Determining changes in the mineral composition of concrete due to chemical corrosion in a sulfate environment

Abstract

The object of this study was the concrete structures of a chemical enterprise for the production of titanium dioxide. In this case, the ore is decomposed with sulfate acid according to the sulfate production technology. In an aggressive environment, chemical corrosion of concrete occurs, prolonged over time. Using X-ray diffraction and X-ray fluorescence analysis methods, the mineral composition of two prototypes of concrete was determined. It was found that the sample obtained from the workshop for processing ore with sulfate acid showed an increased content of sulfur oxide (SO2) on the surface, by 33 %, with a reduced content of carbonates (CaCO3) on the surface, by 52.9 %, at a depth of 2 cm – by 53.65, compared to another (control) sample. At the same time, iron oxide (Fe2O3) was found on the surface in a sample of concrete from the ore storage room (control), the content of which decreased by 10.4 % at a depth of 2 cm, and by 12.4 % at a depth of 4 cm. The results of electron microscopy show sulfur crystals on the surface of a concrete sample. It was also found that the microstructure of concrete was changed under the influence of sulfate corrosion, depending on the intensity of the exposure to a depth of 2 to 4 cm. By the method of thermoprogrammed mass spectrometry, it was established that when a sample of concrete exposed to sulfate acid is heated to a temperature of 400 °C, sulfur dioxide SO2 is released mainly from the surface. From the surface of the control sample, which contains a significant amount of CaCO3, which is easily destroyed by sulfate acid, there is probably a smaller amount of the product of thermal destruction of calcium carbonate carbon dioxide (CO2). The results of the experiment can be used to study the mechanism of development of sulfate corrosion of concrete prolonged over time.