MANUFACTURING PORTLAND CEMENT has always been energyintensive and released a significant amount of carbon dioxide (see sidebar below). Recent awareness of this fact has spurred the development of a variety of low-carbon ways to bind aggregate into a high compressive strength block— what we call concrete.
Time will tell whether any of these binders make major inroads into the concrete market, but there are some heavy hitters investing big bucks in these concepts. One important driver will be whether a carbon tax or energy tax is imposed in the U.S. and around the world —many of these ideas are not financially viable without that added bonus.
That may, however, not be true with geopolymeric concrete (GPC), which can directly compete with portland cement. As far back as Roman times, people have used GPC. Some claim the Egyptians built their pyramids with it.
Modern GPC uses mostly fly ash as the binder. Since the manufacturing of portland cement is concrete's major carbon contributor, reducing cement content reduces the carbon footprint—and using fly ash turns an industrial byproduct from waste to a valuable raw material.
An award-winning HTGeopolymer project at Louisiana Tech University has piqued the industry's interest in GPC. Dr. Erez Allouche leads the research into the mechanical properties of GPC, with a focus on commercialization in precast and specialized applications, such as high-end refractory materials.
Allouche explains the reaction "relies on silica- and alumina-rich, thermally activated, materials." Th is could include minerals (like kaolinite, mica, or clay) and industrial byproducts (like fly ash, blast furnace slag, or rice husk ash). "We are making 5000 psi geopolymer concrete from fly ash that is chemically different from high-volume fly ash concrete," he says. "The hardening mechanism is polymerization, not hydration."
The project includes creating and analyzing a national fly ash database to increase its use in GPC. "We have developed a model that can predict fresh properties of the geopolymer paste and mechanical properties of hardened GPC based on the chemical composition of the fly ash," says Allouche.
ASTM International Committees C01 on Cement and C09 on Concrete and Concrete Aggregates are currently discussing performance of geopolymer binder systems, and how standards for these materials can be incorporated into ASTM standards on building performance. (For updates on new, revised, and developing standards, sign up for ASTM's Standards Tracker at www.astm.org.)
Tecnalia, a Spanish research center, and its Nanomaterials in Construction Team (NANOC), are using nanotechnology to make fly ash concrete without portland cement, which sounds a lot like GPC. Tecnalia claims this technology will reduce the energy demand of the cement synthesis process by 50%.
Another entry into this hot field, C-Crete Technologies, won a $100,000 MIT entrepreneurship prize in 2010. Th ey've been tightlipped about what their material actually is, but it also sounds a lot like GPC—with grandiose claims.
The New York Times quoted one of the judges, Dr. Robert Metcalf, as saying C-Crete, "had made a significant discovery as to the nano-scale structure of concrete. They had a method of making concrete that uses less energy, delivers a cost reduction, and ends up being stronger (than portland cement concrete)."
Nanotechnology has been applied to cement and concrete in research projects with some interesting findings. According to AZoNano.com, the A to Z of Nanotechnology resource, Lafarge has funded research at MIT that shows the key to concrete's strength and durability is the organizational structure of nanoparticles. Th us, high-carbon producing constituents of concrete (portland cement) could be replaced with particles that require less CO2 emissions to produce.
See "Future Cement, Part II: Carbonnegative Cement, Converting Carbon, and Recycled Materials" in October's Beyond Green column.
— 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.
The Facts on Cement and CO2
The Portland Cement Association's Concrete Thinker website provides data on the carbon footprint of cement and concrete production , including:
- One ton of CO2 is released for each ton of cement manufactured.
- Global cement manufacturing accounts for 5% of all anthropogenic CO2 emissions (produced by humans). In the U.S., the figure is 1.5% to 2%.
- Producing one cubic yard of concrete accounts for about 400 pounds of CO2, the equivalent of burning 16 gallons of gasoline.
- China produces 37% of the world's cement, India produces 6%, and the U.S. 5%.
- In the U.S., cement production consumes 0.33% of all energy usage.
Beyond Green Links:
Portland Cement Association's Concrete Thinking website http://www.concretethinker.org/technicalbrief/Concrete-Cement-CO2.aspx
Louisiana Tech University professor honored for Technology Product of the Year (May 2012)
ASTM International's Standards Tracker
AZoNano.com, the A to Z of Nanotechnology resource
Tecnalia and Nanomaterials in Construction Team (NANOC) [http://www.aggregateresearch.com/article.aspx?id=19759
C-Crete Technologies wins $100,000 MIT entrepreneurship prize (The New York Times, May 2010)