Study On Reinforcement And Water Resistance Modification Of Magnesium Oxychloride Cement Cementitious Material

Magnesium oxychloride cement has many advantages such as light weight,high strength,flame retardant,heat insulation,high setting rate,easy-to-process,wear-resistant and impact-resistant,etc.,and is widely used in light industrial fields such as building decoration materials,packaging materials and replacing wood and tiles.However,magnesium oxychloride cement also has the problems of easy warpage and deformation,moisture absorption,and is easily affected by environmental factors such as high temperature and humidity,which limits its application.Therefore,in recent years,many scientific researchers have devoted themselves to the enhancement and modification of magnesium oxychloride cement,using modifiers and fillers to produce high-performance magnesium-based cementitious materials.China is rich in magnesite resources,so it will be of great significance to develop new composite magnesium cement materials,give full play to the role of magnesia resources,and produce light-weight and fire-resistant high-strength building materials.In this thesis,light-burned magnesium oxide powder and magnesium chloride solution are blended to make magnesium oxychloride cement.Study the influence of the ratio of each raw material on the early performance（setting time,flexural compressive strength）of the molded specimen.Use foamed glass powder,sodium methyl silicate solution,hydrated magnesium silicate gel to modify the magnesium oxychloride cement system,respectively,test and calculate the mechanical properties,water resistance,volume stability,etc.of the modified materials,supplemented by SEM,XRD,FT-IR and other microstructure characterization,discuss the modification mechanism of each component preliminary.The main research and results are as follows:（1）The activity of the light-burned magnesia powder used in this experiment is about88.13%,according to the raw material composition of the magnesium oxychloride system,it is divided into two groups:Mg O/Mg Cl₂ and H₂O/Mg Cl₂ to conduct an experimental study of the optimal ratio.When n（Mg O/H₂O/Mg Cl₂）=4:1:13,the flexural strength of magnesium oxychloride cement is about 8.7MPa,the compressive strength is 48.4MPa,shows better mechanical properties.The prepared magnesium oxychloride cement can reach the initial setting state within 1h,and finally set after about 3.5h.（2）Foam glass is light-weight and flame-retardant and has high stability.Its waste scrap is a good filling material,which can improve the flexural compressive strength and volume stability of magnesium oxychloride cement.When the blending amount is 20wt%,the flexural strength can reach 17.3MPa,the compressive strength is 53.4MPa,the shrinkage rate is 0.038%,and the expansion rate is 0.499%.（3）As the main component of organic silicon water repellent,sodium methyl silicate is often used for surface coating of substrates to form a highly water-repellent organic film to prevent outside moisture from entering.In this experiment,we mixed sodium methyl silicate into the magnesium oxychloride cement matrix,when the addition amount is about 1wt%,the softening coefficient of the material can reach 0.96,and the water resistance is greatly improved.Sodium methyl silicate can not only form a waterproof layer on the outside of the material,but also fill the internal pores of the porous material,so it can improve the water resistance and volume stability of magnesium oxychloride cement.（4）The experiment has synthesized the hydrated magnesium silicate whose main composition is Mg（OH）₂ and M-S-H gel,which is used to modify magnesium oxychloride cement.The softening coefficient of the modified material is about 0.61,and the water resistance is enhanced.MSH-MOC prevents expansion and foaming after being immersed in water,which can reduce the warpage and deformation of magnesium oxychloride cement.