Editor's note: This two-part article explores the latest technologies in developing low- and carbon-negative cements. Part One was published in the August-September 2012 issue.
THE NEED TO reduce CO2 emissions has led to the development of many new cementitious materials—a trend that will likely continue for the foreseeable future. But the powerful international portland cement business hasn't given up yet.
Lafarge Canada is producing low-carbon Contempra cement with up to 15 percent limestone content, with plans to introduce it in the U.S. Some work on limestone replacement has increased the content up to 35 percent.
Portland cement isn't going away anytime soon, but new technologies will undoubtedly continue to chip away at its market share. Following are examples of what's coming.
Novacem, a British company, converts magnesium silicate into magnesium oxide, which then carbonates (reacts with CO2 in the air) as it hardens. The company claims that three-quarters of a ton of CO2 is sequestered for each ton of Novacem used. One hang-up may be that although huge sources of magnesium silicates are available, they are not spread evenly around the globe.
Sika Corp. has partnered with Ash Improvement Technology (AIT), which uses a patent-pending CleanCem process at power plants to convert fly ash into a “chemically modified product that mimics the behavior of cement.” The process adds sorbents during post combustion in the boiler and exhaust system, so ash is never created.
Attributes of the resulting byproduct can be altered by varying the types of sorbents, particle sizes, and dosages, but AIT claims the abundant product can reduce concrete's carbon footprint and increase late strength, without the environmental hassles of fly ash.
Even more companies are developing cementitious materials—including Calix calcined products, alumina silicate-based Blue World Crete, and Eco-Cement blended cement with reactive magnesia—any of which could turn out to be the cement of the future.
CarbonCure Technologies in Canada has designed a system to make low- carbon concrete masonry units on a large scale. The process captures CO2 gas in the block as solid limestone as it cures.
It is said to use 10 percent less cement and produce 20 percent less waste than traditional methods, while reducing greenhouse gases by 20 percent and energy use by 38 percent. CarbonCure is now under development for precast panels and pipe. (See “The Evolving World of Green Concrete,” TCP April/May 2012.)
At George Washington University, researchers are using sunlight to make lime for cement without producing CO2. The process uses heat and electrolysis to produce oxygen and carbon or carbon monoxide, rather than carbon dioxide, during lime production. The researchers have reduced about 60 percent of the CO2 generated.
Fly ash and other recyclables
Pozzolanic cements boast benefits such as enhanced concrete durability and rapid set times, in addition to using large amounts of fly ash. Ceratech Inc., of Baltimore, produces carbon-neutral cement that contains 95 percent fly ash, combined with chemical activators, that replaces all of concrete's portland cement with recycled material. These cements create a paste of fine, inert materials for a more dense concrete that resists chemicals and heat.
French manufacturer RVA makes a 70 percent alumina material from salt slag—a byproduct of the aluminum refining industry. Valoxy replaces bauxite during clinker production and forms calcium aluminate. Its fluorspar content also helps form a calcium fluoride/calcium aluminate-based mineral during production. The benefits: a consistently priced material; reduced energy costs due to lower burning temperatures; potentially reduced cement set time; and fewer nitrogen oxide emissions.
Research is underway at Sherbrooke University in Quebec on using finely ground recylced glass as a binder. This material can be blown into a kiln to produce spherical glass particles that are simlar to fly ash.
As you can see, the effort to come up with alternative cements is widespread and ambitious, mostly with the aim of reducing the carbon footprint. But we need to be very careful in doing this so we do not compromise concrete's quality. You probably aren't dropping portland cement from your mixes just yet, but the day may come.
— Guest columnist Bill Palmer is editor in chief of TCP's sister publication, CONCRETE CONSTRUCTION, and editorial director of Hanley Wood's Commercial Construction Group.
Beyond Green Links:
“Cleaning Up Concrete,” Architect (Aug. 2012)
Manufacturers and researchers are pursuing three tactics to reduce the environmental impact of the world's most widely used manmade material.
"The Evolving World of Green Concrete," The Concrete Producer (April/May 2012)
Green products and technologies create a buzz at concrete's big event.
CleanCem - Ash Improvement Technology (AIT) converts fly ash to a cementitious material
"New Cement-Making Method Could Slash Carbon Emissions," Technology Review (May 2012)
George Washington University researchers use sunlight to make lime for cement without producing CO2.
Fly ash and other recyclables
"Cement for Severe Environments," Concrete Construction (Feb. 2012)
New cement chemistry creates concrete that withstands chemical attack and high temperatures.
Valoxy - RVA creates an alumina material made from salt slag - a byproduct of the aluminum refining industry