Composites core supplier ALCAN BALTEK Corp. (Northvale, N.J., USA) has announced that on Sept. 30, the first balsa-cored composite bridge deck installed in Louisiana was opened to traffic over the Pierre Part Bayou in Assumption Parish, La. Although BALTEK end grain balsa had been used previously for other commercial and military road and bridge deck projects, this installation is believed to be the first balsa-cored composite deck project containing single-walled carbon nanotubes (SWCNTs) or Buckytubes, as well as the largest nanotube object molded to date.
The project is part of an Investigational Bridge Research Deployment (IBRD) grant originated with the Louisiana Transportation Research Center (LTRC). The development of the composite bridge deck was jointly undertaken by the Louisiana Department of Transportation and Development (LA DOTD), Louisiana State University (LSU), Crescent City Composites, and the Technical Services team of ALCAN BALTEK Corp., a part of ALCAN COMPOSITES Core Materials.
“This joint development project promotes composite construction as an alternative to steel or concrete bridge structures,” says Marc Anderson, director marketing & sales Americas, ALCAN COMPOSITES Core Materials. “The composite bridge deck design is expected to be the first of many in Louisiana to replace traditional steel grating structures over these many regional bayous.”
The light-weight composite panels allow for fabrication off site and quick installation, which results in less downtime for the bridge and substantially less traffic disruption, as well as less constriction on important evacuation routes during hurricane season. Moreover, the panels are immune to corrosion, which shortens the life-span of steel structures, especially over brackish waters.
Being replacement panels for existing steel construction means that the geometry, specifically the thickness of the panel, is dictated by the existing bridge structure. Therefore, to achieve the required stiffness within the restricted thickness, layers of Hardwire high-tensile strength steel reinforcements were used in conjunction with conventional biaxial glass fiber in the structural skins.
The core chosen for this application was a specific density range of BALTEK end-grain balsa. Only end-grain balsa could absorb both the high compression loads required of a bridge designed to withstand the continuous punishment of fully-loaded sugarcane trucks, and the high shear loads imposed by the restricted thickness and highly-loaded metal and fiberglass skins.
As a long-term research program, LSU has installed fiber optic strain gauges in the bridge panels to monitor the performance of the laminate over several years. The Technical Services Department of ALCAN BALTEK Corp. installed conventional strain gages on an adjacent deck plate, to compare load responses for both methods of monitoring. This monitoring is of particular importance because half of the composite panels on this bridge incorporate SWCNTs in the vinyl ester resin of the laminate, resulting in significant increases in flexural strength and fatigue properties.
All panels were vacuum-infused on site at Crescent City's lamination facilities in East Texas and trucked to the LA DOTD in Baton Rouge, where they were adhesively bonded to steel girders. Future production is expected to take place in Louisiana.