Influence of the Interfacial Transition Zone and Interconnection on Chloride Migration of Portland Cement Mortar

Available experimental studies on the effect of the interfacial transition zone (ITZ) on transport properties of cement-based composite materials appear to be ambiguous. The main objective of this work was to enhance the understanding of the relationship between ITZ and transport properties of Portland cement-based materials by using both a rapid chloride migration test and theoretical calculations. A densification factor which is related to aggregate volume content was introduced to further determine the transport properties of ITZ. Results indicate that the overall porosity decreased with increasing aggregate volume content due to the dilution effect by impermeable aggregates. The porosity was above the theoretical dilution line obtained from P(0)x(1-V-agg) for mortars with more than 20% of aggregate, which can be attributed to the presence of high porous ITZ. On the other hand, more porous ITZ was expected to be accompanied by a denser bulk cement matrix, which leaded to a decrease in the porosity of mortar with less than 35% of aggregate. The ITZ effect would dominate the blocking aggregate, densification and tortuosity of bulk paste when aggregate volume content exceeded 0.35. The ratio between the migration coefficient of the ITZ and that of the matrix (D-ITZ/D-matrix) increased with aggregate volume content and assumed ITZ thickness. In addition, the influence of ITZ increased with increasing the degree of interconnection slightly until 1.0. Beyond this value, a sudden increase in D-ITZ/D-matrix ratio was observed indicating the negative percolation effect when the adjacent ITZ start to interconnect.