Investigation of Asphalt Pavement Slippage Failures on Runway 4R-22L, Newark International Airport

Aeronautical asphalt pavements are susceptible to slippage failures, especially on runways at the high-speed taxiway exits as airplanes brake and turn. Plastic deformation of asphalt usually occurs under loading at high ambient temperatures. To combat this problem asphalt mixes are polymer modified and their aggregate skeletons are designed to have sufficient stone-to-stone contact for adequate structural integrity. The top pavement lift should also provide enough depth for the shear forces to dissipate. Polymer modified asphalt cements, sound aggregate skeletons and the use of textured sands have produced mixes capable of transferring loads to the subbase. However, smoothness criteria outlined in FAA specifications have tight tolerances, which drive the contractor into constructing the pavement with multiple thinner lifts rather than fewer thicker lifts. This allows more opportunities to correct deficiencies as the pavement structure is built to finished grade. The drawback to this method is the multiple layers that comprise the depth of the pavement may not act as one solid unit under shear forces. Precautions are taken to avoid this by treating the surfaces at the interface by cleaning the surfaces of dust and debris and applying a tack coat prior to overlay. In addition to this, there must be some degree of aggregate interlock between lifts provided by protrusions of aggregates of the overlay into the layer below. This happens during the rolling operation and is facilitated through heat transfer. The aggregates that penetrate into the underlying layer act as shear studs, which aid in preventing slippage at the interface of the first and second lifts when undergoing shear and torsion forces. The aggregates however, must have enough strength not to shear themselves.