The influences of the rust layer on the passivation and corrosion of Q235b carbon steel in simulated concrete pore solution were studied. The differences between the inner and outer rust layer were characterized. Results show that the pre-rusted samples could still reach passive state at high pH condition free of chloride ions. However, the quality of the passive film formed on the pre-rusted steel were dramatically lower than that formed on the fine polished steel. The pitting corrosion resistance of the pre-rusted steel was significantly higher than that of the fine polished steel in the chloride-containing pore solution. The pitting corrosion potential would be further promoted after the elimination of the outer rust layer. The reaction between the hydrogen ions and the rust layer could inhibit the pitting initiation. Furthermore, the consumption of the corrosive agents induced by the rust layer could further retard the area expansion of the pits.

A partial pre-rusted wire beam electrode (WBE) was designed to study the influence of the rust layer on rebar corrosion in the carbonated simulated concrete pore solution (SCPS). The results show that the passive film generated on the pre-rusted steel area is more fragile than that formed on the fine polished steel area in carbonaceous media. Nevertheless, the pitting corrosion resulting from the presence of chloride ions still tends to occur on the fine polished steel surface due to the local acidification process being hindered by the rust layer. The rust layer could play a more important role than the passive film in inhibiting the initiation of chloride-induced corrosion on rebar. The expansion path of the corrosion product would be blocked by the rust layer, leading to the pit propagating in the fine polished region. Furthermore, the growth of pitting corrosion is greatly accelerated due to the catalytic cathodic reaction of the rust layer.

No abstract

The adsorption of five polycarboxylate ethers (PCEs) oligomers with different side-chain number and side-chain length on the ettringite (100) surface in explicit solution is studied by all-atom molecular dynamics (MD) simulations. The adsorption conformations, adsorption energies, the radial distribution functions (RDF) between PCEs and ettringite surface and density distribution profile of water perpendicular to the substrate are analyzed. After dynamic equilibrium, negatively charged carboxylate groups are absorbed on the surface of the disordered ettringite crystal and the side-chains are extended to solution. The influence of the number of side-chain on the adsorption strength of PCEs on the ettringite (100) surface is more significant than that of the length of side-chain. The less number of grafted side-chains, the weaker electrostatic shielding, the electrostatic interaction between PCEs and ettringite (100) surface is stronger, which is favorable for the adsorption. The conformation of adsorbed PCEs is closely related to the length of side chain. The greater the length of side-chains is, the larger will be the coverage area of PCE on surface and the degree of water reduction. The mechanism of adsorption of PCEs on ettringite surface is concluded and the major contribution to the adsorption includes ion pairs, hydrogen bonds and an entropic compensation.

A multi-electrode array sensor was developed to study the corrosion behaviors of carbon steel weldments and the effectiveness of the NaNO2 inhibitor in carbonated pore solution. The sensor can simulate a complete weldment, and the measurement results can match well with the coupon immersion test. The galvanic corrosion between the weld area, heat-affected area, and base metal area, as well as the effect of nitrite corrosion inhibitor on the weld area, were observed by measuring the open circuit potential, coupling potential, and galvanic current. The results show that corrosion is likely to happen around the weld metal area and its adjacent heat-affected zone. The intensive galvanic currents can accelerate the localized corrosion, while NaNO2 can inhibit it.