Tunnel spoil recycling for concrete production at the Brenner Base tunnel in Austria

In the construction of major tunnel structures, large quantities of rock material are generated by the excavation of, for example, tunnels or caverns out of the in situ rock mass. Excavated rock material was often considered as undesired by-product and from a legal point of view as waste in the past. Nevertheless, there is the need for construction material at the tunnel construction site directly where the rock material is generated. Broad scientific research is conducted concerning the utilization possibilities and optimization of recycling implementation. This article deals with the recycling of tunnel excavation material substituting conventional aggregate for concrete by the example of the Brenner Base Tunnel in Austria. Concrete design, material processing, and concrete production were affected by challenging geological bedrock conditions. This article presents the scientific approach, experimental setup, verification, and the realization on the construction site. The way from preliminary mixing designs to the final product is illustrated for two main rock types: calcareous schists, which successfully were recycled and processed as aggregate for shotcrete, structural and inner lining concrete; and quartz phyllite with unsuitable rock properties for concrete production due to intense foliation and mica-rich mineral composition. The results are demonstrating the need for detailed examination of rock and concrete properties regarding the usability of tunnel excavation material.