Short-term elastic characterization of an innovative non-cementitious bi-component grout by means of ultrasonic pulse velocity

Backfilling is a crucial process when using a shielded machine for tunneling, and two-component grout (2CG) is undoubtedly the most common solution for backfilling. In re-sponse to environmental concerns, some novel 2CGs are gaining attention for their low carbon footprint. The mechanical characterization of these materials is fundamental to their applicability, although only their elastic properties can be measured soon after the casting. We focus on the elastic characterization of the product Mapequick CBS Active CF System, an innovative cement-free 2CG. The non-invasive geophysical technique called ultrasonic pulse velocity (UPV) was employed to measure the elastic properties of the grout at specific time intervals, ranging from 1 hour up to 24 hours and 28 days after the casting. After analyzing the UPV data, the Poisson’s ratio, as well as the dynamic elastic, shear, and bulk moduli were determined. The obtained results were compared with those of a standard cement-based 2CG. The outcomes of this work prove the suitability of Mapequick CBS Active CF System as an effective backfilling material as well as the prof-itable use of the innovative system based on UPV to investigate the elastic properties of 2CGs.