SINTEF scientists have begun developing an eco-friendly cement – BioZEment – to help reduce our global carbon footprint.
In conventional cement production, limestone is heated to a temperature of 1450 degrees. The process is called calcination and it releases of huge volumes of greenhouse gas (GHG) emissions in the form of CO2.
The emissions double even further when used for building purposes; no less than ten cubic kilometers of concrete (equivalent to the volume of Mount Everest) are used in construction projects every year.
A SINTEF team – led by Simone Balzer Le – has now proposed a new way for creating cement that bypasses the calcination method.
The scientists first started by mixing ground limestone particles and sand in the conventional way. But instead of heating the limestone, specific bacteria are added, which the researchers have discovered close to a limestone quarry in Verdal, Norway.
“The bacteria produce organic acids, including lactic and acetic acid,” explains Balzer Le. “These help to reduce the pH value of the mixture and so partially dissolve the limestone, releasing calcium ions and carbonate.”
“Step two involves mixing sand with another form of bacteria in a mold and feeding this with the prepared mixture of partially dissolved limestone and urea.”
“These bacteria produce an enzyme that splits the urea, which causes the pH to increase again.”
“Under such conditions, calcium is formed together with calcium carbonate crystals, and it is these crystals that act as the binding agent in bacteria-based concrete.”
After drying, the material in the mold becomes a solid.
All these stages are actually an extension of the well-known biogeochemical process known as Microbially-Induced Calcite Precipitation (MICP).
Calcium carbonate precipitates as result of the interaction between natural minerals and bacterial metabolism.
“The advantage of our approach is that both the calcium and the carbonate are derived from the limestone, which enables us to reduce the use of urea compared with another commonly applied form of MICP that obtains its carbonate solely from urea,” notes Balzer Le.
The scientists are now mulling on producing bacteria-based bricks, which they say could cost only about ten percent more to make than standard bricks.
Apart from being recyclable, BioZEment can also be strengthened by reinforcing it with aluminium or timber-derived cellulose fibers.
Image and content: Håvard Egge/SINTEF