grock 2 project assessment.pptx [last saved by...

4/12/2019

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PART 2:PROJECT ASSESSMENT

David Jones, PhDUniversity of California Pavement Research CenterDavis, California

GraniterockTech TalkApril 4, 2019

Outline

• Introduction

• Desktop study

• Preliminary site investigation

• Detailed site investigation

• Strategy selection

• Summary

Introduction

• Project investigation is all about finding out what we have, why it looks like it does, and what we are going to do about it- Essential part of a recycling project

• The information is used to identify the recycling and stabilization strategy

• Existing guidelines- Wirtgen manual

- ARRA manual and www.roadresource.org

- Caltrans and other State DOT guides

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Project Assessment Overview

• Pavement performance is related to:- Traffic- Climate- Materials- Strength of underlying layers- Drainage- Mix and structural designs- Construction procedures- Maintenance

• Project assessment includes:- Desktop study- Preliminary site investigation- Detailed investigation

• Field testing• Preliminary laboratory testing• Analysis

Identify rehab options

Desktop study

Prelim site investigation

Design

Detailed investigation.

Outline

• Introduction

• Desktop study




• Summary

Desktop Study

• Who?- Project engineer

• When?- Early in project scope

• What?- Collect all relevant data

• As-built plans• Photolog and pavement condition reports• Traffic data• Climate data• Maintenance records• Land-use plans

- Desktop study report• Project information, road information, potential problems, fatal

flaws, decision

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Outline

• Introduction

• Desktop study




• Summary

Preliminary Site Investigation• Who?

- Project engineer and maintenance superintendent• When?

- Early in project scope, rainy season• What?

- Windshield survey (walk or bike in city)• Cracking and pumping• Rutting• Previous maintenance• Height of road above subgrade / grade restrictions• Drainage efficiency• Land use adjacent to road• Causes of distress/failure• Underground utilities

- Report• Distress summary• Fatal flaws

– Structure– Drainage– Subgrade failure– Excessive deep patching– Shallow underground utilities

Outline

• Introduction

• Desktop study




• Summary

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Detailed Site Investigation

• Who?- Project engineer, district/city staff

• When?- Rainy season

• What?- Visual assessment

• Distress type and source (top-down or bottom-up)• Drainage

- Depth of distress- Pavement layer thickness- Material sampling and indicator tests- Variability

• Subgrade stiffness assessment- Analysis and report

• Life-cycle cost analysis• Environmental life-cycle assessment

Preferably walk (or cycle) !

See the Whole Scene

Outline

• Introduction

• Desktop study



- Top-down distresses

- Bottom-up distresses

- Drainage

- Roadside activity

- Testing and sampling

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Top-Down Distresses

• Aging and surface defects

Aging / Oxidation

Raveling

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Mix Defects (Paver)

Mix Defects (Binder Content)

Mix Defects (Binder Content)

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Top-Down Distresses


• Potholes

Potholes

Top-Down Distresses

• Aging and surface defects• Potholes• Rutting

- Poor compaction- Extreme temperature- Mix design/PG grade

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Surface Ruts / Densification

Temperature, Mix Design, Incorrect PG

Top-Down Distresses


• Potholes

• Rutting

• Cracking- Extent and nature

- Type and cause• Thermal, aging/oxidation

• Thermal, low temperature

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Thermal Cracks (Aging/Oxidation)

Thermal Cracks (Aging/Oxidation)

Thermal Cracks (Low Temperature)

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Outline

• Introduction

• Desktop study





- Drainage

- Roadside activity


Bottom-Up Distresses

• Rutting- Overloading- Base failure- Subgrade failure

Structural / Overloading

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Base Failure

Subgrade Failure


• Rutting

• Cracking- Extent and nature

- Type and cause• Thermal, freeze thaw

• Fatigue

• Reflection

- Pumping

- Loose blocks

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Thermal Cracks (Freeze-Thaw)

Premature Fatigue Cracking / Pumping

Fatigue Cracks

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Reflective Cracks

From underlying AC and/or CTB

Reflected Fatigue Cracks / Loose Blocks


• Rutting

• Cracking

• Previous maintenance- Routine or necessity?

- Once-off or repeated?

- Frequency?

- Depth?

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Maintenance Digouts

Maintenance Digouts

Edge Breaks / Subsidence

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Outline

• Introduction

• Desktop study





- Drainage

- Roadside activity


Drainage

Drainage

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Drainage

Drainage

Drainage

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Drainage

Outline

• Introduction

• Desktop study





- Drainage

- Roadside activity


Irrigation

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Irrigation

Irrigation

Utilities

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Outline

• Introduction

• Desktop study





- Drainage

- Roadside activity


Visual Assessment

• Locations for additional tests, cores, and sampling- Cores every 1,500 ft, plus where required for

thickness measurements and variability checks- Additional cores for mix design- Test pit locations if forensic is required- FWD testing interval for subgrade assessment

Layer Thickness Assessment

• Ground penetrating radar (GPR) if available

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• Ground penetrating radar (GPR) if available

• Core- Measure and photograph

- Record special characteristics• Rubber, stripping, debonding, fabrics, grids, etc.

- Identify where distresses start

• - Analysis- Plot results against distance

0.5m 0.5m 0.5m

0.5m 0.5m

Every 3m

Core Extraction

Core Extraction

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150

160

170

180

190

200

210

220

230

240

250

260

0 40 400

480

520

1,00

01,

360

1,40

01,

500

1,98

02,

020

2,50

02,

980

3,02

03,

460

3,50

03,

540

3,98

04,

020

4,20

04,

240

4,28

04,

320

4,50

04,

980

5,02

0

Distance (m)

Th

ickn

ess

(mm

)

Average

Digouts Digouts

Variability – Dynamic Cone Penetrometer (DCP)

• Test in core holes- Beware effect of core drill water

• Analysis- Various calculations available

• Software often supplied by vendor

- Suggest use DCP number• (Rate of penetration [mm/blow])

- Plot DCP number against distance

- Determine if low DCP values correspond to pavement distress

DCP Analysis

63

0

5

10

15

20

25

30

35

40

45

50

55

DC

P N

um

be

r (D

N)

Distance (m)

Zone A Zone B Zone A Zone B Zone A

Zone C

Good

Requires attention

Problem

150

160

170

180

190

200

210

220

230

240

250

260

0 40 400

480

520

1,00

0

1,36

0

1,40

0

1,50

0

1,98

0

2,02

0

2,50

0

2,98

0

3,02

0

3,46

0

3,50

0

3,54

0

3,98

0

4,02

0

4,20

0

4,24

0

4,28

0

4,32

0

4,50

0

4,98

0

5,02

0

Distance (m)

Th

ick

ne

ss

(mm

)

Average

Digouts Digouts

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Subgrade Stiffness (Primarily for FDR Projects)

• Why?- Evaluate subgrade

- Identify variability and weak areas

- Identify locations of test pits

• When?- Rain season

• What?- Worst lane

- Between wheel paths

- 65 ft (20m) interval (0.6m/h)

Forensic Test Pits

• Primarily for FDR if required

• Number of purposes- Pavement cross section

- Subgrade moisture conditions

- Source of material for indicator tests and mix design• Grading, Atterberg limits/sand equivalent, R-value/CBR, etc.

Outline

• Introduction

• Desktop study




• Summary

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Analysis Outline

• Visual and test pit assessment- Determine whether distresses are top-down or bottom-up- Extent of distresses- Life of repairs- Effect of road side activities- Utilities

• From the DCP and/or FWD Analysis- Determine percentage of project falling into different zones

• Prefer <10% of project requires special attention (Zone C)- Consider costs/methods for improving these weak areas

• Subgrade stabilization or drainage improvements typically required

• Layer thickness- Is there sufficient material to recycle?

• 3 to 5 inches for PDR/CIR• 6 to 12 inches for FDR

- Pre-milling on thick/variable pavements if necessary• Use RAP in surface mix

Recycling Strategy Selection Summary

• Top-down distresses in top 2 in.- Mill and overlay, HIR

• Top-down distresses in top 2 to 5 in.- PDR-FA or PDR-AE (aka CIR)


Top-down distresses in asphalt layer:

PDR (CIR) with foamed asphalt or asphalt emulsion

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• Top-down distresses in top 2 in.- HIR, mill and overlay

• Top-down distresses in top 2 to 5 in.- PDR-FA or PDR-AE (aka CIR)

• Bottom-up distresses from base, top 10 to 12 in.- FDR-NS for very low volume roads

- FDR-FA or FDR-AE for non-plastic materials with P#200 <15% (i.e.,>50% RAP + CTB or quality AB)• Asphalt + cement or lime hybrids usually best choice for balance of

strength and flexibility

- FDR-PC for materials with P#200 >15% and clay (i.e., predominantly unbound, poorer quality materials)


Bottom-up distresses in asphalt layer and base:

FDR with foamed asphalt or asphalt emulsion


Bottom-up distresses in asphalt layer with no base:

FDR with foamed asphalt, asphalt emulsion or cement (depending on PI and #200)

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• Bottom-up distresses from subgrade- Add new material and stabilize; existing base becomes a

subbase

- Pulverize surface and base, then windrow/stockpile• Stabilize subgrade with lime or cement

• FDR / CCPR of windrowed / stockpiled replaced material

- Be very careful going deeper than 12 in. in a single FDR lift


Bottom-up distresses from base and/or subgrade:

Mill, stabilize, place CCPR with foamed asphalt or asphalt emulsion


Bottom-up distresses from base and/or subgrade:

FDR with cement (not recommended because of compaction and cracking issues)

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Can this be recycled in place ??

LUMPS

0

10

20

30

40

50

60

70

80

90

100

0.1 1 10

Per

cen

tage

Pas

sin

g

Sieve Size (mm)

Required grading Recycled cracked asphalt

#200 #20 3/8 Sieve Size (in.)

AFTER IMPACT CRUSHING…

Either treat in cold central plant

and pave as a new layer

Or, replace in milled‐out cut

and treat in place with a recycler

Mill out and pass through an impact crusher (gap setting ¾ in.)

0

10

20

30

40

50

60

70

80

90

100

0.1 1 10

Per

cen

tage

Pas

sin

g

Sieve Size (mm)

TYPICAL GRADING CURVES FOR MILLED ASPHALT

Fast milling Recycled cracked HMA

Slow milling After impact crushing

#200 #20 3/8 Sieve Size (in.)


Stabilizer Selection

• Asphalt or cementitious?- Both have advantages and disadvantages

• Asphalt– Strong, flexible, but moisture sensitive with high fines

content and clay

– Higher initial cost, but generally lower life cycle cost

• Cement– Very stiff and moisture resistant, but prone to cracking

(“brittle”)

– Shrinkage cracks can be mitigated, but not prevented by microcracking

– Lower initial cost, but generally higher life cycle cost

• Generally better to keep cementitious stabilization in the unbound lower layers– Target unconfined compressive strengths at 300 psi

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High Cement Content in FDR-PC

Crack Mitigation (Microcrack) on FDR-PC

Stabilizer Selection

• Foamed asphalt or asphalt emulsion?- Both have essentially the same end result, but different

mechanism• Foam = “spot welding” of mastic to larger aggregates

• Emulsion = coating of aggregates

- Asphalt emulsion may be limited by in situ moisture content and low temperatures (night work)• In situ moisture content + emulsion = fluid content, which may

exceed optimal compaction moisture content

- Chemistry of emulsion can be affected by addition of active filler• Work with your emulsion supplier!

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Active Filler Selection

• Cement or lime as active filler?- Dependent on material chemistry

- Test during mix design to identify best option (check with emulsion supplier about effect of active filler on emulsion)

• Fly-ash and kiln dust are generally not recommended- Variable properties and quality

- Variable cementing properties

- Questionable early strength

- Fly-ash very difficult to work

- Kiln dust not always readily available where required

Outline

• Introduction

• Desktop study




• Summary

Summary

• Don’t skip the project investigation

• Cost is inconsequential in terms of project and in terms of making the wrong choice

• Level of detail will be dependent on distresses

• Make an informed recycling strategy decision using the information collected

• Sample representative materials for mix design

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Time for another break?

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