Mechanism of cemented soil destruction under sodium sulfate solution

The sodium sulfate in the surrounding environment of cemented soil may affect its mechanical property, which may cause some serious damage to structures. In order to study the erosion effect mechanism, a series of tests were conducted on the cemented soil blocks which were cured in the sodium sulfate solutions with various concentrations and ages. The testing results show that the sodium sulfate solution does make the cemented soil block change, and the influence of sodium sulfate to the blocks is increasing with the concentration of sodium sulfate and curing time increasing. The unconfined compressive strength of cemented soil block is decreased with the increasing of solution concentration, increased with the curing time. The Na⁺ cation and SO₄^2- anion concentrations of the solutions decrease with the corrosive time. Chemical mechanism analysis indicates that, in the sodium sulfate solution, NaOH takes chemical reactions with 3CaO·2SiO₂·3H₂O and 3CaO·Al₂O₃·6H₂O and forms new reactants such as 2Na₂SiO₃ and Na₂O·Al₂O₃, which are poor coagulation and easy to produce an unsteady structure, and the CaSO₄ takes chemical reaction with the cemented soil and products the 3CaO·Al₂O₃·3CaSO₄·32H₂O and CaCO₃·CaSO₄·CaSiO₃·15H₂O crystallizing resultants, which are large enough, the inflating force would be greater than the sticking force within the cemented soil, so cracks may bring about in the cemented soil block and the strength would be reduced. Therefore, the Na⁺ cation corrosion to cemented soil is a sort of dissolving corrosion, the SO₄^2- anion corrosion to cemented soil is a sort of crystallizing corrosion, and the- - corrosion of sodium sulfate solution to cemented soil is a composite action including dissolving and crystallizing corrosions.