Technical literature on the subject of environmental exposure effects related to determining accelerated test methods for the prediction of long-term performance of FRP composite materials for highway structural applications is reviewed in this paper. Effects of environmental exposure of a chemical and a thermal nature on fiberreinforced polymer (FRP) composites are considered. Such exposures include temperature, moisture and chemicals in liquid solutions or in gaseous mixtures. The effects include the changes in the physical and mechanical properties of the composite materials. Such changes are typically related to the degradation or deterioration of the composite material. Synergistic effects of mechanical load and exposure are also reviewed. The review is divided in topics entitled Materials, Exposure Conditions, Experimental Techniques, Failure Mechanisms and Theoretical Modeling.

Studies of the reactions between rare earth salts and phosphoric acid in aqueous or ethanolic media have shown that in both cases stable gels can be formed. Upon drying, gels prepared in aqueous environments yield macrocrystalline REPO 4 products similar to those produced by conventional precipitation and drying. Gels prepared in ethanol, on the other hand, undergo dehydration to form dense microcrystalline products. This observation is based on optical and scanning electron microscopy, as well as on x-ray diffraction studies and infrared spectroscopy. These techniques, as well as differential thermal analysis, indicate that crystal growth of these products takes place around 600-700 ± C. The composition of the dehydrated gels produced in both the aqueous and ethanolic systems corresponds to an orthophosphate structure. Other characteristics of the microcrystalline REPO 4 products include high resistance to attack by water, absence of coloration upon exposure to gamma rays, and a high index of refraction.

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