| New applications of fiber reinforced plastics (e.g., as concrete reinforcements for bridges and buildings) are currently under consideration. It is essential, in order to make such applications possible, to be able to obtain reliable predictions of the long-term performance and service life of FRPs. In order to develop such predictive capabilities, it is necessary to correlate changes in the mechanical characteristics of FRPs upon exposure to service environments with changes in their chemical microstructure. Such predictions require development and validation of quantitative models of the effects of various environments on the fibers, the resin matrix, and the interface at the molecular level.; The present study has sought to make progress toward understanding FRP degradation mechanisms by acquiring a large body of data, including the results of chemical, thermochemical and mechanical measurements on various FRPs. This study showed that the application of thermochemical analysis to the study of environmental and thermal degradation of FRPs provides important information about changes in the molecular structure, specifically matrix depolymerization. This study established a correlation between the effects of environmental degradation as reflected in changes in thermochemical and mechanical properties, respectively. Measurements of the concentration of dissolved silica were used to monitor fiber dissolution and ESEM to study the degradation of fiber/matrix interfaces. In particular, attention was focused on aspects of the interaction between FRPs and aqueous media that may lead to delayed increases in the rate of degradation and are thus of critical importance in predicting the effect of long-term exposure on FRP performance. Such non-linear effects may include changes in pH both around the FRPs and in the interface between the fibers and the matrix, hydrolytic extraction on monomeric acrylic acid from the matrix, fiber/matrix debonding, microcracking, and ensuing enhancement of the area of the composite exposed to further attack leading to enhanced corrosion. In addition, this study showed that raising the temperature of exposure is an effective method of accelerating the degradation of FRPs without changing the corrosion mechanisms. This conclusion, however, has to be qualified to take into account the possibility of a delayed rise in degradation rates at some stage of the exposure. |
