## 1 Introduction  
Due to the high greenhouse gas emissions of the construction industry, which account for 10% of the total CO\({}_{2}\) emissions, new green cement alternatives are necessary [1, 2]. Geopolymer binders offer a substantial reduction of greenhouse gas emissions up to 80% compared to traditional binders [3, 4, 5]. Fly ash (FA) presents a favorable future as cementitious material due to its nature as a byproduct from the coal-based energy generation industry, which reduces both emissions and costs (up to 39% lower costs) [6, 7, 8]. FA geopolymer concrete also presents similar mechanical properties compared to ordinary Portland cement (OPC), displaying a compressive strength of 89 MPa compared to 65 MPa for OPC [9, 10, 11]. It has been found that an increased mechanical behavior of FA as well as a decreased wettability can also be achieved by graphene nanoplatelets addition, due to the specific surface area and aspect ratio, thus providing a uniform stress distribution [12]. Novel ternary ecological concrete mixtures made out of sugar cane bagasse ash and silica tune partially replacing OPC have proven to impart corrosion protection, thus offering an effective alternative for building a more sustainable concrete industry [13]. These new binders present a different microstructure that influences porosity and tortuosity, and consequently the ingress and diffusion of corrosive species, in addition the precursor chemistry and the activation process also modify the nature of the interfaces as well as the alkaline reservoir, which regulate the corrosion behavior [14]. For that reason, further research is needed for disentangling the electrochemical mechanisms that govern corrosion of steel in eco-friendly cements and fly ash geopolymer concrete. Reinforced concrete structures are required to meet the mechanical requirements of modern buildings. Therefore, the integrity of the structure would not only be limited by the stability of the concrete matrix, but also by the durability of the metallic reinforcement. Corrosion of steel embedded in concrete is caused by two processes: (1) carbonation occurs when the atmospheric CO\({}_{2}\) reacts with the concrete matrix forming carbonates and reducing the pH of the concrete, leading to uniform corrosion, and (2) chloride-induced corrosion that comprises the ingress of chloride ions, through the matrix promoting local acidification and causing pitting corrosion [15; 16]. Electrochemical monitoring in simulated concrete pore solution provides a reliable procedure to perform accelerated corrosion tests [17]. Differences between batches of concrete can lead to different electrochemical responses and result in variations in corrosion behavior [18; 19; 20]. In addition, there have been few studies regarding corrosion of steel in FA synthetic pore solution [21; 22; 23]. [PERSON] et al. showed that the little content of Ca in the pore solution of alkali activated materials such as FA or slags makes the buffering role of Ca(OH)\({}_{2}\) present in OPC impossible. Therefore, the alkalinity of the pore solution will be directly influenced by the alkali content, which is crucial to protect the reinforcing steel [17; 24]. [PERSON] et al. simulated the pore solution of low calcium geopolymers, such as FA, showing a higher chloride concentration required to promote pitting corrosion on carbon steel rebars with [Cl\({}^{-}\)]/[OH\({}^{-}\)] that ranged from 0.9 up to 2.4 [25]. This increased protection was due to the relationship found between [Cl\({}^{-}\)]/[OH\({}^{-}\)] which demonstrated that the onset of pitting corrosion required a higher ratio than OPC [25]. In the event of a fire, the increased temperatures can promote changes in the microstructure of the reinforcement material present in the structure. This transformation can lead to a different electrochemical behavior that might affect the structure stability if not properly considered [26; 27; 28].