A concrete path to sustainability
- PDF / 295,328 Bytes
- 2 Pages / 585 x 783 pts Page_size
- 53 Downloads / 222 Views
•
Energy Sector Analysis
Cement production involves low energy, but its carbon footprint is high. The key to reduction is in the clinker.
A concrete path to sustainability By Prachi Patel Feature Editor José Fernando Martirena Hernández
T
hat tourists can still admire the Colosseum and Pantheon built by Roman engineers 2000 years ago is due in large part to the material holding these impressive structures together: cement. In generic terms, cement is a binder that locks together other materials. The highest-quality Roman cement was a mix of burnt lime (calcium oxide) and volcanic ash. The material’s present-day incarnation typically implies “Portland” cement, made by heating limestone (calcium carbonate) and clay in large kilns. Combined with sand and gravel, it makes concrete, the material produced in modern day more than any other. As with anything made on a colossal scale, its environmental impact is fast becoming a concern. The cement industry is by no means an energy hog. Producing cement in the United States consumes 0.33% of the country’s energy, less than the 1.8% used to make steel, according to the Department of Energy. But the carbon dioxide emissions from cement production are not in proportion with the energy used to make cement. Making every ton of cement emits roughly 0.8 ton of CO2, and cement production accounts for 8% of global carbon emissions. The pressing concern is that the current use of cement to make concrete is ballooning. Urbanization is rapidly increasing worldwide, especially in developing countries like China, which produces over 57% of the world’s roughly 4 billion tons of cement. As sidewalks, buildings, and bridges sprout at an accelerating pace, the world could produce up to 4.8 billion tons by 2050, according to the International Energy Agency. Producing cement sustainably is necessary if societies are to continue growing. Governments, industry, and researchers are already aware of this need, and are working—in many cases together—toward this goal. “Around half of all materials we make is concrete,” said Karen Scrivener, a materials science and engineering professor at the Swiss Federal Institute of Technology in Lausanne. “Because there’s so much used, emissions improvements can have a very big impact.” Despite its massive use and long history, cement is one of the most complex materials known. Scientists still do not fully understand its structure and the chemical reactions that happen when it is mixed with water.
The Portland cement-making process requires burning limestone and clay at 1450°C. This drives out CO2 from the limestone to give lime and results in golf ball-sized pellets, called clinker, that are ground to give the familiar gray powder. Converting limestone to lime results in 60–65% of the carbon emissions from cement manufacture; the rest comes from burning fuel to fire the kilns and the electricity used to grind clinker. For decades, the industry has been chipping away at cement’s energy use by making kilns more efficient and using alternative energy sources
Data Loading...
