Reinforced concrete has been widely used in bridge projects as an economical and practical building material. However, the lack of durability caused by corrosion of steel bars has also hampered the normal use of bridge structures. brought serious harm. In some developed countries in the West, it has taken a long time to build reinforced concrete bridges, and the problems that have arisen are relatively obvious. According to statistics, as early as 1992, approximately 14% of the highway bridges in the United States were open to traffic with limited load due to corrosion damage to steel bars caused by the spreading of deicing salt, and the annual maintenance costs were as high as US$50 million to US$200 million. Most of the reinforced concrete bridges built in the 1960s and 1970s in some countries such as the United Kingdom, Norway, Japan, Canada and Australia have suffered from mild or severe corrosion of steel bars. The climax of the construction of reinforced concrete bridges in our country has only been about 10 years, and the hazards caused by steel corrosion have not yet been fully exposed. However, the corrosion and damage of steel bars in some bridges has begun to appear, and some are even very serious. For example, the Xizhimen Bridge in Beijing cannot be used after use. By 20 years, it had to be scrapped and rebuilt due to corrosion of steel bars. Reinforcement corrosion has become the primary cause of damage to reinforced concrete bridges.
Reinforced concrete bridges, especially large and medium-sized bridges, generally have a design life of about 80 years, and some even 100 years, 120 years. To ensure such a long life of the bridge structure, in addition to normal maintenance and periodic replacement of some ancillary components, the durability of the main structure is a very important link. Judging from the corrosion rate of steel bars in existing highway engineering structures, if no anti-corrosion measures are taken, the cement concrete protective layer will crack due to steel corrosion in 3 to 4 years in high-temperature areas in the south; in low-temperature areas in the north, it will take 4 to 5 years The steel bars were severely corroded. This aging rate of the bridge structure makes it difficult to meet the design life requirements. A large bridge often costs tens of millions or even hundreds of millions of yuan to build. Such a big gap between the service life and the design life is itself a huge economic and social loss; moreover, due to insufficient durability, the bridge structure will not survive normal use. The huge maintenance costs will also bring a heavy financial burden.
The corrosion damage of steel bars is so extensive and serious that it has attracted close attention in countries around the world. The United States has begun research on steel corrosion in chlorine salt environments since the 1950s. In the mid-1980s, it implemented a nationwide "Strategic Highway Research Plan" specifically for highway projects to study the corrosion of steel bars in highway bridges; the United Kingdom in the 20th In the 1970s, the "Ocean Research Program" was launched to conduct research on the corrosion of reinforced concrete in the marine environment. Our country's engineering community is increasingly aware of the seriousness of steel corrosion caused by chlorine salt environments. At a conference on the durability and durability of cement concrete structures hosted by the Chinese Academy of Engineering in December 2002, many academicians and experts also strongly called for attention to the harm caused to the country and society by steel corrosion, especially steel corrosion in a chlorine salt environment.
The causes of steel corrosion are complicated, and the corrosion mechanism can be mainly divided into two types: chemical corrosion and electrochemical corrosion. The corrosion of steel bars in a chloride environment is mainly electrochemical corrosion. This corrosion occurs much earlier than the corrosion of steel bars caused by carbonization of cement concrete. Early corrosion damage of steel bars is generally caused by the erosion of chloride ions. This kind of corrosion is fast and produces pitting corrosion, which not only seriously weakens the steel bar section, but also easily leads to stress concentration. Especially for bridge structures that mainly bear fatigue and impact loads, the harm of this kind of corrosion is more serious [.
How to avoid or delay the corrosion damage of steel bars in cement concrete bridges, the key lies in prevention. The failure to take effective anti-rust measures is one of the main reasons why many reinforced concrete bridges are so seriously corroded and damaged. The current anti-rust measures mainly include anti-rust coating method, cathodic protection method, inertized steel bar method and anti-rust cement concrete. Coating methods mainly include cement concrete surface coating, cement concrete surface polymer impregnation, steel bar surface coating, etc. These methods mainly prevent corrosion of steel bars by setting up a dense layer to cut off the path of chloride ions or other corrosive media to the surface of the steel bars. Purpose; Cathodic protection methods mainly include sacrificial anodes, impressed current and other methods. These methods mainly achieve the purpose of preventing corrosion of steel bars by compensating the electrons lost by iron atoms; the inerted steel bar method mainly uses low-activity materials such as stainless steel bars and carbon fiber rods. Metal or inert materials partially or completely replace the steel bars. These methods have high construction technical requirements, relatively complex processes, and high later maintenance costs. Currently, they are mostly used for auxiliary anti-corrosion of key parts or components of large and complex reinforced concrete bridges. A lot of work needs to be done for general promotion.
Rust-proof concrete is made by adding a certain amount of rust inhibitor to the concrete mixture to inhibit the corrosion of steel bars. The dosage of rust agent can meet the requirements of preventing or delaying the corrosion of steel bars during the design life of the structure. Anti-rust cement concrete fundamentally enhances the ability of reinforced cement concrete bridges to prevent rust. Just like humans resist diseases, injections and medicine are an external remedy. Strengthening physical fitness is the most fundamental way to maintain good health and extend life. . Practice has proven that rust-proof cement concreteThe construction technology is simple, economical and effective. It is a rust prevention method with broad application prospects and has been widely used in recent years.
Rust inhibitors are the main agents that play an anti-rust role in anti-rust cement concrete, and their research and engineering applications are developing very rapidly. Currently, there are many types of rust inhibitors on the market with different effects. In order to facilitate the majority of highway engineering technicians to master the technical content and usage requirements of rust inhibitors, standardize the reasonable application of rust inhibitors in highway bridge projects, and achieve the expected effect of improving the durability performance of cement concrete bridges, this article is combined with the 2006 Ministry of Transport issued The "Technical Guidelines for the Application of Cement Concrete Admixtures and Admixtures in Highway Engineering" regarding rust inhibitors provides a brief introduction to the scope of application, performance requirements, dosage and construction technology control indicators of rust inhibitors used in highway and bridge projects. .
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