Concrete Testing for Nuclear Application

NARRATOR: Concrete. A building block. A solution to large-scale construction projects—bridges,
dams, and nuclear plants. But concrete starts cracking after you pour
it. ASR or Alkali Silica Reaction is a major degradation
mechanism often called the cancer of concrete. ASR forms a gel that absorbs water and expands,
and does its damage over time on the surface and deceptively deep inside concrete structures. To study this process, scientists at Oak Ridge
National Laboratory, the University of Tennessee, Knoxville, and a consortium of other universities,
have embarked on a large-scale long-term research project utilizing a top-rate facility at UT—the
John D. Tickle Engineering Building. The experiment involves building three large
concrete specimens—each about 3.5 meters long, 3 meters wide, and 1 meter thick—containing
thick rebar and embedded throughout with acoustic emission and pressure sensors, fiber optics,
and transducers.
HAYES: We’ve got the three concrete specimens. One is confined preventing it from expansion
in the one direction. We’ve got one unconfined reactive specimen
expanding in all three directions and then we’ve got a control specimen to base all of
our measurements off of.
CLAYTON: Well these structures very typical
in the thickness of nuclear power plant concrete structures. Most other concrete structures are typically
thinner for transportation applications from about 8 to 10 inches and in nuclear applications
we talk about a meter thick or more. These specimens a meter thick. LE PAPE: This experiment is truly unique. It’s probably the first time that we put up
an experiment at that scale with so many monitoring sensors. HAYES: We’ve got multiple types of sensors. We’ve got sensors in the concrete and sensors
on the surface. All these are hooked up to four different
data acquisition systems. And the systems on the surface themselves
measure strain and deformation. LE PAPE: We are always monitoring data coupled
with non-destructive testing. It will be really helpful to decide what non-destructive
evaluation makes sense and is actually viable and operational to be implemented in the field. MAHADEVAN: You want to test the structure
without completely damaging the structure, so you want to examine things without being
intrusive or creating any permanent damage. That’s called non-destructive evaluation. Digital image correlation is an optical technique
where we take images of any object (or structure of interest in this case) over a period of
time and then we compare these images to a reference image. ZIEHL: We use acoustic emission sensors. And the acoustic emission sensor is essentially
a little piezoelectric element with a preamplifier in the sensor. Any specimen we have in the lab has three
embedded acoustic emission sensors that are already cast in the concrete. We have four surface mounted acoustic emission
sensors. MA: It takes two years to cure the specimen
inside a chamber. When I say “chamber” we’re talking about
a large-scale chamber about 52 feet long, 30 feet wide, and 12 feet high. Inside the chamber we need to control the
temperature and humidity over a two-year time span. NARRATOR: The environmental chamber is kept
at a constant 100 degrees Fahrenheit and 100 percent humidity. HAYES: In this condition the reaction was
accelerated. Under normal circumstances, in a real-life
scenario, this would occur in 50 years. Maybe 50 years in a nuclear power plant. GIANNINI: In this project we’re doing everything
that we can to make our concrete as representative of how ASR develops in the real world as opposed
to being an ultra-accelerated laboratory experiment. Making a reactive mixture is pretty easy if
you have the right aggregate. You start with a highly reactive aggregate
source and then add alkalis to the mixture—in this case in the form of sodium hydroxide—basically
providing as much fuel for the fire as possible. Or in some cases, with respect to this project,
we actually dial that back a little bit so we don’t see too much expansion too quickly. NARRATOR: Ready Mix Concrete, the concrete
mix supplier, is less than two miles from the Tickle facility. LOVELACE: Fortunately, it’s been a cooperative
effort with multiple universities and our opportunity to work with Tennessee. To be a part of such an experiment gives Ready
Mix producers the opportunity to experiment with this so that in the future, we have a
much better working knowledge with these particular pours, mixes, and all the aspects that come
along with it. MA: I need a group of dedicated personnel
because I cannot do it myself. We’re talking about a large-scale structure. To give you an example, to change one of the
boundary conditions of one specimen takes 50 tons of steel to confine this thick concrete
slab. It weighs 50 tons. NARRATOR: The dedicated personnel spent a
long, hard, and hot day pouring the concrete into three forms. COX: So this is a great opportunity for our
students to work on a really big problem with a world-class team. They may not get another opportunity like
this in their lives, so this could be a landmark opportunity in their career. They’re going to write their master’s theses,
their doctoral theses, research papers based on this research. They’re also getting experience in planning
and executing a large complex project. And that’s a skill very valuable to civil
engineers that they’ll be able to take with them into the workplace. We’re in the knowledge business, and this
is a great opportunity for us to contribute to knowledge related to civil engineering
infrastructure and to develop infrastructure that is safer, smarter, and more sustainable.

Leave a Reply

Your email address will not be published. Required fields are marked *