Using Red Mud To Prepare Ferrite-rich Sulphoaluminate Cement And Its Hydration Hardening Properties

Sulphoaluminate cement,as a kind of cementite material with fast hardening and early strength,anticorrosion and impervious properties,performs well in special construction environment such as emergency repair and construction and ocean engineering.However,due to the high price of raw materials,sulphoaluminate cement has higher production cost,which limits its application.In order to reduce the cost of cement production,this paper uses red mud to replace part of raw materials and as the main source of ferric material to design and prepare ferrite-rich sulphoaluminate cement clinker system,which can reduce the cost of cement production and the calcination temperature.The hydration and hardening properties of ferrite-rich sulphoaluminate cement mixed with different varieties of gypsum were studied and the mechanism of hydration was revealed.By adjusting the appropriate process parameters of the production line,the optimal ratio was scaled up,and the pilot production of low cost ferrite-rich sulphoaluminate cement was carried out in the factory,and the comparison with the ordinary sulphoaluminate cement was analyzed.Through the above research,the following main conclusions are drawn.（1）The clinker with mineral composition of C₄A₃$,C₂S and ferrite can be successfully calcined by using red mud with industrial raw materials.The optimal ingredient group is limestone 51.89 wt.%,anhydrite 10.42 wt.%,bauxite 28.47 wt.%,low alkali red mud 9.23 wt.%,calcination temperature is 1300℃,holding time is 30 min.Microscopic analysis shows that the clinker contains 25.00wt.%ferrite,and when mixed with 15.00wt.%anhydrite,the 3-day compressive strength reaches 58.00 MPa and the 28-day compressive strength exceeds 90.00MPa.The addition of red mud and the increase of ferrite content can reduce the clinker calcination temperature.（2）The effects of anhydrite and desulfurized gypsum on the hydration reaction of cement clinker are different.When anhydrite is added alone,the hydration rate is low in the early stage,but in 9–12 h continuous hydration heat release,the formation of needle-rod ettringite can be observed,and the 3-day strength increases obviously.When desulfurized gypsum is added separately,the early hydration of cement rapidly exotherms heat,and the hydration acceleration stage occurs at 2–4 h.The strength of 4 h exceeds 20.00 MPa,but the sustainable development of the strength cannot be guaranteed.The combination of the two kinds of gypsum can improve the early strength and ensure the strength development.The optimal ratio is anhydrite 12.00wt.%,desulfurized gypsum 3.00 wt.%and clinker 85.00 wt.%.In this case,the 4 h compressive strength of cement is 19.20 MPa,and the 3-day compressive strength is 49.12 MPa.（3）Industrial production equipment was used to carry out scale-up tests in the actual production environment.The experimental results show that the ferrite-rich sulphoaluminate cement can be used for industrial mass production.The low-cost ferrite-rich sulphoaluminate cement clinker with mineral composition of C₄A₃$（46.70 wt.%）,C₂S（27.30 wt.%）and ferrite（23.40 wt.%）has been successfully prepared,and the production line capacity is 500 t/d.By comparing the low-cost ferrite-rich sulphoaluminate cement with the ordinary sulphoaluminate cement,it is found that the cement has the characteristics of faster hydration and higher early strength.Although the 3-day strength of the cement is lower than that of the common sulphoaluminate cement,it still conforms to the Chinese standard and has a good long-term mechanical property development.