# Steel Corrosion Behavior in Light Weight Fly-Ash Based Alkali Activated Mortars
## 2 Materials and Methods
### Characterization  
The mortar characterization was carried out after 28 days of mortar curing. Total open porosity and pore size distribution of the M and LWM mortars were measured by Mercury Intrusion Porosimetry (MIP) using Pascal 140 and 240 instruments (Thermo Fisher Scientific, Como, Italy). MIP analyses were performed on mortar specimens of ~1 cm\({}^{3}\), avoiding the external surfaces of the samples. The microstructure of the obtained mortars was observed by Scanning Electron Microscopy (SEM, Philips XL20, Milan, Italy) using the secondary electron (SE) detector at 10 keV. Prior to SEM observation, samples were sputtered with gold to make them conductive. Steel plates cover by 20-mm thick coatings made of M and LWM were partially exposed to tap water and in a 0.2 M NaCl aqueous solution for 60 days to test the steel corrosion behavior. Prior to exposure, a Cu-wire was soldered on the steel surface to ensure the electrical conductivity of the steel for electrochemical testing. Then all the sample surfaces, except the top one, were coated with epoxy resin in order to ensure solution penetration by capillary, as detailed in Figure 1.  
Samples were partially immersed in 2-mm depth solution in the laboratory conditions. Boxes containing the testing samples were covered to avoid evaporation and solutions were renewed every 14 days. During the exposure, measurements of the corrosion potential (E\({}_{\text{cor}}\)) were daily carried out, as well as anodic polarization curves were recorded after 1 day and at the end of the exposure (after 60 days). Electrochemical tests were performed using an Amel Electrochemistry Potentiostat (model 7050, Milan, Italy), applying the conventional three-electrode cell depicted in Figure 2a: coated steel samples with mortar (M or LWM) layer were set as the working electrode (WE), a saturated calomel electrode (SCE) worked as the reference electrode (RE) and an external stainless steel (SS) net was used as the counter electrode (CE). Polarization curves were carried out after 1 h of immersion in the electrolyte, recording between 0.1 V lower than the open circuit potential (E\({}_{\text{OCP}}\)) up to 1.0 V higher than the E\({}_{\text{OCP}}\), applying a scan rate of 0.167 mVs\({}^{-1}\). At least three samples were tested for all the electrochemical measurements to ensure reproducibility of the results. At the end of exposure low magnification imaging was performed on the steel plate by stereomicroscopy (Olympus SZX10, Milan, Italy). Figure 2: Electrochemical set up consisting of the conventional three-electrode cell for anodic polarization curves of (**a**) coated steel samples with LWM or M mortars and (**b**) steel samples tested in different solutions. To investigate the effect of the alkali activated binder on the corrosion behavior of the steel plates, anodic polarization curves of steel samples (named S) were recorded in different environments, using the electrochemical set up previously described. The only differences were (i) the use of a platinum rod as CE and (ii) the application of a Teflon sample holder applied to have a WE with an exposed area of 2.01 cm\({}^{2}\), as shown in Figure 2b. First, leachate pore solution (LPS) was considered as electrolyte for anodic polarization. It was prepared following the procedure reported in [21; 35]: alkali activated binder was crushed and mixed with distilled water in 1:1 proportion and stirred for 24 h. Then, this solution was filtered using a vacuum pump and the obtained LPS exhibited a pH of 12.8 and a chemical composition reported in Table 2. The pH of the obtained leachate solution was considered as an acceptable approximation of the pH of the mortar pore solution [21; 22]. Secondly, anodic polarization curves were recorded in NaOH aqueous solutions with different concentrations (0.1 M and 0.001 M), selected based on the pH of the mortar samples at different curing stages (after 28 days of curing in sealed conditions and after 1 year of exposure at laboratory conditions).