There are generally two kinds of snow melting agents used at home and abroad.

One is an organic snow melting agent with potassium acetate as the main component: this snow melting agent has good snow melting effect and no corrosion damage, but its price is too high, and it is generally used in important places such as airports.

The other is inorganic deicer with "chlorine salt" as the main component, such as sodium chloride, calcium chloride, magnesium chloride, potassium chloride and so on. Commonly known as "deicing salt". Its advantage is low price, which is only equivalent to110 of organic deicer, but it has very serious corrosion to large public infrastructure. Our common snow melting agent belongs to this kind, and sodium chloride (that is, salt) is the most commonly used.

Second, the snow melting principle of snow melting agent

The deicing principle of "chlorine salt" deicer is that its freezing point is below zero after it is dissolved in water (snow). For example, after sodium chloride (the main component of salt) is dissolved in water, its freezing point is-10℃, calcium chloride is about -20℃, and acetic acid can reach about -30℃. In addition to absorbing heat, the dissolution of salt also has a function that the freezing point of salt water is low, so it is difficult to form ice cubes after salt is dissolved in snow water. In addition, after the snow melting agent is dissolved in water, the ion concentration in water increases, which makes the liquid vapor pressure of water decrease, while the solid vapor pressure of ice remains unchanged. In order to reach the solid-liquid vapor pressure state of the ice-water mixture, the ice melted. This principle can also explain why salt water is not easy to freeze.

We read that water is a special substance, that is, the density becomes smaller after freezing (generally, the density is higher in solid state than in liquid state), so the greater the pressure, the lower the melting point of ice. It is often seen that snow melts easily where the wheels run over. After the snow melting agent is sprinkled on the snowy road surface, it is easier to melt the snow after being crushed by vehicles.

To sum up, spraying snow melting agent is beneficial to snow removal.

Third, the harm of snow melting agent

Although "chlorine salt" snow melting agent is convenient to melt snow and remove snow, it is also cheap. However, melted snow or ice turns into liquid and flows into sewer facilities, farmland and so on. , but it is extremely harmful.

1 has dealt a devastating blow to farmland and green belts on both sides of the road.

After using snow melting agent, the green belt or farmland on both sides of the road often snows. After spring, all its salt residues are piled up in farmland and green belts. Crops and trees are afraid of salt, which will cause a lot of deaths and even destroy green plants. Even if replanting, the soil should be changed, especially the farmland in born to die! Its loss is self-evident.

Because the land in the north is generally salty, the plants in the north can resist saline-alkali, even so, it is hard to bear the harm caused by snowmelt agent, not to mention the plants in the acid-loving soil in the south can't bear the harm caused by salt at all.

2. Shorten road life.

Especially for asphalt concrete pavement, salt substances will react with asphalt, which will greatly reduce the retention capacity of asphalt materials and aggregates, cause the asphalt surface to fall off, and then the pavement will be damaged in a large area under the action of traffic load.

When salt meets water, the salt will rise and the road subgrade will be destroyed, which will directly lead to the death of the road and greatly increase the difficulty of road maintenance in the later period.

Salt is also harmful to cement concrete pavement. There is a simple reason. High-cost salt-resistant cement will not be used on the cement concrete pavement side of urban roads.

3, pollute the environment

Salt is the main deicer in common use, but all environmental deicers on the market are deceptive. After salt substances enter the ground, it will inevitably pollute the local groundwater resources, and eating the water polluted by snow melting agent will cause serious harm to human health.

The northern region is suffering from snow melting agent, so don't make the same mistake again!

Appeal, don't let us use it urgently for a while, causing long-term harm! Harm is easy, but governance is difficult!

Whether researchers can develop cheap and harmless snow melting agent is also a test of nature to human beings!

Advantages and disadvantages of snow melting agent

A snowstorm not only brought disaster to people, but also brought many thoughts to people!

Now that the large-scale and high-intensity rain and snow weather has passed, many places have adopted the method of spraying snow melting agent (chlorine salt) in order to speed up the melting of snow and ice.

Let's first look at the principle, advantages and disadvantages of snow melting agent.

Since 1950s, with the development of transportation, the United States and some Nordic countries began to use snow melting agent, and China first used snow melting agent in Beijing in 1970s. The snow melting agent used now can undertake the task of removing snow and melting ice well. Generally speaking, snow melting agent can melt snow in a few minutes.

The deicing agent is deicing salt.

Sanitation workers often refer to spreading snow melting agent as "spreading salt" because the main components of snow melting agent in the past were chlorine salts, such as sodium chloride and calcium chloride. Magnesium chloride, etc. Therefore, the deicing agent was once called "deicing salt". At present, chlorine salt snow melting agent is widely used all over the world (except for a few cases, all mentioned in this paper are chloride salt snow melting agent punishment). Why can deicing salt melt snow? The freezing point of chloride solution is lower than that of water. Taking sodium chloride as an example, the freezing point of saturated sodium chloride solution with a concentration of about 35% is-19 degrees Celsius, and that of sodium chloride solution with a concentration of 20% is-10 degrees Celsius. When sodium chloride solid particles or a certain concentration of sodium chloride solution are sprinkled on the snow, the snow will melt completely due to the heat release of sodium chloride dissolution. If it snows outside, you can take some salt or salt solution and pour it on the snow to see what happens. But we must control the temperature of the salt water. If the water temperature is too high, the ice will melt and the effect will not be seen.

The sea and some salt lakes are rich in chlorine, which makes the snowmelt agent very cheap. To melt the snow on the road, as long as the solid particles of snow melting punishment are scattered on the snow on the road when it just snows, the snow will slowly melt after being squeezed by vehicles. You can also dilute the snow melting agent into a solution according to a certain proportion, and then sprinkle it on the road surface through a sprinkler. In some overpasses and highways, automatic sprinklers are also installed to spray snowmelt solution.

Reinforced concrete destroyer

1972, Britain built 1 1 bridges on an expressway. However, within a few years, the concrete cracked along the steel bar. By the end of 1987, the maintenance cost of these 1 1 bridges was equivalent to 1.6 times the construction fund. 1993, more than half of the 575,000 bridges in the United States were damaged by corrosion, and 40% of the bridges were under-loaded. Denmark, located in northern Europe, investigated 102 bridges in Gefenghagen area, and 50% of the bridges were seriously corroded.

In Beijing, Tianjin and other places, some bridges have also seen this situation: steel bars are corroded and broken, and concrete cracks along the steel bars. In addition to the aging of buildings in Qiao Liang, snow melting agent has also accelerated the corrosion of bridges. The key is that chloride ions react with iron in steel bars, which accelerates the corrosion of iron. The freezing and expansion of water will lead to concrete cracking, and snow melting agent will increase this destructive effect. Generally, water will expand by 9% when it freezes, while water mixed with snow melting agent can expand by 25% when it freezes. Building protection experts call these phenomena "salt damage".

Living in northern cities, it is easy to find traces of salt damage.

Verify the identity of environment-friendly snow melting agent

In the spring of 2003, when everything was revived, 14 Pinus tabulaeformis was found dead in a green belt on Chang 'an Avenue in Beijing. Later, it was identified by the laboratory of Beijing Bureau of Landscape Architecture that it was caused by snow melting agent.

In the past, people were also very concerned about the harm of sodium chloride to bridges and roads, and they were also very careful when using snowmelt agents. In 2002, an environment-friendly snow melting agent came into being, and people thought it would not cause any harm to the environment. As a result, in winter, this environmentally friendly snow melting agent is widely used in Beijing, and even the green belt has snow sprinkled with snow melting agent. The traffic problem was temporarily solved, but in the second year 14 Chinese pine trees died, which made people realize that the so-called environment-friendly snow melting agent would still destroy the urban environment.

The so-called "environmental protection" only adds some rust inhibitors that can slow down the corrosion of steel bars, but as long as the main component of the snow melting agent is chlorine salt, salt damage will exist. For plants, high-concentration chlorine salt solution penetrates into the roots of plants, which will form reverse osmosis, absorb a lot of water from plants and lead to water loss, and be soaked in salt and die.

Snow water with high salt concentration flows underground, which will not only corrode steel bars and damage plants, but also pollute groundwater and corrode underground pipelines.

After recognizing the true face of snow melting agent, in the winter of 2004, the Beijing Municipal Government clearly put forward that "mechanical snow removal is the main method, supplemented by snow melting agent"

How to kill snow and protect the environment?

In western countries, since the 1960s, roads and bridges have been damaged by snow melting agents, so people have restricted the use of snow melting agents scientifically. Our country has also begun to think about quick solutions.

There are two ways to balance snow melting and environmental protection: improving snow melting agent and strengthening protection.

In addition to chloride snowmelt agent, organic salt snowmelt agent is also used. The freezing point of some ethanolamine organic salts is below zero, which has no corrosive effect on reinforced concrete, but the price per ton is more than 6,543,800 yuan, which is unbearable economically. Generally, this expensive snow melting agent is used in airports and other places with special requirements. It is reported that organic salt snow melting agent is used near the White House.

After paying attention to the harm of sodium chloride abroad, there are also relevant requirements for salt prevention when building bridges and roads. For example, the corroded part of the bridge is coated with protective layer to improve the compactness of concrete and prevent chloride solution from contacting the steel bar as much as possible. At present, some bridges use special steel or add antirust agent to concrete. There is also an epoxy resin coated steel bar, which is wrapped with a layer of resin, just like putting a layer of armor on the steel bar to block the contact between chloride ions and iron ions. This measure has been taken in the construction of some bridges in Beijing.