ENVIRONMENTAL DURABILITY OF COMPOSITES FOR SEISMIC RETROFIT OF BRIDGE COLUMNS

Several composite overwrap systems have been proposed to the California Department of Transportation as alternative column casings for seismic retrofit. A program is being conducted to determine the environmental durability of the proposed composite casing materials. Environmental exposures include 100% humidity, salt water, an alkali solution, diesel fuel, ultraviolet light, elevated temperature (60 degrees C), and a cyclic freeze/thaw test. Most systems are showing excellent durability after 3,000 hour exposures. However, one glass-reinforced system showed a progressive reduction in tensile strength of 10% after 1,000 hours and 15% after 3,000 hours in the humidity exposure. In addition, one carbon/epoxy system had up to a 35% reduction in short beam shear strength and a significant reduction in glass transition temperature associated with moisture absorption. Finally, all carbon/epoxy systems had a small (<10%) reduction in tensile strength after 3,000 hours in salt water.