Causes of corrosion of power line foundations

　　The foundation of transmission line towers generally includes rock foundation, steel structure foundation and concrete foundation, etc. Transmission towers generally use concrete foundation or reinforced concrete foundation. Because groundwater contains various chemical components, when a certain component is excessive, it will have a strong harm to the concrete and steel that constitute the foundation. Therefore, when designing the foundation, the corrosive effects of groundwater, surrounding environment and soil on the corrosion of foundation materials must be considered, and effective protective measures must be taken for the foundation with corrosive groundwater.

　　Groundwater with crystalline erosion contains too much sulfate (SO42-) and reacts with cement in concrete, causing the concrete to be corroded. Therefore, according to the erosion level, measures such as ordinary silicate cement with a high strength grade greater than C50, ordinary sulfate-resistant cement and high sulfate-resistant cement are taken respectively. The judgment method and standard of groundwater with crystalline erosion are as follows: (1) the strata contain fibrous, lenticular, clastic, lamellar and tubercular gypsum; (2) salt lakes, salt pans, saline soils and other salt-containing areas (such as rock salt, mirabilite, halogen, hydromagnesia gypsum, etc.) as well as seawater and seawater infiltration areas; (3) sulfide ore and coal mine water infiltration areas; (4) industrial wastewater (acidic, containing a large amount of sulfate, magnesium salt and ammonium salt, etc.) infiltration areas; (5) topographic conditions that mineralize water.

　　Groundwater with decomposition erosion, hydrogen ions (pH value), bicarbonate ions (HCO3-) and free carbonic acid (CO2) in water have decomposition and destructive effects on concrete. When groundwater has decomposition erosion, cement with a strength grade of not less than C30 should be used; when pH ≤ 4.0, protective measures such as coating asphalt on the concrete surface or filling a clay protective layer around the foundation should be adopted.