Effect of curing compounds on the quality of passive layer development under varying oxygen concentration for RC structures in the course of early curing of concrete

The quality of passive layer development and corrosion progress in reinforced concrete as influenced by varying the oxygen concentration at the initial stages of the curing period was investigated. Specimens with various curing compounds (paraffin emulsion based, bitumen based, and wax based), varying water-to-cement ratios, and different curing environments (air, submerged, and sealed) were used as a mode for varying the amount of oxygen. The experimental measurements made it possible to understand satisfactorily the time dependent effect of the concentration of oxygen on protective layer development and the successive rusting of steel reinforcement in different specified environments. For the unsealed specimens in laboratory environment cured initially using wet burlap with free oxygen availability throughout the curing phase gave lowest corrosion rates (0.1 μA/cm2 and corrosion potential of −240 mV CSE measured after 276 days) indicating the formation of a strong passive layer as sufficient amount of oxygen was present in the vicinity of the specimens. However, the curing compound specimens that were completely sealed to limit oxygen availability showed highest corrosion rates (0.23 μA/cm2 and corrosion potential of −301 mV CSE recorded after 276 days) indicating the development of a fragile protective film in the start which resulted in the maximum rusting of rebars afterwards. The other curing compound specimens that were subjected to varying levels of oxygen availability at the initial stage of curing gave intermediate results. It is believed that the results obtained in this study are novel and should lead to an improved passive layer development on the surface of rebar by adopting an improved procedure for curing compound application (material and geometry) incorporating humidity preservation along with oxygen accessibility.