Many scientists currently think at least 5 percent of humanity's carbon footprint comes from the concrete industry, both from energy use and the carbon dioxide (CO2) byproduct from the production of cement, one of concrete's principal components.
Yet several studies have shown that small quantities of CO2 later reabsorb into concrete, even decades after it is emplaced, when elements of the material combine with CO2 to form calcite.
A study appearing in the June 2009 Journal of Environmental Engineering suggests that the re-absorption may extend to products beyond calcite, increasing the total CO2 removed from the atmosphere and lowering concrete's overall carbon footprint.
While preliminary, the research by civil and environmental engineering professor Liv Haselbach of Washington State University re-emphasizes findings first observed nearly half a century ago--that carbon-based chemical compounds may form in concrete in addition to the mineral calcite-now in the light of current efforts to stem global warming.
"Even though these chemical species may equate to only five percent of the CO2 byproduct from cement production, when summed globally they become significant," said Haselbach. "Concrete is the most-used building material in the world."
Researchers have known for decades that concrete absorbs CO2 to form calcite (calcium carbonate, CaCO3) during its lifetime, and even longer if the concrete is recycled into new construction--and because concrete is somewhat permeable, the effect extends beyond exposed surfaces.
It's decades away most likely, but it's an interesting idea all the same.
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