Causes and classification of bridge cracks

Concrete is composed of cement, sand, stone aggregate and so on. There are cavitation, micropores and micro cracks in the process of hardening. After the component is loaded, the micropores and micro cracks gradually connect and expand, forming macroscopic cracks.

The concrete bridge cracks can be divided into the following types: load cracks, temperature cracks, shrinkage cracks, settlement cracks, and poor construction process quality.

Bridge cracks will cause some harm to the structural

In general, cracks with a width less than or equal to 0.05mm are not harmful to use, and fine cracks are unavoidable in concrete. Therefore, in the theory of reinforced concrete design and calculation, except for members with strict requirements for cracks, the general structure is allowed to work with cracks. However, the excessive crack of concrete will do great harm to the structure, mainly in the following aspects:

First, the effect of freezing. When the concrete has a crack, the water can infiltrate, even if the infiltration is not very deep, when the temperature falls below zero, the water will form ice. The expansion of the ice will lead to the split along the edge of the crack, and the freezing and thawing cycle repeats once, and the crack will occur once so that the crack will gradually widen.

Second, corrosion of steel bars. Once moisture or corrosive gas reaches the steel bar, rust will start. The corrosion reduces the stress area and the expansion of the steel bar, which makes the concrete crack continue to expand and affects the cohesive force of the steel bar and concrete.

Third, reduce the bearing capacity of the structure. Due to the reduction of steel corrosion section and the crack of concrete, the effective height is weakened, and the bearing capacity of members is reduced.

Fourth, accelerate the concrete carbonization spalling, reduce the fatigue resistance, and affect the durability of the structure.

Fifth, damage surface properties, such as beauty and so on.

As mentioned above, the micro cracks in concrete are unavoidable and not much harm, and the larger cracks are very harmful, so the prevention of cracks and the treatment of existing cracks are very important.

Treatment of bridge cracks

1 the surface seal repair method is mainly used in the surface sealing method, which mainly adopts the mortar filling, the crack glue injection reinforcing, the chisel embedding, the surface spraying and so on.

2 the structure has no influence on the structure for a long time, and the pressure grouting method is used to repair the structure for a long time because of the rain and gas erosion, and a certain kind of slurry can be poured into the internal cracks by exerting certain pressure to achieve closed cracks, and the strength, durability and impermeability of the structure can be improved.

3 there are  structural strengthening system to deal with the cracks which have great damage to the structure, such as the steel plate bonding reinforcement, the carbon fiber fabric bonding reinforcement, the reinforcement of the beam body section size and the prestress FRP plate reinforcement method.