FRP Grids for Reinforced Concrete

Principal Investigators:
Renata S. Engel (Engineering Science and Mechanics)
Charles E. Bakis (Engineering Science and Mechanics

Project Sponsor: National Science Foundation

Project Status: In Progress

Current research in fiber reinforced plastic grids in the Composites Manufacturing Technology Center at Penn State University is aimed at developing a cost effective manufacturing and fabrication process for the lattice architectures that are found in reinforced concrete. The attention to these materials is growing for civil infrastructure markets because of their high strength to weight ratios, their resistance to corrosion and the flexible manufacturing. Currently, steel grids are put in place at the construction site by tieing steel rods into the desired shape. This labor intensive on-site construction method has lead to alternate designs that involve FRP reinforced grids that require no on-site assembly. Of particular interest is the 2-D grid with load carrying capibility at the joints, and 3-D lattices--both of which can be dropped into place immediately before pouring the concrete.

The scope of recent FRP grid research includes:

Analysis and measurement of various fiber architecture arrangements for their stiffness and strength in concrete
Scaleable manufacturing processes for making large 2-D grid structures
Development of 3-D FRP lattices for precast construction

The image to the left shows graduate student Mike Croyle (M.S., Engineering Mechanics) filament winding a 2-D FRP grid on a flexible silicone mold. Panex 33-48K carbon fiber tow manufactured by Zoltek is being used in this example, along with Ashland 922 vinylester resin. These materials were chosen for their low cost, environmental durability, light weight, magnetic transparency, and ease of implementation in a future continuous manufacturing process. In this exploratory investigation, the computer controlled filament winder enables the flexible manufacturing of many arrangements of fiber architecture at the joints of the grid.

The image to the right shows a closeup view of the payout eye of the filament winder as it deposits impregnated carbon fiber tow into the silicone mold along the precribed path. The payout eye was specially designed at Penn State to enable the accurate deposition of carbon tow along a prescribed path without damaging the delicate carbon fibers. Nails are used to maintain tow tension at the turn-around points of the payout eye off the ends of the silicone mold. By maintaining proper tow tension during winding, the silicon mold can be later removed from the mandrel, mated to a matching male mold, and placed into a hot press for curing without significant fiber washout.

At the left is an overall view of the first layer of carbon fiber deposited into the mold. In this case, the some of the tows are being turned at right angles at the junctions. Subsequent layers of fibers will be applied such that they pass straight through the joints in both directions. This design will be compared to the more conventional design in which all fibers pass straight through the joint. The overall aim of investigating several different joint architectures is to improve the stiffness and strength of the joint so that the grid acts as a more efficient reinforcement of concrete.

Publications:

Engel, R. S., Bakis, C. E., Nanni, A., and Croyle, M. "FRP Grids for Reinforced Concrete: An Investigation of Fiber Architecture," Proc. Intl. Composites Expo '97, Soc. Plastics Engineers, New York, 1997, pp. 6E.1-6E6.

Bakis, C. E., Engel, R. S., Nanni, A., and Croyle, M. G., "FRP Grid Design and Testing," Proc. FRPRCS-3, Third International Symposium on Non-Metallic (FRP) Reinforcement for Concrete Structures, Vol. 2, Japan Concrete Institute, Tokyo, Japan, 1997, pp. 591-598.

Engel, R. S., Bakis, C. E., Nanni, A., and Croyle, M., "FRP Grid Performance in Concrete Beams: An Investigation of Preform Architecture," Proc. 2nd International Conference on Composites in Infrastructure, Vol. II, H. Saadatmanesh and M. R. Ehsani, Eds., 5-7 Jan. 1998, University of Arizona, Tucson, AZ, pp. 80-91.

Bakis, C. E., Pannala, S., Engel, R. S., and Boothby, T. E., "Analysis and Design of CFRP Grids for Reinforced Concrete," Proc. ICCM-12, 12th International Conference on Composite Materials, T. Massard, Ed., International Committee on Composite Materials, 1999, 8 pp. CD-ROM version.

Engel, R. S., Croyle, M. G., Bakis, C. E., and Nanni, A., "Deflection of Reinforced Concrete Beams Reinforced by Fiber Reinforced Polymer Grids with Various Joint Designs," Proc. 4th Intl. Symp. on Fiber Reinforced Polymer Reinforcement for Concrete Structures, (FRPRCS-4), C. W. Dolan, S. H. Rizkalla, and A. Nanni, Eds., SP-188, American Concerete Institute International, Farmington Hills, MI, 1999, pp. 75-85.

Engel, R. S. Bakis, C. E., Boothby, T. E., Pannala, S. P., and Karnes, S. M, "An Analytic Model for CFRP Grid Reinforced Narrow Concrete Slabs," Proc. 5th Intl. Symp. on Fiber Reinforced Polymer Reinforcement for Concrete Structures, (FRPRCS-5), C. Burgoyne, Ed., Thomas Telford, London, 2001, pp. 927-936.

The Center for Composites Manufacturing Technology (CMTC) at Penn State University is the home of other composites research activities. To obtain more information on FRP Grid research, contact Prof. Renata S. Engel (email: rengel@psu.edu) of the Department of Engineering Science and Mechanics.