The piezoresistivity of cement-based sensors subjected to moisture ambient is changeable due to the porous structures and pore solutions inside of cementitious composites. This study explored the electrical resistivity and self-sensing performance of carbon black (CB) filled cement-based sensors mixed with silicone hydrophobic powder (SHP) and crystalline waterproofing admixture (CWA), especially before and after different durations of immersion in freshwater and 3% sodium chloride solution. The results show that the composites with SHP exhibited the best water impermeability, while the counterpart containing CWA presented the optimal chloride resistance. The piezoresistivity increased in sodium chloride solution because of the increased free ions. The outcomes are expected to illuminate the piezoresistive behavior of hydrophobic cement-based sensors subjected to moisture and chloride environments, thereby promoting structural health monitoring applications in the future.