Study On Preparation Of Alite-sulphoaluminate Cement By Phase-separation Method

Alite-sulphoaluminate cement is an energy-efficient cement with excellent properties.In this paper,the Alite-sulphoaluminate cement is prepared by the phase-separation combination method,According to the principle that the same minerals in the sintering temperature ranges are prepared together and the minerals with different sintering temperature ranges are separately prepared,the Alite-Belite-ferrite phase system clinker?basic clinker?and the calcium sulphoaluminate-Belite-ferrite phase system clinker?sulphoaluminate cement clinker?is mixed at room temperature to get Alite-sulphoaluminate cement.Firstly,the sintering system of the basic clinker was studied.And then the influence of gypsum on the hydration process and hydration degree was studied based on the optimal composition of basic clinker.Finally,the effects of the content of sulphoaluminate cement clinker?CSA?and the content of gypsum on the hydration process of Alite-sulphoaluminate cement.The main conclusions are as follows:For the basic clinker system,when the sintering temperature exceeds 1400?,the ferrite phase composition in the system has almost no effect on burning of clinker.The content of f-CaO fluctuates around 0.4 wt.%.XRD results show that the sintering temperature exceeds 1400?,the content of each mineral in the system is basically consistent with the design.The results of light microscopy analysis showed that the increase of the proportion of alumina in the raw material will cause the size of Alite grain to be larger.For the research on the hydration activity of basic clinker,the addition of gypsum can significantly promote the strength of cement at all ages.The blended cement with 5 wt.%gypsum shows the best performance in terms of the compressive strength development.The hydration heat results show that the induction period of cement after the addition of gypsum is significantly shortened.When the gypsum content exceeds 5 wt.%,the duration of the induction period is not changing.For the hydration degree of the basic clinker:According to Bhatty method results,the addition of gypsum significantly increased the early hydration kinetics of the basic clinker.When the amount of gypsum exceeds 3 wt.%,the early hydration degree is less affected.Monteagudo method results show that the hydration degree is close to100%at 28 days,the rules are consistent with the Bhatty method.For the preparation of alite-sulphoaluminate cement system,when the content of C₄A₃$is less than 3.4 wt.%,the alite-sulphoaluminate cement has excellent mechanical properties.With the increase of the content of C₄A₃$,the mechanical properties of alite-sulphoaluminate cement at all ages were improved.When the content of C₄A₃$exceeds 3.4 wt.%,the hydration of alite will be inhibited,affecting the early strength of cement.Changing the amount of gypsum can improve the hydration rate of alite.When gypsum/C₄A₃$<1.4,the hydration of alite is inhibited.When gypsum/C₄A₃$?1.4,the early strength increase obviously.However,excessive SO₄^2-reacts with AH₃ to form AFt,resulting in the volume expansion of cement and the decrease of compressive strength in the later age in alkaline environment.