## 3 Methodology
### Half-Cell Potential Method  
The Half-Cell Potential (HCP) method is a rapid and cost-effective in situ testing technique used to identify the existence of active corrosion, which was first developed by [PERSON] [32]. Generally, a copper/copper sulfate electrode (Cu/CuSO4) or a silver/silver chloride electrode (Ag/AgCl) reference electrode is placed on the concrete surface right above the rebar and it is connected to the exposed portion of the rebar in order to characterize the electro-chemical behavior of corrosion in the rebar. The HCP method can be used to monitor the corrosion of rebar in concrete bridge decks and other structures, as long as the temperature is more than +2 \({}^{\circ}\)C and the rebar is not epoxy coated [33]. ASTM C876 [33] provides a guideline to interpret half-cell measurements. The relationship between the potential measurements and the likelihood of corrosion presence are provided in Table 2. Higher magnitudes of negative half-cell readings indicate a higher probability of corrosion. The HCP method has several limitations and is becoming decreasingly useful due to the increased use of epoxy coated rebars [33]. HCP does not provide any detailed information regarding the probability of corrosion activity between \(-200\) and \(-350\) mV, or \(10\) and \(90\%\). Further, according to [PERSON] et al. [34], this method is prone to erroneous conclusions in situations where concrete is water-saturated, carbonated, and exposed to very low temperatures. The HCP technique can be used anytime during the life a structure, and in any environment, as long as the temperature is above +2 \({}^{\circ}\)C [33]. Thus, this method can be used non-destructively to monitor corrosion activity in concrete structures. According to [PERSON] [23], the HCP method can be used for one of the following main purposes:  
1. To locate the corroding reinforcing bars, and thus, to assess the condition of reinforcement during the testing process. 2. To define the position for further destructive analysis such as cores for chloride analysis and inspection windows to visually assess the corrosion condition of the rebars. 3. To evaluate the corrosion condition of the rebar after the repair procedure, and thus, to assess the efficiency and durability of the repair. 4. To design an anode layout of cathodic protection systems. [PERSON] [23] also points out that HCP measurements are generally suitable for use on structures that are exposed to the atmosphere. HCP can be used regardless of the depth of the concrete cover, rebar size, and detailing. According to [PERSON] [35], HCP can be used as an indicator of chloride-induced rebar corrosion initiation in RC structures. The top surface of the beam specimens with rebars embedded were subjected to 3% NaCl, followed by exposure to air, in cycles, for a high number of repetitions. It was concluded that HCP is a suitable method to determine the parameter indicating rebar corrosion initiation in chloride-contaminated concrete structures. \begin{table}
\begin{tabular}{c c} \hline \hline
**Half-Cell Potential Measurements (Mv)** & **Probability of Rebar Corrosion Activity** \\ \hline \(>\)\(-200\) & Less than \(10\%\) \\ \(-200\) to \(-350\) & Uncertain \\ \(<\)\(-350\) & More than \(90\%\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: ASTM C876 for interpretation of half-cell measurements [33]. [PERSON] [36] investigated the influence of some parameters, such as temperature, humidity, fly-ash content, and the chloride concentration, on the relationship between the HCP and the corrosion level of the rebar in concrete. The results indicated that the HCP decreases with an increase in temperature under the same corrosion level of the reinforcing bar. A decrease in HCP measurements was also observed with an increase in the chloride concentration. With an increase in the fly-ash level, the HCP measurements also increased. When the corrosion level of the rebar increased, the HCP measurements decreased.