High Performance Concrete Pavements Project Summary
Chapter 22. MINNESOTA 2 (Mn/Road Low-Volume Road Facility)
The Minnesota Road Research Project (Mn/Road) is a major highway research initiative studying the performance of asphalt-, concrete-, and aggregate-surfaced roadways. Opened to traffic in 1994, the purpose of the test road is to gain a better understanding of pavement response and pavement behavior to traffic and environmental loadings, with the expectation that improvements to existing pavement design and evaluation procedures will result.
The Mn/Road facility is located near Albertville, just northwest of Minneapolis-St. Paul (see Figure 59). It consists of two different road segments running parallel to I-94: one a 5.7-km (3.5-mi) mainline roadway in the westbound direction carrying interstate traffic, and the other a 4.0-km (2.5-mi) low-volume road (LVR) loop exposed to controlled truck weight and traffic loadings. A variety of heavily instrumented test sections, consisting of different thicknesses of concrete, asphalt, and aggregate surfaces as well as other design features, have been constructed within each road segment. The asphalt sections on the LVR loop were designed to last approximately 3 years, and after 5 years several of these sections have required rehabilitation or reconstruction (Mn/DOT 2000). By eliminating one of the deteriorated gravel test sections on the LVR, three new JPCP test sections (numbered 32, 52, and 53) were constructed with partial funding from the TE-30 program (Mn/DOT 2000). Figure 60 shows the layout of the Mn/Road facility and the approximate location of the new test sections.
Figure 59. Location of MN 2 project.
Figure 60. Approximate location of new low-volume road test sections at MN/Road facility.
These three new test sections were constructed to obtain data not previously considered in the original LVR designs, as well as to satisfy the data needs of local agencies (Mn/DOT 2000). Specific objectives include the following (Mn/DOT 2000):
- Characterization of early-age and long-term slab curling and warping.
- Measurement of early-age and long-term internal slab stresses and shrinkage.
- Evaluation of long-term joint load transfer behavior of different dowel bar types.
- Evaluation of the performance of a thin, low-cost JPCP for low-volume applications.
- Evaluation of a concrete mixture containing ground granulated blast furnace slag (GGBFS).
- Validation of sensor readings from other Mn/Road test sections.
- Further investigation of the feasibility of retrofitting sensors in a pavement.
Project Design and Layout
The three test sections are located on the southern tangent of the LVR, near the eastern loop. Design characteristics of each section are provided below (Mn/DOT 2000):
- Section 32 - 127-mm (5-in.) JPCP with 3.1-m (10-ft) transverse joints. The pavement rests on a 178-mm (7-in.) aggregate base. The joints are sealed with a hot-poured joint sealant material and do not contain dowel bars. The concrete mix contains 35 percent GGBFS.
- Section 52 - 190-mm (7.5-in.) JPCP with 4.6-m (15-ft) transverse joints. A 127-mm (5-in.) aggregate base is located beneath the pavement slab. The transverse joints are sealed with silicone. The outside lane is 4.0-m (13-ft) wide and the inside lane is 4.3-m (14-ft) wide. Four different load transfer devices are included in the section:
- 25-mm (1-in.) diameter, 381-mm (15-in.) long, epoxy-coated dowel bars.
- 32-mm (1.25-in.) diameter, 381-mm (15-in.) long, epoxy-coated dowel bars.
- 32-mm (1.25-in.) diameter, 457-mm (18-in.) long, fiber-reinforced polymer dowel bars.
- 38-mm (1.50-in.) diameter, 457-mm (18-in.) long, fiber-reinforced polymer dowel bars.
- Section 53 - 190-mm (7.5-in.) JPCP with 4.6-m (15-ft) transverse joints. A 127-mm (5-in.) aggregate base is beneath the pavement. The transverse joints are sealed with silicone. The outside lane is 4.0-m (13-ft) wide and the inside lane is 4.3-m (14-ft) wide. None of the joints is doweled.
Table 28 summarizes some of the key design features for the MN 2 test sections. Figure 61 illustrates the layout of test sections 52 and 53.
|DESIGN FEATURE||SECTION 32||SECTION 52||SECTION 53|
|Slab thickness, in.||5||7.5||7.5|
|Base type||7 in., aggregate||5 in., aggregate||5 in., aggregate|
|Transverse joint spacing, ft||10||15||15|
|Load transfer||None (aggregate interlock)||1-in. epoxy-coated dowels|
1.25-in. epoxy-coated dowels
1.25-in. fiber-reinforced polymer
1.50-in. fiber-reinforced polymer
|None (aggregate interlock)|
|Longitudinal joint tie bars||No. 4 bars @ 30-in. spacings||No. 4 bars @ 30-in. spacings||No. 4 bars @ 30-in. spacings|
|Lane width, ft||12 (both)||13 (outside)|
|Section length, ft||470||285||115|
JPCP = jointed plain concrete pavement; GGBFS = ground granulated blast furnace slag
Figure 61. Layout of test sections 52 and 53 for MN 2 project.
Instrumentation layout for these test sections began in April 2000, with actual construction commencing in June (Mn/DOT 2000). Table 29 summarizes the type and number of sensors in these test sections ( Burnham 2001). Concrete paving was performed on June 30, which was immediately followed by 72 hours of continuous monitoring of the internal shrinkage, strain, and temperatures, as well as the external shape of the slabs (Mn/DOT 2000).
|SENSOR TYPE||MEASUREMENT TYPE||MANUFACTURER||QUANTITIES|
|SECTION 32||SECTION 52||SECTION 53|
|Concrete embedment sensor||Strain||Tokyo Sokki||37||87||20|
|Displacement transducer||Joint opening||Tokyo Sokki||4||8||4|
|Invar reference rod||Elevation||Mn/DOT||4||4|
|Stainless steel reference rod||Elevation||Mn/DOT||2||5||1|
|Concrete embedment sensor||Strain||MicroMeas||8|
|Psychrometer sensor||Relative humidity||Wescor||4||4||4|
|Moisture resistance sensor||Relative humidity||ELE International||6||6||6|
|Dynamic Soil Pressure Sensor||Pressure||Geokon||1||3||3|
|Static soil pressure sensor||Pressure||Geokon||1||2||2|
|Time domain reflectometer||Soil moisture||Campbell Scientific||6||4||4|
|Vibrating wire strain sensor||Strain||Geokon||16||35||34|
State Monitoring Activities
As with all pavements at the Mn/Road test facility, these sections are subjected to an intensive data collection effort. In addition to the data obtained from the instrumented slabs within each section, visual distress data, faulting measurements, ride quality, and FWD deflection data are collected (Mn/DOT 2000).
Preliminary Results and Findings
One of the objectives of this study was to evaluate the long-term joint performance of different dowel bar types. Preliminary data on the dowel bars is provided below in Figures 62 and 63. The initial load transfer efficiency was lower for the FRP bars compared to the steel dowels by about 5 percent. After 2 years in service, the load transfer efficiency for the FRP bars dropped from approximately 80 percent to approximately 70 to 75 percent, which are considered critical minimum levels. The performance of the epoxy-coated steel bars appears relatively constant since construction. The differential deflections measured across each joint are still relatively low, as can be seen in Figure 63.
Figure 62. Load transfer efficiency of joints with different types of dowel bars for MN 2 project.
Figure 63. Differential deflections across joints with different types of dowel bars for MN 2 project.
Another objective of the MN 2 project was to evaluate the early-age and long-term slab curling and warping. Early-age profile measurements made using the Dipstick are provided in Figures 64 to 66. The profiles measurements revealed that large positive temperature moments can produce sufficient deformation in the slab such that the slab is unsupported along the whole length of the transverse joint due to upward curvature. Large negative gradients can result in a deformed slab that forces the bottom of the slab into the base layer along the complete length of the transverse joint. The total range of movement of the corner of the slab adjacent to the asphalt shoulder for the temperature conditions present during measurement period was approximately 3,500 microns. The total movement for the corner of the slab adjacent to the longitudinal joint was 2,500 microns. These measurements were for slabs without dowel or tie bars. A more thorough analysis of the early-age performance data can be found in Vandenbossche (2003).
Figure 64. Transverse profile of unrestrained slab in Cell 53 for MN 2 project
Figure 65. Diagonal profile of unrestrained slab in Cell 53 for MN 2 project
Figure 66. Diagonal profile of restrained slab in Cell 52 for MN 2 project
Extensive research has also been performed on the analysis of measured dynamic strains in the thin concrete pavements on the MN2 project. An in-depth discussion of the findings is provided by Burnham (2003; 2004).
Point of Contact
1400 Gervais Avenue
Maplewood, MN 55109
Burnham, T. R. 2001. Construction Report for Mn/Road PCC Test Cells 32, 52, and 53 - Final Report. Minnesota Department of Transportation, Maplewood.
---. 2003. "Seasonal Load Response Behavior of a Thin PCC Pavement." Proceedings, Eighth International Conference on Low-Volume Roads, Transportation Research Record 1819. Transportation Research Board, Washington, DC.
---. 2004. "Load Proximity Correlation of Dynamic Strain Measurements in Concrete Pavement." Proceedings, Second International Conference on Accelerated Pavement Testing. Minneapolis, MN.
Minnesota Department of Transportation (Mn/DOT). 2000. New JPCP Test Cells at the Mn/ROAD Project. Minnesota Department of Transportation, Maplewood.
Vandenbossche, J. M. 2003. Interpreting Falling Weight Deflectometer Results for Curled and Warped Portland Cement Concrete Pavements. Thesis for the degree Doctor of Philosophy in Civil Engineering, University of Minnesota, St. Paul.