Asphalt Binder Cracking Device to reduce Low Temperature Asphalt Pavement Cracking

EXECUTIVE SUMMARY

Phase 1 of "Asphalt Binder Cracking Device (ABCD) to Reduce Low Temperature Pavement Cracking" project consisted of four tasks including refinement of test procedures, field validation of ABCD, refinement of equipment and analysis software, and ruggedness testing. In January 2008, a new testing facility for EZ Asphalt Technology, LLC, was established in Athens, Ohio. The first three tasks utilized 22 asphalt binders.

Regarding refinement of test procedures, ABCD test precision and duration were improved by modifying the silicone mold, improving the trimming process, and determining an optimum cooling rate of 20°C to 0°C in the first 30 minutes followed by 0°C to –60°C in three hours. ABCD tests of unaged and RTFO/PAV aged SHRP core asphalt binders indicated that, for unaged binders 24 hours of isothermal conditioning at –15°C caused the ABCD cracking temperatures to rise while, for RTFO/PAV aged binders 24 hour conditioning at –15°C significantly lowered cracking temperature. To help increase the ease and consistency of ABCD sample preparation, the use of turntables was incorporated. Turntables helped greatly in preventing overfilling and spillage due to misalignment of the pouring stream and the ¼ in. annular gap between the ABCD ring and the mold.

For field validation, binders from National Pooled Fund Study 776, Ohio DOT paving projects, and SHRP binders were tested. There is a moderate relationship between ABCD strain jump and Direct Tension Test (DTT) failure stress for unaged SHRP binders but no statistically significant relationship for PAV aged binders. There is a significant difference in strength measurement between DTT and ABCD as expected since test temperature is fixed in DTT but intentionally not fixed in ABCD test.

Additionally, refinements of equipment and analysis software were conducted. The Free Piston Sterling Cooler prototype environmental chamber was investigated due to its light–weight, quiet, and vibration–free operation. Unfortunately, it was unable to maintain the desired cooling rate of 20°C per hour, so the Cincinnati Sub–Zero Products cooling chamber will continue to be the mainstay for ABCD testing since it has proven durability and provides consistent cooling rates. Regardless of which chamber is used, if the cooling chamber is opened while still at low temperature, condensation collects on the ring materials sometimes resulting in premature ring and sensor failure. To solve the problem, sensors were coated with water proofing materials. Data collection now runs on both Microsoft Windows XP and Vista, directly controls the temperature in the chamber, and conducts the data analysis

The fourth task was the ruggedness test following ASTM C 1067 – 00. North Central Superpave Center (NC), the University of Wisconsin – Madison (WI), and EZ Asphalt tested RTFO/PAV aged binders (polymer modified and unmodified). Cooling rate, protrusion size, over–trimming, turntable usage, cold joint formation, and conditioning time were studied. Statistical analyses indicated that protrusion size and over–trimming affected cracking temperatures. Additional statistics revealed that the WI lab generally determined colder cracking temperatures than the other two labs. Supplemental tests at all labs using a modified procedure and improved trimming technique at the WI lab resulted in elimination of laboratory variability from cracking temperature statistics.

As will be further investigated in the Interlaboratory Study in Phase 2, the direct determination of binder cracking temperature and strength, ease of sample preparation and conduction of test, repeatability at other laboratories, and cost–savings to the industry since more reliable results than other methods indicate that the ABCD has much potential to provide a better determination of binder cracking temperature and strength compared to other asphalt binder test devices. In addition to describing details of the four Phase 1 tasks, performance specifications and operating procedures are included in the Appendices in the form of a draft ABCD Standard Test Procedure following AASHTO format and the ABCD User's Guide.

Outline

• Acronyms
• Introduction
  • Task 1. Refinement of Test Procedure
    • 1A. Cooling Rate
    • 1B. Physical Hardening
    • 1C. Refinement of Test Procedures
  • Task 2. Field Validation
  • Task 3. Refinement of Equipment and Analysis Software
    • 3A. Free Piston Sterling Cooler (FPSC)
    • 3B. ABCD Ring
    • 3C. ABCD Data Analysis Software
  • Task 4. Ruggedness Test
    • 4A. Seven Factors being studied in Ruggedness Test
    • 4B. Ruggedness Test Results
      • 4B.1. ABCD Cracking Temperature
      • 4B.2. Strain Jump at Fracture
    • 4C. Supplemental Test (Pilot Interlaboratory Study)
    • 4D. Survey of Ruggedness Participants
• Conclusion
• Appendix A. Financial Reports
• Appendix B. Ruggedness Surveys from North Central Superpave Center and University of Wisconsin–Madison

Acronyms

• AASHTO = American Association of State Highway and Transportation Officials
• ABCD = Asphalt Binder Cracking Device
• ANOVA = Analysis of Variance
• AOTR = Agreement Officer's Technical Representative
• ASTM = American Society for Testing and Materials
• Avg = Average
• C = Celsius
• CA = California
• Diff = Difference
• DOT = Department of Transportation
• DTT = Direct Tension Test
• E_ABCD = Young's Modulus of ABCD Ring
• A_ABCD = Cross–Sectional Area of ABCD Ring
• A_binder = Cross–Sectional Area of Asphalt Binder
• EM = Exxon–Mobil
• FHWA = Federal Highway Administration
• FPSC = Free Piston Sterling Cooler
• F value = Statistical Variable
• HfL = Highways for LIFE
• hr = Hour
• ID = Identification
• in. = Inch
• kPa = kiloPascal
• K = Stress Concentration Factor
• LabVIEW = Laboratory Virtual Instrumentation Engineering Workbench (National Instruments, Inc.)
• LIFE = Longer–lasting highway infrastructure using Innovations to accomplish the Fast construction of Efficient and safe highways and bridges
• LLC = Limited Liability Company
• Max = Maximum
• Min = Minimum
• MN = Minnesota
• MPa = Mega Pascal
• NC = North Central Superpave Center
• ND = Not Determined
• NM = Not Measured
• NS = Not Significant
• NT = Not Tested
• OD = Ohio Department (of Transportation)
• OH = Ohio
• PAV = Pressure Aging Vessel
• PG = Performance Grade
• PH = Physical Hardening
• p–value = Statistical Variable
• r² = Coefficient of Determination
• R² = Coefficient of Determination
• Rep = Repetition
• RMSE = Root Mean Square Error
• RTD = Resistance Temperature Detector
• RTFO = Rolling Thin Film Oven
• SBS = Styrene–Butadiene–Styrene
• SD = Standard Deviation
• SHRP = Strategic Highway Research Program
• StDev = Standard Deviation
• T_cr = Cracking Temperature
• US = United States
• W TX = West Texas
• WI = Wisconsin
• x = x–axis value
• WY = Wyoming
• y = y–axis value
• ε = Strain Jump
• σ_f = Fracture Stress
• µε = Microstrain