什么因素影响混凝土结构中加固腐蚀？

Factors influencing Corrosion of Reinforcement

In reinforced cement concrete construction the corrosion of reinforcement takes place due to the presence of chlorides and sulphates beyond a critical limit and when sufficient alkalies is not obtained within the concrete to maintain steel in a positive condition.

以下因素负责混凝土结构中的钢筋腐蚀。

1. Quality of Concrete

具体的consists of coarse aggregate, fine aggregate, cement and water. The right quality of materials with proper w/c ratio, correct mixing, adequate compaction by tamping or vibration and proper curing results in good quality concrete. if any of the above mentioned steps are not done in a specified manner, then that will result in a not so good concrete and there is a chance of corrosion of reinforcement.

High strength concrete, i.e. dense concrete is impervious to a large degree and generally resists the carrion of embedded steel.

2.覆盖混凝土加固厚度

The reinforcement is protected by suitable concrete covering over it. The greater the cover thickness more is the degree of protection against the various climatic and other environmental conditions. For various structural members, the cover thickness should be different depending upon their importance and degree of exposure. Evenness of concrete cover over the reinforcement is also very important for its corrosion protection.

3. Condition of Reinforcement

The surface condition of the steel reinforcement, at the time of its placing in concrete, affects its corrosion rate. If the reinforcement is contaminated with salt or badly corroded, the corrosive action on reinforcement after placement in concrete is promoted rapidly.

4. Effect of Environmental and Other Chemicals

Chemical either from environmental or from within the concrete making materials are the main source of deterioration process. Due to attack of chemicals, the concrete develops cracks, which is the first sign of deterioration. The effect of chemicals is mainly due to presence of salt, carbonation, chloride attack and reaction of sulphates with tricalcium aluminate (C₃a）在水泥中存在。

具体的is an intimate mixture of cement, aggregate and water which in the green state is highly alkaline. The hydration of cement develops calcium hydroxide which increases the pH value up to 12.5. In such alkaline conditions, the reinforcing steel is covered with a film of oxide which protects the steel.

5.混凝土的孔隙率

The penetration of aggressive chemicals is possible due to permeability or porosity of concrete. the porosity of concrete depends on size, distribution and continuity of capillary pores. This depends upon the w/c ratio for given degree of hydration. The porosity also depends upon other factors, such as

• 混凝土的年龄
• Degree of compactness
• 总体的大小和分级
• Type of cement

6.高热应力的影响

普通混凝土可以承受温度高达100⁰C. Beyond this temperature the deterioration of concrete starts. The concrete in industrial plants and power stations required special protective measures otherwise the concrete may develop thermal cracks. Cracked concrete structures are consequently affected by the environmental chemical and the process of corrosion starts.

7. Freezing and Thawing Condition

在寒冷地区，混凝土毛孔中的水分。冰形成产生容积膨胀，这可能会过度围绕混凝土质量突破压力。这导致混凝土中的裂缝的发展，可以导致加固腐蚀。