Several studies have been done on fibre-matrix transition zone of composites. Bentur et al. (1985) shows steel fibre reinforced cement where there is a duplex film close to the fibre with a thickness from 1 to 2 micrometers. The first layer consists of a continuous film on the fibre surface of portlandite crystals with their C-axis perpendicular to this surface. The second layer consists of a film of hydrated calcium silicate, but this film is not continuous and is very difficult to recognize with a microscope. On the duplex layer film they found a portlandite zone with a thickness of 10 micrometers. Covering this zone there is a porous transition zone with a thickness from 10 to 20 micrometers, which becomes more compacted as it farthens from the fibre.