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(gentle music)
(logo whooshing)

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- [Narrator] The Texas
Department of Transportation

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and the University of Texas at El Paso

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studied the upper limits
of field sands to determine

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how they may impact Superpave
mixtures across the state.

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Field sands are used in
pavements to reduce costs

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and binder requirements,
but their use is limited

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in part to their impact on
overall road performance.

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- So in the black roadways
that you drive on,

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there is, of course, aggregate,
intermediate aggregate,

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there's a fine aggregate.

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Typically, that fine aggregate

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is gonna be either a crusher fine,

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so if you're using limestone,
as you're producing limestone,

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in the process of crushing,
you generate dust,

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so that's gonna be more
of a manufactured sand.

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You're just naturally creating
that in the crushing process.

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East Texas uses a lot of
river gravels and granites

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and things like that, so
you have less of those,

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and so typically, your
sands are gonna come

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from natural sand sources,

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which are unclean sands
from things like riverbeds.

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- And some of it has expensive
clays or volatile clays,

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which translates to expensive clays,

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and clay and water doesn't mix well,

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so that can lead to a lot of stripping

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that happens on the pavement,
and that can happen very fast.

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There was several projects
they start constructing.

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Within six months, they were having a lot

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of rutting failure, and the understanding

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is why this early failure is happening.

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- Historically, we had a
test called sand equivalent,

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and so sand equivalent tells
you how dirty the sand is,

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how much clay is on the sand,

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and so it passed all of those tests,

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and then we still had
pretty bad failures rutting

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and stripping in the field,
and so we started looking

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at another test called methylene blue,

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and the methylene blue gives
you the reactivity of the clay,

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not just the quantity of clay.

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So when we ran that
sand, it was very clean,

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but the small amount
of clay that was on it

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was very reactive, and it caused failure,

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so we started this field
project to look at all

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of the field sands throughout the state

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to see what combination of sand equivalent

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versus methylene blue we could utilize

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without seeing the pavement failure.

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- We ended up with 25
sources of field sands

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that they think they use

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that they would like us to look into,

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so we looked at them, and sure enough,

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we start seeing that yes,

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some of these field
sands are very volatile

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because of that amount of
clay they have in them,

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and they do affect early age failures.

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- We did come up with a
rough guideline for that,

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and then we're actually taking this

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into an implementation-type project

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through an inter-agency
contract with the university

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so that we can do more field testing

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on specific mix designs
utilizing those materials,

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and then we're gonna check for stripping

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using the Hamburg wheel tracker test.

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- You don't have to do any other test

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that they don't do right now.

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We're not coming up with a new test.

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It's interpretation of the Hamburg data

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that comes out of the Hamburg test.

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You look at it and you can
calculate a stripping value.

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If that stripping value
is above the limit,

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then you know you're gonna have issues

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in terms of early failure.

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If it's not, you're gonna do well.

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- One project in particular, I mean,

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it was failing before it was
open to the traveling public,

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so we're trying to prevent
that from happening again,

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but we also don't want to
limit available sources,

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so like I mentioned,

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East Texas has locally
available material on site.

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If we just say you can't use it

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because we don't want any failures,

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where's that sand coming from?

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That means they have to rail
it in, so all of a sudden,

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projects increase pretty
drastically in price.

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- [Narrator] For more information

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and to find the publication
for this project,

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please visit the TxDOT research library

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at the link shown below.