Outdoor weathering test sites

Sites in southern Florida (with high solar radiation coupled with high humidity, i.e. a tropical climate) and the Sonora Desert in Arizona (with high solar radiation coupled with low humidity, i.e. a desert climate) were used as sites for outdoor weathering tests. The present direct natural exposure in Miami (Florida) is regarded as real time exposure, against which the results obtained with various accelerated weathering devices may be compared. 

One can see that theoretical acceleration factors, related to the UV exposure in the weathering box (at 0.35 W/m ) and to actual outdoor exposure in the test sites in Florida and Arizona, are rather consistent from year to year. In the real world they certainly would be deviating from the above figures due to difference in colors of samples, moisture content in samples, and so on. Nevertheless, considering that real acceleration factors in Wisconsin and New England are in the range of 5-13 or 11 + 4 (see above), the theoretical acceleration factors of 3.5 in Florida and 3.2 in Arizona certainly make sense. 

Weatherability of plastic materials can be investigated under natural or accelerated laboratory exposure. Typically, standard ASTM (dog-bone shaped) test pieces of the plastic of interest are exposed outdoors in natural weathering exposure sites. Ideally, locations of high insolation (such as AZ and FL) are selected to ensure fast degradation. The samples exposed outdoors, usually on South-facing racks, are periodically removed and tested to determine their extent of degradation. 

Natural outdoor exposure is the oldest method of determining weather resistance. The standard procedure is to expose samples vertically, facing south. There are many standard test sites set up to do outdoor exposure tests on a variety of parts or samples. So-called accelerated tests are those that use inclined racks (5-45° from the horizontal) facing south in southern locations where sunlight is strongest and available... 

Candidate glazing samples are subjected to both realtime outdoor exposure and accelerated weathering. Optical and mechanical properties of interest are measured periodically as a function of exposure time to ascertain useful lifetimes. Outdoor exposure test racks are maintained at NREL (in Golden, CO), in Miami, FL, and in Phoenix, AZ. The outdoor test sites are instrumented to allow monitoring of radiometric and meteorological weather conditions experienced by exposed samples. Samples are tested in accordance with American Society of Testing and Materials (ASTM) standard practice E782. 

Under long-term outdoor exposure, involving frost action and car-bonation, latex-modified mortar shows increased resistance to weathering in comparison with conventional mortar and concrete. The weatherability of the latex-modified mortars is shown in Fig. 4.69The exposure test was done at the Building Research Institute Outdoor Exposure Site in Ibaraki Prefecture, Japan. Except for PVAC-modified mortars, the flexural and compressive strengths of most latex-modified mortars under outdoor exposure conditions tend to become nearly constant at one year or more, and a weatherability factor is greater or similar to that of unmodified mortar. 

---