Research On The Modification And Application Of Basic Magnesium Sulfate Cement

Basic magnesium sulfate cement?BMS?is a high performance magnesia cement which is modified by adding a small amount of admixture to change the composition of the hydrated magnesium cement and endows its high performance.It has the advantages of low consumption of energy,light quality,low density,high strength,high flexural-compression ratio,resistance to abrasion,low alkalinity,corrosion resistance to salt brine,no frost to white and so on.Based on the development of new admixtures,the effects of polypropylene fiber,heavy calcium powder and talc on the mechanical properties of basic magnesium sulfate cement and the possibility of using basic magnesium sulfate cement to prepare light foaming materials are studied,which provides a basis for the application of basic magnesium sulfate cement in woodworking process.In this paper,the main research contents and results could be summarized as follows:1.Using organic acid A and different weak-acid salts B,C to prepare composite admixture respectively,the effects of different kinds and dosages of admixtures on the flexural strength and compressive strength of basic magnesium sulfate cement were studied.Two kinds of excellent composite admixtures AB3 and AC5 were obtained,then using SEM and XRD to characterize.The results show that when the content of AB3 and AC5 is 0.2%of the mass fraction of light-burned magnesium oxide,the flexural strength of 28 d can be increased by more than 300%,and the compressive strength can be increased by more than 120%.With the increase of dosages of composite admixtures AB3and AC5,the early strength of basic magnesium sulfate cement will be reduced,but the later strength will be improved,the composite admixture AC5 can make the basic magnesium sulfate cement form higher early strength than AB3,the flexural strength of 28d with AC5 is higher,and the compressive strength of 28 d with AB3 is higher.Combined with SEM and XRD,it is found that a better basic magnesium sulfate cement 517 phase?5Mg?OH?₂·Mg SO₄·7H₂O?was produced by adding composite admixtures AB3 and AC5.The mechanism of admixture is preliminarily discussed.2.Basic magnesium sulfate cement as a brittle matrix,it is necessary to study the law of fiber reinforcing and toughening,at the same time,in order to reduce the cost,it is necessary to study the influence of mineral additives on the mechanical properties of basic magnesium sulfate cement.To this end,the effect of different amount of polypropylene fiber,heavy calcium powder,talc on the strength of basic magnesium sulfate cement are studied.The results showed that with the increase of the amount of polypropylene fiber,the flexural and compressive strength of basic magnesium sulfate cement increased first and then decreased,and the flexural and compressive strength of basic magnesium sulfate cement remained high and stable at 0.2%?0.8%.Adding heavy calcium powder can increase the compressive strength of basic magnesium sulfate cement,but reduce the flexural strength.Adding talc can greatly improve the flexural strength of basic magnesium sulfate cement,but has a negative effect on the compressive strength.Combined with SEM and XRD,it is found that heavy calcium powder only plays the role of filling material and forming structural skeleton in the basic magnesium sulfate cement.Talc plays not only the filling material and the structure skeleton in the basic magnesium sulfate cement,but also participates in or promotes the reaction of basic magnesium sulfate cement to produce 517 phases.3.Using water cement ratio A,total admixture content B,mass ratio of heavy calcium powder and talc C as 3 factors,3 factors and 3 level orthogonal test are designed to analyze the influence of heavy calcium powder,talc and water cement ratio on the strength of basic magnesium sulfate cement.The results show that water cement ratio has a great influence on the strength of basic magnesium sulfate cement.When the water cement ratio is relatively high,the addition of a large amount of mineral additive can improve the flexural and compressive strength of basic magnesium sulfate cement.In the case of composite additive,the influence of factors B and C further revealed that the talc can improve the flexural strength of basic magnesium sulfate cement,and the heavy calcium powder can improve the compressive strength of basic magnesium sulfate cement,the above research results provide an important basis for basic magnesium sulfate cement composite heavy calcium powder and talc.4.Using hydrogen peroxide as a foaming agent and GTXA as a stabilizer with heavy calcium powder and talc as additives to make a foam BMSC composite material with different density grades and study the strength of foam BMSC.The results show that with the reduction of density grade,the flexural and compressive strength of foam BMSC are a significant downward trend,but the flexural-compression ratio increases.The foam BMSC has the advantages of high strength and high flexural-compression ratio of basic magnesium sulfate cement.With the decrease of water cement ratio,the flexural strength and compressive strength of foam BMSC have been improved in different degrees.While the flexural strength of the specimens is improved,the compressive strength of the specimens is not greatly reduced by adding a small amount of talc.