Salt on the roads: is there an alternative?
In the autumn and winter season, Saint Petersburg roads are abundantly sprinkled with technical salt and salt mixtures, and city residents traditionally complain about their shoes being ruined and dogs’ paws irritated by these reagents. However, the harm is not limited to this: the salt also damages cars and historic buildings, and makes the urban environment less comfortable and safe. We discussed the problem with experts from SPbGASU and found out whether it is possible to correct the situation.
Saint Petersburg in winter. Photo by Maria Shvedova
Is salt dangerous?
Aleksandr Pavlov
According to Aleksandr Pavlov, Associate Professor of the Department of Physics and Chemistry in Construction, a salt mixture is used as the main reagent for combating snow and ice in our city. Its main components are sodium chloride (table salt), calcium and magnesium with the addition of sand. The toxicity of these substances is not high, unless the maximum concentration approved by regulatory documents is exceeded.
“However, these mixtures are highly corrosive. They destroy metals and non-metallic materials, including shoe leather,” explains the scientist.
As an ice-control alternative, experts usually mention fine granite chippings. But its functionality is significantly lower: it cannot melt snow and, moreover, clogs storm drains.
Aleksandr Pavlov believes that in theory granite chips can be replaced with anti-icers based on organic compounds, but in practice this is economically unprofitable. “In my opinion, in the near future there is no alternative to salt and sand mixtures,” he summed up.
Svetlana Danilova
The use of salts also affects the ecological well-being of the city. “Salt accumulates in the soil and negatively affects the natural water balance, and therefore the plants. First of all, trees, not adapted to such conditions, begin to suffer,” says Svetlana Danilova, Associate Professor of the Department of Architectural Environment and Landscape Design.
A good substitute for this mixture, Svetlana says, is the same granite chips, but this scenario requires a specially adjusted storm sewer with a filter system. Otherwise, the crumb will clog the sewer, which leads to icing.
Another possible solution is to heat the sidewalks on the main streets of the city. Due to this technology, the snow turns into water and goes into the ground through the tray system. “This is quite costly, but I think that such a large city as Saint Petersburg can afford it,” told Svetlana Danilova.
Maria Klekovkina
This opinion is also shared by Maria Klekovkina, head of the Department of Roads, Bridges and Tunnels. She notes that such technology, among other things, will ensure safety and comfort for car drivers and pedestrians, excluding the freezing and thawing process, and will also increase the service life of the road surface.
"Positive temperatures allow preserving the architectural and aesthetic characteristics of the surface, which is especially important for the winter maintenance of sidewalks, courtyards, playgrounds, sports grounds, pedestrian areas and parking lots," said the expert.
Maria Klekovkina is convinced that it is necessary to build several heated experimental sites to assess the socio-economic indicators. This technology seems to have good prospects for the near future, especially in the urban environment.
How to reduce damage to buildings
Nadezhda Akulova
Nadezhda Akulova, Associate Professor at the Department of Restoration and Reconstruction of Architectural Heritage, believes that the use of salt reagents has a strong negative impact on building facades. “Initially, such a practice was not envisaged in the historic centre, but now the salts penetrate into the foundations and get on the facades,” she notes. The chemical reaction of salts and facade materials causes specific efflorescence, gradually destroying brick, stone and even concrete masonry elements. It may pose additional difficulties in the restoration of buildings.
Nadezhda thinks that transition to using sand or granite chips or the treatment of facades with special protective mixtures may be a solution to the problem.
The chemical activity of the reagents is so high that it harms other structures as well. In 2009, for instance, technical salt corroded wire insulation, having caused an accident at a power substation in the south of Saint Petersburg.
Larisa Matveeva
“Chlorides are relatively cheap, so they are used in large quantities. As a result of their uncontrolled application, our roads and sidewalks are covered with a salt crust," tells Larisa Matveeva, Professor of the Department of Technology of Construction Materials and Metrology.
However, there are chemical anti-icing materials today that are generally believed to have no adverse effect on building structures. These include complex acetate-, formate- and carbamide-based substances and other chlorine-free compositions, as well as chlorine-containing compounds with anticorrosive and bio-based additives.
Larisa Matveeva considers that utility companies must avoid exceeding the permissible concentrations in the formulations. “To reduce the amount of chemicals on the roads, public utilities should fine-tune the mechanism and logistics of snow removal and ensure strict control over the quantitative use of reagents,” the expert added.
…and to transport
Igor Chernyaev
Reagents also negatively affect the technical condition of vehicles, as they trigger corrosion. Besides electrochemical degradation, it may also cause chemical deterioration, affecting non-metallic materials – rubber, plastic, paintwork.
“Such things do happen during motor vehicle operation and this is not something catastrophic; these are ordinary processes we cannot avoid, especially in the conditions of our climate and road maintenance technologies. But we need to protect the vehicles and try to slow down corrosion by washing the car, using high-quality protective and anti-corrosive coatings,” says Igor Chernyaev, head of the Department of Transport Maintenance.
And what about international experience?
Anatoly Kudryavtsev
It is often believed that other countries do not use anti-icing reagents at all in order to protect the environment, but practice shows the opposite. For example, calcium chloride is used in Switzerland; in Norway the main reagent is industrial salt (sodium chloride); in Finland they use a mixture of salt and marble chips. In comparison with other countries with cold climates or occasional snow and ice (they also widely apply salt mixtures), the difference is only in the use of a large amount of sand, while the preferred choice abroad is stone chips.
To neutralize the negative impacts, multicomponent anti-icing reagents are created on the basis of technical salt. Formates are applied as useful additives. Sodium chloride-based anti-icing reagents with formate additives are used at key facilities in Norway.
“Sodium formate not only decomposes in nature into safe components, but also cleans the biosphere from harmful elements. By the way, it is forbidden to use sand and crushed stone on urban roads and busy highways there”, explains Anatoly Kudryavtsev, head of the Department of Water Use and Ecology. The scientist added that the use of sand and salt mixtures entails negative consequences both for sewer networks and treatment facilities, nevertheless, it does not affect the quality of drinking water, as water intake facilities use surface sources.
Text: Anastasia Blinova, Alexandra Podolnikova
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