Study On Micro Structure And Self-toughenting Mechanism Of MgO-Based Basic Salt Cementitious Materials

With the rapid development of economy in our country,developing the marine economy and safeguarding maritime rights and interests has became a national strategy,so,it is imperative to develop the island and strengthen the construction of the island.However,the ordinary Portland cement has poor seawater-resistance and its impact toughness is not ideal,and there are lots of troubles applying the Portland cement to the construction of the island,thus this paper proposes a new cement mixing with the seawater,MgO-based basic salt cement,who can resist the seawater and has good impact toughness.MgO-based basic salt cement is quaternary system cementitious materials mixed with magnesium oxide,magnesium chloride,magnesium sulfate,and seawater in a certain proportion.In this paper,from the mechanical property of MgO-based basic salt cement,studying the mechanical property and toughness of this cement specimens in different mixing proportion through compression and bending test,and optimizing the range of the mixing proportion.The strength of MgO-based basic salt cement relate to the Microstructure of cement.And there are a lot of basic magnesium chloride whiskers and basic magnesium sulfate whiskers in MgO-based basic salt cement hydrate.In this paper,using X-ray diffraction analysis(XRD)to analysis the phase composition of MgO-based basic salt cement hydrate under different mixing proportion,and using the scanning electron microscope(SEM)to observe the morphology,geometry size and arrangement of the whisker in the MgO-based basic salt cement hydrate,and using energy dispersive X-ray spectrometer(EDX)to analysis the chemical elements of the whisker,to establish the relationship between the mixing proportion ratio and the morphology,geometrical size and the phase composition of the whisker,and optimize design the mixing proportion to make the morphology,geometrical size and arrangement of the whisker best.One of the most important reasons to limit the use of magnesium oxychloride cement is their poor water-resistant.Although magnesium oxychloride cement has high strength,its water-resistant is poor.In this paper,for the phenomenon that the strength of MgO-based basic salt cement reduce after curing in water,the reasons of this cement's poor water-resistance is analysed by using SEM from the perspective of microstructure and the solution to the poor water-resistance is proposed.The softening coefficient of the MgO-based basic salt cement is raised and the cement water-resistance is improved by adding the admixture to cement,and the mechanism that the admixture can improve the water-resistance of the MgO-based basic salt cement is studied by using SEM.