Post on 10-Jun-2020
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
• Preliminary site investigation
• Detailed site investigation
• Strategy selection
• 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
• Preliminary site investigation
• Detailed site investigation
• Strategy selection
• 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
• Preliminary site investigation
• Detailed site investigation
• Strategy selection
• 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
• Preliminary site investigation
• Detailed site investigation
- 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
• Aging and surface defects
• 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
• Aging and surface defects
• 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
• Preliminary site investigation
• Detailed site investigation
- Top-down distresses
- Bottom-up distresses
- Drainage
- Roadside activity
- Testing and sampling
Bottom-Up Distresses
• Rutting- Overloading- Base failure- Subgrade failure
Structural / Overloading
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Base Failure
Subgrade Failure
Bottom-Up Distresses
• 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
Bottom-Up Distresses
• 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
• Preliminary site investigation
• Detailed site investigation
- Top-down distresses
- Bottom-up distresses
- Drainage
- Roadside activity
- Testing and sampling
Drainage
Drainage
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Drainage
Drainage
Drainage
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Drainage
Outline
• Introduction
• Desktop study
• Preliminary site investigation
• Detailed site investigation
- Top-down distresses
- Bottom-up distresses
- Drainage
- Roadside activity
- Testing and sampling
Irrigation
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Irrigation
Irrigation
Utilities
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Outline
• Introduction
• Desktop study
• Preliminary site investigation
• Detailed site investigation
- Top-down distresses
- Bottom-up distresses
- Drainage
- Roadside activity
- Testing and sampling
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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Layer Thickness Assessment
• 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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Layer Thickness Assessment
150
160
170
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190
200
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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
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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
• Preliminary site investigation
• Detailed site investigation
• Strategy selection
• 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)
Recycling Strategy Selection Summary
Top-down distresses in asphalt layer:
PDR (CIR) with foamed asphalt or asphalt emulsion
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Recycling Strategy Selection Summary
• 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)
Recycling Strategy Selection Summary
Bottom-up distresses in asphalt layer and base:
FDR with foamed asphalt or asphalt emulsion
Recycling Strategy Selection Summary
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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Recycling Strategy Selection Summary
• 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
Recycling Strategy Selection Summary
Bottom-up distresses from base and/or subgrade:
Mill, stabilize, place CCPR with foamed asphalt or asphalt emulsion
Recycling Strategy Selection Summary
Bottom-up distresses from base and/or subgrade:
FDR with cement (not recommended because of compaction and cracking issues)
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Recycling Strategy Selection Summary
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.)
Recycling Strategy Selection Summary
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
• Preliminary site investigation
• Detailed site investigation
• Strategy selection
• 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?