Study On Preparation Of Magnesium Oxysulfate Cement With Low Quality And Light Burned Magnesia Powder And Its Application

Magnesium oxysulfate cement handicraftis based on magnesium oxysulfate cement material,adding the filler such as crop waste and industrial waste residue,etc.The light burning MgO used is low-quality light burning MgO calcined by low-grade magnesite with the content of MgO less than 80%.As the content of MgO is different,the content of impurities is also different.So the low quality of light burned MgO style affect the performance of magnesium oxysulfate cement,with low quality light burned MgO style,high quantity of industrial waste residue for the preparation of magnesium oxysulfate cement base material,with agricultural waste?straw,sawdust?for the preparation of green packing,light weight,high strength,permeability,water resistant magnesia products,to solve the low grade magnesite and the problem of efficient utilization of a large number of industrial and agricultural waste,improve the magnesium products added value and economic benefit,service the local economy.This paper studies the activity was 65%,70%and 78%of the light burned MgO style affect the performance of magnesium oxysulfate cement,the results showed that the low activity of the preparation of MgO style of magnesium oxysulfate cement compressive strength is 80.6MPa,freezing-thawing resisting cycles for ten times,the preparation of highly active MgO style magnesium oxysulfate cement compressive strength is 40.6MPa,freezing-thawing resisting cycles is only five.Then Magnesium oxysulfate cement was prepared by lightly burning MgO with four different silicon and calcium contents,and the effect of silicon and calcium contents on properties was studied.The results show that the compressive strength of magnesium oxysulfate cement at 1d phase increases from 31.3MPa to 48.7MPa with the increase of silicon and calcium content,and the increase rate is 55%.The compressive strength of 7d phase increases from 44.5MPa to 55.6MPa with an increase rate of 25%.The compressive strength at 28d increased from 54.2MPa to66.7MPa,with an increase rate of 23%.The strength influence rate decreased from 55%at 1d phase to 23%at 28d phase.However,after 28d of soaking in water,the loss rate of compressive strength increased from 17.2%to 47.8%,and the softening coefficient gradually decreased,resulting in poor water resistance.In order to further study the properties of magnesium oxysulfate cement,the effect of curing conditions on strength was studied.Experimental results show that in90±5%relative humidity,temperature 45±2?condition,themagnesium oxysulfate cement compressive strength of 3d age reached a maximum of 60 mpa,and the temperature 20±2?and temperature 30±2?,the maximum compressive strength at 7d age when maximum.This indicates that the high temperature and high humidity conditions are conducive to the early strength improvement of magnesium oxysulfate cement,but the high humidity conditions in the later stage will lead to the reverse shrinkage of magnesium oxysulfate cement.Finally,the effects of the molar ratio of MgO/MgSO₄,the content of active filler,the type of inactive filler and water-resistant agent on the mechanical properties,crack resistance and water resistance of MgO/MgSO₄ cement handicraft were studied.The experimental results show that the increase of MgO/MgSO₄ molar ratio will lead to the decrease of the flexural strength and compressive strength of MgO cement crafts and the appearance of surface cracking.When the molar ratio of MgO/MgSO₄ is 7:1,10%of the active filler and 35%of the inactive filler,the flexural strength,compressive strength and cracking resistance of the handicrafts reach the best.When Z3 water resistance agent was selected and the content was 1.5%,the water resistance of the handicraft was the best.The flexural resistance and compressive softening coefficient of the sample were up to 0.93 and 0.89,respectively.