ABSTRACT

The Swiss Confederation is presently building the longest railway tunnel in the world. It will have a length of 57 km and the specifications are based on requirements for a 100-year design life. On the basis of the specifications, a comprehensive prequalification procedure for the concrete systems was put out to tender. Sulphate resistance requirements in connection with alkali-free accelerators proved to be difficult to meet, because all alkali-free accelerators contain aluminium salts and sulphates. All aggregate being crushed granite, prepared from excavated rock, the concrete systems had to be designed with a particular focus on the difficult demands with respect to pumpability. This mix design work has led, among other things, to the development of special superplasticisers for sprayed concrete. According to the specifications, the lining of the access shaft to the intermediate excavation site at Sedrun must furthermore meet requirements for increased fire resistance. After a long evaluation phase, the mix design efforts finally concentrated on finding a lime-free aggregate. New developments in nozzle technology allow noticeable reduction of wear costs. Sprayed concrete must be considered as the product of concrete technology and machine design. New developments must take into account the reciprocal dependence of both technologies.