The hydration of Secar 71 aluminous cement at different temperatures
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.
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TL;DR: In this article, the development from conventional high cement materials, through low cement and ultra-low cement castables to the present materials which may be entirely free of CAC is discussed.
Abstract: Castable refractories containing calcium aluminate cement (CAC) are used ubiquitously in a range of furnace lining applications in the iron and steel, cement, glass, ceramic, and petrochemical industries. This review outlines their development from conventional high cement materials, through low cement and ultra-low cement castables to the present materials which may be entirely free of CAC. Castables are defined in terms of both CaO content and installation procedure. Production routes, compositions, and microstructural evolution on hydration, setting, dehydration, and firing are described for pure CACs and castable refractories. The development of the low cement systems is discussed in terms of particle packing, dispersion, and rheology highlighting the influence of colloidal matrix additions of silica and alumina. Recent developments including cement free, self-flowing, shotcreting, and basic castables are described and the potential for carbon-containing systems evaluated.
280 citations
TL;DR: In this paper, the hydration of monocalcium aluminate (CA) in calcium aluminate cements (CACs) was analyzed by the G-factor quantification and the individual contributions of the phases CA and CA2 to the heat flow were calculated based on the amounts dissolved by applying thermodynamic data.
Abstract: Much is already known about the hydration of monocalcium aluminate (CA) in calcium aluminate cements (CACs). CA2 is known to be weakly hydraulic. Therefore, the hydration kinetics of CA2 were not of as great interest as those of the hydration of CAC. We were able to show that the hydration of CA2 begins as soon as the hydration rate of CA has reached its maximum and the first precipitation of C2AH8 has started. The hydration of different CA/CA2 ratios was analyzed by the G-factor quantification. The individual contributions of the phases CA and CA2 to the heat flow were calculated based on the amounts dissolved by applying thermodynamic data. The heat flow as calculated from XRD data was then compared with the measured heat flow. It obtained a good consistency between the two. The very pronounced influence of CA2 during hydration of CAC can be clearly demonstrated.
94 citations
TL;DR: In this paper, a literature review gives an overview of the knowledge on durability of concrete structures, concrete being undeniably one of the most frequently used building materials for solid and slatted floors in animal houses and for manure and silage storage structures.
Abstract: This final part of the literature review gives an overview of the knowledge on durability of concrete structures, concrete being undeniably one of the most frequently used building materials for solid and slatted floors in animal houses and for manure and silage storage structures. Resistance against corrosion caused by lactic and acetic acids is of major importance both for floors and silos. Concrete manure tanks, walls of manure pits in animal houses and the underside of concrete slats and slabs are exposed to biogenic sulphuric acid corrosion. Different demands for producing a high-quality and durable concrete structure are discussed. This includes correct specification of the concrete mix (water/cement ratio, cement content), compaction and curing. The influence of the cement type, pozzolanic additions, aggregate type, polymer additions, application of cement-bound surface layers, impregnation with water repellents or pore blockers and application of coatings, on the corrosion resistance is reviewed.
90 citations
TL;DR: In this paper, the results of a study of the hydration of calcium monoaluminate and Lafarge Secar 71 (CA + CA2) using 27Al MAS and 1H-27 Al CPMAS NMR spectroscopy were presented.
Abstract: This paper presents the results of a study of the hydration of calcium monoaluminate (CA) and Lafarge Secar 71 (CA + CA2) using 27Al MAS and 1H-27 Al CPMAS NMR spectroscopy. CPMAS, high H0 magnetic field strengths (11.7 T), and high MAS spinning speeds (13–14 kHz) provide significant new information about the Al structural environments present during hydration and about the mechanisms of hydration. Important results include the following: (1) Hydrated Al(4) and Al(6) environments are present during the incubation period. This observation is consistent with previously published hydration models. (2) The overall conversion of Al(4) in unhydrated phases to Al(6) in hydrated phases and the crystalline phases detected by XRD are similar to the results of previous studies. (3) There are previously undetected hydrated reaction intermediates present during the main reaction stage. At temperatures above 25°C this phase contains Al(4), and at 4°C it contains Al(4) and possibly Al(5). The incubation period observed for this reaction may be related to the nucleation of this phase.
74 citations
TL;DR: The use of high alumina cement was used widely in the UK after World War I, expressing its higher content of aluminum oxide in comparison to Portland cement as mentioned in this paper, and the reason for looking into alternative cement materials was to develop cements with improved stability against sulfate corrosion.
Abstract: High alumina cement was used widely in the UK after World War I, expressing its higher content of aluminum oxide in comparison to Portland cement. Several descriptions of investigations on calcium aluminate cements appeared, starting around 1850, with a first patent field in 1888 (Scrivener and Capmas, in Hewlett 1998). More widely known is the work of Bied (1909, 1926) filing a patent in 1909 for the fabrication of cement using bauxite or some similar aluminum or iron-rich material, with low SiO2-contents and limestone. In 1918, the trade name Ciment Lafarge Fondue was used for the first time. Meanwhile in the USA, Spackman (1908, 1910a,b) developed cementitious material marketed under the name of Alca natural cements. Several patents were applied and granted (Bates 1921). A description of non-Portland cements was given by Muzhen et al. (1992).
The reason for looking into alternative cement materials was to develop cements with improved stability against sulfate corrosion. Nowadays, calcium aluminate cements are used specifically for their distinct properties (Brown and Cassel 1977), some of which are presented in Table 1.
Calcium aluminate cements do have special applications and are therefore widely used despite the fact that worldwide fabrication is by no means comparable to OPCs (Hohl et al. 1936; Garces et al. 1997; George 1976, 1980a,b, 1983, 1990, 1997; George and Montgomery 1992; George and Racher 1996; Gartner et al. 2002). Scrivener and Taylor (1990) and Scrivener et al. (1997a,b) described calcium aluminate cements and their use and microstructural developments. The use for experimental purposes was described by Auer et al. (1995). Thermal analyses for thermogravimetry of CAC-fraction and formation was discussed by Chudak et al. (1982, 1987). The …
65 citations
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TL;DR: In this paper, the strength of high alumina cement (HAC) concrete is measured as a percentage of the one-day strength, which depends upon the rate, R, at which the conversion reaction takes place, and upon the water/cement ratio.
Abstract: Synopsis High alumina cement (HAC) concrete suffers from a conversion reaction in which the metastable calcium aluminate hydrate compounds change to more stable compounds. This reaction takes place at a rate which depends upon a number offactors including temperature, water/cement ratio, stress and the presence of ‘releasable’ alkalis in the aggregate. As a result of the reaction, the concrete will lose strength and the strength will reach a minimum at various times depending upon conditions of storage; thereafter there may be a small increase in strength. The strength at this minimum, S, expressed as a percentage of the one-day strength depends upon the rate, R, at which the conversion reaction takes place, and upon the water/cement ratio. An empirical relationship for laboratory-prepared specimens is S = (− 37·8 logeR + 39·5) − 100(w/c − 0·4). However, this cannot be used for unknown concretes until a reliable method of determining the original water/cement ratio of HAC concrete is available. Rapidly co...
95 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 paper, a setting time parameter has been determined from the heat evolution versus time curve measured by means of a thermocouple embedded in the cement paste as well as by the Gillmore needle.
Abstract: A setting time parameter has been determined from the heat evolution versus time curve measured by means of a thermocouple embedded in the cement paste as well as by the Gillmore needle. The setting time increases with increasing temperature, until it reaches a maximum between 26 and 30°C, for four out of the five refractory calcium aluminate cements studied. This anomalous retardation is not, therefore, restricted to ciment fondu, as reported elsewhere. The rate of consumption of CA during the first 24 hours of hydration as determined by X-ray diffraction also indicated a retardation at 30°C compared with 20°C for Secar 51 and Secar 71. The cause of the anomaly cannot be the presence of C 2 S, which is virtually absent in most of the cements studied. An alternative explanation must be found, which should also explain why Secar 80 behaves differently from the other cements investigated.
58 citations
TL;DR: In this article, the hydration behavior of C2A7, a component of many calcium aluminate cements, has been studied over a range of temperature using conduction calorimetry, X-ray and thermal analysis techniques.
Abstract: The hydration behavior of C2A7, a component of many calcium aluminate cements, has been studied over a range of temperature using conduction calorimetry, X-ray and thermal analysis techniques. At 4°C, hydration occurs about 2 hours after mixing; hydration is slower at 20°C but at 40°C a very rapid reaction is observed. The initial hydration products are C2AH3 together with CAH10 or alumina gel; considerable amounts of amorphous material are always also formed. At 20°C and above these initial products slowly convert to C3AH6; the conversion becomes faster with increasing temperature. The enthalpies of the hydration and conversion reactions were measured by conduction calorimetry.
44 citations