Academic literature on the topic 'Belite clinker'

Low-lime saturated belite clinkers were prepared under different regimes of burning in the laboratory. Development of compressive strengths of the obtained belite clinkers was evaluated in relation to the reactivity of raw meals, burning temperature and time, and degree of lime saturation. Electron and optical microscopy, X-ray diffraction analysis and high-temperature microphotometry were the methods used for characterization of belite clinkers. It was discovered that the quickly-burnt belite clinker has unexpectedly lower hydraulic activity with respect to the longer-time burnt, recrystallized clinker. The reason could be little contamination of its crystal lattice by secondary oxides as determined by electron microanalysis.

This paper presents a laboratory study on active belite cement clinker using boron oxide as dopant to stabilize high temperature phases of Dicalcium silicate (C2S), and mineral waste as siliceous materials in complete replacement of clay. The clinker samples were soaked in Muffle Furnace at different burning temperatures and for various time durations, and then, cooled down to room temperature using air blower. Quantitative X-ray Diffraction analysis (QXRD) by Rietveld method indicates that major mineral components are Dicalcium Silicate (C2S), Ferrite (C2 (A0.48F1.52) O5) and trace amount of Tricalcium Silicate (C3S) in the cement clinkers. Among them, Dicalcium silicate is over 85 percent, Ferrite around 10 percent and Tricalcium silicate less than 10 percent. Thermogravimetric and Differential Scanning Calorimetric (TGA-DSC) spectrum shows that there is no significant phase change while cement clinker was cooling down, which means significant amount of high temperature polymorphic C2S was stabilized during cooling process. It is agreeable with the results from QXRD analysis. Specifically, among polymorphic belite phases, αH-C2S accounts for around 66% of cement clinker, and αL-C2S for about 22% of cement clinker. In addition, massive belite phase was identified by Scanning Electronic Microscope (SEM) analysis and Light Microscopy analysis. At last, the mechanical tests on active belite cement show that active belite cement clinker has a slow strength development at early ages, but rapid strength gain at 28 days in comparison with belite clinker without adding boron oxide. Thus, this active belite cement clinker demonstrates very promising prospect in sustainable cement industry development. Keywords: Active Belite Cement Clinker; Doped; Boron Oxide; αH-C2S; αL-C2S; Strength Development

In this work, it was found out that dicalcium silicate doped with SO3 shows higher hydraulic activity compared to pure dicalcium silicate. This finding was used to prepare and optimize high-belite cement from SO3 doped clinkers. The belite cement exhibited the same technological parameters, including short-term strengths, as ordinary Portland cement with a high content of tricalcium silicate. The clinker for belite cement is environmentally and economically advantageous. It is possible to burn the clinker at a temperature of 100 °C lower than conventional clinker and with lower consumption of calcium carbonate. In particular, methods of optical and electron microscopy were used for the research.

In this study, with iron ore tailing as an alternative to clay, three belite cement clinker samples were prepared in a muffle furnace at 1400°C for 10, 20 and 30 minutes respectively. And calcium sulphate and calcium fluoride were used as composite mineralizer with attempt to decrease clinkering temperature and improve hydraulic activity of dicalcium silicate. QXRD analysis shows that the major mineral components of the clinker are dicalcium silicate,account for over 80% of clinker, and trace amount of tricalcium silicate and ferrite. Scanning Electron Microscope (SEM) analysis indicates that mineral grains were growing with the prolonged soaking duration. EDS analysis identified that C2S has a Ca/Si ratio varying from 2.07 to 2.32. And XPS analysis shows substantial amount of S and F atoms indented on clinker surface. Using 4×4×16cm mortar specimen, the mechanical strength of belite cement with 5% gypsum addition was investigated based on Chinese National Standard. The testing results show that three belite clinkers give very promising strength development at early ages, and very high strength gain was achieved at 28 days. In addition, this belite cement has a Lime Saturation Factor (LSF) of 0.76, which make it have potential for significant CO2 emission reduction. Also, more than 35% iron ore tailing was exhausted for producing unit ton of belite cement clinker. High utilization rate leads to not only mineral waste exhaustion, also environmental improvement.

The synthesis of belite clinker was studied using industrial wastes: paper sludge, cement kiln dust and rice husk ashes, as substitutes for natural raw materials. Wastes were characterized by XRF, XRD and TG analysis. Different formulations were prepared to produce clinker at 1300, 1350 and 1400 °C. The clinker obtained was characterized using optical microscopy, XRD and f-CaO content determined by ethylene glycol method. Finally, the hydration of prepared cements with the clinkers was evaluated by isothermal microcalo­rimetry. It was found that by mixing paper sludge, cement kiln dust and rice husk ashes, it is possible to obtain belite clinker with f-CaO content below 0.5%, in clinkering temperatures between 1350 °C and 1400 °C without the use of natural raw materials. It was found that these cements have a high hydration kinetic, far above the rate of Ordinary Portland Cement, due mainly by the amorphous phase content in clinkers obtained.

Blended cements were prepared from belite clinker burned in a model kiln and ordinary industrial alite clinker. The mechanical and physical properties of these blended cements were determined. The difference in the development of hydration heat of belite and alite cements by using calorimetric method was determined also. The results show that strengths of prepared belite cement after 28 days of hydration are equal to those of industrial alite cement. Short time strengths are suitable for blended cements up to 30 % content of belite clinker. These results demonstrate the possibility of separate industrial belite clinker production next to common alite clinker manufactory and production of economically and ecologically advantageous blended Portland cements with suitable technological properties.

The paper deals with a formation of artificial rock (clinker). Temperature plays the capital role in the manufacturing process. So, it is useful to analyze a poor clinker to identify the different phases and defects associated with their crystallization. X-ray fluorescence spectroscopy was used to determine the clinker’s chemical composition. The amounts of the mineralogical phases are measured by quantitative XRD analysis (Rietveld). Scanning electron microscopy (SEM) was used to characterize the main phases of white Portland cement clinker and the defects associated with the formation of clinker mineral elements. The results of a study which focused on the identification of white clinker minerals and defects detected in these noncomplying clinkers such as fluctuation of the amount of the main phases (alite (C3S) and belite (C2S)), excess of the free lime, occurrence of C3S polymorphs, and occurrence of moderately-crystallized structures are presented in this paper.

This study investigated the influence of different cooling regimes on the microstructure and consequent reactivity of belite-sulfoaluminate clinkers. The cement clinkers were synthesized by incorporating secondary raw materials, such as titanogypsum and bottom ash, to the natural raw materials. Clinker phases were determined by Rietveld quantitative phase analysis, while the distribution morphology and the incorporation of substitute ions in the phases were characterized by scanning electron microscopy using energy-dispersive X-ray spectroscopy (SEM/EDS). Clinker reactivity was studied using isothermal calorimetry and was additionally investigated through compressive strength, which was determined for the cement prepared from the synthesized clinkers. X-ray diffraction analysis showed that, as well as the three main phases (belite, calcium sulfoaluminate, and ferrite), the clinkers contained additional minor phases (mayenite, gehlenite, arkanite, periclase, and perovskite), the ratios of which varied according to the cooling regime utilized. Microscopic observations indicated that the cooling regime also influenced the crystal size and morphology of the main phases, which consequently affected clinker reactivity. Furthermore, a smaller amount of substitute elements was incorporated in the main phases when cooling was slowed. Results showed that, in comparison to clinkers cooled at slower rates, air quenched clinkers reacted faster and exhibited a higher compressive strength at 7 days.

The potential use of steel slag from treated steel slag in belite-sulfoaluminate cements was investigated in this study. Cement clinkers with two phase compositions were synthesized, allowing the incorporation of different amounts of steel slag. The phase composition and microstructure of cement clinkers at three different sintering temperatures were studied by X-ray powder diffraction and the Rietveld method, as well as scanning electron microscopy with energy dispersive spectrometry. The results showed that the targeted phase composition of clinkers was achieved at a sintering temperature of 1250 °C. However, a higher amount of perovskite instead of ferrite was detected in the clinker with a higher content of Ti-bearing bauxite. Apart from the main phases, such as belite, calcium sulfoaluminate, and ferrite, several minor phases were identified, including mayenite, perovskite, periclase, and alkali sulfates. In both clinker mixtures, a higher content of MgO in the steel slags resulted in the formation of periclase. Furthermore, the hydration kinetics and compressive strength at 7 and 28 days were studied in two cements prepared from clinkers sintered at 1250 °C. As evidenced by the results of isothermal calorimetry, the hydration kinetics were also influenced by the minor clinker phases. Cement with a higher content of calcium sulfoaluminate phase developed a higher compressive strength.

Fly ash and phosphogypsum were used as Naturally Occurring Radioactive Materials (NORM) by-products for the synthesis of belite-sulfoaluminate clinkers. The influence of raw mixture composition and firing temperature was investigated. Clinkers and cements were examined by X-ray powder diffraction and scanning electron microscopy with energy dispersive X-ray spectroscopy. The compressive strength of the cements was determined after 28 days. Clinker phases identified included ye’elimite, ß-phase of belite, ternesite and gehlenite, while the main hydration product of the cement pastes was ettringite. The results showed that belite-sulfoaluminate cements can be fabricated with a compressive strength of 45.9 N/mm2 by firing the raw mixture (70 wt.% marl, 10 wt.% bauxite and 20 wt.% phosphogypsum) at a temperature of 1320°C/1h.

O presente trabalho aborda a incorporação de enxofre no silicato dicálcico (Ca2SiO4), fase cristalina que representa entre 20-40% em massa do clínquer de cimento Portland comum e que no âmbito da indústria cimenteira é conhecida como C2S (2CaO.SiO2), ou belita. Este composto apresenta cinco polimorfos, sendo que o polimorfo monoclínico ?-C2S de alta temperatura é o que apresenta maior reatividade com água. Realizou-se síntese de amostras de C2S, a partir de reagentes de alta pureza, com adições de enxofre na forma de CaSO4.2H2O segundo a proporção estequiométrica 2Ca:(1-x)Si:xS, onde x é a proporção catiônica de enxofre, que assumiu os seguintes valores: 0; 0,05; 0,3; 0,6; 0,1 e 0,2. Para determinar a composição das amostras sintetizadas, bem como os parâmetros de cela dos polimorfos de C2S, utilizou-se o método de Rietveld com dados de difração de raios-X. A determinação da micro-deformação e do tamanho médio de cristalito foi feita através do refinamento de parâmetros de função de perfil de pico após a calibração do difratômetro com óxido de cério. Os valores de micro-deformação de cristalito mostram correlação com o teor de enxofre incorporado no C2S. A reatividade com água foi determinada por calorimetria exploratória diferencial (DSC - differential scanning calorimetry), avaliando-se o calor de hidratação das amostras. Os resultados revelam maior reatividade com água e consequentemente maior formação de portlandita após hidratação, quanto maior o teor de enxofre. Os resultados revelam também que o enxofre estabiliza o polimorfo de mais alta temperatura ?-C2S. O máximo de incorporação de SO3 no C2S, em substituição ao SiO2, foi de 5 mol%, conforme checagem por balanço de massas com base na composição química determinada por fluorescência de raios X. A incorporação de enxofre causou uma variação progressiva dos parâmetros de cela: até 0,1% (Å) nos eixos cristalográficos (a, b, c) e 0,4% no ângulo ?. Esta variação sugere uma solução sólida do tipo substitucional (silício-enxofre) na estrutura do C2S.O presente trabalho aborda a incorporação de enxofre no silicato dicálcico (Ca2SiO4), fase cristalina que representa entre 20-40% em massa do clínquer de cimento Portland comum e que no âmbito da indústria cimenteira é conhecida como C2S (2CaO.SiO2), ou belita. Este composto apresenta cinco polimorfos, sendo que o polimorfo monoclínico ?-C2S de alta temperatura é o que apresenta maior reatividade com água. Realizou-se síntese de amostras de C2S, a partir de reagentes de alta pureza, com adições de enxofre na forma de CaSO4.2H2O segundo a proporção estequiométrica 2Ca:(1- x)Si:xS, onde x é a proporção catiônica de enxofre, que assumiu os seguintes valores: 0; 0,05; 0,3; 0,6; 0,1 e 0,2. Para determinar a composição das amostras sintetizadas, bem como os parâmetros de cela dos polimorfos de C2S, utilizou-se o método de Rietveld com dados de difração de raios-X. A determinação da micro-deformação e do tamanho médio de cristalito foi feita através do refinamento de parâmetros de função de perfil de pico após a calibração do difratômetro com óxido de cério. Os valores de micro-deformação de cristalito mostram correlação com o teor de enxofre incorporado no C2S. A reatividade com água foi determinada por calorimetria exploratória diferencial (DSC - differential scanning calorimetry), avaliando-se o calor de hidratação das amostras. Os resultados revelam maior reatividade com água e consequentemente maior formação de portlandita após hidratação, quanto maior o teor de enxofre. Os resultados revelam também que o enxofre estabiliza o polimorfo de mais alta temperatura ?-C2S. O máximo de incorporação de SO3 no C2S, em substituição ao SiO2, foi de 5 mol%, conforme checagem por balanço de massas com base na composição química determinada por fluorescência de raios X. A incorporação de enxofre causou uma variação progressiva dos parâmetros de cela: até 0,1% (Å) nos eixos cristalográficos (a, b, c) e 0,4% no ângulo ?. Esta variação sugere uma solução sólida do tipo substitucional (silício-enxofre) na estrutura do C2S.O presente trabalho aborda a incorporação de enxofre no silicato dicálcico (Ca2SiO4), fase cristalina que representa entre 20-40% em massa do clínquer de cimento Portland comum e que no âmbito da indústria cimenteira é conhecida como C2S (2CaO.SiO2), ou belita. Este composto apresenta cinco polimorfos, sendo que o polimorfo monoclínico ?-C2S de alta temperatura é o que apresenta maior reatividade com água. Realizou-se síntese de amostras de C2S, a partir de reagentes de alta pureza, com adições de enxofre na forma de CaSO4.2H2O segundo a proporção estequiométrica 2Ca:(1-x)Si:xS, onde x é a proporção catiônica de enxofre, que assumiu os seguintes valores: 0; 0,05; 0,3; 0,6; 0,1 e 0,2. Para determinar a composição das amostras sintetizadas, bem como os parâmetros de cela dos polimorfos de C2S, utilizou-se o método de Rietveld com dados de difração de raios-X. A determinação da micro-deformação e do tamanho médio de cristalito foi feita através do refinamento de parâmetros de função de perfil de pico após a calibração do difratômetro com óxido de cério. Os valores de micro-deformação de cristalito mostram correlação com o teor de enxofre incorporado no C2S. A reatividade com água foi determinada por calorimetria exploratória diferencial (DSC - differential scanning calorimetry), avaliando-se o calor de hidratação das amostras. Os resultados revelam maior reatividade com água e consequentemente maior formação de portlandita após hidratação, quanto maior o teor de enxofre. Os resultados revelam também que o enxofre estabiliza o polimorfo de mais alta temperatura ?-C2S. O máximo de incorporação de SO3 no C2S, em substituição ao SiO2, foi de 5 mol%, conforme checagem por balanço de massas com base na composição química determinada por fluorescência de raios X. A incorporação de enxofre causou uma variação progressiva dos parâmetros de cela: até 0,1% (Å) nos eixos cristalográficos (a, b, c) e 0,4% no ângulo ?. Esta variação sugere uma solução sólida do tipo substitucional (silício-enxofre) na estrutura do C2S.
The present study regards the incorporation of sulfur in dicalcium silicate (Ca2SiO4), a crystalline phase that represents 20 to 40 wt. % of the common Portland cement clinker. In the cement industry this compound is known as C2S (2CaO.SiO2) or belite. It has five polymorphs, and the monoclinic high temperature ?-C2S has the highest reactivity with water. The synthesis of the C2S samples was made with high purity reactants with addition of sulfur as CaSO4.2H2O, mixed according to the stoichiometric proportion 2Ca:(1-x)Si:xS, in which x corresponds to the cationic proportion of sulfur, with the values 0; 0.05; 0.3; 0.6; 0.1 and 0.2. The composition of the samples, as well as the cell parameters of the C2S polymorphs, was determined with the Rietveld method using X-ray diffraction data. Determination of micro-deformation and crystallite average size was made by peak profile function refinement, after calibration of the instrument with a cerium oxide standard. Micro-deformation values show a positive correlation with the sulfur content in the C2S structure. The reactivity of C2S with water was measured by the differential scanning calorimetry (DSC) of the heat of hydration. The results reveal a higher reactivity and consequently higher rate of portlandite formation after hydration, in samples with increasing sulfur contents. The presence of sulfur in the C2S structure stabilizes the high temperature polymorph ?-C2S. The highest SO3 incorporation in C2S, replacing SiO2, is 5 mol%, according to mass balance calculations with chemical composition obtained by X-ray fluorescence. The presence of sulfur caused a rogressive variation in the cell parameters: up to 0.1% (Å) in the crystallographic axis (a, b, c) and 0.4% in the ? angle. This variation suggests a substitutional solid solution between Si and S in the C2S structure.

DIPLOMA THESIS IS FOCUSED ON THE PREPARATION AND PROPERTIE OF BELITE CLINKER. IT IS BASED ON THE STUDY OF SCIENTIFIC ARTICLES DEALING WITH THE ABOVE MENTIONED TOPIC AS WELL AS THE ANALYSIS OF THE BRNO THD INSTITUTE´S RESEARCH RESULTS. AS PART OF MY EXPERIMENTAL WORK, A PROPOSAL OF THE COMPOSITION OF RAW MEAL TO EXTRACT BELITE CLINKER IN THE PRESENCE OF POTASSIUMS CARBONATE AND SULPHATE WAS MADE TO MODIFY RAW MEAL. THE PURPOSE OF MODIFYING RAW MEAL IS A POTENTIAL INCREASE IN BELITE CLINKER REACTIVITY. FURTHER THE EXTRACTION OF BYPASS DUST FROM A LOCAL CEMENT PLANT WAS CONDUCTED. THE EVALUATION OF THIS RESEARCH WAS MADE BY THE X-RAY DIFFRACTION (XRD) ANALYSIS METHOD.

Diploma thesis discusses about design composition and firing process modification of belite clinker. It also deals with the summary of knowledge about chemistry and production technology of portland cements with respect to its ecology and economy.

DIPLOMA THESIS IS DEVOTED TO THE STUDY OF PREPARATION OF PURE BELITE CLINKER FOR THE POTENTIAL INCREASE OF KINETICS OF THE HYDRATION PROCESS BY CHEMICAL ACTIVATION. THE THESIS OF THIS WORK IS BASED ON RESEARCH FINDINGS CONCERNING BELITE CLINKER AND RESEARCH AT THE INSTITUTE OF THD. THE THESIS AIMS TO DESIGN COMPOSITION OF THE RAW MEAL BURNING BELITE, FOLLOWING MODIFICATION BY SULPHATE AND POTASSIUM CARBONATE IN ORDER TO POTENTIALLY INCREASE THE REACTIVITY OF THE BURNT BELITE CLINKER AND THE LABORATORY FIRING OF PREPARED SAMPLES. THE LAST STEP WAS TO ASSESS THE MINERALOGICAL COMPOSITION OF BURNED SAMPLES XRD ANALYSIS AND FOLLOWING COMPARISON CELL PARAMETER OF BELITE WITH AND WITHOUT ADDED MODIFYING ADDITIVES.

The dissertation thesis is devoted to the study of belite clinkers and to the possibilities of the increase in their hydraulic activity. The mechanism and the kinetics of belite clinker formation were studied together with the relation of the velocity of these processes and the hydraulic activity of clinker. The influence of various parameters (degree of lime saturation, duration and temperature of burning) of the belite clinker preparation on the belite clinker development in time, on belite polymorphism, on the chemical composition of belite crystals and on the belite cement hydraulic activity was studied, too. The research methods used for the investigation involved electron microscopy, optical microscopy, X-ray diffraction analysis, high-temperature microphotometry and calorimetry. The resulting clinkers were hydraulically activated by addition of calcium sulfate. The experiments have proven that the higher rate of belite formation does not lead to the increase of its hydraulic activity, as opposed to that of alite. On the other hand, the chemical activation by sulfate anions enables to prepare clinker with relatively higher degree of lime saturation with minor admixture of alite and anhydrite, which is hydraulically activated. The work was concluded by experimental burning of belite clinker doped with sulfate anions in a model rotary kiln and by the preparation of cements blended with common industrial alite clinker. The results indicate the possibility of separate industrial production of special belite clinker alongside with common alite clinker and the production of economically and environmentally beneficial blended Portland cements with suitable technological parameters, or targeted production of special cements with properties corresponding to their required utilization.

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 master’s thesis 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 sulfate 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 integration), as well as the effects on the variations of temperature of the phase formation (TG-DTA) and 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, and the solubility of barium phases by ICP-OES. The hydration of clinker minerals containing barium was studied by isothermal calorimetry.

L’objectif de ce travail a été d’apporter une meilleure compréhension des mécanismes réactionnels de l’hydratation de ciments appartenant à la famille de ciment BCSAF afin de développer des schémas réactionnels simplifiés permettant d’optimiser les ciments à base d’un clinker BCSAF et d’autres constituants pour des applications spécifiques. Les ciments étudiés ont été réalisés à partir d’un clinker contenant 52% de belite, 33% de ye’elimite and 14% de ferrite et diverses quantités d’anhydrite et de calcaire. A partir de l’étude détaillée de l’hydratation d’un ciment contenant 95% de clinker et 5% d’anhydrite, il a été démontré que le mécanisme de l’hydratation est constitué de deux périodes successives : le début de l’hydratation est contrôlé par l’hydratation de la ye’elimite réagissant avec l’anhydrite, tandis que la suite de l’hydratation est contrôlée par les hydratations de la belite et de la ferrite qui réagissent avec certains des hydrates formés lors de la première période. La vitesse de nucléation de la strätlingite contrôle le début de l’hydratation de la belite. Le principal paramètre qui contrôle cette dernière est la concentration en sulfate de la phase aqueuse qui doit être très faible. Ainsi C-S-H n’est pas formé au début de l’hydratation de la belite certainement à cause de l’inhibition de sa nucléation par de trop fortes quantités d’aluminate en solution. Par conséquence, c’est indirectement la concentration en sulfate de la solution qui contrôle le début de l’hydratation de la belite and ainsi les réactions conduisant à sa réduction à travers la précipitation de phase notamment lors de l’hydratation de la ye’elimite pour former de l’ettringite. Ainsi d’une façon générale, la strätlingite commence à nucléer quand la ye’elimite a complètement réagi. D’autre part, une synergie entre les hydratations de la belite et de la ferrite permet de former des hydrogrenats et des C-S-H à des temps longs au détriment de la strätlingite formée auparavant. Un mécanisme d’hydratation similaire a été trouvé pour les ciments contenant des quantités plus importantes d’anhydrite à l’exception de ceux qui contiennent une quantité d’anhydrite supérieure que la quantité théorique permettant de faire réagir toute la ye’elimite en ettringite. Toutefois pour le premier type de ciments, une augmentation de la quantité d’anhydrite allonge à la fois le temps d’apparition de la seconde période et la durée des différentes étapes de cette dernière. Donc l’hydratation est globalement plus lente. Pour le second type de ciment, contenant de fortes quantités d’anhydrite, le mécanisme d’hydratation est assez différent car l’hydratation de la belite commence dès le début de l’hydratation et conduit à la formation, soit d’ettringite contenant Si, soit de C-S-H. L’effet de 15% de calcaire a également été étudié pour le ciment contenant 95% de clinker et 5% d’anhydrite. Les résultats ont montré que le calcaire ne change pas la première période de l’hydratation mettant en jeu principalement la ye’elimite et l’anhydrite. Par contre la seconde période, durant laquelle la belite et la ferrite s’hydratent, est fortement retardée à son début. Ceci peut être dû à un retard de la nucléation de la strätlingite à cause de concentrations en sulfate de la solution restant plus longtemps élevées par le fait que l’ettringite est stabilisée en présence de carbonate par la formation de phases AFm carbonatées qui inhibent la formation de monosulfoaluminate de calcium hydraté. Pour finir, des perspectives sont données notamment afin de réduire la durée de la première période de l’hydratation et ainsi permettre un démarrage plus rapide de l’hydratation de la belite et de la ferrite
The objective of this work was to better understand the hydration mechanisms of cements belonging to the family of BCSAF cement in order to develop simple mechanistic models which can help us to optimise mixtures of BCSAF clinker and other compounds for specific applications. The studied cements were made from a clinker containing 52% of belite, 33% of ye’elimite and 14% of a ferrite phase and various amounts of anhydrite and limestone. From the Detailed investigation of the hydration of cement containing 95% of clinker and 5% of anhydrite, it has been demonstrated that the mechanism of hydration has two main successive periods of hydration: the beginning of hydration is controlled by ye’elimite and anhydrite, while the remaining of hydration is governed by belite and the ferrite phase that react with some of the hydrates formed during the first period. It is C2ASH8 nucleation rate that governs the beginning of the hydration of belite. The main parameter that governs the nucleation rate of strätlingite is [SO4]2- that has to be low. C-S-H does not form as the initial hydrate for belite hydration due to the inhibition effect of high aluminate concentration on C-S-H nucleation. As a consequence, this is indirectly the sulphate concentration that controls the beginning of belite hydration and thus the reactions leading to its reduction, mainly the hydration of ye’elimite to form ettringite. Globally it is once ye’elimite has been completely reacted that strätlingite may nucleate. A synergy between the reactions of belite and ferrite is found to accelerate the formation of later hydrate, hydrogarnet and C-S-H at the expense of strätlingite.A similar mechanism of hydration has been found for cements having higher anhydrite contents at the exception of cements that have more anhydrite than the theoretical anhydrite content to consume all ye’elimite to form ettringite. For the former cements, more anhydrite can strongly delay the second period of the hydration where both belite and ferrite react. In the later cases, the mechanism of hydration is quite different as belite does start to react till the beginning of hydration certainly forming either a Si containing ettringite or C-S-H. The influence of 15% of limestone was investigated on the cement containing 95% of clinker and 5% of anhydrite. The results showed that limestone did not change the first period involving anhydrite and ye’elimite, but strongly delayed the beginning of the second period where both belite and ferrite hydrate. This may be due to a delayed nucleation of strätlingite induced by a longer period having higher [SO4]2- as ettringite is stabilised by the precipitation of carbonated AFm at the expense of calcium monosulfoaluminate hydrate, thanks to the carbonate ions brought by limestone. Finally some perspectives are given in order to reduce the duration of the first period and then to enable the hydration of both belite and ferrite more rapidly

博士
國立成功大學
環境工程學系碩博士班
93
Feasibility of municipal solid waste incineration (MSWI) bottom ash and heavy metal containing sludges as raw materials for cement production is investigated in this study. Uniaxial compression strengths (UCS) of hydrated clinkers produced from wastes replaced raw material are tested to clarify the influence of interference introduce by wastes. Also, a crystalline quantification technique is developed in order to investigate the effects of heavy metal oxides on the formation of silicate phase in clinkers. 　In this study, the MSWI ash is pretreated with techniques including magnet separation, water washing, EDTA separation and dense media separation to remove the possible interferences such as iron and salts prior to addition to raw mix. The results show that when the replacement percentage is below 10%(w/w), the UCSs of hydrated cement are higher than 18MPa, which could meet the Chinese National Standard (CNS) criteria for ordinary Portland Type I cement. But when the replacement percentage is higher than 10%(w/w), a dramatic drop of the UCSs is observed due to the insufficiency in calcium oxide. By adjusting the chemical compositions of replaced raw mix according to the compositional parameters (lime saturation factor, silica ratio, aluminum ratio and hydration modulus), the UCS of sintered clinker is as strong as commercial cement. The heavy metal containing sludge is added to the raw material with compositional parameter fulfilled. The results of QXRD show that when the total heavy metal contents in raw material is smaller than 3%, a increase to 140% of the tricalcium silicate (C3S) phase could be observed. But when the amount of total heavy metals is greater than 3%, significant decreases of C3S intensity could be observed. When the total amount increase to 6%, the intensity of C3S is only 80% relative to commercial cement. In summary, utilization of MSWI ash and heavy metal containing sludge is applicable if appropriate control of compositional parameters and heavy metal amount is applied. 　By adding 10%(w/w) of α-Al2O3 as internal standard to the NIST certificated reference material, X-ray powder diffraction (XRD) analysis is performed with short (1 hour) and long (8 hour) scanning time. The following crystalline quantification analysis show that the XRD profiles with scanning range of 15˚-75˚ (2θ), 0.03˚ per step, and 2s/step (short scanning time) are good enough for the following refinement. The crystalline quantification is performed with software package designed on quantitative Rietveld method basis; combinations of polymorphs of C3S are selected as initial model input for the refinement. The results show that both the RM and the RMT (rhombohedral, monoclinic and triclinic) combinations could cover all the variety of cements characterized by the three kinds of standard reference material. The cumulative relative error between the refined and certificated values is in the range of 7-23%. The method is stable to be used as crystalline quantification. Also, the amorphous weight percentage could be obtained by inverse derivation from the contents of α-Al2O3. In summary, combining the XRD operating condition described previously and the RMT combination for initial model in refinement, an optimal, fast and reliable crystalline quantification method is established. The established method could be used for the quantification of crystalline in future experiments. 　At last ,a full factorial experimental design is applied to three heavy metal oxides including CuO, NiO and ZnO. In the experiments three kinds of heavy metal oxide levels (1%, 3% and 5%) are tested. With adding heavy metal oxides, the simulated cement raw materials are sintered at 950, 1100, 1250 and 1400°C for 3 hours. The heavy metal oxide incorporation analyses of clinkers show that almost all the ZnO would evaporate during the sintering process. ZnO evaporated at 950-1100°C. On the other hand, 80-90% and 55-70% respectively of CuO and NiO would be retained in the clinkers. By means of crystalline quantification assisted with differential thermogravimetric analysis (TG/DTA), the addition of 3% heavy metal oxides could lower the liquid melting temperature and hence increase the amount of dicalcium silicate (C2S) formation. The ability of lowering liquid formation temperature is ZnO>CuO>NiO in sequence. NiO has almost no effect on the melting temperature lowering. The crystalline quantification analyses of 1400°C clinkers show that CuO and NiO would have statistically significant effect on the amount of the two major silicate phases (C2S and C3S) formed. Nevertheless, the total moles of silicates per unit weight of clinkers would not change. The total moles of silicates do not have statistically difference with respect to the addition of heavy metal oxide is added. The high temperature sintering system could be considered as in equilibrium, heavy metal oxides could not affect the partition ratio between C2S and C3S. The partition ratio in clinkers (C3S/C2S molar ratio) could be expressed as an empirical equation with amounts of CuO and NiO as parameters. 　In summary, the MSWI ash and heavy metal containing sludge could be utilized as alternative raw materials as long as appropriate controls on compositional adjustments and heavy metal thresholds are taken into consideration. If heavy metals were introduced into the raw material in low dosage, heavy metal would not affect the total amount of silicate phases. Instead the partition ratio between C2S and C3S would be altered. Empirical model developed in this study could be utilized as a reference for future modification of equation. Reuse of industrial inorganic wastes as alternative raw material for cement production could solve the dilemma in waste treatment and waste disposal.