Alberto N. Scian

Burning wastes as an industrial resource. Their effect on Portland cement clinker

Abstract The use of industrial wastes as an alternative fuel in the cement industry is a reality in several countries because wastes are removed and economic incomes are obtained preserving non-renewable energy resources. In the present work, the effect of the addition of small amounts of ashes from pyrolysis of used oil from cars in the clinkering process of Portland cement is studied. The study simulates the burning process in an industrial furnace that uses up to 30% of this kind of waste fuel. The different behaviours of the clinker so obtained (clinkering, milling, phases, hydration, etc.) are discussed and these behaviours are compared with those of a clinker obtained without additions. Chemical analysis, X-ray diffraction, Blaine specific surface, calorimetry, Differential thermal analysis-thermal gravimetry (DTA-TG), pyrometric cone equivalent, porosimetry and mechanical strength were used as the main evaluation techniques.

Effect of induced structural modifications on the physicochemical behavior of bentonite

Abstract The effect of impact and friction milling on the structure and texture of a bentonite, in its natural and in several monoionic forms (H + , Na + , Ca 2+ , Al 3+ ), is studied. An increase of treatment time shows progressive damage to the crystalline structure. The presence of different exchangeable ions does not exert a great influence on the behavior of the mineral. The physicochemical and structural alterations are studied by XRD, DTA, TGA, IR, CEC and swelling index.

MAGNESIA-AMMONIUM PHOSPHATE-BONDED CORDIERITE REFRACTORY CASTABLES: PHASE EVOLUTION ON HEATING AND MECHANICAL PROPERTIES

A cordierite refractory castable was developed using the MgO-NH4H2PO4 reaction. This castable was made with cordierite–mullite aggregates from scrap refractory material and a cement paste based on magnesia, calcined alumina, silica fume, and ammonium dihydrogen phosphate, which forms cordierite (2MgO·2Al2O3·5SiO2) during heating at high temperature. The mix with water was cast into steel molds; the cold setting occurs within 30 min. The set castables were thermally treated and the evolution of the phases was observed. Struvite (NH4·MgPO4·6H2O) was identified at room temperature; between 110 and 750 °C, the present phosphates were amorphous to X-ray diffraction (XRD). At 1100 °C, magnesium orthophosphate (Mg3(PO4)2) and aluminum orthophosphate (AlPO4) were present. At 1350 °C, the main crystalline phases were cordierite and mullite. Cold and hot flexural strength, thermal shock resistance, and physical properties were measured. The properties of magnesia–phosphate-bonded cordierite castables were compared with cordierite material obtained by conventional slip-casting method from aggregates, clay, talc, and calcined alumina.

Magnesia–phosphate bond for cold-setting cordierite-based refractories

A cold-setting refractory material was developed using the magnesia–phosphate reaction. A cement paste based on alumina, silica fume, magnesia and orthophosphoric acid or monoaluminum phosphate was designed to form cordierite–mullite during heating. This cement paste set at room temperature and MgHPO4·3H2O phase (newberyite) was observed, but amorphous phases were predominant. Two exothermic effects were detected during the setting process corresponding to the acid–base reaction of magnesia with phosphates and to the formation of bonding hydrates. At 1100 °C, C-AlPO4 was formed by reaction of alumina with orthophosphoric acid or monoaluminum phosphate. At 1350 °C, the principal crystalline phases were cordierite and mullite. A refractory concrete with the obtained cement paste and a cordierite–mullite aggregate (scrap refractory material) was prepared. At 1350 °C, this concrete had a thermal expansion coefficient of 1.0×10−6 °C−1 and a flexural strength of 10 MPa.

Mechanochemical activation of high alumina cements - hydration behaviour. I.

Abstract The influence of amorphization induced by milling in the hydraulic behaviour of a commercial high alumina cement (CA25) was studied. The original starting cement and others with different degrees of treatment were characterized by XRD, Blaine and BET specific surface area, mean particle size and SEM. The hydraulic behaviour was attained by conduction calorimetry, XRD and EPMA. At 18°C, the treated cements showed longer setting times respect to the original one and also an increase in the ionic ratio Al 3+ /Ca 2+ in the solution. At 39°C, the setting times were shorter than in the starting cement. The setting accelerators as Li 2 CO 3 increase their effect with the amorphized cements. In all cases, the activated cements showed greater hydraulic activity than in the starting state.

High alumina cements. Study of CaO.Al2O3 formation. I. Stoichiometric mechanism

Abstract The reaction of formation of CA(C=CaO; A=Al2O3) was studied using CaCO3 and Al(OH)3 as starting materials, in the temperature range 1100–1400°C and during times from 5 min. up to 5 hours. The reaction was followed by x-ray diffraction, quantifying C, C3A, C12A7, CA, CA2 and α-A, making also an estimation of the consumption of transition aluminas. A stoichiomtric-mathematical model was designed to interpret the experimental results.

High alumina cements. Study of CaO.Al2O3 formation II. Kinetics

From the experimental information obtained in Part I of this study, the kinetics of CA formation (C=CaO; A=Al2O3) were studied through two ways: a) by disappearance of C12A7; b) by appearance of CA. In both cases, it was concluded that the reaction rate is controlled in a first stage by a mechanism of surface reaction, passing afterwards to a diffusional mechanism. The kinetic parameters (E,k,A) were calculated, resulting in an average apparent activation energy -- using data from both methods -- of 72.4 Kcal/mole for the reaction control mechanism, and of 74.0 Kcal/mole for the diffusional process.

Activación térmica de bentonitas para su utilización como puzolanas

Se analiza la reactividad de dos bentonitas calcinadas, procedentes de diferentes regiones de Argentina para su utilizacion como adiciones puzolanicas al cemento Portland. A traves de tecnicas de: DRX, espectroscopia IR, ensayos de reactividad con Ca(OH)2. porosimetria por intrusion de mercurio y resistencia a la compresion; se relacionan los cambios estructurales producidos durante el tratamiento termico con el comportamiento puzolanico. Palabras clave: Puzolanas, bentonitas, cemento.

Mechanochemical activation of high alumina cements — hydration and thermomechanic behaviour. II

Abstract The study about the hydraulic behaviour of the CA25 and the mechanochemical activated CA25 cements started in Part 1 is completed. The hydration anomalies are studied through the analysis of the Al +3 and Ca +2 ions in solution at the end of the solubilization period. With this purpose a non-conventional analysis technique has been developed. The thermomechanical behaviour of concretes made with both the original and the activated cements are analysed, understanding its performance through their microstructure and texture. The observed differences are correlated with the proposed interpretation for the hydration of these kind of cements.

Blended Cements with Limestone Filler and Kaolinitic Calcined Clay: Filler and Pozzolanic Effects

AbstractIn this paper, binary and ternary blended cements (BC) based on calcined clay (CC, 0–30%) obtained from low-grade kaolinitic clay and limestone filler (LF, 0–10%) were developed and the int...