Papers by Keyword: Anhydrite

Abstract: The properties of various thermal modifications and forms of calcium sulfate and the conditions of their mutual transition are studied. It is established that the mode of heat treatment of gypsum raw materials affects significantly the nature of the subsequent hydration of the gypsum binder. It is established that the values of pH and pCa suspensions of gypsum binders depend on the temperature of heat treatment of natural gypsum, vary over time and characterize the processes occurring during hydration and hardening of gypsum binders. The values of pH and pCa suspensions of gypsum binders can serve as design criteria for innovative multiphase gypsum binders.

Abstract: This paper deals with the development and research of sulphate binder based on anhydrite for the industrial production of dry mortar self-leveling mixtures. As part of the experimental activity, selected plasticizers for the sulphate binders were tested. These additives were added in various weight ranges. The tests were carried out first on anhydrite pastes and then on anhydrite mortars of standard composition. Their influence was mainly observed on the achieved basic technological properties, such as the consistency, the initial setting time and the achieved strength.

Abstract: This study examined the effect of natural anhydrite (CaSO₄) powder additions on the microstructure and frictional properties of a 95 Bronze - 5 Graphite composite prepared by a powder metallurgy process. Natural anhydrite powder, ranging in content from 2 to 8 weight percent, was added to a premixed bronze powder composed of copper and tin and mixed, before the graphite was added. The powder mixture was compacted into disc shaped samples under a pressure of 500 MPa. The compacted samples were sintered at 750 °C for 30 minute in a reducing atmosphere. The green and sintered densities of the samples were measured. A microstructural analysis of the sintered samples was also performed. It was found that the green density of the samples decreased with increased anhydrite content. The sintered densities were lower than the green densities due to sample expansion. A finer microstructure was observed in the samples containing anhydrite. The anhydrite additions resulted in the reduction of both the friction coefficient and wear of the bronze-graphite samples. The amount of anhydrite from 2 to 8 weight percent clearly altered the microstructure of the bronze-graphite samples, however, the level of reduction of the friction coefficient and wear were quite similar among the anhydrite containing samples.

Abstract: In this paper, the effect of anhydrite on the cement-based self-leveling mortar performance was studied. The construction operation of mortar and its mechanical property testing were based on the standard JC/T 981-2005. The results showed that the anhydrite played a significant role on the performance of compressive strength and flexural strength. Furthermore, the best performance of dimensional change rate, abrasion resistance and adhesive strength was obtained with 8% anhydrite content. This study has guiding significance for the construction and application of cement-based self-leveling mortar.

Abstract: Paper is aimed at study of preparation possibilities of cementitious binders with waste diatomaceous earth. In the first step, the influence of ground diatomaceous earth on properties of cement mixture was studied. In the next step, diatomaceous earth was calcinated and, lastly, the influence of replacing FGD-gypsum with anhydrite II as a setting controller in the mixture containing calcined diatomaceous earth was monitored. Technological properties of the prepared mixtures were measured and compared with cement standard. For studying the influence of phase composition and microstructure of cements hardened by both untreated and calcinated diatomaceous earth, hardened cements were tested by DTA and their porosities were measured. The results show that it is possible to prepare binder containing calcinated diatomaceous earth which has slightly lower early strengths but higher long-term strengths and lower hydration heat development.

Abstract: The objective of this work is a research in the sector of preparation of anhydrite II based sulphate binder made from secondary raw material resources applicable in industry specialised in production of mortar mixtures. In particular it was a laboratory burnout of anhydrite II from phosphogypsum, which is formed during production of phosphoric acid. The selection of burning mode was done upon the results [1]. The selected burning mode influence on mineralogical composition of formed anhydrite was monitored with subsequent setting of basic technological properties and monitoring of hydration process course.

Abstract: The objective of this experimental work was to monitor the influence of applied external exciter on anhydrite obtained properties. As a basic raw material anhydrite imported from Poland was used, as hydration exciter a mixture of anhydrous sodium sulphate and Portland cement CEM I 42.5 R in total dose of 5 % by anhydrite weight was applied. In the first step the anhydrite underwent the setting of mineralogical composition using the X-ray diffraction analysis (XRD) and monitoring of grain size and shape by the scanning electron microscopy (SEM). In the next step the influence of applied mixing exciter on obtained basic technological properties according to standard CSN EN 13454 was monitored. It was the setting of basic technological properties of anhydrite binder with and without addition of the mixing external exciter and also the setting of strengths of standard anhydrite mortar with addition of external mixing exciter. Upon the obtained values the comparison with technical requirements of the standard for calcium sulphate binders was carried out and this anhydrite mortar was classified as well.

Abstract: The territory of our country is very poor in natural resources of gypsum and the natural resource of anhydrite is missing completely. A considerable amount of gypsum is produced in the country as a secondary raw material originating during the desulphurization of flue gases in thermal power plants using limestone washing and in the chemical industry. This paper describes the different types of industrially generated gypsum, the production technology, and its potential use in the construction industry.

Abstract: Within the task the so called high-temperature X-ray diffraction analysis (HT-XRD) was used in the field of sulphated binders. Gypsum or calcium sulphate CaSO₄.2H₂O is the basic raw material for the sulphated binder production. As it is known by gradual warming of gypsum its different phase transformations can be obtained which significantly differ in its properties. Using this analysis identifications of temperatures of particular phase transformations in the CaSO₄·xH₂O system can be performed.

Abstract: Due to the very gradual hydration of anhydrites and their very low strengths, modification of the properties of anhydrite by a suitable external exciter was resolved within the work. The experimental work was conducted on natural anhydride, and as possible exciters for hydration, the following products were selected and tested: water-free sodium sulphate; Portland cement CEM I 42,5 R; hydrated lime CL 90 Carmeuse. The dose of the exciter was consistent, i.e. 4.5 wt%. The affect on the increased speed of the hydrating process and the quality of the technological properties was monitored. The catalytic effect was evaluated by monitoring the course of the hydration process (using XRD analysis and thermo-gravimetric analysis) and also on the basis of the achieved technological properties.