Study On The Preparation Of Ternesite-calcium Sulfosilicate Cement

Sulphoaluminate cement(SAC)has the characteristics of early strength,fast hardening,low alkalinity,micro expansion and so on.It is widely used in various special projects,but it has the problems of high production cost and slow strength growth in the later stage of cement hydration.Compared with SAC,belite-sulphoaluminate cement(BCSA)has higher mineral content,lower calcium sulphoaluminate(C4A3 S)content,and lower requirements for aluminum raw materials.Therefore,it can be considered to replace the raw materials with industrial waste to prepare BCSA.However,belite mainly exists in the form of ?-C2S,and its hydration activity is low,which leads to the low strength of cement in the later stage of hydration,which limits the application of BCSA to a certain extent.In the process of sac firing,a transition mineral,calcium sulphosilicate(C5S2S),usually appears.The latest research shows that when C5S2S and C4A3S coexist,C5S2S shows higher hydration activity than belite.Therefore,this paper studies the influence of aluminum bearing minerals and curing conditions on the hydration activity of C5S2S and the influence of trace elements on the formation of C5S2S single ore and cement clinker minerals,so as to realize the coexistence of C5S2S and C4A3S minerals at low temperature,and to make C5S2S and C4A3S minerals coexist at low temperature minerals are introduced into BCSA in order to improve the slow growth of strength in the later stage of BCSA and form a kind of ternesite-calcium sulfosilicate cement with good performance,which is of great practical significance for the development of new low-carbon cement.In this paper,the effect of calcium fluoride on the synthesis of C5S2S and the hydration activity of C5S2S are studied.The purity of C5S2S synthesized with 0.5%calcium fluoride,the calcination temperature of 1200?,the holding time of 4h and the second calcination is about 98%.The results show that both C4A3S and C3A can promote the hydration activity of C5S2S and the activation of C3A to C5S2S mineral is stronger than C4A3S.Secondly,the hydration of C5S2S mineral was tested by changing the curing temperature and humidity.The results show that the hydration of C5S2S in the sealed condition is not promoted obviously by increasing the curing temperature.The increase of curing humidity promoted the hydration of C5S2S single ore and C5S2S mixed in C4A3S system,but did not promote the hydration of C5S2S mixed in C3A system.Then,the effect of trace elements on the formation of C5S2S mineral was studied.The results show that the effect of phosphorus and iron on the formation of C5S2S is not obvious,while sodium promotes the formation of C5S2S and reduces the temperature of its full formation.At the same time,the effect of trace elements on the coexistence of C5S2S and C4A3S minerals was also studied.The results show that the co-existence of the two minerals can be promoted by the appropriate content of trace element P,trace element Na and trace element Fe,and in the mixed trace elements,the effect of the mixed effect of trace element Na,P,f or trace element Fe,P and F is not as good as that of the mixed effect of P and F,and the effect of the mixed effect of P and F is not as good as that of the single mixed effect of P..The raw material ratio of ternesite-calcium sulfosilicate cement and the calcination process of cement clinker were further optimized to obtain cement clinker with good performance.In order to ensure that C5S2S and C4A3S minerals in cement clinker can be fully formed as much as possible,16%gypsum is selected as raw cement;the appropriate calcination temperature of cement clinker is 1150? and 1200?,and the heat preservation time is 30min.On this basis,the properties of ternesite-calcium sulfosilicate cement are studied and compared with BCSA.The results show that the setting time of ternesite-calcium sulfosilicate cement clinker is shorter than that of BCSA clinker.From the point of view of the strength of cement paste,the strength of BCSA increases slowly in the later stage,and the strength of ternesite-calcium sulfosilicate cement increases continuously in the later stage.The addition of trace element sodium will reduce the hydration activity of C5S2S in ternesite-calcium sulfosilicate cement,and reduce the early compressive strength of cement paste.