Showing papers on "Ettringite published in 1990"

Mechanisms of hydration reactions in high volume fly ash pastes and mortars

Abstract: This paper describes investigations of high-volume fly ash (HVFA)-Portland cement (PC) binders, the physical and chemical properties of which have been characterized up to 365 days of curing Physical investigations were made of compressive strength development, pore structure by porosimetry, and morphology by scanning electron microscopy Chemical examination was conducted for solid phase composition and degree of hydration by X-ray diffraction and thermal analysis, and for pore-fluid composition by high pressure extraction and analysis Up to 365d the cement in the HVFA pastes is not fully hydrated However, the ash participates in both early (sulpho-pozzolanic) and late (alumino-silicate) hydration reactions In addition to the usual products of cement hydration, ettringite (AFt) has been identified as a product of the early hydration of the fly ash It has not been possible to identify long term hydration products of fly ash which appear to be non-crystalline A two-step mechanism for pozzolanic reaction between fly ash and Portland cement has been proposed involving: (a) depolymerization/silanolation of the glassy constituents of the ash by the highly alkaline pore fluids, followed by (b) reaction between solubilized silicate and calcium ions in solution to form CSH

Gypsum Dehydration During Comminution and Its Effect on Cement Properties

Abstract: A mix containing fixed amounts of gypsum and ordinary portland cement clinker was ground in plant and laboratory ball mills to examine the effect of grinding in different mills on the cement properties. Mineralogical examination showed that in the plant mill (1200 cm×260 cm), because of the rising temperature during grinding, gypsum was dehydrated to hemihydrate, while there was no dehydration in the laboratory mill (45 cm×45 cm) grinding. Study of hydration of the cement pastes showed that the presence of hemihydrate increased the rate of ettringite formation. Hemihydrate also was rehydrated to gypsum and in the process retarded the setting times and reduced the strength development of the cement. This has been further confirmed by examination of cements prepared with gypsum, hemihydrate, and anhydrite.

Strength enhancement in type k expansive cement using additives

Abstract: Type K cement belongs to a special class known as shrinkage‐compensating cement. A literature survey reveals that very little research has been conducted on the performance of this type of cement when additives are used with it. The writer studies the physical, chemical, and microstructural characteristics of a type K cement to which up to 10% of a silica fume and a superplasticizer are added. Several techniques, such as conduction calorimetry, X‐ray diffraction, thermal analysis, and SEM/EDXA are used for this investigation. It is demonstrated that significant strength increase can be obtained through the use of additives in type K cement. Changes in rheological properties, however, can result from such additions. Adjustments in the amount of sulphate and aluminate components may lead to better control of setting and viscosity in this cement.

Effect of Fly Ash on the Microstructure and Durability of Concrete

Abstract: The influence of fly ash on the microstructure and durability of concrete was investigated. It was found that the use of 50% fly ash in concrete reduced greatly its resistance to freezing-and-thawing even though the concrete was well cured and contained an adequate amount of air. On the other hand, the same concrete showed better resistance to sulfate attack. Results from the SEM examination indicated that the decrease in the resistance to freezing-and-thawing might be due to migration of the microcrystalline Ca(OH) 2 and fibrous ettringite from the dense C-S-H zone to the air voids during cycling. However, the improvement in the sulfate resistance might be due to the reduced amount of ettringite in fly ash concrete.

Material for cultivation soils and method of manufacturing thereof

Abstract: A material for cultivation soils having a continuous porous structure comprising combustion ash and carbon powder in which electrostatic charges are desorbed and neutralized and ettringite crystals for coagulating to connect the particles of the combustion ash and the carbon powder to each other, and the continuous porous structure comprising relatively large holes and smaller pores for connecting the holes to each other. The material for cultivation soils is produced by mixing the combustion ash and the carbon powder in which electrostatic charges are desorbed and neutralized, with either one of cement or calcium hydroxide, potassium chloride, magnesium chloride, sodium chloride, calcium chloride, sodium nitrate, ferric chloride, citric acid, cobalt chloride and water and then drying them.

Effects of Sodium Gluconate on the Formation of Ettringite

Abstract: The initial setting time of Portland cement containing sodium gluconate is quickly than that of cement without sodium gluconate. Such a behavior of early hydration is due to an action of the formation of ettringite. The formation process of ettringite from hydration of synthesized C3A and CaSO4⋅2H2O with the addition of sodium gluconate was investigated from the changes in composition of liquid phase within several minutes with standing time. The results are summarized as follows. Calcium and sulfate contents in liquid phase increase by the addition of sodium gluconate, and the solubility of CaSO4⋅2H2O is also enlarged. The time shown high concentration of calcium and sulfate contents is longer than that without additives. It is resulted to form Ca complex with gluconic acid and Ca2+ in liquid phase. Ettringite was produced in this period and unreacted CaSO4⋅2H2O was disappered. The concentration of calcium content in liquid phase immediately increased after contact with water, and decreased after their, That is, the phenomenon of deposition happens rapidly after the dissolution. After the formation of Ca complex, gluconic acid was adsorbed on the surface of unhydrated particles. CaSO4⋅2H2O depressed the adsorption of gluconic acid on C3A.

Calcium aluminate cements : proceedings of the international symposium held at Queen Mary and Westfield College, University of London, July 9-11, 1990, and dedicated to the late Dr. H.G. Midgley

Abstract: Part 1 Clinker: effect of morphology on the hydration characteristics of high alumina cements, I.N.Chakraborty et al high alumina cements based on calcium aluminate clinker with different phase compositions and sintering degrees, J.Sawkow. Part 2 Hydration: microstructural development in a paste of a calcium aluminate cement, K.L.Scrivener and H.F.W,Taylor on the change of microstructure during the hydration of monocalcium aluminate cement, W.Gessner et al effect of temperature on setting time of calcium aluminate cements, A.Capmas the use of nuclear magnetic resonance (NMR) in the study of high alumina cement hydration, D.J.Greenslade and D.J.Williamson investigations of the composition of phases formed in low cement castables during hydration and after thermal treatment, W.Gessner et al. Part 3 Admixtures: the influence of superplasticizing admixtures on cement fondu mortars, S.M.Gill et al the effect of admixtures on the hydration of refractory calcium aluminate cements, J.H.Sharp et al properties of fresh mortars made with high alumina cement and admixtures for marine environment, N.C.Baker and P.F.G.Banfill. Part 4 Calorimetry: role of foreign cations in solution on the hydration of alumina cement, M.Murat and El.H.Sadok calorimetric studies on high alumina cement in presence of chloride, sulphate and seawater solutions, D.L.Griffiths et al. Part 5 Durability: manufacture and performance of aluminous cements - a new perspective, C.M.George long-term performance of high alumina cement concrete in sulphate-bearing environments, N.J.Crammond behaviour of high alumina cement in chloride solutions, W.Kurdowski et al acidic corrosion of high alumina cement, J.P.Bayoux et al the effect of limestone fillers on sulphate resistance of high alumina cement composites, W.G.Piasta. Part 6 Blended systems: hydration of calcium aluminates in presence of granulated balst furnace slag, A.J.Majumdar et al the effect of curing conditions on the hydration and strength development in fondu slag, J.P.Bayoux et al the microstructure of blast furnace slag/high alumina cement pastes, I.G.Richardson and G.W.Groves effect of microsilica on conversion of high alumina cement, S.Bentsen et al study of hydration properties of aluminous cement and calcium phosphate mixes, J.P.Bayoux et al Ettringite-based cements, S..Brooks and J.H.Sharp. Part 7 Miscellaneous: effect of autoclaving on the strength of hardened calcium aluminate cements, R.Baggott and A.Sarandily effect of temperature rise on properties of high alumina cement grout, S.A.Jefferis and R.J.Mangabhai activation of hydraulic properties of the compound CaO.2Al(2)O(3), T.W.Song et al.

High temperature mold made of high strength cement and manufacture thereof

Abstract: PURPOSE:To mold a high temp. molding having no crack by kneading a high strength cement composition, which is based on a binding material prepared by compounding alumina cement, an ultrafine powder and an ettringite forming substance, with water and curing the resulting mixture. CONSTITUTION:5-30pts.wt. of an ettringite forming substance, 1-5pts.wt. of a dispersant per 100pts.wt. of the total composition, which consists of 5-1,000pts. vol. of an ultrafine powder per 100pts.vol. of alumina cement, alumina cement and the ettringite forming substance, and 30pts.wt. or less of water are mixed and kneaded with 100pts.wt. of the total composition to obtain a high temp. mold made of high strength cement. As the ultrafine powder to be used, there is an ultrafine powder such as siliceous dust or alumina having a particle size smaller by one order than that of alumina cement and, as the dispersant, there is a salt of a melamine sulfonic acid/formaldehyde condensate.

Fiber-reinforced cellular gypsum cement board and production thereof

Abstract: PURPOSE:To obtain the subject gypsum cement board having a high strength and toughness by continuously forming a kneaded material of principal materials consisting of gypsum and slag cement and fiber-reinforced cellular gypsum cement containing fibers as a reinforcing material and bubbles on a belt and curing the formed product. CONSTITUTION:A kneaded material of a fiber-reinforced cellular gypsum cement containing hemihydrate gypsum and slag cement as principal materials and fibers, such as PVA fibers, as a reinforcing material in an amount of 0.3-20wt.% based on the principal materials and further bubbles is prepared. The resultant kneaded material is then continuously injected onto a belt, set for 10-30min and placed in a curing vessel at 40-100 deg.C and cured or dried normally for >=8hr to afford the objective fiber-reinforced cellular gypsum cement board. Furthermore, the afore-mentioned cement board is a lightweight formed product and ettringite is present around the fibers. The bending strength thereof satisfies the formula [bending strength/(specific gravity) ] >=50kg/cm with >=25kg-cm toughness.

Production of hydraulic binder rapidly hardened after preparation of water

Abstract: Method of making a rapidly hardening hydraulic binder for mixing with water, the hardened mass produced therefrom having a defined water resistance. Calcium sulphate alpha -hemihydrate is used as the rapidly hardening component in a predetermined starting quantity, the hardened mass thereof having a time-dependent water resistance curve which, starting from a high initial strength value of the rapid hardening, shows a negative slope in the first twentyeight days. Granulated blast-furnace slag is admixed to the calcium sulphate alpha -hemihydrate. The quantity of granulated blast-furnace slag is matched to the starting quantity of calcium sulphate alpha -hemihydrate in such a way that, after the rapid hardening, formation of crystalline ettringite and formation of calcium hydrosilicate phases occurs and the time-dependent water resistance curve of the hardened mixture shows a constant positive slope in the first twentyeight days.