# Steel Corrosion Behavior in Light Weight Fly-Ash Based Alkali Activated Mortars
## 3 Results and Discussion
### Corrosion Behavior of Coated Steel with Mortars
This could be related to the presence of a larger number of capillary pores that allowed the aggressive solution to firstly reached the steel surface than LWM sample [36]. At last, the morphological observations reported in Figure 6 are in accordance with the recorded E\({}_{\text{cor}}\), confirming that the corrosion potential decrease after 40 days of exposure in chloride-containing solution corresponded to steel corrosion condition. Figure 7 reports the anodic polarization curves obtained from M and LWM coated steel samples exposed in tap water and 0.2 M NaCl chloride solution. For each exposure, anodic polarization curves were recorded after 1 day and 60 days (end of exposure) of partial immersion. For short exposure (1 day), all the anodic polarization curves showed a value of E\({}_{\text{cor}}\) of \(-0.2\) V vs. SCE and a passive behavior with low values of corrosion current densities (i\({}_{\text{cor}}\)). For M sample, an order of magnitude was recorded between i\({}_{\text{cor}}\) values measured in the two different solutions: \(1.5\cdot 10^{-9}\) A/cm\({}^{2}\) in tap water and \(1.7\cdot 10^{-8}\) A/cm\({}^{2}\) in chloride-containing solution. However, LWM exhibited comparable i\({}_{\text{cor}}\) results of \(5.0\cdot 10^{-8}\) A/cm\({}^{2}\) for both the tested environments. After 60 days of exposure, all  
Figure 6: Macro and low magnification images of the carbon steel plates coated with 20 mm thick M or LWM layers after 60 days of immersion in tap water and in 0.2 M NaCl aqueous solution. the anodic polarization curves showed more electronegative E\({}_{\text{OCP}}\) values. In particular, E\({}_{\text{OCP}}\) of \(-0.4\) V vs. SCE and \(-0.6\) V vs. SCE were measured for samples exposed in tap water and chloride-containing solution, respectively. These values well corresponded to the corrosion potentials reported in Figure 5 after 60 days of exposure. In addition, an increase in i\({}_{\text{cor}}\) values was detected especially for LWM sample exposed in chloride-containing solution that exhibited the greatest corrosion current density of \(2.7\cdot 10^{-7}\) A/cm\({}^{2}\). This could be related to the fact that the larger extent of corrosion products, precipitated on steel surfaces when M layer was applied, acted as a physical barrier, slowing down the corrosion kinetic measured by anodic polarization curves for M sample (i\({}_{\text{cor}}\) = \(9.5\cdot 10^{-8}\) A/cm\({}^{2}\)). Thus, chloride-containing solution induced the more relevant changes in polarization curves at the end of exposure, especially for LWM sample. The investigation of corrosion behavior of coated steel with LWM mortars, and its comparison with M mortars, highlighted that the presence of chloride ions fastened the occurring of corrosion. This was demonstrated (i) by the lowering of E\({}_{\text{cor}}\) values to more electronegative potentials after 40 days of exposure, (ii) by the larger extent of corrosion products observed in the steel surfaces and (iii) by the higher i\({}_{\text{cor}}\) values, when compared to tap water exposure. Secondly, it was observed that the different pore size distribution of M and LWM layers partially influence the steel corrosion behavior. This was demonstrated (i) by comparable E\({}_{\text{cor}}\) values between LWM and M in both the tested environments, and (ii) by comparable i\({}_{\text{cor}}\) values recorded after 60 days of exposure by anodic polarization curves, especially for tap water exposure. Lastly, increasing the aggressiveness of the electrolyte (by adding 0.2 M NaCl in aqueous solution) induced a larger extent of corroded surfaces, compared to tap water exposure. All the presented results allowed to conclude that, due the fact that LWM and M mortars were prepared using the same mix design of the binder (precursor and activating solution), also the binder pH and the composition of the pore solution in contact with steel could influence the corrosion behavior of the coated steel, as demonstrated also in other studies [18; 21; 38].