Concrete may absorb more CO2 than previously believed

May 19th, 2009 - 2:38 pm ICT by ANI  

Washington, May 19 (ANI): A new study has determined that concrete may absorb more carbon dioxide (CO2) than earlier estimates suggested.

Many scientists currently think at least 5 percent of humanity’s carbon footprint comes from the concrete industry, both from energy use and the 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 new study 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.

“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,” she added.

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.

While such changes can be a structural concern for concrete containing rebar, where the change in acidity can damage the metal over many decades, the CaCO3 is actually denser than some of the materials it replaces and can add strength.

Haselbach’s careful analysis of concrete samples appears to show that other compounds, in addition to calcite, may be forming.

Although the compounds remain unidentified, she is optimistic about their potential.

“Understanding the complex chemistry of carbon dioxide absorption in concrete may help us develop processes to accelerate the process in such materials as recycled concrete or pavement,” she said.

“Perhaps this could help us achieve a nearly net-zero carbon footprint, for the chemical reactions at least, over the lifecycle of such products,” she added. (ANI)

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