Showing papers on "Ettringite published in 1986"

Bound Water in Cement Pastes and its Significance for Pore Solution Compositions

Abstract: The problem of defining bound water in a cement paste is discussed; a reasonable definition is one that includes interlayer water in C-S-H and AFm phases, structural water in ettringite, and adsorbed water, but not water in micropores or in larger pores. On this basis, structural considerations indicate a value of around 32% on the ignited weight for a fully hydrated paste. ‘Non-evaporable’ water, typically around 22% on the ignited weight at full hydration, cannot be identified with bound water, because dehydration to the state in which only non-evaporable water remains causes major loss of interlayer water and destruction of ettringite. In the interpretation of pore solution data, the definition of bound water, and the value assumed for this quantity, are important, because the ionic concentrations in the pore solution are greatly affected by the volume of free water available to dissolve them. If cement is partially replaced by low calcium fly ash, the quantity of bound water at any given age is substantially reduced. This effect contributes to the relatively low concentrations of alkali metal and hydroxyl ions that are observed in the pore solutions of many portland-fly ash cement pastes.

Aluminum Sulfate Hydration Retarders for High-Calcium Fly Ash Used in Highway Construction

Abstract: The rapid hydration and setting associated with the use of high-calcium fly ash as an additive in soil and aggregate base stabilization in highway construction imposes certain limitations in regards to operational time and volume of work executed. Aluminum sulfate and its ammonium salt were evaluated as hydration reaction retarders. Mixtures of Ottawa sand and Class C high lime fly ash in a 1:1 weight ratio were used for the evaluations. These additives minimized the adverse effects of delayed compaction by recovering some of the compressive strength lost to the rapid hydration, although in all cases the density of the mixes decreased. The recovery of strength was related to the heat of hydration, wherein the peak temperature was reduced from 90°F to the range of 86–78°F at 2 hours; further temperature decreases were observed as reaction time increased. The availability of the sulfate ions, as manifested by the presence of ettringite, helps the hydration process continue, minimizes the adverse effects of delayed compaction and assists positively in the reduction of the void area of mixes and in stratlingite formation, which contributes to a strong crystalline framework.

Mixture for producing quickly hardening mortars for stuccoes and repairs

Abstract: 1 A mixture for making quick-setting mortar for plaster and repairs and containing binders, conventional aggregates and additives, characterised in that it contains : a 10 to 40 parts by weight of reactive calcium silicates, b 3 to 8 parts by weight of reactive aluminates, calculated as CA, c 08 to 5 parts by weight of calcium hydroxide, d 005 to 2 parts by weight of calcium sulphate hemihydrate and/or anhydrite-III, e 04 to 65 parts by weight of calcium sulphate anhydrite-II, and f 003 to 05 parts by weight of organic setting retarders which inhibit nucleation and the growth of calcium aluminum sulphate hydrate, the ratio of components b:c being less than 5, so that the reaction sequence is via the following reaction products : primary ettringite, monophases (calcium aluminate monosulphate), secondary ettringite and calcium hydrosilicate

Method for dehydrating and caking rapidly waste containing organic material or organic material and much water

Abstract: PURPOSE:To cake waste in a short time by adding a material, obtained by adding calcium sulfate, etc to the material which is obtained by calcining and activating alunite in presence of cement, to the remaining flocculated material obtained by removing water to the utmost from said waste contg an org material or an org material and a large amt of water CONSTITUTION:A material obtained by adding, if necessary, calcium sulfate, alumina, etc to the calcined and activated alunite or the material added with low sulfuric acid-type ettringite double salt contg 14-16 molecules of water of crystallization, calcium sulfate, alumina, etc is added to the remaining flocculated material obtained by adding a flocculant to waste contg an org material or an org material and a large amt of water to remove water to the utmost Consequently, ettringite is effective ly formed and grown in the presence of cement, and a porous mixture or the mixture having many capillaries is prepared Or a highly water-absorptive substance such as bentonite, if necessary, is added to the waste in the absence of cement, and the whole material is caked by a layered acid clay derivative and its caking catalyst Consequently, said waste can be caked in a short time (46-96hr on average) without heating and under natural conditions

The Role of Sodium Hydroxide in the System C3A-CaSO4-H2O at 30°C

Abstract: The hydration reaction of C 3 A with gypsum (molar ratio = 1:1.5) has been studied in water and in sodium hydroxide solutions at 30°C. The hydration product were analyzed microscopically and by means of X-ray diffraction. The concentration of sulfate and aluminum in solution was determined spectrophotometrically. In the absence of alkali, the amount of ettringite formed passes through a maximum and is accompanied by almost complete consumption of sulphate ion in solution. Alkali depresses the formation of ettringite and accelerates that of calcium hydroxide. The monosulfate hydrate appears immediately in alkaline solutions and water then reappears after a day as a solid solution with the tetracalcium aluminate hydrate. The formation of the monophase solid solution is accompanied by the consumption of C 3 A, ettringite, and calcium hydroxide and by an increase in the amount of the dissolved aluminum. The presence of alkali markedly increases the initial sulfate ion concentration from solution.

Relationships Among Retardation, Expansion, Microstructure, and Phase Composition For a Salt-Saturated Expansive Grout

Abstract: A salt-saturated and sulfate-expansive grout was formulated with four levels of sodium citrate to determine effects on workability and setting time. Linear expansion of restrained grout prisms increased with amount of citrate used, apparently a function of extent of retardation of the grouts. This relationship was observed both for grouts cured for at least 53 days, and for a concrete formulated from the same cementitious materials cured for at least 180 days age. The microstructures of the grouts at 28 days age showed notable increases in extent of reaction of the sulfate phases and in formation of ettringite with increasing citrate content, and thus with increasing retardation of set. XRD also revealed an increase in well-crystallized ettringite and decrease in gypsum with greater retardation. These observations provide a microstructural and compositional link between retardation and expansion of cementitious materials formulated to be expansive.