Previous: Results and discussion
A systematic mercury intrusion study of mortars of varying sand contents has suggested the occurrence of percolated interfacial zone pores. A hard core/soft shell computer model has been applied to simulating percolation of the interfacial zones present in mortar and concrete specimens. The interfacial zone thickness provided by the mercury intrusion experiment and computer model for mortar, 15-20 micrometers, is somewhat less than that conventionally measured using the SEM imaging technique, but the difference is to be expected given the inherent differences in the two measurement methods. The model indicates that for an interfacial zone thickness of about 20 micrometers, interfacial zone percolation will occur in most typical construction concrete mixes. This is supported by the generally large permeability of concrete relative to plain cement paste. By decreasing the interfacial zone thickness or the porosity in the interfacial zone, or reducing the quantity of aggregates in a concrete, the probability of interfacial zone percolation can be reduced. Since the concept of interfacial zone percolation is relatively new, ultimate effects on transport and durability are uncertain at this time. However, it does seem likely that interfacial zone percolation would adversely affect the long term performance of concrete so that the engineering of interfacial zone microstructure and aggregate content and size distribution may be critical in increasing the service life of concrete.
While the interfacial zone pores present in conventional mortar are most likely due to residual porosity never filled in during hydration, the interfacial zone pores present in mortar containing silica fume may actually be due to a dissolving network of early age calcium hydroxide crystals and small cement particles. If this is the case, these pores and their connectivity may perhaps be reduced by using a sufficiently low w/c ratio or a sufficiently large addition of silica fume.