Christian Paglia1*, Giuliano Frigeri1 and Armando Chollet1

The demolished rock materials of part of a 50 km long tunnel through the Alps, was characterized and used to produce shotcrete to secure the tunnel walls. The granulometric curves needed to match with reference curves. This was sometimes difficult because of the different mineralogy encountered. Then, the material was mixed to produce concrete with silica fume and steel fibres for the shotcrete. The fresh concrete properties were measured on site. Furthermore, the hardened state was controlled on site and in laboratory. The compression strength exhibited good values that correlated with the mixing proportion of the ingredients. The punch tests indicated relatively high values. They verified the safety of the worker, where material enrichment was present on the tunnel roofing parts. The steel fibre increased the ductility of the specimens. The porosity, the water permeability and the freeze / thaw resistance were also tested. The mixtures were continuously optimized by having the water / cement ratio and the superplasticizer dosage under control. All these adaptations allowed to reuse the big amount of tunnel demolition material. The concrete was produced in a mixing plant on site. This reduced the transportation and increased the environmental sustainability of such a long infrastructure.

Keywords: tunnel, demolition, rock, aggregates, shotcrete.

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