1. PPRA Fall Meeting, 2014
“Extending the Nation’s Road Maintenance Dollars”
Experience with Emulsion-Stabilized FDR on Lower Volume Roadways in Wisconsin: Design Considerations & Field Observations
Dan Swiertz
Materials Engineer & Director of Mix Design Laboratories
Bitumix Solutions, a Division of H.G. Meigs, LLC

2. Why FDR, why right now? 71% for Wisconsin
“Extending the Nation’s Road Maintenance Dollars”

3. Why FDR, why right now? “The right treatment on the right road”
Rehab/Re-const. strategy on many lower volume roadways in Wisc. is an AC overlay
With or without full or partial depth pulverization
Typical Result:
High(er) life-cycle cost
(Comparatively) Poor Long-term Performance:
Does not disrupt crack pattern (with no pulverization)
Does not fix stability issues
Maintenance: side slope (mowing operations)
Safety – edge effects: “growing the road”
Less efficient use of funds, not “performance-effective” solution

4. Cost justification for FDR
All else equal: decision to use FDR will still be made on COST
However, there are other costs to consider:
Who is producing the new mix? Doing the paving?
Virgin materials usage
Haul costs
Maintenance costs
Direct Materials Savings
Utilize increased structural support from FDR-emulsion to reduce thickness of a new layer
Capacity Insurance
To address long term uncertainty in traffic volumes
-- OR --
Take a holistic approach to life cycle cost analysis…

5. Identifying candidate pavements
Identifying candidate pavements “The right treatment on the right road”
Extensive structural distress; could be accompanied by functional distress
Adequate base stability – soft spots/drainage need to be corrected
Subgrade quality
Sufficient base depth
Patching: OK, but adds variability in materials
Wheel edge longitudinal fatigue cracking
Partial depth patching
Bottom-up fatigue cracking of thin AC layers (alligator cracking)

6. Identifying candidate pavements
FDR-asphalt is not the right (i.e. most cost-or performance-effective) choice when:
Signs of severe base in-stability (unless confined to a small, repairable area)
High-clay content [PCC and/or lime a better choice]
Very high P200 (maybe >20% (?))that can’t be corrected with added material
Drainage issues (often accompanied with base-instability)
Inadequate base depth to support construction train

7. Early field work is key to success
Whichever design method (more later) is chosen, in-place analysis required for repeated success:
FWD/GPR (structural analysis) + coring $$$
Coring/Boring, design data if available $$
Visual assessment , design data if available $
Balance costs with expectations of finished product
More Labor Intensive

8. Lab design considerations
Most widely used design method: Do Nothing!
No unified method exists:
Widely varying source properties
No “consensus” properties
Volumetric approach difficult
Understanding how FDR materials are expected to behave in the field is critical to any lab design:
Designs should address fundamental distresses
Use equipment available in most contractor labs
Reduce costs incurred to customer!
From NCHRP Synthesis 421

9. Full-Depth Reclamation: Theory of stabilization
The Asphalt Academy. Technical Guideline: Bitumen Stabilised Materials, TG 2, Second Edition. The Asphalt Academy, Pretoria, South Africa, 2009.

10. Full-Depth Reclamation: Theory of stabilization
FDR-asphalt materials are considered ‘non-continuously bound’
Increased cohesion between particles
Relatively unchanged level of internal friction (for sufficiently small asphalt contents)
Primary mode of failure: permanent deformation
Fatigue cracking not considered unless total AC > ~3-4%
Wirtgen Cold Recycling Technology, 2012

11. Full-Depth Reclamation: Theory of stabilization
Theoretical Behavior of Stabilized Materials under Loading
Increased cohesion; not necessarily as split tensile strength, although that could be a surrogate for measuring it, but as resistance to aggregate re-orientation and slippage – which manifests in permanent deformation
Limit before fatigue cracking – 3% (?)

12. Framework for ‘mix design’ procedure
Build off of SC-DOT, T-99 procedure with modification:
Focus on permanent deformation resistance:
Hypothesis: There exists a ‘optimum’ emulsion content that gives the highest permanent deformation resistance
If needed, local minimum limits can be determined empirically and/or mechanistically (M-E design procedure)
Equipment should be available and representative:
Gyratory produced samples
6” stability frame
Test “initial” and fully cured specimens

13. Framework for ‘mix design’ procedure
Obtain representative field materials
Conduct gradation, clay content, gravities/abs. as needed
Determine appropriate blend ratios based on geometry
Select aggregate moisture content representative of field conditions
Produce samples at several EC
Gyratory 600 kPa, 30 gyrations
1%, 2%, 3%, 4% have worked well
Check volumetrics (Density, VMA, air voids)
Cure samples
Curing should focus expected field conditions
Use mass loss to determine ‘full’ cured condition
Test samples for permanent deformation resistance
From 6” Diameter stability through FN
Retained split tensile strength

14. Determination of ‘optimum’ emulsion content

15. Determination of design emulsion content
Behavior ‘controlled’ by residual asphalt binder properties
Behavior ‘controlled’ by inter-particle friction
Peak stability may not max. density

16. Determination of design emulsion content Effect of blend ratios*
*Aggregate gradation kept nearly constant
Change in OEC from blend ratio ~0.5%

17. Observations from lab testing:
An ‘optimum’ EC exists for the blends tested
Depends on blend ratios: ↑ base, ↑ resid. AC
↑ base, ↓ maximum stability (preliminary)
As base % ↓, optimum becomes less apparent (behaves more like typical HMA)
OEC seems to be the same for initial and cured specimens
OEC does not occur at maximum density, but density may still control behavior at emulsion contents < OEC

18. Application to field projects
Coring operations
Soils information
Traffic levels provided
Determine/estimate OEC from lab design

19. Field Project Details Existing Structure:
Avg. 3.5” AC layer
Avg. 8” Base Agg.
Moderate Subgrade
(SSV = ~4.2)
Initial Pulverization Depth: 6”
Blend ratio: 58% AC / 42% base
5.5” 6” 8”
3.5”

20. Lab Evaluation 2% added emulsion selected as design OEC
Blend ratio maximum change was 25%  expected OEC change was 0.5%
Retained tensile strength also evaluated

21. Field order of operations
Material pre-pulverized to specified depth
Material is compacted using padfoot rollers until feet walk out
Moisture content monitored
Graded to rough shape
Stabilization train injects material to predetermined depth < initial pulverization depth
Compacted using padfoot rollers
Graded to shape and drum rollers to finish
Graphic adapted from Wirtgen Cold Recycling Technology, 2012

22. Compaction is critical
Freshly injected material

23. Field Quality Control Gradation/AC samples Moisture content
Pre-injection
Post-inject
Moisture content
Check thickness
Contamination
Use best
judgment

24. Field observations Compaction is key to performance
NMAS controls effective lift thickness
Residual AC most important
Need to understand your project emulsion:
CSS-1 vs. Engineered
Base asphalt grade

25. Field observations
‘Cure’ for at least 1 week under ‘normal’ conditions before overlay:
Emulsion sets and cures much quicker
Suggested terminal moisture content of 2.5%
Reduced thickness overlays used in 2 of 3 projects (~1” reduction based on structural design)
Performance through 2 years is encouraging with no major PD noted
Severe winter with excessive moisture

26. Concluding remarks
Agencies/owners should adopt a procedure that fits their unique climactic and traffic needs:
Several questions still exist for mix design procedures:
The complete existing cross-section does not need to be reclaimed if already overbuilt:
Mill 2-3 inches, save RAP
FDR on remaining layer
Overlay with mix incorporating RAP from millings
Do we need a structural overlay in all instances?
Experience is no, but more research is needed
“Extending the Nation’s Road Maintenance Dollars”

27. E: dswiertz@bitumixsolutions.com
Thank You
Dan Swiertz
Bitumix Solutions,
a Division of HG Meigs P: E: