers, such as slippage cracking, fatigue cracking, shoving or surface layer delamination. These distresses become more serious in pavement areas often adversely affected by horizontal loads due to traffic wheels. There are many factors affecting the quality of bond between asphalt layers including temperature and application rate of tack coat. In an elemental study, the modified Leutner shear test, which allows determining shear strength and shear stiffness modulus at the interface of double-layered cylindrical specimen, was used. Tests were carried out at a range of temperatures between 20 and 60 °C and with different application rates between 0.0 and 0.9 l/m2 (non-residual) using a Cationic Rapid Setting 1 (CRS-1) emulsion. Results of the elemental study are then used to establish regression equations, relating bonding strength, temperature and application rate which are used as part of larger studies to investigate the influence of interface bond on premature failures in pavement structures, such as premature fatigue cracking or rutting. Some interesting results of these studies cast additional light on the behavior of bonding between asphalt layers.