Optimization Of Preparation And Hydration Of Barium Calcium Sulphoaluminate Minerals Based On Rietveld Method

Sulphoaluminate cement plays an important role in construction and repairing of hydraulic engineering.Calcium sulphoaluminate mineral?C4A₃S?is an important component of sulphoaluminate cement.By substituting Ca²⁺ in C4A₃S with Ba²⁺,calcium barium sulphoaluminate(C_4-xB_xA₃???)can be synthesized to improve the performance of sulphoaluminate cement;simultaneously barium chemical waste can be used to reduce environmental protection pressure.But research on the sintering system and hydration mechanism of C_4-xB_xA₃??? minerals is not systematic.Based on Rietveld full-spectrum fitting quantitative analysis method,the synthesis and hydration of C_4-xB_xA₃??? were studied and the sintering system was optimized,meanwhile hydration process of C_4-xB_xA₃??? and the compositions of hydration products were analyzed.The main results include the following:With regard to optimization of C_4-xB_xA₃??? synthesis,the solid-phase reaction process of C_4-xB_xA₃??? at 25-1440 ? was summarized by high-temperature XRD and Rietveld full-spectrum fitting quantitative analysis method.Effects of different sintering temperature and prolong time on substituting ability of Ba²⁺ for Ca²⁺ in C4A₃S was analyzed by Rietveld method and characterized by substitution rate and utilization rate.Based on the analysis of the Ba²⁺ substitution rate,Ba²⁺ utilization rate and C_4-xB_xA₃??? content,it is concluded that the optimal sintering system is 1400? for 180min.For C_4-xB_xA₃??? prepared by BaCO3,the cubic crystal system accounted for 90.3 wt.%of the C_4-xB_xA₃??? content and the orthorhombic crystal system accounted for 9.7 wt.%of the C_4-xB_xA₃??? content,which was different from C4-XBXA₃S prepared with BaSO4 under the same condition.In condition of increasing substituting amounts,content of C_4-xB_xA₃??? increased first and then reduced.Mesophases of BaAl2O4,BaSO4 and Ca3Al2O6 were found in the clinkers of C_4-xB_xA₃???.When the Ba²⁺ replacement equaled to 0.6 mol,the content of C_4-xB_xA₃??? was 97.3 wt.%.In addition,with the gradual increase of Ba²⁺ replacement,the interplanar spacing of C_4-xB_xA₃??? increased gradually,the increasing rate increased rapidly when the replacement of Ba²⁺ was between 0.2mol and 1.4mol and the increasing rate tended to be slower when the replacement of Ba²⁺ was more than 1.4mol.With regard to hydration of C_4-xB_xA₃???,the hydration process and hydration products of C_4-xB_xA₃??? minerals were studied.Amounts of Ba²⁺ replacement have an impact on solid solution,hydration process,and hydration products and cement stone gelling performance.When the replacement of Ba²⁺ was 1.4mol the compressive strength reached the maximum,the compressive strength of 3d,7d respectively reached 50.9MPa,54.8MPa,which were higher than that of C4A₃S 96.5%and 85.8%in the same conditions at the same age.The dissolution of Ca²⁺ and Ba²⁺ in C_4-xB_xA₃??? was significantly increased by Ba²⁺ substitution,and the hydration activity was increased,meanwhile porosity of the pastes was decreased.Amount of hydrated product was the highest when the replacement of Ba²⁺ was 1.4mol.The combination of C_4-xB_xA₃???,gypsum and lime can be generated for tri-sulfur hydrated calcium barium sulphoaluminate?Ba-AFt?,monosulfate hydrated calcium barium sulphoaluminate?Ba-AFm?.The results by XRD,SEM-EDS and Rietveld fill-spectrum fitting show that the variation of interplannar spacing value of Ba-AFt and Ba-AFm is within 7%with various Ba²⁺ replacement.The average size of Ba-AFt and Ba-AFm was less than 4 times of AFt and AFm generated by C4A₃S under the same condition.The Rietveld full-spectrum fitting quantitative analysis showed that only about 90%Ba-AFt and about 80%Ba-AFm were prepared based on theoretical ratios for preparing absolute Ba-AFt and Ba-AFm.