We investigated the formation of the conductive network of carbon nanotubes (CNTs) in alkali-activated nanocomposites for sulfate-sensing applications. The matrix was a one-part blend of fly ash and ground granulated blast-furnace slag, activated by sodium silicate and water. Sodium dodecylbenzenesulfonate was used as the surfactant for dispersion of the CNTs in the aqueous media. The nanocomposites were investigated by a laboratory-developed setup to study the electrical and sensing properties of the alkali-activated material. The electrical properties (i.e., conductivity) were calculated and assessed to discover the percolation threshold of the nanocomposites. Furthermore, the sensing behavior of nanocomposites was studied upon sulfate (SO42- ) exposure by introduction of sulfuric acid ((H₂SO₄) ) and magnesium sulfate (MgSO₄ ). The sensors were able to preliminarily exhibit a signal difference based on the introduced media (H₂SO₄& Mg SO₄ ), CNT content and H₂SO₄ volumetric quantity. The results of this research demonstrated a sensing potential of CNT alkali-activated nanocomposites and can be applied in the concrete structural health monitoring.