1993

Vares, Sirje; Häkkinen, Tarja

The publication comprises two experimental parts. In the first part, 14 different kinds of steel, polypropylene and polyacrylonitrile fibres are studied in order to make high-strength fibre-reinforced concrete. The effect of fibre type and volume on the load-deflection behaviour of FRC is studied and discussed. When the steel fibre volume fraction is low there is usually no significant increase in the "first crack" and flexural strengths, but the toughness of concrete can be significantly increased over that of plane matrix. Thin fibres with rather high specific surface area increase the most significantly the "first crack" strength of the composite. The effectiveness of increasing the fibre volume depends on the fibre type. Roughly speaking, the more effective the fibres are in terms of flexural strength, the more advantageous is the increase in fibre volume. On the other hand, the best fibres give the composite very good toughness already at low fibre contents. The fibre-spreading and slurry-infiltration method can be employed to make steel FRC with very high fibre content. The maximum obtainable fibre volume depends significantly on the stiffness and shape of the fibres. However, the mechanical properties of composites depend not only on the fibre volume content, but significantly on the properties of steel fibres. The relatively high specific surface area of the polymer fibres (PAN and PP) affects advantageously the "first crack" strength of the composite. The results indicate that the bending of PAN fibres to the high-strength matrix is too high in relation to their strength to provide the composite with good toughness. In the second part of the report the influence of aging on the load-deflection behaviour of different kinds of FRC is studied. Different matrices reinforced with steel or polypropylene fibre were subjected to aging and temperature and humidity changes. High-strength fibre-reinforced concrete composites, especially those reinforced by steel fibres can withstand large variation of temperature and humidity without the performance of fibres being significantly weakened.