Drexel engineers have developed a cement that is more energy efficient and cost effective to produce than the more common Portland cement, according to a Feb. 20 Drexel press release.
The research, which was published in “Cement and Concrete Composites,” was produced by a group of Drexel professors and alumni that founded Greenstone Technologies Inc. in 2008. Their goal is to commercialize their research on the more environmentally friendly material, an alkali-activated composition known as AAC. Michel Barsoum, a professor in the materials science and engineering department, and assistant professor Alexander J. Moseson have worked with Aaron Sakulich, who has a doctorate in materials engineering from Drexel, and Sean Miller, who graduated in 2011 with an undergraduate degree in biological sciences.
AAC consists of slag, which is an industrial byproduct, and 68 percent limestone, which is common, cheap and contains a low amount of carbon dioxide. AAC also emits 97 percent less carbon dioxide compared to Portland cement. A small amount of commercial alkali chemical is added with the slag product, and the entire process requires very little heat in comparison to the more common Portland cement, which is fired in a kiln that requires a large amount of energy and produces a great deal of carbon dioxide. Portland cement also contains only five percent limestone and uses a substitute mixture, clinker, which is formed by heating limestone, clay, bauxite and iron ore in the kiln.
AAC also recycles materials as it uses the industrial byproducts of slag and fly ash in the production process. Additionally, it costs half as much to make AAC as it does to make Portland cement because AAC uses less heat. In terms of the environment, every ton of Portland cement production results in a ton of carbon dioxide emissions.
Three billion tons of carbon dioxide were emitted from cement production in 2010 alone. Carbon emissions from the production of cement make up five percent of human-made carbon dioxide. With increasing industrialization in developing countries, these carbon dioxide emission statistics are increasingly relevant. Plus, AAC is naturally white, which makes it even more valuable in the market.
The difficulty of marketing this cement is convincing the world that it is better than Portland cement, which has been used and trusted for the past 200 years.
“Even passing those tests, it’s an uphill battle. It’s a political battle more than anything” Barsoum said. “We don’t have an important ingredient: longevity.”
AAC cement can be used in multiple ways, including mortars and concretes, and it can also replace ordinary Portland cement in roads, buildings and specialty work. However, it could also be used, among other projects, for the construction of back porches, driveways and sidewalks.
“If we can get it in some niche application, I’ll be happy,” Barsoum said.
His interest in cement began in 2002 when he heard a rumor that the Egyptian pyramids were cast in cement on their outer layer. He received samples taken from the pyramids to decide for himself.
Four years later, he announced in the Journal of the American Ceramic Society that some of the blocks were suspicious and did not appear to be natural. He is still continuing this research.
“A small percentage, 10 percent, if not less, were cast by cement, especially by the top,” he said.
Sakulich began working with Barsoum on the research, and they discovered that there were only four ingredients to the Egyptian cement: limestone powder, water, lime and diatomaceous earth, a naturally occurring sedimentary rock that crumbles into a fine white or off-white powder. Miller confirmed this formula for the Egyptian cement. Their experimentation is directly related to the discovery of AAC.
“It led us to think that if the ancient Egyptians could make a cement out of nothing and very little equipment, what could we do today to make cement that is more sustainable?” Moseson said.
The researchers began by replacing the diatomaceous earth, which is abundant around the world and is present in the United States, especially in New Mexico and Nevada, with iron slag. They then replaced the ingredient of lime with sodium carbonate. Moseson also worked on developing the cement into a hydraulic version like Portland cement that would harden by itself because of its water content.
AAC is still more similar than modern Portland cement to the cement the ancient Egyptians used. Additionally, a few buildings in Ukraine were built during the 1960s using cement similar to Drexel’s AAC variety. Thus far, AAC seems to be very durable, and the same is expected for Greenstone, which can hold in environments such as harsh marine, freeze-thaw, acidic, and others.
Because of this close similarity, the research team has an estimate of the cement’s sustainability over time. Greenstone Technologies Inc. expects to have its cement pass the ASTM C1157 standard for U.S. markets, which judges the cement on its strength and setting time.
“The good thing about this cement is that you only need to blend it. You don’t need to invest in a multimillion-dollar kiln the size of a football field that has to be maintained 24 hours a day by people with advanced degrees,” Moseson said.
He was inspired to create affordable, environmentally friendly materials during his time at the Indian Institute of Technology Bombay in Mumbai from June to December of 2010. The purpose of the trip was to investigate how the green AAC could make building materials more affordable and accessible to those living in the nearby slums.
During this time he worked on developing AAC products that could be used in an industrializing country and also be sustainable for a local environment in an industrializing country. Using only local materials and techniques, Moseson developed three different strengths of AAC.
“They really liked the idea of cement that was cheaper and more accessible,” he said.
His dedication to using science and technology to meet human needs started after he helped to gut a house that was destroyed by Hurricane Katrina.
“That put me on a path to think about what I could do as an engineer. If breaking things down was that valuable, what could I do in building things up?” he said.
Moseson became focused on the use of technology to promote development and especially overcoming global poverty, which led him to co-found Drexel’s chapter of Engineers Without Borders and later join Barsoum in research.
Since the creation of the company, Greenstone Inc has won over $100,000 in grants from the U.S. Environmental Protection Agency and other investments.Partnerships are in place with a concrete design and building firm as well as several universities. Following collaboration with IIT Bombay, a standards-compliant product line is ready for the Indian market. Products for the U.S. market are in development, and discussions on commercialization are in progress with several manufacturers and investors.