'Green' cement modeled on Roman buildings

Posted by Kate Taylor

Engineers have found a way to cut the CO2 and energy footprint of cement by 97 percent - and the recipe's much cheaper, too.

A Drexel University team has created an alkali-activated cement based on  an industrial byproduct, slag, and simple limestone, and which doesn't require heating to produce.

They say their alternative production method and the cheapness of the ingredients makes their version 40 percent cheaper than Portland cement.

"Cement consumption is rapidly rising, especially in newly industrialized countries, and it's already responsible for five percent of human-made carbon dioxide," says researcher Dr Alex Moseson.

"This is a unique way to limit the environmental consequences of meeting demand."

While forms of alkali-activated cement have been around in the former Soviet Union since the 1950s and 1960s, the team was more directly inspired by the pyramids in Egypt, as well as buildings in ancient Rome.

"Our cement is more like ancient Roman cement than like modern Portland," says Moseson. "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 percent unfired limestone, a plentiful, cheap, and low-carbon dioxide resource. 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.

"Our results and the literature confirm that it performs as well or better than OPC," says Dr Michel W Barsoum.

"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 team now hopes to get it to market through a start-up company called Greenstone Technologies.