U.S. Department of Transportation
Federal Highway Administration
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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
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Publication Number: FHWA-HRT-06-106
Date: September 2009
In JPCP highways and roads, inadequate load transfer across the joint will cause substantially higher stresses and deflections due to joint loading than those due to interior loading. A dowel bar transfers part of an applied wheel load from the loaded slab across the joint to the adjacent unloaded slab. Load transfer through dowel bars significantly reduces stresses and deflections due to joint loading, leading to minimized faulting and pumping (figure 2). Faulting is a difference in elevation across the joint of two slabs, while pumping is defined as the expulsion of subgrade material through joints and along the edges of the pavement.(5)
FRP dowels have not been widely used in concrete pavements for highways. However, a number of projects in the United States and Canada have used these composite materials for highway pavement on an experimental basis.
In 1983, the Ohio Department of Transportation installed several FRP dowel bars to evaluate long-term performance in sections of Interstate 77 in Guernsey County and Ohio State Route 7 in Belmont County. In 1998, the Market Development Alliance of the composites industry organized the extraction and testing of samples of these dowel bars. Glass fiber reinforced polymer (GFRP) dowel bars were found to be virtually unaffected by approximately 15 years of field service and exposure in pavement service.
In 1997, FRP dowel bars were installed in a high-performance pavement project on the U.S. Route 65 bypass near Des Moines, IA. Lengths of the pavement sections with FRP dowels were
134.11 and 127.10 m (440 and 417 ft) with 6.10-m (20-ft) joint spacing (skewed) and dowel bars on 30.48- and 20.32-cm (12- and 8-inch) spacing, respectively. Indications are that the FRP dowels have been performing well. Additional alternative dowel bar projects utilizing FRP dowels have been installed in Illinois, Iowa, Kansas, Minnesota, Ohio, Wisconsin, and Manitoba.
Brown and Bartholomew found that FRP dowels made of vinyl ester resins compared well with steel dowels in the scaled model tests.(6) Experimental load transfer percentages were in agreement with theoretical values and fell within the 35–40 percent range predicted for standard joints under typical subgrade conditions. They recommend an approximately 20–30 percent increase in dowel diameter to maintain deflections, concrete bearing stresses, and load transfer percentages at comparable levels with joints containing steel dowels.(6)
Ahmed et al. from the University of Manitoba, Canada, have conducted research on GFRP dowels.(7) In their experimental program, a round GFRP dowel bar having a 38-mm (1.5-inch) diameter and a concrete-filled GFRP pipe having a 60-mm (2.36-inch) outside diameter were evaluated in a laboratory setting and in a field implementation. The field test section was constructed on a regional highway in Winnipeg, Manitoba.(7)
They concluded that GFRP dowels subjected to Falling Weight Deflectometer tests in the field showed that LTEs of GFRP dowels were comparable to those produced by steel dowels, provided that the diameter of the GFRP dowel was 20–30 percent larger than the steel dowel. The larger diameter resulted in a reduction in bearing stresses that in turn reduced the potential for faulting.
Tests conducted by Eddie et al. showed the joint effectiveness of GFRP dowels to be in the range of 86–100 percent using a weak subgrade, and 90–97 percent using a stiff subgrade.(8) An American Concrete Pavement Association (ACPA) criterion for successful joint load transfer is 75 percent.(8)
Porter and other researchers at Iowa State University studied the use of GFPR dowels for JPCP with contraction.(9) They concluded the following:
The literature review indicates contradictory conclusions on the LTE of 3.81-cm (1.5-inch) FRP dowels. Suggestions are also provided by the researcher to increase dowel bar diameter from 3.81 cm (1.5 inches) to 4.45 cm (1.75 inches). Some researchers have noted increased RD with an increased diameter. Hence, it was decided to utilize 3.81- and 2.54-cm (1.5- and 1.0-inch) dowel diameters in this research with 69.47 percent and 72 percent FWF, respectively. Chapter 3 describes materials and laboratory test setup used in this research.