(upbeat music)
- [Narrator] Use of recycled pavements
and shingles in some asphalt pavement mixed designs is
common practice for departments of transportation
across the nation.
While this is undoubtedly better for the environment
and economically wise,
it's important for the Texas Department of Transportation
to continue improving the quality of these mixes
in order to reduce cracking and rutting
on the state's highways.
Research at the University of Texas at El Paso is
looking at current guidelines
to see how they may be adjusted
to create better performing recycled mixtures.
- This research was aimed
at trying to increase the performance of our current mixes.
So in our traditional hot mix design,
what we do is we do what we call volumetrics.
Everything's just density driven.
All of the bidding for projects is done based on low bid,
so you're not always getting the performance out of it.
So at the start of this project,
we had what we call RAP and RAS,
so recycled asphalt pavement and recycled asphalt shingles.
Economically, it seems like a good choice up front,
because it seems like free binder, free asphalt,
and we don't always see the long-term performance.
And so this project was look looking at,
how do we increase the life of that pavement
while still utilizing these materials?
So we didn't just do volumetric with density design.
We actually would put in a cracking
and a rutting performance test,
and try to balance the performance
while also balancing economics
and still getting that density.
- Here we are also focusing on rutting,
we are also focusing on the cracking,
so the term balanced mix.
So we are not focused just on rutting,
we're gonna look at cracking,
and we started doing a cracking test,
which was the overlay test.
TxDOT is adapted to the overlay test.
So we worked on that,
and to make it easier,
we developed a couple of tools online.
One of 'em for the cracking test.
Instead of, a lot of people have different equipments,
and reducing the data, sometimes you have variation.
We put the online tools,
so anybody can go in with their raw data, reduce it,
and come up with the same answer.
The other thing we did is, the mix design itself,
the text that has been using traditionally
is done in Excel,
and as you know, Excel versions change year after year.
Not only that, it's very cumbersome.
What we wanted to do is add the balanced mix design to that.
We came up with an online tool
which goes in there
and grabs components from that Excel sheet,
mainly the gradation,
and we optimize the gradation
that you need for the balanced mix,
and then you save it,
and it puts it back into same Excel sheet
and everybody else could use it.
So we simplified the process.
- From this research,
we actually developed a special specification, 3074.
From that balanced mix design specification,
it has performance tests for cracking and for rutting.
We've since placed two sections on the NCAT Test Track.
Those have been in cycle for about four years now.
And then we've also developed a,
what we call interagency contract
with TTI, UT El Paso, and UT Austin,
and we actually placed 34 test sections across the state.
- So we put over 30 sections out there
that are balanced mix design.
We varied the RAP content.
We varied the rejuvenator.
Some of 'em had no RAP versus RAP.
Hopefully, within a few years,
we continue to monitor those projects
and see how good this balanced mix design is going to be.
- So through this monitoring, the idea would be,
we come up with an improved, special specification
and that would be our new statewide.
And so we currently have another interagency contract
right now with TTI
and the idea is to continue to monitor that,
create a new specification,
and then to start implementing this in some districts.
- [Narrator] For more information
and to find the publications for this project,
please visit the TxDOT research library
at the link shown below.