Study On The Preparation And Engineering Performance Of Hydrophobic Magnesium Oxychloride Cement

Magnesium oxychloride cement（MOC）is an air-hardening gel material prepared by mixing and stirring active MgO,MgCl₂ and water in different molar ratios.It is widely used because of its excellent performance.However,poor water resistance is also an important shortcoming that restricts its development.This article starts with the preparation of the overall hydrophobic magnesium oxychloride cement,hoping to further increase its durability by slowing the rate of water erosion of the magnesium oxychloride cement,and studies the effects of modifiers on its hydrophobicity,compressive strength and other engineering properties influences.The main research contents are as follows:We pre-cohydrolyzed tetraethylorthosilicate（TEOS）and triethoxy-1H,1H,2H,2H-tridecafluoro-octylsilane（FAS）in MgCl₂solution containing H₂O₂and H₃PO₄ to prepare bulk density The overall hydrophobic magnesium oxychloride foam material of 300-1200 kg·m^-3,and its performance and structure have been systematically studied.The results showed that the addition of 0.5-2.5 wt%silane copolymer in the system did not change the phase composition,strength phase content and compressive strength of the MOC material,and the addition of the silane copolymer made the pore distribution of the foamed material more uniform.Not only makes the overall water contact angle reach 156°,but also the mechanical polishing has less influence on the water contact angle.The moisture absorption rate drops by 16.2%,and the quality can be restored to 98.1%of the original quality after dehumidification.The water resistance is significantly improved.We directly added hexadecyltrimethoxysilane（HDTMS）and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer（P123）into the MgCl₂ solution to prepare the internal water contact of the material A hydrophobic MOC material with an angle of132°-142°.The results prove that due to the amphiphilic effect of P123,the porosity of the MOC sample with HDTMS and P123 is greatly reduced,and the five phases of the needle tube are increased.Compared with the actual use of the control sample,the strength of 28d can be retained by 63%.The softening coefficient of blisters increased from 0.73to 0.90 after 28 days,the water absorption rate is only 50%of the actual use of the control sample.Firstly,use hexadecyltrimethoxysilane（HDTMS）to hydrophobically modify fly ash,and add hydrophobic fly ash to magnesium oxychloride cement to modify it.When the modified fly ash is added at 5%,the softening coefficient of magnesium oxychloride cement can reach 0.84,but due to the addition of organic groups,the porosity increases,the compressive strength is significantly reduced,and the quality loss is about 20%.So we added cetyltrimethylammonium bromide（CTAB）,polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer（P123）and sodium lignosulfonate,Studying the effect of different types of surfactants on the porosity of magnesium oxychloride cement,it is found that P123 and CTAB can improve the porosity of the sample after adding hydrophobic fly ash and the decrease of compressive strength.At the same time,the porosity and average pore size are reduced.,The finished product is denser,and the softening coefficient is also improved.Sodium lignosulfonate will further reduce the compressive strength of magnesium oxychloride cement.