Samuel Cooper III Louisiana Transportation Conference February 18-20, 2013 Baton Rouge, Louisiana

Transcription

1 Testing and Analysis of LWT and SCB Properties of Asphaltic Concrete Mixtures Samuel Cooper III Louisiana Transportation Conference February 18-20, 2013 Baton Rouge, Louisiana

2 Acknowledgements LTRC Asphalt Research Group Jeremy Icenogle, Patrick Frazier, Willie Gueho, Md. Kabir, Bill King

3 Introduction LADOTD s current QA/QC practice relies upon: Gradation AC Content VFA, VMA, % Air Voids Moisture Susceptibility Test (Modified Lottman), and Roadway Parameters: Density, Smoothness But these volumetric properties are not adequate to reflect the pavement performance in the field. Must develop methods to evaluate pavement performance indicators

4 Introduction New laboratory tests are required to evaluate the as-built pavement qualities. The test will screen materials prone to rutting, cracking and alternative moisture damage indicators. Create a Balanced Mixture Design

5 Cracking Resistance Introduction What is a balanced mixture design? Process to ensure adequate resistance to rutting and cracking distress Two laboratory tests are proposed: Rutting: Loaded Wheel Tracking (LWT) Test Cracking: Semi-Circular Bend (SCB) Test Rutting Resistance High Temperature Performance Volumetric Parameters Cracking Performance

6 Research Objective To implement the Loaded Wheel Tracking (LWT) test as a measure of mixture rutting resistance. To evaluate a simplified Semi-Circular Bend (SCB) tests as an end result parameter for intermediate temperature cracking resistance. Rutting Cracking

7 Laboratory Experiment: LWT Test Performance Indicator Resistance to Rutting and Moisture Sensitivity Test Protocol AASHTO T324 Temperature 50 C Loading Wheel Diameter: mm (8 inch) Wheel Width: 47mm (1.85 inch) Fixed Load: 703 N (158 lbs) Rolling Speed: 1.1 km/hr Passing Rate: 52 passes/min

8 Laboratory Experiment: LWT Test Performance Indicators Resistance to Rutting and Moisture Sensitivity Rutting Indicator: Plot Rut Depth vs Number of Passes Report Rut Depth at 1000, 5000, 7500, 10000, 15000, and Passes Moisture Sensitivity Indicator Determine Stripping Inflection Point The point where slope of the line begins to steepen

9 Laboratory Experiment: SCB Test Performance Indicator Resistance to Crack Propagation Test Protocol Mohammad et al. [2004] Temperature 25 C Loading 0.5 mm/min vertical deformation The Critical Value of Fracture Resistance, P 1 J c ( ) b du da b = sample thickness, a = notch depth, U = strain energy to failure P 2 a 2s 2r d notch P 2 b

10 SCB Sample Preparation 150mm x 57mm

11 Laboratory Experiment: Conventional SCB Test Servo Hydraulic Test System Environmental Chamber Expensive Complicated Deformation Load

12 Force (Kn) Laboratory Experiment: Modified SCB Test Load Original Data Max of Data set Fitted Curve Peak of Curve 0.4 Deformation Length(mm) 1 J c ( ) b du da

13 Laboratory Experiment: Modified SCB Test

14 Laboratory Experiment: Modified SCB Test

15 Force (Kn) Laboratory Experiment: Modified SCB Test Original Data Max of Data set Fitted Curve Peak of Curve Length(mm) 1 J c ( ) b du da *Temperature is controlled using an external environmental chamber

16 Analysis: Loaded Wheel Tester 90%! Volumetric Parameters Level 1 Level 2 High Temperature Performance Cracking Performance

17 Preliminary Analysis: Semi-Circular Bend 42% 58% 72% 0% Volumetric Parameters High Temperature Performance Cracking Performance

18 Preliminary Analysis: Balanced Design Level 2 Level 1 50% Volumetric Parameters High Temperature Performance Cracking Performance

19 Preliminary Analysis: Balanced Design Level 1 50% Volumetric Parameters High Temperature Performance Cracking Performance

20 How do we get there? A system to conduct mechanical property test to determine the anticipated performance of asphalt mixtures is needed LTRC has been using LWT and SCB test as forensics investigative tools and performance indicators. Incorporate tests into state specification compliance evaluation. Develop a simplified SCB test procedure. Adapt SCB test to a commonly used load frames Must control TEMPERATURE!

21 How do we get there? Nominal Max., Size Agg. Type of Mix Asphalt Binder Incidental Paving ² 0.5 inch (12.5 mm) Wearing Course Wearing Course 0.75 inch (19 mm) Binder Course Binder Course 1.0 inch (25 mm) Base Course ATB ⁸ 1.5 inch (37.5 mm) Base Course Level ³ A Table 502-2, (3% minimum for Asphalt Treated base (ATB), 6% min for SMA) Friction Rating ³ Table RAP, Max. % of Mix ⁴ Air Voids, % ⁶ VFA, % ⁶ Compacted Mix Volumetrics 4 SMA Wearing VMA, Min. %⁵ n/a ( );; (no limit for ATB) (69-80); no limit for ATB N initial 90% max. ⁷ (Gyrations) n/a 7 7 N design 96.5±1 % (Gyrations) N max 98 % max. (Gyrations) n/a LWT, max. rut-design, # 50⁰ C Dust/Effective Asphalt Ratio, % 10,000 Lift Thickness, inch (mm) 2.0- (50-) (38-50) (38-50) (50-75) (65-100) 2.5+ (65+) 3.0+ (75+) 4.0+ (100+) (38-50)

22 How do we get there? Nominal Max., Size Agg. Type of Mix Asphalt Binder Incidental Paving ² 0.5 inch (12.5 mm) Wearing Course Wearing Course 0.75 inch (19 mm) Binder Course Binder Course 1.0 inch (25 mm) Base Course ATB ⁸ 1.5 inch (37.5 mm) Base Course Level ³ A Table 502-2, (3% minimum for Asphalt Treated base (ATB), 6% min for SMA) Friction Rating ³ Table RAP, Max. % of Mix ⁴ Air Voids, % ⁶ VFA, % ⁶ Compacted Mix Volumetrics 4 VMA, Min. %⁵ n/a ( );; (no limit for ATB) (69-80); no limit for ATB N initial 90% max. ⁷ (Gyrations) n/a 7 7 N design 96.5±1 % (Gyrations) N max 98 % max. (Gyrations) n/a LWT, max. rut-design, # 50⁰ C Dust/Effective Asphalt Ratio, % 10,000 Lift Thickness, inch (mm) 2.0- (50-) (38-50) (38-50) (50-75) (65-100) 2.5+ (65+) 3.0+ (75+) 4.0+ (100+) SMA Wearing (38-50)

23 What s Next? Continued evaluation of the SCB test Validate Jc criteria for mixture design Communicate with other on-going research projects: 10-4B

24 What s Next?

25 Thank You!