High Performance Concrete Pavements
CHAPTER 3. COLORADO 1 (S.H. 121, Wadsworth, Colorado)
The Colorado Department of Transportation (CDOT) constructed three experimental thin whitetopping test sections in 1996 and 1997. An additional 6.4-km (4-mi) test section was constructed in 2001 on S.H. 121 just south of Denver near Wadsworth, Colorado. The original three test sections were instrumented, and the resulting pavement response and performance data were used in the development of a design procedure for thin whitetopping overlays. The fourth test section was constructed to validate the design procedure that was developed.
The objective of this project is to instrument, construct, load test, and monitor the performance of a thin whitetopping test section. The results will be used to validate the design procedure developed based on the test sections constructed in 1996 and 1997. More information on the test sections constructed in 1996 and 1997 can be found in the report by Tarr, Sheehan, and Okamoto (1998).
Project Design and Layout
A 10-year, 1.3 million 18-kip ESAL design was developed for the thin whitetopping test section using the CDOT design procedure. The resulting design consisted of milling to promote bonding between the existing hot mix-asphalt (HMA) and the overlay. A 152.4 mm (6-in.) PCC overlay was then placed on the remaining 140 mm (5.5 in.) of HMA. Both the longitudinal and transverse joints were sawed 1.8 m (6 ft) apart. This section contained four additional designs, which contained various combinations of overlay thicknesses and joint spacing, as shown in Table 2.
The concrete mix did contain fibers. Dowel bars were not included in any of the test sections, but tie bars were included along all longitudinal joints at 762-mm (30-in.) spacings.
The volume of traffic on this section of roadway is relatively high but the traffic consists primarily of cars and light trucks.
State Monitoring Activities
Monitoring activities included collecting strain measurements in conjunction with static load testing, performing distress surveys, recording temperature gradients, and performing shear bond strength testing on pavement cores. These activities were performed at 28 days and at 1 year after construction. Load testing was performed again in 2003. The load testing consisted of applying an 18-kip rear axle load. In 2003, a 30-kip tandem axle load was also used. Loads were applied at the corner, edges, and midpanel of the slab. Temperatures throughout the slab and asphalt were collected every 15 minutes while the load testing was being performed.
Table 2. Summary of CO 1 Project Test Sections
|TEST SECTION||PCC OVERLAY THICKNESS (IN.)||HOT-MIX ASPHALT THICKNESS (IN.)||LONGITUDINAL JOINT SPACING (FT)||TRANSVERSE JOINT SPACING (FT)|
The average bond shear strength was 100 lbf/in2, and this appears to be sufficiently high to provide good performance for the overlay designs represented on State highway 121.
The strains induced by the static 18-kip single-axle load placed along the edge of the slab were converted to stress and are summarized in Table 3. The data show a reduction in stress as the slab thickness increases and the panel size decreases.
The stress predicted by the design equations was calculated for the loading conditions in the field. The predicted stresses were lower than the stresses determined using the measured strains. This is expected because the measured strains did not capture curling and warping restraint stresses.
Table 3. Ranges of Edge Stresses Measured Under an 18-Kip Single-Axle Load on the CO 1 Project Test Sections
|TEST SECTION||PCC THICKNESS(IN.)||PANEL SIZE (FT)||STRESS RANGE (LBF/IN2)|
|1||3.9||4 x 4||80-175|
|2||4.5||6 x 6||75-160|
|3||6.5||6 x 9||55-110|
|4||6.5||6 x 6||60-100|
Current Project Status, Results, and Findings
A final report on the revisions to the thin whitetopping design procedure (Sheehan, Tarr, and Tayabji 2004) is available from the Colorado Department of Transportation.
Point of Contact
Colorado Department of Transportation
4201 East Arkansas Ave, Rm A-100
Denver, CO 80222
Sheehan, M. J., S. M. Tarr, and S. D. Tayabji. 2004. Instrumentation and Field Testing of Thin Whitetopping Pavement in Colorado and Revision of the Existing Colorado Thin Whitetopping Procedure. Report No. CDOT-DTD-R-2004-12. Colorado Department of Transportation, Denver.
Tarr, S. M., M. J. Sheehan, and P. A. Okamoto. 1998. Guidelines for the Thickness Design of Bonded Whitetopping Pavement in the State of Colorado. Report No. CDOT-DTD-R-98-10. Colorado Department of Transportation, Denver.