Many bridges, subjected to weights, loads, and traffic volumes exceeding their design limits are operating beyond their projected life expectancies. Collapse of several bridges draws attention to a need to develop a new bridge or repair the existing ones at a quicker pace. The economic impact of bridge replacement is not only the direct costs associated with demolition and construction of a new bridge, but also by the indirect costs associated with the loss of roadway use and traffic disruption. Many organizations are working to develop rapid bridge replacement technology, building modular components off-site, that are assembled and joined on site. These technologies allow for bridges to be replaced in as little as 24-48 hours, once the construction site is cleared of the previous debris. Though currently, these systems are slightly higher in cost than conventional bridge construction, once volumes go up, costs are estimated to come down. Polymeric composites are beginning to play a more significant role in many of these technologies for repair, rehabilitation and construction of bridges. These materials have long and useful lives; are light in weight and easy to construct; provide excellent strength-to-weight characteristics; and can be custom built. Some advantages of composite materials over conventional are :
• Tensile strength of composites is 4-6 times greater than that of steel or aluminum
• Higher fatigue endurance limit (up to 60% of the ultimate tensile strength)
• 30-45% lighter in weight than aluminum structures
• Lower vibration transmission than metals
• Being more versatile, they can be tailored to meet complex design requirements
• Long life offers excellent fatigue, impact, environmental resistance
• Reduced maintenance
• Excellent corrosion resistance and fire retardancy
• Improved appearance with smooth surfaces
Composite parts can eliminate joints/fasteners, providing part simplification and integrated design compared to conventional metallic parts. They can strengthen bridges without reduction of vertical clearance; they can be applied in severe exposure environments that have resulted in deterioration of the original structure, and used to extend the life of girder-system bridges because their low dead weight allows for an increase in live-load carrying capacity.
University of Maine's Advanced Structures & Composites Center has developed a comprehensive system. This versatile technology provides a faster, more durable, and less costly method to build a wide variety of single- or multi-span concrete bridges, freeway under- and overpasses, and railroad bridges. It can even be used to rapidly erect building structures. This unique system starts with fabric sleeves of carbon, glass, and other undisclosed fibers that are sized, cut, and joined, then mounted on custom-built fixtures and inflated with air (after tube ends are sealed). Then the inflated tubes are resin impregnated (using unnamed thermoset resins) to form a light, hollow arch. The inflatable composite arches have 3 functions of provision of permanent form for concrete, elimination of rebar, provision of protective, waterproofing covering. No additional heat or pressure is required to cure the resin, so inflation/impregnation can be carried out at the worksite if needed. Once cured, the arches are brought to the construction site and temporarily affixed while shallow concrete footings are poured. Next, the arches are covered with bridge decking, then filled (through holes cut through the decking at the top of each arch) with the University's special-formulation Portland cement - which is slightly expansive to ensure a continuous seal between composite skin and cement core and allowed to cure. Subsequent steps proceed much as with conventional bridge construction, with the arches and decking being covered with a wear surface, such as conventional or polymer concrete or asphalt, concrete or composite spandrel walls erected, and the area backfilled. Length, diameter, thickness, and number of tubes are variables used to optimize each bridge design, with longer and larger diameter arches spaced closer together carrying higher loads. Special mathematical models and predictive tools developed by the university are used to determine these variables and to predict failure and fatigue behavior. Adverse environmental testing has shown the arches are effective over the same temperature range (-34°C to 66°C) as conventional concrete bridges.