Papers by Keyword: Belite

Abstract: The study of the influence of selected temperature regime and potassium ions on the process of synthesis of belite (2CaO·SiO₂, C₂S) was carried out. The basic raw material was calcium carbonate (CaCO₃) and amorphous silica (SiO₂). The dosage of both components was based on the stoichiometric ratio of CaO:SiO₂ in belite. The modification of the raw meal was carried out in the form of potash, K₂O. Potash was dosed in the form of potassium carbonate, K₂CO₃, and potassium sulfate, K₂SO₄. The firing process was performed in a superkanthal furnace with two temperature modes, firing temperature: 1150 °C / 3 hours soaking and 1450 °C / 5 hours soaking. The evaluation performed by the experiment was based on mineralogical analysis by XRD analysis.

Abstract: Cement industry is seeking alternative raw material and process to reduce the energy consumption and environmental impacts from conventional cement manufacture. This paper describes process of belite cements synthesis. Geothermal sludges, an undesired waste from Dieng Geothermal Power Plant as amorphous silica source and calcium hydroxide were used to form belite cement at elevated temperatures. Experimental results showed that principal phase of belite cement (larnite or β-Ca₂SiO₄) was formed at temperature as low as 800 °C. Thus, the geothermal silica is shown to be very promising starting material for the low-temperature production of belite cement.

Abstract: Cement clinker with low CO₂ emission was prepared in laboratory, which mainly consist of belite (C₂S), calcium sulfoaluminate (C₄A₃S), and ferrite (C₄AF). The mineral composition of clinker was optimized for better compressive strength development. The chemical and physical properties of this prepared cement were characterized through X-ray diffraction (XRD), back scattered electron-scanning electron microscopy (BSE-SEM) and differential thermal analysis (DTA). The results reveal that C₄A₃S governs most of the compressive strength at early ages, while C₂S contributes to the later strength development. C₄AF is in liquid when fired to 1300°C, beneficial to the mass transfer but causing high crystallinity of C₂S when excessive. Finally the results of experiments suggest that the optimal composition of clinker is 50wt. % C₂S, 40wt. % C₄A₃S and 10wt. % C₄AF.

Abstract: Main phase of belite cement is β-C₂S. This modification is distinguished by low hydration speed compared to alite, which is main mineral of commonly produced cement. It is possible to increase the low hydration speed by modification of raw mixture by potassic ions, which basically change the belite structure. It leads to the content increase of internal free energy and therefore its reactivity too. Positioning of potassic ions in produced clinker is solved by combined burning.

Abstract: Portland clinker is thanks to its large-scale production a continuously studied topic. Clinker, or Portland cement, is used for construction purposes or for insulation and special applications. One of these special applications could be shielding of different types of radiation by making use of the content of barium ions. The present article examines the influence of barium oxide on the formation and properties of Portland clinker, which could be, by incorporation of barium ions into the system, used as a binder for buildings resistant to various types of radiation. Barium sulphate and barium carbonate were added to the raw meal in order to prepare clinkers with different content of barium oxide. The effect of barium on the formation of clinker phases was studied (by XRD – Rietveld analysis and by the microscopic point counting method), as well as the rate of alite formation under isothermal conditions. Furthermore, the ability of barium to become a part of clinker minerals was studied by SEM with EDS.

Abstract: Within the research at Institute of Technology of Building Materials and Components the questions of belite cement hydration speed improvement have been solved for a long time. In comparison with common Portland cements (alite type) these cements obtain almost identical final properties but the main shortage of them due to which they are not practically produced is their very low hydration process speed and thus insufficient initial strength for construction practice. A development of lower hydration heat is another difference of the belite cement from common Portland cements. In case of concreting of massive constructions as for example water dams this can be perceived as an important benefit, however in case of concreting during cold season of the year this appears as a definite negative. The belite cement also shows a lower inclination to concrete efflorescence and higher strength to aggressive environment due to lower CaO content. Both of the properties can be definitely understood as benefits compared to orthodox alite clinker. The raw material base of belite cements require less lime than production of common Portland cements and on that ground the implementation of its production would be a positive benefit for ecology in sense of CO₂ emission reduction and also in improvement of economy of non-renewable raw material sources. The raw material is burnt to lower temperature than alite cement resulting in lower CO₂ emission released in the atmosphere during the cement production. In addition at reduction of the temperature for more than 100 °C also heat consumption is reduced for 10 to 14 %, which has positive economical and ecological effects due to lower consumption of fuels. Within the research focussed on improvement of belite cement properties the study of hydration process course and technological properties of belite (C₂S) prepared using low-energy burning modes was the aim of the research.

Abstract: The paper focuses on the study of the formation mechanism of belite (dicalcium silicate) catalyzed with potassium ions in the form of chemically pure salt of potassium sulphate at various modes of firing in order to increase its reactivity. To verify the function of potassium sulphate as a substance enhancing the reactivity of C₂S, 3 material mixtures were tested; they contained 0, 1 and 2 % of K₂O recalculated per fired dicalcium silicate.

Abstract: The effect of MgO on performance of belite-barium calcium sulphoaluminate cement (B-CBAS) was investigated through orthogonal tests. The results show that the formation of C₃S can be improved at low temperatures by mixing MgO. SO₃ decreasing the viscosity of fused mass in sintering process was beneficial to solid solution of MgO in B-CBAS clinker. The solid solubility of MgO in B-CBAS was higher than that of Portland cement, which indicated that high-magnesium limestone can be used in B-CBAS. Even MgO content reached 5.14%, the soundness of B-CBAS was still in safe, whose compressive strength at 3d and 28d curing age were 49.1MPa and 81.9MPa. This indicated that this kind of cement has good mechanical properties.

Abstract: The mineral structure and performance of belite-barium calcium sulphoaluminate cement clinkers were investigated by petrographic analysis, X-ray diffraction and scanning electron microscopy. The experimental results showed that the minerals of calcium barium sulphoaluminate (C_2.75B_1.25A₃) and C₂S could coexist in the belite-barium calcium sulphoaluminate cement clinker, and the optimal sintering temperature was 1380°C, at which, more C_2.75B_1.25A₃was formed, well developed and also evenly distributed in the optimal sintering condition. If the sintering temperature exceeded 1380°C, the decomposition of C_2.75B_1.25A₃ would speed up and the C₃S became inactivate for its excessive development. In the optimal sintering condition, the compressive strength of the prepared cement at 3, 7, 28 d were 32.6, 47.9, 88.5 MPa respectively, which exhibited excellent mechanical properties.

Abstract: The mineral structure and performance of belite-barium calcium sulphoaluminate cement clinker were investigated by petrographic analysis, X-ray diffraction and scanning electron microscopy, while raw materials were studied by differential thermal analysis, thermogravimetric analysis and X-ray diffraction. The results show that high-silicon limestone has low decomposition temperature which can promote the development of alite by adding small quantity. The formation and development of C3S is hindered in α-quartz while C3S is formed easily by mixing magnesite and dolomite in the low temperature. The proper proportions of high-silicon limestone and ordinary limestone is 1:5, and the compressive of this cement at 3, 7, 28 d are 37.9, 60.3, 87.9 MPa, which shows excellent mechanical properties.