Thermal analysis of hydrated calcium aluminates
01 Sep 1996-Journal of Thermal Analysis and Calorimetry (Kluwer Academic Publishers)-Vol. 47, Iss: 3, pp 765-774
TL;DR: Differential scanning calorimeter has been used to study the dehydration characteristics of hydrated calcium aluminates such as CA, CA2 and C12A7 where C and A stand for CaO and Al2O3 respectively.
Abstract: Differential scanning calorimeter (DSC) has been used to study the dehydration characteristics of hydrated calcium aluminates such as CA, CA2 and C12A7 where C and A stand for CaO and Al2O3 respectively. Dehydration of CAH10 and C2AH8 (whereH=H2O) occur ∼ at 160–180°C and 200–280°C respectively. These two phases are unstable and ultimately get transformed to AH3 and C3AH6. Dehydration of AH3 and C3AH6 occur between 290 and 350°C and overlap at lower scanning rate. The activation energy for dehydration of the stable AH3 and C2AH6 phases has been found to be 107.16 and 35.58 kJ mol−1 respectively. The compressive strength of the hydrated calcium aluminates has been determined. The result shows that in the case of CA, almost 90% of ultimate strength has been attained in 1 day whereas in CA2, ultimate strength has been attained in 14 days and in C12A7 in 1 day. DSC results have been correlated with the rate of strength developments.
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Dissertation•
11 Dec 2014
TL;DR: In this paper, the authors propose a methodologie for pallier a ce problem, based on the methode de traitement des sols a la chaux, which is used to ameliorer les mecaniques de sols aux performances insuffisantes.
Abstract: Le traitement des sols a la chaux est une methode couramment utilisee pour ameliorer les proprietes mecaniques de sols aux performances insuffisantes. Cependant, ces ameliorations mecaniques ne sont pas prises en compte dans les calculs de dimensionnement. Cette these propose une methodologie pour pallier a ce probleme. Un programme experimental approfondi est realise afin de decrire avec precision le comportement mecanique d’un sol traite et les processus associes a la structuration introduite par le traitement. La composition chimique, et notamment la quantite de composes cimentaires hydrates, est determinee par analyses thermogravimetriques et thermodifferentielles. Un couplage non-lineaire entre la quantite d’hydrates et la limite elastique se basant sur ces resultats experimentaux est propose. A partir de ces resultats, une nouvelle formulation a ete developpee afin de modeliser la degradation de la structure en plasticite, et a servi au developpement d’une nouvelle loi de comportement elasto-plastique basee sur le modele de Cam Clay Modifie. Cette derniere a montre reproduire correctement les principaux traits de comportement specifiques aux sols traites. Il est demontre que ce modele est egalement adapte aux sols naturellement structures. Afin de prendre en compte les effets du traitement et la presence de structure dans le dimensionnement, un programme base sur la methode des elements finis, comprenant le pre- et le post-processing de la geometrie et des resultats du probleme, a ete developpe. Une validation rigoureuse a confirme l'implementation correcte de la methode et son potentiel pour l’optimisation du dimensionnement des ouvrages
6 citations
Cites background from "Thermal analysis of hydrated calciu..."
...Some studies have shown that the decarboxylation processes of these three compounds were associated with three temperature domains (Alarcon-Ruiz et al., 2005; Das et al., 1996; Saikia et al., 2002)....
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...Some studies have shown that the decarboxylation processes of these three compounds are associated with three temperature domains (Das et al., 1996; Saikia et al., 2002; Alarcon-Ruiz et al., 2005)....
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TL;DR: In this article, the authors showed from respective paste thermal analysis data, how microcrystalline cellulose and microfibrillated cellulose (MFC) affect differently the formation of Class G cement pastes hydration products from early (2h) to later hydration ages (672h).
Abstract: The interest in the use of cellulose fibers of increasingly smaller sizes in cementitious materials has increased in recent years. This paper brings new contributions in this field showing from respective paste thermal analysis data, how microcrystalline cellulose (MCC) and microfibrillated cellulose (MFC) affect differently the formation of Class G cement pastes hydration products from early (2 h) to later hydration ages (672 h). Pastes containing 0, 0.25 and 0.5% of cellulose per cement mass and a water/cement mass ratio of 0.45 were cured at 23 °C, and the TG/DTG tests were carried out after 2, 6, 12, 24, 168 and 672 h. The results show that the pastes with MCC and MFC additions presented higher total combined water content than the reference paste, especially after 24 h of hydration. However, this is strongly related to the quantity of water adsorbed by different celluloses and their concentrations in the mixture. Comparing cellulose pastes, MFC pastes showed lower total combined water up to 28 days, attributed to the fiber’s microfibrillar form. No higher amount of calcium hydroxide was formed in the presence of cellulose, but it was more crystalline than that obtained in the reference. Other hydrated phases (dehydration from 200 to 400 °C) are differently affected by the presence of the celluloses, the highest formation occurring for 0.25% MCC paste. This behavior was attributed to an additional cure of these mixtures related to morphological characteristics and water retention capacity of cellulose.
3 citations
TL;DR: In this article, the role of crystal morphology of hydrated calcium aluminates towards strength development in refractory concrete is investigated and it has been observed that crystal morphology depends on rate of hydration and chemistry of calcium aluminate cement (CAC).
Abstract: Synthetically prepared calcium aluminates such as CA, CA2, C12A7 (C = CaO, A = Al2O3) and their various combinations have been subjected to hydration in water for three days. SEM technique has been applied to study the microstructure of the hydrated phases. Attempts have also been made to investigate the role of crystal morphology of hydrated calcium aluminates towards strength development in refractory concrete. It has been observed that crystal morphology depends on rate of hydration and chemistry of calcium aluminate cement (CAC).
2 citations
TL;DR: In this article, the influence of iron on the mineral composition and microstructure of the phase Q (C20A13M3S3) clinker and its hydraulic property was investigated.
Abstract: The present task is to investigate the influence of iron on the mineral composition and microstructure of the phase Q (C20A13M3S3, in the text below C = CaO, A = Al2O3, M = MgO, S = SiO2, F = Fe2O3) clinker and its hydraulic property by using XRD, Rietveld refinement, BSE, isothermal calorimeter, DSC, non-evaporable water content and compressive strength measurements. Results reveal that incorporating 4% of iron leads to the formation of the accompanying minerals which are spinel (MA), gehlenite (C2AS) and tetracalcium aluminoferrite (C4AF), and 6% of iron results in the formation of 15.3% of monocalcium aluminate (CA). Additionally, the lattice parameters of phase Q change with the doped-iron content which could be due to Ca2+ and Si4+ being substituted by Fe3+. Although the formation of C4AF coating layer around the clinker grains inhibits the hydraulic activity of clinker within the first 1 day, it has no adverse impacts on the later-age (28 days) hydration and is favorable to improve the 28-day compressive strength. The formation of CA accelerates the hydration of clinker, shortens the time span of the acceleration and deceleration periods, and may influence the hydration reaction of phase Q. Considering compressive strength, the threshold limit of iron incorporated into phase Q raw meal is found to be 4.0 mass%, beyond which an obvious decrease in 28-day compressive strength is detected.
2 citations
Dissertation•
19 Dec 2019
TL;DR: In this article, a modele cree est un modele de thermochimie ou les quantites de matieres sont pilotees par des equations differentielles-algebriques.
Abstract: Ces travaux s’articulent autour de la modelisation cinetique de l’hydratation des ciments alumino-calciques (CAC) pour en ameliorer la comprehension et la maitrise. L’aspect cinetique pour ces ciments est essentiel en raison des nombreux etats metastables qu’ils traversent (e.g. conversion).Des modeles de cinetique integres dans l’espace existent deja pour simuler des pâtes de mortier mais ils requierent la connaissance des lois de cinetiques. Malheureusement, ces lois sont mal identifiees pour les CAC et c’est ce qui motive la creation d’un modele pour des suspensions minerales. L’etude de suspensions permet d’etudier ces lois sans l’influence de l’empilement granulaire et du reseau poreux. Le modele cree est un modele de thermochimie ou les quantites de matieres sont pilotees par des equations differentielles-algebriques. L’information sur la granulometrie est, elle, portee par des Population Balance Equations permettant de repercuter chaque phenomene physico-chimiques (e.g. Nucleation, Dissolution, Croissance, Agglomeration...) de maniere adaptable et independante sur les tailles de particules. L’etude de ce modele a permis de mettre en evidence le role fondamental que joue la formation de l’hydroxyde d’aluminium dans l’hydratation des CAC. Cette formation permet l’apport en solution d’ions hydroxyde deficitaires a la formation de la plupart des hydrates en consommant des ions aluminates. Cette formation d’hydroxyde d’aluminium a ete demontree comme etant complexe a expliquer experimentalement et a modeliser. Toutefois, l’utilisation de precurseurs pre-hydroxyles permet de la modeliser partiellement.
1 citations
Cites background from "Thermal analysis of hydrated calciu..."
...La stratégie de stubstitution consiste à "diluer" ce ciment Portland riche en chaux par des matériaux de substitution tels que les cendres volantes, les laitiers de hauts fourneaux ou du métakaolin (ciment LC3 [3])....
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...[3;4] Il devient alors possible de simuler d’un point de vue atomistique la croissance cristalline qui peut être préférentielle selon une direction, selon différents mécanismes (pilotée par la nucléation, les défauts....
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...[2;3] (non-détaillé dans ces travaux) avant d’en proposer un nouveau plus précis....
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...[3] Karen Scrivener, Fernando Martirena, Shashank Bishnoi, et Soumen Maity....
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...Calcined clay limestone cements (LC3)....
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References
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10,842 citations
TL;DR: The chemistry of hydration of monocalcium aluminate, CA, has been studied at several temperatures using conduction calorimetry, X-ray diffraction and other techniques as discussed by the authors.
Abstract: The chemistry of hydration of monocalcium aluminate, CA, has been studied at several temperatures using conduction calorimetry, X-ray diffraction and other techniques. At 4 °C, hydration to the decahydrate CAH 10 occurs about 15 hours after mixing; this hydration time increases with increasing temperature up to 30 °C, and C 2 AH 8 appears as a hydration product. At 40 °C rapid hydration to C 2 AH 8 is followed over a period of weeks by the ‘conversion’ reaction producing C 3 AH 6 . The reaction of CA to form crystalline hydrates was monitored by X-ray diffraction analysis; the results indicate that hydration also produces significant amounts of noncrystalline material. The enthalpies of the reactions involved in hydration and ‘conversion’ were measured by conduction calorimetry.
63 citations
TL;DR: In this article, the authors studied the hydration behavior of Secar 71 refractory aluminous cement using conduction calorimetry, X-ray diffraction and thermal analysis techniques.
Abstract: The hydration behaviour of Secar 71 refractory aluminous cement has been studied over a range of temperature using conduction calorimetry, X-ray diffraction and thermal analysis techniques. The first reaction is the hydration of monocalcium aluminate, CA, producing a sharp calorimeter peak within 12 hours of mixing. Following this reaction the other major component, calcium dialuminate (CA 2 ), undergoes slow hydration over a period of weeks. The enthalpies of these two reactions have been measured. The initial hydration products of both components are CAH 10 , or C 2 AH 8 with alumina gel. These can subsequently convert to C 3 AH 6 ; after one month significant conversion is observed even at room temperature. A method of estimating the degree of conversion based on X-ray measurement of C 3 AH 6 is proposed.
46 citations
TL;DR: Differential scanning calorimetry (dsc) was used to investigate the freezing behaviour of hardened cement paste (hcp) subjected to nacl and cacl2 solutions containing up to 5.4 mol cl/l as mentioned in this paper.
Abstract: Differential scanning calorimetry (dsc) was used to investigate the freezing behaviour (-175 deg c to 20 deg C) of hardened cement paste (hcp) subjected to nacl and cacl2 solutions containing up to 5.4 mol cl/l. Thermograms were also recorded for samples dried to relative humidities (rh) between 61% and 96%. The low-temperature phase transition at -38 deg c exhibited the freezing behaviour of an aqueous solution in gel pores of approximately equal to 4 nm radius. Chloride ions strongly reduce the coupling forces between gel particles and structure the gel pore water. On desorption critical behaviour of the low-temperature transition energy was observed at 0.52 mol cl/l which is the concentration most damaging to hcp. Above 1.3 mol cl/l freezing of supercooled bulk water in macropores was observed at more than one temperature. (Author/TRRL)
31 citations
TL;DR: In this paper, the hydration process of a high alumina cement was investigated through ultrasonic wave propagation techniques, and a correlation between wave amplitude and velocity and breaking strength of the cement was demonstrated.
Abstract: The hydration process of a high alumina cement was investigated through ultrasonic wave propagation techniques A correlation between wave amplitude and velocity and breaking strength of the cement is demonstrated The wave behaviour through hydrating cements was found to be a function of the cement-to-water ratio between values of 2 and 4 Changes in the temperature of the hydrating samples were found to exhibit a similar dependence
6 citations