Effect of Sodium Nitrite as Corrosion Inhibitor against Chloride-Induced Corrosion of Steel Rebar in Geopolymer Concrete Containing Fly Ash and GGBS

Abstract

This study investigated the effectiveness of sodium nitrite (NaNO2) as a corrosion inhibitor against chloride-induced steel rebar corrosion in fly ash–ground granulated blast furnace slag (GGBS)–based geopolymer concrete (GPC). The GPC was prepared with two different blends of fly ash and GGBS and two different molarities of sodium hydroxide solution. Sodium chloride (NaCl) and sodium nitrite (NaNO2) were admixed in the GPC mix during preparation. The effectiveness of NaNO2 against chloride-induced corrosion in GPC mixes was evaluated through corrosion measurements. The microstructure of GPC in the presence of NaCl and NaNO2 was studied through X-ray diffraction (XRD) analysis and energy-dispersive X-ray spectroscopy (EDS) analysis. The obtained results showed that NaCl decreased the workability, whereas NaNO2 improved the workability of the GPC mix with a significant effect at higher dosages. The NaNO2 reduced the compressive strength of GPC with more effects at higher dosages. However, the retarding effect of NaNO2 on strength development decreased with age. The addition of NaNO2 in chloride admixed GPC lowered the probability of occurrence of corrosion and the corrosion current density of steel rebar. The inhibiting efficiency of NaNO2 against chloride-induced rebar corrosion in GPC was enhanced with an increase in its dosage. Furthermore, the inhibiting efficiency of NaNO2 decreased with age. However, the reduction with age was significantly less at a higher dosage. The variation in compressive strength of GPC in the presence of NaCl and NaNO2 is in line with the variation in the formation of N-(C)-A-S-H and N-A-S-H type gels as observed from the XRD analysis.