Modificiation mechanism of the ITZ and bulk cement matrix with GGBS in relation to chloride migration

The influence of the Ground granulated blast-furnace slag (GGBS) on the microstructure of the interfacial transition zone (ITZ) and the bulk matrix was determined by using MIP measurements. The ITZ quantity was controlle by systematically varying the aggregate volume fraction. Correlating the chloride migration coefficients with the variations in the microstructure, the relative importance of the improved ITZ to the enhancement of the overall properties was discussed. Results indicated that the incorpooration of GGBS as a partial substitute of OPC tends to refine the pore structure, particularly in the range superior to 100 nm. The Dnssm values of the series containing GGBS decrease significantly when the replacement rate of GGBS increases regardless of aggregate volume fraction and size. From the results provided in the transport measurements, the differences in the transport coefficients between the reference series and the blended series were more apparent for the neat paste samples. Moreover, the variations of transport coefficient were highly dependent on the changes in the capillary porosity rather than on changes in the coarse pore size range. This is presumably because the large pores at the interfacial zones are not interconnected with each other but rather the relatively small pores of the matrix. The observed improvement of chloride resistance of the GGBS blended samples must be more importantly due to the marked densification of the bulk cement matrix.