**2. Experimental procedure**

Four different steel rebars such as Fe-600, galvanized steel, stainless steel and plain rebars were chosen for this study. The approximate diameters of these samples were 12 mm, 8 mm, 16 mm, and 11 mm, respectively. Notably, Fe-600 and galvanized rebars are thermomechanically treated, whereas the other two (stainless and plain) rebars were not subjected to thermomechanical treatment. The nominal chemical compositions (wt. %) of all the rebar samples are given in **Table 1**. First, the samples of suitable size were cut from these steel rebars as per the requirement of optical, hardness, tensile and corrosion tests. All the samples were then tested in an optical emission spectrometer (Thermo 3460) to analyse the chemical compositions of the rebars. Standard metallographic sample preparation techniques such as grinding (belt and paper) followed by polishing (coarse, fine and diamond) and etching by using 2% nital and Snyder solutions were used to observe the microstructural constituents under an optical microscope (Leica) and scanning electron microscope (SEM).

The etched samples were further used for the Vickers Micro-Hardness Testing (Leica-VMHT) under 300 gf load and 20 seconds dwell time to analyse micro-hardness profile throughout the cross sections with a particular interval of distance. Hardness was measured on the sample surface as a function of distance from the edge to edge, keeping an interval of 50 μm, and the recorded variation in hardness values was then plotted. It is important to mention here that the hardness profile instead of surface hardness was recorded because the hardness values were expected to decrease from the periphery to the centre. A universal testing machine (UTN-10) was utilized to conduct the tensile test with a crosshead speed of 4.5 mm/min and a gauge length of 65 mm.

The electrochemical measurements were performed using a working electrode (embedded rebar specimen); a counter electrode (graphite) was placed to one side of the rebar specimen and also an independent reference electrode; that is, saturated calomel electrode (SCE) was used to observe the corrosion behaviour. Precise electrode placement was not critical, since the conductivity of the electrolytes was high. The equipment used to observe the corrosion behaviour of the rebar samples was Origalys Potentiostat, combined with the Origamaster 5 module. Electrochemical impedance spectroscopy (EIS) was utilized in the frequency range of 100 kHz–100 MHz with an AC voltage of 5 mV. The characteristic capacitance of this frequency band was maintained in between 10<sup>9</sup> and 10<sup>6</sup> F/cm<sup>2</sup> [10]. The rebar samples of standard size (area) were prepared and then immersed in two different types of solution of 3.5% NaCl and 1% HCl. These particular concentrations were chosen to simulate the saline conditions possible in marine and acidic rain in industrial areas [31, 32]. In this context, it is important to mention that the area was ≈76 mm<sup>2</sup> for Fe 600 rebar, whereas the same for the other three samples was kept at ≈75 mm<sup>2</sup> for the EIS study.
