Effect Of Doping BaO And BaSO₄ On Synthesis And Performance Of Alite-rich Cement Clinker

With the development of the society, cement is developing in the trends which are high property, low energy consumption, excellent durability and conforming to the development of ecology. The cement clinker with high cementing property plays a key role in preparation of high performance cement, and increasing the amount of alite (C3S) in clinker is deemed to be one of effective ways to enhance the performance of cement. The doping technology is the most important method to prepare alite-rich Portland cement clinker. Therefore, the influence of BaO on composition, structure and performance of alite-rich cement clinker and burnability of raw material were studied in this paper. In addition, this paper studied the kinetic mechanism of formation process of alite-rich cement clinker doped BaO in order to gain the kinetic data of reaction. The addition of BaSO4 into clinker can decrease the formation temperature of alite-rich cement clinker, and furthermore form a new kind of calcium barium sulphoaluminate mineral (C2.75B1.25A3S ) with prominent rapid hardening and early-high strength. Calcium barium sulphoaluminate modified alite-rich Portland cement was synthesized at the base of this mineral. The composition and sintering condition of this kind of clinker were primary confirmed by using orthogonal test. The compositions, structures and performances of the doped clinker were analyzed by the means of X-ray diffraction, scanning electron microscopy-energy dispersive spectroscopy and metallographic microscope.The reasons why the mechanical performance of doped alite-rich Portland cement is better than that of Ordinary Portland Cement were illustrated further. Chief conclusions as follows:The addition of BaO can decrease the formation temperature and viscosity of the liquid phase.In the alite-rich Portland cement clinker, the optimal adding content of BaO was 1.5%, and the proper sintering temperature was 1400℃, which meaned great reducing of energy consumption since it was about 50℃lower than traditional Portland cement's calcining temperature. Under these processing conditions, the compressive strength of alite-rich Portland cement reaches 41.9, 73.7 and 110.4 MPa at 3 d, 7 d and 28 d curing ages, respectively, which shows excellent performance of mechanical strength. The addition of BaO can decrease the activation energy of the reaction and accelerate the formation rate of C3S. Formation reaction of this clinker belongs to diffusion kinetics, which meets the Glinstling kinetic equation: f(a)=1-2/3a-(1-a)2/3=Κt. However, the content of f-CaO increasesd and the crystallinity of C3S decreased at the temperature of 1450℃on the condition of doping BaO.On the condition of doping BaSO4, the optimal mineral compositions of alite-rich Portland cement clinker achieved in this paper are as are as follows: C2.75B1.25A3S 4.0%, C3S 65.8%, C2S 10.9%, C3A 7.7% and C4AF 11.7%. it means that the clinker contains C2.75B1.25A3S as 4.0% and alite-rich Portland cement clinker as 96.0%, thereinto, the modulus of the alite rich Portland cement clinker are: n=2.3, p=1.4, KH=0.94. The optimal sintering temperature, heat preservation time and cooling method are 1380℃, 60 min and two-stage cooling, respectively. Under these processing conditions, the compressive strength of calcium barium sulphoaluminate modified alite-rich Portland cement reaches 43.4, 80.6 and 123.8 MPa at 3 d, 7 d and 28 d curing ages, respectively, which shows excellent performance of mechanical strength. The addition of BaSO4 into raw material can decrease the formation temperature of cement clinker, and dramatically improve the general performance of this cement. At the same time, this calcination temperature means great reducing of energy consumption. The amount of alite in this clinker is much larger, in which the majority of them are irregular tabular and their outlines are quite clear. The outline of belite in this clinker is round-granule, and on whose surface obvious cross-double-crystal patterns distribute. In addition, the colour of belite is blue after being dipped, and the activity is enhanced.The addition of BaO and BaSO4 into raw material can increase the content of C3S mineral in clinker, promote alite and belite crystal's growth. Meanwhile it also can further contribute to the performance of the alite-rich Portland cement by activating the belite crystal structure.