Clinker Mineral Composition Design And Performance Regulation Of High-silic Ferro-sulphoaluminate Cement

Sulphoaluminate cement and ferro-sulphoaluminate cement are all derivative products of sulphoaluminate cement which is considered as“the third series of cement”independently invented by China.It has attracted much more attention in cement research and industry area due to its low-carbon nature,such as the lower energy and limestone consumption.Compared to that of sulphoaluminate cement with the main mineral composition ofC4A3Sand C₂S,ferro-sulphoaluminate cement are mainly composed ofC4A 3S,brownmillerite（C₄AF）and C₂S.Therefore,characteristics of sulphoaluminate cement,such as rapid hardening,early strength,high strength and micro-expansion are also inherited by ferro-sulphoaluminate.Furthermore,corrosion resistance of the cement will be improved by the increase of C₄AF.The developing of ferro-sulphoaluminate can overcome the demand of rare and expensive high-grade bauxite in production of sulphoaluminate cement clinker,which makes it more potential for extensive promotion and application.In fact,C4A3Sabove 55%,C₂S below 30%and C₄AF below 15%in ferro-sulphoaluminate clinker are generally adopted in order to make sure the higher early strength of the cement,that is,C₄AF and silicates phases are relatively lower.However,higherC4A3Sin ferro-sulphoaluminate clinker will lead to the concentrated early hydration heat and later mechanical properties shrinkage of the cement,and the greater reliance on high-quality raw materials will also be the problem.In the study,C₄AF and C₂S were proposed to be further increased which differed from traditional ferro-sulphoaluminate clinker,and a high-silic ferro-sulphoaluminate clinker（HSFC,C₂S≥40%,C₄AF≥15%andC₄A ₃S≤35%,as the three rate value was Cm:0.98±0.02,P:2.90±0.10,N:0.80±0.40.）and the cements were designed and prepared.It is expected that a new-type cement with wide adaptability of raw materials,rapid setting and hardening,high early strength and continued steady late strength growth can be obtained by the clinker design,mineral optimization and hydration regulation,to solve the matching problem of stable coexistence of high C₂S（C₂S≥40%）,high C₄AF（C₄AF≥15%）,and C₄A ₃S≤35%.Further,the industrial trial production was carried out to obtain the key process parameters for the production of HSFC cement.The new application fields of cement are explored to provide a direction for the application of high silicon iron aluminate cement.Firstly,based on the formation and coexistence theory of C₄AF,C4A3Sand C₂S,C4A3S-C₂S-C₄AF system was designed and prepared,formation process,composition and structures of C₄AF were emphatically studied.The formation mechanism of high gelling C₄AF was established.Fe content was mainly existed as C₄AF with high cementitious property in five-component Ca O-Fe₂O₃-Al₂O₃-SO₃-Si O₂system in the presence of sufficient Ca O.In this case,long needle like C₄AF mineral was well developed.Width and edge of long needle like C₄AF crystal increased with the increase of Fe content.Al₂O₃preferentially participated in the formation of C₄AF,so when the mass ratio was m（Al₂O₃）:m（Fe₂O₃）>2:1,which can ensure the suitable content ofC4A3Sin the system.Based on the above theoretical foundation,HSFC was prepared by using industrial raw materials in laboratory based on the above design method.Calcination and the composition,structures,properties of the HSFC were researched.The technology of stabilizing industrial raw materials to produce HSFC had been realized.HSFC could be obtained at a relatively lower calcination temperature（below 1330℃）.Optimal compressive strengths of the HSFC cement were obtained when design content of C₄AF was15%-25%,which reached 38.0-43.0 MPa at 1 day,58.0-62.0 MPa at 28 days,and 68.0-73.0 MPa at 60days,respectively.C₂F with lower hydration activity was observed when design content of C₄AF was greater than 25%,which would lead to a significant decrease in later strength.It is found that 20%content of C₄AF in HSFC was much more proper,flexural and compressive strength of the HSFC were 5.3MPa and 29.9MPa at 1 d,6.7MPa and 56.9MPa at 28 d,7.8MPa and 67.2MPa at 60 d,respectively.Total heat release of the HSFC during 7 days was less than 250 k J/kg.Industrial production of HSFC and the cement was realized based on the theorical design and experiments above,and successfully prepared for the first time on a 500 t/d NSP kiln.laid a theoretical foundation for the industrial production of high silicon iron aluminate cement Influence of particle size distribution,retarders and blend mateials on performances of HFSC cement were studied.It is found HSFC had better burnability,coal consumption and calcination temperature were significantly lower than that of ferro-sulphoaluminate cement clinker,and the HFSC produced by industrial production was better than that of experimental research.Optimized performances of HFSC cement were obtained when the surface area was controlled to 410 m²/kg,in this case,the35.0 MPa of 1 d compressive strength,69.3 MPa of 60 d compressive strength and below 251 k J/kg of the total hydration heat release during 7 days were observed.HFSC cement was prepared by HFSC,8-10%of anhydrite,less than 10%of limestone,and 20%of others containing slag and fly ash,28 d mechanical performance of the HFSC cement was comparable to that of P.O 42.5 ordinary Portland cement,and the early strength is significantly better than that of P.O 42.5.Finally,according to the physical characteristics of HFSC cement,such as rapid setting,rapid hardening,early strength and continuous strength growth in the later period,and the advantages of low production cost and green low-carbon,the new application of HSFC cement in well cementation under low temperature,planting concrete and shotcrete were explored,which will provide new directions for the application of HSFC cement.