Field Evaluation of Precutting Technique for Maintaining

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

2

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


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Non-active precut Active precut


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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



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


life


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



Cost Calculation_Healy

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No. Section


life


life


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





Moose

CreekI

25-ft spacing & 1/4 DR Yes No No

25-ft spacing & 1/2 DR Yes Yes Yes



40-ft spacing & 1/2 DR Yes Yes` Yes


Precut on-crack & 1/4 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

Documents

Field Evaluation of Precutting Technique for Maintaining