Why Measure Corrosion in Concrete Structures?
Measuring for corrosion in concrete structures is essential to determine the strength and longevity of the structure. There can be corrosion of steel reinforcements embedded within the concrete or deterioration of the actual concrete through aggregate expansion or contamination.
Many times, corrosion test results can be used to determine the prescriptive solution that a structure need. For example, if corrosion on a structure developed “hot spots” where spalling is already present and exposed rebar is visible, a vapor phase corrosion inhibitor might be more effective than a migratory corrosion inhibitor. Depending the condition of the concrete and the corrosion measurements, a solution will be designed with the sole objective of stopping and reverting the corrosion that is affecting.
How To Measure Corrosion in Concrete?
There are many tests that contractors and engineers can utilize to determine the corrosion level of a structure. Most corrosion testing methods are based on examining the electrochemical condition of the embedded steel. Most corrosion tests that are utilized in the field are conducted from the surface of the concrete structure.
Many different tests have been developed and used for testing the amount of steel corrosion and concrete corrosion. Some of these tests include resistivity meters, half-cell potential testing, and Gava Pulse
How Do You Test the Potential for Corrosion in Concrete?
Resistivity Test – When the steel inside of concrete corrodes, it is an electrochemical process that creates a current. The concrete’s resistance to this current can be telling of the probability of corrosion. The lower the resistance, the greater the probability of corrosion as the current flows through the concrete much easier because the steel inside the concrete creates that electrochemical flow.
This is a simple technique that uses the association of these two factors to accurately predict the probability of corrosion. This test is mostly used for the corrosion of the steel reinforcement that is embedded in the concrete, not the actual concrete itself. Resistivity meters are used in most of today’s tests. The tool has two or more probes that are connected to the surface of the concrete with a conductive gel between the probes and the concrete surface. A current is then passed from the probes into the concrete. The results of the concrete’s resistivity are displayed on a screen on the meter.
Half Cell Test – A good indicator of current flow is the difference in potential between steel and the concrete surface. This electrochemical process produces a current, which can be measured as an electric field from the surface of the concrete. This field can be measured with an electrode, which is known as half-cell potential testing. Standards for this type of testing are set by the ASTM (American Society for Testing and Materials) international
standard. Measurements are taken over the entirety of the surface of the structure or concrete to compare results from different areas. This can help to measure the health of the entire structure, but also to know if specific areas are corroding at a quicker rate. In this case study, Surtreat Solutions utilized Half Cell testing to measure the impact our solutions had on the structure.
Galva Pulse Test – The Galva Pulse evaluates the corrosion rate of reinforcement by measuring polarization resistance using the galvanostatic pulse technique. A current pulse is imposed on the reinforcement from a counter electrode placed on the concrete surface. A guard ring confines the current to an area of the reinforcement below the central counter electrode. The applied current is usually in the range of 5 to 400 and the typical pulse duration is 5 to 10 seconds. The reinforcement is polarized in the anodic direction compared to its free corrosion potential. The resulting change of the electrochemical potential of the reinforcement is recorded as a function of time using a reference electrode.
How Do We Use These Results?
Surtreat Solutions utilizes these results in many ways. First, we use these tests to determine the types of solutions a structure requires. If results are low on the corrosive scale, we can apply preventative solutions such as a corrosion inhibitor or a protectant. If the structure or concrete needs treatment to clean contaminants and excessive corrosion, we can apply a multitude of solution to extend the service life of the structure.