Study On The Water Resistance Of Magnesium Oxychloride Cement

Magnesium oxychloride cement?MOC?was a kind of gas cementing material.It had a series of excellent properties such as early strength,high strength,rapid solidification,wear resistance,corrosion resistance,fire resistance,frost resistance,strong adhesion,low alkali,good processing performance.But it also had many drawbacks such as poor water resistance,moisture absorption and deformation of brine,reduction in strength rapidly on prolonged exposure to water.So the engineering application of magnesium oxychloride cement was greatly limited.It was mainly used to make floor materials,packaging materials,decorative materials and other non bearing materials.It was also used to make refractory products,abrasives tools,wooden products,and etc.For the poor water resistance of MOC,an innovatial modification mothed would be proposed.It would be achieved by adding composite modifying additives composed of phosphoric acid and polymer.The project focused on the structure and formation mechanism of magnesium phosphate and polymer on the surface of the hydration products.Combined with XRD,SEM and FTIR,the water resistance mechanism of phosphate-MOC and polymer-MOC and phosphate-polymer-MOC was deeply studied.The modification mechanism of composite modifier composed of phosphoric acid and polymer was discussed.It provided theoretical basis and technical support for the extensive application and effectively improved the water resistance of MOC.The main experimental results and conclusions were drew as following:?1?Phosphoric acid could significantly improve the water resistance of MOC.But phosphoric acid had a retarding effect.So the content of phosphoric acid was generally selected as 1%.Through the method of phosphoric acid solution processing the surface of blank sample,it found MgHPO₄·3H₂O generating on the surface of the sample,which could significantly improve the water resistance of MOC.The result of phosphoric acid improving the water resistance would be the [PO₄]^3-and Mg²⁺generated insoluble phosphate to attach to the crystal surface,which could prevent orinhibit the hydrolysis of hydration products.?2?Only blending styrene acrylic emulsion into MOC could not improve the water resistance,even became worse.This was because the oligomer in the styrene acrylic emulsion could not been adsorpted spontaneously into the surface of hydration products,which could not to form the effective protection of water film.However,the water resistance of MOC could be improved effectively by adding sodium phosphate and styrene acrylic emulsion,and the softening coefficient could reach to 0.93 when mixed with 1% sodium phosphate and 8% styrene acrylic emulsion.In the existence of phosphate ion([PO₄]^3-),[PO₄]^3-combining Mg2+ adsorpted on the surface of hydration products.As the result of this,the surface of the hydration products showed the strong electronegativity and larger Zeta potentials.It induced the colloidal particles in the system to migrate and adsorpt to the surface of hydration products.The formation of uniform and stable water film improved the water resistance of magnesium oxychloride cement.?3?A thermosetting resin cured at room temperature could improve the water resistance of MOC to a certain extent,and compositing phosphoric acid and resin had a better effect.The experiment studied unsaturated polyester resin,vinyl resin,amino resin.Amino resin was the best modifier,and the modification effect of liquid amino resin was better than powdery amino resin.The softening coefficient could reach 1when admixed 1% phosphoric acid and 10% amino resin.When the phosphoric acid was present,the amino resin was easy to form a waterproof film on the surface of the hydration product.So the protective effect of the 5 phase crystal was better.