Effect Of Minor Components On The Formation Mechanism Of Clinker,Hydration And Performance Of Belite-barium Calcium Sulphoaluminate Cement

Belite-calcium barium sulphoaluminate cement is a new type of cement characterized by low calcium, low carbon oxide emissions and low energy consumption. It will make significant sense to realize its industrial production and application. C urrently, high-quality limestone resources have been becoming increasingly scarce, so the utilization of industrial residue and low- grade limestone such as magnesia-rich limestone gains more attention. There exist various trace components in these materials, which may have a great influence on the sintering and properties of cement. This paper mainly investigates the influence of trace components(Na2O, K2 O and Mg O) on the formation mechanism of belite-barium calcium sulphoaluminate cement clinker and the hydration properties. It is hoped available data could be offered for further industrial production of this cement and effective utilization of magnesia-rich limestone in this type of cement clinker. The following major conclusions can be drawn:For the C2 S system, SO3 combined with Ba O, as well as cooperation of SO3, Ba O and Mg O can respectively decrease the amount of C2 S formed at 1000℃ by 22.95% and 26.56%, while they affect little on the large amount formation temperature and temperature of complete reaction. Codoped SO3, Ba O and Sr O can decrease the amount of C2 S formed at 1350℃ by 5.00%, but has little effect on the formation process. In contrast, Codoped K2 O and Na2 O both enhance the formation process of C2 S, and Na2 O has a more significant promotion effect. The amount of C2 S formed at 1000℃ is as high as 84.99% in the sample doped with SO3, Ba O and Na2 O, and the temperature of complete reaction is lowered to 1300℃。In addition, the trace components can stabilize β-C2 S and α’L-C2 S, in which Na2 O has the best ability to stabilize β-C2 S.The sampe systems of doping elements have the similar influence rule on C 3S with C2 S. Cooperation of SO3, Ba O and K2O/Na2 O can favor the formation of C3 S. In contrast, Na2 O plays a more significant role. When the sintering temperature is 1450℃, the content of C3 S in the sample with Na2 O is up to 73.31%. Besides, SO3, Ba O and Mg O simultaneously promotes the formation of C3 S at low temperatures, however, in which the total amount formed at 1450℃ decrease slightly. All the five kinds of dopants can stabilize M3-C3 S.The effect of K2 O 、Mg O and Na2 O on the formation and hydration activity ofC2.75B1.25A3 S is investigated. It is found that the decomposition temperature ofC2.75B1.25A3 S mineral gradually decrease with the dosage of dopants rising, while its thelarge amount decomposition temperature is still over 1380℃. When the dosage of K2 O is0.5%~0.8%, C2.75B1.25A3 S is synthesized better, and its hydration rate and release heat ishigher than that without K2 O. 3.0%~4.0% Mg O significantly favors the formation ofC2.75B1.25A3 S and Mg O(2.0%~5.0%) can promote the hydration activity of C2.75B1.25A3 S,moreover, the optimum dosage is 4.0%. In contrast, the promotion of Na2 O is realitivelyweaker, and excess Na2O(>0.6%)lead to an adverse effect.For the cement clinker, with low content of alkali, 3.0%~5.0% Mg O can obviously enhance the formation of C3 S and C4 AF. The hydration activity and properties can be improved at the optimum dosage of 5.0%. Furthermore, the soundness of cement is still qualified at 7.0% Mg O. Under the condition of high content of alkali, 3.0% Mg O promotes the formation of C3 S, besides, high content of Mg O(>5.0%) can also favors the sintering of cement clinker and mechanical properties. At a Mg O dosage of 7.0%, the cement develop higher compressive strength at required ages. In details, the compressive strengths of the cement at 1, 3, 7 and 28 days are 45.1, 66.8 and 103.2 MPa. Moreover, the cement with high content of Mg O(>5.0%) shows qualified soudness.Large amount of C3 S and C2.75B1.25A3 S forms in the cement clinker at 1300℃,while C3 A and C4 AF completely form at 1100℃. The suit sintering temperature for cement clinker is 1350℃. The above temperatures is not influenced by doping Mg O, Na2 O and K2 O, wherease the dopants can promote the formation of alite at low temperature and the formation of alite in small size of 3.5~14μm, especially when the dosage of Mg O and alkali is 7.0% and 1.290 Na2 O.eq, in which condition the content of C3 S at 1000℃ is18.37%, and it climbs up to 35.88% at 1350℃.