Innovative two-component grout produced with sludge from ornamental stone cutting process = Innovative two-component grout produced with sludge from ornamental stone cutting process

Tunnel Boring Machines, also known as TMBs, are the most versatile, adaptive and technologic methodology to perform tunnel excavations. In the last years, the demand for tunnels has progressively increased and these machines are being continuously improved to face greater challenges, to improve safety and to reduce environmental impacts. Through the main features of TBMs, there is surely the backfilling, that is an operation that is performed between the gap that is created during the excavation because of the bigger dimension of the cutterhead respect to the body of the machine, to minimize surface settlements. Two – component grout is, by far, the most used technology in modern backfilling practices, composed by two components: one cement – based (component A) and one accelerant (component B) that, mixed and injected at the tail of the machine, starts to gel in a few seconds. Taking into account that sustainable production needs have improved research on reusing waste materials, this work of thesis tries to propose the result of the study of an innovative approach that involves the substitution of a portion of the cement in the grout mix with waste materials, specifically marble sludge and inert waste materials coming from gneiss cutting process. This study, in particular, aims to assess the performance of such mixes in practical backfilling applications. This work is articulated in three different phases: an overview of TBM machines, with a focus on the backfilling as highlighted feature, then, an overview of the quantities of the waste materials that were used to perform this analysis and, last, the result of the characterization of four different mixes, in which different quantities of cement was substituted with waste material. This last part was conducted in different phases, each focusing on different aspects of the grout mix performance. Since the lack of standard in the field of two – component backfill test, the main objectives of this phase were to guarantee that the stability, the pumpability and the workability of the component A and to assess the mechanical properties of the hardened grout (component A + component B) in a short time, in particular the Surface Compressive Strength after 1 hour and 3 hours, and in a long time, in particular Uniaxial Compressive Strength after 1 day, 7 days and 28 days.