Undergraduates aid faculty in the study of a synthetic nano-clay called laponite

Purdue researchers continually innovate how structures are built — and that includes improving the very soil that structures are built upon.

A chief concern when designing structures in areas vulnerable to earthquakes is liquefaction. Liquefaction is a phenomenon in which the strength and stiffness of a soil are reduced by earthquake shaking or other rapid loading. It is a result of the pressure build-up, during shaking, in the water-filled space present between the sand grains. Liquefaction is a common occurrence during seismic events and can lead to catastrophic failure of structures and lifelines.

Clay you can see through

Enter Marika Santagata, associate professor of civil engineering. Together with colleagues Antonio Bobet, Cliff Johnston and Joe Sinfield, Santagata first explored the use of a nano-clay called laponite for treating sand deposits susceptible to soil liquefaction. NSF-sponsored research by PhD student Felipe Ochoa — now assistant professor at the University of Chile in Santiago — provided the first evidence of the effect of laponite in increasing the liquefaction resistance of sands, at least at the lab scale.

Laponite is a synthetic nano-clay that has found application in many industries, from consumer products to electronics. With it, Santagata says, there is great potential for a number of applications — including preventing liquefaction. "Working with this synthetic clay provides a number of opportunities in geotechnical research," Santagata says.

Though referred to as "clay," laponite looks considerably different from clay one would find in the ground. Once mixed with water, the material, which starts as a dry powder, transforms into a clear substance that initially exhibits fluid behavior close to that of water, but, over time, develops a gel-like structure.

"Laponite presents a novel approach to addressing liquefaction," Santagata says. "In its fluid form, the material could be used to infiltrate the ground around existing structures."

Undergraduate researchers

Assisting Santagata in her most recent research on laponite are civil engineering undergraduates Hailie Swanson and Daniel Espinoza and PhD student Amy Getchell. This work is examining how the flow properties of laponite water dispersions can be carefully tailored using dispersants and how such chemical modification affects the structure of the gel formed over time.

Espinoza says it has been a privilege to work alongside Santagata.

"This is definitely something I never would have learned about in class," Espinoza says. "This has been an incredible opportunity to aid Professor Santagata in a pretty new area of study."

Swanson echoed Espinoza, adding that her participation will surely aid her beyond the classroom.

"Having a chance to actively participate in high-level research like this has been great for me — not just for getting exposed to a whole new class of soft materials, but also for my resume," says Swanson, a senior. "Being able to say I've been a member of a research team at Purdue University, and that I have published a paper on my work, has definitely helped me stand out."

For Getchell, this work has provided an opportunity to interact with researchers from other universities. Last summer the work on laponite took her to Politecnico di Torino — one of the top universities in Italy — for a joint study of the material.

Santagata says, "The current study provides insights into laponite behavior relevant to applications well beyond civil engineering."

Once mixed, laponite takes on a clear, gel-like form.