High Performance Concrete Pavements Project Summary
Chapter 39. FEDERAL HIGHWAY ADMINISTRATION 1 (FHWA's Pavement Test Facility, McLean, VA)
A joint venture between FHWA and the American Concrete Pavement Association (ACPA) was initiated in 1998 to study the design and performance of ultrathin whitetopping (UTW) overlays. The research consisted of constructing eight 15.2-m (50-ft) test lanes of UTW placed on an existing hot mix asphalt (HMA) surface. Loading of the test sections occurred between May 1998 and November 1999.
The objective of the study was to validate the design equations and performance prediction models used in the ACPA UTW design procedure. The specific research objectives were as follows:
- Evaluate UTW performance under controlled wheel-loads and temperature.
- Study the effects of a range of design features (thickness, joint spacing, and fiber reinforcement) on the performance of UTW.
- Measure pavement response and develop mechanistic models based on these responses.
- Verify existing models and develop new models for predicting load-carrying capacity.
Project Design and Layout
The test sections were loaded by two accelerated load testing machines capable of applying simulated truck loads under a controlled pavement temperature. A single wheel load of either 10 or 12 kips was applied, and the speed of the loaded tire was a constant 16 km/hr (10 mi/hr). An average of 35,000 loads were applied per week. The HMA was 5 years old and a range of severities of rutting were present prior to milling. The HMA was milled to a depth of either 63.5 or 88.9 mm (2.5 or 3.5 in.) depending on the depth of the rutting that was present. The thickness of the overlay was equal to the milled depth so the existing elevation could be maintained. The design parameters for each test section are provided in Table 58, and a layout of the test sections is provided in Figure 109.
|LANE NO.||PCC OVERLAY THICK (IN.)||HMA THICK (IN.)||HMA MIXTURE, BINDER1||JOINT SPACING (FT)||FIBERS IN CONCRETE MIXTURE||DESIGN 12-KIP LOAD APPLICATIONS2|
|5||2.5||5.5||SM, AC-10||4 x 4||Yes||210,000|
|6||2.5||5.5||SM, AC-20||4 x 4||No||140,000|
|7||2.5||5.5||SM, PM||3 x 3||Yes||420,000|
|8||2.5||5.5||SM, PM||3 x 3||No||350,000|
|9||3.5||4.5||SM, AC-5||6 x 6||Yes||350,000|
|10||3.5||4.5||BM, AC-20||6 x 6||No||245,000|
|11||3.5||4.5||BM, AC-5||4 x 4||Yes||455,000|
|12||3.5||4.5||BM, AC-20||4 x 4||No||350,000|
|1SM = surface mixture; BM = base mixture; PM = polymer modified asphalt.|
2Estimated design life was calculated using American Concrete Pavement Association design procedure based on as-built strengths, overlay design thicknesses, and 12-kip loads.
Figure 109. Layout of test sections and instrumentation for FHWA 1 project (FHWA 2004).
ALF = accelerated loading facility; LVDT = linear value displacement transducers; THK = thick
The test sections were instrumented with between 15 and 18 dynamic strain gauges. The gauges were installed near the top and bottom of the concrete overlay and on the surface of HMA. Deflections were measured in the interior of the slab and adjacent to the joint using linear variable displacement transducers.
State Monitoring Activities
Monitoring activities included collecting distress data and measuring faulting and roughness. Deflections and strains induced by the applied wheel loads were also recorded. Laboratory data collected included layer modulus values, flexural strengths, and bond strengths.
A summary of the performance of the test sections is provided in Table 59. Although a few of the sections exhibited significant cracking, many experienced very little cracking. The primary types of distress documented were corner, transverse, and longitudinal cracks with corner cracking being the most predominant distress. A small amount of faulting along some of the longitudinal and transverse joints was measured, but overall very little faulting developed. Test sections that contained an HMA with binders having a higher penetration tended to exhibit a slightly higher level of cracking. Reducing the panel size when overlaying an HMA with a soft binder tended to increase the performance of the overlay.
|LANE NO.||ACTUAL LOAD APPLICATIONS||NUMBER OF PANELS LOADED||NUMBER OF PANELS EXHIBITING CRACKING||RANGE OF LONGITUDINAL FAULTING (IN.)||RANGE OF TRANSVERSE FAULTING (IN.)|
|5||194,500 @ 12 kips||12||18||0.1-0.7||None|
|6||359,000 @ 12 kips||12||11||0.1-0.3||None|
|7||283,500 @ 12 kips||16||4||0-0.1||None|
|8||628,000 @ 12 kips||16||3||0.1-0.2||0-0.1|
|9||266,000 @ 12 kips||8||10||0.1-0.0.3||0-0.2|
|10||441,000 @ 12 kips||8||4||0.1-0.2||0-0.2|
|11||310,000 @ 10 kips|
762,630 @ 12 kips
|12||310,000 @ 10 kips|
762,630 @ 12 kips
Design recommendations based on the findings from this study are being prepared, and the database of information produced will be available to the public in conjunction with a report on the contents of the database.
Current Project Status, Results, and Findings
The cracked slabs in Lane 6 and Lane 10 were repaired on April 28, 2000. Mostly panels with multiple cracks or loose or missing pieces of concrete were replaced. Five panels were replaced in Lane 6 and three panels in Lane 10. The steps followed in performing the repairs appear below.
- Identify panels to be repaired.
- Mark boundaries for saw cuts, which should be at located at least 101.6 mm (4 in.) on the inside of each joint.
- Perform saw cuts.
- Used jackhammer to break-up slabs and to dislodge the bonded portions of the concrete overlay from the HMA.
- Remove debris and clean surface in the repair area.
- Place new concrete.
- Saw joints.
The average depth of the repair area after the panels were removed for Lane 6 was 96.5 mm (3.8 in.) and 119.4 mm (4.7 in.) for Lane 10. This resulted in an increase in overlay thickness of 33 mm (1.3 in.) for the repairs in Lane 6 and 33 mm (1.3 in.) for the repairs in Lane 10. More information on the repairs can be found in the report prepared by CTL (2001).
The slump, air content, concrete temperature, and unit weight of the repair concrete were measured. The compressive strength, split tensile strength, modulus of rupture, and modulus of elasticity of the concrete were also measured. Information on the test results is available in the report prepared by CTL (2001).
Four panels were also removed from Lane 9 to investigate the removal of slabs using a small front-end loader. Additional loadings were not applied to Lane 9.
Additional 12-kip dual wheel loads were applied to each lane beginning 8 days after the repair and continuing until early August 2000. During this time, Lane 6 accumulated 400,000 load repetitions and Lane 10 427,000 repetitions. Two of the five panels repaired in Lane 6 exhibited cracking, and two of the three panels repaired in Lane 10 cracked. These cracks were primarily corner cracks.
Point of Contact
Office of Infrastructure Research and Development
Turner-Fairbank Highway Research Center
6300 Georgetown Pike
McLean, VA 22101
Construction Technologies Laboratories, Inc. (CTL). 2001. UTW Pavement Repair Demonstration. Final Report. Innovative Research Foundation, Falls Church, VA.
Federal Highway Administration (FHWA). 2004. Ultra-Thin Whitetopping (UTW) Project.