| Abstract [eng] |
In this study properties of natural raw and industrial waste materials was determined in order to use them to create hydraulically active belite and belite sulfoaluminate cements. For this purpose, various technologic parameters for manufacture of belite cement were investigated: optimal conditions for hydrothermal synthesis of α-C2SH; the kinetics of the products burned at 450–1000 °C temperature and their hydration process. In purpose to create belite sulfoaluminate cement there were theorical calculations made for the primary mixture, moreover, clinker‘s burning conditions were determined, ivestigated its hydration process and the impact of the impact of different amounts of gypsum addition to the clinker‘s hydraulic properties. The purpose of this work was to determine the formation of dicalcium silicates during the hydrothermal synthesis and thermal activation, to investigate the impact of mineral composition of the products on the hydraulic activity and to create the mixtures for manufacture of belite and belite sulfoaluminate cements. Mixture which was prepared for belite cement contained of burned lime and burned opoka. The optimal temperature for burning the lime was determined to be 900 °C for 1 h, because under these conditions the biggest amount of free CaO was obtained (82.5 %). Opoka needs to be burned 775 °C for 1 h (19.15 % of free CaO). For primary mixture belite sulfoaluminate cement, these materials were used – hard coal fly ash, limestone and anhydrite. The amounts of required primary materials were calculated in order to obtain ~70 % β-C2S and ~25 % ye‘elimite (Ca4Al6O12(SO4)) during the burning process. α-C2SH was synthesized by processing opoka-lime mixture (molar ratio CaO/SiO2 =2.0) under hydrothermal conditions. The optimal conditions of synthesis were determined: duration of the isothermal curing at 200 °C – 12 h, water/solid ratio W/S =10.0, stirring speed – 50 RPM. It was found that during the thermal activation of hydrothermal synthesis products at 450–1000 °C temperature, forms various polymorphs of dicalium silicates. x-C2S and γ-C2S were formed and remained stable until 700 and 800 °C, respectively. β-C2S starts composing at 600 °C temperature and remains stable even after thermal treatment at 1000 °C, α‘L-C2S appears only at 900 °C and the amount of it increases after burning at at 1000 °C. It was determined that during the thermal activation of milled α-C2SH and quartz sand mixture phases are changing differently. At 450 °C only x-C2S was formed and remained stable until 800 °C, while β-C2S started forming at 600 °C, the maximum quantity of it has been reached at 900 °C and most of it transited to α‘L-C2S or decomposed to wollastonite at 1000 °C. Calorimetric analysis for α-C2SH and α-C2SH in mixture with quartz sand, burned at 450–1000 °C temperature, was performed. The results showed that samples, burned at 450–600 °C temperature have hydraulic properties. According to the results, the most hydraulically active sample is α-C2SH in mixture with quartz sand, burned at 450 °C temperature: after 72 h of hydration it released the biggest amount of total heat – 67.52 J/g. This material is suitable for manufacture of fast curing binder material. During the manufacture of belite sulfoaluminate cement, β-C2S and ye‘elimite were obtained during the burning of primary mixture at 1225–1275 °C temperature for 1–6 h. The amount of these phases dependence on burning conditions was investigated and it showed that increasing the temperature and prolonging the duration of burning does not have a significant impact on the amounts of these phases: the amount of β-C2S increases from 61.4 to 66.3 %, ye‘elimite – from 21.6 to 25.1 %. For this reason the samples burned at 1225, 1250 and 1275 °C temperature for 1 h were chosen for calorimetric analysis. This analysis showed that the biggest amount of heat after 72 h was released in the sample, burned at 1275 °C temperature – 133.08 J/g. The influence of different amount of gypsum addition to the clinker‘s hydration was investigated. Three different SO3:ye’elimite molar ratios were chosen: 1, 1.5 and 2 (3.57, 6.64 and 9.52 wt.% of gypsum, respectively). The biggest value of total heat after 72 h of hydration was reached in the sample where SO3:ye’elimite molar ratio was equal to 1.5 – 133.55 J/g. The mortar strength test after 1, 7 and 28 days was performed and compressive strength was equal to 15.78, 19.92 and 20.70 MPa. The results of this study can be used for the manufacture of environmental-friendly, low burning temperature hydraulic cements. |
