1. Corrosion hazard of traditional chlorine salt deicing agent to reinforced concrete structure

Lessons from abroad

Chlorine salt snow-melting agent makes a double-edged sword. Due to the low price, while melting ice and snow, it has brought a huge negative impact on roads and facilities, especially corrosion hazards. The corrosion performance of chlorine salt snow melting agents (NACL, CaCL₂/MgCL₂, etc.) is similar, and they are all highly corrosive. After the early western countries used a large number of chlorine salinized ice and snow on roads and bridges, there were (within 5-15 years of use) damage phenomena characterized by steel corrosion. In 1981, 1/4 of the 500000 bridges in the United States received corrosion damage. In 1993, more than 1/2 of the bridges were damaged by corrosion, and 40% of them had insufficient bearing capacity. In recent years, the cost of repairing only bridges in the United States has reached 155 billion US dollars. Infrastructure damage is particularly prominent in Canada due to the widespread use of deicing salts. Repairing all infrastructure damaged by corrosion would cost more than $500 billion. There are also typical cases of being harmed by deicing salt in Britain. For example, in 1972, 11 bridges were built on a 20km long highway. Due to the use of chlorine salt snow melting agent, concrete and steel bars cracked a few years later. The 15-year repair cost was 1.6 times of the bridge construction cost. By 2004, the cumulative repair cost reached 6 times of the bridge construction cost. A large overpass in Berlin, Germany, due to the use of chlorine salt snow melting agent, the service life is less than 20 years, and the steel corrosion damage is serious, so we have to build a new overpass next to it. Taking the Copenhagen area of Denmark as an example, 102 bridges were investigated, of which 50% had serious steel corrosion damage, the main reason is the use of chloride salt ice salt.

Concrete durability is a big problem in today's world, reinforced concrete structure is still the main body of engineering structure, especially large public infrastructure, reinforced concrete is the main material and structural form, and infrastructure is the lifeblood of the country's economy, its durability, enough to affect the national economy and sustainable development. Professor Mehta, a world-renowned expert, pointed out that "steel corrosion is the main reason for the destruction of reinforced concrete structures", and chlorine salt is the main reason for the corrosion of steel.

Current status of snow-melting agent (deicing salt) use in China

At present, our country still use a large number of chlorine salt snow melting agent (early mostly use sodium chloride, recently also use calcium chloride, magnesium chloride, etc.) In the northern part of China, highways, bridges, etc. have the phenomenon of chloride corrosion damage. In fact, where the frequency of chlorine salt high bridge, with the passage of time, there are different degrees of corrosion damage. In addition, chlorine salt also corrodes underground pipelines, surrounding buildings, and pollutes the environment.

2. The appearance and performance comparison of new snow melting agent

The United States, Europe and other Western countries have maintained a leading position in the development and use of snow-melting agents. They have successively introduced a series of organic snow-melting agents and gradually replaced "chlorine salt". They are widely used in airports, highways and other traffic places. Remarkable results have been achieved in the use of salt snow-melting agents and fully ensuring the efficient and safe operation of traffic. The main varieties include calcium and magnesium acetate, biological organic matter, alcohols (ethylene glycol, propylene glycol), carboxylate series (sodium formate, potassium formate, sodium acetate, potassium acetate, potassium lactate, etc.), urea, etc. At present, the use of this series of organic snow-melting agents has gradually begun to be partially promoted and implemented in China.

Organic snow melting agent reflects the complementary nature of different advantages, its main performance is shown in the table below:

Note: In the above table, the comprehensive performance of formate snow melting agent is very prominent, and our company produces Lutong. D environmental protection solid particle snow melting agent and Lutong. K environmental protection solid particle snow melting agent belongs to the formate snow melting agent.

3. Corrosion test comparison of formate deicing agent and traditional chlorine salt deicing agent on steel

Luton. D environmental protection solid particle snow melting agent is a kind of organic snow melting agent, with formic acid as the main component, add a variety of additives to the deicing agent, its melting ice speed, ice ability, only on the corrosion of reinforced concrete structure, relative to the chlorine salt is significantly different. According to GB/T23851-2009 road deicing and snow melting agent (national standard), the road shall be tested. D and chlorine salt on the corrosion of steel were tested, the 20# carbon steel test piece in the deicing agent solution 40 ℃ continuous immersion for 48 hours, the test results are as follows

Test Results of Corrosion Test of Carbon Steel in Snow Melting Agent Solution

4. Test comparison of the influence of several deicing agents on pavement cement concrete

The corrosion of cement concrete by snow melting agent on pavement is a key point in its performance assessment. The following chart is a price comparison chart drawn by testing the corrosion of several deicing agents on pavement cement concrete according to the American standard SHRP H205-8 test method. The test method is the international common method formulated by the Strategic Highway Reseatch Program (SHRP) of the United States. Through this chart, it can be found that the corrosion rate of sodium formate (potassium) and acetic acid on cement is only 1/3 of that of sodium chloride, while potassium acetate is slightly higher than that of sodium chloride.

According to the American standard SHRP H205-8 test method to test the corrosion rate of several deicing agents on the pavement cement concrete.

5. The development direction of snow melting agent

Snow melting agent should have less corrosion on the reinforced concrete of highway, bridge, airport road and other buildings, lower corrosion on vehicles and road facilities, extremely low damage to the environment and vegetation, and low chemical oxygen consumption, low biological oxygen consumption, low water biological toxicity and other characteristics. The SAE-AMS-1431D standard of the United States has fully considered the requirements of snow melting agent for the environment, metal materials and aircraft materials, and countries around the world have used it as the selection standard of airport snow melting agent.

●Chloride salt snow melting agent is low in price, highly corrosive to reinforced concrete, and causes great damage to bridges and highways. It has been widely concerned by the society, and it is an inevitable trend to be eliminated.

● Organic salt snow melting agent has small corrosiveness, many varieties and large price deviation. Different types are suitable for different places: potassium formate and potassium acetate are expensive and are mainly used for liquid spraying and deicing at airports. Ethylene glycol propylene glycol is mainly used for deicing aircraft fuselage. The discharge of biological organic matter into water bodies will lead to hypoxia of aquatic organisms and should not be used in large quantities. High content of urea, easily lead to eutrophication, has been rarely used.

● [Lutong-D] Environmental Protection Solid Particle Snow Deicing Agent and [Lutong-K] Environmental Protection Solid Particle Snow Deicing Agent are mainly composed of formate and added with other additives, which meet all requirements of US SAE-AMS-1431D and 1435C and have high cost performance. They are currently the first choice for deicing snow deicing agents such as airport roads, expressways, bridges and railways.