|
|
Pozzolans vary widely in color. Shown here, left to right, are fly ash, metakaolin, silica fume, fly ash, slag and calcined shale. Image courtesy of Portland Cement Association.
November 2008 Vol. 8 No. 7
Greener Cement
By Loretta Hall
Since manufacturing portland cement damages the environment, more and more concrete makers are giving alternatives a chance.
According to the LEED certification system, concrete has several green qualities, including a long lifetime and recyclability. Portland cement, one of concrete’s primary ingredients, is another story.
Making portland cement starts with environmentally destructive ore mining. That’s followed by heating the crushed ore to 2,650 degrees Fahrenheit, a process that consumes an average of 4.6 million BTUs of energy per ton of cement. Manufacturers are reducing that energy demand by improving their processes. “Between 1972 and 2006, they’ve reduced their total energy consumption by 37.3 percent per ton,” says Terry Collins, a concrete construction engineer with the Portland Cement Association. “And they’re recycling waste for use as fuel — tires, paints and solvents, polymers, anything that will burn with a very high BTU rating.”
|
|
|
|
|
|
