Presentation delivered at the CalAPA Spring Asphalt Pavement Conference April 9-10, 2014 in Ontario. Topic: Non-destructive testing, including the use of both FWD and GPR testing, how they are done, results from the testing and how they are used in pavement management / preservation decision-making.
6. Things We Know
All pavements when constructed are the
same
Materials
Gradation
Binder content
Aggregate shape
Aggregate Size
7. Things We Know
All pavements when constructed with the
same
Relative compaction
8. Things We Know
All pavements when constructed with the
same
Thickness
Smoothness
Surface texture
Skid resistance
9. Things We Know
All pavements are exposed to the same
Weather cycles
Rainfall
Landscape irrigation runoff
Temperatures
Heat
Cold
Freezing
10. Things We Know
All Pavements have the same
Crown
Cross slope
Longitudinal slope
Frontage Improvements
11. Things We Know
All Pavements are constructed over the same
soil subgrade with
Identical wet and dry strengths
Identical moisture contents
Identical drainage characteristics
12. Things We Know
They are subjected to the same
Axle weights
Tire pressures
Numbers of axle loads
Travel speed
13. Things We Know
They are subjected to the same
Vehicle operation
Speed
Stopping
Starting
Standing
Acceleration
Turning movements
14. Things We Know
All Pavements are maintained with
Same pavement seals
Same crack filling
Same interval of maintenance
Same pavement rehabilitation, maintenance and
resurfacing
15. Things We Know
All pavements require
Arbitrary 2” thick asphalt concrete overlays every
10 or 20 years
Identical Crack preparation
Identical Local reconstruction
Identical Edge milling and surface preparation
17. Things We Ignore
Axle weights increased from 18,000 to 20,000
pounds on trucks
Axle weights increased from 18,000 to 28,000
pounds on buses
Tire pressures for trucks and buses have increased
to >120psi
18. Things We Ignore
Traffic volumes have increased
Asphalt binder characteristics are changing
Recycling is increasing
Waste reduction legislation
19. Things We Need to Know
Pavement construction variations
What
Why
Where
Impact
20. Things We Need to Know
Pavement use variations
Pavement maintenance differences
Environmental differences
21. How Do We Find Out?
We use pavement management to define
similarities
We use engineering properties to define
differences
22. What Sources Do We Have?
Historical plans
As-built drawings
Visual observations
Pavement coring and potholing
Ground Penetrating Radar
23. The Evolution of Subsurface
Exploration
1970’s GPR
1970’s
Oil and Mineral Deposits
Archaeologists
Military
Big Money $$$$$$
Availability?
Equipment and Power
DataCapacity
Mobility
Trained Personnel
TODAY’S GPR
Availability
Smaller Equipment
Mobility
Power needs
Analysis time
Trained Personnel
DataCapacity
GPSCompatibility
MultipleTypes
24. GPR: Definition
Electromagnetic Radiation
Microwave band (UHF/VHF
Frequency)
Radio waves transmitted into the
Ground
Conductivity Increases Depth
Increases
Higher Frequencies=
Low Penetration
Low
Frequencies=Deep
Penetration
How itWorks
Changes inVelocity
Change in Dielectrics
Typically change in Material or
Density
Components
Antenna
Operating System
Large Data Storage Capacity
Spatial Control
GPS
DMI
25. GPR Types
Low Frequency Applications
Less than 16 - 200 MHz
LongWave Length
Deep Penetration
Range 30 Ft to 150 Ft
Poor Resolution
Cart Mounted or Sled
Geotechnical
Mining
Archeological Investigation
Ice, Snow Pack
26. GPR Types
Mid Frequency
Applications
270 MHz to 900 MHz
LongWave Length
Not as Deep Penetration
Range 50 ft to 12 ft
Better Resolution
Cart Mounted or Sled
Geotechnical
Archaeological Investigations
Utility
Large SubsurfaceVoids
Ice, Snow Pack
27. GPR Types
High Frequency Applications
1600 MHz to 2600 MHz
ShortWave Length
Shallow Penetration
Range 0 Ft to 1.5 Ft
Good Resolution
Hand Held Device
Concrete Structures
Bridge Deck (PCC)
Rebar
PostTension Cables
Corrosion
28. GPR Types
High Frequency Applications
1 GHz to 2 GHz
ShortWave Length
Shallow Penetration
Range 0 Ft to 2.5 Ft
Good Resolution
HornAntenna
RoadwayThickness
ShallowUtility
ShallowVoids
44. How is it behaving?
How strong is the roadway?
Areas of strength and weakness
How does that compare with past use?
Explain current behavior
How will it support projected future use?
Magnitude of reinforcement required
45. Impacts on performance
Indirect estimates
Estimates from component analysis based on
Thickness information
Visible conditions
In-situ moisture conditions
Subgrade strengths
46. Impacts on performance
Direct measurement
In-place strength testing
Multiple locations
Magnitude of deflection
Shape of deflection basin
Load/stress distribution
56. Real Information
Pavement Coring
Defines layer types and history
Ground Penetration Radar
Provides continuous documentation of
thicknesses
Estimating/Guessing
Based on past observable damage
In Place StrengthTesting
Permits modeling of future use and needs