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NCHRP Project 14-38: Guide for Timing of Asphalt-Surfaced Pavement Preservation

Gonzalo R. Rada, Ph.D., P.E.

AASHTO MaC Meeting – Charlotte, NCJuly 24, 2018

Presentation Outline

1. Project background2. Formulation of timing framework3. Development of timing framework4. Summary & conclusions

2

Project Background

Pavement Preservation & Performance

4

Pavement Age

xx Threshold Condition

Preservation TimingPreservation timing is defined as point in time when benefits and costs are optimized• Majority of approaches based on Cost-Benefit

analysis – definitions of benefit and cost vary ► Require estimation of pavement performance and

expected costs

• Timing is affected by condition and non-condition factors► Factors that affect pavement

performance affect timing

5

Cos

t / B

enef

itTime

Project Objectives

To develop guide for identifying timing for preservation of asphalt-surfaced pavements considering:

► Condition factors► Pavement condition at time of treatment► IRI, cracking, rutting, etc.

► Non-condition factors► Treatment type► Pavement structure► Subgrade soil► Traffic► Climate

6

Formulation of Timing Framework

Literature Review, Survey & Interviews

• Objective:► To gather relevant information relating to

timing of pavement preservation treatments► Timing of treatments► Definition of costs and benefits► Pavement performance after treatment

• Findings:► Preservation timing problem lends itself to

CBA► Agency pavement management goal is

providing acceptable LOS for lowest cost► Leverages existing agency practices such as

life cycle cost analysis

8

Defining Costs

► Approaches:► Net present value ► Equivalent uniform annual costs

► Components:► Agency costs – e.g., treatment and traffic control costs► User costs – e.g., delays and safety costs associated with

crashes► Life cycle cost analysis approaches

Timing framework needs to accommodate multiple cost approaches and components

0

20

40

60

80

100

0 10 20 30 40

Pave

men

t Con

ditio

n

Time

Condition Threshold

Life Extension

Change in Performance

Defining Benefits

► Approaches:► Service life extension► Change in performance

► No preference cited in literature to either approach, but…

► Important advantages to “change in performance” approach

Recommended Timing Framework

► Performance and benefit models

► Cost models

► Optimization function

► Uncertainties

DefineIndicators and cutoff valuesPerformance curves and cost functionUncertainties on or of each inputEffect of preservation on performance & costs

For time t = t + 1, predict pavement condition

Calculate distribution of benefits (i.e., the range of possible benefits

accounting for uncertainties)

Calculate distribution of costs (i.e., the range of possible costs

accounting for uncertainties)

Calculate objective function using Monte Carlo simulation

Store expected value, 5th, and 95th

percentile values

Cutoff values reached?

Output: Preservation Timing

Time t = 0

YesNo

Development of Timing Framework

Pavement Data

Agency No. of Years of Condition Data

Thin AC OL

Chip Seal Micro-surfacing

Slurry Seal

MD-SHA 15 VDOT 8 KSDOT 30+ (entire database) ITD 15 UTDOT 3 TXDOT 10 OHDOT 30+ (entire database) TNDOT 16 MEDOT 16 LADOTD 15 LTPP 15

indicates data received Blank cell indicates no data were provided

Other Data

• Developed climate and subgrade resilient modulus databases► Climate data for every county from NASA’s Modern-Era

Retrospective Analysis for Research Application (MERRA) Climate database

► Subgrade soil from Natural Resources Conservation Service (NRCS) maps and further development in NCHRP Project 9-23A

120 ° W

110 ° W 100

° W 90

° W 80

° W 70

° W

30 ° N

40 ° N

50 ° N

30

40

50

60

70

80

Tem

pera

ture

in D

egre

es F

ahre

nhei

t

120 ° W

110 ° W 100

° W 90

° W 80

° W 70

° W

30 ° N

40 ° N

50 ° N

5

10

15

20

25

30

35

Mod

ulus

(tho

usan

ds o

f Pou

nds

per S

quar

e In

ch)

Pavement Performance Models

► Example models developed using State DOT and LTPP data plus default databases

► Models developed for more frequently used treatments and measures (based on NCHRP 14-33)

IRI Rutting Transverse Cracking

Fatigue Cracking

NWPLong.

CrackingThin Overlay

Chip Seal

Microsurfacing

Slurry Seal

Immediate Change in Condition

• Trends generally consistent across DOTs

0 0.1 0.2 0.3 0.4 0.5 0.6

Rutting before Overlay (inches)

-0.2

0

0.2

0.4

0.6

Rut

ing

befo

re m

inus

Rut

ting

Aft

er O

verl

ay (

inch

)

LTPP DataAgency 1 DataAgency 2 DataLine of Maximum ImprovementRut Depth After = 0.1 Inch

Change in Performance

► Chip seals do not have immediate effect on IRI, but… they do affect IRI growth

IRI growth rate = f(….)

• Mean annual freeze thaw cycles

• Mean annual air temperature

• IRI before treatment• Subgrade modulus• Mean annual

precipitation• Average annual daily

trafficMeasured Values (inches/mile/year)Pr

edic

ted

Valu

es (f

inch

es//m

ile/y

ear)

-5 0 5 10 15 20

-5

0

5

10

15

20

Adjusted r2 = 0.32

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8Correlation Between Factor and Predicted Value

Mean Annual Number of Freeze Thaw Cycles

Preservation Indicator

Subgrade Resilient Modulus

IRI Before Chip SealMean Annual Air Temperature

Mean Annual Precipitation

AADT

Benefit Definition

► Approaches:► Service life extension► Benefit area = Area A / (Area A + Area B)

Time (Years)

Perf

orm

ance

M

easu

re V

alue Control Curve

Treatment Curve Case 1

Treatment Curve Case 2

Area B

Service life extensionThreshold condition

Cost Models

► Cost data provided not consistent► Contract cost versus expected treatment cost versus

expected preservation cost (i.e., preservation cost independent of treatment type)

► Attempted to assess variation in cost with pavement condition ► Kansas data show increased cost with worsening condition

for thin overlays

Flexible approach chosen to accommodate costs in timing framework

Optimizing Costs and Benefits

Approaches – minimizing:1. Cost / benefit ratio2. Distance “d” from “hypothetical” optimal solution

Most Benefit

Least Benefit

Lowest Cost

Highest Cost

d

Distance approach recommended because CB can be adjusted independently and their contributions weighted separately

Uncertainties

► Performance models – computed during model development effort

► Cost models – estimates to be developed based on information available to agency

IRI Before Overlay (inches/mile)0 50 100 150 200 250

Impr

ovem

ent i

n IR

I (in

ches

/mile

)

-100

-50

0

50

100

150

Improvement = 0.63*IRI B e f o r e - 31

RMSE = 17

DataBest Fit Robust Regression

Immediate Change in IRI

Summary & Conclusions

Timing Framework

• Example performance models that explain effects of preservation were developed for more frequently used treatments and measures

• Benefit was defined as area encompassed by treated and untreated curves

• Flexible approach to costs was selected to accommodate multiple cost approaches and components

• Distance function recommended for optimizing costs and benefits

• Uncertainties can be estimated for performance models, but qualitative approach required for costs

Implementation Guide

Year0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Obj

ectiv

e Fu

nctio

n V

alue

0.5

1

1.5

2

2.5

3

50 t h Percentile

5 t h Percentile

95 t h Percentile

Select Performance MeasuresActivity 1

Establish Performance ModelsActivity 2

Establish Cost ModelsActivity 4

Select Preservation TimingActivity 5

Estimate Preservation BenefitsActivity 3

Process

Output

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