Hardening the Infrastructure
It’s not only severe weather that causes infrastructure damage. Over time, environmental elements like moisture, salt and chemicals can cause the concrete in bridges and similar structures to spall or crack. Water seeps in, rusting the steel rebar and the bridge structure eventually weakens.
State departments of transportation (DOTs) began testing carbon fiber reinforcement plates in the 1990s to strengthen and extend the life of these bridges. Caltrans, the California Department of Transportation, started using glass fiber wraps (wet layups) to harden bridge piers and H-piles against potential earthquake damage. Now, with two decades of data supporting composite materials’ performance in bridge applications, most DOTs are convinced of its effectiveness, according to Dave White, vice president of technical services at Sika.
Contractors generally use carbon-based composites for preserving and strengthening bridges because they are stronger and offer better resistance to the continuing dynamic loads generated by traffic. “Glass fibers are better for a one-time event like an earthquake,” says White. “You are not trying to strengthen the bridge for heavy truck loading; you’re trying to get it so it will stand up to the one time when an earthquake hits.”
To help engineers find the right composite material, the American Concrete Institute (ACI) Committee 440 has developed numerous documents on the use of composites with concrete in infrastructure applications. These documents provide technical equations and design examples for using composites.
In addition, the International Code Council (ICC) has an evaluation service program that tests composite materials for tensile strength, tensile modulus, elongation and other mechanical properties. “They will also require full-scale testing at times, where you have to put your products on concrete beams and columns to have it tested,” White says. Composite materials that meet all the test criteria receive an ES report number from the ICC. Agencies working on infrastructure projects may require a composite product to meet this ICC acceptance criteria.