Research progress on coupling effect of multi-ion ionic attack of concrete in the coastal area

The corrosion on concrete from seawater has an ion coupling effect. This paper analyzed the results of two species ionic coupling attack, three species ionic coupling attack, and seawater attack, which obtained the following results: (1) The internal pores will be blocked by the attack products of $\mathrm{SO}_{4}^{2-}$ and Mg2+ in the early stage, which inhibits the transportation of $\mathrm{C}1^{-}$; the degradation of concrete will increase the transport speed of $\mathrm{C}1^{-}$. (2) Sulfate attack is influenced by cation type. Taking expansion rate as deterioration index, Na2So4 and K2SO4 have the highest attack speed and degree, while CaSO4 has the lowest attack degree. Taking compressive strength as the deterioration index, the attack degree of MgSO4 is the highest, and that of Na2SO4 and K2SO4 is the lowest. (3) Temperature will affect the deterioration degree of concrete, and the deterioration degree of concrete is more severe at low temperatures. $\mathrm{CO}_{3}^{2-}$ and $\mathrm{C}1^{-}$ will aggravate the MgSO4 attack at low temperature $(5^{\circ}\mathrm{C})$ but not affect the MgSO4 attack at room temperature. (4) Due to the different transport rates of ions in concrete, the surface layer of concrete is divided into Mgrich zone, S-rich zone, and Cl-rich zone according to the rich elements.