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The most common cement setting retarder used in industry is natural gypsum, which is primarily a dihydrated product of calcium sulfate (CaSO 4 · 2H 2 O). The need for …
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The invention relates to the technical field of building materials, and discloses natural anhydrite self-leveling anti-crack mortar which comprises the following ingredients, wherein the ingredients comprise natural anhydrite, water, sand, cement, fibers, a water retaining agent, a retarder, a water reducing agent, a deing agent, an exciting agent and a plasticizer, the raw …
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As it is well known, the workability property of cement solutions depends on reaction rate of C3A with water and to justify this, retarder raw materials are used. In cement industry, natural …
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In China, more and more cement factories are trying to use the chemical gypsums as a cement retarder instead of natural gypsum (NG). Cement is the most massive man-made material, 0.04–0.08 ton of gypsum is needed to produce 1 ton of cement, and there were around 1.5 billion tons of cement produced in China in 2008.
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The most common cement setting retarder used in industry is natural gypsum, which is primarily a dihydrated product of calcium sulfate (CaSO 4 · 2H 2 O). The need for gypsum in cement increases with increasing amount of C 3 A and alkalies in the clinker and the fineness of the cement [1], [2], [3].Gypsum also promotes cement strength at an optimum …
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Approximately 4–5 tons of PG are generated for every ton of P 2 O 5 produced. According to statistics, the worldwide PG generation exceeded 280 Mt/yr [4], of which 75 Mt/yr were generated in China with a total stockpile of more than 600 Mt [5].Up to now, only 15% of the worldwide PG were recycled as cement retarder [[6], [7], [8]], road filling materials [9, 10], soil …
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In Portland cement, usually natural gypsum is added to act as an effective retarder controlling the hydration of the C 3 A phase [10]. Tzouvalas et al. have investigated the replacement of natural gypsum with natural anhydrite and by-product gypsum [11], [12].
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The experimental data conclude that natural anhydrite can be a very efficient retarder of the setting of cement, with no significant change in the physicomechanical properties of the hardened ...
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This article reports on the use of alternative calcium sulfate-bearing materials, notably anhydrite, as cement retarders in cement pastes of CEM-I and CEM-II types. The aim of the study is to …
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The cement test proved that treated PG could partially replace natural gypsum as a retarder.Keywords: phosphogypsum treatment, phosphorus pentoxide removal, calcium sulfate transition phase ...
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In the process of cement production a certain amount of gypsum is added in order to adjust setting time of cement, contribute for strength acceleration in early stage and reduce drying shrinkage of hardened cement paste [1], [2], [3].In Portland cement, usually the added gypsum is natural dihydrate gypsum, but mixed gypsum and chemical gypsum are also used in cement …
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The aim of this paper is to investigate the possible displacement of natural gypsum in cement with anhydrite in CFBC ash in terms of setting time, strength development, volume stability and hydration process. Experimental results indicated that anhydrite in CFBC ash can be used as an efficient setting retarder but lead to lower mortar strength.
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The phosphate impurities in phosphogypsum (PG) were removed efficiently by a novel two-step crystal transformation approach, and the mechanism of the two-step transformation method for removing phosphate and metal impurities from PG was described. The effects of modified PG, natural gypsum, and PG as Portland cement retarders on the cement …
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However, due to environmental concerns and the lack of natural deposits of gypsum, various gypsum by-products, such as phosphor-, citro-, desulpho-, boro- and FGD gypsum, are used as setting retarders to replace the natural gypsum (Papageorgiou et al., 2005, Kavas et al., 2005, Ozkul, 2000, Tzouvalas et al., 2004).
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cement retarder by a combined ... A large quantity of natural gypsum is used by the cement industry as a set ... anhydrite cement by using -anhydrite
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clinker blended with 10 wt.-% of the natural anhydrite (labelled CAH). ... were tested at a single addition rate of 0.5 % by cement weight. The impact of retarders was evaluated by measuring the ...
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The experimental data conclude that natural anhydrite can be a very efficient retarder of the setting of cement, with no significant change in the …
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The mineral composition of fluorogypsum is similar to that of natural anhydrite, which can replace natural anhydrite under certain conditions and is mainly used as a cement retarder [13, 14], but ...
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Regardless of the retarder used, ... The mechanism of CSA-type cement hydration depends mainly on the cement clinker composition [13], [14], the amount and reactivity of the added calcium sulphate [15] [16] and on the processing conditions [17]. ... CSA clinker and natural anhydrite (AH) were used to prepare the cements. The chemical ...
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This paper briefly describes the results of utilization of natural anhydrite in cement pastes of CEM-I and CEM-II types. The aim of the study has been to inquire the extent of natural gypsum replacement by natural anhydrite.
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The anhydrite in CFBC ash is a suitable alternative to gypsum to act as an efficient retarder of the setting of cement based on the setting results but lead to lower strength of the …
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Cement pastes with hemihydrates also present a higher amount of hydrated sulfoaluminate phases, mainly monosulfoaluminate formations, than those with dihydrates [27]. The use of natural anhydrite as set retarder has been also studied, and the reduction of strengths in the first three days was the main difference found [7].
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Experimental results indicated that anhydrite in CFBC ash can be used as an efficient setting retarder but lead to lower mortar strength. The effect is harmless to volume stability of cement …
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The aim of this paper is to investigate the possible displacement of natural gypsum in cement with anhydrite in CFBC ash in terms of setting time, strength development, volume stability and ...
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The aim of this paper is to investigate the possible displacement of natural gypsum (CaSO4·2H2O) in cement with an alternative setting retarder, such as the industrial by-product derived from ...
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This paper briefly describes the results of utilization of natural anhydrite in cement pastes of CEM-I and CEM-II types. The aim of the study has been to inquire …
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In the cement industry, natural gypsum (CaSO 4 ·2H 2 O) is added during grinding of Portland cement to delay the rapid reaction between C 3 A (3CaO·Al 2 O 3) and water and to regulate cement setting properties [1], [2].However, its continuous use has led to the reduction of its high-purity stock in some countries. In certain cases, anhydrite (CaSO 4) has proven to be …
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Taking China's production of 2.377 billion tons of cement in 2020 as an example, and if phosphogypsum modified by CFB fly ash and carbide slag is used as a retarder, around 95.08 million tons of natural gypsum can be saved; in addition, approximately 85.57 million tons of phosphogypsum, 5.7 million tons of carbide slag, and 3.8 million tons of ...
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Natural gypsum and anhydrite, which exist as evaporites in numerous places around the world, are the principal sources of calcium sulfate. Open-cast quarrying or deep mining can both be used to obtain them.
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