Professor John Ma is leading a four-year research project in partnership with ORNL, a consortium of other universities including Vanderbilt, the University of Alabama and the University of South Carolina, as well as Ready Mix USA to study a concrete specimen in steel confinement that will have potential implications for the nuclear industry. This video shows the scope of the project, along with explanations from various partners involved in the collaboration.
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 m long, 3 meters wide and 1 m thick containing thick rebar and embedded throughout with acoustic emission and pressure sensors, fiber optics and transducers.
“We’ve got the three concrete specimens. One is confined, preventing it from expanding in one direction,” said Nolan Hayes, Graduate Research Assistant at UT. “We’ve got on unconfined reactive specimen expanding in all three directions, and then we’ve got a control specimen to base all of our measurements off of.”
“These structures are very typical of the thickness of nuclear power plant concrete structures,” said Dwight Clayton, Research Operation Manager at ORNL. “Most other concrete structures are typically thinner for transportation application, from about 8-10 inches and in nuclear applications, you’re talking about a meter thick or more. These specimens are a meter thick.”
“This experiment is truly unique,” said Dr. Yann LePape, Concrete & Civil Structures Expert at ORNL. “It’s probably the first time that speed up an experiment at that scale with so many monitoring sensors.”
Hayes added: “We’ve got multiple types of sensors. We’ve got sensors in the concrete, sensors on the surface. All of these are hooked up to four different data acquisition systems and the systems on the surface themselves measure strain information.”
“All this monitoring data coupled with non-destructive testing will be really helpful to decide what non-destructive evaluation makes sense and is actually viable and operational to be implemented in the field,” said LePape.
“You want to test the structure without completely damaging the structure,” said Sankaran Mahadevan, Professor of Civil and Environmental Engineering at Vanderbilt University. “You want to examine things without being intrusive or creating any permanent damage. It’s called non-destructive evaluation. So 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.”
“We use acoustic emission sensors, and the acoustic emission sensors essentially a piezoelectric element with a preamplifier and the in the sensor,” said Dr. Paul Ziehl Professor of Civil and Environmental Engineering at the University of South Carolina. “With any specimen in the lab, we have three embedded acoustic emission sensors that are already cast in the concrete and we have four surface mounted acoustic emission sensors.”
“It takes two years to cure the specimen inside the chamber,” said Dr. John Ma, Professor of Civil and Environmental Engineering at UT and the project’s principal investigator. “When I say chamber, we’re talking about a large-scale chamber about 50 ft. long by 30 ft. wide by 20 ft. high. Inside chamber we need to control the temperature and humidity. Over two years’ time.”
Then the environmental chamber is kept at a constant 100 degree F and 100 percent humidity.
“In this condition the reaction is accelerated and under normal circumstances in a real-life scenario this would occur in maybe 50 years, maybe fifty years in a nuclear power plant,” said Hayes.
“In this project we’re doing everything we can to make our concrete representative of how ASR develops in the real world as opposed to meeting an ultra-accelerated laboratory experiment,” said Dr. Eric Giannini, Assistant Professor of Civil, Construction and Environmental Engineering. “Making a reaction mixture is pretty easy if you have the right aggregate. Start with the highly reactive aggregate ores and then add alkalis to the mixture, in this case the form of sodium hydroxide and basically providing it much fuel for the fire impossible or in some cases with respect to this project we actually dial that back a little bit so that we don’t create too much expansion too quickly.”
Ready Mix concrete, the concrete mix supplier is less than two miles from the John D. Tickle facility.
“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 four mixes that I have all the aspects that come along with it and need oppressive” said Kenneth Lovelace, Quality Control Sales Rep for Ready Mix USA.
Dr. Ma added: “You need a group of dedicated people because I cannot do it myself because we’re talking a large-scale structure. Give you an example. Change one of the boundary conditions of my specimen and it takes 50 tons of steel to confine this state. “
Dedicated personnel spent a long, hard and hot day pouring the concrete into three forms.
“This is a great opportunity for our students to work on a really big problem with a world class team,” said Dr. Chris Cox, Professor and dead of the Civil and Environmental Engineering Department at UT. “They may not get another opportunity like this in their lives. This could be a landmark opportunity in their career. They’re going to write their masters’ theses their doctoral theses and 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 to develop infrastructure that is safer, smarter and more sustainable.”