Regularity Of Proportioning And Key Properties Of Basic Magnesium Sulfate Cement

Basic magnesium sulfate cement was developed by using the modern admixture technology to form basic magnesium sulfate cement whisker as the main hydration products of new type high folding strength of cement. It has a fast setting, early strength, high strength, water, water resistance, heat resistance,corrosion resistance, carbonation resistance, etc, its mechanical performance and durability such as protection of reinforcement ability with the same condition of Portland cement. In this paper,burned magnesia powder, magnesium sulfate, and admixture as the main raw material,by the determining setting time,strength and soundness of different molar ratio of basic magnesium sulfate cement systematically and exploring the relationship among the physical and mechanical properties of basic magnesium sulfate cement and raw materials, ingredients and curing process, the content of active magnesium oxide in caustic burned magnesia powder, magnesium sulfate crystallization water, the molar ratio of active magnesium oxide and magnesium sulfate are made in the reasonable scope.Main conclusions are drawn as follows:(1) Admixture is the key core technology for the producing of basic magnesium sulfate cement, under formed the condition of 5Mg(OH)2·Mg SO4·7H2O(5·1·7), the effect of different additive effect is very different.When a-Mg O:Mg SO4:H2O is determined,dosage of different admixture exists the best value.Admixture of Z8, Z10, Z12 can promote basic magnesium sulfate cement high-early-strength and shorten the setting time. Basic magnesium sulfate cement setting time is shorten with the increasing of the dosage of fly ash.As fly ash quantity additive to 50%, the setting time is shorten with admixture Z8 obviously.(2) Light burned magnesia mineral composition have different influences on the strength and setting time of basic magnesium sulfate cement. When the content of activity of Mg O is higher and the content of burnt Mg O and free calcium oxide(f-Ca O) lower, the mortar strength of basic magnesium sulfate is higher and setting time is shorter.When burnt Mg O content exceed 15% of the light burning magnesium powder and f-Ca O content more than 1.5%, and magnesium oxide activity is lower than 60%, the strength of cement mortar decreased obviously and net pulp setting time is extended; Among them, when the content of boron oxide over 0.7% in magnesium sulfate, it affects the mortar strength of basic magnesium sulfate cement seriously, especially the early strength.(3) Different crystallization of magnesium sulphate cement can be made into basic magnesium sulfate cement, but the basic performances are different.When the mole ratio of basic raw materials are determined, the highest strength of cement mortar strength and the shortest setting time is basic magnesium sulfate cement which is made by magnesium sulfate tetrahydrate, under the same admixture effect.The second is magnesium sulfate monohydrate basic magnesium sulfate cement, the last the seven water magnesium sulfate.(4) When a-Mg O/Mg SO4 is 8, specimens flexural strength and compressive strength of basic magnesium sulfate cement mortar are the best. The incorporation of concrete admixture, magnesium sulfate cement strength decreased significantly, with sodium nitrite and nitrate on the impact strength of cement mortar.(5) Curing humidity has significant effect on performance of basic magnesium sulfate cement Curing humidity, cement grinding process is oppositely.The higher the curing humidity, the longer the setting time of cement paste and the lower the strength of cement mortar. When relative humidity is 60%, the strength of cement mortar decreases to the same condition 62.5 R ordinary Portland cement standards.When relative humidity is 90%, the strength of cement mortar decreases to the same condition 32.5 R ordinary Portland cement standards.In high humidity environment, moisture-proof bag works best.(6) Basic magnesium sulfate cement can be divided into ordinary and super early strength cement, ordinary type basic magnesium sulfate cement which is using the original admixture are divided into 62.5R, 52.5R, 42.5R;Super early strength basic magnesium sulfate cement which is using the new type admixture are divided into 62.5R, 52.5R. With 50% of fly ash or slag to replace light burning magnesium powder, strength grade can reach 52.5 R, and flexural strength higher 149% than that of silicate cement.(7)Hydration products of basic magnesium sulfate cement is 5·1·7.The content of 5·1·7 phase in cement increases under the effect of admixture obviously, the content of Mg(OH)2 decreases significantly, magnesium oxide relative surplus increase.Namely, it inhibit the Mg O in magnesium sulfate solution transforming to Mg(OH)2 by adding additive, promoting the transformation of 5·1·7 phase consequently.New phase 5·1·7 whisker morphology for long and thin shape, diameter of about 200 nm ~200 nm, length is 8 microns ~15 microns, length to diameter ratio of 40~50, whisker freely crisscross, forming dense spatial reticulated structure, so the basic magnesium sulfate cement has the very high flexural strength cement.