Effects of shrinkage-reducing admixtures and expansive agents on the self-sensing behavior of nanomodified cement-based materials

Abstract

Shrinkage control is needed to ensure an appropriate installation of cementitious sensors used in the Structural Health Monitoring of concrete elements. However, the effects of shrinkage-reducing admixtures (SRAs) and expansive agents (EAs) on the self-sensing properties of the cementitious sensors is still unknown. Therefore, the present work evaluated the effects of a SRA and EAs based on calcium oxide (CaO) or calcium sulfoaluminate (CSA) on the shrinkage behavior, microstructure, self-sensing response and compressive strength of mortars containing carbon black nanoparticles (CBN). The SRA provided shrinkage reductions up to 47.4%. CaO-based EA and CSA-based EA provided an expansive behavior. The admixtures caused increases in electrical resistivity and gauge factor up to 37.1% and 71.0%, respectively. In contrast, they did not cause statistically significant changes in stress sensibility and compressive strength. A microstructural analysis suggested that portlandite and ettringite crystals provided by the inclusion of EAs caused interruptions in conductive paths inside the mortars, which decreased contact conduction mechanisms and increased the amount of insulating tunneling gaps between CBN, enhancing the gauge factor of the materials. Therefore, shrinking control admixtures were found to be promising alternatives to enable the dimensional compatibility between cement sensors and old concrete elements, and increase the self-sensing properties of smart cementitious composites.