Deicing salt is used on roads every winter to improve driving conditions, but the calcium chloride salt commonly used in this application reacts with the calcium hydroxide in concrete, forming a chemical byproduct called calcium oxychloride that causes roadways to degrade, crack, and crumble.
According to a Drexel University press release provided to Phys.org, Yaghoob Farnam, a civil engineer, assistant professor and director of Drexel’s Advanced and Sustainable Infrastructure Materials Research Group, is using cast-off furnace products—fly ash, slag and silica fume—to create a new concrete that is resistant to chemical erosion. He recently published his findings in the journal of Cement and Concrete Composites.
“Many departments of transportation have reduced the amount of calcium chloride they use to melt ice and snow, even though it is very efficient at doing so—because it has also been found to be very destructive,” Farnam says. “This research proves that, by using alternate cementitious materials to make concrete, they can avoid the destructive chemical reaction and continue to use calcium chloride.”
Farnam is working to produce a concrete mix strong enough to build roads, but that contains less calcium hydroxide that reacts with road salt to form calcium oxychloride. His research led him to the conclusion that “supplementary cement materials” could be substituted into the mix to prevent the chemical reaction. Testing his cement mixture against ordinary Portland cement confirmed his theory when samples containing more cement substitute materials did not produce as much calcium oxychloride.
“There is a great push to use these power industry byproducts because they take up space and some of them can be harmful to the environment,” Farnam told the news agency. “We believed that portions of the byproducts such as fly ash, slag and silica fume could be used to make concrete that is both durable and cheaper, because it uses recycled materials.”
“An additional concern is that calcium oxychloride can form even if the concrete is not undergoing a freeze-thaw cycle. It is a chemical reaction that can happen at room temperature, so it can take place when the roads are pre-salted, even if ice doesn’t form. And as the salts remain on the surface after a snowstorm, the reaction will continue to degrade the road, so it is vitally important to minimize this reaction in order to preserve the infrastructure,” Farnam added.
Farnam plans to continue to search for ways to improve the materials used in infrastructure. His lab is currently researching a way to use bacteria to create a protective layer on the surface of concrete that can prevent calcium oxychloride from forming.