Concrete structures serve in various environments, and different service environments can cause different types of durability damage to concrete structures; As the service life of the structure increases, durability issues will become increasingly apparent, thereby affecting the functionality and even safety of the structure. The following will elaborate on some durability failure phenomena of actual concrete engineering under different service environments, aiming to illustrate the universality and severity of durability problems in concrete structures.
1. Salt spray erosion causes structural damage
A power plant in Zhejiang Province is located in Zhenhai District, Ningbo City, on the coast of the East China Sea. The factory is located at the mouth of the lower reaches of the Yongjiang River, with a maritime climate. It has been 36 years since the construction of the power plant. Due to the long-term salt spray erosion of the power plant, under the continuous erosion of chloride ions, concrete cracking, peeling, and steel corrosion occurred in all stages of the concrete structure. Wide longitudinal rust expansion cracks appeared in the concrete protective layer, and the steel bars were severely corroded. After investigation, it was found that 70% of the concrete columns and 25% of the concrete beams in the main load-bearing components of the booster station have severe durability damage such as longitudinal cracks and exposed reinforcement (Figure 1-3 (a)); The durability damage of the frame is the most severe, with 100% of the frames showing severe surface concrete erosion and exposed steel bars (Figure 1-3 (b))
2. Damage to structures caused by humid environments
A bridge in Jinhua, Zhejiang Province, is located in Lanxi City. It was built in 1975 and is a concrete double curved arch bridge structure spanning the Lanjiang River. The durability damage of the bridge is mainly caused by the poor working condition of the drainage system, water seepage in the bridge area, and the durability damage of the concrete components of the bridge: vertical cracks appear at the junction of multiple columns and the cover beam, and some columns even have exposed reinforcement. There are large pieces of concrete protective layer peeling off at the corners (Figure 1-4 (a)); Due to issues with the drainage system, the end of the frame cover beam is in a damp state, resulting in large pieces of concrete peeling off and severe corrosion of the steel bars (Figure 1-4 (b)).
3. Direct action of seawater on structural damage
The concrete dock project is directly in contact with seawater, and the concrete components in the tidal zone are subjected to the most severe chloride ion erosion environment. Investigation has found that docks that have been in operation for 20 to 30 years generally have serious durability problems. For example, a dock in Zhoushan has been in use for more than 20 years since its construction (Figure 1-5), and various parts of it have suffered varying degrees of corrosion damage, especially the upper structure has reached a serious level of damage: large areas of rust spots have appeared on the dock beams, and most of the beam bottoms have obvious cracks along the main reinforcement direction, with a width of 1-3mm. The sky shaped plates placed on the dock beams have suffered severe corrosion, and a large number of longitudinal cracks have appeared along the main reinforcement direction in the components. 70% of the plates have rust expansion cracks with a width greater than 3mm, while the width of the longitudinal rust expansion cracks on the remaining plates is 1-3mm. The dock must be reinforced and repaired in order to continue its use.
4. Structural durability damage in other environments
Figure 1-6 shows the corrosion of steel bars in a shopping mall building constructed in the 1970s. It can be seen from the figure that the steel bars in the structural floor panels and beams serving in the atmospheric environment are severely corroded. After undergoing certain renovations and reinforcements, the building is still in use. Figures 1-7 and 1-8 respectively reflect the effects of freeze-thaw failure and alkali aggregate reaction on the structure. Figure 1-9 illustrates the durability damage suffered by concrete structures under chemical corrosion environmental conditions.
Figure 1-10 shows the phenomenon of steel reinforcement corrosion found in damaged structures after the 2008 Wenchuan earthquake. Although the Wenchuan earthquake is rare and cannot be entirely attributed to steel reinforcement corrosion, steel reinforcement corrosion can lead to a decrease in the stiffness, hysteresis characteristics, energy dissipation capacity, ductility, yield strength, and bearing capacity of the structure. Therefore, it can be said that corrosion is also an important cause of the failure of reinforced concrete structures.
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