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- Evaluating existing, but unused data

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derived from overlay testers
could be a key in creating

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longer lasting pavements.

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Researchers with the
University of Texas at El Paso,

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looked at mixed design characteristics.

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In combination with that mixtures fatigue

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cracking resistance numbers.

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- TxDOT put all of their
kinda eggs in one basket

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if you will,

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with the overlay testers
10 plus years ago.

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Other states are using,
you know, semicircular,

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bending beam, these other
tests, and on a national level,

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at one point,

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they compared all of them
and really their standard

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deviations and coefficient
variation on all of these

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tests were all very very high.

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Overlay was a little bit better.

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So, and it was developed in Texas.

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So we naturally said,

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that's the one we want to progress with.

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- [Imad] The issue with this
test was the variability.

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You know what,

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the way they run this test is
you test how many cycles it

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takes for the specimen to
fully crack from bottom to top.

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And the variability of the
number of cycles that it took for

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this to happen was a lot greater than 20%.

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And this was always an
issue that TxDOT that had.

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But if you look at the load versus cycle,

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you would see that this test
behaves very, very well.

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So we start describing that curve,

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looking at an equation.

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And from that equation,
you come up with an index

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and that index seemed
to be very repeatable.

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And not only that, it was repeatable,

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we were also being able to
delineate between the different

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mixes.

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The problem was when you
get close to the margin

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as Mike says, you know,

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it's very difficult to interpret.

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If one test you run three times
and one says that it's good.

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The other one says it's bad.

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And the third one, it says
good or bad, doesn't matter.

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So you don't have a good feeling.

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Now we consistently get three
results that all three of them

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are bad, or all three of them
are good, even at the margin.

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So there's more confidence in
the results that you get from

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the system, because there
is also more repeatable.

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- This is a national thing
that everybody's looking at a

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balanced mix design process,

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and everybody has the same
thought that you have to balance

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cracking and you have to balance rutting.

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To my knowledge at this
point, with the new analysis,

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this has the lowest
coefficient of variation.

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So this is now a reliable cracking test.

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It gives you a much higher
level of confidence on that

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cracking side. And so I
think to balance them,

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you have to have both cracking
and rutting so that we can

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move forward with this balanced mixes on.

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- 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.