High Performance Concrete Pavements Project Summary
Chapter 13. IOWA 4 (IA 330, Jasper, Story, and Marshall Counties)
The Iowa DOT research project Dowel Bar Optimization: Phase I and II (Porter, Guinn, and Lundy 2001) and information from other dowel bar research studies (Porter and Guinn 2002) provided laboratory research results on spacing and bearing stresses for installing conventional round dowels and elliptical dowels. Field evaluation and calibration of the results are important to the application of the results to the pavement design process. To achieve this goal, the Iowa State University, in conjunction with the Iowa Department of Transportation (Iowa DOT), investigated the relative performance of elliptical and conventional round dowels in field conditions. Test sections were constructed in 2002 on Iowa 330 in Jasper, Story, and Marshall counties. Figure 39 shows the location of this project.
Figure 39. Location of IA 4 project.
This project is evaluating the performance of elliptical dowels and the constructibility of such devices in an actual construction project. Specifically, the field research is designed to answer the following questions (Cable, Edgar, and Williams 2003):
- What is the relative performance of medium- and large-sized elliptical steel dowels as compared to that of conventional steel dowels?
- What is the impact of dowel spacing on the relative performance of the elliptical and round dowels in field conditions?
- What is the impact on performance of the various dowel shapes when placed in cut or fill sections of the roadway?
- What constructibility problems, if any, are associated with the installation of dowel shapes other than round?
Project Design and Layout
Two types of elliptical steel dowels (medium and heavy) in addition to conventional 38-mm (1.5-in.) round steel dowels were installed and monitored in this project. The specifications of the dowel bars are as follows (Cable, Edgar, and Williams 2003):
- Heavy elliptical (major axis is 50.013 mm [1.969 in.]; minor axis is 33.985 mm [1.338 in.]; area is 1344.513 mm2 [2.084 in2]).
- Medium elliptical (major axis is 42.012 mm [1.654 in.]; minor axis is 38.321 mm [1.508 in.]; area is 950.321 mm2 [1.473 in2]).
- Standard round (diameter is 38 mm [1.5 in.] and area is 1139.998 mm2 [1.767 in2]).
Each type of dowel bar was placed at three different spacings across the transverse joints: 305 mm (12 in.), 380 mm (15 in.), and 460 mm (18 in.). Three replicate sections of each dowel size and spacing were placed in cut, fill, and transition roadway sections.
Twelve test sections were constructed where dowel bars were placed only in the wheelpaths. A set of four bars at 305-mm (12-in.) spacings was installed in each wheelpath. Six sections were constructed using elliptical medium dowels and the other six sections using conventional 38-mm (1.5-in.) diameter round dowels.
Each test section consisted of 20 transverse joints placed at 6-m (20-ft) intervals and separated from the next test section by a minimum of five joints containing 38-mm (1.5-in.) round steel dowels.
To measure the actual strain responses within the bars, six baskets in the outside lane were fitted with strain gauges. The basket configurations chosen for instrumentation were:
- Medium elliptical dowels at 305-mm (12-in.) spacing.
- Medium elliptical dowels at 460-mm
- Heavy elliptical dowels at 305-mm
- Heavy elliptical dowels at 460-mm
- Heavy elliptical dowels at 380-mm
- Standard 38-mm (1.5-in.) dowels at
305-mm (12-in.) spacing.
State Monitoring Activities
The research team is monitoring the performance of these test sections for 5 years. FWD tests, visual distress surveys, joint faulting and joint opening measurements, and longitudinal profile measurements are being conducted twice per year (spring and fall) (Cable, Edgar, and Williams 2003). In addition, strain gauge responses were monitored using loaded trucks 1 to 7 days after paving and will be monitored 1, 3, and 5 years after paving (Cable, Edgar, and Williams 2003).
The following conclusions can be drawn from the construction process (Cable, Edgar, and Williams 2003):
- The use of elliptical dowels had no effect on the handling or installation of standard, full-lane width, dowel baskets.
- The wheelpath-only baskets provide for more options in the pavement placement process, are easy to handle, and require less dowel materials. However, the wheelpath-only baskets require more time to align on the base than conventional baskets of full-lane width.
- Current construction practices make it somewhat difficult to install and protect the strain gauges during the various phases of construction.
A general concern about the use of elliptical dowel bars is their suitability for placement with a dowel bar inserter.
Points of Contact
Iowa Department of Transportation
800 Lincoln Way
Ames, IA 50011
Max L. Porter
Iowa State University
Center for PCC Pavement Technology
2901 S Loop Drive, Suite 3100
Ames, IA 50010-8632
Cable, J. K., L. Edgar, and J. Williams. 2003. Field Evaluation of Elliptical Steel Dowel Performance - Construction Report. Iowa State University, Ames.
Porter, M. L., and R. J. Guinn. 2002. Assessment of Dowel Bar Research. Project HR-1080 Final Report. Iowa Department of Transportation, Ames.
Porter, M. L., R. Guinn, and A. Lundy. 2001. Dowel Bar Optimization: Phases I and II. Final Report. American Highway Technology and Center for Portland Cement Concrete Pavement Technology, Ames.