ABSTRACT
The challenge of this era is to realise sustainable infrastructures and tunnels are not an exception. Mechanised tunnelling is the most used technology nowadays for excavating long tunnels and, behind the construction phases typical of the excavation process, backfilling is one of the most important when shielded machines are used. According to the market trend, this construction phase is commonly carried out using the two-component grout, a cement base material that reacts with an accelerator making gel in a few seconds. The mix-design drawing is carried out following very precise rules; since each ingredient is strongly connected to the others, dosages are carefully studied to comply with the technical specifications of construction sites.
This research focuses on introducing two innovative ingredients in the two-component grout production, i.e. marble sludge and gneiss powder. These two materials are considered waste in the dimension stones sector, but their production is inevitable, being part of the cutting process necessary for the exploitation and cutting of blocks and slabs. The outcomes reported in this study, based on a laboratory test campaign, confirm that by carefully calibrating the mix-design of the two-component grout, the innovative ingredients become an added value in the view of the sustainability of tunnel construction, allowing the reduction of the filling of landfills from one side (reducing waste of the dimension stones work chain) and, on the other side, the reduction of dosages of standard row ingredients (partially replaced by the innovative ones) without worsen the final properties of the grout. The mixing and casting procedures, carried out according to the well-established procedure set-up at Politecnico of Turin, has foresees dosages of 200 kg/m3 of the innovative ingredients. Mechanical parameters highlighted strengths at short and long term of the same order of magnitude of the reference grout.
