Engineering professor researches seashell-based cement

A University of Massachusetts Dartmouth professor is using seashells to develop a cement mixture that is both structurally sound and reduces one’s carbon footprint.

Nima Rahbar, assistant professor, Department of Civil and Environmental Engineering, is mixing ordinary cement with seashell waste from the local shellfish industry for potential use as structural supports and in other decorative applications.

Concrete is the glue that holds most construction materials, such as concrete, together. But its production is an energy-intensive process that involves grinding rocks and kilns that can reach temperatures of 1170C, according to Rahbar.

By mixing shells into it, Rahbar said he can reduce the energy used to make the cement and help the shellfish industry at the same time.

“I saw a fisherman who said they have a lot of shells and don’t know what to do with them,” Rahbar said. “They have to pay somebody to get rid of these shells.”

But Rahbar pointed out, studies have shown that seashells are as tough as lightweight biological materials. And, he said, they are economically advantageous because of their wide availability and low cost.

“The industrial use of this material significantly decreases the carbon footprint of concrete by reducing the amount of cement in concrete and consequently decreasing the processing energy,” he said. “It also helps the public health by eliminating the waste materials, and creates technology for the region by establishing (the new cement) as a sustainable structural material.”

Rahbar already has a sample of the material, and is currently performing testing for strength and toughness. He is seeking funding to continue his work, through grants, private industry, or venture capitalist interest.

Rahbar first started studying shells and other materials for a thesis he did at Princeton University, where he earned his Ph.D. in civil engineering in 2008. The theme of his research group is sustainable materials.

He has also studied other materials and has students working on the mechanical processes of bamboo, a material he says has a strength-to-weight ratio that is higher than concrete and steel.

“And in many parts of the world, it grows like a weed,” he said.

He finds many of his ideas by looking at nature.

“You look into nature to see how nature does things, and how can we build materials like that?” Rahbar said of his work. “You are looking to nature, and one of the most amazing materials in nature is actually seashells. These materials are very tough and very light. The idea is (to find out) how nature does it.”

One of Rahbar’s goals is to develop a sustainable multifunctional composite with higher toughness and superior thermal property compared to ordinary composites. He’s been working with a variety of shells, and said conk shells have been the most promising. He is currently working to improve the quality and strength of his material, and has already started the patent process.

Helping Rahbar in the process is a team of UMass graduate students who are working on marketing the material and determining applications for it. The students — Lukas Cavallini, Otilia Gomes and Mackendy Mondesir — created a PowerPoint presentation on the material, calling it “shellcrete”.

Mondesir, who has an undergraduate degree in mechanical engineering and is currently working toward an MBA, said he and the other students also broke down the classes of concrete and their minimum “specs,” such as compressive strength and aggregate size, for slabs and beams, columns, footings, and slab on grade and foundation walls.

http://www.southcoasttoday.com/apps/pbcs.dll/article?AID=/20110531/NEBULLETIN/106010317/1036

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