S. Feliu

Comparison of rates of general corrosion and maximum pitting penetration on concrete embedded steel reinforcement

Local attack of reinforcement is observed usually in chloride-contaminated concrete. When mechanical weakening of the concrete structure is affected by the bar section loss in the places where corrosion is intensified, the maximum penetration of the deepest pits happens to be a very relevant datum. In this work average corrosion values are compared with maximum pit depth values. Using natural corrosion tests and accelerated tests, it has been found that the maximum penetration of localized attack on steel embedded in concrete containing chlorides is equivalent to about four to eight times the average general penetration.

The prediction of atmospheric corrosion from meteorological and pollution parameters—I. Annual corrosion

Abstract Worldwide atmospheric corrosion and environmental data, compiled in a comprehensive literature survey were statistically processed for establishing general corrosion damage functions for mild steel, zinc, copper and aluminium, in terms of simple meteorological and pollution parameters. The regression equations thus developed account for 83, 62, 59 and 41% of the variance in the annual corrosion data for zinc, steel, aluminium and copper, respectively. The goodness of the fits of data from rural atmospheres is considerably lower.

Equivalent circuit for modelling the steel-concrete interface. I. experimental evidence and theoretical predictions

This paper experimentally confirms the participation of diffusion in the response of reinforced concrete specimens to the different electrical signals applied. Therefore, in the modelling of the steel-concrete system, it seems necessary to incorporate elements representing the diffusion together with the effects of the corrosion reaction and the non-ideal capacitative behaviour at the interface. A knowledge of the interaction between all these phenomena is indispensable for interpreting the response of the system to the application of DC and AC signals, and for the correct estimation of the corrosion rate of reinforcements. An examination is made of which equivalent circuit might be most suitable for modelling the system.

THE PREDICTION OF ATMOSPHERIC CORROSION FROM METEOROLOGICAL AND POLLUTION PARAMETERS--II. LONG-TERM FORECASTS

Abstract Long-term atmospheric corrosion forecasts often rely on the fulfilment of equations of the form C = At n , where C is the corrosion after t years and A represents corrosion after the first year of exposure. Appropriate values must be assigned to constants A and n . In the first part of the work an analysis was performed on the possibility of expressing A as a function of usually available environmental parameters. In this second part data compiled in a comprehensive literature survey are used to determine whether the exponent n of the above equation can also be expressed as a function of such environmental parameters.

The charge transfer reaction in Nyquist diagrams of painted steel

Abstract When applying the AC impedance technique to metal-paint systems, it is of interest to identify the corrosion reaction of the metallic substrate in the arcs appearing on the complex plane of the Nyquist diagrams. This article shows how difficult it sometimes is to obtain direct information on this reaction on the basis of the diagrams obtained. The use of peelable films has been demonstrated to be very useful for this research. With these films it is possible to separate the effect of the metallic substrate from that of the film in the impedance diagrams, first measuring with the film adhered to the metallic surface and then with the same film detached from the substrate.

XPS study of the surface chemistry of conventional hot-dip galvanised pure Zn, galvanneal and Zn-Al alloy coatings on steel

This study uses X-ray photoelectron spectroscopy (XPS) to analyse the outer surfaces of galvanised, galfan and galvanneal metallic coatings obtained by hot dipping. Considerable aluminium segregation towards the surface, principally as Al2O3, has been seen in all the studied coatings. The aluminium content on the surface was surprisingly similar to or even greater than the zinc content, which is the major element in the chemical composition of these coatings. The formation of Al2O3 seems to prevent the oxidation of the zinc in the metallic coating.

CONFINEMENT OF THE ELECTRICAL SIGNAL FOR IN SITU MEASUREMENT OF POLARIZATION RESISTANCE IN REINFORCED CONCRETE

The paper proposes a galvanostatic method for on-site determination of the polarization resistance of reinforcement in large reinforced concrete structures and for subsequent estimation of corrosion rates using the Stern-Geary equation. The method uses two conterelectrodes to apply the electrical signal (polarization) to the reinforcement. The current applied from the external conuterelectrode (guard ring) tends to repel the line from the central counterelectrode, confining them to an area of the structure located approximately under this last electrode. The originality of the method is its use of a pair of sensors to bound the field of action of the signal emanating from the central counterelectrode. Results confirm interesting possibilities for the method.

ON-SITE DETERMINATION OF THE POLARIZATION RESISTANCE IN A REINFORCED CONCRETE BEAM

Abstract Corrosion potential mapping is a useful qualitative technique for measuring the risk of corrosion for reinforcements. However, occasionally this requires not only knowing whether or not th...

Determining polarization resistance in reinforced concrete slabs

Abstract Direct estimation of the true polarization resistance (RT) of embedded metallic bars in concrete is not feasible in a large concrete structure, since the electric signal tends to vanish with increasing distance from the smaller counter electrode located on its surface. Measurements give apparent values of polarization resistance and erroneous corrosion rates when this parameter is introduced into the Stern-Geary equation. The possibility of estimating the true RT value in large-sized reinforced concrete slabs by means of a simple model of easy mathematical treatment is discussed. Despite the approximations made, the model proves sufficiently correct for such a purpose.

An interpretation of electrical impedance diagrams for painted galvanized steel

Abstract The physical significance of various arcs which appear on impedance diagrams for painted galvanized steel exposed to an aggressive medium is discussed. These diagrams undergo various changes during exposure, i.e. when the paint coating is still intact the response is almost purely capacitive, but as the coating degrades the impedance value decreases and the plots exhibit two arcs. Measurements with detached films confirm the relationship between the single arc appearing in the impedance diagrams during early stages of paint degradation and the intrinsic paint properties. However, it is more difficult to find an interpretation for the two-arc diagrams. The hypothesis that the low-frequency arc arises from effects associated with the double-layer capacitance and charge-transfer control at the pore base leads to unacceptable conclusions. Various arguments seem to support the view that the low-frequency arc is determined by a finite diffusion impedance.