2017 CESTiCC Summer Workshop, Pullman, WA
Jenny Liu and Sheng Zhao
University of Alaska Fairbanks
August 10, 2017
Field Evaluation of Precutting Technique for Maintaining AC Pavements with
Thermal Cracking
Introduction
Alaska field sections
Field survey results and analysis
Preliminary conclusions
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Outline
Introduction
Thermal cracks are perhaps the most noticeable form of crack-related damage in asphalt pavement in cold climates
Previous experience in Alaska and other northern states demonstrated that using precut technique to reduce thermal cracks is promising
ADOT&PF’s first attempt at Phillips Field Road, Fairbanks, AK remained in very good condition after over 30 years
A systematic approach has not been developed to implement application of precutting in AC pavements
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Phillips Field Road
32 years old
Single evaluation was conducted in June 2016
The pavement was resurfaced in summer 2016
Moose creek project
Constructed in 2012
Data was collected in 2013, 2014, 2016, and 2017
Healy project
Constructed in 2014
Data was collected in 2015, 2016, and 20174
Field Sections
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Moose Creek Project Design
Note: Precut depth ratio is the ratio of precut depth over the thickness of AC layer
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Healy Project Design
Pavements structure V is the strongest, most sound structure for the road followed by II, IV, III and I
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Description of Pavement Structure
Document the crack amount (the same with previous monitoring)
Label the crack severity
Measure the crack width
Document if precuts are active
Document each crack on the survey sheet and will keep it for the record
Number the point of interest (cracks, special surrounding environment, precuts, other pavement deterioration, etc.) and take photos
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Field Evaluation
Philips Field Road Observations
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Block Cracks Longitudinal Cracks
Philips Field Road Observations
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Non-active precut Active precut
Philips Field Road Observations
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Potholes
Phillips Field Road Survey Summary
Many longitudinal cracks were observed
Many block cracks
Only 7 transverse cracks were observed, including 2 low severity cracks
13 out of 23 precuts were active
Many potholes were observed when longitudinal cracks meet precuts
32 years old, but its general driving condition was found to be pretty good. All the cracks seemed not to deteriorate the pavement condition in a significant level
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General Precut Installation
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Precutting Operation, Distant View Measuring Precut Depth Measuring Precut Width
Laying out Precuts Thin Saw Used for Precuts12” Diameter x 1/8” Thick Blade
Precutting Operation
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Moose Creek Sections Overview
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Healy Sections Overview
High Severity Transverse Cracks Observed
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Low Severity Transverse Cracks Observed
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Bifurcating Transverse Cracks
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Conditions of Precuts
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Closed Partially open Very Active
“Controlled” Cracks
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Partially “Controlled” Cracks
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Cracks Adjacent to Precut but not “Controlled”
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Crack Filling Observed on One Section
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Moose Creek Project Survey Results
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0
20
40
60
80
100
120
140
Na
tura
l cr
ack
sp
aci
ng
(ft
)
Sections
Survey in 2013
Survey in 2014
Survey in 2016
Survey in 2017
Healy Project Survey Results
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0
200
400
600
800
1000
1200
Na
tura
l C
rack
Sp
aci
ng
(ft
)
Sections
Survey in 2015
Survey in 2016
Survey in 2017
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Effect of Precut Spacing
Using the 2017 survey results and holding the precut depth ratio at 3/4
0
100
200
300
400
500
600
700
800
900
1000
I II III IV V
Na
tura
l C
rack
Sp
aci
ng
(ft
)
Pavement Structure
25 ft precut spacing
35 ft precut spacing
40 ft precut spacing
Effect of Precut Depth
Using the 2017 survey results from structure I and IV sections
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0
100
200
300
400
500
600
700
800
900
1000
Structure I, 25-ft
spacing
Structure I, 40-ft
spacing
Structure IV, 25-
ft spacing
Structure IV, 35-
ft spacing
Na
tura
l C
rack
Sp
aci
ng
(ft
)
Sections
Depth ratio of 1/4
Depth ratio of 1/2
Depth ratio of 3/4
Effect of Pavement Structure
Using the 2017 survey results and holding the precut depth ratio at 3/4
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0
100
200
300
400
500
600
700
800
900
1000
25-ft precut spacing 35-ft precut spacing
Na
tura
l C
rack
Sp
aci
ng
(ft
)
Pavement structure I
Pavement structure II
Pavement structure III
Pavement structure IV
Pavement structure V
Success Rate
Developed by Minnesota researchers (Janisch and Turgeon 1996)
85% was used by Minnesota DOT’s saw and seal advisory as the level at which a project was considered successful or not
Success rate ranged from 47 to 100% for a total of 50 test sections reviewed in the Minnesota study
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Success Rate Results_Moose Creek
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0
10
20
30
40
50
60
70
80
90
100
Su
cces
s R
ate
(%
)
Test Section
Moose Creek 2013
Moose Creek 2014
Moose Creek 2016
Moose Creek 2017
Success Rate Results_Healy
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0
10
20
30
40
50
60
70
80
90
100
Su
cces
s R
ate
(%
)
Test Section
Healy 2015Healy 2016Healy 2017
Preliminary Cost Analysis
Necessary information collected from Alaska DOT&PF and local agencies, and reasonable assumptions:
2.33 $/ft for the precut installation, 3.5 $/ft for crack sealing for Moose Creek project and 3 $/ft for Healy project
Precuts are categorized as high-quality cracks that do not need to be maintained
Crack sealing will be done annually
Every new crack will be sealed when observed
A sealed crack will be re-sealed when sealant fails
The sealing maintenance will be stopped when pavement life is reached (e.g., the last sealing maintenance will be done on the 19th year after the construction of a 20-year pavement
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Preliminary Cost Analysis
Three combinations are considered in this study:
30-year pavement life and 3-year sealant life (sealant will fail every 3 years)
30-year pavement life and 5-year sealant life
20-year pavement life and 5-year sealant life
The concept of net present value (NPV) is used to calculate the cost
The discount rate i is 4% (a common number in Alaska)
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N
kni k
FutureCosttInitialCosNPV1
1
1
Calculation Example
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Selecting 30-year pavement life and 5-year sealant life
The precut installation year is year 0, the amount of cracks observed on the 1st, 2nd…year is n1, n2…for each section
The n1 cracks will be sealed on the 1st, 6th, 11th, 16th, 21st, 26th years, the n2 cracks on the 2nd, 7th, 12th, 17th, 22nd, 27th years…
Section Total Cost
Control The total cost of sealing (n1, n2…)
Precut The total cost of sealing (n1, n2…) + precut installation cost
Cost Calculation_Moose Creek
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No. Section
Maintenance cost ($/1000 ft) for 30-year pavement life and 3-year sealant
life
Maintenance cost ($/1000 ft) for 30-year pavement life and 5-year sealant
life
Maintenance cost ($/1000 ft) for 20-year pavement life and 5-year sealant
life
1 Control 26881.4 16761.2 13086.8
2 25-ft spacing & 1/4 DR 24943.5 17088.5 14234.3
3 25-ft spacing & 1/2 DR 15268.8 10995.1 9445.3
4 25-ft spacing & 3/4 DR 19232.0 13359.5 11232.3
5 40-ft spacing & 1/4 DR 21758.9 14541.5 11948.8
6 40-ft spacing & 1/2 DR 14306.3 9833.2 8248.4
7 40-ft spacing & 3/4 DR 19137.8 13095.7 10812.4
8 Precut on-crack & 1/4 DR 20606.4 13575.2 10927.5
9 Precut on-crack & 1/2 DR 19248.5 13046.1 10652.2
10 Precut on-crack & 3/4 DR 21077.9 14287.9 11634.4
Cost Calculation_Healy
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No. Section
Maintenance cost ($/1000 ft) for 30-year pavement life and 3-year sealant
life
Maintenance cost ($/1000 ft) for 30-year pavement life and 5-year sealant
life
Maintenance cost ($/1000 ft) for 20-year pavement life and 5-year sealant
life
1 Type III Control 14454.8 9241.2 7262.9
2 Type III, 25-ft spacing & 1/4 DR 9524.4 8542.8 8157.6
3 Type III, 35-ft spacing & 1/4 DR 12863.0 9857.4 8792.6
For Healy sections, data of sections using Type III pavement structure are used for cost analysis only. Other structures, II, IV, and V, are so strong that only a few cracks have been observed so far, with most sections containing 1 or 2 cracks. Cost analysis using these small numbers may cause very high variations.
Cost Effectiveness Results
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ProjectPavement Structure
Section
30-year pavement life
and 3-year sealant life
30-year pavement life
and 5-year sealant life
20-year pavement life
and 5-year sealant life
Moose
CreekI
25-ft spacing & 1/4 DR Yes No No
25-ft spacing & 1/2 DR Yes Yes Yes
25-ft spacing & 3/4 DR Yes Yes Yes
40-ft spacing & 1/4 DR Yes Yes Yes
40-ft spacing & 1/2 DR Yes Yes` Yes
40-ft spacing & 3/4 DR Yes Yes Yes
Precut on-crack & 1/4 DR Yes Yes Yes
Precut on-crack & 1/2 DR Yes Yes Yes
Precut on-crack & 3/4 DR Yes Yes Yes
Healy III25-ft spacing & 3/4 DR Yes Yes No
35-ft spacing & 3/4 DR Yes No No
If the NPV of a precut section is lower than its control section, the section is considered as “Yes” for cost-effectiveness
Preliminary Conclusions Precutting treatment appears promising to control
natural thermal cracks. Shorter precut spacing and strong pavement structure
look promising in crack control according to preliminary results. There may have an optimum precut depth that produces the best crack reduction effect.
These findings were based on preliminary results from relatively short time periods.
A preliminary cost analysis showed that precutting technique could be cost-effective on most sections. The cost benefit of precut technique may be highly improved with a few more years’ data.
Continuing evaluation and monitoring of these test sections are needed to recommend an effective design methodology and construction practice for Alaska and cold areas of other northern states. 38
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Thank you