UMaine has spent the last eight years focusing on a solution to the problems associated with steel-reinforced concrete in bridge structures. Specifically, UMaine's design focus is to reduce the cost and time of bridge assembly while prolonging the service life of the bridge.
To realize UMaine's design goals, A&P Technology custom designed braided sleevings that meet the mechanical requirements of the bridge arches. These lightweight sleevings are rolled up and shipped in a bag the size of a large duffle bag to the installation site, where they are unrolled and inflated to meet the length and curvature specifications required for the bridge arches. Using a vacuum process, the braid is then infused with resin and made into a composite; curing occurs at room temperature and normal atmospheric pressure. When dry the composite arches are lowered into place with just a single boom; they are then filled with concrete and left to cure again. The braided composite arches serve three purposes: they act as a stay-in-place form for the concrete, they provide an exoskeleton reinforcement so no rebar is needed, and they provide a protective layer from the elements.
Bridge arches made with A&P braided sleevings have been subjected to extensive testing in UMaine's 35,000-square-foot lab (soon to be 60,000-square-foot). Accelerated fatigue testing proved that the concrete-filled arches retained full load-bearing capacity after experiencing the equivalent of 50 years of truck traffic. Testing also revealed that compared to reinforced concrete, composite arches are extremely ductile, maintaining peak loading during strength testing. As a result of this testing, UMaine has developed software to help optimize bridge design. This software predicts the fatigue and failure behavior of a structure based on bridge size, the diameter and thickness of the braided sleeve, and the number of arches needed. To date, the predictions made by the software have been within 5% of the actual measured results.
UMaine predicts that the cost for this new bridge technology will eventually be 20% less than the cost of traditional bridges. Couple that with the fact that the lifespan of these bridges will double, and the savings add up quickly. Lighter, stronger, and faster, composite bridge arches—thanks to the University of Maine and A&P Technology—will soon be changing the way we build bridges.