Marble sludge in two-component grout applications

The two-component grout is currently the most used backfilling technology in shield tunnel-ling applications. The technology is widely used all around the world thanks to its versatility. In fact, properly calibrating dosages and types of raw ingredients can easily satisfy the technical specifications of a certain construction site. In this work, an innovative two-component grout mix design is introduced, in which a marble sludge is added to component A of the two-component grout system as a new ingredient. The marble sludge obtained during the cutting process of ornamental stones in marble quarries is commonly considered a waste, an environmental problem that must be correctly managed. The idea of the authors was, hence, to use the marble sludge as an ingredient in the two-component grout by physically blocking it in the gelling reaction and making it permanently part of the backfilling material, confined between the bored medium and the lining extrados. This paper reports a laboratory test campaign on the potential use of marble sludge in the two-component grout technology. A standard two-component grout and an innovative one have been compared according to standardized testing protocols. Outcomes highlight that the innovative grout has properties similar to the standard grout and that the addition of marble sludge does not worsen the grout’s properties.