The objective of this proposal is to characterize degradation mechanisms in polymeric topcoat and finish systems used to protect steel structures and bridges. Analyses will include determination by positron spectroscopy on nano-scale defect size profiles and distributions as a function of depth from the top surface and from interfaces with primers and the metal surface; detection, quantification and identification by electron spin resonance of free radicals associated with photo degradation and photo-oxidative degradation as a function of real-time and accelerated aging; and common optical and mechanical properties. Samples will be subjected to accelerated aging in ultraviolet light, oxygen and elevated temperature and to actual exposure on bridges and other structures. The results will be combined to develop an understanding of the degradation mechanisms responsible for failure of coating systems on structural steels.
