Effect of Carbonation and Drying-Wetting Cycles on Chloride Diffusion Behavior of Coral Aggregate Seawater Concrete

Based on seawater immersion,drying-wetting cycles,carbonation and drying-wetting cycles for coral aggregate sea-water concrete(CASC)with different strength grades,the effect of carbonation and drying-wetting cycles on chloride diffusion be-havior of CASC is studied.The results show that the free surface chloride concentration(Cs),free chloride diffusion coefficient(Df)and time-dependent index(m)of CASC in the drying-wetting cycles is obviously higher than that in seawater immersion.The Df and m of CASC of carbonation and drying-wetting cycles is higher than that in the drying-wetting cycles.Carbonation increases the Df and m of CASC,which is against CASC to resist chloride corrosion.The corrosion possibility of CASC structures in different ex-posed areas is as follows:splash zone(carbonation and drying-wetting cycles)>tidal zone(drying-wetting cycles)>underwater zone(seawater immersion).Besides,the chloride diffusion rate of C65-CASC is 17.8%-63.4%higher than that of C65-ordinary aggre-gate concrete(OAC)in seawater immersion(underwater zone).Therefore,anti-corrosion measures should be adopted to improve the service life of CASC structure in the oceanic environment.

Evolution of the Corrosion Product Film and Its Effect on the Erosion–Corrosion Behavior of Two Commercial 90Cu–10Ni Tubes in Seawater

The composition and structural evolution of the corrosion product film of two commercial 90Cu-10Ni tubes, namely TubeA and Tube B, after being immersed in natural seawater for 1, 3, and 6 months were characterized by scanning electronmicroscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, and its effecton the erosion--corrosion behavior of the tubes was determined through a rotating cylinder electrode system using variouselectrochemical techniques. For the freshly polished samples used as contrast samples, the flow velocity mainly enhancedthe cathodic reaction at low flow velocities while both the anodic and the cathodic reactions were remarkably accelerated athigher flow velocities. The corrosion product films formed on the two commercial 90Cu-10Ni tubes after being immersedin seawater for up to 6 months are of a complex three-layer or multilayer structure. The structural evolution of the films isout of sync for the two tubes. A continuous residual substrate layer depleted of Ni was observed in the inner layer of thefilms on Tube B after 30, 90, and 180 days＇ immersion, while it was observed in the film on Tube A only after 180 days＇immersion. The nature of the inner layer plays a crucial role in the erosion-corrosion resistance of the 90Cu-10Ni tubes athigher flow velocity. The film with a compact and continuous inner layer of Cu20 doped with Ni2＋ and Ni3＋ which bondsfirmly with the substrate could survive and even get repaired with the increased flow velocity. The film on Tube Bpossessing a hollow and discontinuous inner layer composed of the residual substrate was degraded rapidly with increasingrotation speed in spite of its quite good resistance at the stagnant or lower speed conditions.