Synthesis Of Belite-Barium Calcium Sulphoaluminate Cement Via Low Grade Raw Materials

Conventional Portland cement has increasingly the shortcomings and deficiencies. But the construction and the infrastructure quality are required more than bofore, and energy saving and environmental protection are concerned more and more by the international community. Under the pluralism of modern sociefy, the cement for construction projects demand is multi-purpose, high-performance requirements, saving energy and conserving resources and protecting the environment. Belite-calcium barium sulphoaluminate cement is a new cementing materials, which has the characteristics of saving energy, high strength and good durability. In this paper, low-grade raw materials and industrial waste slag are used to synthesis Belite-calcium barium sulphoaluminate cement of energy-efficient and high early strength. And technological condition, the effect of MgO and mechanism of hydration are studied, too. XRD, SEM-EDS, hydration heat analysis and lithofacies are used to analyze the composition of the cement clinker and structure morphology. The main conclusions are as follows:MgO had an important influence on cement sintering. MgO could promote the formation of C₃S at low sintering temperature, when Belite-barium calcium sulphoaluminate cement raw materials doped with MgO. It is benefit to absorb f-CaO, when MgO content was less than 3%. C₂S stability could be improved by effect of Mg²⁺ which dissolve in C₂S. High activity of C₂S was saved, which promoted C₂S hydration. And early mechanical properties improved significantly. SO₃ also had important influence on cement sintering. In Belite-barium calcium sulphoaluminate cement clinker burning process, Mg2+ was easy to transfer and dissolve in belite-barium calcium sulphoaluminate cement clinker. That's due to mineralization effect of SO₃, which decreased solution viscosity, and Mg2+ could be easy to diffusion.Belite-barium calcium sulphoaluminate cement clinker could have good soundness with excessive MgO. Belite-barium calcium sulphoaluminate cement clinker suitable burning temperature was 1380℃, low temperature sintering reduced the level of MgO over burning, which reduced the impact of hardened cement paste. Belite-barium calcium sulphoaluminate cement clinker had a high solid solution capacity to MgO. When MgO content was even 5.14%, soundness of belite-barium calcium sulphoaluminate cement was still in good statement, whose compressive strength at 3d and 28d curing age were 49.1MPa and 81.9MPa. This mean that this kind of cement has good mechanical properties. Therefore, high-magnesium limestone could be used to produce Belite-barium calcium sulphoaluminate cement.Belite-calcium barium sulphoaluminate cement could be produced by limestone of low-calcium and high-silicon. The optimal composition was confirmed with Portland cement as 91% and C_2.75B_1.25A₃S|- as 9.0%. And the optimal composition of Portland cement was iron modulus, silica modulus and lime saturation factor was 1. 3, 3.1 and 0. 81, respectively. Belite-calcium barium sulphoaluminate cement was prepared with the condition of sintering temperature was 1380℃and the optimal composition. Belite minerals were the eggs granular. It had good crystallinity, whose size ranging from 20μm to 35μm. Alite minerals were mostly long cylindrical and hexagonal plates, its crystal outline clear and complete, whose size ranging from 30μm to 50μm. Development of crystal was good. The compressive strength of the cement prepared under these conditions reached to 41.5MPa and 84.8MPa at 3d and 28d curing ages.Meanwhile, clay could be instead of the part of shale to prepare Belite-calcium barium sulphoaluminate cement. Shale could improve the raw material burnability, which had good for formation of cement minerals. The number of C₃S by shale preparation were more than by shale preparation in Belite-calcium barium sulphoaluminate cement clinker, alite crystal outline clear and complete, and the cement early strength was improved. This is due to shale had poor crystallinity, which had low heat requirements and beneficial to solid state reaction. That help to promote the formation of minerals. The clay crystal was fairly good, its doesn't easy to burn, which wasn't conducive to form C₃S.Because low-grade raw materials contain more MgO and other trace elements or are easy to burn. Those improved the formation of cement clinker and crystal structure, which increased activity of mineral. And cement hydration was faster. At 3 days curing age, AFt crystal of the needle intertwined each other. And it built into the cement matrix with Ca(OH)₂, the early strength was improved. At 14 days curing age, strength of the cement more than or close to the Portland cement. At 28 days curing age, a large number of C-S-H gels appeared, and it were flower-shaped. It intertwined with AFt and Ca(OH)₂, and the structure of the hardened cement paste was dense.