A.J. Majumdar

Bio: A.J. Majumdar is an academic researcher. The author has contributed to research in topics: Monocalcium aluminate. The author has an hindex of 1, co-authored 1 publications receiving 39 citations.

The hydration of Secar 71 aluminous cement at different temperatures

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.

Castable refractory concretes

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.

Hydration kinetics of CA2 and CA—Investigations performed on a synthetic calcium aluminate cement

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.

Durability of Building Materials and Components in the Agricultural Environment, Part II: Metal 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.

Hydration of Calcium Aluminate Cements: A Solid‐State 27 Al NMR Study

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.

Calcium Aluminate Cements - Raw Materials, Differences, Hydration and Properties

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 …