The microstructure of the steel fibre-cement interface

The microstructure of the steel fibre-cement paste interface was studied by scanning electron microscopy. The interfacial zone surrounding the fibre was found to be substantially different from the “bulk” paste further away from the fibre surface. The interfacial zone consisted of (a) a thin (1 or 2Μm thick) duplex film in actual contact with the reinforcement, (b) outside of this, a zone of perhaps 10 to 30Μm thickness, which, in reasonably well hydrated systems, is largely occupied by relatively massive calcium hydroxide crystals, with occasional interruptions of more porous regions, and (c) outside of this, a highly porous layer parallel to the interface. The interaction of cracks initiated in the matrix with this interfacial zone was observed.