Formation Mechanism And Dynamics Of Belite-barium Calcium Sulphoaluminate Cement Clinker

Belite-calcium barium sulphoaluminate cement is a new type cementious material. It ischaracterizied by low Ca(OH)2content after hydration, excellent resistance and volumestability, high long-term strength and low hydration heat. Besides, owing to relative lowersintering temperature, low energy consuming and low lime saturation factor, low caloric fueland low grade limestone can be utilized during the manufacture of clinker. In order to controlthe manufacture of the new type cement clinker effectively and regulate the phasecomposition as well as the performance of cement clinker system, it is meaningful to gain adeep insight into the formation mechanism and formation kinetics of the new type cementclinker, which can provide theoretical and technical reference for engineering application. Theresults of the investigation are as follows:BaO, BaSO4and CaF2can promote the formation of belite. The main polymorphs ofbelite are β-C2S and γ-C2S. BaO, BaSO4and CaF2can stabilize β-C2S.When the amount ofBaSO4and BaO exceeds3.0%, there is a minor amount of α’-C2S in the sample. The apparentactivation for the formation of belite with0and0.6%CaF2are206kJ·mol-1and164kJ·mol-1separately. Therefore, minor CaF2can lower down the barrier of the formation of belite.When the sintering temperature is1450℃, the main alite polymorph is M3-C3S. Alsothere is a minor amount of T3-C3S, R3-C3S and T1-C3S in the sample. With the rise of BaSO4content, there is a decrease of alite content in the sample, proving that BaSO4can restrain theformation of alite. CaF2can promote the formation of the alite, the main polymorph of aliteare M3-C3S, T3-C3S and R3-C3S when the sintering temperature is1380℃. With the rise ofCaF2content, there is a rise in M3-C3S content while T3-C3S and R3-C3S do not varysignificantly.C2.75B1.25A3Smineral begins to form at1100℃, form largely at1350℃and start todecompose at1370℃. The formation of C2.75B1.25A3Smineral follows the followingchemical reaction equation:11/4CA+BaSO4+1/4Al2O3+1/4BaOâ†'C2.75B1.25A3S11/48C12A7+BaSO4+67/48Al2O3+1/4BaOâ†'C2.75B1.25A3S1/4CaO+BaSO4+3Al2O3+1/4BaOâ†'C2.75B1.25A3S 11/48C12A7+BaSO4+1/4BA+55/48Al2O3â†'C2.75B1.25A3C2.75B1.25A3Smineral formation is controlled by the diffusion mechanism and comply withthe kinetics model of D4=1-2α/3-(1-α)2/3. In range of1100-1300℃, C2.75B1.25A3Smineralformation, the apparent activation energy of C2.75B1.25A3Smineral formation is227.5kJ·mol-1. When sintering temperature rises to1300-1380℃, the apparent activation energylowers to175.9kJ·mol-1. The decomposition of C2.75B1.25A3Sis controlled by interfacialchemical reaction mechanism and complys with kinetics model of R2=1-(1-α)1/3. The apparentactivation energy of C2.75B1.25A3Smineral decomposition is calculated to be449.78kJ·mol-1.The main products are C3A, BA and SO3after the decomposition of C2.75B1.25A3S.In binary system of C2S-C2.75B1.25A3S, the formation of belite is promoted owing to Sand Ba. The main polymorph of belite is β-C2S. In the range of1300-1350℃,belite providessurface to the formation of C2.75B1.25A3S, which inevitablely lower down the nucleationbarrier. Therefore, the formation of C2.75B1.25A3Sis promoted. Besides, the decomposition ofC2.75B1.25A3Sis inhibited. C2.75B1.25A3Stends to grow on the surface of belite. In the binarysystem of C3A/C4AF-C2.75B1.25A3S, at1350℃and1380℃, intermediate phase with highFe2O3content can promote the formation of C2.75B1.25A3S.16%intermediate phase can alsopromote the formation of C2.75B1.25A3S. Besides, intermediate phase with high Fe2O3andhigh content of the intermediate phase can promote the formation big size C2.75B1.25A3Smineral.In the clinker system, MgO can promote the absorption of f-CaO as well as the formationof alite and white intermediate phase. With1.0%MgO added into the meal, at1380℃, belitecan decompose and the size of the formed is small. When the amount of MgO rises to3.0%-5.0%, alite with big size can form and the size of alite becomes inhomogeneous. Thevolume stability of belite-calcium barium sulphoaluminate cement clinker is disqualified with7.0%MgO added into the raw meal. It mainly attributes to the formation of MgO ore pocket.The apparent activation energy for the formation of clinker with0.6%CaF2calculated to be195kJ·mol-1which lowers55kJ·mol-1compared with the apparent activation energy (250kJ·mol-1) for the formation of clinker without CaF2.