(logo swooshes)
- [Narrator] The road construction industry
is a leader in sustainability.
Recycled materials,
especially Reclaimed Asphalt Pavements, or R.A.P.,
and Recycled Asphalt Shingles, or R.A.S.,
dramatically reduce road building costs,
while being environmentally friendly.
But getting the right formulations
in order to achieve good engineering performance
is a challenge, thanks to all the variables.
To make needed improvements,
a synthesis project was performed
by the Texas A and M Transportation Institute.
Designed to revise TxDOT's standards and specifications.
- Sustainability efforts motivate the increased use
of recycled asphalt materials in asphalt pavements.
So we are trying to increase the amount
of reclaimed asphalt pavement or RAP,
and/or recycled asphalt shingles or RAS
in our asphalt pavements,
for both economic and environmental benefits.
- Traditionally at TxDOT we've used
a lot of recycled material.
The problem is, is when we use recycled material
we don't have a good way to quantify
how much binder we're actually getting.
- [Amy] We have to make sure that we're going to engineer
the combination of materials that's unique
for every set of virgin materials, aggregate and binder,
and recycled asphalt materials,
as well as any additives.
And so part of that focus of engineering
the combination of materials,
is to understand how much old-aged stiff binder
you're getting off your RAP and RAS.
- [Travis] On a national standard,
what you, most people use,
is either solvent extraction or ignition oven,
which is essentially it's a very, very hot oven.
The problem with that is
if you put something in there,
it will burn it off regardless.
If you put it in solvent,
it will pull all of the asphalt out.
But it could be in the middle of that rock, right,
that you're removing this binder,
and we're accounting for it as if it's actually
contributing in the mix;
and most the time it's not.
Across the state,
what we're finding is anywhere from 16 to 96%
of your recycled binder is actually usable
in recycled asphalt pavements.
On average, it's 40 to 45%,
and then we just call it a good average and go with it.
You have to account for the climatic conditions,
how long it's been out there,
so we really do need a test to quantify
how much is in there.
- We did come up with a recommendation
of using 75% recycled binder availability
when a few conditions are met.
What they should do is try to get ahold of
a few of their RAP sources
and extract and recover the binder would help,
to know how stiff their binder is
in the recycled asphalt pavement.
And that that can help them know, in mixed design,
should I reduce the binder availability
from a hundred percent, which is what's currently assumed,
down to 75%, for example.
And I think that alone,
would go a long way to making sure
that we have enough effective binder from the old material,
the RAP, and from the new virgin binder,
to coat and bind our aggregates together.
- [Narrator] For more information
and to find the publications for this project,
please visit the TxDOT Research Library
at the link shown below.