Showing papers on "Ettringite published in 1997"
TL;DR: Arsenate sorption by ettringite [Ca6Al2(SO4)3(OH)12·26H2O] is examined as adsorption and coprecipitation systems at alkaline pH (10.0−12.5) and for a wide range of As(V) concentration (2.0 mM) precipitated new unidentified microcrystalline minerals at the expense of ettricite.
Abstract: Arsenate sorption by ettringite [Ca6Al2(SO4)3(OH)12·26H2O] is examined as adsorption and coprecipitation systems at alkaline pH (10.0−12.5) and for a wide range of As(V) concentration ( 2.0 mM) precipitated new unidentified microcrystalline minerals at the expense of ettringite. Concentrated As(V) solution exposure to coprecipitating ettringite poisoned ettringite crystal growth, with precipitation of some microcrystalline minerals. Sorbed As(V) was also not desorbable in the presence of concentrated sulfate and high ionic strength solutions. Details of As(V) adsorption and coprecipitation systems and inferences on As(V) molecular interactions are proposed.
132 citations
TL;DR: In this article, fly ash was activated by these calcium salts and activation influenced hydration rates as determined by the rates of heat evolution, and X-ray diffraction analysis determined the phases formed as a result of hydrothermal treatment.
110 citations
TL;DR: In this paper, four low-C3A Portland cements with different C3S content (40 to 74%) were stored for two years in sodium sulfate solution, and the expansion and flexural strength were monitored as mechanical properties, while the microstructural changes were studied by Xray diffraction and scanning electron microscopy using X-ray microanalysis.
82 citations
TL;DR: The early strength development of ordinary Portland cement (OPC)/calcium aluminate cement (CAC) pastes (92.5/7.5, 80/20, and 20/80) was studied in this paper.
76 citations
TL;DR: The changes occurring in the crystallised phases during degradation of an ordinary Portland cement have been studied in this paper, showing that in the zones with no change in mineralogy, local chemical equilibrium and decreasing gradients in calcium and hydroxyls between the core and the surface explain the precipitation of secondary phases, like AFm, ettingite and calcite.
Abstract: The changes occurring in the crystallised phases during degradation of an ordinary Portland cement have been studied. Leaching of cement paste with demineralised water generates a series of dissolution boundaries. Portlandite, then AFm, ettringite and calcite dissolve successively. In the zones with no change in mineralogy, local chemical equilibrium and decreasing gradients in calcium and hydroxyls between the core and the surface explain the precipitation of the secondary phases, like AFm, ettingite and calcite. Hydrogarnets in the surface layer in contact with the aggressive solution only dissolved slightly, or not at all. The very low solubility of hydrotalcites at pH values near neutrality explains the preciptation of these magnesium-containing phases in the surface layer.
47 citations
TL;DR: In this article, it was shown that the reaction between Na2SO4(0.41~0.82 mole metallic aluminum fine powder in 1 liter 1N NaOH solution may be considered as the most efficient way for synthesizing the U phase.
37 citations
TL;DR: In this article, two aspects of the possible reactivation of fluidized bed combustion (FBC) residues are considered: the behaviour of aluminosulfates such as ettringite, which may form when excess water is used in hydration methods designed to reactivate the lime in the FBC residues.
34 citations
Patent•
03 Apr 1997
TL;DR: In this paper, the ettringite is produced in situ within an aqueous suspension while in proximity to the fibers, aggregates, or other fillers to form a mineralized composite material.
Abstract: Compositions and methods for the deposition of ettringite (3CaOA12O33Ca(SO4)30-32H2O) onto the surfaces of fibers, aggregates, and other fillers The ettringite is produced in situ within an aqueous suspension while in proximity to the fibers, aggregates, or other fillers to form a mineralized composite material comprising ettringite coated fibers, aggregates or other fillers Ettringite treated fibers, aggregates, or other fillers are formed by adding chemical reactants such as calcium oxide and aluminum sulfate, which react together in the presence of water to form ettringite, which then precipitates onto the surface of the fibers or other substrates being treated The ettringite treated fibers, aggregates or other fillers can be added to hydraulically settable materials to improve the chemical and mechanical bond between the fibers or other substrates within the resulting hardened hydraulically settable composite material, particularly a cementitious or concrete material
31 citations
TL;DR: In this paper, an air entrained cement:lime:sand mortar containing high purity powdered calcite was crushed and portions stored in water together with varying quantities of gypsum, all mixes are stored at 5 °C.
26 citations
TL;DR: In this paper, a wide range of chemical and physical techniques have been used to differentiate the actual speciation of cubes treated for up to 150 days with CERCHAR hydration process and combined with PFA.
Abstract: The hydration reactions that occur with CFBC materials treated via the CERCHAR hydration process and combined with PFA have been examined and compared with materials produced via the LIFAC (limestone injection into the furnace and activation of unreacted calcium) process. A wide range of chemical and physical techniques have been used to differentiate the actual speciation of cubes treated for up to 150 days. The two materials behave very differently, with FBC-derived ashes being dominated by sulphate chemistry, i.e., the formation of gypsum and ettringite. The CERCHAR-treated ashes appear to make portlandite available for sulpho-pozzolanic reactions, and this seems to be the key to understanding why these materials display superior performance in applications with PFA or cement substitution. The LIFAC materials, with much less sulphate and Fe 2 O 3 and more Al 2 O 3 , still produces ettringite, but no gypsum, and hydrated tetracalcium aluminate appears as the major hydration product.
20 citations
TL;DR: In this article, during the leaching of simulated highly sulphated OPC/BFS cements, cured at room temperature and containing U-phase, sodium sulphate, and ettringite, physico-chemical transformations have been pointed out (transformation of U -phase into ettricite).
TL;DR: In this article, three landfill test cells were constructed using AFBC byproducts and Class F coal fly ash at a site in central Illinois and were monitored over a 5 year period as part of a DOE METC effort to characterize by-products from clean coal technologies.
TL;DR: In this paper, the sulfate resistance of concrete pavers was determined using a method based on ASTM C 1012, and the results showed that the concrete paves had excellent sulfate resistances, even above that expected when using moderate sulfate-resisting type II cement.
Abstract: The sulfate resistance of concrete pavers was determined using a method based on ASTM C 1012. Specimens were submerged in a 5% sodium sulfate solution for a period of one year. Length change and loss in mass were determined. Effect of mixture proportions on sulfate resistance; and relationships between expansion, mixture proportions, and concrete bulk properties are presented and analyzed. In addition, the expansion of the test specimens is compared to proposed acceptance limits found in the literature. Test results showed that the concrete pavers had excellent sulfate resistance, even above that expected when using moderate sulfate-resisting ASTM C 150 type II cement. Sulfate resistance was found to be directly related to the aggregate-cement ratio of the mixture and bulk properties of the concrete. The continued expansion measured throughout the experiment and the absence of any visual signs of softening appear to indicate that the principal factor in the sulfate attack was the in-situ formation of ettringite.
01 Apr 1997-Journal of Environmental Science and Health Part A-toxic\/hazardous Substances & Environmental Engineering
TL;DR: In this paper, microstructural studies of interactions between silica fume, Na-bentonite, containing adsorbed organically contaminated harzardous wastes, and a cement matrix are presented.
Abstract: As one of major deficiencies in cement-based waste stabilization/solidification (S/S) processes is their difficulty in treating inorganic wastes containing organic material, silica-fume and Na-bentonite are studied as potential pozzolanic reagent and pre-solidification adsorbent of organic components. This paper presents microstructural studies of interactions between silica fume, Na-bentonite, containing adsorbed organically contaminated harzardous wastes, and a cement matrix. The scanning electron microscopy/ energy dispersive spectroscopy (SEM/EDS) analysis of the waste/OPC mix showed that the ettringite crystals were in needle shape deposited in the voids or on the surface of hydration material. Microstructural studies of solidified wastes with silica fume and/or Na-bentonite showed that their presence caused an inhibition to the ettringite formation. The results indicated that the incorporation of silica fume and/or Na-bentonite into the cement matrix minimized the detrimental effects of organic materials on the cement hydration reaction.
01 Sep 1997
TL;DR: In this article, Petrographic observations and SEM/EDAX analysis were conducted in order to determine chemical and mineralogical changes in aggregate and cement paste of samples taken from Iowa concrete highways that showed premature deterioration.
Abstract: A significant question is: What role does newly-formed expansive mineral growth play in the premature deterioration of concrete? These minerals (ettringite and brucite) are formed in cement paste as a result of chemical reactions involving cement and coarse/fine aggregate. Petrographic observations and SEM/EDAX analysis were conducted in order to determine chemical and mineralogical changes in the aggregate and cement paste of samples taken from Iowa concrete highways that showed premature deterioration. Mechanisms involved in deterioration were investigated. A second objective was to investigate whether deicer solutions exacerbate the formation of expansive minerals and concrete deterioration. Magnesium in deicer solutions causes the most severe paste deterioration by forming non-cementitious magnesium silicate hydrate and brucite. Chloride in deicer solutions promotes decalcification of paste and alters ettringite to chloroaluminate. Calcium magnesium acetate (CMA) and magnesium acetate (Mg-acetate) produce the most deleterious effects on concrete, with calcium acetate (Ca-acetate) being much less severe.
Patent•
26 Nov 1997
TL;DR: The ettringite used in this invention is represented by 3CaOAl 2 O 3 3CaSO 4 nH 2 O [(n] is 30-32] and can be synthesized by compounding a CaO source such as staked lime or quick lime with an Al 2 O3 source such to alumina gel, a CaSO 4 source such such as gypsum dihydrate, hemihydrate gypsumin and anhydrous gypsumm at a molar ratio for producing the ettringsite and stirring the resultant mixture in water or
Abstract: PROBLEM TO BE SOLVED: To obtain an artificial culture medium for mushrooms capable of providing the mushrooms in a high yield and to provide a method for artificial cultivation of mushrooms using the culture medium SOLUTION: This artificial culture medium for mushrooms contains ettringite The method for artificial cultivation of mushrooms uses the artificial culture medium The ettringite used in this invention is represented by 3CaOAl 2 O 3 3CaSO 4 nH 2 O [(n) is 30-32] and can be synthesized by compounding a CaO source such as staked lime or quick lime with an Al 2 O 3 source such as alumina gel, a CaSO 4 source such as gypsum dihydrate, hemihydrate gypsum and anhydrous gypsum at a molar ratio for producing the ettringite and stirring the resultant mixture in water or hot water or is simply synthesized by a hydrating reaction of aluminum sulfate with the CaO source Furthermore, the ettringite is synthesized by the hydrating reaction of a calcium aluminate such as 3CaOAl 2 O 3 , 12CaO7Al 2 O 3 , CaOAl 2 O 3 , CaO2Al 2 O 3 , and an alumina cement with the CaO source and the CaSO 4 source COPYRIGHT: (C)1999,JPO
TL;DR: In this article, a tuff-lime-gypsum system with and without small addition of Portland cement has been studied in the range 25-85°C and up to 28 days curing.
01 Apr 1997
TL;DR: In this article, the extent of the infilling depends on the period of moist curing as well as the wet/dry treatment of the concrete samples and the material used to infill the air voids.
Abstract: Examination of field portland cement concrete cores, from Iowa pavements with premature deterioration, reveals extensive infilling of calcium sulfate aluminum (CSA) compound in their air voids. A previous study (Phase I) has shown some evidence of the correlation between freeze-thaw durability of concretes and ettringite infilling. To further verify the previous observation, a more extensive experimental program was conducted in this Phase 2 study. A total of 101 concrete mixes were examined. Seven cements, six fly ashes, two water reducers and three coarse aggregates were used in the concrete mixes. Specimens were under moist curing for up to 223 days before being subjected to the freeze-thaw cycling. An environmental treatment consisting of three consecutive wet [70 deg F (21 deg C) in distilled water]/dry [120 deg F (49 deg C) in oven] cycles was applied to some specimens. Immediately prior to the freeze-thaw cycling, most specimens were examined by a low-vacuum scanning electron microscope (SEM) for their microstructure. The results obtained further demonstrate the correlation between concrete freeze-thaw response and CSA compound infilling in the air voids. The extent of the infilling depends on the period of moist curing as well as the wet/dry treatment. The extent of the infilling also relates to materials used. Concrete mixes with extensive infilling are more vulnerable to the freeze-thaw attack. Based on the obtained results, material criteria on cements and fly ashes for mainline paving were proposed for minimizing potential infilling of CSA compound in concrete.
Patent•
22 Sep 1997
TL;DR: A mixing agent consisting of nickel sulfate, a surfactant and either one kind among potassium chloride, calcium chloride, magnesium sulfate or sodium sulfite is mixed to sludge together with cement or an ettringite forming auxiliary such as fly ash at need and the mixture is solidified.
Abstract: PROBLEM TO BE SOLVED: To execute a soil amelioration of sludge, the sludge high in water content especially and to utilize the sludge effectively. SOLUTION: A mixing agent consisting of nickel sulfate, a surfactant and either one kind among potassium chloride, calcium chloride, magnesium sulfate, potassium permanganate, sodium sulfate or sodium sulfite is mixed to sludge together with cement or an ettringite forming auxiliary such as fly ash at need and the mixture is solidified.
31 Dec 1997
TL;DR: The Provence 250 MW Circulating Fluidized Bed Combustion Unit (Gardanne, France) is burning a high sulfur (2 to 4%), high ash content (30%) local lignite.
Abstract: The Provence 250 MW Circulating Fluidized Bed Combustion Unit (Gardanne, France) is burning a high sulfur (2 to 4%), high ash content (30%) local lignite. This peculiar fuel already contains about 15% of CaO which allows it to capture the sulfur dioxide in situ without adding any complementary sorbent. The ash chemical composition (bed ash and ESP ash) reflects the particularities of the coal: calcium compounds are mainly preponderant (40% assessed between 19% as CaSO{sub 4}, 12% as free lime and 9% as calcium silicates and aluminates) compared to silica (13%) and other oxides (less than 5% each). The presence of calcium sulfide ({approximately} 0.3%) can be attributed to both intensified air staging and high SO{sub 2} concentration in the furnace. It could pose handling and disposal problems due to reaction with moisture (H{sub 2}S release). Batch leaching tests have shown that considerable amounts of sulfates are released into the water (up to 2 g/l). However, the rainwater effect on a landfill is different from a batch test: due to high lime content, wetted ash tends to harden and becomes impermeable. The hardening is due to hydration and partial crystallization (gypsum and ettringite formation). However, hardened samples do not seemmore » to retain compounds from leaching: high quantities of calcium and sulfates are still leached from these crushed samples.« less
01 May 1997
TL;DR: In this paper, five low-rank coal combustion fly ash samples extensively characterized in previous projects were used as a pool of candidate materials for potential use as waste stabilization agents, two of these fly ash sample were selected because ettringite formed in the solid in long-term leaching experiments, and an associated reduction in leachate concentration of at least one trace element was noted for each sample.
Abstract: Five low-rank coal combustion fly ash samples extensively characterized in previous projects were used as a pool of candidate materials for potential use as waste stabilization agents. Two of these fly ash samples were selected because ettringite formed in the solid in long-term leaching experiments, and an associated reduction in leachate concentration of at least one trace element was noted for each sample. The stabilization experiments were designed to evaluate the removal of relatively high concentrations of boron and selenium from a simulated wastewater. Sulfate was added as one variable in order to determine if high concentrations of sulfate would impact the ability of the ettringite to include trace elements in its structure. The following conclusions can be drawn from the information obtained in this research: CCBs (coal combustion by-products) can be useful in the chemical fixation of potentially hazardous trace elements; indication of ettringite formation alone is not adequate for selecting a CCB for waste stabilization applications; moderate sulfate concentrations do not promote or inhibit trace element sorption; ettringite formation mechanisms may impact trace element fixation and need to be elucidated; laboratory demonstration of the CCB with the stabilization process being proposed is necessary to verify the efficacy of the material and process; and the final waste form must be evaluated prior to management according to the required regulatory procedures.
Patent•
03 Jun 1997
TL;DR: In this paper, a heat-dehydrated material of ettringite (3CaO.Al2 O3.3CaSO4.30-32H2 O) or tricalcium monosulfoaluminate hydrate (3 CaOO.
Abstract: PROBLEM TO BE SOLVED: To obtain a less expensive composition having a soil quality-stabilizing activity stronger than an ordinary cement, quick lime or slaked lime on soft weak soil having high water content or mud. SOLUTION: This composition contains a heat-dehydrated material of a calcium sulfoaluminate hydrate. An example of the heat-dehydrated material includes a heat-dehydrated material of ettringite (3CaO.Al2 O3 .3CaSO4 .30-32H2 O) or tricalcium monosulfoaluminate hydrate (3CaO.Al2 O3 .CaSO4 .10-18H2 O). The addition of one kind or more selected from quick lime, slaked lime, an ordinary portland cement, an alumina cement, water granulated slug from a blast furnace and gypsum to a heat-hydrated material further improves soil-quality stabilizing activity.
01 Dec 1997
TL;DR: In this article, a laboratory study was developed to examine the role of ettringite in freeze-thaw deterioration of concrete, and the following hypotheses were found: (1) Gypsum-bearing deicing salt diffuses into the concrete.
Abstract: In investigations of frost damaged concrete, white deposits are commonly found in air voids. These deposits are often identified as ettringite. Questions arise as to what role ettringite has on freeze-thaw deterioration of concrete. A laboratory study was developed to examine these issues. The following hypotheses wre usggested: (1) Gypsum-bearing deicing salt diffuses into the concrete. Gypsum, a common component of deicing salts, reacts with the hydration products of tricalcium aluminate in the cement paste to form ettringite that fills the air voids until there are unable to protect the concrete from frost damage. (2) Excess gypsum already present in the cement reacts with tricalcium aluminate hydration products, filling the air voids with ettringite and compromising the air-void system as described above. (3) Deterioration is due to frost damage of inadequately air-entrained concrete. As the paste breaks up microscopically, ions go into solution and recrystallize as ettringite in voids or cracks. The ettringite seen in the air voids is thus a consequence, not a cause, of frost damage.
Patent•
21 Jan 1997
TL;DR: In this article, a hardened material of a cement-based hydraulic binder is kneaded and hydrated and the ratio of water to the binder thereof is 15-40wt.
Abstract: PROBLEM TO BE SOLVED: To remarkably improve the hardening performances of a hydraulic binder by kneading and hydrating a hardened material of a cement-based hydraulic binder so as to provide the composition of the hardened material of the cement-based hydraulic binder and the ratio of the water to the binder within specific ranges. SOLUTION: A hardened material of a cement-based hydraulic binder is kneaded and hydrated and the ratio of water to the binder thereof is 15-40wt.% to produce ettringite (3CaO.A12 O3 .2CaOSO4 .32H20) and/or an iron type ettringite (3CaO.Fe2 O3 .3CaSO4 .32H2 O). Thereby, fire resistance performances of the hardened material of the hydraulic binder are improved. Preventing effects on explosion possessed by the ettringite are manifested according to this method and the explosion can completely be prevented while maintaining the strength as a high-strength concrete. Since sharp-cornered grains possessed by a slag or gypsum especially form fine voids in the hardened material, a rise in pressure is suppressed in dehydration to prevent the explosion.