UK researchers have announced the development of sensors that purportedly spot early signs of rebar corrosion in concrete, while standing up to long-term marine exposures.
The work of researchers based at City University London and Queen's University Belfast, the sensors are said to last longer than traditional corrosion sensors and to allow more effective monitoring of bridges, coastal defenses and other structures.
Withstanding Long-Term Exposures
Rebar in tidal and splash zone areas is at particular risk of corrosion, due to continual wetting and drying, the researchers note. In addition, seawater contains a cocktail of dissolved inorganic material, including chloride, which plays a major role—in the air, in the splash zone, and below the surface—in the corrosion of marine structures.
National Research Council Canada
|A bridge deck in Alberta shows damage from corrosion of the reinforcing steel. Tidal and splash zones are particularly vulnerable to rebar corrosion.|
The new sensors, however, are made of a polymer that helps them survive long-term placement within concrete, the team says.
The sensors constantly monitor conditions and send an email or text warning via an Internet connection when conditions for the corrosion threshold have been crossed, the team reports.
The heart of the system is a trio of probes: one that monitors temperature, one for humidity, and one for chloride and pH levels. Changes in these factors indicate the onset of potentially destructive corrosion.
The probes contain patented, advanced optical sensors developed in City University's laboratories.
“Key to this successful prototype is our monitoring the variation of the sensor signals of a sample as an indicator of corrosion levels,” says principal investigator Tong Sun, professor of sensor engineering at City.
“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 typically last 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, the researchers say.
“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,” said Sun. “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.”
The four-year project, “Corrosion Monitoring Systems for Structures in Extreme Marine Environments,” was supported by the Engineering and Physical Sciences and Research Council. Partners included Amphora Non-destructive Testing Ltd., Ove Arup Ltd., and the Canadian National Energy Board.
The success of the initial sensor development, completed in 2010, has led to additional exploration of the commercial potential of the technology. Researchers also report improvement on the sensor design, especially the chloride probe.