Zhu to lead development of monitoring system for ASR-induced cracks in concrete structures

Jinying Zhu, assistant professor of civil engineering at UNL, will lead a team of engineers and scientists from across the country to develop an online monitoring system for evaluation of the health and durability of concrete structures, particularly nuclear power plants, that are affected by alkali-silica reaction (ASR). The research will begin in October 2016.

In 2010, ASR damage was discovered in concrete structures in the Seabrook Station nuclear power plant in New Hampshire.

Since then, research has begun on how ASR affects the safety and capacity of concrete structures. However, there was limited ASR research, and no long-term studies exist on nuclear plants.

Last August, the U.S. Department of Energy (DOE) sent out a call for proposals to evaluate ASR-induced degradation of concrete structures and its effect on long term operation of nuclear power plants. Zhu’s team earned a three-year, $800,000 grant from the DOE’s Nuclear Energy University Program (NEUP) to develop an online monitoring system that evaluates the initiation, extent and rate of ASR degradation, and eventually provide support to plant operators to make long-term operational and maintenance decisions.

ASR takes place when the alkali in cement reacts to the aggregate (sand and gravel) used in a concrete mixture, causing cracks in the concrete that can have a pattern resembling that of a turtle’s shell.

Most often, the ASR reaction is very slow, Zhu said, and the cracks that occur usually happen years, even decades, after construction is complete.

“Just because you have cracks, it doesn’t mean a structure will collapse immediately,” Zhu said.

Those cracks, Zhu said, can allow other detrimental chemicals - such as sulfate and salt - to seep in. Those chemicals lead to damage - like the corrosion of rebar used to strengthen the concrete in buildings, dams, bridges and pavement - that affects the durability of the materials and the long-term capacity of the structure.

Zhu said ASR is often caused by the concrete’s exposure to high temperatures and high humidity. Power plants operate at high internal temperatures and are often built near coastlines and waterways.

To date, no nuclear power plants have experienced a significant incident from ASR-caused cracking in the concrete.

“While our research focuses on building a model that can be used to predict the existence and extent of damage at nuclear power plants – it should be useful in diagnosing problems in any concrete structure,” Zhu said. “As a result, this will help any agency to make a decision about whether the structure is safe.”

To diagnose the affects, Zhu’s team will use both “passive” and “active” sensing techniques to monitor the initiation and development of ASR. Zhu’s previous research has included work with ultrasonic waves, which will be used to evaluate the damage to the concrete.

Other team members will implement “passive” techniques such as sensors that will pick up the sounds created by the cracking and record data that will be used to create models and for other research at the DOE’s Idaho National Laboratory.

Just like ASR is “a slow process,” Zhu knows she will have to be patient to begin research since the grant period begins in two months.

“I cannot call myself a patient person, but in some aspects, I have to be,” Zhu said.

“I’m really excited about this and working with this primary research team. I believe we are going to bring new knowledge to the ASR research field, publish high-quality papers, and have a good opportunity to train graduate students.”