Corrosion environment and concrete deterioration mechanism of shaft wall in coal mines

The shaft, a key engineering facility in coal mining, serves as an important construction channel for materials and personnel during the development of new mines. With the progression of coal mining, various harmful media will appear in the natural environment of the shaft. Through environmental detection in seven coal mines across eastern China, this paper discovers that the internal environment of the reinforced concrete shaft wall contains multiple media that are harmful to rebar and concrete. The gas media mainly contains H2S, HCl, SO2, NO2, and CO2; the liquid media contains Ca2+, Mg2+, SO42-, and HCO3; and the solid media contains SiO2, CaO, Al2O3, Na2O, Fe2O3, etc. It remains hot and humid for a long time. The external environment of the shaft wall has harmful ions, such as Na+, K+, SO42-, and Cl-, and consistently faces a high geo-stress; the concrete was corroded by the CO2 in the harmful media through neutralization, which led to physical or chemical changes within the cementing material. Various acidic media produces soluble corrosion in the concrete. The calcium salt generated by the reaction dissolves in the flowing water and separates from the concrete, gradually reducing the alkalinity and strength of the concrete. Sulfate produces expansive corrosion in concrete, which causes concrete to suffer expansive damages and, coupled with the lasting geo-stress on the shaft wall, speeds up the deterioration of rebar and concrete in the wall, posing a serious threat to the safety and service life of the shaft. © 2021, Saudi Society for Geosciences.