Drexel University researchers developed a method on how to make infrastructure stronger.
Roads are kept safe for travel by adding chemicals to prevent formation of ice and accumulation of snow. An example of these road salts is calcium chloride that can also bring road surface deterioriation and potholes. Concrete is broken down when chemicals react with it and the water in ice and snow to form CAOXY, calcium oxychloride, that produces internal expansions and distresses.
The team from Drexel's College of Engineering recently published their findings in the journal Construction and Building Materials. They demonstrated that CAOXY can be stopped in its formation by mixing concrete with a bit of bacteria.
Yaghoob Farnam, PhD, Christopher Sales, PhD, and Caroline Schauer, PhD were studying Sporosarcina pasteurii, a strain of bacteria that can induce a chemical reaction to produce calcium carbonate. Only a number of bacteria can perform this "biomineralization" or microbial induced calcium carbonate precipitation.
S. pasteurii has been the subject for various researches such as repairing cracks in statues and concrete infrastructure, making bricks in a sustainable amnner, as well as prevention of formation of cracks.
"We were actually looking at the end product of a chemical reaction involving these bacteria - calcite - but we came to realize that the way they produce it could be quite useful when it comes to diverting the reaction that turns road salt into a road-deteriorating compound," Farnam said. "We knew the bacteria require calcium chloride to produce the calcite, which is a harmless compound. So if we could work out a way to have the bacteria present when the calcium chloride road salt hits the concrete it could interact with the bacteria and curtail the reaction that causes road degradation."
The scientists conducted an experiment by making concrete samples using the kind of cement commonly used in roads. S. pasteurii and other nutrients were mixed with the concrete. Road treatment was simulated for 28 days by exposing the mixture to calcium chloride. Structural integrity and the amount of CAOXY present were tested.
The strength of the sample can be measured through the acoustic vibrations and the development of micropores in the mortar sample. The researchers were able to find out that the concrete with bacteria mixture did not experience degradation after calcium chloride exposure.
Moreover, CAOXY levels were lower with the bacteria mixture. This implies that the microbial induced calcium carbonate precipitation can also be used to strengthen the road surface.
"The bacteria are capable of changing the micro-environment around them," Sales said. "Specifically, they create a high pH environment by converting the chemicals in the nutrient slurry into a weak base, ammonia. This environment promotes the precipitation of calcium ions and carbonate ions into calcium carbonate- rather than the formation of CAOXY."
"Because the bacteria occur in nature and are non-pathogenic, they would be an environmentally safe solution to the problem of road deterioration. Sales and Farnam are hoping to push this work to the next level by collaborating with local and national departments of transportation for additional testing and development," according to Eureka Alert.
