Study on the deterioration mechanism of alkali dissolution of concrete mixed with Na2SO4 in external water sources

Abstract

Although this chemical reaction of Na2SO4 eroding concrete can be proven based on the erosion products, the chemical reaction is difficult to reveal the deterioration process from quantitative to qualitative change. To reveal the reaction mechanism by which Na2SO4 erodes concrete, concrete specimens mixed with Na2SO4 were placed in environments with and without external water for long-term erosion tests. The appearance and mechanical properties of the specimens were tested at regular intervals. The erosive phase composition of concrete in different periods was analysed. The results show that external water sources are necessary for concrete eroded by Na2SO4 to fail. The specimens without external water sources did not change in appearance or show any erosion damage after 4 years of erosion testing, and their compressive strength did not change significantly. In contrast, the specimens exposed to external water sources showed increasingly serious erosion damage. In external water sources, the dissolution of the erosion product NaOH causes the Na2SO4 to consume the Ca(OH)2 in the cement matrix. This causes the CSH gel to decompose, which leads to the deterioration of concrete mixed with Na2SO4 in external water sources.