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As a ubiquitous material that provides the literal foundation of modern urban landscapes, concrete has a major influence on construction practices, costs and environmental impact. However, at the fundamental level, concrete chemistry has remained strikingly similar to what was used by the ancient Romans. Now, researchers are capitalizing on nanotechnology to innovate a new generation of concrete materials that meet the demands of an aging infrastructure and a more sustainable society.
Every day, concrete structures crack and erode prematurely due to alkali silica reactivity (ASR), a chemical reaction that causes fissures in the material as it sets. Jon Belkowitz, a concrete expert and doctoral student at Stevens Institute of Technology, aims to put an end to this problem through his study of chemical reactions within concrete at the nanoscale. Taking advantage of Stevens' nanostructure characterization tools and materials, his research into the optimal use of nanosilica will create a new concrete mixture that will result in longer-lasting buildings, roadways, sidewalks, stairs, sewers, and dams.
"With the advent of nanotechnology, the material properties of concrete, including ASR mitigation, allows engineers and architects the ability to use concrete in applications that were once impossible," Belkowitz says.
Understanding ConcreteOn the most basic level, concrete is a mixture of finely powdered cement, rock aggregate and water. A reaction between the cement and water yields calcium silicate hydrate, which gives concrete its strength, as well as ASR gel. The ASR gel forms at the interface of the alkaline cement and the non-crystalline silica found in the aggregate. As the concrete hardens, the ASR gel expands, causing residual stresses that weaken the concrete and cause it to deteriorate. As pressure builds at the interface, the concrete starts to crack and crumble from within, over a period spanning from days to years.
"Using nanostructure characterization tools, we are now able to understand the many mysteries of concrete, for example, that there are three types of water in hydrated concrete, and those three different types of water have three different types of molecular movements, which means three different forces," Belkowitz says. According to Belkowitz, the more you know about concrete, the more complex it becomes. He hopes his research will uncover new methods of increasing the mechanical properties of concrete.
Research SpecificsBelkowitz's research takes a three-tiered approach. "Not only am I using this new nanotechnology to stop ASR from being produced, I'm also using nanosilica to strengthen the hydrated cement matrix of concrete to resist the expansive nature of the ASR gel," he explains. "I'm also trying to change the properties of the excess water within the concrete so that it can't react with soluble alkalines in silica to cause ASR gel."
Despite the material's ubiquity, the reactions within concrete as it dries and strengthens are difficult to control. "This is an ongoing problem in the concrete industry," Belkowitz says. "In the past, we really had no way to understand the development of the crystallgraphic grains of the concrete matrix. We could set up models, or use other minerals to compare to calcium silica hydrate. We don't create the same structure every single time. Through the use of nanostructure characterization tools, we now have the ability to gain a better understanding of the hydrated cement matrix that makes up concrete."
Belkowitz has 15 years of concrete experience: 10 years in the U.S. Air Force placing concrete on civil engineering projects around the world; and five years at LaFarge, where he designed new types of concrete in a lab and translated these into products with real-world applications. Currently, he owns Intelligent Concrete LLC, which is dedicated to concrete research, development and education.
Belkowitz's research is being conducted in the Nanomechanics and Nanomaterials Laboratory under the guidance of Frank Fisher, Ph.D., associate professor of Mechanical Engineering and co-director of the Nanotechnology Graduate Program. Though Belkowitz says he hopes to apply his research in civil engineering applications, his work is multidisciplinary, combining solid-state physics, mechanical engineering, polymer synthesis and chemical engineering.
Belkowitz's research is funded by the New Jersey Alliance for Engineering Education (NJAEE), through the National Science Foundation (NSF) Graduate Teaching Fellows in K-12 (GK-12) Program. He works in a local high school in Bayonne, NJ, for 10 hours a week as part of the program, and says he enjoys the opportunity to share his passion with students. "It's exciting to open up their minds to new possibilities," he says. "They eat it up."
This wide-ranging experience reportedly allows him to converse equally well with scientists, business and laypeople. It also gives him a realistic approach. "One of the hardest things to do in the concrete industry-or in any industry-is to take lab data and translate it into commercial industry," Belkowitz says. "In the lab you have nearly perfect conditions. In the real world, it's messy."
As he looks to the future, Belkowitz says he is confident that his work at Stevens studying the smallest reactions within concrete will yield big rewards in the future.
For additional details, visit www.stevens.edu/ses/me.