•Growth of ternesite crystallinity.•The effect of the firing temperature to the mineralogical composition is demonstrated.•Using the Scherrer ́s equation for calculating the crystallites size.
This ...work describes the crystallization and subsequent decomposition processes of ternesite when fired in an open air system. The effects of temperature and sintering period on phase composition and crystallinity were assessed post-mortem in samples fired in platinum crucibles in a laboratory furnace. High temperature XRD was used for observing phase and crystallinity changes in situ. The results indicate that the temperature of 1150 °C is neither high enough for a full synthesis of ternesite of sufficient quality nor high enough for its decomposition. It appears that the temperature of ternesite decomposition in an open system is around 1250 °C. The crystallites grow very fast at the beginning, until the size of 160 nm above which the grow rate is decreasing.
Up to now, questions related to the preparation of pure sulphate binders, ie anhydrite mortar, alpha gypsum and beta gypsum, have been monitored at laboratory and pilot plant level within the ...framework of the work carried out at BUT. However, beta gypsum cannot be considered a high-grade sulfate binder. Therefore, the subject of this article is the use of beta gypsum to develop a gypsum premix that can be classified as a mixed sulfate binder universally applicable to the preparation of dry mortar mixtures. 1,2
17th International Conference Silicate Binders (ICBM 2018)Selected, peer reviewed papers from the 17th International Conference Silicate Binders (ICBM 2018), December 6, 2018, Brno, Czech Republic.
This book was prepared by results of the 17th International Conference Silicate Binders (ICBM 2018) that was held December 6 in Brno, Czech Republic and focused on the scientifical and practical ...knowledge of inorganic binders and materials. The most important topics were chemistry and technology of cement and other hydraulic and silicate binders and chemistry and technology of lime and gypsum based binders. We hope this collection will be useful for many specialists in the field of building materials.
Gypsum, or sulphate, binders are inorganic powder binders, which are among the so-called aerial mortars. These, after mixing with water, form a material that is well-workable for a certain time, ...which solidifies, hardens and is stable only in the air. Gypsum as a building material is formed by heating a raw material called plaster stone - CaSO4·2H2O and can acquire various properties depending on how it is produced. Its resulting properties can be affected to some extent by the source from which the raw material for its production is obtained, whether it is plaster stone or whether it the source is a secondary product from industrial production. 1 Production and use result from the ability of the original raw material to release crystalline-bound water under elevated temperatures and to bind it again after it has been added thus recreating a solid structure.
Ashes from fluidized bed combustion, i.e. FBC ashes, are not being practically used for the production of hydraulic binders. The problem is their chemical and mineralogical composition. FBC ashes are ...characterized by a higher content of SO3, highly active free CaO and sometimes higher loss on ignition. The higher proportion of these substances has resulted in volume and temperature instability. However, FBC ashes could be used within a certain limit concentration in binders with relatively similar chemical-mineralogical composition such as Portland cement. The potential use of FBC ash for the preparation of blended Portland cements was studied in this paper. For this purpose, two types of FBC ashes and one type of traditional fly ash were selected. The first representative was a filter FBC ash, the second one was a bed FBC ash. Fly ash from pulverized coal combustion was used for comparison. The samples were prepared by co-grinding of the selected ash, Portland clinker and gypsum in a laboratory ball mill to a given value of specific surface area. Ash content was 15% and 30% of the total sample weight. The samples were subjected to the determination of basic technological properties – the water/cement ratio, setting times, strength, and soundness. The course of the hydration process was monitored by the qualitative method of X-ray diffraction analysis (XRD). The hydration product quantification was performed by the thermogravimetric analysis (TGA/DTA). The amount of CaO attributable to Ca(OH)2 and CaCO3 was quantified. Based on the results, a conclusion was made that the utilization of FBC ash in blended Portland cement production is possible. The values of the physical-mechanical properties of the blended cements based on FBC ashes are similar to the reference. In the case of lower FBC ash content, they are even comparable with ordinary Portland cement.
Fluidized bed ash, which is the youngest industrial waste can be considered on the basis of research, a high-quality secondary raw material base which can be easily used in the production of Portland ...cements and, in general, other hydraulic binders. Regarding the direct effect of anhydrite on the course of hydrating mixed cement with the fluidized fly ash and the consequent behaviour of the originated cement stone, its reaction with clinker materials on the mentioned Aft (Al2O3–Fe2O3-–tri) phase is clear. The creation of AFt phases, if they originate additionally, due to their morphology, is accompanied by significant volume changes which may lead to deformation up to the destruction of the cement stone. Some foreign publications show the possibility of the transformation of this thermo-dynamically unstable mineral into the further mineral from the group AFt phase, which is thaumasite, Ca3Si (CO3)(SO4)(OH)6.12H2O.
•Hydration of ternesite containing sulphosilicate clinkers was monitored for up to 810 days.•Thaumasite can be formed as one of the hydration products of sulphosilicate clinkers.•Besides ecological ...benefits of the application of sulphoaluminate cements, the possible risk of sulphate attack should also be considered.•A novel way of thaumasite synthesis is demonstrated.
Extensive research on sulphosilicate clinkers has been performed, primarily given by the ecological aspects. The formation of thaumasite and ettringite has become an important issue due to possible concrete deterioration, and also reducing greenhouse gas emissions. This work was aimed at hydration of ternesite based clinkers at low temperatures, with respect to thaumasite formation. Five clinkers with various compositions corresponding to stoichiometric ratios of elements in thaumasite and ternesite were prepared. Clinker-water suspensions were stored at 5 °C for up to 810 days. X-ray diffraction, DSC/TG, and SEM/EDS were used as the analytical tools. All the clinkers contained ternesite, belite, anhydrite, and free lime. As shown by the results, ternesite and belite preferably hydrate to CSH gels, and sulphate ions forming ternesite become a part of gypsum. The remaining portion of gypsum originated from anhydrite hydration. Gypsum reacted with silica and carbon dioxide to form thaumasite. Thaumasite was clearly identified already after 28 days of hydration, and for one sample, its content finally reached approximately 34 wt. %. It should be considered that the application of sulphoaluminate cements may possibly be connected with the sever risk of sulphate attack.
This article describes the results of experimental works, dealing with long-term observing of ettringite stability (Ca6Al2(SO4)3(OH)12·26H2O). Thermodynamic stability of this mineral is important in ...terms of potential use of fluidized bed combustion (FBC) ash as an additive to Portland cement. Within the experimental work it was carried out observing of the ettringite formation by hydration of yeelimitu (Ca4Al6(SO4)·O12) in laboratory conditions. For the preparation of yeelimite it was proposed a three-component raw material mixture, consisting of a high percent limestone and gypsum and corundum. This mixture was subsequently placed in platinum crucibles and burnt in superkanthal kiln at 1200 °C. Formed clinker was mixed in chosen ratio with water and it was prepared a set of testing samples. These samples were exposed in the laboratory environment for up to 180 days. The hydration of the clinker was carried out using X-ray diffraction analysis (XRD) by determining the mineralogical composition.
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