Steel fibre developments in South Africa

Abstract

This article discusses an extensive South African research and development study of steel fibre reinforcement for precast concrete lining segments. The study developed a suitable concrete mix for a pressurised water tunnel in South Africa, using two different types of fibre, Dramix and Ferro-Fibres. It also included full-scale production in the on-site casting factory, and full-scale testing of both steel fibre reinforced concrete (SFRC) and bar-reinforced segments. Several of the segments, built into the tunnel, are fitted with instruments for continuous monitoring during segment production, handling and tunnelling operations; they will also provide for long-term on-site observation. The research study had three stages: (1) development of an SFRC mix, also suitable for the batching plant; (2) full-scale testing of SFRC and bar-reinforced segments using an on-site test rig; and (3) testing of complete rings as part of the permanent works. As a result, a form of SFRC segmental lining was found, which met all the design criteria and was significantly cheaper than the bar-reinforced design. Such SFRC segments also had some other advantages over bar- reinforced segments.