Leaching effect on concrete - part ii: mechanical behaviour evolution of itz during leaching at the local scale

Cement paste/aggregate bond influences durability of concrete subjected to leaching, following the existence of a particular, more vulnerable zone in cement paste, adjacent to aggregates - the interfacial transition zone (ITZ). In order to assess the mechanical behaviour of concrete at local scale of cement paste/aggregate bond, tensile tests were carried out on cement paste and cement paste/aggregate composite samples. The relationship between chemical degradation and mechanical properties (Young's modulus and tensile strength) was expressed through the notion of chemical degradation rate. Other aspects discussed, such as the leaching kinetics, chemical dissolution and cracking were used to highlight the origin of the loss of mechanical properties of the cement paste and of the cement paste/aggregate bond. Following an important dissolution within ITZ, a total loss of adhesion between cement paste and aggregate following leaching occurs gradually. Concerning the cement paste, it undergoes a smaller decrease of Young's modulus and tensile strength compared to the composites, being also less affected by cracking. Overall, this study highlights the mechanism by which the mechanical behaviours of cement paste and cement paste/aggregate bond are affected by leaching.