Commercial and recycled carbon-based fillers and fibers for self-sensing cement-based composites: Comparison of mechanical strength, durability, and piezoresistive behavior

The possible use of industrial by-products as carbon-based fillers and/or fibers to produce Multifunctional Cement-based Composites (MCC) with piezoresistive behavior for Structural Health Monitoring (SHM) was investigated. As fillers, Used Foundry Sand (UFS) and Gasification Char (GCH) were compared with commercial Graphene Nanoplatelets (GNP). As fibers, 6 mm -long recycled carbon fibers (RCF) were compared with virgin ones. Mortars were tested in terms of mechanical strength, water absorption, microstructure, and piezoresistive behavior. UFS and GCH are more effective than GNP in decreasing the mortar electrical resistivity (-30%), total porosity (-11%), water absorption (-27%) and in increasing the compressive strength (+10%). The combination of UFS with RCF in mortars provides the best results in terms of fluidity, strength, water absorption, and piezoresistive parameters. Generally, a lower mortar resistivity, even if with lower piezoresistivity properties, allows the use of cheaper instrumentation for SHM, thanks to the lower full scale and the better correlation strength between the change in resistivity with strain.