Designing Open-Graded Mixes
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
PFC Reduces splash and
spray and increases wet
weather friction
PCC PFC
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
20 Years Old!
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
PFC Mixture Design
Steps
• Selection of Materials
• Design Aggregate Structure
• Design Binder Content
• Performance Test
• Test Section
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
AASHTO T104
15 max
Fractured Faces
One face
Two faces
ASTM D5821
100 min
90 min
Maximum 15% RAP allowed
VDOT PFC Fine Aggregate
Requirements
Test Method Specification
Fine Aggregate
Angularity
AASHTO T304
Method A
40 min.
Sand
Equivalent
AASHTO T176 45 min.
VDOT PFC Binder Grade
• PG 70-28 with 70% Elastic
Recovery (ASTM D6084).
VDOT PFC Specifications
Sieve Size 9.5 mm
% Passing
12.5 mm
% Passing
19.0 mm (3/4 in) 100 100
12.5 mm (1/2 in) 100 90-100
9.5 mm (3/8 in) 85-100 55-75
4.75 mm (No. 4) 20-40 15-25
2.36 mm (No. 8) 5-10 5-10
0.075 mm (No. 200) 2-4 2-4
1% hydrated lime required
Alternative anti-stripping additive can only be used
If approved by the Engineer
VDOT Mixture Requirements
Property Test Method Requirement
AC% 5.75-7.25
Draindown % VTM-100 0.3% max.
VCA VTM-99 <VCADRC
Design Gyrations AASHTO T312 50
Air Voids, % Corelok 16 min.
Cantabro
Abrasion Loss, %
20% max.
TSR, % T283 Modified 0.80 min
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
Corelok Method
Corelok Process
Sometimes double bagging is recommended
to prevent pumctures
Overview of Cantabro Test
•Compacted specimen evaluated at 25 oC 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 oC for 5 d (R30)
Three keys to Cantabro test
1. Cheap and easy
2. Cheap and easy
3. Cheap and easy
Example Cantabro
Samples
Blend 2 PG 76 Blend 3 PG 67 Blend 5 PG 76
Draindown
6% PG 76-22, no fiber Passing result with fiber
Why Draindown
Fines content influences draindown potential
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 60oC for 24 hours
Soak at 25oC for 2 hours
Calculate the Tensile
Strength Ratio (TSR)
Minimum of 80% needed for PFC
Moisture Sensitivity AASHTO T 283
Determine the tensile strengths
of both sets of 3 specimens
TSR = Avg. wet tensile strength
Avg. dry tensile strength
Construction
• Tack
– Polymer modified emulsion with spray paver
– Trackless tack
• Minimize handwork
• Mix must be hot – care at transverse joints
• Roller on seats aggregate
Polymer Modified Tack TEST ON EMULSION METHOD Min Max
Viscosity at 77° F, SSF AASHTO T59 20 100
Sieve Test, % (Note 1) AASHTO T59 — 0.05
24 hour storage stability, % (Note 2) AASHTO T59 — 1
Residue from distillation at 400° F, %
(Note 3)
Oil portion from distillation ml of oil
per 100g emulsion
AASHTO T59 63
2
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 T301 60 —
Penetration @ 77° F, 100 g, 5 sec. dmm. AASHTO T49 60 150