1. Perpetual Pavements Concept and History Iowa Open House
October 5, 2005
In this presentation, the idea of perpetual asphalt pavements will be introduced. These pavements are designed and constructed from the bottom up to provide a structure having more than 50 years of useable life with a renewable asphalt surface. A durable, strong asphalt pavement will ensure minimal disruption of traffic and reduced maintenance costs over its life.

2. 40-75 mm SMA, OGFC or Superpave}
40-75 mm SMA, OGFC or Superpave
100 mm to
150 mm
Zone
Of High
Compression
High Modulus
Rut Resistant Material
(Varies As Needed)
Flexible Fatigue Resistant
Material mm
Max Tensile Strain
This is the concept underlying the perpetual pavement.
Traffic stresses are highest near the surface of the pavement, so materials in the upper pavement layers must be resistant to rutting.
The intermediate or binder courses should be comprised of rut-resistant material. Materials which have worked well include large-stone mixtures or others which provide a strong stone skeleton.
Fatigue resistance is important in the lowest HMA layer or base layer. It is well documented that the most costly form of distress to fix in a pavement is bottom-up fatigue cracking.
The pavement foundation serves as the ultimate support for the structure during construction and service, so it must be considered an integral part of the pavement.
Pavement Foundation

3. Value
Quality is what the customer gets out [of a product] and is willing to pay for. A product is not quality because it is hard to make and costs a lot of money This is incompetence. Customers pay only for what is of use to them and gives them value. Nothing else constitutes quality.
Peter Drucker

4. Economics
Total
Costs
Alternative
Perpetual
Pavement
Time

5. Why are Perpetual Pavements Important?
Lower Life Cycle Cost
Better Use of Resources
Low Incremental Costs for Surface Renewal
Lower User Delay Cost
Shorter Work Zone Periods
Off-Peak Period Construction

6. Design

7. Mechanistic Performance Criteria
Under ESAL
Thick HMA
(> 200 mm)
Limit Bending to < 65me
(Monismith, Von Quintus, Nunn,
Thompson)
The thickness of the HMA pavement will be determined according to the response of the pavement structure to load.
(mouse click) A standard single axle load of 18,000 lbs will be used in modeling these responses.
According to a number of researchers, the amount of bending strain in the bottom layer of HMA should be less than 65 microstrain and the amount of compressive strain at the top of the subgrade should be limited to 200 microstrain.
A design approach is needed whereby a traffic analysis shows the probability that these strain levels will be exceeded in a given situation. In this way, the concept could be applied at all traffic levels.
Base (as required)
Subgrade
Limit Vertical Compression to < 200me (Monismith, Nunn)

8. Fatigue Resistant Asphalt Base
Minimize Tensile Strain with Pavement Thickness
Thicker Asphalt Pavement = Lower Strain
Strain Below Fatigue Limit = Indefinite Life
Compressive
Strain
Indefinite
Fatigue
Life
Strain
A thick asphalt layer will dramatically reduce the tensile strain at the bottom of the HMA. The thickness should be such that the strain is lower than the fatigue limit, and the fatigue limit is the strain below which fatigue damage in the pavement does not accumulate. Using a sufficiently thick asphalt layer will effectively prevent bottom-up cracking in the pavement structure.
Fatigue Life
Tensile Strain

9. PerRoad

10. RATE OF RUTTING vs ASPHALT THICKNESS
Thickness of bituminous layer (mm)
Rate of
rutting
(mm/msa)
100
200
300
400
0.1 1 10
1000
At TRL in England, Nunn and his colleagues found that high rates of rutting were associated with thin asphalt pavement sections. They noted that those over about 200 mm or 8 inches tended to show a relatively slow rate of rutting.
TRL

11. Thickness of asphalt layers
500
TRL Design Chart
DBM
DBM50
HDM
400
300
Thickness of asphalt layers
(mm)
200
The result of the TRL work was a design chart to determine the thickness of the asphalt structure above the subbase layer. This varies according to mix type as shown here.
A thinner structure is allowed for a heavy-duty macadam mixture, designated as HDM, than for a conventional dense-graded mixture with a stiff asphalt (DBM50) or a conventional dense-graded mixture with a normal asphalt (DBM).
In any case, the minimum thickness of HMA is about 8 inches (200 mm) and the thickest HMA structure is about 16 inches (400 mm).
100
TRL 10
100
Design life (msa)

12. Perpetual Pavement versus Conventional Design
AASHTO
PerRoad

13. Construction

14. Foundation - Illinois 5 10 15 20 25 1 2 3 4 6 7 8 9 CBR5 10 15 20 25 1 2 3 4 6 7 8 9
CBR
Required Thickness Above
Subgrade, inches
No remedial procedure required
Remedial procedure
required
Remedial
This is Illinois’ requirement for foundation stiffness. If the CBR of the subgrade is below 6, then an improvement must be made by means of lime modification or a thickness of granular material.
procedure
optional

15. Mass
Rod
Reference

16. Leads to Poor Compaction!
Compaction Support
Weak Support
Leads to Poor Compaction!
Weak!!!

17. Compaction Support
Strong Support
Helps Compaction!
Strong!!!

18. 30OF Surface, 40OF Air Temperature, 15 mph wind

19. Performance

20. Time from Original Construction to First Resurfacing
Performance of Washington Interstate Flexible Pavements (based on 284 km)
12.4
230 (9.2)
31.6
Average
2 to 25
100 to 345
23 to 39
Range
Time from Original Construction to First Resurfacing
(years)
Thickness of Original AC (mm (in.))
Time Since Original Construction (years)
Statistic
The ability to obtain long lasting pavement structures from HMA is shown by the performance of asphalt interstate highways in the state of Washington.
These pavements range in age from 23 to 39 years, with an average of about 32 years since their original construction.
They have a little more than 9 inches of HMA thickness on average, although the thickest is about 14 inches.
Another interesting point is that the first resurfacing of these pre-Superpave HMA pavements occurs at about 12.5 years. With recent changes in technology, this resurfacing time should increase dramatically.

21. Ohio Study of Flexible Pavements
Examined Performance on 4 Interstate Routes
HMA Pavements - Up to 34 Years without Rehabilitation or Reconstruction
“No significant quantity of work for structural repair or to maintain drainage of the flexible pavements.”
Only small incremental increases in Present Cost for HMA pavements.
A study funded by Flexible Pavements, Inc. of Ohio surveyed the performance of four interstate pavements. This work proves the point that Perpetual Pavements have been in use for some time.
It was found that the HMA pavements provided up to 34 years of service without the need for expensive rehabilitation or reconstruction.
The report from the study states that, “No significant quantity of work was done for structural repair or to maintain drainage of the flexible pavements.”
An examination of life-cycle costs for these roads showed that HMA pavements produced only small incremental increases in present worth as overlays were added.
This underscores the principles of the Perpetual Pavement: Design: build it for the traffic, soil and climate, and the only cost thereafter should be associated with periodic overlays.

22. FHWA - Data from Long-Term Pavement Performance Study
Data from GPS-6 (FHWA-RD )
Conclusions
Most AC Overlays > 15 years before Rehab
Many AC Overlays > 20 years before Significant Distress
Thicker overlays mean less:
Fatigue Cracking
Transverse Cracking
Longitudinal Cracking
An FHWA report documenting the performance of rehabilitated asphalt pavements from the Long-Term Pavement Performance study found that most asphalt overlays last 15 years or more before further rehabilitation is needed and that many HMA overlays last beyond 20 years.
Further, it was concluded that thicker HMA overlays had less cracking type distresses than thinner overlays.
Again, the point is made that if the pavement structure remains in tact, then the surface can be periodically rehabilitated.
While the pavements in the LTPP GPS-6 study performed well, it should be remembered that these represent pre-Superpave mixtures.

23. Structure Remains Intact
Rehabilitation
Possible Distresses
Top-Down Fatigue
Thermal Cracking
Raveling
Solutions
Mill & Fill
Thin Overlay {
High Quality SMA, OGFC or Superpave mm
20+ Years
Later
Structure Remains Intact
What makes the Perpetual Pavement perpetual is that, while the surface will need periodic replacement, the bulk of the pavement structure will remain intact.
Depending on the type of surface material used and the environmental conditions present, the types of distress which may arise could include top-down fatigue cracking, thermal cracking and raveling.(Click mouse to activate animated cracks.)
Although surface layer lives may vary, current technology allows for achieving over 20 years, if so desired.
Solutions for these distresses could include milling off the old layer and replacing it with a new surface (Click to show overlay) or simply overlaying the pavement.
One advantage to this approach is that new innovations in technology can be applied to the pavement surface as they become available, possibly further extending the surface life.

24. Should break costs into
Important to consider
Initial Costs
Rehabilitation and Maintenance Costs
Reconstruction costs
Should break costs into
Agency costs
User Costs
Life Cycle Costs
Time

25. Design Comparison – Low Volume
50 year design
1 mile, 2 Lane, 12 ft lanes
Traffic: ADT (Rural Setting)
6” HMA
Perpetual
($360,000)
Conventional
($230,000)
12” Granular Base
3” HMA
6” Granular Base
Subgrade
Muench, et al., 2004

26. Rehabilitation Schedule
Conventional Design (3” HMA/6” GB)
1.75” Overlay in years 6, 15, 31 and 40
Rebuild at 25 years
Perpetual Design (6” HMA/12” GB)
1.75” overlay every 13 years
Values based on WSDOT Experience
Muench, et al., 2004

27. Considered variability of inputs User delay not significant
Cost Analysis
Used LCCA Software
Considered variability of inputs
User delay not significant
Muench, et al., 2004

28. What About User Delay Costs?

29. WZ User Cost Comparison
4-lane
40,000 AADT
LCCA Software
Delay calculations based on Highway Capacity Manual
Compare work-zone alternatives
24 hour closure
20 hour closure
11 hour closure

30. 85% of cost is waiting to move through WZ
Option 1 – 24 Hr Closure
Cost/mile/day $116,000
85% of cost is waiting to move through WZ

31. Option 2 – 20 Hr Closure
Cost/mile/day $42,000

32. Option 3 – 11 Hr Closure
No stopping!
Cost/mile/day $12,000

33. Perpetual Pavement Structure Lasts 50+ years.
Bottom-Up Design and Construction
Indefinite Fatigue Life
Renewable Pavement Surface.
High Rutting Resistance
Tailored for Specific Application
Consistent, Smooth and Safe Driving Surface.
Environmentally Friendly
Avoids Costly Reconstruction.
The Perpetual Pavement requires that the structure be designed and constructed from the bottom-up and that it have a combination of thickness and HMA characteristics which preclude fatigue cracking and durability problems.
The renewable pavement surface must be designed to resist rutting and tailored for specific applications.
In the end, the Perpetual Pavement will provide a uniform, smooth and safe driving surface, and it will avoid the huge expense associated with reconstruction.