High Performance Concrete Pavements Project Summary
Chapter 11. IOWA 2 (US 65, Des Moines)
The Iowa Department of Transportation's second TE-30 project consists of an evaluation of alternative dowel bar materials and spacings. The experimental project was constructed in 1997 on the US 65 Bypass near Des Moines (Cable and McDaniel 1998b). Figure 32 shows the location of this project.
Figure 32. Location of IA 2 project.
Because of the susceptibility of steel dowel bars to corrosion, the Iowa DOT has expressed interest in the use of alternative dowel bar materials to provide load transfer across transverse joints in concrete pavements. Therefore, one of the goals of this project is the comparative study of concrete pavement joints containing fiber-reinforced polymer (FRP) dowel bars, stainless steel dowel bars, and conventional epoxy-coated steel dowel bars under the same design criteria and field conditions (Cable and McDaniel 1998b). Another goal of the project is the investigation of the transverse joint load transfer characteristics of alternative dowel bar spacings (Cable and McDaniel 1998b). This evaluation is a 5-year study being performed through the combined efforts of the Iowa Department of Transportation and the Iowa State University.
Project Design and Layout
This project was constructed in 1997 on the northbound lanes of the US 65 Bypass near Des Moines. The basic design for the project is a 305-mm (12-in.) JPCP on a 152-mm (6-in.) granular base course (Cable and McDaniel 1998b). Transverse joints are located at 6.1-m (20-ft) intervals and are skewed 6:1 in the counterclockwise direction (Cable and McDaniel 1998b). Both transverse and longitudinal joints are sealed with a hot-poured sealant. Number 5 tie bars, 914 mm (36 in.) long and spaced at 762-mm (30-in.) intervals, were mechanically inserted by the paver across the longitudinal centerline joint (Cable and McDaniel 1998b).
The shoulder for the JPCP is a 203-mm (8-in.) asphalt concrete (AC) layer, paved 2.4 m (8 ft) wide on the outside edge and 1.6 m (6 ft) on the inside edge (Cable and McDaniel 1998b). Longitudinal subdrains are located under the outside shoulder and adjacent to the edge of the outside driving lane (Cable and McDaniel 1998b).
Four different load transfer systems are included in the study: a fiber composite dowel bar manufactured by Hughes Brothers, a fiber composite dowel bar manufactured by RJD Industries, a solid stainless steel dowel bar, and a conventional epoxy-coated steel dowel bar (Cable and McDaniel 1998b). The Hughes Brothers dowel bar is 48 mm (1.88 in.) in diameter, whereas the other dowel bars are 38 mm (1.5 in.) in diameter. The required diameters for the alternative dowel bars were determined from laboratory testing and experimental research performed by the manufacturers (Cable and McDaniel 1998b).
A standard spacing of 305 mm (12 in.) was used for each load transfer system included in the study. In addition, sections were constructed using a spacing of 203 mm (8 in.) for the alternative dowel bar materials. The experimental design matrix for this project is shown in Table 16, and the layout of the test sections is shown in Figure 33. The dowel bar spacing configurations used on this project are illustrated in Figure 34.
|305-MM (12-IN.) JPCP, 6.1-M (20-FT) JOINT SPACING (SKEWED)|
|203-mm (8-in.) Dowel Spacing||305-mm (12-in.) Dowel Spacing|
|38-mm (1.5-in.) Diameter Dowel||48-mm (1.88-in.) Diameter Dowel||38-mm (1.5-in.) Diameter Dowel||48-mm (1.88-in.) Diameter Dowel|
|Fiber composite dowel bars (Hughes Brothers)||Section 1 (440 ft)||Section 2 (417 ft)|
|Fiber composite dowel bars (RJD Industries)||Section 3 (100 ft)||Section 4 (80 ft)|
|Stainless steel dowel bars||Section 5 (222 ft)||Section 6 (556 ft)|
|Epoxy-coated steel dowel bars||Section 8 (477 ft)|
Figure 33. Layout of IA 2 project.
Figure 34. Illustration of dowel bar spacing configurations on IA 2.
Fiber composite tie bars were also provided by the fiber composite dowel bar manufacturers for installation in their respective test sections. However, these fiber composite tie bars had a tendency to "float" to the top of the surface during or immediately after their placement (Cable and McDaniel 1998b). This was attributed to either an incompatibility of the automatic tie bar inserter to the smaller diameter of the fiber composite tie bars or to the lighter weight of the fiber composite bars themselves (Cable and McDaniel 1998b). After several bars surfaced in succession, the epoxy-coated steel tie bars were used on the remainder of the project.
State Monitoring Activities
The performance of these test sections was monitored under a 5-year monitoring program (from the fall of 1997 through the spring of 2003) being conducted jointly by the Iowa DOT and the Iowa State University (Cable and Porter 2003). The following monitoring activities were conducted (Cable and Porter 2003):
- Visual distress survey using LTPP procedures. As part of these surveys, joint openings were monitored using PK masonry nails placed along joints in each section, and joint faulting was measured using a Georgia Digital Faultmeter.
- Deflection testing using a Dynatest Falling Weight Deflectometer (FWD). Within each section, deflection testing was performed at three joints and at three center slab locations per lane. Testing was performed twice a year, once in March or April (to represent a "weak" foundation condition) and once in August or September (to represent a "strong" foundation condition).
In addition, ground penetrating radar (GPR) was used to establish the location (depth and orientation) of dowel bars and tie bars (Cable and Porter 2003). At the end of 5 years, selected joints in each section were cored and the condition of each dowel bar type was inspected (Cable and Porter 2003).
During the construction of the project, several items were noted to be of importance to future installations of alternative dowel bars in concrete pavements (Cable and McDaniel 1998b):
- The original method of securing the fiber composite and stainless steel dowel bars to the basket was inadequate. To address this, plastic zip ties were fastened around each basket brace loop and end of dowel to hold them in place. Any excess tie length was cut or turned down to prevent surface finishing problems.
- The placement of the stainless steel dowels required three to five people to handle the baskets. Future use of stainless steel dowels will require "x" braces welded to the basket to prevent side sway and collapse during handling.
- Nails were attached to the bottom of the fiber composite tie bars to facilitate their location using both cover meters and GPR.
- As stated previously, the fiber composite tie bars, placed using the automatic tie bar inserter on the paver, were susceptible to "floating" to the surface. If this is a continuing problem, the placement of these bars in tie bar baskets or the use of conventional epoxy-coated tie bars may be required.
Project test sections were tested twice a year, beginning in the fall of 1997, with the final tests in the spring of 2002 (testing could not be performed in the fall of 2000). The results of the FWD testing were interpreted through calculating LTE.
The results of the load transfer analysis are illustrated in Figure 35 (Cable and Porter 2003). In Figure 35, the dowel bars are labeled according to their material and spacing: standard epoxy (std. epoxy), stainless steel (S.S.), and fiber composite (FRP). Figure 36 displays the overall average faulting over the period of research (Cable and Porter 2003). Figure 37 illustrates the changes in joint openings over the research period (Cable and Porter 2003). Visual surveys of this project resulted in only minor corner cracking being noted immediately after construction. There are no visible signs of pavement distress that can be associated with joint reinforcement or typical highway loading over the 5-year monitoring period (Cable and Porter 2003).
Figure 35. Average load transfer efficiency for IA 2 project.
FRP = fiber composite; S.S. = stainless steel; Std. Epoxy = standard epoxy
Figure 36. Average faulting on IA 2 project.
FRP = fiber composite; S.S. = stainless steel
Figure 37. Joint opening trends on IA 2.
FRP = fiber composite; S.S. = stainless steel; Std. Epoxy = standard epoxy
The following summaries and conclusions have been reached based on the data gathered during the study (Cable and Porter 2003):
- All dowel materials tested are performing equally in terms of load transfer, joint movement, and faulting over the 5-year analysis period.
- Stainless steel dowels do provide load transfer performance equal to or greater than epoxy-coated steel dowels in this study on the average over 5 years.
- FRP dowels of the sizes tested in this research should be spaced no greater than 203 mm (8 in.) apart to gain load transfer performance at the same level as epoxy-coated steel dowels at 305-mm (12-in.) spacing.
- No deterioration due to road deicers was found on any of the dowel materials retrieved in the 2002 coring operation.
Points of Contact
Iowa State University
Department of Civil and
378 Town Engineering Building
Ames, IA 50011
Iowa Department of Transportation
100 Lincoln Way
Ames, IA 50011
Cable, J. K. and L. L. McDaniel. 1998b. Demonstration and Field Evaluation of Alternative Portland Cement Concrete Pavement Reinforcement Materials. Iowa DOT Project HR-1069. Iowa Department of Transportation, Ames.
Cable, J. K., and M .L. Porter. 2003. Demonstration and Field Evaluation of Alternative Portland Cement Concrete Pavement Reinforcement Materials. Iowa DOT Project HR-1069. Iowa State University, Ames.