Experimental investigation of the corrosion mechanism of cemented soils in magnesium sulfate solution

Soils stabilized by cement are found to be influenced by the environmental condition such as acid rain, seawater invasion, or industrial pollution. These adverse effects will lead to the deterioration of a structure. In order to study the process of corrosion effects including the changes of the corrosion rate of the surface, compression strength of the cemented soils and the Mg²⁺ and SO₄^2- ion concentrations of the corrosive solutions have been determined. A series of experiments were conducted on the cemented soil blocks cured with different concentrations of MgSO₄ solution. Specifically, the experimental work includes photo documentation, compressive strength tests and measurements of Mg²⁺ and SO₄^2- ion concentrations. The test results show that the rate of corrosion for the sample surface increases with increasing concentration of the corrosive solution, while, the compressive strength decreases accordingly. Moreover, the corrosion rate degree intensifies with corrosion time. Chemical analysis of the corrosive environment indicates that CaSO₄ reacts with the cemented soil, resulting in crystallizing corrosion products of 3 CaO × A1₂O₃ × 3 CaSO₄ × 32 H₂O and CaCO₃ × CaSO₄ × CaSiO₃ × 15 H₂O. Mg(OH)₂ reacts with 3 CaO × 2 SiO₂ × 3 H₂O (C-S-H) and forms new dissolving corrosive reactants such as MgO × SiO₂ × H₂O (M-S-H). It is concluded that the corrosion of cemented soils in MgSO₄ solution is a complex reaction involving the resolving and crystallizing corrosive processes. Finally, a strength model for cemented soils is proposed based on the relationship between the compressive strength and the concentrations of Mg²⁺ and SO₄^2- ions.