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

Jay Thompson, PE

State Pavement Design Engineer, SCDOT

thompsonju@scdot.org