Results 1 - 10 of 2064
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[en] TL properties of barite occuring in Yugoslavia are investigated from room temperature up to 4000C. The samples taken from Foca and V. Kladusa localities show only one peak on TL curves as predicted by the theory of Tl processes in ideal crystallophosphors with one level of capture centres. The samples from other localities show two and more peaks indicating them to be policomponent systems. Using the criteria of Luscik, the basic parameters of the capture centres are determined: the energy of thermal activation (Esub(T)) and the frequency factor (p0) for samples with one peak on TL curve. The shift of Tsub(m) for quoted samples is attributed to different effects, including also thermal effects during geological history of the mineral. Radicals SO4-, SO3-, and SO2- formed in barite are the traps of electrons and holes. By heating, the holes are released from the traps and they recombine with recombination centres. The light energy radiated in this process is emitted by luminescence centres
[en] In this paper, properties of composite materials containing ternary binders are determined. Except gypsum, ternary binders containing also pozzolans and alkaline component, which serve as an activator of pozzolanic reaction. The main aim of this research was to investigate changes in physical and chemical properties and pore structural characteristics due to additions of ternary binders. Experimental results showed that changes in the properties of the composite depend not only on the amount of the addition, but also on the kind of pozzolan. (paper)
[en] The quality of secondary materials is imperative to promote a circular economy. In order to improve the way in which the quality of recycled gypsum is assessed, European guidelines on recycled gypsum (RG) quality criteria have been outlined in the framework of the Life+ Gypsum to Gypsum (GtoG) project. Such GtoG guidelines, along with the European Standard on gypsum plasterboard EN 520, provided the basis for this study. During the GtoG project, gypsum recycling and plasterboard manufacturing processes were monitored by testing the gypsum feedstock and the plasterboard produced. The aim of this paper is to discuss the results obtained on relevant parameters that characterize gypsum as a secondary raw material, as well as the resulting product. The minimum requirements were fulfilled by 56% of the RG samples and 86% of the plasterboard with increased RG.
[es]La calidad de las materias primas secundarias es fundamental para promover una economía circular. En el marco del proyecto Life+ Gypsum to Gypsum (GtoG), y con el objeto de mejorar el análisis de la calidad del yeso reciclado, se han desarrollado orientaciones en cuanto a los criterios de calidad del material. Estas directrices voluntarias, junto a la norma europea EN 520, son la base del presente trabajo. Los procesos de reciclaje y fabricación se monitorizaron durante el proyecto GtoG, mediante el ensayo de materias primas y placas de yeso laminado. El objetivo del presente artículo es discutir las propiedades del yeso como materia prima secundaria, así como del producto obtenido. Un 56% de las muestras de RG y un 86% de las placas con aumento de contenido de RG cumplieron los requisitos mínimos establecidos.
[en] Heavyweight concrete has been used for the prevention of seepage from radioactive structures due to the harmful effect of radioactive rays to living bodies (i.e., carcinogenic, etc.). The most important point about heavyweight concrete is the determination of w/c ratio. Selected cement dosage should be both high enough to allow for radioactive impermeability and low enough to prevent splits originating from shrinkage. In this study, heavyweight concrete mixtures at different w/c ratios were prepared in order to determine the most favorable w/c ratio of heavyweight concrete produced with barite. Physical and mechanical experiments were first carried out, and then by comparison with the results of other related studies the findings of this study were obtained. At the end of the study, it was found that the most favorable w/c ratio for heavyweight concrete is 0.40 and the cement dosage should not be lower than 350 kg/m3
[en] The paper presents the results of studies on preparation and structure of water- resistant gypsum compositions using mineral materials and modifying additives as a filler. Using gypsum-based compositions and fuel slags, fine-grained concrete and wall blocks were obtained, characterized by ρ = 1750-1850 kg / m3, compression testRcompr= 5-8 MPa, frost resistance 10 cycles, and thermal conductivity λ = 0.41-0.42 W / (m • K). (author)
[en] Phosphogypsum (PG), an industrial by-product from the manufacture of phosphoric acid, can be processed into non-fired ceramic tiles by an intermittent pressing hydration process. In order to promote the practical application of the technology, calcium sulfate whisker (CSW) was used as reinforcing agent to increase the mechanical strength of PG tiles in this research. The bending strength of the resulted PG tiles with 1wt.% CSW reached 27.2MPa, a resulting increase of 80% compared to the specimen without CSW. The reinforcement of the mechanical strength is mainly attributed to the fact that, the dispersed CSW in the tile body act as “bridges” and strongly bond with gypsum crystals, thus forming a complete tighter-linked tile network.
[es]Los fosfoyesos (PG), un residuo industrial obtenido en la fabricación de ácido fosfórico, pueden ser reutilizados en forma de baldosas cerámicas crudas, sin necesidad de una etapa de cocción, mediante un proceso intermitente de prensado e hidratación. Para poder llevar a cabo una aplicación práctica de esta tecnología, en este trabajo se propone utilizar sulfato cálcico en forma de fibras (CSW, por sus siglas en inglés) como agente de refuerzo, para incrementar la resistencia mecánica de las baldosas finalmente obtenidas. Con la adición de un 1% (en peso) de CSW se incrementó la resistencia mecánica a la flexión de las baldosas hasta un valor de 27,2MPa, lo que representa una mejora del 80% con respecto a las baldosas de PG obtenidas sin adición de CSW. Este incremento en la resistencia mecánica a la flexión se atribuye a que el CSW actúa formando puentes que se enlazan fuertemente con los cristales de yeso, creando una red fuertemente unida.
[en] Full text: Plaster of Paris is a widely used construction material, which is considered a challenge as far as recycling is concerned. This may be so because not only the sulphates can contaminate water reservoirs. Also, current recycling technologies are not sufficiently effectiveness in terms of cost and engineering properties. This work aims to evaluate the effect of gridding on the hardening properties of calcium sulphate hydrate pastes as a tool to improve gypsum hardening properties. An experimental programme was designed to assess the effect of two levels of gridding time (5 and 20 minutes) on mechanical and microstructure properties. The morphology of gypsum crystals was evaluated by means of scanning electron microscopy. Crystal structural parameters were determined via x-ray diffraction and mechanical properties by means of compressive and flexural strength. The data suggests a strong influence of gridding time with the aspect ratio of the crystals. Also, considerations will be given on the mechanisms of hardening, especially in systems where the calcium dehydrate phase were originated either from bassanite hydration and from gypsum dehydration. (author)
[en] The behaviour of thermoluminescence glow peaks of natural barite after exposure to doses less than 2000 rads show some differences, both in the shape of the glow curve as well as in the order of kinetics relative to doses of more than 2000 rads. Details are given of the glow-curve kinetics which are of a type not previously reported for natural barite. Determination of the fundamental parameters, activation energies and frequency factors enables theoretical estimates of the glow curve shape to be made using computer calculations. The agreement between theory and experiment is quite satisfactory. (author)