Long-term durability of composites in secondary infrastructure applications

Pultruded glass-fiber-reinforced composite coupons and I-beams were subjected to four-point-bend environmental fatigue, freezing and thawing, and salt spraying in the laboratory to study their long-term durability for infrastructure applications. Specimens have survived to over five million cycles under four-point bend fatigue at 30% of the flexural strength in air without showing signs of degradation. However, preliminary results suggested that water is detrimental to the life of the material during long-term fatigue. Freezing and thawing in 2% (by weight) NaCl solution resulted in a decrease in dynamic modulus, flexural modulus, flexural strength, and toughness of the composite. Spraying of composite I-beams and hybrid I-beams with carbon fiber outer layers with salt solution for nearly 1,300 hours at 19 °C does not seem to change their flexural moduli. Two composite structures are monitored in addition to laboratory testing. Field data collected from an all-composite pedestrian bridge for over 7 months does not suggest any change in its flexural modulus, and two composite walkway sections on a steel lift bridge have performed well in corrosion resistance since they were installed in November, 1995.