Executive Summary : | Delamination (slippage cracking) of bituminous (asphalt) layers is one of the main failures found in flexible pavements. Distress appears as crescent/ half-moon shaped cracks, especially in areas such as intersections, climbing lanes where the horizontal traction forces applied by the vehicle due to acceleration/breaking is predominant. This failure is more observed in overlay projects, where the fresh bituminous layer placed above the old bituminous surface is poorly bonded. Soft grade bituminous binders (VG10) or rapid setting bituminous emulsions (RS-1) are generally used as tack coat for binding the bituminous layers. The MoRTH (2013), India has given guidelines regarding the dosage of bituminous emulsion that have to be placed as tack coat. The IRC SP 100-2014 recommends a minimum bond shear strength of 2 kg/cm2 as an acceptable value. However, the minimum bond strength that has to be mobilized at interfaces depends on several factors such as magnitude of interface shear stress that is experienced, modular ratio of the layers, fatigue life, temperature of testing, and mean texture depth of the layers. Several studies have evaluated the influence of various factors which influences interface shear strength. Extensive cracking, delamination, and pot holes may appear if layers are separated. Majority of the pavement analysis methods, considers the interfaces to be perfectly bonded, and horizontal shear stresses coming on pavement surface is not considered. In order to model the interface, a bonding coefficient needs to be assigned. However, there is no standard test method to evaluate the same. Interface failure of bituminous layer is indeed a fatigue problem, However, very few research efforts have evaluated the fatigue behaviour of bituminous interfaces. Laboratory fatigue equations, along with modelling of bituminous layer interfaces can distinguish the performance of various tack coat materials. The present study intends to develop laboratory fatigue relationships. The fatigue relations developed in the study can be latter calibrated using field performance data. Appropriate selection of tack coat type/preparation of the old bituminous surface before laying the overlay, in-order to mobilize adequate interface shear strength, and fatigue life, could prevent the premature delamination failure of bituminous wearing course layer/overlays. The interface deterioration models developed in the study, after field calibration, can be used to schedule minor rehabilitation (thin overlay) strategies. The durability of bituminous interfaces is also an important aspect that has not been studied extensively by previous researchers. Depending on the aggregate skeleton, and thickness of the wearing course/overlay, moisture intrusion along with traffic loading can damage the bituminous layer interfaces. Hence the study also intends to investigate the durability of bituminous interfaces between two asphalt layers. |