ABSTRACT
Abstract The influence of the interfacial transition zone (ITZ) on the resistance of well-cured ordinary and high strength mortars (W/B=0.25 and 0.45) to calcium leaching was studied by soaking small disks of mortars in two different pH-controlled solutions over a six month period. The results indicate that the kinetics of degradation (calcium leaching) depends on the water/binder ratio, the type of binder, and the nature of the aggressive solution, but does not appear to be significantly influenced by the presence of numerous ITZ in the material. SEM observations revealed a clear front of degradation with no preferential decalcification around aggregates beyond this front. Keywords: calcium leaching, chloride ions, ITZ, silica fume, water/binder ratio
1 Introduction
The interfacial transition zone (ITZ) formed at the vicinity of aggregate particles in concrete is a very thin layer of hydrated cement paste where the microstructure differs significantly from that of the bulk cement paste. Many studies indicate that this zone has a higher porosity and portlandite content [1, 2, 3]. From a theoretical point of view, the higher porosity of the ITZ, especially if they are interconnected, should facilitate the ingress of external aggressive agents as well as the leaching of calcium. Furthermore, the higher portlandite concentration in the ITZ should increase the potential risk of calcium leaching caused by the dissolution of Ca(OH)2, and therefore detrimentally affect the resistance of concrete to ion penetration and modify the mechanical properties of cementitious systems.
