Pavement Preservation and the Role of Bituminous Surface Treatments—A Washington State View

Rocky Mountain Asphalt Conference February 20, 2009

1

The Situation

• WSDOT policy, in essence, mandated use of BSTs for routes with an ADT < 2,000.

• Pavement preservation funding level (real dollars) is down. – Pavement preservation funding is a WSDOT

account used to pay for contract HMA and BST projects.

• Questions– What is a reasonable ADT upper limit for

application of BSTs?– What kinds of pavement performance can we

expect if more BSTs are done and fewer HMA overlays?

2

3

WSDOT Pavements by Surface Type

BST28%

PCC11%

HMA61%

Surface Lane Miles

BST 5,000

HMA 11,000

PCC 2,000

Total 18,000

4

Preservation Policies and Practices

Surface Common Preservation

Comments

Hot Mix Asphalt 45-mm overlay • 8-16 year intervals most common• All traffic levels• All ESAL levels

Bituminous Surface Treatment

Single shot (application) BST

• 5-10 year intervals most common• Lower traffic pavements• AADT < 4,000• ESALs < 50,000/yr

Portland Cement Concrete

Either HMA overlay or dowel bar retrofit plus grinding

• Most over 30 years old• Limited rehabilitation to date• Most prevalent on NHS routes

WSDOT Lane-Miles by ADT

AADT

Lane-miles

BST HMA

Flexible(BST+HMA

)

All Types(BST+HMA+PCC

)

0-2000 3,157 1,834 4,9914,993

(28%)

2000-4000 819 1,645 2,4642,486

(14%)

4000-6000 190 1,423 1,6131,631

(9%)

6000-8000 8 840 848934

(5%)

8000-10000 1 567 568660

(4%)

10000-20000 4 2,094 2,0982,572

(15%)

20000-40000 0 1,610 1,6102,029

(11%)

40000-80000 0 1,032 1,0321,360

(8%)

80000-160000 0 436 436640

(4%)

>=160000 0 132 132360

(2%)

5

42%

FHWA IRI Thresholds for Interstate Highways

Description PSR Rating

IRI NHS Ride Quality

Very Good 4.0 1.0 m/km

Acceptable

(0-2.7 m/km)Good 3.5-3.9 1.0-1.5 m/km

Fair 3.1-3.4 1.5-1.9 m/km

Mediocre 2.6-3.0 1.9-2.7 m/km

Poor ≤2.5 >2.7 m/km Less than Acceptable

(>2.7 m/km)

6

Existing IRI Sorted by ADT

ADT (2002) Average IRI (m/km)

0-2000 1.7

2000-4000 1.6

4000-6000 1.7

6000-8000 1.6

8000-10000 1.8

10000-20000 2.0

20000-40000 1.4

40000-80000 1.3

80000-160000 1.2

>=160000 1.6

7

8

WSDOTPavement Preservation Funds

BienniumTotal Funds1,2

Funds by Pavement Type1,2

HMA BST PCC Other

1995-1997 258.9 163.2 16.4 28.7 50.6

1997-1999 305.1 234.1 18.1 36.0 17.0

1999-2001 259.7 198.8 23.7 27.2 9.9

2001-2003 248.2 213.2 17.7 5.3 11.9

2003-2005 221.0 184.0 21.7 1.6 13.8

2005-2007 206.9 145.0 37.8 20.1 4.0

2007-2009 241.9 177.1 46.5 16.6 1.7

Average 248.8 187.9 26.0 19.4 15.6Note 1: Includes project engineering, construction engineering, safety, taxes.Note 2: Funds shown unadjusted for inflation.

Percentages of Pavement Preservation Funding by Type

Biennium HMA BST Other

1995-1997 63% 6% 31%

1997-1999 77% 6% 17%

1999-2001 77% 9% 14%

2001-2003 86% 7% 7%

2003-2005 83% 10% 7%

2005-2007 70% 18% 12%

2007-2009 73% 19% 8%

9

10

Preservation Pinch

0%

50%

100%

150%

200%

250%

1990 1992 1994 1996 1998 2000 2002 2004 2006 2008

Year

Pe

rce

nt

Dif

fere

nc

e f

rom

19

95

Va

lue

HMA Price per Ton in Place

WSDOT Preservation Funding

1995

Bas

elin

e =

100

%

Preservation Funds by Lane-Mile per Year

11

Biennium Overall Funding Per

Lane Mile Per Year1,2

Preservation Funds by Pavement Type

$/Lane-Mile/Year1,2

HMA BST PCCP

1995-1997 7,200 7,600 1,700 6,3001997-1999 8,500 10,900 1,900 8,0001999-2001 7,300 9,200 2,500 6,0002001-2003 6,900 9,900 1,800 1,2002003-2005 6,200 8,500 2,200 4002005-2007 5,800 6,700 3,900 4,4002007-2009 6,800 8,200 4,800 3,700Averages

(1995-2009)

7,000 8,700 2,700 4,300Note 1: Funding shown includes project engineering, construction engineering, safety, and taxes.Note 2: Amounts shown not adjusted for inflation.

Initial Bottom Line

• Not enough funding to fully preserve the route system.

• Increasing use of BSTs in lieu of 45mm thick HMA overlays—however overlays are still and will continue to be the preservation treatment of choice.

• How did we examine the efficacy of increased BST use?

• First, let’s quickly look at HMA performance.

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Quick look at HMA Overlay Performance

• Performance for more recent (post Superpave) projects– Rutting– IRI– Life by western and eastern Washington

• Projects placed between 1996 and 2001– Evaluated with 2006 pavement condition

survey– Pavement age: 5 to 10 years– ½ inch HMA only– 26 projects

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Average Performance

0

1

2

3

4

5

6

7

8

9

0

25

50

75

100

125

150

175

200

225

7 8 9 5 7 8 10 5 7 9 5 6 8 5 7 5 9 6

Ru

t (m

m)

IRI (

in/m

i) o

r P

SC

Age (yrs)

IRI

PSC

Rut

PG 58-22 PG 58-34 PG 64-22 PG 64-28 PG 64-34

PG 70-28

PG 70-34

PG 76-28

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Rutting

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

PG 58-22 PG 58-34 PG 64-22 PG 64-28 PG 64-34 PG 70-28 PG 70-34 PG 76-28

Rut

(m

m)

15

Ride

16

17

HMA Overlay Life

• Pavement life is also a function of– Construction

practices– Specifications– Material

selection

6

8

10

12

14

16

18

1996 1998 2000 2002 2004 2006

Aver

age

Ove

rlay

Life

(yea

rs)

East West All

18

$240,000 per lane-mile$21,000 per lane-mile

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Key Question

• What is the effect on the WSDOT preservation budget?• What is the effect on long-term network performance?• What is the effect on the traveling public?

• Further– What is a reasonable upper level of AADT, at which BST

resurfacings can be used? – What is a reasonable upper level of annual ESALs at which

BST resurfacings can be used? – What combination of BST resurfacings and HMA overlays

produce a cost effective rehabilitation strategy?

Could we save money by using BSTs on some roads that are currently surfaced with

HMA?

20

HDM-4 (v2.03)The Highway Development and Management System software

• Integrates multiple models in a unified analysis– Economic– Material– Structural– Condition

• UW and WSDOT has experience with HMD-4

21

HDM-4 Modeling Observations

• Model may be biased towards existing trends• The treatment strategy selected is highly

dependent on the initial roughness• The BST/HMA combination strategy is often

selected regardless– Not able to fine-tune the BST effects enough

• The HDM-4 model schedules a large number of treatments in the first year

• HDM-4 is difficult to master• HDM-4 software support is almost non-existent.

22

HDM-4 Estimated Roughness Conditions

0

1

2

3

4

0 5 10 15 20 25 30 35 40 45

Year

IRI (

m/k

m))

BST applictaion only

Open selection

HMA overlay only

50

BSTs interspersed w ith HMA overlays triggered at 3.5 m/km IRI

AADT less than 8,000 and annual design lane ESALs less than 40,000

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HDM-4 Results

• The NPV of all strategies are the same– Increasing the use of BSTs appears to be economically

feasible

• Agency expense and user costs increase over time for all strategies except the HMA overlay only option

• Reduced agency expenses will result in rougher pavements and higher user costs

• Higher BST use shifts cost from the agency to the user unless…

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HDM-4 Conclusions

• HDM-4 is of limited but some use.• Routes with AADT > 2,000 are viable for BSTs. • Considering more BSTs is not a mistake.• The cost of maintaining a road network is

largely a zero-sum game.

Overall Assessment (1)

• Analyses via HDM-4 showed that more lane-miles of BST OK from a NPV view. ADT criterion increases from 2,000 to 4,000-5,000.– WSDOT Pavement Policy has been changed to reflect this.– And…there physically is no ADT limit for BSTs.

• More BSTs will likely increase the IRI on the route system but by a limited amount (cycles of BST/HMA overlays, level-up quantities, etc, limit IRI increases).

• BSTs will rarely be used through towns and cities or at major intersections.

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Overall Assessment (2)

• Performance in Washington State – BSTs apparently exceed typical national stats.– HMA at or above national stats. Differences between

western and eastern Washington need to be reduced.

• Does WSDOT need more pavement preservation funds?– Of course—but how much?– Likely something close to $10,000/lane-mile/year.

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Overall Assessment (3)

• Is WSDOT likely to get that much pavement preservation funding anytime soon—NO.– So what can be done?– Tweak the mix of BST and HMA overlays (in progress).– Maximize quality of both hence performance life.– Monitor carefully via PMS.– Don’t do anymore HDM-4 analyses!

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Thanks for you attention

Contributors include Steve Muench, UW and Linda Pierce, WSDOT

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Questions?