Résumé
The study of the durability of concrete subjected to leaching requires knowledge of the mechanisms of chemical degradation of cement paste and of cement paste/aggregate bond. The Interfacial Transition Zone (ITZ), the portion of cement paste in contact with aggregates, is a vulnerable zone in the context of chemical degradation due to its high degree of solubility and diffusivity. In order to evaluate the leaching kinetics as well as the chemical dissolution of bulk cement paste and of the ITZ, parallelepiped cement paste samples and cement paste/aggregate composites were produced and submitted to accelerated leaching. The measurement of the degraded depth was carried out by image analysis of the cross sections of the cement paste and of the interface. The degradation kinetics of the bulk cement paste is proportional to the square root of time. On the other hand, that of the ITZ initially follows the same trend, but slightly accelerates after a critical threshold. Chemical analyses were performed by Energy Dispersive Spectroscopy (EDS) to measure the Ca/Si molar ratios of ITZ and cement paste for a single degradation time. The greater drop of the Ca/Si ratio at the ITZ reveals a significantly greater dissolution of the portlandite than in the bulk cement paste.