Performance Of Belite-Barium Calcium Sulphoaluminate Cement Preparaed By Low Grade Raw Materials And Industrial Wastes

With the rapid development of cement industry, the consumption of high-quality limestone and clay becomes larger and larger. In addition, the conventional Portland cement which has such disadvantages as high energy consumption, heavy pollution and poor concrete durability is difficult to meet the requirements of low-carbon emission, energy saving and high-performance concrete production. Therefore, it has become a hot topic of substituting industrial wastes and low-grade raw materials for high quality mineral resources to produce high-performance cement. Belite-barium calcium sulphoaluminate cement is new low-calcium cement, which has such advantages as energy-efficient, high early strength and excellent durability. All of these characteristics make it suitable for preparing high performance concrete. In this paper, low-grade raw materials and industrial wastes are used to prepare the cement clinker. And systematic investigations involving its preparation, structure and performance are conducted through XRD, SEM-EDS and HTM analysis. Meanwhile, the effect of BaO on the composition and structure of C₂S is studied by XRD, SEM-EDS analysis. The main conclusions are as follows:The belite-barium calcium sulphoaluminate cement can be prepared by high-silica limestone as raw material at a relatively low temperature about 1380℃, and the minerals of C₂S, C3S, C3A, C4AF and C_2.75B_1.25A₃S can coexist in this system. In addition, the high-silicon limestone can decompose at a relatively low temperature. Though theα-quartz inside can hinder the formation and development of C₃S, its intrinsic trace constituents such as MgO can promote C3S formation. With high-silicon limestone content increase, the compressive strength of samples in each age increase sharply firstly, and then decrease afterward. Finally, the compressive strength returns to growth slowly. The proper proportions of high-silicon limestone and ordinary limestone is 1:5, and the compressive of this cement at 3, 7, 28d are 37.9, 60.3, 87.9MPa, which shows excellent mechanical properties.Since the calcium carbide residue has a relatively low decompose temperature, its addition can decrease the temperature for liquid phase appearance, increase the liquid content, optimize the burn-ability of raw material and promote the formation and growth of silicate minerals. Using calcium carbide residue and high-silica limestone as raw materials can prepare belite-barium calcium sulphoaluminate cement at 1380℃, and the minerals of C₂S, C₃S, C₃A, C₄AF and C_2.75B₍1.25_A3S can coexist in the clinker. In addition, with decreasing the amount of calcium carbide residue, the compressive strength of cements in each curing age decreases firstly and then increases slowly. The proper proportions of calcium carbide residue and high-silicon limestone is 1:0. When all the calcium is provided by calcium carbide residue, and the compressive of this cement at 3, 7, 28 d are 29.3, 40.5, 81.1MPa respectively, which exhibits a favorable mechanical property.The optimal sintering conditions for preparing belite-barium calcium sulphoaluminate cement by fly ash are 1380℃in sintering temperature, 90min in time of heat preservation, and rapid cooling in cooling mode. Under the optimal sintering conditions, there are more C_2.75B_1.25A₃S minerals in clinker and the silicate minerals are well developed and evenly distributed. At 1380℃, the compressive of the belite-barium calcium sulphoaluminate cement at 3, 7, 28d are 32.6, 47.9, 88.5MPa respectively. With the increasing of sintering temperature between 1350℃and 1410℃, the compressive strength of samples in each age increases firstly, and decreases subsequently.Fly ash which can optimize the burn-ability of raw material, promote formation and growth of silicate minerals is in favor of the improvement of performance of belite-barium calcium sulphoaluminate cement, whose system the ratios of cement are designed as KH 0.81, IM 1.1 and SM 1.3. Furthermore, the proper proportions of clay and fly ash is 2:1, and the compressive of this cement at 3, 7, 28d are 34.6, 49.8, 92.2MPa respectively, which shows favorable mechanical properties.The C2S monomineral can be synthesized after two repeated calcination which is designed as 5℃/min in sintering rate, 1350℃in sintering temperature, 10h in heat preservation time, and furnace cooling in cooling mode.With external and internal addition of BaO content increase, the pulverization ratio of each sample decreases gradually. The addition of BaO is propitious to belite crystal growth and crystal stability at room temperature. When the external addition content of BaO is 5% (by the mass) which is the solid solubility limit, the pulverization ratio of each sample is touching bottom and the content of f-CaO is nearly maximized. At this time,β-C₂S is evenly distributed, appearing rounded crystal outline. When the mineral is designed as Ca_1.997Ba_0.03SiO₄, the content of f-CaO is close to the minimum and the size of mineral is about 7μm. As the doping content of BaO increases, the content of f-CaO is increases gradually. There is great degree of fusion between the crystals, which is not conducive to the formation and development of minerals.With the times of calcination and cooling rate increasing, the pulverization ratio decreased indistinctly. Compared with the doping effect of BaO, the times of calcination and different cooling mode are less obviously beneficial to theβ-C₂S stability.