Alternative methodology for linear polarization resistance assessment of reinforced concrete structure

International audienceFor reinforced concrete structures, several corrosion detection methods exist: concrete resistivity, half-cell potential or linear polarization resistance (LPR) measurement. The LPR value can be linked to the corrosion rate thanks the Stern-Geary equation if strong hypotheses are made. Existing commercial devices use a guard ring to canalize the current on specific steel rebar area and assume that the steel rebar is uniformly polarized. However, recent works reveal that the top part of the steel rebar, right under the counter electrode, is the most polarized point. The particular point is referred as the point of interest (PI). This works belongs to the DIAMOND project which aims to produce a new corrosion rate measurement device. Comsol® software was used to model the influence of concrete cover, resistivity and injected current on the current density at the PI. Moreover, a significant influence of the steel rebars diameter was also demonstrated. Two types of abacus are built. The first one links to polarization measured on the surface to the polarization on the rebar at the PI. The second links the ratio between the current density at the PI and the density of injected current to concrete cover and steel rebar diameter. The Stern-Geary equation can now be used at the PI without using the approximation of a uniformly polarized rebar. The corrosion state of reinforced concrete structure can be controlled more precisely. The methodology is then applied on two concrete slabs in which three metal bars are embedded at different concrete covers. The first slab is prepared with ordinary concrete while the second contain chloride to artificially activate the corrosion process. The results reveal that the rebars embedded on the first slab are not corroding (icorr ≤0.2 μΑ/cm2) while the second rebar are corroding (icorr>0.2 μΑ/cm2)

Implementation of an Embedded Sensor Based on Electrical Resistivity to Monitor Drying in Thick Concrete Structures

Electrical resistivity is a parameter sensitive to several properties of concrete, including water content, which is one of the key parameters governing concrete long-term durability. In this paper, the monitoring of the concrete water content profile throughout its entire thickness is discussed using an electrical approach as a measurement method. This is very relevant to applications requiring a centimeter resolution over a large thickness. The aim of this paper is to implement a multi-electrode embedded sensor in a concrete slab to determine the resistivity profile over concrete depth in order to monitor its drying. The sensor, designed as a printed circuit board (PCB), is integrated in two 30 cm thick concrete slabs. Different measurement configurations are presented. Following qualification in laboratory and controlled conditions, the study focuses on characterizing the sensor‘s response during the drying of the slabs. The results demonstrate the capability of the sensor to monitor concrete drying by measuring the resistivity profiles with a spatial centimetric resolution

Approche probabiliste de la durée des bétons en environnement marin

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

An alternative method to measure corrosion rate of reinforced concrete structures

International audienc

Corrosion de béton armé (développement d'un essai accéléré par carbonatation et couplage galvanique)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Significance of macrocell corrosion of reinforcing steel in partially carbonated concrete: numerical and experimental investigation

WOS:000347554900015International audienceConcrete carbonation is usually assumed to induce microcell corrosion of reinforcing steel by uniform depassivation. However, the carbonation front evolves continuously as a slow, time-dependent process and concrete carbonation is often non-uniform in real concrete structures. Hence some areas of the steel reinforcement network in concrete are likely to be depassivated before others and, consequently, the theoretical conditions of macrocell corrosion appear to occur quite frequently in real concrete structures. This paper therefore focuses on steel corrosion phenomenology in partly carbonated concrete structures. The conclusions are supported by an experimental and numerical study based on accelerated macrocell corrosion tests, carried out on partly carbonated concrete specimens with embedded active and passive steel bars. The specimen design allowed for electrically connecting one active bar with one or several passive bars in order to form macrocell corrosion systems with various cathode-to-anode (C/A) surface ratios. Despite the high resistivity of the carbonated concrete layer, direct measurements of galvanic current revealed high macrocell corrosion rates, even in cases of low C/A ratio. The significance of galvanic coupling in carbonation-induced corrosion was thus confirmed experimentally. In addition to experiments, a synthetic, but comprehensive, theoretical description of macrocell corrosion is proposed and finite element simulations of experiments are reported. The agreement between numerical and experimental results is demonstrated regarding both potential field and C/A influence on macrocell current intensity. This consistency highlights the relevance of the modeling and simulation approach

Proposal for an alternative operative method for determination of polarisation resistance for the quantitative evaluation of corrosion of reinforcing steel in concrete cooling towers

WOS:000356548500005International audienceThis paper summarises the results obtained from numerical simulations of an operational measurement mode of polarisation resistance adapted for evaluating corrosion of reinforcing steel in concrete on cooling towers. A simple operational measurement mode of R-p, is proposed, adapted for cooling towers prone to corrosion due to carbonation. By means of numerical experimentations, calculation diagrams and semi-empirical equations are built involving the different influencing parameters: concrete cover to steel reinforcement, concrete resistivity and current intensity injected from the counter electrode. Finally, a first application of the proposed procedure for calculating the real value of R-p, in laboratory conditions is presented. (C) 2015 Elsevier B.V. All rights reserved

Influence of the reinforcement on concrete resistivity with a new measurement technique

WOS:000393044500033International audienceWater is a key factor influencing the concrete durability including corrosion of reinforcement. In order to study the water content in concrete the electrical resistivity, due to its sensibility to water, is considered to be one of the most efficient non-destructive solutions. This paper describes a novel method of resistivity measurement developed in laboratory using four-probe array. This technique allows the study of the water content in function of depth in concrete structures. Impacts of reinforcement steels and cover depth on measurement are also studied by measurement over the rebar. Results show that the presence of reinforcement modifies significantly concrete resistivity. This technique also shows the interest of measurement to evaluate the water content gradient in concrete