- [Narrator] Seal coats on Texas roads are unique.
In addition to using pre-coated aggregates,
most binders are applied to the roadway hot.
The process improves adhesion between the aggregate
and binder and eliminates dust, but questions have remained
about how much to pre-coat and what types
of tests are best to determine ideal coverage.
Working with the Texas Department of Transportation,
researchers at the University of Texas
Center for Transportation Research
evaluated the overall effectiveness of re-coating aggregates
and developed an image analysis
and testing procedure to obtain an ideal coverage rate.
- We've got 25 districts in TxDOT
and everybody does something different.
So our spec doesn't really say that
we have to have it exactly this certain way.
That's why this was developed,
so that everybody would be pre-coating
with the same target value rather than just
this is the way we do it over here
and this is the way we do it over here.
- Item 301 chip seal aggregate says
that the aggregate, if it's pre-coated,
should be pre-coated to the satisfaction of the engineer.
And the question is, well what does that really mean
in terms of how much re-coating is satisfactory to
produce good results in a chip seal?
- So there is an optimal amount of coating that is needed
and so far that has been very subjective
and experience-based.
But the purpose of this study was to
systematically study this and find out
for different kinds of aggregates what that window is
or how much re-coating is optimal.
- They kind of thought outside the box
and came up with testing to figure out
how they could do performance testing.
They did this sweep test to see how well it was bonding.
- What we determined is that the optimum amount of
pre-coating of asphalt on chip seal aggregate
is approximately 50%.
And we have developed a image analysis process to look
at that.
So you can determine whether you have 50 to
about 85% coverage of the surface with asphalt.
That seems to be the optimum amount
of surface covered to give you the best bang for the buck
in terms of retention of aggregate in a chip seal project.
- The next steps would be to provide the engineers
in the field with some kind of a quick and easy tool
by which they can assess that the aggregates are pre-coated
to the extent that they should be pre-coated
and more education.
Making sure that they understand the findings
from this study and implement it on a day-to-day basis.
- For us to have the knowledge of what the ideal rate
of application for the pre-coat would be,
it's better for everybody.
It's better for the contractors when they bid it.
They know exactly what percentage that they need to have
and then also it makes a more durable seal coat
for TxDOT because it's gonna last longer,
we're not gonna lose that material.
So it's just a win-win for everybody.
- [Narrator] For more information
and to find the publications for this project,
please visit the TxDOT Research Library
at the link shown below.