The half-cell potential of the Activated carbon (AC), due to its high double layer capacitance (EDL), remains stable in high ionic electrolyte. The open circuit potential (OCV) of the AC, with EDL of 40 – 50 F, shows a stable potential (10 mV variation) over two weeks in the cement pore solution (sat. Ca(OH)2). The OCV is less sensitive to the pH change from pH 8 to 12 (range inside concrete). The potentiometric response of a Ag/AgCl vs. AC pseudo-reference shows a near-Nernstian response (-51 mV/decade). The AC electrode can be proposed as a pseudo-reference for the potentiometric monitoring inside concrete.