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 3. Experimental Design and Results 4. Summary and Recommendations - Future Work TxDOT

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

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

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

3. Experimental Design and Test Results Selected Mixtures MixtureAsphalt Type OAC (%) Aggregate Other Materials I-35 PG Sandstone, Limestone Lime (1%), Fibers (0.3%) US-59Y5.8Limestone IH-306.6Sandstone US ‑ Limestone IH-206.5Limestone US-595.9Granite, Limestone US-281 Asphalt Rubber 8.1Sandstone, Limestone None US Sandstone US Granite, Limestone TxDOT

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

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

Method 2-dimensional V t =  *r 2 *h Bulk Specific Gravity, G mb Method 1-vacuum

G mm Comparison and Variability, AR Mixtures Calculated G mm : less variability and less asphalt-loss error Asphalt Content (%) Theoretical Maximum Specific Gravity Average Meas. G mm Calculated G mm G mm -Ignition SampleG mm Compacted Sample Shift due to asphalt loss Results and Discussion 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

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

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

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

Summary and Recommendations-Volumetrics 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

2.4’’ 3.2 Durability 3.2 Durability Number of Cycles Rut (mm) Wet Conditioning Hamburg Wheel-Tracking Test (Hamburg) Current practice: No durability test applied

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

Cantabro Loss Test (Cantabro) No Conditioning (dry) 300 rev. Before (W 0 ) After (W f ) 4.5’’

Test Specimen Preparation Air Voids Variability (COV) Availability of Equipment (in Texas) Testing Time (hours) Results Variability (COV) HamburgSaw trimming0.030Medium50.02 to 0.57 Overlay Saw cutting, drying, final AV checking, and gluing 0.030Low20.22 to 1.17 CantabroNot required0.016High to 0.36 Comparison of Mixture Evaluation Tests Additional Cantabro Testing: Additional Cantabro Testing: wet (24 60  C + drying), cold (3  C), & aged (3 & 6 60  C) Results and Discussion

Cantabro Results - Effect of Conditioning PG mixtures

Summary and Recommendations-Durability 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

TxDOT 3.3 Drainability 3.3 Drainability 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)

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

TxDOT Evaluation of Current Practice Lack of correlation can be related to differences in: (i) Total AV content, (ii) Specimen thickness, and (iii) Internal structure of the mixture Results and Discussion

TxDOT 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

TxDOT (iii) Expected Value of Permeability (E[k]) and Calculated Permeability (Modified Kozeny-Carman Equation) Road cores 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 SGC specimens

TxDOT Summary and Recommendations-Drainability 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

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

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

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

Effect of Densification on Durability TxDOT Hamburg-Wheel Tracking test Cantabro testOverlay test

Effect of Densification on Drainability Laboratory permeability Field drainability (WFV) 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 TxDOT Summary and Recommendations-Densification Summary and Recommendations-Densification 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

Thank you! Questions? TxDOT

Total AV Content Comparison Based on G mm and G mb Calculations AV (vacuum G mb, calculated G mm ) – AV (vacuum G mb, measured G mm ) AV (vacuum G mb, calculated G mm ) – AV (dimensional G mb, calculated G mm )

Effect of Volumetric Parameters on OAC US-281-AR lab. mixture Dim G mb -Meas. G mm Dim G mb -Calc. G mm Vacuum G mb -Meas. G mm Vacuum G mb -Calc. G mm

Hamburg Results PG mixtures Asphalt-rubber mixtures Results and Discussion

Overlay Results PG mixtures Asphalt- rubber mixtures

Cantabro Results (Dry) PG mixtures Asphalt-rubber mixtures

Cantabro Results - Effect of Material Quality DURABILITY

Cantabro Results - Effect of AV Content PG & Asphalt-rubber mixtures

TxDOT Internal Structure of the Mixture

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

Effect of Densification on Hamburg-Wheel Tracking Test TxDOT

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

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

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