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Natural aging tests suffer greatly from the long time period required for completion; testing time is of the same order of magnitude as the lifetime. Correlation of the results of the natural aging test with that of the accelerated test is difficult. With certain materials, such as plastics and organic coatings, some progress has been made. Plastics when exposed to ultraviolet radiation or when irradiated and heated undergo a deterioration process which can be described by the exponential relation of the type that can be described by the exponential relation of the type E = Eȯe-γt. It appears to be possible to establish performance criteria of aging from the parameters of the exponential term which depend on the nature and shape of the material tested. Also, for the decay caused by other factors, for example, change in temperature and humidity, the same relationship may be applicable.
aging of plastics, aging of building materials, building materials, durability
Professor, University of Sao Paulo, Sao Paulo,