Showing papers on "Ettringite published in 1980"

Analytical Electron Microscopy of Cement Pastes: II, Pastes of Portland Cements and Clinkers

Abstract: Three hundred sixty-five particles of C-S-H, Ca(OH)2, AFm phase, and AFt phase from pastes of normally ground portland cements and of finely ground cements and clinkers were analyzed. All the phases, except the Ca(OH)2, showed significant variation in composition among paste specimens and among particles within each specimen. The C-S-H contains significant amounts of Al, Fe, and S; for that of a normally ground portland cement paste, cured for 28 days, the median Si:AI, Si:Fe, and Si:S ratios were 11, 43, and 15, respectively, whereas the mean Ca:Si ratio for all the particles analyzed was 2.0. The AFm phase in cement pastes is not pure monosulfate but has a mixture of sulfate, hydroxide, and Al- and Si-bearing ions in its interlayer sites; the AFt phase is not pure ettringite but contains Si and its sulfate is probably partly replaced by hydroxide. The Al and Fe contents in the C-S-H and the Si contents in the AFm and AFt phases are greater when finely ground starting materials are used. This fact, together with the marked variation among particles, emphasizes the difficulty of ionic transport in cement pastes.

Structure and Properties of Portland Cement Clinker Doped with Zinc Oxide

Abstract: ZnO added to the raw meal accelerates the rate of portland clinker formation. Due to ZnO doping, the amount of alite and C2(AF) formed increases at the expense of belite and C3A. The ZnO is preferentially taken up by the interstitial phase. The initial rate of tricalcium silicate hydration is retarded and the formation of ettringite is moderately accelerated in cements made from ZnO-doped clinkers. The set time of these cements is gradually prolonged and their strength development retarded with increasing degrees of ZnO doping.

Factors affecting sulfate resistance of mortars

Abstract: : The ability of a mortar made using portland cement, fine aggregate, and water to resist attack by sulfates is affected by the proportions of the mortar (water-cement ratio and cement content), by the maturity, by the amount of tricalcium aluminate in the portland cement, by the presence of tricalcium aluminate-sodium oxide solid solutions with different structures and reactivities, and by the composition, reactivity, and amount of pozzolan used together with the portland cement. Cements investigated included: portland cements of Types (I-III), and V meeting ASTM C 150; blended cements including Type IP's meeting ASTM C 595 that were made from the same clinkers as the Type I's; and Type I's blended with pozzolans including fly ashes produced by burning bituminous, subbitumous, and lignitic coals, calcined natural volcanic glass high in silica, and silica fume. Silica fume forms glassy microspheres that may contain over 90% SiO2; it is a by-product of the production of silicon metal. Some of the fly ashes produced from subbituminous and lignitic coals replacing 30% by volume of cements increased the expansion of mortars containing the blends when stored in sulfate solutions. This behavior reflects SiO2 below 50%, Al2O3 16 to 26%, and CaO 5 to 30%. Al2O3 and CaO in the fly ash glass are readily available to combine with sulfate to form ettringite. With cement of lower C3A content, some of the subbituminous and lignitic fly ash blends improved the sulfate resistance of mortars, except when SiO2 in the fly ashes was 38% or less.

Microstructure of Concrete in Aggressive Environments

Abstract: All the constituents of concrete can be attacked. Some degradations occur after a long period of time. So, it is important to know the chemical and physical mechanisms of the corrosion and the behavior of built structures. In our studies on the durability of concrete, chemical and technological tests have been completed by microstructure examination with scanning electron microscopy and X-ray diffraction. In the present stage of our research into the attack of concrete by seawater, several factors can be noted. The formation of expansive ettringite is related to the content, the crystalline form, and the granularity of tricalcium aluminate. The carbonation reaction transforms ettringite into thaumasite. The dissolving of lime-rich compounds like hydrated silicates C-S-H brings about their progressive transformation into Ca-Mg silicates. Some aggregates have been found to have reacted with alkalis. A dense concrete with a high cement content will offer a good resistance to chemical and physical attacks.

CaSO₄刺戟에 의한 高爐水碎 슬래그의 水和反應

Abstract: In order to clarify the mechanism of the hydration of supersulphated slag cement, the experiments of suspension hydration were performed in the mixtures of slag+CaSO₄+water or NaOH solutions with a liquid/solid ratio of 10. The liquid and solid phase of the suspension was chemically analysed and discussed. In the slag CaSO₄-NaOH system, Al₂O₃ was dissolved under high pH condition, and the ettringite was formed by a reaction of CaSO₄ and Al₂O₃ released in the solution. As hydration progressed, ettringite coated the surface of unhydrated slag grains and inhibited the hydration reaction of slag. CaSO₄ was not only an activator for slag hydration, but a reactant in the hydration.

Preparation of drying agent

Abstract: PURPOSE:To obtain an easily regenerable and handleable drying agent with high hygroscopicity and without deliquescence, by using anhydrous ettringite obtained by heating within a specific temperature range as a drying agent. CONSTITUTION:Ettringite 3CaO.Al2O3.3CaSO4 obtained by reacting alumina source and slaked lime or the like contains as many as 30-32 molecules of water of crystallization. When this ettringite is heated at a temperature of 100-400 deg.C, anhydrous ettringite which is amorphous from a standpoint of X-ray examination is obtained by dehydration. When this anhydrous ettringite is used as a drying agent, it shows a property as an easily regenerable as well as non-harmful excellent drying agent with high hygroscopicity and without deliquescence.

Durability of Cement Mortars and Concretes

Abstract: This paper presents the results of theoretical and experimental studies concerning the durability of cement mortars and concretes. The behavior of different cements in mortars and concretes which are exposed to attack by carbon dioxide in the atmosphere, sulfate ions or the alkali silica reacton (ASR) is described. The principal results which have been obtained during the past 10 to 15 years, part of which already have been published [1-11], 2 also are summarized. Carbonation of cement mortars and concretes follows a t relation. The increasing total lime content of mortars and concretes with portland cement together with the compaction of the microstructure due to carbonation leads to better durability of this type of cement as compared with cements of lower lime content. The attack of sulfate solutions causes the initial cracking by topochemical ettringite formation which is followed by the formation of gypsum as a secondary reaction. The latter explains the often observed interim rehealing. The alkali silica reaction (ASR) is considered as the result of dynamic osmosis equilibrium. The minimum relative humidity necessary for ASR is 80 « X < 85 percent. The delayed ASR leads to an increased deterioration of the structure. Water repellent agents are suitable to prevent the ASR. Pozzolans and blast furnace slags in cements reduce or prevent the ASR. The maximum expansion forces are observed to be 1.7 N/mm 2 . The damages on buildings can be determined on drill-core samples.

Ettringite synthesizing method

Abstract: PURPOSE:To obtain ettringite for building materials having heat insulating and self-flame-retarding effects by turning aluminum silicate such as kaolin and lime raw material into a suspension in the presence of alkali; subjecting the suspension to hydrothermal reaction to form tobermolite; separating the tobermolite; and reacting the filtrate with a specified amt. of lime and gypsum. CONSTITUTION:Aluminum silicate such as kaolin or acidic clay and lime raw material such as CaO, esp. CaC2 sludge are turned into a suspension in the presence of alkali such as 10-20 g/l NaOH. The suspension is then subjected to hydrothermal reaction with steam of 4-40 kg/cm to form tobermolite (5CaO.6SiO2.5H2O), which is filtered. To the filtrate are added about 1.5 mols of lime and about 1.5 mols of gypsum to 1 mol of NaAlO2 in the filtrate, and they are reacted at ordinary temp. -90 deg.C for above 5 hr. By this method tobermolite useful for building materials can be synthesized and extracted in the middle of the processes.

Material for solidifying flimsy ground

Abstract: PURPOSE:A solidifying agent of cement that contains cement and an inoganic ammonium salt, thus being capable of rapidly solidifying even organic soil containing humus in a short time. CONSTITUTION:An inorganic ammonium salt as ammonium sulfate is added to a solidifying agent of cement. The addition of the inorganic ammonium salt to cement accelerates the hydration of cement even when the soil contains humus that inhibits the hydration reaction. Futher, the formation of ettringite is observed, which is thought to be a factor to develop the high strength.

Hydration reactions of C/sub 3/A contained in an unusual flyash

Abstract: Flyashes produced from certain lignite and sub-bituminous coals have high contents of analytical CaO, presumably derived from limestone within the coal deposits. In the US a special category, Class C flyash has been designated for these materials. The mineralogy of the non-glassy portions of some of these flyashes is different from conventional flyashes, and in the material described C/sub 3/A, free lime, and anhydrite are all present. The flyash sets rapidly when mixed with water, and produces ettringite and C/sub 4/ASH/sub 12/. The unique spherical morphology of the flyash grains makes the morphological relationships between the hydration products and the unhydrated material unusually clear. The early reactions are similar to those of C/sub 3/A in portland cement, and the ash might serve as a useful model system for the study of the influence of various admixtures and other substances on C/sub 3/A reactions and setting behavior. Presumably ettringite and C/sub 4/ASH/sub 12/ are also produced when flyashes similar to the one studied are incorporated in concrete, and their production should enhance early strength development.