(light music)
- [Narrator] Reflective cracking is a type of cracking
that occurs when a new asphalt overlay is placed
over older pavement with pre-existing cracks.
Often new cracks will form, mirroring the cracks
in the underlying layer.
Geogrids placed between the two layers
have shown promise in mitigating the issue,
but further research was needed
to develop design criteria.
The Texas Department of Transportation
and researchers with the Center
for Transportation Research conducted a field study
to quantify the structural benefits of geogrids.
- We use the same concept for this geosynthetics
because we've been using geosynthetics for a long time,
textile on bases, on the soils and aggregates.
But now this research
was using the same materials, a little bit modified
for the asphalt, for the top layers.
- By having that geosynthetic reinforcement,
not only you mitigate the reflective cracking,
but you also increase the structural capacity.
And we knew that that happened, but we had not quantified
and we even, and without being able to quantify it,
we do not know how to incorporate it into the design.
So the objective of this project was to quantify
the structural benefits of geosynthetics
when used with asphalt overlays.
- The research included a comprehensive, full scale monetary
program included in SH21 in Bastrop county, Texas.
This program involved the use
of varied geosynthetic reinforcement products,
placed between the asphalt layers
across multiple test sections,
- Something on the order of 24 test sections, all of them
with different types of geosynthetics,
some of them without geosynthetics.
Now, the problem with roadway projects when we have these
test sections is that we need to wait 15, 20 years
to understand the differences between these 24
test sections.
So in order not to have to wait for that long,
we installed a significant number of sensors.
- [Speaker] Some of these test sections were equipped
with a range of sensors,
including asphalt strain gauges, thermocouples,
geophones, and moisture sensors to monitor performance.
- These were all instrumented test sections,
so we were able to understand the response
and the benefits immediately or soon after construction.
And we gather a lot of data from this monitoring project,
and we evaluated the data.
- We will continue monitoring projects like SH21
to document the long-term benefits
of the geosynthetic reinforcement.
Updating specifications
and test procedures will also help
to ensure the technology is applied effectively.
- Essentially, when we use geosynthetic to reinforce
as faultic layer, we have an increased structural capacity.
This increased structural capacity has not been
accounted for in the past,
and by accounting for it,
we can have significant cost benefits,
either by decreasing the thickness of,
or the required thickness of a given asphalt overlay,
or for a given thickness of the asphalt overlay
to extend its design life.
- [Narrator] For more information
and to find the publications for this project,
please visit the TX DOT Research Library
at the link shown below.