Effect Of Protogenetic Sulfate On Physical Properties Of Portland Cement

With the development of technology and energy conservation and emission reduction, the content of protogenetic sulfate in Portland cement clinker improves, some of the development of desulfurization technology also improves the SO3 content in the mixed material. In order to prevent and suppress the adverse effects brought by the excessive sulfate in cement, the national standard restriction the total SO3 content on cement, also SO3 content of the mixed material. The restriction of SO3 makes the high sulfate residue difficult to get actual application. Some people even worry about the excessively high sulfate content in clinker causing adverse effects. Indeed in cement production often requires some gypsum. If the protogenetic sulfate can replace gypsum to a certain extent, we do not have to worry about the negative impact brought by excessive sulfate content, and we can even use the residue which SO3 content exceeding the national standard restriction. Therefore, we must understand the differences between the effect of protogenetic sulphate and gypsum on cement performance.①The 3K2SO4·Na2SO4 and 2CaSO4·K2SO4 are simulated by the high-temperature synthesis. Through calcinating the temperature to 1000 oC and holding 2 hours, we get 3K2SO4·Na2SO4. By the same procedure, at the temperature of 920 oC and holding 2 hours, we get 2CaSO4·K2SO4. We tested the differences of dissolution properties between the protogenetic sulphates and gypsum by means of the aqueous method. The dissolution rate is 3K2SO4·Na2SO4 > 2CaSO4·K2SO4> gypsum.② Adding the 3K2SO4·Na2SO4 and 2CaSO4·K2SO4 to cement clinker to study the effect of these protogenetic sulfates on cement setting time, compressive strength and volume stability. The protogenetic sulfates can significantly prolong the cement setting time and increase early compressive strength and improve the volume stability. But the effect of these protogenetic sulfates is different. On the whole, the effect of the 2CaSO4·K2SO4 is nearly equal to gypsum, but the 3K2SO4·Na2SO4 is not as good as gypsum.③ For studying the effect of tricalcium aluminate content on sulfates, it need to add some 3K2SO4·Na2SO4 and 2CaSO4·K2SO4 to the cement clinker with different content of C3 A, and test setting time, compressive strength and volume stability of the different cement system. In terms of setting time, although the tricalcium aluminate content increases, the setting time of the cement added 2CaSO4·K2SO4 still very long. But the setting time of the cement added 3K2SO4·Na2SO4 becomes short sharply when the C3 A content improves. When the C3 A content reaches 11.8%, it can’t meet the national standard on setting time. 3K2SO4·Na2SO4 increases the early strength of cement, but the later strength of cement retracts. The contraction and expansion of 3K2SO4·Na2SO4 cement are higher than gypsum and 2CaSO4·K2SO4 cement. 2CaSO4·K2SO4 improves the compressive strength and the dimensional stability of the cement. Overall, the effect of 3K2SO4·Na2SO4 second to gypsum, and it’s vulnerable to the content of C3 A. The effect of 2CaSO4·K2SO4 equal to gypsum, and it isn’t vulnerable to the content of C3 A.④ Studying the effect of 3K2SO4·Na2SO4 and 2CaSO4·K2SO4 on the cement hydration products and microstructure by XRD and SEM methods. The hydration products still mainly C-S-H, hydroaluminate hydrate, Ca(OH)2 and so on. There is a big difference in the SEM picture between the cements with different sulfate. There are many sodium hydroxides in the microstructure of 3K2SO4·Na2SO4. But at the same time, in the microstructure of 2CaSO4·K2SO4 is relatively compact.