Coupling Effect Of Mg²⁺ And SO₄^2- On Cement Stone Erosion

In recent years,with the development of the central and western regions of our country and the construction of"the belt and road initiative",a large number of new concrete projects will be built.However,as there are a large number of sulfate ions and magnesium ions in the waters and soil of the coastal areas and the western regions,these two ions will erode the concrete and reduce the strength of the concrete.Based on virological principles,this paper aims to modify slag cement by adding light burned magnesium oxide and magnesium sulfate into slag cement.It also studies the erosion of magnesium ions and sulfate ions on different cement stones and the coupling mechanism of the two ions on the erosion of different cement stones.By studying the erosive effects of magnesium ions and sulfate ions on portland cement（P·Ⅱ）,ordinary portland cement（P·O）,slag cement（P·S）,super sulfate cement（SSC）,sulphoaluminate cement（SAC）,Mg O modified slag cement（MSC）,Mg SO₄ modified slag cement（SMSC）and other kinds of cements,the erosive mechanism was explored and the coupling action model was established.Referring to the"K"method in GB/T749-2008,cement molding mortar specimens were soaked in clear water and 0.6 mol/L magnesium nitrate,sodium sulfate and magnesium sulfate corrosive solution respectively.Through testing the flexural and compressive strength of cement mortar specimens at different ages,and combining with XRD,SEM and EDS tests,the erosion mechanism of different corrosive ions on different cement mortar specimens was obtained.The results show that:In the three kinds of erosion solutions,the cement mortar specimens were damaged to different degrees,with obvious peeling marks on the surface and passivated edges and corners,of which the specimens in magnesium sulfate erosion solution were the most damaged.On the other hand,white material is precipitated on the surface of cement mortar specimens soaked in magnesium nitrate solution,which is caused by nitrate crystallization.（2）The flexural and compressive strength of cement specimens in corrosive solution have different losses;After being modified by magnesium oxide and magnesium sulfate,slag cement has improved corrosion resistance to magnesium ions,and magnesium sulfate modified slag cement has the best corrosion resistance to sulfate ions and magnesium ions among 7 kinds of cements,so the cement modified based on virus immunology principle is effective for improving corrosion resistance.（3）Due to the different hydration products of the seven cements,the corrosion mechanisms of sulfate ions and magnesium ions are different.The common point for improving the corrosion resistance of sulfate ions and magnesium ions is to reduce the content of tricalcium aluminate and calcium hydroxide in hardened cement paste,and to improve the corrosion resistance of the specimen by increasing its compactness.（4）Through the research on the erosive coupling effect of sulfate ions and magnesium ions,the erosive coupling effect model is established.It is concluded that the coupling coefficient is related to the type of cement specimen and the erosive age.The larger the coupling coefficient,the greater the erosive coupling effect of sulfate ions and magnesium ions on the specimen.