An innovative non-destructive approach for the shrinkage assessment in two-component grout application

In this study, a well-known technology known as the Fiber Bragg Grating (FBG) has been employed for the first time for the study of the two-component grout (2CG), the most used material for the backfilling phase in mechanised tunnelling. Using FBG, it has been possible to monitor both the temperature and the shrinkage of the 2CG since the first moments after the gelation of the grout. The procedure proposed and the outcomes presented in terms of shrinkage put alight the validity of the proposed approach, and the crucial importance of the curing environment. For a fixed mix design, values of shrinkage lower than 500 microepsilon have been founded after 16 days of curing in water irrespective of the tested bentonite, while in dry environment the shrinkage reached values higher than 3000 microepsilon.