Test you: Causes of corrosion damage of northern overpass

This post was last edited by mopeizhi on 2010-1-31 10:40 Steel bar corrosion induced by freeze-thaw, salt crystallization, carbonization, salt corrosion, alkali aggregate reaction and other factors

This post was last edited by mopeizhi at 2010-1-31 10:40 ] First of all, the quality of construction is questionable, and there is basically no daily maintenance, and no care is taken after construction, erosion by acidic rainwater, etc.

This post was last edited by mopeizhi on 2010-1-31 10:41 ] It should be chloride ion corrosion. After snowfall in northern winter, in order to melt the ice and snow on the road in time, snow melting agent is usually sprayed. Currently commonly used snow melting agents are hydrochlorides, such as sodium chloride, calcium chloride, etc. Large amounts of chloride ions can cause corrosion to the steel bars of bridges.

Why do you have to look back after replying? You will reply with useless information.

This post was last edited by sjyygh on 2009-10-22 19:02 Corrosion caused by snow melting agent or acid rain

Corrosion from air pollution, corrosion from snow melting agents or acid rain, corrosion from automobile exhaust

The main reason is that the load of ice and snow increases various stresses, which must be taken into consideration during design. :lol

This post was last edited by mopeizhi on 2010-1-31 10:41 1. Corrosion of steel bars due to loose concrete or cracks. Poor concrete density and cracks on components are often important causes of steel corrosion. ~Especially when the amount of cement is too small, the water-cement ratio is improper and the vibration is poor, or the concrete produces exposed bars, honeycombs, pitted surfaces, etc. during the pouring process, the corrosion of the steel bars will be accelerated. When the density of the concrete is poor and the protective layer of the steel bars is insufficient, the relative humidity in the air has a great influence on the corrosion of the steel bars. When it is moderately greater than 60% and less than 100%, and the air contains a large amount of corrosive gases and compounds of sulfur dioxide, sulfur trioxide and chlorine, the steel bars are prone to serious corrosion. Cracks in concrete have an impact on the corrosion of steel bars. Transverse cracks are cracks perpendicular to the steel bars and have little effect on corrosion. For cracks above 0.2mm and wider, in an environment with a relative humidity greater than 60% and corrosive media, and when there are longitudinal cracks along the length of the steel bars, the corrosion of the steel bars is not serious. 2. Due to the intrusion of corrosive gases and media into the concrete, corrosion of steel bars is caused. The carbon dioxide gas in the air is gradually absorbed by the alkaline solution of calcium hydroxide in the surface layer of the concrete, and reacts with each other to form calcium carbonate (CaCO3). This phenomenon is called concrete carbonization (Ca(OH)2+CO2=CaCO3+H2O). When the carbonization concentration reaches or exceeds the protective layer of the steel bar, the passivation film on the surface of the steel bar is partially destroyed, causing the steel bar to be corroded. (To test the carbonization depth, you can use 1% phenolphthalein alcohol solution. The concrete that has not yet been carbonized will be purple-red, and the pH value is 12 to 13. ； Carbonized concrete does not change color and has a pH value of 8 to 9. ) The carbonation depth of concrete has a great relationship with the density of concrete. The degree of carbonation of concrete with good density is only limited to the surface layer. ； If the density is poor, the carbonization depth will be large. Secondly, the carbonation depth of concrete is related to the humidity. In a very humid environment, it is difficult for carbonization to penetrate deeply because the voids in the concrete are full of moisture and it is difficult for CO2 to penetrate. Concrete carbonization generally has no direct impact on the strength of concrete. Its main hazard is that it causes corrosion of steel bars. As the steel bars corrode and expand, the concrete will spall and be damaged, thereby reducing the mechanical properties of the steel bars and concrete. 3. Corrosion of steel bars due to the addition of chlorine salts into concrete. In order to improve the early strength of concrete, it is very effective to add a certain amount of chlorine salts (such as calcium chloride) into concrete. However, excessive chloride salt will cause the following damage: 1) Chloride ions can destroy the passivation film of steel bars and acidify the surface of steel bars, thereby corroding the steel bars. 2) Cement combines with calcium chloride to form calcium chloroaluminate hydrate. If formed during the hardening and crystallization stage, it will expand in the solid phase to form micro-cracks. 3) Chloride salts will increase the drying shrinkage of concrete and may easily cause drying shrinkage cracks in the early stages. Moreover, chlorine salt itself is highly hygroscopic. 4) The ferric chloride in the corrosion products of steel bars is highly hydrolyzable, causing chloride ions to act repeatedly for a long time. Chloride ions in concrete mainly come from raw materials, admixtures such as sea sand, seawater or water with high chloride salts, calcium chloride as a coagulant, and sodium chloride as an antifreeze.

The main reason is that the Cl salt in the snow melting agent in winter penetrates into the steel bars, causing corrosion and damage to the steel bars.

This post was last edited by mopeizhi on 2010-1-31 10:42. The main reason is that salt corrosion in winter is a major problem worldwide, and our country should pay special attention to it. In winter, in order to speed up the melting of snow, salt water (mainly sodium chloride, calcium chloride, magnesium chloride, etc.) is often sprinkled on roads and overpasses. Since the salty snow water flows onto the reinforced concrete structure of the bridge, chloride ions penetrate into the steel bars through the pores of the concrete, causing corrosion of the steel bars, expansion of the corrosion products, and cracking of the concrete, which will accelerate the destruction of the infrastructure structure and shorten its lifespan. * * shorten. (The media once described this type of ice-melting salt as an "environmentally friendly snow melting agent", which is very inappropriate and misleading)