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This paper presents results concerning the partial substitution of a calcium aluminate cement by calcium carbonate. The experimental parameters monitored in this study are the mechanical properties, the microstructure evolution through density measurements and the structure through analysis by X-ray diffraction. The major results of this study are the following: (1) It is possible to substitute a portion (10 wt%) of an aluminous cement by calcium carbonate, while improving the mechanical properties of the hardened material. This is achieved with a mass percentage of the carboxylic acid between 1 and 5%, relative to the dry mass, which acts as a good dispersant and leads therefore to densification of the hardened material. (2) When the mix consists of 50 wt% of aluminous cement and 50 wt% of calcium carbonate, the mechanical properties of the cured material are low and this happens whatever the percentage of added dispersant is. [ABSTRACT FROM AUTHOR]

Abstract: Porous cordierite ceramics were produced from stevensite-rich clay and andalusite mixture using oil shale (OS) as a natural pore-forming agent. The pressed pellets of powdered samples were sintered at 1300°C for 2h using both conventional sintering (CS) and three-step sintering (TSS) cycle. The mechanical properties were evaluated by three-point bending test, Brazilian test and ultrasonic measurements. The microstructure and mechanical properties are strongly influenced by the sintering conditions and the amount of (OS) added (0–20wt%). The (CS) cycle and the maximum addition of (OS) resulted in an increase in pore size and open porosity from 17.7% to 52.8%. The samples sintered using (TSS) exhibited a higher flexural and tensile strengths (25.4 and 16.8MPa, respectively) than those of samples sintered via (CS) cycle (11.2 and 7.54MPa, respectively). However, the gradual increase in (OS) addition revealed a strong decrease in mechanical properties such as flexural strength (44.6–17.8MPa), tensile strength (19.2–13.3MPa) and Young׳s modulus (70.5–46.8GPa). The formation mechanism of the porous structures by adding (OS) are also reported and discussed. [Copyright &y& Elsevier]

This present paper concerns the structural and microstructural characterization of 1mm thick calcium aluminate cement tapes prepared by tape casting. A study of the effect of environment, time and the consolidation temperature on the structural properties and microstructure has been undertaken. Consolidation environments studied are air, water and an environment saturated in humidity for storage durations of 1, 4 or 30 days at a temperature of 20 or 70°C. The structural characterization was carried out using XRD. The microstructural characterization was carried out through the distribution of pore volume by mercury porosimetry measurements and SEM micrographs. The effects of the various consolidation parameters were compared and discussed. The tape consolidated for 30 days in water at 70°C has the most advanced hydration with the formation of stable hydrates. This is evidenced by the reduction of the inter-granular pore size and the microstructure densification. [ABSTRACT FROM AUTHOR]

Abstract: Aluminous cement pastes (Secar 71 from Lafarge) containing increasing quantities of acetic acid, HOAc, are prepared ((wHOAc/wcement) × 100 ranges from 0 to 10%). Pastes containing HOAc present a Newtonian behavior. The best dispersion is obtained when the mass content of acid with respect to the cement is equal to 0.5%. Microstructural characterizations of samples aged for 4 days at 20°C and 95% relative humidity reveal a significant increase in density, a reduction in porosity as well as a displacement of pore diameter towards low sizes. The open porous volume decreases with time from 25 to 9vol.% when samples are 4 days and 6 months old, respectively. The addition of HOAc also has a beneficial effect on the flexural strength of set samples. [Copyright &y& Elsevier]

This article is devoted to the description of the microstructure of ye'elimite, calcium aluminates and ferritic phase when iron oxide is present and when the synthesis is carried out at 1300 °C for 3 h. The incorporation of iron in ye'elimite structure (general formula: Ca 4 Al (6-2x) Fe 2x SO 16 with x = 0.00 to 1.13) is complete when x < 0.12. Beyond this composition, the ferritic phase (CaO) 2 (Al 2 O 3 ,Fe 2 O 3) appears as a minor phase which can develop two forms: needle-like morphology and melt morphology. The presence of iron favors the formation of an iron-rich liquid phase which leads to the growth of ye'elimite grains by material diffusion mechanisms and increases the conversion rate of alumina and calcium aluminates in ye'elimite phase. Also a clear distinction between calcium aluminate and ye'elimite grains is presented. • Complete and detailed description of microstructure of ye'elimite containing iron; general formula: Ca 4 Al (6-2x) Fe 2x SO 16 with x = 0.00 to 1.13 • The incorporation of iron is complete when x < 0.12. • Beyond this composition, the ferritic phase (CaO) 2 (Al 2 O 3 ,Fe 2 O 3) appears as a minor phase which can develop two forms: dendritic morphologies and melt morphology. • A clear distinction between CA and ye'elimite grains has been reported for the first time. • The presence of iron favors the formation of an iron-rich liquid phase, which leads to the formation of larger ye'elimite grains, through a liquid phase reactive sintering. [ABSTRACT FROM AUTHOR]