Showing papers on "Ettringite published in 1982"
TL;DR: In this paper, C 4 A 3 S hydration reactions and consequent expansion mechanisms upon formation of ettringite were investigated using SEM studies using polished sections and EDX, as well as DSC and XRD.
95 citations
TL;DR: In this article, the amount of ettringite formed and the degree of C4A3S hydration were determined in systems deficient in Ca(OH)2 and in NaOH- and NaCl-containing systems.
82 citations
75 citations
TL;DR: In this paper, the chemistry of the calcium alumino-sulphate hydrates has been reassessed using the methods developed in a previous paper [10] and estimates of the expected column length under various conditions are made.
Abstract: The chemistry of the calcium alumino-sulphate hydrates has been reassessed using the methods developed in a previous paper [10]. Ettringite does not have a constant solubility product. The rise in the ionic activity product of solutions in equilibrium with “ettringite” as a function of pH and sulphate activity is attributed to disordering of the crystal structure. This is due to removal of aluminium from the calcium aluminate hydrate columns which form the framework of the ettringite structure. The columns are terminated by these defects and estimates of the expected column length under various conditions are made. Qualitative explanations of changes in the stability of “ettringite” with respect to calcium aluminate monosulphate hydrate and of the action of certain admixtures on Portland cement are made on this basis.
54 citations
TL;DR: In this article, the temperature at which Portland clinker and gypsum are ground together to produce Portland cement is shown to influence the subsequent early hydration behaviour, and the results have been interpreted on the basis of a through solution mechanism involving primarily the reaction of tricalcium aluminate from the cement clinker component with available soluble Ca2+ and SO42− ions in the aqueous medium.
33 citations
27 citations
TL;DR: In this paper, expansion of hydrated mixtures made with C3A, CaSO4 · 2H2O, Ca(OH)2 and SiO2, at 22, 30, 40, 50, 60°C, was studied to verify if expansion is associated with colloidal ettringite formation or with the solid state conversion of C4AH13 to monosulfate hydrate in presence of calcium hydroxide.
22 citations
01 Sep 1982
TL;DR: In this paper, the authors evaluated the free energy of reaction of aqueous ions with tricalcium aluminate to form salts, and showed that the results indicated that the presence of excess silica should make higher-silica phases such as hillebrandite, tobermorite, or others more stable.
Abstract: Cements are being considered for sealing boreholes, shafts, and tunnels in nuclear waste repositories. The phases which will be stable in the long run are those which have the lowest free energies under repository conditions. In order to identify these phases, the relevant thermodynamic literature has been reviewed and evaluated, and some calculations of thermodynamic properties have been made for plausible repository conditions. Best values of heats, entropies, and free energies of formation are presented for calcium silicates, aluminates, and ferrites. Data for C-S-H gel are presented, considering the gel to have a composition of Ca/sub 3/Si/sub 2/O/sub 7/.3H/sub 2/O, and compared to the data for comparable crystalline phases. Equations and thermodynamic properties, including temperature dependence, are given for the hydration of cement components. Calculations for specific reactions show that hydration of tricalcium silicate should produce hillebrandite, 2CaO.SiO/sub 2/.1.17H/sub 2/O; the presence of excess silica should make higher-silica phases such as hillebrandite, tobermorite, or others more stable. The equilibrium between tobermorite, 5CaO.6SiO/sub 2/.5.5H/sub 2/O, and xonotlite, 6CaO.6SiO/sub 2/.H/sub 2/O, was calculated. Calculations of free energy of reaction of aqueous ions with tricalcium aluminate to form salts show that under normal atmospheric pressure and temperature Friedel's salt, the tricalcium aluminate monochloride more » hydrate, is stable both in typical brines and in a basalt groundwater. Similarly, in a brine from Los Medanos in the Delaware Basin of New Mexico, the tricalcium aluminate trisulfate-hydrate ettringite is stable with respect to tricalcium aluminate and to tricalcium aluminate monosulfate hydrate, but not with respect to hydrogarnet (tricalcium aluminate hexahydrate). 3 figures, 23 tables. « less
16 citations
TL;DR: Sulfate resistance of Portland-pozzolanic cements, prepared by gradual replacement of Portland cement by pozzolana, were studied in relation to their transverse strengths as discussed by the authors.
8 citations
TL;DR: In this paper, the effects of solid lime, initial porosity and liquid-solid ratio on the reaction of ettringite formation and on the expansion of uniaxially unrestrained comapacts of C4ASH12-2CS mixture have been studied at 20°C.
TL;DR: In this paper, the authors show that the mechanism of developing the hydrated calcium sulphates and aluminates, especially the trisulphated one, is a decisive factor for the expansion characteristics of the expansive cements.
TL;DR: Hardened pastes in this system were studied by infrared spectroscopy as mentioned in this paper, and the results confirmed ones previously obtained by X-ray diffraction and thermal analysis, unless the lime content was also increased.
01 Dec 1982
TL;DR: In this article, two main reactions are described: formation of ettringite by reaction of aluminate phases with free CaO and CaSO/sub 4/, and reaction of BETA-C/sub 2/S to form C-S-H having surface area similar to that of portland cement gel.
Abstract: The ash obtained by burning of oil shales at 800/sup 0/C is a hydraulic material capable of forming cementitious products on reaction with water. The hydration with water consists of two main reactions: formation of ettringite by reaction of aluminate phases with free CaO and CaSO/sub 4/, and reaction of BETA-C/sub 2/S to form C-S-H having surface area similar to that of portland cement gel. The first reaction is completed within the first day of curing; the second one becomes dominant later on. Formation of hydration products in the ash mix is also characterized by space-filling effect (reduction in porosity with increased hydration). The reactivity of the ash, as estimated by increase in w /SUB n/ , is high. The rate of development of relative strength was similar to OPC systems, but the lower strength values were the result of the high water requirement of the ash mixes, leading to a more porous structure.
Patent•
24 Jul 1982
TL;DR: In this article, a method was proposed to increase strength of treated soil in a very improved manner, by a method wherein a gypsum dihydrate, 40-55wt% cement, and 60-45wt% a blast furnace water deposit having a particle size of below that of cement were simultaneously added to and mixed with a hydrated soft soil, and a weight ratio of the two is set to 10/90-30/70.
Abstract: PURPOSE:To increase strength of a treated soil in a very improved manner, by a method wherein a gypsum dihydrate, 40-55wt% cement, and 60-45wt% a blast furnace water deposit having a particle size of below that of cement are simultaneously added to and mixed with a hydrated soft soil, and a weight ratio of the two is set to 10/90-30/70. CONSTITUTION:In the increase in strength of a hydrated soft soil, an additive A consisting of gypsum dihydrate in particle or powder, and an additive B, being of a mixture of 60-40wt% a blast furnace water deposit pulverized unto minute powder whose particle size is equivalent to or more than that of cement and has a ratio surface area of 2,000cm /g or more, and 40-55wt% cement, are simultanously added, and this causes the additives A and B to react to each other. The minute blast furnace water deposit prepares ettringite rapidly through hydrating reaction of a cement component to promote the increase in strength of the hydrated soft soil. The soil is increased in the strength in an improved manner at a weight ratio A/B of the additives A and B covering a range of 10/90-30/70.
Patent•
16 Dec 1982
TL;DR: In this article, the authors proposed a method to synthesize ettringite in a short time by dissolving sodium aluminate, a starting material for lime and a starting materials for gypsum in water to prepare an aqueous soln.
Abstract: PURPOSE:To synthesize ettringite in a short time by dissolving sodium aluminate, a starting material for lime and a starting material for gypsum in water to prepare an aqueous soln. having a specified concn. on the basis of the amount of formed ettringite and agitating the soln. with heating for a specified time. CONSTITUTION:Sodium aluminate, a starting material for lime and a starting material for gypsum are dissolved in water to prepare an aqueous soln. having about 0.01-0.1mol/l concn. on the basis of the amount of formed ettringite. When the amount of formed ettringite is Xmol and the amount of the aqueous soln. is Yl, the concn. is adjusted to X/Ymol/l. In case where the concn. is not within the range, ettringite forming reaction proceeds hardly. By agitating the aqueous soln. with heating for 20min - 2hr, ettringite is formed rapidly. By continuing the agitation for >=2hr, formed ettringite crystals are broken.