FDR Project Selection and Upfront Testing

Tom Scullion TTI

FULL DEPTH RECLAMATION WITH ASPHALT BINDERS

STATE OF THE ART

Lubbock Jan 2019

Overview of Presentation

1. Why Asphalt Treatment

2. Challenges/Opportunities for FDR in Texas1. For TxDOT and Counties

3. Critical steps in FDR Design process

4. Use of NDT in upfront testing

5. Case study on US 84 Lubbock

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Comparative Costs of FDR materials and TreatmentTreatment TxDOT Project Lettings from May 2014 to November 2018

TREATMENT EMULSION FOAMED ASPHALT CEMENT

Districts

AmarilloBeaumont

OdessaSan Angelo

AtlantaLaredo

LubbockSan Antonio

Waco

Districts that have used emulsion & foamed asphalt.

# Projects 15 5 82

$/TON (Material) $507.25 $498.14 $152.25

$/SY (Treatment) $3.99 $4.14 $2.36

Total $/SY $12.23 $9.93 $4.07

Assumptions: Treatment Depth of 8 inches Unit Weight of 125 LBS./CF

238 Gallons of Emulsion per Ton

Total $/SY for Emulsion & Foamed Asphalt include 1% cement. Cement Treatment at 3%

Why Asphalt Treatment?

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• Curing time is less.

• Traffic can be returned onto lane sooner minimizing lane closures.

• Not prone to shrinkage cracking.

• Less susceptible to fatigue damage under heavy loads.

• Flexible to bridge softer and expansive soils.

• Better resistance to moisture prior to sealing.

Texas…

• Opportunities No shortage of candidates

• Inadequate structure for loads

• Inadequate width

Challenges

• Variable pavement structure

• Construction on top of expansive clays

• Often poor existing base materials

• Early opening requirements in Energy Sector

• Need to accelerate Lab designs

• Need updated Specs and Design recommendations

TxDOT Challenges and Opportunities for FDR

Challenges for Counties

Working with Williamson CountyJeff Ivey Point of Contact

2 locations samples 8 inches deep

Dried, Sieve Analysis, PI -determines Job Mix options

Critical Steps in TxDOT’s FDR Process1. Assemble Background information

Coring logs

Maintenance

Typical section

2. Non-destructive testing

Ground Penetrating Radar (GPR)

Falling Weight Deflectometer (FWD)

Determine thickness & strength variability

Determine sampling locations

3. Verify Pavement Structure & Sampling

Auger or milling machine for sampling.

Drill logs for project

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4. Laboratory Mixture Design

Plasticity Index

Moisture-Density Curve

Binder tests (foaming)

Asphalt %, additive %, add rock % and foaming water %

5. Pavement Thickness Design

6. Construction Quality Control

Depth of pulverization

Gradation

Moisture content

Emulsion content

Foaming asphalt properties

7. Construction Quality Assurance – Density

8. Performance Evaluation – FWD and Visual

E. Preparation of the Base Specimens Stabilized with the Emulsion-Cement Mix - CONTINUED

–

10. Mix for no more than 60 ± 10 seconds.

11. Place the loose mixture into a bowl.

12. Move the blended specimens into an oven and

cure at 60°C (140°F) for 30 minutes. Do not mix

during curing.

–

13. Compact the cured mixtures according to (B).

14. Place the compacted specimens on the porous

stones.

Day 3

Day 4

15. Move the specimens into a climate chamber set

at 60°C (140°F).

16. Cure the specimens in the chamber for 48 hours

(2 days).

17. Remove the specimens from the hot chamber

and cool them at 25°C (77°F) for 24 hours (1 day),

but not more than 48 hours (2 days).

Upfront Site Investigation

PI Soil Maps

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Step 2 NDT Air-Coupled GPR (use visual + GPR to select sampling locations)

• Integrated Video and FWD

• Data collected at highway speed (60 mph)

• Effective depth of penetration 20 ins

• TxDOT has 5 available units

• Measures layer thickness and locate subsurface defects and section breaks

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Bottom HMA

Bottom base

FM 1996 Waco

Step 2 in the FDR ProcessFalling Weight Deflectometer

(FWD)

Subgrade Modulus determination

Step 3 in the FDR Process

Sampling Equipment

• Use GPR/visual information to determine sampling locations.

GradallMilling AttachmentAuger

Critical Steps in the FDR ProcessCoring Log

.

CENTER/BETWEEN WHEELPATHS OUTSIDE WHEELPATHSEVERE RUTTING, ALLIGATOR & LONGITUDINAL CRACKING

Why Upfront TestingTxDOT’s 1st foamed asphalt project (2000) < 1 year old

Recycled 10 inches deep - Problem: locally only 7 inches of pavement over black clay

374+2439

382 +2439

383+4488

Section SB 1

SB 2

SB 3

SB4

NB 1

NB 2

Is SB 2/3 FDR candidates?

383+ 5254

Corridor Study on US 84

SB 2 Problem Section7.7 miles section

2 Inches HMA surfacing6 inches Type B or ASB11 – 12 inches “reworked base”Subgrade (sand to clay with sulfates)

50 full depth patches SB OL Each patch 12 to 14 inches deep Multiple full depth patches inside lane

Condition• Lots of maintenance on-going• 2 inch mill/fill just completed by

TxDOT forces• Localized failures still exist

Start SB 2

End SB 2

patch Patch 12 – 14”BottomHMA 8-9”

GPR dataExamples of full depth patches

surface

Current failures - sample recovery

Typical failure

Recent 2” Mill/Fill

Sampling Base and Surface

South Bound Drill LogsSite HMA Base (PI) Subgrade (PI) Sulfates

(ppm)Comments

1 7.5” 12” Red Clay Top 2 inch Stripped over crack

1A 7.5” 8” (9) Red Clay (39) 480 Top 2 inch Stripped over crack

2 7.0” 12” (25) Grey Clay (33) 950 Poor base (High PI)

3 8.5” 11” Silty Sand Poor base – FDR Sampling location

3A 8.0” 12” (15) Silty Sand (15) 1310

4 3” 17” (9) Red Clay (21) 27000 Very Thin HMA cracked

Low QualityReworked Base

Cause of Problem

• Water entering low quality base material thru cracks in the HMA layer

• 8 inches of HMA reasonable quality

• “Reworked Base” PI ranges from 15 to 25

• FDR options to address problem layer and structural needs– FDR on base materials

– CIR on salvaged HMA

Lime Treatment of Existing base3% lime works fine

How good is the US 84 RAP(Active/Inactive Binder)

US 84 judged to be excellent RAP attains passing wet strength with no treatmentLocation sampled had a new 2 inch mill/fill

IDT on 100% RAP samplesEverything except Hamburg looks good SS 3254

Because of success in Amarillo recommend 1.5% lime plus either emulsion or foam

Proposed FPS 21 Pavement Design

Conclusions

• Upfront testing is important to

– Select sampling locations

– Hopefully avoid surprises in construction

– Part of the structural evaluation to determine if FDR or CIR is an alternative for this highway

– To determine what thickness of surfacing is required to handle traffic loads