Even if the quality of concrete materials, design and construction are very good, various diseases will still occur in the bridge structure as the service time increases. If the quality of concrete materials or construction is poor, or the design is defective, the occurrence and development of the disease will be accelerated. Among the various factors that affect the durability of concrete, the effect of chloride ions is the most obvious. Its penetration will cause severe corrosion of steel bars, thereby causing delamination and fragmentation of concrete. High-quality materials, construction, and design can improve the durability of new bridges, but there are still many reasons to protect these new bridges so that they can meet or exceed their design service life. For bridges that have been in service for a certain period of time, regular protection and maintenance must be carried out so that they are always in good conditions and extend their service life.
A 1975 survey by the American Bureau of Standards showed that the annual corrosion loss in the United States was US$70 billion, of which the corrosion loss of steel bars in concrete accounted for 40%. In 1989, the US transportation The department's report to Congress on the condition of America's highways and bridges states: "The current backlog of repairs to concrete bridges is $155 billion." By 1995, total corrosion losses in the United States were US$300 billion, of which corrosion of infrastructure steel bars accounted for 50%. Corrosion losses were higher than water, wind, and fire combined. The American Highway Research Strategic Plan revealed that by the end of the 20th century, it will cost an estimated $400 billion to replace or repair damaged highway concrete decks caused by winter deicing salt, most of which is caused by corrosion of steel bars.
In recent years, due to a series of reasons such as environmental degradation, the number of domestic railway concrete beam diseases has increased dramatically, which has become a major problem for bridge maintenance workers. Domestic highway and municipal departments also have similar situations. For example, many of the reinforced concrete overpasses in Beijing and Tianjin have not been in use for a long time, but they have widely shown signs of damage due to steel corrosion and concrete expansion and cracking, thus prematurely losing their functionality.
Technical measures to prevent corrosion of steel bars can be divided into two categories. The first type is to pay attention to the quality of concrete and improve the protective ability of the concrete itself, such as using high-density, crack-resistant concrete, etc.; the second type is to use concrete outer coating, special steel bars (such as epoxy coated steel bars, stainless steel steel bars, etc.), cathodes Technical methods for additional measures such as protection and steel bar rust inhibitors. As a durability measure, the American Concrete Institute (ACI) considers all three methods, in addition to concrete exterior coatings, to provide long-term effective corrosion protection. Each of these three measures has its own characteristics, pros and cons, and steel bar rust inhibitor has proven to be the simplest, most economical and most effective technical measure. The American Steel Bar Rust Inhibitor Association (CCIA) report states that “commercial steel bar rust inhibitors have been used for more than 20 years and are widely used in marine concrete, bridges, parking lots and other structures. ... Proving that steel bar rust inhibitors are the most effective protection method.” .
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