Tensar Webinar - Understanding Pavement Failures July 2024.pdf

Causas de la Fisuras en las Mezclas Asfalticas en Caliente

1. Tommy James, P.E.
Technology Development Manager –Pavements
Tensar
Understanding Pavement
Failures

2. Today’s Webinar and Tensar/Geopier’sEducation Programs
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3. Meet the Presenter
Tommy James, PE
Technology Development Manager - Pavements, Tensar

4. Tommy James, P.E.
Technology Development Manager – Pavements
Tensar
Understanding Pavement
Failures

5. Question for Today
When an asphalt pavement fails to achieve its expected design life:
How often is the failure a result of asphalt quality?
Is it the asphalt’s fault?

6. Agenda
•How do we define pavement failure?
•Causes of Pavement Failure
•Failure Prevention and Performance Improvement

7. Pavement Design Life, Condition, and Failure
All pavements wear out over time
The Design Life of a pavement is defined as the expected time period from original
construction to a terminal condition, when the pavement must be reconstructed
Pavement condition is measured based on several factors, which can include roughness,
surface distress, skid resistance, and rutting, and is usually reported as a score or index
Pavement failure occurs when a pavement reaches terminal condition in a time period shorter
than the design life
All pavements eventually wear out – failure

is when they wear out early.

8. How Do We Define Pavement Failure?
•PSR (Present Serviceability Rating)
•PCI(PavementCondition Index)
•IRI (International Roughness Index)
•NICCCC (Number of Irate Constituent Calls to County Commissioners)

9. Some Causes of Early Pavement Failure
•Design
•Variability inaggregate base materials
•Variability insite subgrade conditions
•Traffic above design values
•Aggregate basedegradation andsaturation
•Subgradeinadequacies
•Reflective cracking

10. Get the structure right, so
the asphalt can do the work

11. Standard Pavement Sections
Common practice, especially at the local level
Limited resources and information
Over designed, under designed
4 in
8 in
5 in
12 in
138,000 ESALs 1,091,000 ESALs

12. Standard Pavement Sections - Example
•Use of standard sections maintained for practical reasons
•Review conducted to determine most efficient and reliable way to improve performance
•Implemented new standard sections maintaining thicknesses and incorporating multi- axial
geogrid for aggregate base stabilization
4 in
8 in
5 in
12 in
742,000 ESALs 5,204,000 ESALs

13. Pavement Optimization for Typical Road
Original Design Life
≈261,000 ESALs
5x Original Design
Same Cross Section
≈1,285,000 ESALs
3x Original Design
Life with Reduced
Asphalt Thickness
≈944,000 ESALs
Same ESAL
Capacity but saved
1.5” of Asphalt and
2.0” of Stone
≈262,000 ESALs
Crushed Stone Base 6.0”

14. Water Kills Roads
SN = a
1D
1 + a
2D
2m
2 + a
3D
3m
3

15. Geocomposite Drainage Layer
Drainage beneath base course
Beneath frost-susceptible soils or
where capillary rise is problematic

16. Material Variability
Source MDD (lb/ft3) As Received
Moisture
Resilient Modulus
Range (psi)
Derived Layer
Coefficient
1 137.3 0.10% 19,000 - 66,000 0.15
2 116.0 5.53% 12,000 - 45,000 0.18
3 135.0 0.74% 9,500 - 35,000 0.12
4 144.8 0.07% 20,000 - 72,000 0.21
Test Results from State DOT Approved Aggregate Sources

17. Material Variability
Effects of variability in ABC layer coefficient are non-linear.

18. Addressing Variability
Stabilized Unstabilized
18” Salvaged Base
with geogrid

19. Variability in Site Conditions
•What’s the typical length of time between the start of design and the start
of construction?
•How many samples are collected to characterize the subgrade?

20. Variability in Site Conditions

21. Subgrade Variability
Effects of variability in subgrade resilient modulus are non-linear.

22. Traffic Assumptions
Average Daily Traffic (ADT) is not the same as Equivalent Single Axle Loads
(ESALs)
=
One loaded dump truck
creates the same
damage to a pavement
as approximately 4,500
cars

23. LoadVariability
Damage to a pavement is not linear with load.It is exponential.

24. Construction Sequence

25. Construction Sequence

26. Construction Sequence

27. Staged Roadway Construction
Section As Designed
Actual Section During
Construction
Reinforced Section
During Construction
Traffic Capacity
55,000 ESALs
Traffic Capacity
10,000 ESALs
Traffic Capacity
60,000 ESALs
TriAx Geogrid

28. Staged Roadway Construction
Section As Designed
Actual Section During
Construction
Stabilized Section
During Construction
Traffic Capacity
55,000 ESALs
Traffic Capacity
10,000 ESALs
Traffic Capacity
81,000 ESALs
Multiaxial Geogrid

29. Incorporating New Technology
•All pavement design, including M-E, has an empirical component
•Full scale testing is essential for proper design
•Not just any testing

30. Subgrade and Base Failure
•Asphalt is the stiffest material in a flexible pavement, but it requires support
•Even a full depth asphalt design assumes a strength value for the subgrade
Subgrade/base failure =
Asphalt failure =
Road failure

31. “Roads wear out from the top down, but
they fall apart from the bottom up.”
National Association of County Engineers

32. Small Scale Trafficking Tests
In the early
2000’s Testing
Conducted as
Internal
Validation
Unstabilized Biaxial
Aggregate
Surface
Subgrade

33. Small Scale Trafficking Tests
In 2020 Testing
conducted
using the same
Machine, and
Aggregate Base
and Subgrade
material that
met the same
standards.
Aggregate
Surface
Subgrade
Unstabilized InterAx
NX750 InterAx NX850

34. Small Scale Trafficking Tests
What does innovation provide?Improved Performance.

35. Avoiding Subgrade and Base Failure
•Can’t fix a bottom-up problem with a top- down solution
•Avoiding subgrade and base failures is the most important element of
minimizing the life cycle cost of pavements
Move the failure up!

36. Perpetual Pavement
•Definitions tend to focus on the asphalt layers
•Underlying assumption is that the base, sub base, and
subgrade hold up
Get the structure right, so the
asphalt can do the work

38. Asphalt Cracking
Cracking causes failure in two ways:
•Reduced surface quality
•Water intrusion to the pavement structure
Maintenance is the first line of defense – seal the cracks
Asphalt requires support
•A crack is a discontinuity with zero strength
•Provides no support to an asphalt overlay
•Reflective cracking is the result

39. Asphalt Interlayer Technology
Geosynthetic asphalt interlayers can:
•Reduce fatigue cracking
•Arrest reflective cracking
•Prevent water intrusion
The need for millability and recyclability should always be considered

40. Asphalt Interlayer Technology
Reinforcement – Stress-Based
•Stiffer materials compensate for HMA lack of tensile strength
•Fiberglass grids, fiberglass reinforced paving mats (also function as a moisture barrier), steel mesh

41. Asphalt Interlayer Technology
Moisture Barrier – Strain-Based
•Soft materials absorb strain energy while maintaining membrane effect
•Non-woven geotextiles

42. Reflective Crack Arrested by Fiberglass Grid Interlayer

43. Goal:
Pavements wear out (not fail),
on time (not early)

44. How we get there:
1. Improve design
2. Get the structure right
3. Move the failure up
4. Let the asphalt do the work

45. Summary
•Pavements Wear Out – Failures are the problem
•Reliable Foundation so asphalt can do the work
•Innovative materials to provide reliability

46. Tensar+ is a free, cloud-based software that allows engineers, contractors,
and owners to design with geogrid in a variety of applications, including
pavement construction, soft soil stabilization and haul road design.
You can calculate the total value of the Tensar solution compared to
conventional construction alternatives. And now, you can create, save,
and access designs across your multiple devices.
Sign up & start
designing today at:
www.TensarPlus.com
Powerful
Reliable
Versatile

47. Please complete our short survey.
Attendees will receive a follow up email
and PDH certificate
Thank You
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