Hicham Marzagui

Abstract

Study of two silico-aluminous castable refractory concretes: microstructures and thermomechanical behaviors in traction and four points bending tests

Hicham Marzagui - 22 march 2005

In this work, two silico-aluminous castable refractory were studied: a castable refractory concrete based on andalusite and with very low content of cement (And-BTC), a castable refractory concrete containing bauxite and with ultra low content of cement (Beam-UBTC). The objectives of this work, completed within the framework of national project PROMETHEREF, relate to the study of the microstructural evolutions at the time of the first thermal cycle and the thermomechanical behavior in traction and inflection. The characterization of the microstructure at the time of the first rise in temperature highlighted phenomena of withdrawal in the matrices of the two concretes. From 900°C, follow-ups in-situ out of electron microscope with sweeping environmental showed the development of the liquid phases and the phenomena of crystallization and sintering. The thermal damage was also studied. Because of the differential dilatometric behaviors of the various components of these two concretes, the first thermal cycle generates local damage mechanisms. The latter appear in the form of decoherences with the interfaces matrice/granulats and of matric microfissuartion in the case of the And-BTC concrete. In the case of the concrete Beam-UBTC, they appear primarily in the form of matric microfissuring. The study of the mechanical behavior was carried out at ambient temperature and high temperature according to the temperature of cooking. With ambient temperature, the And-BTC concrete knows a decreasing evolution of its mechanical properties. Its behavior is characterized by a linear behavior at the beginning of loading followed by one not - linearity to the peak, with a behavior lenitive post-peak. While going up in temperature of cooking, the field not - linear becomes wider with an increase in the deformation to the peak. The concrete Beam-UBTC knows an evolution different according to the temperature from cooking. Initially, it is characterized by a followed elastic linear behavior of a non-linear field to the peak. The extent of this field is narrower. The unstable propagation of macrofissure does not produce a behavior softening after the peak. In the second place, starting from 900°C, this concrete knows a consolidation by sintering which results in an increase in the values of its mechanical properties. Measurements by stereophony-correlation of numerical optical images highlighted phenomena of localization in the fields of deformation at the time of the requests in traction of the two concretes. At high temperature, the mechanical behavior of the two concretes does not know notable evolution in the interval of temperature [ 20°, 700°C ], the behavior is similar with that obtained with 20°C. With 900°C, the two concretes know a transition from behavior which becomes non-linear very wide by the fact of the liquid appearance of the phases and the development of the networks of microfissuring and decoherence. This study highlighted also differences in behaviour between inflection and traction and the mechanisms influencing the measurement of modulus Young and constraint at rupture.

Keywords:
castable refractory concretes, andalusite, bauxite, thermomechanical behavior, damage, traction, modulus Young, microstructure

Last modified: 11/23/2005 03:35 AM