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- [Narrator] Seal coats
on Texas roads are unique.

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In addition to using
pre-coated aggregates,

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most binders are applied
to the roadway hot.

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The process improves adhesion
between the aggregate

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and binder and eliminates dust,
but questions have remained

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about how much to pre-coat and what types

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of tests are best to
determine ideal coverage.

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Working with the Texas
Department of Transportation,

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researchers at the University of Texas

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Center for Transportation Research

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evaluated the overall effectiveness
of re-coating aggregates

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and developed an image analysis

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and testing procedure to
obtain an ideal coverage rate.

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- We've got 25 districts in TxDOT

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and everybody does something different.

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So our spec doesn't really say that

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we have to have it
exactly this certain way.

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That's why this was developed,

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so that everybody would be pre-coating

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with the same target
value rather than just

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this is the way we do it over here

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and this is the way we do it over here.

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- Item 301 chip seal aggregate says

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that the aggregate, if it's pre-coated,

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should be pre-coated to the
satisfaction of the engineer.

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And the question is, well
what does that really mean

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in terms of how much
re-coating is satisfactory to

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produce good results in a chip seal?

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- So there is an optimal amount
of coating that is needed

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and so far that has been very subjective

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and experience-based.

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But the purpose of this study was to

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systematically study this and find out

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for different kinds of
aggregates what that window is

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or how much re-coating is optimal.

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- They kind of thought outside the box

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and came up with testing to figure out

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how they could do performance testing.

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They did this sweep test to
see how well it was bonding.

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- What we determined is
that the optimum amount of

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pre-coating of asphalt
on chip seal aggregate

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is approximately 50%.

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And we have developed a image
analysis process to look

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at that.

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So you can determine
whether you have 50 to

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about 85% coverage of
the surface with asphalt.

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That seems to be the optimum amount

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of surface covered to give
you the best bang for the buck

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in terms of retention of
aggregate in a chip seal project.

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- The next steps would be
to provide the engineers

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in the field with some kind
of a quick and easy tool

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by which they can assess that
the aggregates are pre-coated

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to the extent that they
should be pre-coated

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and more education.

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Making sure that they
understand the findings

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from this study and implement
it on a day-to-day basis.

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- For us to have the knowledge
of what the ideal rate

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of application for the pre-coat would be,

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it's better for everybody.

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It's better for the
contractors when they bid it.

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They know exactly what
percentage that they need to have

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and then also it makes
a more durable seal coat

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for TxDOT because it's gonna last longer,

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we're not gonna lose that material.

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So it's just a win-win for everybody.

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- [Narrator] For more information

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and to find the publications
for this project,

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please visit the TxDOT Research Library

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at the link shown below.