Formation of ye'elimite in Portland Cement Clinker by Annealing

【Author】

Xuerun Li;Xiaodong Shen;Jie Xu;Wenlong Xu;Yu Zhang;

【Abstract】

<正>Ye 'elimite contained Portland cement clinker was synthesized and the formation mechanism was investigated Microscope,back scattered electrical image and HRTEM were used to investigate the secondary formation of ye'elimite by heat treatment.The mineral composition of the clinker was gained with the help of GSAS with EXGUI based on the Rietveld method.Secondary formation temperature of ye 'elimite was 1250℃,and the reaction time was less than one hour. The proposed reaction was 3C_3A + C$ -> C_4A_3$ + 6C(C = CaO,S = SiO_2,A = Al_2O_3,F =Fe_2O_3, M = MgO,$ = SO_3).Such a reaction was validating for mixture of synthetical C3A and chemical pure C$.But for the clinker system,the calculated mineral contents were not quite suitable for the equation,the observed free lime of which was much less than the theoretical value obtained from the equation.The other reactants and products were under the rule of the equation.And the observed content of C_4AF increased after the treatment.This was probably caused by the following reason:there were some other reactions taking place to consume the free lime. Evidences from the microscopic images and the BSE picture with EDS mapping technology showed that separation of the phases among the interstitial phase took places during the heat treatment process.The Fe rich phase which was the C_4AF series while Al rich phase which was the C_4A_3$,separated into two main regions.Under the BSE image there existed white and black areas.And under the microscopic view one could see black dots in the interstitial phase.A more detailed examination of the sample with HRTEM showed that the both the C_3A and C_4A_3$ were incorporated with Fe.While the C_4AF series were quite different from the composition of C_4AF,in which the Al content was far away from the composition of C_4AF,instead,they were more close to the composition of C_2F with doped Al.The exsitence of other mineral other than C_4A_3$ might be in the clinker system,or there was a fertile related reaction occurred Originality Ye 'elimite was introduced to the cement clinker with the secondary formation.Before the secondary formation,the clinker was sinter at 1450℃to form a moderate content of alite.Finally one can get a clinker with both alite and ye 'elimite.A moderate content of alite certify the early and late performance of cement while the ye'elimite can enhance the early strength.The other existing phases were the usual phases of Portland cement,which could also contribute to the performance of cement.The secondary formation could be accomplished by a further treatment process during the cooling of clinker.This could be done with an additional reactor in the cooler or.just a modification of the existing cooler.But the overall economic efficiency should be confirmed.

【Keywords】

secondary formation;;ye 'elimite;;phase separation

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