What substances can be added to concrete to prevent corrosion?

Anti-corrosion coatings for concrete.

Summary. Kissing, corrosive cementitious material - hardened cement slurry, which can corrode concrete.

Kissing, corrosive cementitious material - hardened cement slurry, which can corrode concrete.

The hardened cement slurry is mainly composed of cement hydration reactions, producing the clan substances, silica kernels, calcium moganate, gel, calcium hydroxide, calcium sulfoaluminate, etc. For low-strength concrete, without mineral admixtures (mineral fines, fly ash, silica fume), the cement hydration products have a high calcium hydroxide content and high permeability, and the use of low concentrations of acids and sulfates can effectively corrode calcium hydroxide. For high-strength and mineral-mixed concrete, the use of hydrofluoric acid to corrode is faster than several bridges.

Hydrofluoric acid is effective in breaking down calcium silicate gels. The intrinsic conditions that affect the velocity, range, and results of the migration of water, gas, and harmful dissolved substances in the pores are the pore structure and crack form of the concrete. The strength, deformation, shrinkage, deformation, penetration, frost resistance, migration and various erosions of concrete after induration are all closely related to pores, and it can be said that the internal pores of concrete determine the material properties of concrete.

The corrosion of coagulation by groundwater is divided into three categories, crystallization, decomposition, and crystallization decomposition.

Crystalline corrosion is mainly able to generate hydrated calcium sulfur aluminate, and the increase in volume produces great internal stress in concrete. Sulfate ion is the evaluation index of crystalline corrosivity.

This paragraph breaks down the class.

The corrosive carbon dioxide content is too high and the bicarbonate ion content is too low, the more corrosive it is to the concrete. Bicarbonate ion is the evaluation index of decomposition corrosivity.

This section is a crystalline decomposition class.

It is also known as crystalline composite corrosion. When the content of ammonia, nitrate ions, chlorine and magnesium ions in groundwater is excessive, the corrosive effect occurs with calcium hydroxide in concrete.

Answer]: B Tips: General acids can cause the corrosion of cement mortar and mixed Dongchang concrete, but a few types of acid buckets such as grass trembling acid, tannic acid, tartaric acid, hydrofluoric acid, phosphoric acid can react with Ca(OH)2 to generate insoluble and non-expansive calcium salt, which has no corrosive effect on mortar and concrete.

Concrete is a porous structure, carbon dioxide, water vapor can enter the inside of the concrete through the void, concrete is alkaline, contains calcium oxide and other substances, will react with carbon dioxide, water to produce salts, over time the salt substances accumulate more and more, will crack the concrete.

The inside of the concrete is reinforced, and the cracked concrete makes it easier for water vapor and corrosive medium to enter, corroding the rebar and weakening the rigidity of the concrete structure. Therefore, not only the concrete should be anti-corrosion, but also the internal steel bar.

Generally, steel bars use cold galvanized paint, inorganic zinc-rich primer and other coatings for anti-corrosion.

The concrete is coated with epoxy sealing primer, epoxy micaceous iron intermediate paint, fluorocarbon paint, acrylic polyurethane topcoat, etc.

When the concrete structure is anti-corrosion, it should be treated in accordance with the provisions of Article 1 of the GB50212-2014 "Building Anti-corrosion Construction Code".

1. For C40 and above concrete, shot blasting, sand blasting, and high-pressure jet treatment should be used to treat the base layer.

2. C30-C40 concrete should be treated with shot blasting, sandblasting, high-pressure jet and grinding.

3. C20-C30 concrete should be treated with shot blasting, sandblasting, high-pressure jet, grinding, grinding and milling.

4. Concrete below C20 should be treated by grinding, high-pressure jet, milling and grinding.

Concrete material is a durable material, but it is essentially a non-uniform porous material, under the erosion of carbon dioxide, water, chloride ions, sulfate and other media, it is inevitable to be affected by external factors and corroded, concrete will accelerate the damage, and the service life is greatly shortened.

Crystallization corrosion of salts.

When the concrete comes into contact with water containing a large number of soluble salt compounds, these salt compounds will penetrate into the concrete Concrete porous bricks, after the evaporation of water, the salts continue to concentrate in the concrete, and finally form crystals, and the crystallization process is often accompanied by an increase in volume. As a result, cracking and damage of concrete materials are caused. Typical is sulfate corrosion.

In the use of concrete materials, the most widespread and common form of chemical corrosion is sulfate corrosion. The sulfate reacts with the calcium vanadium stone in the cement to form sulfoaluminate, which is accompanied by an increase in volume, resulting in cracking of the concrete material. This cracking further accelerates the corrosion of the concrete matrix by the sulfate.

Diafiltration and salt frost corrosion.

When moisture can seep out of the concrete surface, salt frost will always appear on the concrete surface. These salts are crystallized by evaporation of concrete, or by interaction with atmospheric carbon dioxide. It shows that obvious percolation occurs inside the concrete, and severe percolation leads to an increase in porosity, which reduces the strength of the concrete layer and increases the effect of corrosive compounds.

Acid and alkali corrosion concrete material is an alkaline material and generally does not suffer from corrosion by alkaline substances. However, in chemical companies, prolonged exposure to high concentrations of alkaline substances can also cause damage to concrete materials. Concrete materials are less resistant to acids.

For example, carbonic acid reacts with calcium hydroxide to form soluble calcium bicarbonate. Therefore, carbon dioxide is more corrosive to concrete, that is, the cause of carbon dioxide in the air to corrode concrete materials.