Half-cell Potential Method & Resistivity Method

Half-cell Potential Method & Electrical Resistivity Method By, K.SANGEETHA RAJ

Non-Destructive Testing  Non Destructive Testing serve as a vital tool not

only in estimating the strength, integrity and types of active deterioration mechanism, but also guide the engineers to plan and devise strategies for executing repair & rehabilitation projects. The

Presence assessed by

of

Corrosion

Activity

can

be

1)Half-Cell Potential Method 2)Electrical Resistivity Method d and interpreted by experienced specialists because to many engineers the features, and especially

the limitations of available test methods are unknown and consequently left to ‘experts’.

Half Cell Potential Survey  This test method covers the estimation of

the electrical corrosion potential of uncoated reinforcing steel infield and laboratory concrete, for the purpose of determining the corrosion activity of the reinforcing steel. Copper-Copper Sulphate Electrode (CSE) Silver-Silver Chloride Electrode (SSE) The potential values become more and more negative as corrosion becomes more and more active

HALF-CELL POTENTIAL METHOD Principle: “Electric Potential Difference”

Transparent Plastic Tube Copper Rod

Copper Sulphate Solution Porous Plug (Sponge)

Weak Half Cell of a Battery Electrod e

Electrolytic Material

Reinforcement Potential Measurement

Test Procedure

Example

Grid Marking & Wetting of Concrete Surface

Measurement of Electrical Potential Difference

Digital Values

Colored Scale

Iso - Potential Contours

Gray Scale

Testing is in Progress

According to ASTMC876

ELECTRICAL RESISTIVITY METHOD Principle:“Electrical Resistance of Concrete” Flow of current generated is assessed in terms of electrolytic Resistivity of concrete.

Instrume nt

Resistivity Meter (RESI)

Resistivity of Concrete () = 2  S V/I kcm

Resistivity Measurements

Electrical Resistivity Method

 The

electrical resistance of concrete plays an important role in determining the quality of concrete from the point of view ‘corrosion susceptibility potential’ at any specific location. This parameter is expressed in terms of “Resistivity” in ohm-cm. For general monitoring, a resistivity check is important because long-term corrosion can be anticipated in concrete structures where accurately measured values are below 10000 ohm-cm. further if resistivity values fall below 5000 ohm-cm, corrosion must be anticipated at a much earlier period (possibly within 5 years) in the life of a structure.

Resistivity ohm-cm Greater than 20,000 10,000 – 20,000 5,000 – 10000 Less than 5,000

Corrosion Probability Negligible Low High Very high

CANIN+ INSTRUMENT

The CANIN+ instrument provides two methods for investigating and assessing the corrosion of steel in concrete. 1)Measurement of corrosion potential 2)Measurement of electrical resistivity of reinforced concrete components ) The Windows based software CANIN ProVista, developed by Proceq SA, makes it possible to download, present and edit data measured by the CANIN+ half-cell instrument in a fast and easy way using an IBM-compatible PC. 

CANIN+ INSTRUMENT

The program generates a potential map, a

relative frequency and a cumulative frequency diagram and provides a chipping graph. This statistical presentation is the basis for an efficient interpretation of the half-cell potentials by the corrosion engineer. Single files can be opened and processed separately. By rotating or mirroring in intervals of 90° the single potential maps can be combined to form a complete graph representing the total investigated surface area.

CANIN+ INSTRUMENT

Based on the user defined threshold

potentials that represent certain conditions of the structure, up to four characteristic potential intervals can be chosen. The corresponding partial areas are marked with different colors in the presentation as a “Chipping graph“.

Potential Map, Relative and Cumulative Frequency Diagram

CANIN+ INSTRUMENT- CORROSION POTENTIAL APPLICATION

The CANIN+ Corrosion Analyzing Instrument

highlights corrosion activity before rust becomes visible. This early detection can be key in preventing an unanticipated structural failure. CANIN+ is ideally suited for assessment of corrosion potentials on large areas of 8,000 m²or multiple thereof, depending on the individual selectable grid size.  235,000 values can be stored by the intelligent memory.

CANIN+ INSTRUMENT- CORROSION RESISTIVITY APPLICATION

Secondly, the instrument can measure the resistivity of the

concrete. A lower concrete resistivity indicates a greater chance of corrosion of the reinforcement and also a greater corrosion rate. The resistivity of concrete can vary extensively depending on the local conditions and environmental influence factors. The combination of resistivity and potential measurement improves the information about the corrosion condition of the rebar's. The concrete resistivity is measured by the four-point Wenner probe. All information is indicated on a large clear display. The instrument can also store up to 5,800 resistivity values and the data can be transferred to a PC for further analysis.

Testing Instrument

Corrosion Analyzing Instrument (CANIN)

Wire & Clip for Reinforcement Connection Rod Electrode

Multi Electrodes

Wheel Electrode

Corrosion Probability based on Resistivity and Potential Mapping

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