Drexel
engineers have found a way to improve upon ordinary Portland cement
(OPC), the glue that’s bonded much of the world’s construction since the
late 1800s. In research recently published in Cement and Concrete
Composites the group served up a recipe for cement that is more energy
efficient and cost effective to produce than masonry’s most prevalent
bonding compound.
Drexel’s
“green” variety is a form of alkali-activated cement that utilizes an
industrial byproduct, called slag, and a common mineral, limestone, and
does not require heating to produce. According to Dr. Michel W. Barsoum,
A.W. Grosvenor professor in the Department of Materials Science and
Engineering, this alternative production method and the ubiquity of the
mix ingredients, lessens the cost of materials for Drexel’s cement by
about 40% versus Portland cement and reduces energy consumption and
carbon dioxide production by 97%.
“Cement
consumption is rapidly rising, especially in newly industrialized
countries, and it’s already responsible for 5% of human-made carbon
dioxide. This is a unique way to limit the environmental consequences of
meeting demand,” Dr. Alex Moseson, one of the lead researchers on the
project, said.
While
forms of alkali-activated cement have been used as far back as the
1950s and 1960s in several buildings in the former Soviet Union, much of
the inspiration for this research came from the Pyramids in Egypt, as
well as buildings in ancient Rome.
“Our
cement is more like ancient Roman cement than like modern Portland,”
Moseson said. “Although we won’t know for 2,000 years if ours has the
longevity of Roman buildings, it gives us an idea of the staying power
of this material.”
In
contrast to ordinary Portland cement, Drexel’s cement is made of up to
68% unfired limestone, a plentiful, cheap, and low-carbon dioxide
resource; American Society for Testing and Materials’ standards for
Portland cement limit the amount to 5%. To this base, a small amount of
commercial alkali chemical is added along with the iron slag byproduct.
In Portland cement the substitute for this mixture, called clinker, is
produced by firing a number of ingredients in a kiln, thus requiring
more energy and generating more carbon dioxide.
During
Moseson’s work in India to commercialize the technology, he developed
products that meet local standards, using entirely local materials and
techniques. He also investigated how the availability of green cement
could help make quality building materials more affordable and
accessible to marginalized populations living in slums, and create jobs
by jump starting small-scale cement manufacturing in the country.
“Our
results and the literature confirm that it performs as well or better
than OPC,” Barsoum said. “We are very close to having the cement pass an
important commercialization milestone, ASTM C1157, a standard that
judges cement-like products on performance, such as strength and
setting-time, regardless of composition”
The
next step for the cement is getting it to the market, which the group
is working toward via a start-up company called Greenstone Technologies,
Inc.
