Main varieties and properties of concrete rust inhibitors
In reinforced concrete structures, due to the strong alkali content of the concrete itself (pH>12). At the same time, steel bars generally undergo “passivation” treatment to form a Fe2O3 protective film with a thickness of several hundred nanometers on the surface of the steel bar, which is called a passivation film. Steel bars are not easy to develop when tightly wrapped in concrete. Rusty. When the chloride ions in the concrete exceed a certain amount, the hydrogen ions enter the concrete and reach the surface of the steel bar. When it is adsorbed on the local passivation film, the value there can be rapidly reduced, causing the purification film to be rapidly destroyed, resulting in the appearance of the steel bar. rust.
The mechanism of the concrete rust inhibitor to prevent corrosion is: the concrete rust inhibitor can easily oxidize the ferrous oxide dissolved in the concrete medium and generate it on the surface of the steel bar. The ferric oxide (Fe2O3) hydrate protective film gradually exposes no new surface of the steel bars. Under the action of a sufficient concentration of concrete rust inhibitor, the corrosion process of the steel bars will stop, thereby achieving the purpose of preventing the corrosion of the steel bars.
1. Types of concrete rust inhibitors
Rebar rust inhibitors work by inhibiting concrete The anodic or cathodic galvanic corrosion reaction occurs in the interface pore solution with the steel bars to directly protect the steel bars. Therefore, according to the inhibition process of the electrode process, steel bar rust inhibitors can be divided into anodic rust inhibitors, cathodic rust inhibitors and composite rust inhibitors.
1. Classification according to usage
Incorporated rust inhibitor (DCI) Incorporated rust inhibitor is a type of steel bar rust inhibitor that was developed earlier and has relatively mature technology. It means that the rust inhibitor is directly added to the concrete. It is mainly used in new construction projects and can also be used in repair projects. This type of rust agent was used earlier and more widely in the United States, Japan and the former Soviet Union. Commonly used are inorganic rust inhibitors, organic rust inhibitors and mixed rust inhibitors.
Penetrating rust inhibitor (MCI) Penetrating rust inhibitor is a new type of rust inhibitor developed abroad in recent years, which is to apply the rust inhibitor to the concrete On the surface, the strong penetrating power of the rust inhibitor is used to penetrate into the concrete and reach the surrounding steel bars. It is mainly used for the repair of old projects. The main components of this type of rust inhibitor are organic substances (such as fatty acids, amines, alcohols, esters, etc.), which are volatile and permeable and can penetrate into the interior of concrete. These substances can be “adsorbed” and “film-formed” These principles protect steel bars, and some varieties also have the function of increasing the density of concrete.
2. Classified according to different principles of action
(1) Anode type steel bar rust inhibitor The anode-type steel bar rust inhibitor acts on the “anodic zone” to inhibit the corrosion of steel bars by preventing and slowing down the anode process of the electrode. Typical anodic rust inhibitors include oxidizing compounds such as sodium nitrite, chromate, and phosphonate. Anodic rust inhibitors are also called “dangerous” rust inhibitors. Insufficient dosage will aggravate corrosion. They usually need to be used in combination with other rust inhibitors.
①Sodium nitrite. In the early days, sodium nitrite was commonly used as the main component of steel bar rust inhibitor. The disadvantage of this type of rust inhibitor is that when the chloride ion concentration reaches a certain level, it will cause local corrosion and accelerated corrosion, and is called a “dangerous” rust inhibitor. In addition, this type of rust inhibitor also has shortcomings such as causing cancer, causing alkali aggregate reaction, and affecting the dam drop, so it is rarely used as a rust inhibitor.
②Calcium nitrite. Calcium nitrite is a white crystal. It also has an early strengthening effect in concrete and can prevent the occurrence of alkali aggregate reaction. It gradually replaces sodium nitrite and becomes a new generation of rust inhibitor, but it requires a larger dosage.
③Calcium nitrate. Calcium nitrate can be used as an early strength agent and rust inhibitor for concrete. The dosage is generally 2% to 4% of the cement dosage. The specific value should be determined according to the use.
④Double inscription acid salt. Cyanide is a strong oxidant and a source of toxic heavy metal pollution. Its function is the same as sodium nitrite. The dosage is generally 2% to 4% of the cement dosage.
In addition, acid, sodium benzoate, etc. also have good rust-inhibiting effects and can be selected according to the actual project.
(2) Cathodic steel bar rust inhibitor The cathodic steel bar rust inhibitor generates an insoluble film at the cathode, thereby protecting the steel bars. effect. Carbonates, phosphates, silicates, polyphosphates, etc. all belong to cathodic rib rust inhibitors. This type of rust inhibitor has poorer anti-rust ability than the anode type steel bar rust inhibitor, and is usually used in larger amounts.
① Surfactant substances. Mainly including higher fatty acid salts, phosphate esters, etc. These rust inhibitors are not as effective as anode-type steel bar rust inhibitors in preventing corrosion, and the cost is higher, but they are safer.
②Inorganic salts. Sodium carbonate, sodium hydrogen phosphate, silicate, etc. all have a certain rust inhibitory effect, but the dosage is larger.
(3) Composite steel bar rust inhibitor Some substances can increase the resistance between the anode and the cathode, thereby preventing the electrochemical process of corrosion. However, more composite steel bar resistors with multiple rust-resistant components are used.The overall effect of this agent is much better than that of a single-component rust inhibitor. In fact, most of the currently used steel bar rust inhibitors are composite steel bar rust inhibitors, which have the functions of early strength, water reduction, antifreeze, and rust prevention.
3. Classified according to different chemical compositions
Inorganic steel bar rust inhibitor inorganic The components of steel bar rust inhibitor are mainly composed of inorganic chemicals, such as inorganic salts, phosphates, nitrites, etc. The research on inorganic rust inhibitors started early, and early products include sodium nitrite, inorganic acid salt and sodium benzoate. However, these rust inhibitors have varying degrees of negative effects on the setting time, early strength and later strength of concrete. Calcium nitrite in the later stage is carcinogenic
Organic steel bar rust inhibitor Organic steel bar rust inhibitor is mainly composed of organic chemicals. Research has found that under the premise of the same anti-corrosion effect, compared with inorganic steel bar rust inhibitors, the natural potential of organic steel bar rust inhibitors is generally higher, and the polarization curve is generally lower. Alcohol and amine rust inhibitors are good organic steel bar rust inhibitors. Their rust inhibition mechanism is: forming a protective film on the surface of the steel bar, and adsorbing Ca(OH)2 on the outer layer of the protective film. When the dosage is 1.5% of the total cementitious material, it can effectively protect the steel bars.
Hybrid steel bar rust inhibitor Hybrid steel bar rust inhibitor is based on the comprehensive requirements for preventing corrosion of reinforced concrete, which combines inorganic steel bar rust inhibitors and organic steel bar rust inhibitors. The steel bar rust inhibitor is mixed together in a certain proportion to form an admixture that not only satisfies the corrosion prevention of steel bars, but also meets other functions.
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