Methods used in these experiments are by measureing half-cell potential [14,15], corrosion potential and polarization resistance  in accelerated corrosion condition in laboratory.
By applying electric current via a rectifier and using calomel as the standard electrode, the half-cell potential of the steel can be measured.
Figures 3 and 4 show the half-cell potential measured every day since charging from day-1 to day-10 for the steel reinforcement in, respectively, fly ash-based and kaolin-based geopolymer concrete immersed in ASTM seawater and distilled water.
A voltage known as the half-cell potential develops across the interface due to an uneven distribution of anions and cations.
A very popular electrode is silver/silver choloride (ag/AgCl) because of its very low half-cell potential of approximately 220 mV and its ease of manufacturability.
It uses the half-cell potential
method to locate the areas without the expense and time consumed by demolition.
Also, continuous monitoring of the potential difference between two working electrodes and two half-cell potentials against Hg/[Hg.
cell(ORP)] as both half-cell potentials are measured against the standard Hg/[Hg.
In addition to the skin impedance, the electrical transducer comprises the resistance of the electrolytic gel and the double layer at the electrode-electrolyte interface, as well as half-cell potentials
caused by different energies of the electrode, electrolyte, and skin.
A relation between AE activity and half-cell potentials in the accelerated corrosion test is given in Fig.
3) It is found that AE monitoring could provide earlier warning of the corrosion than the half-cell potentials.
Measurements of macrocell voltages, half-cell potentials
, electrical impedance spectroscopy, linear polarization, and mat-to-mat resistances were used in conjunction with visual observations to determine the effectiveness of each system.