Showing papers on "Ettringite published in 1988"
TL;DR: In this article, the authors found abundant thaumasite, a complex calcium-silicate-hydroxide-sulfate-carbonate-hyd rate mineral, forming a solid solution series with ettringite.
Abstract: Expansive reactions between lime and sulfate-bearing clay soils have attracted little attention until relatively recently. Lime treatment of Stewart Avenue in Las Vegas, Nevada, had induced heave in excess of 12 in. Heaved areas are found to contain abundant thaumasite, a complex calcium-silicate-hydroxide-sulfate-carbonate-hyd rate mineral. Thaumasite forms a solid solution series with ettringite, a calcium-aluminum-hydroxide-sulfate-hy drate mineral. In the presence of aluminum, ettringite forms first and is replaced by thaumasite only at temperatures below 15°C. The mechanism of heave is a complex function of available water, the percentage of soil clay, and ion mobility. Only the long-term possolanic chemistry of normal lime-soil reactions is disrupted. Cation exchange, agglomeration, and carbonation are unaffected. With the present state of knowledge, lime-induced heave is difficult to predict for all but most obvious conditions.
365 citations
154 citations
TL;DR: In this article, the authors examined tricalcium silicate hydrate, carboaluminate complex and cubic calcium aluminate hydrate phase in the presence of 5-50% CaCO3 for different lengths of time (a few minutes to 28 days).
97 citations
TL;DR: In this paper, the authors used a TG/DTG method to identify the decomposition products of synthetic ettringite and quantified the results using XRD techniques and quantification by the TG and DTG method, which indicated a two-stage decomposition mechanism essentially accelerated by increasing temperature.
79 citations
TL;DR: In this article, the origin of sulfate expansion was studied on a series of cements of different compositions and on mixes of pure compounds and the observed data support the theory that the expansion is related to a topochemical formation and/or oriented growth of ettringite.
Abstract: The origin of sulfate expansion was studied on a series of cements of different compositions and on mixes of pure compounds. The observed data support the theory that the expansion is related to a topochemical formation and/or oriented growth of ettringite. An uptake of water from the environment is not essential for the expansion to take place even though it enhances the extent of expansion. The absence of expansion in iron-rich cements appears to be due to reduced and delayed ettringite formation in these cements and to an altered morphology of the formed ettringite.
67 citations
TL;DR: In this article, a mathematical model for the kinetics of hydration of tricalcium aluminate in the presence of gypsum was developed, and the model was solved, illustrated and compared to experimental heat release data.
44 citations
Patent•
22 Nov 1988
TL;DR: In this paper, a process for conditioning radioactive or toxic waste which can contain boron in a cement-based matrix is described, where the waste is mixed in a drum in the presence of water with non-aluminous cement, aluminous concrete, and optionally a siliceous compound.
Abstract: A process for conditioning radioactive or toxic waste which can contain boron in a cement-based matrix comprises mixing the waste in a drum in the presence of water with non-aluminous cement, aluminous cement and optionally a siliceous compound and/or a boron-containing compound, in order to form a cement matrix containing stable phases of the straetlingite, calcium monoboroaluminate and borated ettringite type and, if desired, placing around the drum a mortar layer, which can be prepared from cement, deflocculated fumed silica, siliceous sand, smectic clay and water.
25 citations
TL;DR: The effect of introducing chloride into the mixing water of an ordinary Portland cement and a sulphate resistant Portland cement (SRPC) has been investigated over a range of hydration times as discussed by the authors.
Abstract: The effect of introducing chloride into the mixing water of an ordinary Portland cement and a sulphate resistant Portland cement (SRPC) has been investigated over a range of hydration times. A simplified system of C3A, CaSO4 and Ca(OH)2 was also studied to facilitate clarification of results. A further investigation involving exposure of hardened cement pastes to chloride solutions was studied over a range of exposure times. The hexagonal β-monochloroaluminate corresponding to the formula 3CaO.Al2O3.CaCl2.10H2O has been identified by X-ray diffraction (XRD) in both sets of experiments; semiquantitative studies using XRD and thermogravimetry show increasing amounts of chloroaluminate formation with time. From the system using C3A, CaSO4 and Ca(OH)2 it was clearly shown that chloroaluminates do not form in the presence of sulphate ions. The order of preference of formation was found to be ettringite > chloroaluminate > monosulphate.MST/759
11 citations
Patent•
02 Aug 1988
TL;DR: In this paper, a continuously porous adsorbent material consisting of zeolite type clay powder particles, magnetized magnetite particles and ettringite crystals bonding the clay particles and the magnetic particles is presented.
Abstract: A continuously porous adsorbent material substantially comprising zeolite type clay powder particles, magnetized magnetite particles and ettringite crystals bonding the clay particles and the magnetic particles, wherein the adsorbent material possesses continuous pores comprising relatively large cages connected with one another through smaller channels, the porous material suitable for the purification of various kinds of fluid by adsorption of the impurities contained in the fluid.
10 citations
Patent•
11 Nov 1988
TL;DR: In this article, the authors proposed to use an alumina cement-based mixture and a binder made of an ettringite forming material as essential components to reduce shrinkage during hardening.
Abstract: PURPOSE: To considerably reduce shrinkage during hardening by using an alumina cement-based mixture and a binder made of an ettringite forming material as essential components. CONSTITUTION: An alumina cement-based mixture consisting of alumina cement (A), superfine powder (B) of ≤2μm average particle size such as silica fume or superfine alumina powder obtd. by the Bayer process and a dispersant (C) such as a condensation product of naphphalenesulfonic acid with formaldehyde and a binder (D) made of an ettringite forming material are used as essential components and water is added to them to obtain a high strength cement compsn. The amt. of the superfine powder used is 5-1,000 pts.vol., preferably 10-500 pts. vol. per 100 pts. vol. of the component A, that of the dispersant is 1-5 pts.wt., preferably 1.5-4 pts.wt. per 100 pts. wt., in total, of the components A, B, D and that of the water is ≤30 pts.wt., preferably ≤25 pts.wt. per 100 pts.wt. powder. COPYRIGHT: (C)1990,JPO&Japio
6 citations
Patent•
29 Jan 1988
TL;DR: In this article, the authors proposed a method to heighten ability to adsorb metal ions by forming a continuous porous body having relatively large holes and comprising a zeolite-type clay powder and ettringite crystal coagulatively bonding the particles of the clay powder.
Abstract: PURPOSE: To heighten ability to adsorb metal ions, etc., by forming a continuous porous body having relatively large holes and comprising a zeolite-type clay powder and ettringite crystal coagulatively bonding the particles of the clay powder. CONSTITUTION: After electric charge of a zeolite-type clay powder is neutralized and removed, the powder is mixed with magnetite, cement, potassium chloride, magnesium chloride, sodium chloride, calcium chloride, sodium sulfate, citric acid, cobalt chloride, and water. After dried, the resulting mixture is magnetized to form a magnetic magnetite-contg. continuous porous body for adsorption where the porous body is comprised of a zeolite-type clay powder and an ettringite crystal coagulatively bonding the clay powder and the continuous pores are comprised of relatively large holes and pores linking the holes. COPYRIGHT: (C)1989,JPO&Japio
TL;DR: In this article, a computer program was developed to calculate the chemical equilibrium compositions of a complex cement system, and higher curing temperature and the addition of NaOH were identified as effective methods to avoid ettringite formation.
Abstract: In order to provide stable cement packages, ettringite formation, a major cause of cement deterioration, was studied theoretically and experimentally. A computer program was developed to calculate the chemical equilibrium compositions of a complex cement system. Higher curing temperature and the addition of NaOH were identified as effective methods to avoid ettringite formation. These findings were confirmed by measuring the amount of ettringite in solidified cement by an X-ray diffraction method.
TL;DR: Differential calorimetry was used to determine the heat evolution and kinetics of hydration processes of the calciumsulphatealuminate phase Ca4(Al6O12)(SO4) with gypsum CaSO4 · 2H2O at room temperature with one mole of water added to the solid phase as discussed by the authors.
Abstract: Differential calorimetry was used to determine the heat evolution and kinetics of hydration processes of the calciumsulphatealuminate phase Ca4(Al6O12)(SO4) with gypsum CaSO4 · 2H2O at room temperature with one mole of water added to the solid phase. An increasing content of sulphate ions in the sytem results in substitution of the monosulphate Ca4(Al2O6)(SO4) · 12H2O in the reaction products by ettringite, Ca6(Al2O6)(SO4)3 · 32H2O. Higher contents of ettringite influence the rates of hydration reactions and the values of the evolved heat.
TL;DR: In this article, a model for the mixures under internal sulfate attack is proposed based on a progressive fracturing concept, which is defined as a function of the Powers' gel-space ratio.
Abstract: Results from a series of tests conducted to determine the extent of sulfate attack in cement-based mixtures containing phosphogypsum are presented. A model for the mixures under internal sulfate attack is proposed based on a progressive fracturing concept. A damage variable is defined as a function of the Powers' gel-space ratio. The sulfate attack evidenced by the expansion of the matrix is incorporated as additional nucleated voids. The compressive properties of cement-based mixtures containing phosphogypsum is found to be predicted well by this model.
TL;DR: In this paper, the authors report on work in progress that is examining parameters, measurable through chemical and XRD analyses, that could indicate whether a fly ash will enhance, degrade or have no effect on the sulfate resistance of fly ash concrete.
Abstract: The objective of this summary is to report on work in progress that is examining parameters, measurable through chemical and XRD analyses, that could indicate whether a fly ash will enhance, degrade or have no effect on the sulfate resistance of fly ash concrete. Mehta [1–4] has discussed the factors that contribute to attack of sulfates on fly ash concrete. As noted in his review paper on this subject in the preceding volume in this series [1], the agents responsible for concrete expansion and cracking are alumina-bearing hydrates, such as calcium monosulfoaluminate and calcium aluminate hydrate, that are attacked by the sulfate ion to form ettringite, calcium trisulfoaluminate. Acidic type interactions between sulfate ions and calcium hydroxide also lead to strength and mass loss.
01 Jan 1988
Patent•
10 May 1988
TL;DR: In this paper, a quick-setting cement admixture and an expansive material are combined to prevent the falling of concrete due to cracking and to improve the durability by using a quicksetting cement admixture and a expansive material in combination.
Abstract: PURPOSE: To prevent the falling of concrete due to cracking and to improve the durability by using a quick-setting cement admixture and an expansive cement admixture in combination. CONSTITUTION: An expansive cement admixture (expansive material), e.g., consisting of calcium aluminate and gypsum (ettringite gypsum) is prepd. and a quick-setting cement admixture (quick-setting material), e.g., consisting of calcium aluminate and other aluminate is also prepd. Both the materials are added to fresh concrete and mixed immediately before spraying. COPYRIGHT: (C)1989,JPO&Japio
TL;DR: In this paper, the authors investigated pozzolanic binders by the addition of artificial pozzolans (siliceous fly ashes, slag and clay minerals) which had been calcined at moderate temperatures.
Abstract: Because of their high SO3 content (∼11%), sulfo-calcic fly ashes cannot be used as a cement admixture without pretreatment. The fly ashes contain mainly quicklime (CaO), anhydrite (CaSO4) and larnite (BC2S). At ambient temperatures and at normal consistency, their hydration leads to the formation of ettringite, slaked lime and gypsum. As a result, cracking and splitting of the hydrated product quickly occurs due to the crystallization of the ettringite. The ability of these fly ashes to produce Portlandite, Ca(OH)2, led the authors to investigate pozzolanic binders by the addition of artificial pozzolans — siliceous fly ashes, slag and clay minerals — which had been calcined at moderate temperatures. The sulfo-calcic fly ashes are ground, then slaked either in ambient or hydrothermal conditions (2 or 6 hours at 130°C). In the case of slaking under ambient conditions, ettringite is quickly produced with a definitive crystallographical structure. As a result, no volume change is observed after re-hydration of the material. By comparison, autoclave slaking does not lead to this phenomenon, and only slaked lime is produced. The rate of hydration is studied through the development of compressive strength and by analyses of the products by differential thermal analysis (DTA) and X-ray diffraction (XRD) at various hydration times. The best results are obtained using calcined laterite or blast furnace slag.
Patent•
17 Sep 1988
TL;DR: Water-resistant gypsum is produced from milled smelter byproducts slag lime, slag sand or slags from steelworks and natural gypsums together at temperatures between 150@C and 1500@C in appropriate equipment.
Abstract: Water-resistant gypsum or gypsum cement is produced from milled smelter byproducts slag lime, slag sand or slags from steelworks and gypsum from flue-gas desulphurisation plants or other chemical gypsums or natural gypsums together at temperatures between 150@C and 1500@C in appropriate equipment. In the low temperature range, the smelter products are activated by the gypsum so that setting reactions occur on addition of water, as a result of the calcium silicate or calcium aluminate content. From 200@C to 700@C, the FGD gypsum is converted into hemihydrate (CaSO4.1/2H2O) or anhydrite (CaSO4), with the smelter byproducts being activated and, after quenching and milling, solidifying on addition of water. Between 1300@C and 1500@C, a slag-sulphate melt containing -Ca2SiO4, Ca3Al6 O12.CaSO4 and anhydrite is formed, which are, after quenching and milling, the base components of the hydraulically reacting product. The product after setting consists mostly of the minerals portlandite Ca(OH)2, hydrogranate Ca6 Si2 O8(OH)4, ettringite Ca6 Al2(SO4)3(OH)12.26H2O, thaumisite Ca6Si(SO4)2(CO3 )2(OH)12. 24(H2O), spurrite Ca5(SiO4)2CO3 and Ca3Al6O12.CaSO4. It has high compressive and flexural strengths which increase over long periods of time. The product is well suited for fixing heavy metals and is thus particularly useful in the field of environmental protection.