A team of University of Arkansas researchers is searching for the most effective way to slow - and hopefully halt - the crumbling of an Interstate 540 median barrier in Washington County.
Micah Hale, an associate professor of civil engineering with the university’s College of Engineering, and three graduate students are measuring the effectiveness of several different sealants to counter what’s known as an alkali-silica reaction.
The reaction, which occurs between rock minerals and alkaline found in concrete, causes structures to expand, microscopically at first, allowing moisture to penetrate the concrete until it ruptures, cracks and crumbles.
Hale said that in January after months of preliminary testing and measurements, his research team began applying the sealants to portions of the concrete median barrier that separates north and south-bound traffic on I-540, extending north for about 4 miles from the Bobby Hopper Tunnel.
Hale said the project,which began in May 2012 and is to conclude in June 2014, is an opportunity to apply classroom theory to a real-world situation.
“We’re still pretty early in our learning curve,” Hale said. “As we get more data, we’ll learn more.”
The research team - which also includes graduate students Richard Deschenes Jr., Cameron Murray and Casey Jones - began by establishing baseline information on the barrier. They did that by drilling “guide studs” into the barrier - a series of four bolts, each exactly 500 millimeters apart - in 15 locations. Five of the locations show minimal cracking, another five show moderate cracking and the final five have advanced cracking in the concrete.
The team applied one of four sealant combinations to 12 of the 15 locations, with the remaining three - one good, one fair, one poor - left bare as a “control” group.
Over the course of the study, the team will measure the guide studs, using gauges that can detect changes as small as a few thousandths of an inch, to see which of the sealants is most effective in halting expansion in the concrete. The team will also monitor the internal humidity of the structure, which the team hopes to limit to under 80 percent, the level that triggers the alkali-silica reaction.
According to the team’s research proposal, the sealants being used are linseed oil, paints often used for exterior rock surfaces known as elastomeric paint, and silane, a silicone-hydrogen compound, and a mixture of silane and elastomeric paints.
The research project is funded by a $220,000 grant from the Arkansas Highway and Transportation Department, which pays for materials, testing equipment and stipends for the three graduate students.
Danny Straessle, a spokesman with the department, said the team’s project is one of only two university-affiliated research projects currentlybeing conducted in association with the department. The other project, with which Hale is also affiliated, is addressing alkali-silica reactions on Interstate 30 in south Little Rock and is being conducted by University of Arkansas at Little Rock researchers.
Hale said that as the team gathers data on the effects of the sealants on the barrier wall, the results may be applied to the highway pavement in the same location, which is made of the same compounds, but is five to 10 years younger.
As part of the project, Hale said Deschenes and the graduate students will write a paper for publication in one of several peer-reviewed journals in the engineering field, such as ACI Materials Journal or the Cement and Concrete Composites journal.
Deschenes, who said he is pursuing a doctorate in engineering and plans to concentrate on material durability research, said he attended a week-long conference about the alkali-silica reaction in Texas after he was recruited by Hale for the research project.
“The first thing I did was to read several papers and get a good baseline on the literature, as far as what’s been done in the past in similar situations,” Deschenes said. “What’s taught in the classroom is the basics of problems-solving. Actually doing it involves a lot of research of previous methods, and adapting it to your situation.”
Northwest Arkansas, Pages 7 on 05/30/2013