Jay Thompson, PE State Pavement Design Engineer, …...Pavement must be defended from many types of...
Transcript of Jay Thompson, PE State Pavement Design Engineer, …...Pavement must be defended from many types of...
Jay Thompson, PE
State Pavement Design Engineer, SCDOT
Pavement must be defended from many types of attackers and resulting damage
Water is one attacker that can create damage in different ways
Today we are going to focus on a typically slow mode of attack
Stripping
Loss of bond between aggregate and asphalt binder
Observed as the asphalt binder having been stripped from the aggregate.
Detachment
Displacement
Emulsification
Pore Pressure Induced Damage
Scour
Environmental Factors
(Taylor and Khosla 1983, Kiggundu and Roberts 1988, Terrel and Al-Swailmi 1994)
1986 – Bushing, Burati, Amirkhanian – Clemson
Found widespread occurrences of stripping statewide
Commonly see stripping on older pavements, especially where maintenance has been deferred
Mix Design Anti-Stripping Additives – Lime – LASA
Effectiveness can be sensitive to aggregate type
Testing – ITS/TSR – Boiling Test
Anything that keeps water out Preservation – Different Types
Rehabilitation
Drainage – Cross-slope and shoulders
Good construction practices Joint compaction
Mix type selection and porosity
Duration of exposure to weather for coarse mixes
Normal crown, inside lane I-126
Superelevation, inside lane, no water, no distress I-126
Choose Your Game Mode
The attackers are known. While predicting susceptibility is complicated. We know how to design tower defenses for the attack.
Good mix design and testing
Good construction practices
Good drainage
Keep it good – regular preservation/maintenance
The attackers are known but their path is undefined. Investigation may be required to understand risks.
What happens if we place traffic on a milled surface?
Can we get compaction on the new lifts?
When does stripped HMA have to be replaced? That’s a good question, here are a few more:
How bad is it? Is it isolated or wide spread?
How deep in the structure is it?
What is the significance of the road and what types of traffic does it carry?
Do we have enough money? Is there another project coming along? Can we seal it off for now to stop the mechanism of attack?
How long will that last?
What if stripping is just begining? Can we seal it off and fix it later? What if our funding gets decreased later?
When does stripped HMA have to be replaced?
I’m always going to start with the fix it approach. If a problem is fixed we can have a higher degree of certainty concerning future funding needs.
Reality is that decisions must be made based on available funding and risk. Risk to the immediate area first
Risk to the system next
Last but not least, risk considering future cost