(gentle music) (air whooshes)
(vehicles whooshing) (horn blaring)
- [Narrator] High quality surfaces are paramount
on roadways being built and resurfaced across Texas.
A well compacted and smooth asphalt pavement
is often achieved by paving in multiple layers
or lifts using an asphalt paving machine.
Researchers at the Texas A&M Transportation Institute
are working with the Texas Department of Transportation
to evaluate a specialized paving machine
called a tamper bar paver
that may be able to lay
thick lifts of asphalt more efficiently.
- Thick lift paving is when you place asphalt concrete
in lifts that are greater than what's allowed
by the TxDOT specifications.
So this lets you put down,
let's say, four or six inches of asphalt at one time
instead of breaking it up into two or three different lifts.
- Can we be more efficient?
Can we place this all in the six-inch lift
or can we be even more extreme and place this in,
say, an eight-inch lift
and still get the same performance
and the same density and the same quality?
- The problem is that thick lift paving has its own hurdles.
One, there's concerns
that you're not gonna get uniform compaction
or uniform density.
There's concerns that it's gonna take a long time
to cool down,
and it's more difficult to get a good ride quality.
So a tamper bar paver is a special piece of equipment
that puts down more compaction right behind the screed.
So the objective of the research was to see
if a tamper bar paver could effectively place
thick lift asphalt,
and what are the best practices to do that?
We got tamper bar pavers onto some thick paving projects,
and we placed those layers somewhere 6, 8, 10-inches thick.
And we placed them with a single lift
and with two lifts.
We modified the compaction settings,
changed the rolling patterns,
and we evaluated,
you know, how long did it take to cool down?
How good was the compaction quality?
And what was the final ride quality?
So we've found that using thick lift paving,
you can actually get better compaction,
more uniform compaction,
than if you did it in separate lifts
'cause you're eliminating that interface
that has poor compaction quality.
So using a thick lift,
you actually get a higher quality,
possibly a better, longer lasting pavement.
- The tamper bar paver did give more uniform
air-void distribution throughout the depth.
However, when they placed these eight
or maybe even 10-inch lifts,
what they found is the top tended to cool off
but the inside stayed warm for a very, very long time.
So we still had to keep it closed to traffic
for eight to 10 hours until it cooled off.
- Given the very limited use of tamper bar pavers
in the United States
and the challenges with temperature and ride quality,
TxDOT decided against modifying
their lift thickness requirements.
- Had this panned out completely,
I think it would have been a really good option
to placing a larger base material
prior to putting surface mix.
I do still think that there's a potential for that,
but it also kind of gave us an idea of,
you know, can we do this with traditional pavers
and just put an extra roller?
So I do think there's still room to expand
from that perspective.
- [Announcer] For more information
and to find the publications for this project,
please visit the TxDOT Research Library
at the link shown below.