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