Durability Aspects of Polymer Composites Used for Restoration and Rehabilitation of Structures

The acceptance of the fiber-reinforced polymers (FRP) in the strengthening of civil and monumental structures is due to a combination of suitable properties and manufacture/installation capability. With respect to traditional building materials, such as steel and concrete, polymer composites offer high strength/weight ratio, good resistance to fatigue, excellent chemical and corrosion resistance. The long term behavior of FRP subjected to weathering is still not well understood. Environmental factors can have a crucial effect on their performance in service. The various environmental factors that have been identified as having a deleterious effect on the durability of FRP are: moisture, temperature changes, freeze-thaw, alkaline environment, ultraviolet radiations. The durability in severe environments, however, is one of the key factor which has contributed to the acceptance of polymer composites in demanding applications, such as the aerospace industry. In this chapter, the properties of several FRP's employed in civil engineering applications are analyzed in relation to the environmental agents to which they can be exposed. Specific interactions can be identified between the different external agents and the based materials composing the FRP. Different thermosetting matrices and fibers, employed for restoration and strengthening applications, are considered. Epoxy, vinyl ester and polyester matrices are reviewed, evidencing the susceptibility of their mechanical properties and adhesive strength to weathering. The performance of an FRP exposed to a harsh environment depends also on the vulnerability of fibers towards the external agents. The fibers most commonly used in FRP for structural reinforcements are based on three types of compounds: carbon, glass and aramidic. Laboratory simulations of environmental agents are compared to natural exposure, emphasizing advantages and limits when reproducing the weather conditions with laboratory procedures. Some remarks and considerations are, finally, drawn