Designing Open-Graded Mixes

Transcription

1 Designing Open-Graded Mixes

2 Open Graded Mixes Designed to allow water to flow through the mix (rapidly) Porous Friction Course (PFC) or open-graded friction course Porous European Mix - coarser PFC used by Georgia DOT Porous Asphalt Mixture porous mix used for constructing porous pavements for storm water management Open-graded drainage layer used under pavement

3 PFC Reduces splash and spray and increases wet weather friction PCC PFC

4 What are Porous Pavements? Open-Graded HMA ~ 2 ½ ½ Agg. (#57) ~ 1 2 Thick Clean Uniformly Graded 2-3 Crushed Agg. (#2) 40% Voids Non-Woven Geotextile Uncompacted Subgrade

5 20 Years Old!

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7 Conclusions Porous pavements offer good alternative to conventional stormwater mitigation Site Conditions must be right Need to protect pavement from contamination during and after construction Properly designed and constructed will last more than 20 years

8 PFC Mixture Design Steps Selection of Materials Design Aggregate Structure Design Binder Content Performance Test Test Section

9 VDOT PFC Coarse Aggregate Requirements Test Method VDOT 248 L.A. Abrasion AASHTO T96 40 max Flat & Elongated,% 3 to 1 5 to 1 ASTM D4791 (VTM-121) +4 material 25 max 5 max Absorption, % AASHTO T85 2 max Soundness, % Magnesium Sulfate Fractured Faces One face Two faces AASHTO T104 ASTM D max 100 min 90 min Maximum 15% RAP allowed

10 VDOT PFC Fine Aggregate Requirements Test Method Specification Fine Aggregate Angularity Sand Equivalent AASHTO T304 Method A AASHTO T min. 45 min.

11 VDOT PFC Binder Grade PG with 70% Elastic Recovery (ASTM D6084).

12 VDOT PFC Specifications Sieve Size 9.5 mm % Passing 12.5 mm % Passing 19.0 mm (3/4 in) mm (1/2 in) mm (3/8 in) mm (No. 4) mm (No. 8) mm (No. 200) % hydrated lime required Alternative anti-stripping additive can only be used If approved by the Engineer

13 VDOT Mixture Requirements Property Test Method Requirement AC% Draindown % VTM % max. VCA VTM-99 <VCA DRC Design Gyrations AASHTO T Air Voids, % Corelok 16 min. Cantabro Abrasion Loss, % 20% max. TSR, % T283 Modified 0.80 min

14 Options for Determining Air Voids of Open Graded AASHTO T166 does not work. Water drains out of sample to quickly to obtain accurate SSD weight. Dimensional analysis Corelok analysis

15 Corelok Method

16 Corelok Process Sometimes double bagging is recommended to prevent pumctures

17 Overview of Cantabro Test Compacted specimen evaluated at 25 o C in an LA Abrasion drum for 300 revolutions without steel spheres Mass Loss (ML) = % mass change with respect to original mass Some type of conditioning can be performed prior to testing (approaches vary) 85 o C for 5 d (R30) Three keys to Cantabro test 1. Cheap and easy 2. Cheap and easy 3. Cheap and easy

18 Example Cantabro Samples Blend 2 PG 76 Blend 3 PG 67 Blend 5 PG 76

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22 Draindown 6% PG 76-22, no fiber Passing result with fiber

23 Why Draindown

24 Fines content influences draindown potential

25 Moisture Sensitivity AASHTO T 283 Measured on proposed aggregate blend and asphalt content VDOT specifies samples compacted to 50 gyrations 3 Conditioned Specimens 3 Dry Specimens Vacuum saturate specimens at 26 mm Mercury for 10 min. Freeze Cycle for 16 hours Soak at 60 o C for 24 hours Soak at 25 o C for 2 hours

26 Moisture Sensitivity AASHTO T 283 Determine the tensile strengths of both sets of 3 specimens Calculate the Tensile Strength Ratio (TSR) TSR = Avg. wet tensile strength Avg. dry tensile strength Minimum of 80% needed for PFC

27 Construction Tack Polymer modified emulsion with spray paver Trackless tack Minimize handwork Mix must be hot care at transverse joints Roller on seats aggregate

28 Polymer Modified Tack TEST ON EMULSION METHOD Min Max Viscosity at 77 F, SSF AASHTO T Sieve Test, % (Note 1) AASHTO T hour storage stability, % (Note 2) AASHTO T59 1 Residue from distillation at 400 F, % AASHTO T59 63 (Note 3) Oil portion from distillation ml of oil 2 per 100g emulsion Demulsibility, % 35 ml 0.02 N CaCl2 or 35 ml 0.8% dioctyl sodium sulfosuccinate AASHTO T59 60 Test on Residue From Distillation Min Max Elastic Recovery, % (Note 4) AASHTO T F, 100 g, 5 sec. dmm. AASHTO T

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