seal coat asphalt selection

2018 Transportation Short Course October 16, 2018

SEAL COAT ASPHALT SELECTIONJerry Peterson, MTD


Table of contents

2

2-7

8-10

9-10

11-15

16-17

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18-20

Intro

Specifications

Design Method/Seal Coat Manual

Seal Coat Material Selection Table


Other Considerations

Discussion/Recap/Conclusions

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2

3

4

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Seal Coat Asphalt Selection

A “Black Art” Usually done by experience. What’s important?

– Not too runny.– Not too brittle.– Sticky.

How to choose the right one?

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Seal Coat Specifications

Item 316 – “Seal Coat” “Furnish asphalt materials meeting the requirements of Item 300” Temperature limits hint at the binders, but Binder selection is kicked on down the road.

Who’s responsible for this evasion?

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Item 300, “Asphalts, Oils, and Emulsions”

Item 300 has LOTS of details on binder grades.– In fact, too much.

Hot applied asphalts:

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Emulsified Asphalt (1 of 4)

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Typical Material Use

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Seal Coat Design Method

Modified Kearby Design Method– Seal Coat Manual, Chapter 4

A = 5.61 E (1-W/62.4 G) T +V Translation:

Asphalt Rate = Voids in Loose Aggregate X Aggregate Rate X % Embedment

In other words: The binder grade doesn’t come into it.

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Seal Coat Manual

Selection of Binder – Chapter 3.2 What you need:

– When applied, the binder should be fluid enough to spray and cover the surface uniformly, yet viscous enough to remain in a uniform layer and not puddle in depressions or run off the pavement.

– After application, it should retain the required consistency to wet the applied aggregate.

– It should develop adhesion quickly. – After rolling and curing, the binder should hold the aggregate tightly to the

roadway surface to prevent dislodging by traffic. – When applied in the proper amount, it should not bleed or strip under

traffic or with changing weather conditions.

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Seal Coat Manual

Binder Types:– Asphalt Cement – Emulsion– Cutback

But which grade?

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Developed about 2008– “Pennies to the Pavement”

Was required on every project.– Now it’s a district decision.

Guidance is still valid. Form 2388

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12



Tier I – Heavy Use (>5,000 ADT) About 25% of our seal coat roads. Grades

– AC-20-5TR– AC-20XP– AC-15P– A-R Type II– A-R Type III

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Tier II – Moderate Use (500 to 5,000 ADT) About 50% of our seal coat roads. Grades

– AC-10-2TR– AC-15P– AC-20XP– CRS-2P– HFRS-2P– CHFRS-2P– (AC w/ latex)

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Tier III – Light Use (>500 ADT) The other 25%. Grades

– AC-10– (AC-5)– CRS-2– HFRS-2– CRS-2H

Be vary careful about these tiers; very soft and no polymer!

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Winter Grades

Try to stay within the temperature limits of Item 300. When outside of those limits:

– Maybe switch to emulsion (CRS-2P/HFRS-2P/CHFFRS-2P)– Maybe use AC-12-5TR– Maybe CRS-1P/RS-1P (with caution)– Or Cutback, RC-250

Maintenance might use CMS-2P. – Winter or non-winter– More general purpose– Stable – can store longer.

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Asphalt Type Selection

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How did we get here?

Binder spec is generic– Not aimed at an application or process.– Differentiates one binder from another.– Leaves out some properties that are tough to measure (stickiness)

Solution– Have a seal coat binder spec.– Designed around the seal coat application.– Grades tell you something about selection.– SPG?

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Recap

Seal coat asphalt selection often based on experience. Design methods and specs don’t help too much. Seal Coat Material Selection Table (Form 2388) is an OK guide.

– But it’s just a starting place.

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In Conclusion…

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seal coat asphalt selection

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