[Music]
(Narrator) Sustainable pavements are those that
1. Achieve the engineering goals
for which they were constructed.
2. Preserve and ideally restore
surrounding ecosystems.
3. Use financial, human, and
environmental resources wisely.
4. Meet basic human needs
such as health, safety, equity,
employment, comfort, and happiness.
These remain aspirational goals
as sustainability practices
continue to evolve.
Recycled Concrete Aggregate (RCA)
is created when concrete is purposely crushed
to create aggregates for use in
construction applications.
Reusing old concrete pavement in this way
can lead to cost savings and
reductions in virgin material usage and
can help agencies meet their
sustainability goals.
This was demonstrated on a concrete pavement
reconstruction project on I-10,
a 10-lane divided interstate located on the
West side of Houston, Texas.
(Andy Naranjo) In the 1990's, the Texas DOT struggled
with a lack of suitable, locally available
aggregate sources and rising costs
of virgin materials.
At the same time, we also experienced
some performance issues with virgin aggregates
and continuously reinforced
concrete pavements.
The growing availability of concrete for recycling
prompted us to explore the use
of RCA and infrastructure projects.
In 1995, we reconstructed a 5.8-mile segment
of I-10 in the Houston metropolitan area
using RCA to gain a
better understanding of its use in CRCP.
This was the first project in the Nation
that used 100 percent RCA in the
reconstructed pavement.
(Narrator) The project included two typical pavement sections:
One reconstructed section and one overlay.
All the RCA used
on the project conform to the same
TXDOT specification requirements as
virgin aggregates.
An initial challenge was producing a
concrete mixture with consistent
workability and strength.
The workability issue was related to
inadequate moisture control.
This was mitigated through the
installation of a sprinkler system for
aggregate stockpiles.
Fluctuations in strength values resulted
in adjustments to the mix proportioning.
Construction crews also noted
inconsistent concrete and premature setting
during placement
due to the presence of the high volume
of recycled fines in the mixture.
This prompted TXDOT to limit the fines
to a maximum of 20 percent
beginning in 1999.
Shortly after construction, 15 cores
were extracted throughout the project
and evaluated for strength.
The results were generally lower than
typical values for concrete constructed
with virgin aggregates
but still met TXDOT specifications.
Concrete made with RCA is generally
similar to concrete made with virgin aggregates.
However, there typically are
some key differences:
RCA concrete is less stiff,
RCA concrete is less dense,
and RCA concrete absorbs more water.
Since its construction in the mid-1990s,
TXDOT has been pleased with the
performance of this project.
The pavement has exhibited fewer
meandering cracks and less crack spalling,
which are observed on many CRCPs
in Texas constructed with
siliceous river gravel.
TXDOT believes that the lower stiffness
of the RCA concrete and the strong bond
between the RCA and new mortar
are likely contributing
to the good performance.
The use of RCA resulted in: cost savings,
a lower impact from reduced virgin aggregate demand,
and a reduction in
off-haul of demolished concrete.
(Andy Naranjo) The I-10 project demonstrated that
RCA can be used to replace virgin aggregates
and achieve adequate levels of performance
on high-volume
roadway facilities.
As of 2020, the ride quality has remained good
with an average IRI of
106 inches per mile.
A major outgrowth of this work on this project was
TXDOT's development and implementation
of a specification in 2004
for using RCA in concrete pavements
as a cost savings measure.
RCA is a part of TXDOT's construction program today,
particularly in areas of the state
where quality virgin aggregates
are not available.
(Narrator) To learn more about how the
Sustainable Pavements Program can help you
please visit our website.
[Music]