Transcript TRB_BST_2008 - Rocky Mountain Asphalt Conference and
Pavement Preservation and the Role of Bituminous Surface Treatments —A Washington State View
Rocky Mountain Asphalt Conference February 20, 2009 1
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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?
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WSDOT Pavements by Surface Type
PCC 11% BST 28%
Surface BST HMA PCC Total Lane Miles 5,000 11,000 2,000 18,000
HMA 61%
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Preservation Policies and Practices
Surface
Hot Mix Asphalt Bituminous Surface Treatment Portland Cement Concrete
Common Preservation
45-mm overlay Single shot (application) BST Either HMA overlay or dowel bar retrofit plus grinding
Comments
• 8-16 year intervals most common • All traffic levels • All ESAL levels • 5-10 year intervals most common • Lower traffic pavements • AADT < 4,000 • ESALs < 50,000/yr • Most over 30 years old • Limited rehabilitation to date • Most prevalent on NHS routes
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WSDOT Lane-Miles by ADT
AADT
0-2000 2000-4000 4000-6000 6000-8000 8000-10000 10000-20000 20000-40000 40000-80000 80000-160000 >=160000
BST
3,157 819 190 8 1 4 0 0 0 0
HMA
1,834 1,645 1,423 840 567 2,094 1,610 1,032 436 132
Lane-miles Flexible (BST+HMA)
4,991 2,464 1,613 848 568 2,098 1,610 1,032 436 132
All Types (BST+HMA+PCC)
4,993 (28%) 2,486 (14%) 1,631 (9%) 934 (5%) 660 (4%) 2,572 (15%) 2,029 (11%) 1,360 (8%) 640 (4%) 360 (2%) 42%
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FHWA IRI Thresholds for Interstate Highways Description
Very Good Good Fair Mediocre
Poor PSR Rating
4.0
3.5-3.9
3.1-3.4
2.6-3.0
≤2.5
IRI
1.0 m/km 1.0-1.5 m/km 1.5-1.9 m/km 1.9-2.7 m/km
>2.7 m/km NHS Ride Quality
Acceptable (0-2.7 m/km)
Less than Acceptable (>2.7 m/km)
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Existing IRI Sorted by ADT
ADT (2002)
0-2000 2000-4000 4000-6000 6000-8000 8000-10000 10000-20000 20000-40000 40000-80000 80000-160000 >=160000
Average IRI (m/km)
1.7
1.6
1.7
1.6
1.8
2.0
1.4
1.3
1.2
1.6
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WSDOT Pavement Preservation Funds
Biennium 1995-1997 1997-1999 1999-2001 2001-2003 2003-2005 2005-2007 2007-2009 Average Total Funds 1,2 258.9
305.1
259.7
248.2
221.0
206.9
241.9
248.8
Funds by Pavement Type 1,2 HMA BST PCC Other 163.2
234.1
198.8
213.2
184.0
145.0
177.1
187.9
16.4
18.1
23.7
17.7
21.7
37.8
46.5
26.0
28.7
36.0
27.2
5.3
1.6
20.1
16.6
19.4
50.6
17.0
9.9
11.9
13.8
4.0
1.7
15.6
Note 1: Includes project engineering, construction engineering, safety, taxes.
Note 2: Funds shown unadjusted for inflation.
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Percentages of Pavement Preservation Funding by Type
Biennium
1995-1997 1997-1999 1999-2001 2001-2003 2003-2005 2005-2007 2007-2009
HMA
63% 77% 77% 86% 83% 70% 73%
BST
6% 6% 9% 7% 10% 18% 19%
Other
31% 17% 14% 7% 7% 12% 8%
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Preservation Pinch
250% 200% 150% 100% 50% HMA Price per Ton in Place WSDOT Preservation Funding 0% 1990 1992 1994 1996 1998
Year
2000 2002 2004 2006 2008
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Preservation Funds by Lane-Mile per Year
Biennium 1995-1997 1997-1999 1999-2001 2001-2003 2003-2005 2005-2007 2007-2009 Averages (1995-2009) Overall Funding Per Lane Mile Per Year 1,2 7,200 8,500 7,300 6,900 6,200 5,800 6,800 7,000 Preservation Funds by Pavement Type HMA 7,600 10,900 9,200 9,900 8,500 6,700 8,200 8,700 $/Lane-Mile/Year BST 1,700 1,900 2,500 1,800 2,200 3,900 4,800 2,700 1,2 PCCP 6,300 8,000 6,000 1,200 400 4,400 3,700 4,300 Note 1: Funding shown includes project engineering, construction engineering, safety, and taxes.
Note 2: Amounts shown not adjusted for inflation.
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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
225 200 175 150 IRI PSC Rut 125 100 75 50 25 0 7 8 PG 58-22 9 5 7 8 PG 58-34 10 5 7 9 5 6 PG 64-22 Age (yrs) PG 64-28 8 5 7 5 9 6 PG 64-34 PG 70-28 PG 76-28 PG 70-34 0 2 1 5 4 3 7 6 9 8
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Rutting
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
PG 58-22 PG 58-34 PG 64-22 PG 64-28 PG 64-34 PG 70-28 PG 70-34 PG 76-28
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Ride
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HMA Overlay Life
• Pavement life is also a function of – Construction practices – Specifications – Material selection 18 16 14 12 10 8 6 1996 1998 East West All 2000 2002 2004 2006
18 $21,000 per lane-mile $240,000 per lane-mile
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Key Question
Could we save money by using BSTs on some roads that are currently surfaced with HMA?
• 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?
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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
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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.
HDM-4 Estimated Roughness Conditions
AADT less than 8,000 and annual design lane ESALs less than 40,000 4 3 BST applictaion only Open selection BSTs interspersed w ith HMA overlays triggered at 3.5 m/km IRI HMA overlay only 2 1 22 0 0 5 10 15 20 25 Year 30 35 40 45 50
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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.
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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!
Thanks for you attention
Questions?
28 Contributors include Steve Muench, UW and Linda Pierce, WSDOT