The Middle East with its high temperatures and extremely high saline content of its sea-water & ground water forms an extremely aggressive environment in terms of corrosion. When constructing structures that are exposed to this environment the challenge is how to ensure corrosion durability.
For diaphragm walls that are cast in situ, this is a special challenge for two reasons.
The first reason is that during construction, some methods employed involve the boring of the excavation, lowering the steel cage into the bored excavation and then casting. The excavation is typically inundated with bore -hole chemicals to ensure that the excavation does not collapse. During this period, it can be expected that chlorides from the surrounding groundwater permeate the excavation walls. Therefore it follows that the reinforcing steel cage will, once it is lowered, be immediately exposed to potentially high levels of chloride.
The second reason that diaphragm walls are a challenge in terms of ensuring durability, is the exposure after construction. On one side the reinforcing steel is exposed to highly saline sea-water, while on the soil side, the wall is exposed to highly saline ground-water. The wall is seemingly sandwiched between to very corrosion environments.
By deploying a well-designed cathodic protection system using impressed current, the corrosion of the reinforcing steel can be stopped or significantly reduced to a negligible amount. Cathodic protection (CP) is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. A simple method of protection connects the metal to be protected to a more easily corroded "sacrificial metal" to act as the anode. These systems (also known as sacrificial cathodic protection) can be designed with a service of approaching 20 years.
For longer service life systems, the ‘sacrificial metal’ method above is not sufficient. Metals made from coated titanium cast into the concrete matrix. These provide a means to create electrochemical cell, by introducing direct current onto the steel to be protected, in this case the reinforcing steel. The source of the direct current is typically located close to the structure in an electrical room. These systems can be designed in excess of 50 years.
Once deployed, these systems can be monitored with extreme ease remotely. Many asset owners fret about the upkeep of these systems. In fact, the upkeep is insignificant. With IoT devices, Ducorr has already developed systems that can be monitored from your smart phone or tablet, sending you updates at intervals you chose.
These systems are extremely powerful durability tools providing a hands-on and active approach for managing corrosion – almost unheard off a few decades ago.