When calcium chloride de-icer is spread on sidewalks or roads, it reacts with the calcium hydroxide in concrete, creating calcium oxychloride. Also known as CAOXY, this substance expands within the concrete, causing it to crack. Adding bacteria, however, may keep that from happening.
Led by Drs. Yaghoob Farnam, Christopher Sales and Caroline Schauer, scientists at Philadelphia's Drexel University started with a strain of bacteria called Sporosarcina pasteurii. Utilizing a process known as microbial induced calcium carbonate precipitation, that microbe is able to convert calcium chloride into calcium carbonate, which is a natural cement.
The researchers proceeded to mix S. pasteurii with a type of cement commonly used in roads, along with the nutrients required by the bacteria. The result was a series of concrete samples, which were exposed to a calcium chloride solution for a period of 28 days.
When subsequently compared to samples of traditional concrete that had also been subjected to the de-icer, the bacteria-laden samples were found to have much lower levels of CAOXY – this was because by converting the calcium chloride to calcium carbonate, the bacteria kept it from being available to react with the calcium hydroxide.
Additionally, by analyzing the special concrete's micropores and the manner in which it reacted to acoustic vibrations, it was determined that the material had experienced virtually no deterioration. In fact, it's possible that the formation of calcium carbonate within the concrete could actually boost its strength.
And as an added bonus, because S. pasteurii occurs naturally and is non-pathogenic, concrete that contains it shouldn't pose any environmental or health risks.
A paper on the research was recently published in the journal Construction and Building Materials.
Source: Drexel University
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