A recently completed project led by the Texas A&M Transportation Institute (TTI) focused on improving the safety, cost and performance of bridge barriers by using a nondestructive testing (NDT) approach.
“This project is part of the Transportation Pooled Fund Program and was proposed in 2011 by the Louisiana Department of Transportation,” says TTI Associate Research Scientist and project supervisor Chiara Silvestri. “A few years ago the TL-3 F-shaped precast concrete barrier was approved for use in Louisiana. The important thing about this type of barrier is that when it’s used in bridge decks, it has a slotted hole design that allows for a pin to be drilled to secure the barrier to the bridge deck.”
According to Silvestri, the problem occurs when the pin installation conflicts with the reinforcing steel (rebar) of the bridge deck. To locate the rebar and avoid this problem, contractors can either destroy part of the concrete bridge deck, costing time and delay, or use an NDT method, which is popular for routine inspection of bridge members. The goal of the research team was to determine which NDT method would be best at detecting locations of rebar in bridge decks.
The researchers performed a literature review of the primary techniques used to detect steel rebar embedded in concrete structures. Then five reinforced concrete specimens were built to test the capabilities of each rebar locator device considered. The research team tested the concrete specimens with ground-penetrating radar and covermeter devices. For more details about the research results of each device, please see Chapter 7 of the research report Rebar Locator for Pinned Precast Barrier Application.
“Using NDT methods, contractors can accurately locate the placement of the concrete barrier rails in reference to rebar during construction,” says Silvestri. “This prevents costly destruction of the bridge deck and traffic delays.”
For more information about this research and to access the available reports, visit the project page at http://www.roadsidepooledfund.org/2011/05/03/rebar-locator-for-pinned-precast-barrier-application-405160-32/.