Characteristics And Durability Of Magnesium Phosphate Cement

【Author】

Haihe Yi;Yi Zhang;Dongxu Li;

【Abstract】

<正>The cement were prepared by mixing dead-burned magnesia(M),and mono-potassium phosphate(mPP),with/without fly ash;in addition,borax(B) and di-potassium phosphate(dPP) were used as the retarders.The durability of MPC were investigated by means of strength,weight loss,the linear expansion rate,XRD,scanning electron microscope and pore structure analysis.This paper also has investigated the hydration characteristics and durability of magnesia-phosphate cements(MPC) at low temperature(-5 V).The hydration behaviors were compared with that of MPC materials curing at a ambient temperature of(20 V).The results indicate that,the strength of MPC cured in air exceed much more than those cured with high humidity,and harmful pores are more below,which indicate that,water curing are unfit for MPC-based materials.Fly ash can improved omnifaceted behaviors,including color,strength,and durability.The setting reaction of MPC are slowed down in low temperature,however, the long-term mechanical strength are not affected dramatically.Through incorporating fly ash,the compressive strength and properties for low temperatures of MPC materials could be improved significantly.The XRD patterns indicate,MgKPO_4-6H_2O are the main hydrate in MPC materials,and morphology analysis was taken by SEM,in 28d specimen,dense microstructure with deep hydration degree progressively forms,the Surface of fly ash was erosion,the rod-like and tabular MKP crystalline is present. Originality The setting time of portland cement setting is long under low temperature conditions (0—-20℃),it unable to meet the construction requirements in winter.Magnesium phosphate cements are materials that belong to chemically bonded materials.It sets rapid,the early strength is high,and the performance in low temperature is excellent. But its water resistance and the durability under low temperature is Poor.Fly-ash can improve the water-resistance,and decrease the cost of the cement.Effects of fly-ash in matrix of magnesium phosphate cement will be researched,and feasibility to increase dosage of inorganic fillers will be discussed Failure mechanism in water will be studied leaching model of soluble phosphate from matrix will be built up,and influences of hydrate variations on material microstructure will be analysedOn such basis,with fly-as,the water-resistance and frost resistance of magnesium phosphate cement will be apparently improved.The research will widen the application scopes of magnesium phosphate cement,it will provide theoretical and technical support for the civil engineering under low temperature.

【Keywords】

magnesia-phosphate cement;;hydration characteristics;;durability;;low temperature;;fly ash

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