Synthesis Of Ternersite-caicium Sulfoaluminate Cement From Low-grade Raw Materials

Ternesite-calcium sulfoaluminate（ye’elimite）cement,a new type of cement with a lower calcination temperature than sulfoaluminate cement about 100℃.And the carbon emission of the cement is lower than belite-sulfoaluminate cement about 46%.It’s a typical low-carbon and low-energy cement with great developmental prospects.The preparation of sulfoaluminate cement is restricted to large demands for high-grade bauxite.It’s a challenge for sulfoaluminate cement to expand the source of raw materials to lower the costs.Ternesite can theoretically reduce the demand for bauxite and expand the use of low-grade raw materials when introduced to sulphoaluminate cement.In this paper,low-grade raw materials with different Al₂O₃to Si O₂ratios will be used to prepare ternesite-ye’elimite cement.Cement with high content of ternesite will be designed and its hydration propertities will be researched.Firstly,the calcination of ternesite-ye’elimite cement is researched in this paper.The mix designing of the clinker mainly includes two aspects:one is to prepare a series of cement clinker with a gradient content of ternersite with the same raw material.The other is to prepare cement clinker with high ternersite content with raw materials of low Al₂O₃to Si O₂ratio.The results show that,clinkers with different ternesite content（30%～65%）can be prepared by bauxite and high-alumina fly ash at 1150℃with mineralizer.And clinkers with ternersite over 70%can be prepared by raw materials of low Al₂O₃to Si O₂ratio at 1150℃.Huge-sized ternesite whose crystallization completely have been observed in the clinkers as the calcination temperature is low.The structure is tighter and the porosity is lower in the clinker with higher ternersite content.Then,the effect of ternesite content on hydration performance of cement is researched.Properties including setting time,mechanical strength,dimensional stability are investigated for the macro performance.And the hydration is illustrated by p H value and XRD analysis.It is demonstrated that,the higher the content of ternesite,the slower the early strength developed.Although ternesite lower the early strength.Cement with a great value of ternesite（65.28%）shows compressive strength of 35MPa at 28d and up to45MPa at 91d,which increase at later ages is caused by the hydration of ternesite.Meanwhile,the p H value of the cement presents a trend of decreasing first and then increasing,which caused by the hydration product Ca（OH）₂.Finally,the hydration properties of cement with high ternersite content are studied,which prepared by different kinds of raw materials with low Al₂O₃to Si O₂ratio.Properties including mechanical strength,dimentional stability p H value and XRD results are investigated for the hydration.The results show that,the differences in raw material types also affect the macroscopic perfomance of cement,but the development of high ternersite content cement varies slightly.The early strength of cement developed slowly and the later strength develop steadily.Cement with～80%ternesite prepared by shale presents less than 15MPa at 28d,but the strength still maintains growing slowly in the later period.Superplasticizer and Al（OH）₃is added to the cement respectively to improve the performance of cement,which affects weakly at the early ages.The compatibility of superplasticizer varies in different raw materials.The research in this paper shows that ternesite-ye’elimite cement can be prepared from a wider range of low-grade raw materials.The performance of the cement is related to the content of ternesite.