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Zoe Lallas (M.S. CE ’22, Ph.D. Candidate CE) considers herself an all-out concrete fanatic, and for the past five years she’s found a home among equally concrete-obsessed people in ��ñ��’s Concrete Materials and Structures Laboratory run by Assistant Professor Matthew Gombeda.

She has researched how changing the recipe for concrete impacts properties such as its strength and has been running experiments to gather data, which she has been using to hone simulations aiming to describe how the concrete components hold up under pressure in general and using the results to optimize their design.

Lallas fixated on engineering at an early age. A visit to a Six Flags amusement park when she was in first grade led to a love of roller coasters, and she reasoned that the best way to ride a bunch of roller coasters without waiting in line was to be the person making them.

She carried that dream through high school until she took her first dynamics course.

“I realized I wasn’t really good at the moving parts thing, but I was good at designing things that shouldn’t move and that resist motion,” she says.

As an undergraduate student at Massachusetts Institute of Technology, she found a new focus for her passion: concrete, which was solidified by a research trip to Italy.

“We were looking at Roman concrete. It was framed to me as this big mystery. We don’t know how it became as strong as it is. How do we figure out what went into it?” she says.

By the time she applied to ��ñ��, she was obsessed enough with concrete that her application caught Gombeda’s attention.

“I probably put the word concrete in there at least a dozen times,” she says. “[He] reached out to me personally and gave me an offer I really couldn’t refuse.”

That offer was to work on a big research project studying the use of fly ash in concrete.

“I got even more obsessed with all the concrete stuff than I already was, which I didn’t think was possible,” says Lallas.

She began as a master’s student and within a year decided she wanted to stick around for her doctoral degree.

After the fly ash project wrapped up, she continued to explore how changing the ingredients in concrete impacts its physical properties.

“Concrete is kind of like baking a cake. The stuff that you can put into it is always changing. There’s a lot of manufacturing waste byproducts that get put into concrete for any number of reasons based on chemical composition, sequestering of carbon sources, and available materials,” she says. “What exactly can you put into this, essentially, inedible cake to make it as strong and, I guess the analogy is, delicious as possible.”

Her lab work is essentially recipe testing: she makes concrete cylinders and small un-reinforced beams out of a range of material combinations and proportions, breaks the concrete to test its strength, and then makes 10-plus-foot beams out of the best recipes. The beams then go into a universal testing machine that crushes them to failure while recording data about how the beams hold up.

She then takes that data and uses it to check the computational models that she is working on that aim to mathematically describe the results.

“It’s been fun to be working in the lab, getting my hands dirty, and essentially working with really big LEGOs, and then going back and saying, ‘There’s an equation that governs this, and we figured it out, and we’re looking at the relationship that maximizes the use of all of the different material components in a meaningful way for the industry,’” she says.

Lallas experienced gender bias against her as an undergraduate engineering student and says she braced for more of the same at ��ñ�� but was pleasantly surprised.

“I haven’t had any sort of questioning of my abilities or my capabilities as an engineer. It’s always been like, ‘Obviously, Zoe can do this. We value your input and your thoughts’…It’s been really satisfying to get in the lab and be lifting 100 pounds of cement and [for other people to] just kind of be like, ‘Yeah, Zoe’s got it,’” she says.

When she thinks about the future, Lallas says she finds herself returning to the Roman concrete that started it all: the researchers that Lallas traveled to Italy with have since figured out the solution to its strength, pockets of unground limestone that end up creating a sort of self-healing property. Lallas loves the idea of trying to integrate that idea into modern concrete.

“It’s a lot more difficult in this day and age, because there are higher demands. The Romans would make a single-story structure in the span of 10 years and call it a day, whereas now we’re like, ‘All right, we’ve got to make a 40-story high rise tomorrow,’” Lallas says. “But I think it would be so cool to get back to our roots of making self-healing concrete.”

That is part of what Lallas sees as her role as an engineer: “I think it’s always really important to recognize the bigger picture and the ‘why’ of what we’re working on as engineers to make an impact that exists beyond the end of your specific research journey. It’s been nice to have that be the framing focus for my entire time at ��ñ��. Our lab exists in a vacuum, but we look at the big picture framework of how our work can be applied globally.”