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Advanced High-Performance Materials for Highway Applications: A Report on the State of Technology
Chapter 6, Candidate Metallic and Polymer Materials
Vitreous Ceramic Coatings for Reinforcing Steel
Most concrete pavements include steel as part of their design and construction, whether it is for reinforcement in the slabs (e.g., deformed longitudinal bars used in CRCPs), load transfer across transverse joints (e.g., smooth dowel bars in jointed plain concrete pavements), or connectors across longitudinal joints (e.g., tie bars across adjacent pavement lanes). Generally, such steel in concrete is protected from corrosion by a passive oxide film that forms in the high pH environment; however, if this film is disrupted or penetrated by caustic chloride ions, corrosion of the steel can occur, the products of which create a severe volume change that can lead to cracking, spalling, or delamination of the concrete.
To address these concerns, most highway agencies are using epoxy-coated dowel bars and tie bars, and some agencies are using epoxy-coated reinforcing steel for CRCP. This adds an additional layer of protection to the steel from the ingress of chloride ions. However, the epoxy coating may become damaged or may still be susceptible to corrosion under some conditions, and therefore may not provide the desired long-term performance. Furthermore, in the case of CRCP, there are concerns about the suitability of the bond between the epoxy-coated steel and the concrete.
In an effort to reduce corrosion, some agencies are evaluating the use of non-corrodible materials or non-corrodible coatings that are expected to provide a higher degree of protection than conventional epoxy coating. Vitreous ceramic coatings are an example of materials being evaluated as alternatives to epoxy coatings. These coatings not only reduce the corrosion potential but also promote better bonding between the steel and the concrete (when such bonding is desired). This material is a specially formulated durable glass that is fused to metal under very high temperatures (typically 1,100 to 1,600 °F [593 to 871 °C]). This process forms a layer at the interface that merges the chemical makeup of the glass and the underlying metal, the result of which are very high bond strengths (10,000 to 12,000 lb/in2 [703 to 842 kg/cm2]) between steel and enamel (Weiss et al. 2009).
Vitreous enamel coatings typically have hardness levels in the range of 3.5 to 6 on the Mohs hardness scale, whereas organic coatings are in the range of 2 to 3. These coatings generally are resistant to fracture and to moisture penetration (Weiss et al. 2009).
The applications for vitreous ceramic coatings include the following:
The use of vitreous ceramic coatings is expected to provide the following benefits:
No cost data are currently available for this product. Costs are expected to be higher than for conventional epoxy-coated steel reinforcing.
Laboratory testing of this product has been completed that demonstrated the increased bonding levels and the reduced potential for corrosion.
For More Information
Weiss, C. A., S. W. Morefield, P. G. Malone, and M. L. Koenigstein. 2009. "Use of Vitreous-Ceramic Coatings on Reinforcing Steel for Pavements." Proceedings, National Conference on Preservation, Repair, and Rehabilitation of Concrete Pavements. Federal Highway Administration, Washington, DC.
Fiber-Reinforced Polymer Bars for Continuously Reinforced Concrete Pavements
CRCP is a long-lasting, premium pavement often used in urban corridors subjected to heavy truck traffic. Containing no regularly spaced transverse joints, a key feature of CRCP design is the use of deformed longitudinal steel reinforcing bars that are designed to create tight, hairline cracks at intervals of approximately 3 to 8 ft (0.91 to 2.44 m). However, corrosion of the steel reinforcement has compromised the performance of CRCP designs in some areas, and in response a number of agencies have adopted the use of epoxy-coated reinforcing steel to minimize the problem. Nevertheless, this coating can be damaged during construction, once again leading to corrosion problems, and the epoxy coating reduces the bond between the concrete and the steel, which can affect the steel design requirements and also increase the lap length required on splices of the bars.
Due to these concerns, alternative materials that are more corrosion-resistant are being considered for the longitudinal reinforcement in CRCP designs and one material in particular that has seen some application is FRP bars. FRP composite materials consist of a matrix of polymeric material (polyester, vinyl ester, or epoxy) that is reinforced by fibers or other reinforcing materials (fiberglass, carbon fibers, or graphite fibers) (FHWA 2009). Filler materials (such as calcium carbonate, clay, or hydrated alumina) may also be added to improve specific properties of the composite or to lower its costs.
The applications for FRP bars in CRCP include:
The use of FRP bars in CRCP projects is expected to provide the following benefits (FHWA 2009):
In addition, the electromagnetic transparency of FRP bars makes them suitable for use at toll collection booths where electromagnetic vehicle detectors are used (FHWA 2009).
No current cost data are available for the use of FRP bars in CRCP. The cost of FRP reinforcing bars is higher than conventional epoxy-coated steel bars, and higher reinforcement contents are required when using FRP bars in CRCP. Consequently, the use of FRP in CRCP is expected to be more expensive than using epoxy-coated, steel deformed reinforcing bars.
Two experimental field projects have been constructed recently in North America. One was constructed in Quebec in 2006 and contained 18 different experimental sections including three sections with galvanized steel reinforcement (Thebeau, Eisa, and Benmokrane 2008). A second project was constructed in West Virginia in 2007, featuring one FRP-reinforced CRCP section and one black-steel-reinforced control section (Chen et al. 2008). Performance evaluations of these experimental sections are underway.
For More Information
Chen, R. H. L., J.-H. Choi, H. V. GangaRao, and P. A. Kopac. 2008. "Steel Versus GFRP Rebars?" Public Roads, Vol. 72, No. 2. Federal Highway Administration, Washington, DC.
Federal Highway Administration (FHWA). 2009. Evaluating the Use of FRP Bars in Continuously Reinforced Concrete Pavements. FHWA-HIF-09-012. FHWA, Washington, DC.
Thebeau, D., M. Eisa, and B. Benmokrane. 2008. "Use of Glass FRP Reinforcing Bars instead of Steel Bars in CRCP in Quebec." Proceedings CD, 9th International Conference on Concrete Pavements, San Francisco, California.
Fiber-Reinforced Polymer Dowel Bars
Dowel bars have been shown to be very effective in preventing transverse joint faulting and ensuring a long-lasting, smooth-riding surface for jointed concrete pavements. Traditionally, smooth, round, solid steel bars have been used, with an epoxy coating for protection against corrosion. However, with many agencies moving toward longer life concrete pavements (40 to 60 years) and because of concerns about the long-term effectiveness of epoxy coatings, there is increased interest in investigating the use of alternative dowel bars that have improved corrosion resistance (FHWA 2009).
One product that shows promise as a replacement for steel dowel bar is FRP bar. FRP composite materials consist of a matrix of polymeric material (polyester, vinyl ester, or epoxy) that is reinforced by fibers or other reinforcing materials (fiberglass, carbon fibers, or graphite fibers) (FHWA 2009). Filler materials (such as calcium carbonate, clay, or hydrated alumina) may also be added to improve specific properties of the composite or to lower its costs. Although FRP material is widely used in the United States as reinforcing bars in structural applications, there has not been much use of FRP bars as a load transfer device in concrete pavement joints. During the last 20 years, several demonstration projects have investigated the use of alternate dowel bar materials, and many of these projects included FRP dowel bars (HITEC 2005; Porter et al. 2005, 2006; Eddie, Shalaby, and Rizkilla 2001). The findings from these studies indicate mixed performance for joints incorporating FRP bars. A recent study sponsored by FHWA found that FRP dowels were good alternatives to traditional steel dowels for transferring joint loads in concrete pavements (Vijay et al. 2009).
FRP bars can provide positive load transfer in jointed concrete pavements. During the summer of 2010, Idaho DOT elected to use about 36,000 FRP dowel bars for a 10-lane-mile new concrete pavement project along a section of I-84. Also, the use of FRP dowel bars has been approved by Virginia DOT, and agencies in other States (Wisconsin, New Jersey) have plans to construct test sections that incorporate FRP dowel bars.
The use of FRP bars for load transfer at concrete pavement joints is expected to provide the following benefits:
No current cost data are available for the use of FRP dowel bars in larger construction projects. Based on the use of the dowel bars in the Idaho project, it appears that use of FRP dowel bars is cost-competitive with the conventionally used epoxy-coated steel bars.
Idaho DOT is installing about 36,000 FRP dowel bars along a section of I-84. New Jersey DOT is testing the use of FRP bars in precast concrete repair applications. Virginia DOT has approved the use of FRP bars in new concrete pavement construction.
For More Information
Eddie, D., A. Shalaby, and S. Rizkilla. 2001. Glass Fiber-Reinforced Polymer Dowel for Concrete Pavements," ACI Structural Journal, March - April.
HITEC. March 2005. "Evaluation of Alternative Dowel Bar Materials," report prepared by Applied Pavement Technology, Inc., Highway Innovative Technology Evaluation Center, Washington, DC.
Porter, M. L., et al. June 2005. Field Evaluation of Elliptical Fiber Reinforced Polymer Dowel Performance, Report No. DTFH61-01-X-00042, Project 5, FHWA, Washington, DC. www.intrans.iastate.edu/reports/frp_dowel.pdf
Porter, M. L., et al. April 2006. Laboratory Study of Structural Behavior of Alternative Dowel Bars, Report No. DTFH61-01-X-00042, Project 7, FHWA, Washington, DC. http://publications.iowa.gov/4407/
Vijay, P. V., V. S. GangaRao Hota, and H Li. September 2009. Design and Evaluation of Jointed Plain Concrete Pavement with Fiber Reinforced Polymer Dowels, Report No. FHWA-HRT-06-106. Federal Highway Administration, Washington, DC.
Zinc-Clad Dowel Bars
Dowel bars have been shown to be very effective in preventing transverse joint faulting and ensuring a long-lasting, smooth-riding surface. Traditionally, smooth, round, solid steel bars have been used, with an epoxy coating for protection against corrosion. However, with many agencies moving toward longer life concrete pavements (40 to 60 years), and because of concerns about the long-term effectiveness of epoxy coatings, there is increased interest in investigating the use of alternative dowel bars that have improved corrosion resistance (FHWA 2009).
One relatively new material that is seeing some use on a limited basis is rolled zinc alloy - clad dowels. In this application, zinc cladding of 0.040-in. (1.02 mm) minimum thickness is placed over a Grade 60 carbon steel bar. These dowels have exhibited superior corrosion resistance during laboratory studies (Snyder 2005) and have seen some limited use in long-life pavements in Minnesota, Pennsylvania, and Ohio (Miller 2006).
Zinc-clad dowel bars provide positive load transfer in jointed concrete pavements, and are allowed as an alternative dowel bar in at least three States (Minnesota, Washington, and Michigan).
The primary benefit of zinc-clad dowel bars is their superior resistance to corrosion (as compared to conventional, epoxy-coated bars) at only a slightly higher cost. They are also expected to be less susceptible to damage during transportation and construction operations.
The cost of zinc-clad dowel bars is slightly higher than conventional epoxy-coated dowels (by a factor of about 1.6) but less than stainless steel and FRP alternatives.
Currently, zinc-clad dowel bars are being allowed as an acceptable alternative material by at least three highway agencies. A number of laboratory studies comparing them with other alternative materials have been completed or are underway. While laboratory experiments have been promising, long-term performance data are not available.
For More Information
Federal Highway Administration (FHWA). In press. Alternative Dowel Bars for Jointed Concrete Pavements. ACPT TechBrief. FHWA, Washington, DC.
Miller, W. 2006. Cathodically Protected Load Transfer Dowels for High-Performance Pavements. www.allzinc.com/techdata/Lifejacket_Dowel06.pdf. Accessed September 2, 2009.
Snyder, M. B. 2005. "An Evaluation of Cathodically Protected Dowels for Concrete Pavements," in Proceedings of the Eighth International Conference on Concrete Pavements, Colorado Springs, CO, 2005.
Microcomposite Steel for Dowels and Tie Bars
As described above, the quest for alternative dowel bars with high corrosion resistance has become a critical issue as agencies move towards the construction of long-life concrete pavements. Microcomposite steel (a proprietary product of the MMFX Technologies Corporation, sometimes simply referred to as MMFX steel) is a relatively new material that contains less than 1 percent carbon and typically 8 to 10 percent chromium, making it more corrosion resistant than carbon steel (FHWA 2009). The MMFX 2 smooth round dowel bar is available in 1.25- and 1.5-in. (32- and 38-mm) diameters.
MMFX bars provide positive load transfer in jointed concrete pavements, and currently are allowed as an alternative in at least two States (Minnesota and Washington). This material can also be manufactured in a deformed configuration for use as a tie bar across lanes.
Laboratory studies have shown microcomposite steel to be superior in corrosion resistance to conventional carbon steel and similar to epoxy-coated steel, although several laboratory studies comparing it to other metallic materials have shown mixed results (Clemeña 2003; Mancio et al. 2008). The cost of MMFX bars is also only slightly higher than conventional epoxy-coated steel bars, making them attractive as a potential alternative dowel bar material.
Recent data suggests that MMFX is about 1.4 times the cost of conventional epoxy-coated steel bars, and less expensive than zinc-clad, FRP, or stainless steel bars.
MMFX steel bars have seen a limited amount of use in field studies, but they are being specified for use by the Washington State DOT in certain environments (FHWA 2009). Wisconsin has completed a 5-year field evaluation indicating generally good performance, but not necessarily superior to that being provided by epoxy-coated bars (Battaglia 2008). Laboratory evaluations of this material have been completed or are underway to compare performance with other metallic options including stainless steel and epoxy-coated steel. Long-term field performance data are not available.
For More Information
Battaglia, I. K. 2008. Evaluation of MMFX 2 Steel Corrosion-Resistant Dowel Bars in Jointed Plain Concrete Pavement. Report No. WI-03-08. Wisconsin Department of Transportation, Madison, WI.
Federal Highway Administration (FHWA). In press. Alternative Dowel Bars for Jointed Concrete Pavements. ACPT TechBrief. Federal Highway Administration, Washington, DC.
Clemeña, G. G. 2003. Report on the Investigation of the Resistance of Several New Metallic Reinforcing Bars to Chloride-Induced Corrosion in Concrete. Report No. VTRC 04-R7. Virginia Transportation Research Council, Richmond, VA.
Mancio, M., C. Carlos, Jr., J. Zhang, J. T. Harvey, and P. J. M. Monteiro. 2007. Laboratory Evaluation of Corrosion Resistance of Steel Dowels in Concrete Pavement. Final Report UCPRC-RR-2005-10 (FHWA No. S/CA/RI-2006/27). California Department of Transportation, Sacramento, CA.
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