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

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

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

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…

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)

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

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

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

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.

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

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% (?)

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

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 compaction @ 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

Determination of ‘optimum’ emulsion content

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

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

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

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

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”

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

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

Compaction is critical Freshly injected material

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

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

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

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”

E: dswiertz@bitumixsolutions.com Thank You Dan Swiertz Bitumix Solutions, a Division of HG Meigs P: 608-742-5354 E: dswiertz@bitumixsolutions.com