Alberto A. Sagüés

Chloride Corrosion Threshold of Reinforcing Steel in Alkaline Solutions—Open-Circuit Immersion Tests

Abstract Reinforcing steel bars with three types of surface conditions (as-received mill scale, prerusted in 3.5% sodium chloride [NaCl] solution, or sandblasted) were exposed in open-circuit immersion (OCI) tests in pH 12.6 saturated calcium hydroxide (Ca[OH]2) solution (SCS) and pH 13.3 (SPS1) and pH 13.6 (SPS2) simulated concrete pore solutions. These solutions were free of chlorides at the beginning of the test to allow the steel specimens to passivate. Then the chloride concentration ([Cl−]) was increased in several steps. The corrosion potential was monitored, and electrochemical impedance spectroscopy tests were performed periodically on selected specimens. It was found that active corrosion for all three surface conditions tookplace in the pH 12.6 SCS andpH 13.3 SPS1, when the [Cl−] reached threshold levels. However, sustained active corrosion of steel was not found inpH 13.6 SPS2 in a testing period of ∼ 2 years, although the final [Cl−] in that solution reached 3.0 M. Removing the mill scale or ...

PRACTICAL EVALUATION OF RESISTIVITY OF CONCRETE IN TEST CYLINDERS USING A WENNER ARRAY PROBE

Cell constant correction values (K) for concrete resistivity measurements on cylindrical test samples performed with the four-point Wenner array probe technique are presented. Specimens dimensions correspond to standard cylinder sizes used for compressive strength or rapid chloride permeability tests, as well as typical concrete core sizes. The values of K were determined experimentally and numerically, by means of Finite Element (FE) simulation. The effect of different maximum aggregate sizes and aggregate types on the variability of the resistivity readings was evaluated. Cell constant correction values are given to allow quick determination of concrete resistivity.

THE TIME-DOMAIN RESPONSE OF A CORRODING SYSTEM WITH CONSTANT PHASE ANGLE INTERFACIAL COMPONENT: APPLICATION TO STEEL IN CONCRETE

Abstract The time-domain response of reinforcing steel in concrete during a polarization resistance test was examined based on the electrochemical impedance spectroscopy behavior of the system. The analysis considered the effect of apparent interfacial capacitances that approached the behavior of a constant phase angle element (CPE). The response of an interface behaving as the parallel combination of a polarization resistance and a CPE was examined analytically. The calculations showed that significant error could develop in the estimation of corrosion rates from the apparent polarization resistance obtained during a potential scan experiment. The predicted error was largest when corrosion rates were small. The error could be significant at commonly used potential scan rates (0.1 mV s−1) and constant phase element exponents (0.7

Detailed modeling of corrosion macrocells on steel reinforcing in concrete

Numerical modeling of the distribution corrosion of steel reinforcing bars (rebars) in concrete structures is complicated by the spatial distribution of the rebars in the volume of concrete, by nonlinear boundary conditions associated with the polarization of the corrosion reactions at the steel surface, and by mass transfer processes of the reactants in the bulk of the concrete. A computational method for solving the governing equations has been developed from finite difference representations and a solution procedure that retains the nonlinear character of the boundary conditions. A strategy was successfully devised to compute the local potential and current density at the rebar surface with a minimum of computational effort. Both the problem of free corrosion and cathodic potential are discussed for the example of a square slab, reinforced with a double mat of crossing rebars.

Corrosion macrocell behavior of reinforcing steel in partially submerged concrete columns

Abstract The corrosion behavior of reinforcing steel embedded in laboratory concrete columns partially submerged in a 5% NaCl solution, under different wetting conditions of the region above water line, has been investigated. A macrocell corrosion pattern developed in the test columns, with steel in the upper portions of the columns being mainly the site of the oxygen reduction reaction and a small passive current. When the columns were dry or partially moist, the cathodic reaction in the upper portions of the columns was primarily under activation polarization, while under full wetting nearly complete diffusional control took place.

Characterization of Activated Titanium Solid Reference Electrodes for Corrosion Testing of Steel in Concrete

Abstract Small bars of Ti activated with mixed-metal oxide (commercially produced for permanent impressed-current anodes in cathodic protection) were used as embedded reference electrodes (RE) in c...

Concrete cracking by localized steel corrosion-geometric effects

Steel reinforcement embedded in normal, uncontaminated concrete is usually well protected against corrosion. When the chloride-ion concentration at the reinforcing bar depth exceeds a critical threshold value, however, the protective passive layer on the steel surface breaks down and active steel corrosion begins. This article reports on a study that experimentally estimated the critical amount of steel corrosion (xCRIT) needed for concrete cover cracking of a reinforced concrete element when only a fraction of the steel bar length is corroding. The authors established that the amount of corrosion needed to crack the concrete cover (xCRIT) was 0.030 to 0.272 mm in specimens with localized corrosion, in comparison to 0.003 to 0.074 mm for more uniform corrosion reported for other investigations in comparable systems. The authors propose an empirical equation for xCRIT as a function of specimen dimensions (concrete clear cover C, reinforcing bar diameter f , and anodic length L).

Modeling the Effects of Corrosion on the Lifetime of Extended Reinforced Concrete Structures

Abstract A modeling approach is presented for quantitative projections of corrosion damage in the substructure of marine bridges, taking into account the compounded variability of concrete cover, c...

Chloride Corrosion Threshold of Reinforcing Steel in Alkaline Solutions—Cyclic Polarization Behavior

Abstract Cyclic polarization (CYP) experiments were performed on reinforcing steel bars of various surface finishes in chloride-containing alkaline solutions (pH 11.6 ∼ 13.6). Pitting initiation was observed at potentials below the oxygen evolution potential (EOE) when the solution [Cl−]/[OH−] ratio (CR) was high enough. The pitting potential (Ep) was not a unique function of a given test condition. Both the average value and the variability of Ep tended to decrease with increasing CR. Increasing passive film maturity and steel surface smoothness effectively elevated Ep values. The repassivation potential (Er also showed certain variability, but it was insensitive to steel surface conditions and solution compositions. Er was instead a strong function of the severity of corrosion attack (represented by imax) that had occurred on the steel surface before repassivation. The experimental results were examined using a statistical approach. Based on simplifying assumptions, the chloride corrosion threshold (CRT...

Impedance Behavior of TiO2 Nanotubes Formed by Anodization in NaF Electrolytes

The impedance behavior of nanotubular self-organized porous TiO 2 (PTO) films with thickness of >2 μm, 100 nm pore diameter, and 150 nm average spacing formed on titanium by anodization in 1 M Na 2 SO 4 solution +0.5 wt % NaF was investigated and compared to the behavior of compact TiO 2 layers (CTO). At potentials close to the flatband potential (E FB ), PTO had an apparent interfacial capacitance at 30 Hz that was greater than the capacitance of CTO. This effect, however, was not only related to the larger effective area of PTO. Differentiation between both surface conditions vanished both at potentials significantly higher than E FB and with increasing test frequency to 1 kHz. These findings together with observations of appreciable frequency dispersion suggest that the pore walls are rich in deep-lying localized states, which become evident only at lower test frequencies and at potentials negative enough that depletion zones do not merge at pore walls. PTO did not show a transmission line effect at frequencies as high as 100 kHz. Model calculations based on pore dimensions and electrolyte conductivity predicted that those effects could only take place at much higher test frequencies, but the slow response of deeper states might impair observation anyway.