Investigating rebar corrosion of cement mortar and concrete with fly ash and inhibitor based on experimental and numerical tests

The corrosion of reinforcements in concrete is one of the major reasons for structure failure. This paper aims to evaluate the combined effect of fly ash and inhibitors on rebar corrosion through experimental test and numerical simulation. Different mortar samples containing ordinary Portland cement (OPC), class F fly ash (FA), and Sodium nitrite (SN) are prepared and tested. Similarly, concrete samples were prepared with OPC and FA to compare mortar results. The water-absorption percentage, rapid chloride permeability, compressive strength, and splitting tensile strength of presented mortar or concrete groups are measured to obtain the transporting and mechanical properties. The impressed current (IC) accelerated corrosion test is then performed to induce the corrosion of embedded rebar. At different corrosion durations, the corrosion potential ($E_{\mathrm{corr}}$) and linear polarization resistance ($R_p$), rebar pull-out strength (${\tau }_p$), and steel mass loss of retrieved rebar are measured to reveal the corrosion development process. Result shows that the theoretical calculated steel mass loss (Faraday’s law) at early stage is higher than the gravimetric-measured values, which can be explained by low impressed current efficiency at early age due to the protection of passive layer. FA lowers the corrosion rate by reducing the chloride penetration rate and forming a denser pore structure. SN slightly increases the chloride permeability but still postpones the corrosion development due to the increased chloride concentration threshold and delayed disruption of passive layer. Numerical simulation depicts the first crack initiation and crack development associated with rust accumulation and rebar pull-out strength reduction in the crack. Overall, the findings of this research enhance the understanding of reinforcement corrosion and its detrimental effect on reinforced-concrete mechanical strength changes with corrosion process.