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Microscopic views of concrete made with 100% portland cement (top), and concrete with 80% portland cement and 20% Calera SCMA (bottom), show the density the supplementary cementitious material creates.
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When most of us think about cement, we think of bags, terminals, and grey powder. But it's probably a safe bet that Dr. Brent Constantz is the only one whose expertise with cement has taken him from mending bones to saving the planet with concrete.

Constantz is a Ph.D. geochemist whose initial focus was in the field of medical cement. He founded two companies that manufactured a special cement that enabled physicians to initially set fractured bones in five minutes, and more importantly, sped up the final set by achieving a compressive strength of 15,000 psi in one hour. The medical cement revolutionized orthopedic procedures, providing value to the healing process at a cost of about $200 a gram.

After selling these two businesses and a heart valve company, Constantz became a consulting professor at Stanford University. There, he became affiliated with the Woods Institute for the Environment, with an interest in carbon dioxide sequestration in concrete and the built environment. This opened his eyes to the environmental challenges faced by traditional cement production techniques.

Calling on his experience with medical cement production and enlisting the aid of venture capitalist and Sun Microsystems founder Vinod Khosla, Constantz started Calera Corp. in 2007. He plans to market a process that captures the carbon released during the cement-making process, and to develop a commercially viable byproduct.

This way, the Calera process offers an environmentally elegant solution for creating greener concrete. No carbon is released in cement manufacturing. The resulting byproduct can be used as a recycled material in concrete. The processing unit is an easy add-on, installed at the end of the cement-making process.

Producers can make concrete with a lower carbon footprint by using a supplementary cementitious mineral admixture (SCMA) byproduct, and at the same time, reduce industrial waste. Calera SCMA can replace fly ash and slag as a recycled admixture, or it can be a supplement, with fly ash and slag adding strength and durability. “Rather than competing with cement, Calera SCMA makes portland cement a viable sustainable product,” says Andy Young, Calera's director of applications development and testing.

Fly ash alternative

It may also be ideal for producers who have difficulty finding fly ash sources. Changes in emissions requirements and tighter regulations for coal-fired power plants require scrubber systems and alternative fuels that reduce carbon emissions, but do not yield Class F fly ash. Although fly ash can still be imported, transportation costs add to the carbon footprint.

Calera can also offer performance benefits, where 50% recycled material mixes are specified. Young says a concrete mix using 60% portland cement, 20% fly ash, and 20% Calera SCMA has the same set time, workability, and strength gain as a regular 100% portland cement mix. But it has the same carbon footprint as a mix using 50% portland cement and 50% fly ash. The price of Calera SCMA will be comparable to portland cement.

Calera Corp. will unveil the product at World of Concrete next month in hopes of meeting producers interested in joining a testing group. Young estimates the evaluation process will take six months, and the product will be in full-scale production in early 2010.

Constantz will present a seminar on Calera SCMA at World of Concrete with Terry Holland, a member of Calera's scientific advisory board. The 90-minute seminar, “New Carbon Dioxide Reducing Cementitious Material,” takes place at 3:30 p.m., Feb. 3.

See www.calera.biz, or visit Calera Corp. at World of Concrete, booths #S22325, S22427, and SG22525.