Pultrusion of Smart, Hybrid FRP Reinforcement for Concrete
Principal Investigators:
Antonio Nanni (Currently at Univ. Missouri-Rolla)
Charles E. Bakis (Engineering Science and Mechanics)
Project Sponsor: National Science Foundation
Project Status: Completed
Researchers in the Composites Manufacturing Technology Center (CMTC) at Penn State University have investigated the use of smart, hybrid fiber reinforced plastic composites as an improved reinforcement for concrete structures. The aim of the investigation was to design and fabricate reinforcement rods that exhibit a pseudo-ductile failure mode and provide the means of monitoring for dangerous deformation. Prototype rods were pultruded in the CMTC using several fibers (carbon, aramid, glass, and polyvinyl alcohol) and resins (polyester and vinylester). By properly proportioning and placing various types of fibers in the cross section of the rod, both design objectives were achieved. The prototypical rods studied here were smooth, but various surface treatments could be done to improve the mechanical interlock with concrete. Engineering Science and Mechanics graduate Scott Koehler is showing the electrical connections as well as the reusable, resin-potted glass/epoxy anchors in the figure above/left.
In Figure 1,
carbon (black), aramid (yellow) and polyvinyl alcohol (white) fibers that have just been impregnated with resin are located by an array of smooth bars so that they end up in their proper positions in the cross-section of the rod. It was found that maximizing the dispersion the 12-K tows of carbon fibers provided the best pseudo-ductile stress-strain behavior. After the fibers are properly positioned, they pass through a series of forming dies which gradually squeeze them into an 11-mm-diameter circular rod (toward the upper-left corner of
Figure 2).
The linear production rate of the rod was typically 22-30 cm/min. As the now fully-cured rod emerges from the heated die
(Figure 3),
it it ready to be cut off and used. For tensile and electrical testing, the rods were fitted with electrically nonconductive anchors and wired via aluminum end-connectors to a voltage divider circuit.
Carbon fibers, which have the lowest strain to failure of all the fibers considered, were used in all the rods to provide added strength and stiffness, as well as a degree of electrical conductivity that could be monitored during tensile deformation. As the carbon fibers elongate, their resistance increases due to the piezorestistive effect. Therefore the carbon fibers could be used as "internal strain gages" to quantify reversible deformations in the material. The gage factor for the carbon fibers, defined as the normalized resistance change divided by the strain, was found to be approximately 2. Gage factor was not significantly affected by repeated loads to 50% or less of ultimate. At higher increments of applied strain where the weakest carbon fibers fail, accelerated, nonreversible increases in resistance were detected. Once all the carbon fibers fail, the resistance of the rod goes essentially to infinity. Properly designed rods were shown to be capable of sustaining loads beyond the failure of the carbon fibers so that ample electrical warning before overall failure of the rod is obtained.
To the left is shown a cross section of a hybrid rod pultruded with 6% by volume carbon, 17% aramid, and 27% polyvinyl alcohol fibers. Special pultrusion techniques were developed in consultation with project partners at Creative Pultrusions to handle the variety of fibers present in this rod. Of great importance in the ability of the rod to sustain noncritical damage prior to failure is the relative amount of each fiber present, the relative strains to failure of each fiber, and the placement of the fibers in the cross section. Below and to the left is another rod cross section where the carbon fibers in the core comprise 13% of the volume and the glass fibers in the sheath comprise 36%.
In our experience, the dispersed fiber approach seems to provide more pseudo-ductility than the concentrated fiber approach. Of the six types of rods tested, all provided ample electrical warning of imminent failure. Although all of the rods demonstrated some degree of load carrying capability beyond failure of the carbon fibers, two of the seven rod types carried higher loads after failure of the carbon. This latter behavior is considered safer and most desirable for materials to be used as concrete reinforcement.
Publications:
Bakis, C. E., Nanni, A., and Terosky, J. A., "Smart, Pseudo-Ductile, Reinforcing Rods for Concrete: Manufacture and Test," Fiber Composites in Infrastructure, Proc. 1st Intl. Conf. on Composites in Infrastructure, H. Saadatmanesh and M. R. Eshani, Eds., Tuscon, AZ, 15-17 Jan. 1996, pp. 95-108.
Bakis, C. E., Nanni, A., Terosky, J. A., and Koehler, S. W., "Self-Monitoring, Pseudo-Ductile, Hybrid FRP Reinforcement Rods for Concrete Applications," Composites Science and Technology, 61:815-823 (2001).
Back to the Penn State CMTC Homepage
To obtain more information on smart, ductile reinforcement for concrete, please contact
Prof. Charles E.
Bakis (email: cbakis@psu.edu)
of the
Department of Engineering Science and Mechanics.
Last substantial update: 16 Aug 01. Copyright 1999, 2001, C. E. Bakis.
Researchers in the Composites Manufacturing Technology Center (CMTC) at Penn State University have investigated the use of smart, hybrid fiber reinforced plastic composites as an improved reinforcement for concrete structures. The aim of the investigation was to design and fabricate reinforcement rods that exhibit a pseudo-ductile failure mode and provide the means of monitoring for dangerous deformation. Prototype rods were pultruded in the CMTC using several fibers (carbon, aramid, glass, and polyvinyl alcohol) and resins (polyester and vinylester). By properly proportioning and placing various types of fibers in the cross section of the rod, both design objectives were achieved. The prototypical rods studied here were smooth, but various surface treatments could be done to improve the mechanical interlock with concrete. Engineering Science and Mechanics graduate Scott Koehler is showing the electrical connections as well as the reusable, resin-potted glass/epoxy anchors in the figure above/left.
