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TxDOT

TxDOT. Permeable Friction Course (PFC) Mixtures are Different! 36 th Rocky Mountain Asphalt Conference and Equipment Show 1 st Annual Flexible Pavement Research Symposium Amy Epps Martin, Allex E. Alvarez February 18, 2009. TxDOT. OUTLINE. 1. Introduction 2. Current Research

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TxDOT

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  1. TxDOT Permeable Friction Course (PFC) Mixtures are Different!36th Rocky Mountain Asphalt Conference and Equipment Show1st Annual Flexible Pavement Research SymposiumAmy Epps Martin, Allex E. AlvarezFebruary 18, 2009

  2. TxDOT OUTLINE 1. Introduction 2. Current Research 3. Experimental Design and Results 4. Summary and Recommendations - Future Work

  3. TxDOT 1. Introduction Dense-graded mixtures VsPorous friction course mixtures (PFC or OGFC) as surface courses Kringos et al., 2007

  4. TxDOT • PFC Advantages • Reduce splash and spray • Improve skid resistance in wet conditions • Decrease noise • Produce cleaner runoff

  5. TxDOT • 2. Current Research • Improve TxDOT PFC mix design procedure and • recommend construction practices based on: • Volumetrics • Durability • Drainability • Densification Effects

  6. TxDOT 3. Experimental Design and Test Results Selected Mixtures

  7. 3.1 Volumetrics a. Total AV Content Gmm: theoretical max. specific gravity of the mixture Gmb: bulk specific gravity of the compacted PFC mixture • Current practice: • Total AV content (or corresponding density) • Vacuum method or dimensional analysis for Gmb • Measured Gmm

  8. or mixture at low binder content (3.5 to 4.5%) Method 2-calculated Gmm Theoretical Max. Specific Gravity, Gmm Method 1-measured Gmm mixture at the design asphalt range (6 to 10%)

  9. Method 2-dimensional Vt=*r2*h Bulk Specific Gravity, Gmb Method 1-vacuum

  10. 2.49 2.45 Shift due to asphalt loss 2.41 Specific Gravity Theoretical Maximum 2.49 0.03 2.37 2.45 2.33 2.41 0.02 2.29 Specific Gravity Theoretical Maximum Standard Deviation 2.37 2.25 2.33 0.01 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 2.29 Asphalt Content (%) Average Meas. Gmm Calculated Gmm 2.25 0.00 Gmm-Ignition Sample Gmm Compacted Sample 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 Asphalt Content (%) Calculated Gmm Measured Gmm Standard deviation Results and Discussion Gmm Comparison and Variability, AR Mixtures Calculated Gmm: less variability and less asphalt-loss error Gmb Dim: Simpler, faster, less expensive, cleaner, required equipment is readily available, and data can be directly used to analyze X-ray CT images

  11. b. Connected AV Content Water-Accessible AV Content Method 1-vacuum method Method 2-dimensional analysis

  12. Object Source Detector 3D render B&W image Grayscale image TxDOT Interconnected AV Content - X-ray Computed Tomography and Image Analysis

  13. Good agreement for interconnected AV and water-accessible AV Dimensional analysis with vacuum Comparison of Water-Accessible AV and Total AV Content Most AV in PFC are water accessible

  14. Summary and Recommendations-Volumetrics • Use dimensional analysis for determining both Gmb and • water-accessible AV content • Use calculated Gmm • The methods used for determining Gmm and Gmb affect: • OAC, mixture aggregate gradation, and fibers content • Include mixture-durability test for PFC mix design • Future work: • Explore the use of connected AV content for mix design and evaluation

  15. 3.2 Durability 16 12 Rut (mm) 8 2.4’’ 4 0 0 5000 10000 15000 Number of Cycles • Current practice: • No durability test applied Hamburg Wheel-Tracking Test (Hamburg) Wet Conditioning

  16. Zhou et al., 2003 Cracking life TTI Overlay Test (Overlay) No Conditioning (dry)

  17. 300 rev. Before (W0) After (Wf) 4.5’’ Cantabro Loss Test (Cantabro) No Conditioning (dry)

  18. Additional Cantabro Testing: wet (24 hrs @ 60C + drying), cold (3C), & aged (3 & 6 months @ 60C) Results and Discussion Comparison of Mixture Evaluation Tests

  19. Cantabro Results - Effect of Conditioning PG 76-22 mixtures

  20. Summary and Recommendations-Durability • Cantabro Loss test recommended • Cantabro test results suggest: • Mixture resistance to disintegration is affected more by aggregate than binder properties • The test can be used as a screening tool for PFC mix design, but it may not provide enough sensitivity for selecting the OAC • Cantabro Loss values showed a direct relationship with water-accessible AV content • Future work: • Evaluate relationships between field and lab. responses • Use analytical performance models to improve PFC mix design

  21. 3.3 Drainability TxDOT • Current practice - design (SGC specimens): • Ensure total AV content (min. 18%) • Measure lab permeability (min. 100 m/day) • Current practice - field • Measure field drainability: water flow value (max. 20 secs)

  22. Field drainability Lab drainability Water flow value (outflow time) Coefficient of permeability (k) TxDOT Laboratory and Field Measurement of Drainability

  23. TxDOT Results and Discussion Evaluation of Current Practice • Lack of correlation can be related to differences in: • Total AV content, • Specimen thickness, and • Internal structure of the mixture

  24. TxDOT Alternatives Evaluated • Relationship of water-accessible AV content and • lab-measured permeability, • (ii) Relationship of lab and field drainability, and • (iii) Analytical prediction of permeability (Expected value of permeability using modified Kozeny-Carman Eq.) (ii) Relationship of lab and field drainability

  25. TxDOT (iii) Expected Value of Permeability (E[k]) and Calculated Permeability (Modified Kozeny-Carman Equation) Road cores SGC specimens • Parameters for E[k]: • Average and variance of both aggregate-particle size (gradation) • andtotal AV content (X-ray CT) • Covariance of aggregate-particle size and total AV content • Empirical calibration coefficient • Aggregate, asphalt and fluid (water) parameters

  26. Summary and Recommendations-Drainability TxDOT • Current practices led to poor drainability evaluation of • field-compacted mixtures • Water-accessible AV content may be used as a surrogate of the total AV content to indirectly assess permeability • Use the Expected value (E[k]) as an estimator of permeability. Alternatively, the WFV can be used to asses field drainability • Future Work • Further assess permeability of field-compacted mixtures using laboratory-compacted mixtures

  27. 3.4 Densification Effects Objective Assess effects of densification on PFC based on: Internal structure (air voids [AV] characteristics) Macroscopic response (durability and functionality) FOR TWO COMPACTION LEVELS TxDOT • Current Construction Control • Asphalt content, gradation • Visual inspection: density, material variability, segregation • Minimum smoothness • No field density requirements for PFC

  28. TxDOT Results and Discussion Comparison of Total AV Content Field AV content reproduced at 15 gyrations of the SGC Ongoing Research! Field Vs Lab (SGC) air voids content Distribution of AV content US-59Y mixture

  29. Ongoing Research! TxDOT Compaction Curve and Stone-on-Stone Contact Stone-on-Stone Contact US-59Y-PG mixture

  30. TxDOT Effect of Densification on Durability Cantabro test Overlay test Hamburg-Wheel Tracking test

  31. Field drainability (WFV) TxDOT Effect of Densification on Drainability Laboratory permeability

  32. Summary and Recommendations-Densification TxDOT • High levels of densification (after reaching stone-on-stone contact) are required for mixture durability • These findings suggest the necessity of: • Checking stone-on-stone contact during mix design • Including a construction density control • Short-term action: • Increase efforts to establish required roller patterns • Future Work • Develop techniques (e.g., nondestructive methods) to evaluate the field density and enforce a density specification • Improve the current SGC compaction protocol • Evaluate long-term mixture performance to obtain final recommendations for field density control

  33. TxDOT Thank you! Questions?

  34. 5 Zone I Zone II 0 Zone III Zone IV -5 -2.0 0.0 2.0 Total AV Content Comparison Based on Gmm and GmbCalculations AV (vacuum Gmb, calculated Gmm) – AV (dimensional Gmb, calculated Gmm) AV (vacuum Gmb, calculated Gmm) – AV (vacuum Gmb, measured Gmm)

  35. 22 20 Total AV Content (%) 18 16 OAC 14 7.9 8.1 8.3 8.5 8.7 8.9 9.1 Asphalt Content (%) Dim Gmb-Meas. Gmm Dim Gmb-Calc. Gmm Vacuum Gmb-Meas. Gmm Vacuum Gmb-Calc. Gmm Effect of Volumetric Parameters on OAC US-281-AR lab. mixture

  36. Asphalt-rubber mixtures Results and Discussion Hamburg Results PG 76-22 mixtures

  37. Overlay Results PG 76-22 mixtures Asphalt- rubber mixtures

  38. Cantabro Results (Dry) PG 76-22 mixtures Asphalt-rubber mixtures

  39. DURABILITY Cantabro Results - Effect of Material Quality

  40. Cantabro Results - Effect of AV Content PG 76-22 & Asphalt-rubber mixtures

  41. TxDOT Internal Structure of the Mixture

  42. TxDOT Effect of Densification on Cantabro Loss US-59Y-PG mixture US-290-AR mixture

  43. TxDOT Effect of Densification on Hamburg-WheelTracking Test

  44. TxDOT Effect of Densification on Overlay Results US-59Y-PG mixture US-290-AR mixture

  45. 3.5 Stone-on-Stone Contact (SOS Contact) TxDOT • Current practice • No test applied • Assessment methodology available (NCAT, 2002) based on voids in coarse aggregate (VCA) Ongoing Research Approach VCAmix = AV in the coarse aggregate of the compacted mixture VCADRC = AV in the coarse aggregate using dry-rodded unit weight

  46. TxDOT Determination of Breaking-Sieve Size Ongoing Research Approach Mechanical modeling based on Discrete Element Model (DEM)

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