Have you found that the part of the Prepainted Steel Coil that has just been put into use and the cement is rusted? Are you bothered by this problem? Wondering what could be causing this.
The hydrates formed after cement hardening include calcium sulfoaluminate and calcium sulfate hydrate. Due to the evaporation of excess water, more or less pores remain. Under the action of corrosive liquids and gases, or the dissolution of infiltrating water, the strength of the hardened cement will gradually decrease or even be destroyed. This phenomenon is called cement corrosion.
There are three reasons for cement corrosion:
01 The product of the interaction between tricalcium silicate and water in cement is continuously dissolved in water, thereby reducing the strength and destroying the cement;
02 The hardened cement is subjected to the action of corrosive liquid or gas, and the new compound formed is not only low in strength but also easily soluble in water. Such as industrial wastewater and other acid erosion;
03 Due to the formation of new compounds, such as ettringite, its accumulative expansion is 2 to 2.5 times, and the expansion stress causes severe cracking of the hardened cement block (this is related to the great destructive effect of a large amount of sulfuric acid infiltrated into the cement).
Different color-coated substrates have different effects.
The difference between galvanized and galvanized sheets mainly lies in the difference in the coating layer. A layer of zinc material is evenly distributed on the surface of galvanized sheet, which acts as anodic protection for the base metal; the surface of the galvanized sheet is made of 55% aluminum, composed of 43.5 zinc and a small amount of other elements, microscopically, the surface of the galvanized coating is a honeycomb structure, and the “honeycomb” composed of aluminum contains zinc. In this case, although the galvanized coating also plays a role It plays the role of anodic protection, but on the one hand, due to the reduction of zinc content, on the other hand, because the zinc material is wrapped in aluminum and is not easy to be electrolyzed, once the galvanized sheet is cut, the cut edge basically loses its protection. Rusts quickly.
Since cement is an alkaline material, it is easier to react with aluminum in the galvanized substrate, resulting in corrosion. Therefore, the effect will be better if the galvanized substrate is used.