Yves Berthaud

Coupling between kinetics of dehydration, physical and mechanical behaviour for high alumina castable

Abstract The dehydration of a high alumina cement castable and its influence on physical and thermomechanical behaviour is studied for temperatures below 800°C. The hydrated cement paste is composed of non-hydrated constituents (CA, CA 2 and C 12 A 7 ) and two stable hydrates (AH 3 and C 3 AH 6 ). The decomposition of the hydrates is analysed by TGA–DTA and XRD analyses. The complex chemical reactions are modelled by several kinetic laws characterising the conversion rate of the initial and intermediate formed hydrates. The variation of porosity and shrinkage of the cement paste as well as the shrinkage of the castable due to dehydration are also measured. A model, including local information at different micro-scales (constituents of the cement paste and their physical properties, volume fraction of aggregates), is proposed for both the paste and the castable.

Analysis of cracking due to shrinkage restraint on the mechanical behaviour of reinforced concrete

Shrinkage may lead to tensile stresses and cracking in reinforced concrete structures due to several mechanisms: gradients of drying shrinkage, restraint of autogeneous and drying shrinkage by reinforcement or concrete members of different thickness or ages etc. This contribution focuses on the effect of drying shrinkage on the behavior of concrete tie members, with a focus on the restraint by reinforcement. It is showed that, if it is not taken into account, numerical simulations show an overestimation of cracking and force at first crack when submitted to uniaxial tension when compared to experimental results. Besides, an appropriate interface model should be also introduced in order to be relevant.