ABSTRACT
The strength of the fibre-hardened cement paste bond is a quality which determines to a considerable degree such properties of the FRC as: strength, modulus of rupture and fracture energy. This inter facial bond strength in theory should be equal to the shear strength of the weaker component, in this case, of the cement matrix. However, in practice this strength assumes markedly lower values. The reason for this is its specific layered structure resulting from the heterogeneous nucleation and crystallization of calcium hydroxite taking place on the fibre surface.
This phenomenon has been described for steel fibre reinforced concrete and for GRFC. In case of organic fibres, in particular those produced only in a cut with the surface rendered rough on purpose, there exists the problem of determining the real value of the strength of the fibre-matrix boundary using direct methods. In the present study an attempt has been made to estimate the value of τ basing on the post-cracking behavior of the material,i.e, the work of fracture and the fracture modulus. The investigations were carried out on FRC reinforced with short, space oriented polypropylene fibres. The Krenit Standard type of fibres, produced by Danaklon were used. The properties of fibers and its application for cement pastes and mortars were described by Krenchel [9] and Davies [10]. The cement matrix was modified with an addition of acrylene resin or silica fume. In case of autoclaved samples an addition of ground quartz sand was used
