sensors

Open Circuit Potential

Embeddable half-cell reference electrode for monitoring the thermodynamic probability of rebar corrosion.

Model No
G94-900CP
Reference Element
Ag/AgCl or MnO2 (Standard)
Potential Stability
±5 mV over 24 hours

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Overview

Embeddable half-cell reference electrode for monitoring the thermodynamic probability of rebar corrosion.

The Geolook G94-900CP Open Circuit Potential (OCP) sensor is a permanent reference electrode designed to be embedded in concrete structures. It measures the electrochemical potential of the reinforcing steel relative to a stable reference point, providing a direct indication of whether the steel is in a "passive" (protected) or "active" (corroding) state. By monitoring the potential difference over time, engineers can detect the breakdown of the protective oxide layer on the rebar due to chloride ingress or carbonation, even before physical damage like cracking or spalling becomes visible on the concrete surface.

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Benefits & Features

  • Provides a stable electrochemical reference point
  • Available with Silver/Silver Chloride (Ag/AgCl) or Manganese Dioxide (MnO2) elements
  • Designed for a service life exceeding 30 years
  • Rugged, alkaline-resistant housing for direct embedment
  • High-input impedance measurement to prevent polarization
  • Essential for evaluating the risk of chloride-induced corrosion
  • Compatible with automated structural health monitoring systems

Detailed Description

The Science of Half-Cell Potential

Corrosion is an electrochemical process. When rebar starts to corrode, it acts like a battery, creating a negative electrical potential. The G94-900CP acts as the 'ground' or reference point of that battery.

By measuring the voltage difference (potential) between the rebar and our stable reference electrode, engineers can consult standard charts (like ASTM C876) to determine if there is a high (>90%), uncertain, or low (<10%) probability of active corrosion.

Detecting the 'Invisible' Threat

One of the biggest challenges in infrastructure is that corrosion happens inside the concrete. By the time you see a crack or a rust stain, the structural integrity may already be compromised. The G94-900CP provides 'early warning' data, identifying the chemical onset of corrosion years before physical symptoms appear.

Ag/AgCl vs. MnO2 Elements

Depending on the environment, we offer two primary sensing elements:

  • Silver/Silver Chloride (Ag/AgCl): The standard for marine environments where high chloride concentrations are expected.
  • Manganese Dioxide (MnO2): Highly stable in the high-pH environment of new, chloride-free concrete, making it ideal for long-term monitoring of new-build bridges.

System Integration

The G94-900CP is typically installed in arrays across a structure. The sensors are wired back to a high-impedance data logger (such as the Geolook GL-DL series), which ensures the measurement itself doesn't drain the very small currents being measured, maintaining the accuracy of the structural 'health map'.

Available Models

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Specifications

Model No
G94-900CP
Reference Element
Ag/AgCl or MnO2 (Standard)
Potential Stability
±5 mV over 24 hours
Internal Resistance
< 10 kΩ
Operating Temp
-10°C to +60°C
Housing Material
High-density Ceramic / Polymer
Design Life
30+ Years in concrete