Newly uncovered City of Edmonton memo raises questions about impacts of calcium chloride
A memo from the City of Edmonton obtained by Global News reveals information never publicly released that shows there may be negative impacts to city roads and infrastructure from calcium chloride, the controversial de-icing agent being tested on city roads.
The four-page document, obtained through a Freedom of Information request, contains preliminary results of research that show, for the first time, that the city is aware of the extent of damage that calcium chloride could have on roads and buildings.
The practice of using calcium chloride for de-icing has been contentious in Edmonton, with some city councillors saying they had received complaints from residents of rust and corrosion on vehicles. There has, so far, been no discussion about the impacts on infrastructure.
The study, done by the city in February 2018 with a calcium chloride brine, looked at the impacts of brine exposure to concrete and asphalt. It found a brine-exposed concrete sample was more prone to early degradation and that it was “roughly 20 per cent more detrimental than salt-exposed samples.”
It also found there were more detrimental impacts to asphalt pavement treated with brine than when it was treated with sodium chloride.
The findings align with comments made by three experts Global News spoke with who say calcium chloride is more corrosive and more detrimental to concrete than sodium chloride.
David Darwin, the chair of civil, environmental and architectural engineering at the University of Kansas, researches the effects of de-icers on concrete deterioration. He reviewed the memo obtained by Global News.
“Calcium chloride is more detrimental to concrete under the regular cycles of wetting and drying than, for example… sodium chloride,” he said.
“Because of the relatively more negative effects it has on concrete as a material, you will have increased costs of maintaining your concrete infrastructure because of the damage that it does.”
The memo states brine-soaked asphalt samples had, on average, 12 per cent deeper ruts compared to sodium chloride-soaked samples, and had 1.5 times the mass loss compared to sodium chloride-soaked samples. In both situations, the sodium chloride-soaked samples fared worse than untreated samples.
Darwin said that although calcium chloride works better at lower temperatures, any city can expect increased infrastructure costs if no changes are made to the composition of the concrete.
He said he has seen firsthand that roads in his city of Lawrence, Kansas have damage associated with calcium chloride.
“The key thing is [the city] needs to be aware of the longer-term impact. The relatively better effectiveness of calcium chloride will have an effect on the concrete over a period of time and they need to plan for that, either by modifying the concrete they use… or planning an earlier degradation of the concrete.”
The product, which is applied in a thin layer once per snowfall, prevents the snow from sticking to the pavement, the city has said in the past. The product, which has a lower freezing point than sodium chloride, is meant to make it easier for crews to remove snow from the streets.
Watch below: (From Oct. 9, 2018) After heated debate, Edmonton councillors voted to continue with the calcium chloride pilot project on wintry roads even as corrosion complaints roll in. Kendra Slugoski reports.
Edmonton is in the second year of a calcium chloride snow-removal pilot. The decision pitted councillors against one another over whether extending the pilot was a good idea. A city report from June 2018 found savings of $4.3 million from using the calcium chloride solution.
The city said it was adjusting the solution this winter to include a corrosion inhibitor, however, two civil engineers told Global News that would have no effect on concrete.
‘That will become serious’
David Bastidas, a corrosion engineering professor at the National Center for Education and Research on Corrosion and Materials Performance at the University of Akron, said calcium chloride is more corrosive than sodium chloride, if equal concentrations are compared.
Bastidas, who also reviewed the memo, said the findings in it are concerning.
“That will become serious with time, that’s for sure,” he said.
Bastidas agreed city infrastructure can be vulnerable to corrosion when it comes to calcium chloride.
He said time is of the essence when it comes to the de-icing agent; he recommends consistent corrosion management and a better balance of using sodium chloride and calcium chloride.
“I won’t wait until 10 years. That needs to be controlled, I think,” Bastidas said.
Moh Boulfiza, a professor of civil engineering at the University of Saskatchewan, estimates the detrimental effects of calcium chloride on concrete could be seen two to three times faster than using road salt or another anti-icing agent.
“It can attack the integrity of the concrete and that can lead to some degradation,” Boulfiza said. “If concrete is damaged, there is steel inside that’s supposed to be protected by concrete. [If] the cover is damaged, it will have a faster pathway rather than just the regular pores [of concrete] where permeability is slow.
“It could lead to corrosion problems sooner than we want them to be.”
Boulfiza said there is a cost-benefit analysis that must be done.
“How many interventions will I need to do? Maybe go not with the cheapest, maybe [go with] something [that is] a little more expensive now but will require less interventions over the long-term?” he said.
Response from the city
Janet Tecklenborg, director of infrastructure operations with the City of Edmonton, said the research cited in the memo was done in a lab and does not tell the whole story.
She said the city is doing in-house experiments, jurisdictional reviews of what other cities are using and also collecting field data to determine what is best for residents. She also reiterated several times that the chemical is only one tool in the city’s toolbelt when it comes to snow removal.
“One of the reasons we’re continuing the pilot this year is to understand the trade-offs,” Tecklenborg said.
“The best option for infrastructure and the environment is to do nothing, to not put anything on the roads and not remove the snow — but that’s not an option because we need to keep the roads safe.
“It can’t just be looked at like one isolated component,” Tecklenborg said when asked to respond to the comments that engineering experts made to Global News. “It has to be looked at in a broader perspective of, ‘How — in a winter city — do we maintain mobility throughout the winter?’”
“Anything we do is going to have an impact on infrastructure. The question is, are the safety benefits going to outweigh the potential impacts on infrastructure, and what are those impacts?”
Calcium chloride not used on Edmonton river bridges except for Groat Road Bridge
Emails also obtained by Global News show the city does not use calcium chloride on bridges that cross the river. Rather, the calcium chloride brine is turned off 30 metres before the bridge deck, and crews use sand, salt and mechanical snow removal instead.
Tecklenborg said using the chemical on those bridges could potentially impact the environment, which is why it is not being used there.
However, she said calcium chloride is being piloted on the Groat Road Bridge to understand potential impacts to infrastructure.
Bastidas said the policy with bridges is a good strategy but he still has concerns.
“You will have chlorides also on the bridge because, if cars are crossing, they will probably move some of the chlorides through the bridge. It is impossible to avoid the chlorides on top of the bridges if they are using chlorides,” he said.
COMING UP ON TUESDAY: City councillors react to the newly uncovered memo. That story is coming up on Global News’ television newscasts and online at globalnews.ca
-With files from Global News
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