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Pavement distress occurs through a variety of mechanisms, but it is always controlled by the adhesive and cohesive performance of the asphalt binder. Although the causes of pavement failures are known, the precise mechanisms by which they occur remain to be understood. Observation of the fracture morphology of asphalt concrete can provide some information in this respect. The fracture morphology of asphalt concrete is dependent on the morphology of the binder. A network structure was observed in thin asphalt binder films and the fracture morphology and engineering properties of asphalt concrete were found to be dependent on the network morphology of the asphalt binder. Addition of polymers to asphalt binders causes changes in the nature of the network structure, and its effect can be qualitatively determined by characterizing the fracture morphology. Styrene butadiene styrene (SBS), styrene ethylene butylene styrene (SEBS), styrene butadiene rubber (SBR) latex and an epoxy-terminated reacting polyolefin (Elvaloy AM) were used in this study. A quantitative method to determine the effect of polymer modification on the fracture properties of asphalt concrete is the J-contour integral fracture toughness measurement. An experimental protocol to measure the critical J-integral fracture toughness ( J1 c) was developed and the low temperature (-10°C) J1 c values were determined for SEBS and Elvaloy AM-modified asphalt concrete at three different concentrations.

The effect of ultraviolet (UV) radiation in the presence of ozone as a surface treatment for polycarbonate is examined in regards to changes in the wettability, adhesion, and surface mechanical properties. Standalone, 175-mm-thick films of a commercially available polycarbonate were exposed to UV radiation from sources of different power with various treatment times in the presence of supplemental ozone. Significant decreases in the water contact angle were observed after exposure to UV radiation in the presence of ozone. After several variations in the experimental setup, it was determined that the change in water contact angle is a function of the UV irradiance and the work of adhesion follows a master curve versus UV irradiance. Nanoindentation experiments revealed that the modulus of the top 500 nm of the surface is increased following UV exposure, attributable to surface cross-linking. Adhesion tests to the surface (conducted by a pneumatic adhesion tensile test instrument) showed little change as a function of UV exposure. Analysis of adhesion test failure surfaces with X-ray Photoelectron Spectroscopy (XPS) showed the locus of bond failure lay within the bulk polycarbonate and the measured bond strength is limited by the bulk properties of the polycarbonate and=or the creation of a weak boundary layer within the polymer.

Surface modification using UV/ozone was explored as an approach towards ensuring robust intercoat adhesion in multilayered automotive coating systems. This study was directed toward reducing the variability in adhesion performance associated with changes in coating surface chemistry that can result from the surface migration of formulation additives. The evaluated coating system included a melamine‐cross‐linked polyester layer applied over a commercially available epoxy layer, which is known to become surface‐enriched by a polyether‐based crater‐control additive (CCA) in its formulation. X‐ray photoelectron spectroscopy established that UV/ozone treatment oxidizes the epoxy CCA overlayer and forms carboxyl species. Contact angle measurements identified a concomitant increase in surface wettability. Epoxy‐to‐polyester adhesion improved slightly after exposure to ozone alone and dramatically after exposure to UV/ozone. X‐ray photoelectron spectroscopy of interfacial epoxy surfaces, exposed by delamination of the polyester coating, disclosed that bond‐line fracture occurs within a CCA‐enriched region, with a trend of decreasing CCA concentrations in proportion to the UV/ozone exposure time initially received by the epoxy. Copyright © 2000 John Wiley & Sons, Ltd.

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