Influence of the interfacial zone on the chloride diffusivity of mortars

Three different series of mortars with variable sand volume contents were cast in two different laboratories to study the influence of the interfacial transition zones (ITZ) on the transport coefficient of chloride ions. The first series was prepared and tested at Laboratoire Matériaux et Durabilité des Constructions (LMDC, Toulouse, France). The water/cement (w/c) ratio was 0.38 and the sand volume fractions were 0, 19, and 57%. The transport properties were investigated using a diffusion test. The two other series were prepared and tested at Centre de recherche interuniversitaire sur le béton (CRIB, Québec, Canada). The w/c ratios were 0.25 and 0.45 and the sand volume fractions were 0, 30, and 50%. The transport properties were assessed using a migration test. The test results indicate that aggregates modify the microstructure and the transport properties of mortars. The transport coefficient of chloride ions was found to decrease with an increase of the sand volume fraction. At the same time, the transport coefficient of the corresponding paste fraction was found to increase. The increased tortuosity of the matrix induced by the presence of aggregates thus appears to be more important than the influence of ITZ. The interconnection of ITZ was not found to lead to a rapid increase of the chloride ion transport coefficient.