Two-component grout is one of the most popular backfilling techniques in shielded TBM projects thanks to its versatility and ability to minimize surface settlements compared to other backfilling technologies. A main component in two-component grout is bentonite, hence, a laboratory test campaign has been performed in order to determine its effects regarding the technological properties and mechanical strengths of grout. For this purpose, 20 mix designs have been tested, each one with a different type of bentonite and activation time. Bleeding, gel time, surface compressive strength (SCS), unit weight, and viscosity have been measured and the results are presented and discussed considering also the operational point of view.