The breakthrough has been made by researchers based at City University London and Queen’s University Belfast following several research projects funded by the Engineering and Physical Sciences Research Council (EPSRC).
Because the sensors can withstand long-term placement within concrete – unlike any equivalent sensors currently available – they can constantly monitor conditions, enabling a warning to be sent when conditions for corrosion threshold have been crossed. Thanks to an internet connection, the notification can be sent in the form of an email or text to the structure’s maintenance team.
A trio of novel, robust probes is at the heart of the team’s work. One monitors temperature, one watches humidity, the other senses chloride and pH levels. Changes in these factors indicate the onset of the potentially destructive corrosion. Within the probes are advanced optical sensors specifically designed and built for this project in City’s laboratories. These have been patented for potential commercial exploitation.
Dr Su Taylor, from the School of Planning, Architecture & Civil Engineering at Queen’s University (left) worked with the project Principal Investigator Tong Sun, Professor of Sensor Engineering at City (right)
Professor Sun says: “Key to this successful prototype is our monitoring the variation of the sensor signals of a sample as an indicator of corrosion levels.
"This means we can use optical sensors made of polymer, which is much more resistant to the high alkaline environments of these structures than sensors currently on the market.”
Traditional optical corrosion sensors have only a limited lifetime, usually of several weeks, because of the corrosive alkaline levels within concrete.
The new sensors are expected to last for several years, with proper protection, even where pH levels are higher than 12. For comparison, domestic bleach has a pH value of between 12 and 13.
“Our design means several probes can be installed semi-permanently in a structure and then connected to a computer data logger, which will constantly collect readings. This can be left until the readings indicate conditions have changed enough to warrant a full investigation. Remedial work will be simpler, cheaper and more effective at this stage, rather than waiting until there is visible damage, such as parts of the concrete coming away,” said Professor Sun.
FOOTNOTE: CONCRETE SENSORS
In the USA sensors made of concrete take a bow on TheBestCaseScenario where their creator made a "CAD-Model of the two sensors for the front. A 5-axes CNC milled them for me and I made a negative from it with silicon. In that form I cast concrete to get real concrete sensors at the end. At the other I build the “inner-space” with 6mm thick Plexiglas."