Revamping the nanoscale chemical reactions that cause concrete structures to crack and erode is the focus of promising new research at Stevens Institute of Technology.
Doctoral student Jon Belkowitz is using nanosilica to create a new concrete mixture that will result in longer-lasting sewers, dams, roadways, sidewalks, buildings and other concrete structures, reports Stevens, in Hoboken, NJ.
Focus on Reactivity
Every day, Belkowitz says, these structures crack and erode prematurely due to Alkali Silica Reactivity (ASR), a chemical reaction that causes fissures in the material as it sets. Change the chemical reaction, and you can reduce the fissures, figures the self-avowed “concrete geek,” who is conducting his research at Stevens’ Nanomechanics and Nanomaterials Laboratory.
|Researcher candidate Jon Belkowitz discusses his use of nanosilica to strengthen concrete.|
“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,” he says.
Although Belkowitz hopes to apply his research in civil engineering applications, his multidisciplinary work also takes in solid-state physics, mechanical engineering, polymer synthesis, and chemical engineering.
‘Many Mysteries of Concrete’
On the most basic level, concrete is a mixture of finely-powdered cement, rock aggregate and water, Stevens explains in a release.
A reaction between the cement and water yields calcium silicate hydrate, which gives concrete its strength, and ASR gel. The gel forms at the interface of the alkaline cement and the non-crystalline silica found in the aggregate.
As the concrete hardens, the 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 days to years.
“Using nanostructure characterization tools, we are now able to understand the many mysteries of concrete,” says Belkowitz. For example, he notes, “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.”
The research takes a three-tiered approach: “I’m using this new nanotechnology to not only stop ASR from being produced, but I’m also using nano silica to strengthen the hydrated cement matrix of concrete to resist the expansive nature of the ASR gel,” Belkowitz 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, Stevens notes.
“This is an ongoing problem in the concrete industry,” Belkowitz says, who spent 10 years in the U.S. Air Force placing concrete on civil engineering projects around the world and five years developing new types of concrete for manufacturing giant LaFarge.
“In the past, we really had no way to understand the development of the crystallgraphic grains of the concrete matrix,” he said. “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.”
The research is funded by New Jersey Alliance for Engineering Education (NJAEE), through the National Science Foundation (NSF) Graduate Teaching Fellows in K-12 (GK-12) Program.