Permeable Friction Course (PFC) Mixtures are Different!

Transcription

1 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, 29

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

3 1. Introduction Dense-graded mixtures Vs Porous friction course mixtures (PFC or OGFC) as surface courses Kringos et al., 27

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

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

6 3. Experimental Design and Test Results Selected Mixtures Mixture I-35 Asphalt Type OAC (%) Aggregate 6.1 Sandstone, Limestone US-59Y 5.8 Limestone IH Sandstone US-83 PG Limestone IH Limestone US Granite, Limestone US Sandstone, Limestone US-29 Asphalt Rubber 8.3 Sandstone US Granite, Limestone Other Materials Lime (1%), Fibers (.3%) None

7 3.1 Volumetrics a. Total AV Content Total AV Content G 1 mb (%) Gmm *1 G mm : theoretical max. specific gravity of the mixture G mb : bulk specific gravity of the compacted PFC mixture Current practice: Total AV content (or corresponding density) Vacuum method or dimensional analysis for G mb Measured G mm

8 Theoretical Max. Specific Gravity, G mm Method 1-measured G mm W Measured Gmm W W pyc, w mix pyc mix, w W mix mixture at the design asphalt range (6 to 1%) or mixture at low binder content (3.5 to 4.5%) Method 2-calculated G mm G se 1 1 G mm Pb P G b b Calculated G mm 1 1 P G se b P G b b

9 Bulk Specific Gravity, G mb Method 1-vacuum G mb Vacuum W b W W W bs, w Wb CF Method 2-dimensional W Vt Gmb Dim w V t = *r 2 *h

10 Results and Discussion G mm Comparison and Variability, AR Mixtures Theoretical Maximum Specific Gravity Shift due to asphalt loss Asphalt Content (%) Average Meas. G mm Calculated G mm G mm -Ignition Sample G mm Compacted Sample Theoretical Maximum Specific Gravity Asphalt Content (%) Calculated G mm Measured G mm Standard deviation Calculated G mm : less variability and less asphalt-loss error G mb Dim: Simpler, faster, less expensive, cleaner, required equipment is readily available, and data can be directly used to analyze X-ray CT images Standard Deviation

11 b. Connected AV Content Water-Accessible AV Content Method 1-vacuum method WA AV W b W W W b bs, w W Wb _ ( W CF Wb Wbs, w CF W SV ) *1 (%) Method 2-dimensional analysis WAAV dimensional V td ( W W w V td s ) 1 (%)

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

13 Comparison of Water-Accessible AV and Total AV Content Ratio Water-Acces. AV /Total AV (%) Vacuum, PG Dimensional, PG Vacuum, AR Dimensional, AR Total Air Voids (%) Good agreement for interconnected AV and water-accessible AV Most AV in PFC are water accessible Interconnected AV, With Surface AV (%) Equality Line PMLC-PG PMLC-AR Cores-PG Cores-AR Water-Accessible AV (%) Dimensional analysis with vacuum

14 Summary and Recommendations-Volumetrics Use dimensional analysis for determining both G mb and water-accessible AV content Use calculated G mm The methods used for determining G mm and G mb 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 Current practice: No durability test applied Hamburg Wheel-Tracking Test (Hamburg) 16 Rut (mm) Number of Cycles 2.4 Wet Conditioning

16 TTI Overlay Test (Overlay) Zhou et al., 23 Load (lb) No Conditioning (dry) Cracking life Number of Cycles

17 Cantabro Loss Test (Cantabro) 3 rev. Before (W ) After (W f ) 4.5 Cantabro Loss (%) W - W o W o f *1 No Conditioning (dry)

18 Results and Discussion Comparison of Mixture Evaluation Tests Test Specimen Preparation Air Voids Variability (COV) Availability of Equipment (in Texas) Testing Time (hours) Results Variability (COV) Hamburg Saw trimming.3 Medium 5.2 to.57 Overlay Saw cutting, drying, final AV checking, and gluing.3 Low 2.22 to 1.17 Cantabro Not required.16 High.3.7 to.36 Additional Cantabro Testing: wet (24 6 C + drying), cold (3 C), & aged (3 & 6 6 C)

19 Cantabro Results - Effect of Conditioning Cantabro Loss (%) Dry Wet Low Temp. 3 Months Aged 4 6 Months Aged Asphalt Content (%) PG 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 Current practice - design (SGC specimens): Ensure total AV content (min. 18%) Measure lab permeability (min. 1 m/day) Current practice - field Measure field drainability: water flow value (max. 2 secs)

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

23 Results and Discussion Evaluation of Current Practice Permeabilty (m/day) 2 1 Best fit lines Watson et al.' relationship SGC - PG Cores - PG NCAT Minimum Total Air Voids (%) Lack of correlation can be related to differences in: (i) Total AV content, (ii) Specimen thickness, and (iii) Internal structure of the mixture

24 Alternatives Evaluated (i) 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 Core Permeability (m/day) PG Mixtures AR Mixtures R 2 =.82, PG R 2 =.75, AR NCAT Minimum Water Flow Value (s)

25 (iii) Expected Value of Permeability (E[k]) and Calculated Permeability (Modified Kozeny-Carman Equation) E[k] and Calculated Permeability (m/day) 2 1 Expected Value of Perme. Calculated Perme. Equality Line SGC specimens 1 2 Measured Permeability (m/day) E[k] and Calculated Permeability (m/day) 2 1 Expected Value of Perme. Calculated Perme. Equality line 1 2 Road cores Measured Permeability (m/day) Parameters for E[k]: Average and variance of both aggregate-particle size (gradation) and total 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 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 Current Construction Control Asphalt content, gradation Visual inspection: density, material variability, segregation Minimum smoothness No field density requirements for PFC Objective Assess effects of densification on PFC based on: Internal structure (air voids [AV] characteristics) Macroscopic response (durability and functionality) FOR TWO COMPACTION LEVELS

28 Results and Discussion Comparison of Total AV Content Total Air Voids (%) Road Cores AV Design Range I-35- PG US- 59Y- PG IH- 3- PG PMLC Specimens US- 83- PG US AR Field Vs Lab (SGC) air voids content US- 29- AR US AR Distribution of AV content US-59Y mixture Field AV content reproduced at 15 gyrations of the SGC Position (mm) Ongoing Research! Air Voids Content (%) Core, Total AV 15G Total AV 5G Total AV 5G Interc. AV

29 Compaction Curve and Stone-on-Stone Contact Change in Height (mm) US-59Y-PG-5G US-59Y-PG-15G US-29-AR-5G US-29-AR-15G Number of Gyrations, N Stone-on-Stone Contact VCAmix VCA DRC Ongoing Research! US-59Y-PG mixture VCA-Mix and -DRC (%) VCA-Mix 12G VCA-Mix 5G VCA-DRC VCA-Mix 15G Replicate Specimen

30 Effect of Densification on Durability Cantabro test Overlay test Cantabro Loss (%) Gyrations 15 Gyrations Cracking Life (Cycles) Replicate Result Average Dry Wet Low Temper. Aged 3 Months Aged 6 Months Number of Gyrations Hamburg-Wheel Tracking test Mixture US-59Y-PG SGC Gyrations Total AV Content Cycles to 12.5 mm Rut 2 Cycles (mm)

31 Effect of Densification on Drainability Water Permeability (m/day) US-29-AR-15G US-29-AR-5G US-59Y-PG-15G US-59Y-PG-5G Total Air Voids (%) Laboratory permeability Water Flow Value (s) Total AV=23.4% US-29-AR Total AV=21.7% Total AV=26.7% 3 Passes US-59Y-PG Number of Static Roller Passes Field drainability (WFV)

32 Summary and Recommendations-Densification 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 Thank you! Questions?

34 Total AV Content Comparison Based on G mm and G mb Calculations AV (vacuum G mb, calculated G mm ) AV (dimensional G mb, calculated G mm ) 5 Zone I Zone II Zone III Zone IV AV (vacuum G mb, calculated G mm ) AV (vacuum G mb, measured G mm )

35 Effect of Volumetric Parameters on OAC Total AV Content (%) OAC Asphalt Content (%) Dim G mb -Meas. G mm Vacuum G mb -Meas. G mm Dim G mb -Calc. G mm Vacuum G mb -Calc. G mm US-281-AR lab. mixture

36 Results and Discussion Hamburg Results Rut Depth at 2 Cycles (mm) Asphalt Content (%) AVERAGE I-35-PG I-35-PG COV PG mixtures COV Cycles to Failure at.49 in (12.5 mm) Asphalt Content (%) COV AVERAGE US-281-AR US-281-AR COV Asphalt-rubber mixtures

37 Overlay Results Cracking Life (Cycles) Asphalt Content (%) AVERAGE, I-35-PG COV, I-35-PG PG mixtures COV Cracking Life (Cycles) Asphalt Content (%) COV AVERAGE, US-281-AR COV, US-281-AR Asphalt- rubber mixtures

38 Cantabro Results (Dry) 4.4 Cantabro Loss (%) COV Asphalt Content (%) PG mixtures Cantabro Loss (%) COV Asphalt Content (%) Asphalt-rubber mixtures

39 Cantabro Results - Effect of Material Quality DURABILITY Cantabro Loss (%) 2 1 US-281-AR US-29-AR-15G AR I- 35-PG Limestone, 1% Lim./San., 5/5% Sandstone, 1% PG NA NA US-59Y-PG-15G

40 Cantabro Results - Effect of AV Content 45 Cantabro Loss (%) Total Air Voids (%) Cantabro Loss (%) PG & Asphalt-rubber mixtures Water Accessible Air Voids (%) Linear (Vacuum)

41 Internal Structure of the Mixture Air Voids Content (%) Position (mm) PG-P1 2-PG-C2 3-PG-P1 3-PG-C1 AV design range Average Air Voids Radius (mm) Position (mm) PG-P1 2-PG-C2 3-PG-P1 3-PG-C1 1

42 Effect of Densification on Cantabro Loss Cantabro Loss (%) Gyrations 15 Gyrations Dry Wet Low Temper. US-59Y-PG mixture Aged 3 Months Aged 6 Months Cantabro Loss (%) Gyrations 15 Gyrations Dry Wet Low Temper. Aged 3 Months Aged 6 Months US-29-AR mixture

43 Effect of Densification on Hamburg-Wheel Tracking Test Mixture US-29-AR US-59Y-PG SGC Gyrations Total AV Content Cycles to 12.5 mm Rut 2 Cycles (mm)

44 Effect of Densification on Overlay Results Cracking Life (Cycles) Number of Gyrations US-59Y-PG mixture Replicate Result Average Cracking Life (Cycles) Replicate Result Average Number of Gyrations US-29-AR mixture

45 3.5 Stone-on-Stone Contact (SOS Contact) Current practice No test applied Assessment methodology available (NCAT, 22) based on voids in coarse aggregate (VCA) Ongoing Research Approach VCA VCA mix DRC n; n 1 VCA mix = AV in the coarse aggregate of the compacted mixture VCA DRC = AV in the coarse aggregate using dry-rodded unit weight

46 Determination of Breaking-Sieve Size Ratio VCA mix /VCA DRC PG 2-PG 3-PG 4-PG 5-PG 6-PG 1-AR 3-AR No 4 sieve Slope of gradation 1% sieve Ongoing Research Approach Mechanical modeling based on Discrete Element Model (DEM)