Understanding and measuring the corrosion of steel reinforcement in concrete structures is crucial for assessing their strength and durability. The corrosion not only shortens the lifespan of the structure but also escalates inspection and maintenance costs significantly. In this exploration, we will delve into various techniques for measuring reinforcement corrosion, shedding light on their principles and applications.
Corrosion in concrete begins when ions penetrate through pores, turning concrete into an electrolyte and triggering the corrosion of embedded steel bars. The foundation for studying this corrosion lies in the electrical potential field generated as electrons move within the concrete over the steel bars. Most corrosion measurement techniques focus on examining the electrochemical condition at the rebar-concrete interface, typically conducted from the concrete surface.
The electrochemical process of steel corrosion generates a current flow within concrete. The resistivity of concrete influences this current flow, with lower electric resistance indicating a higher probability of corrosion. The resistivity meter is a portable device equipped with probes and conductive gel for assessing the probability of corrosion. The measurements can be easily conducted in the field, providing valuable insights into the corrosion potential.
To measure resistivity, metallic probes are placed on the concrete surface, and a known current is passed through the outer probes. The resulting potential drop between inner probes is measured, and resistance is computed by dividing the potential drop by the current. The resistivity values are categorized into different levels, indicating the possible corrosion rate, as shown in Table 1.
| Resistivity Level (Kilo-ohm / cm) | Possible Corrosion Rate |
|---|---|
| < 5 | Very high |
| 5 to 10 | High |
| 10 to 20 | Moderate to low |
| > 20 | Insignificant |
The potential difference between the concrete surface and steel offers insights into the current flow and corrosion activity. The half-cell potential test utilizes an electrode to measure this potential field, allowing a distinction between corroding and non-corroding locations.
Measuring values over the entire surface reveals likely corroding and non-corroding locations. The potential values are categorized into different levels, indicating the possible corrosion rate, as shown in Table 2.
| Potential Value | Possible Corrosion Rate |
|---|---|
| <= 0.20 V | 90% probability of no corrosion |
| 0.20 to -0.35 V | Corrosion activity uncertain |
| > 0.35 V | More than 90% probability of corrosion |
The iCOR® test tool provides a cost-effective and non-destructive approach, capable of performing three tests on concrete—electrical resistivity, hall-cell potential, and steel bar corrosion rate.
Employing Connectionless Electrical Pulse Response Analysis (CEPRA) technology, iCOR® measures the electrical response of reinforcement inside concrete without physically connecting to the rebar. This eliminates the need for drilling holes in concrete, making it a convenient and efficient solution for corrosion assessment.
In conclusion, these techniques offer valuable insights into the corrosion potential of steel reinforcement in concrete structures, enabling informed decisions for maintenance and ensuring the longevity of the infrastructure.