By Paul Rincon
BBC News science reporter
Technology to "look inside" concrete structures could not only monitor them for corrosion, but also locate the remains of murder victims, experts say.
Concrete structures have a finite lifetime
It works using ultrasound, the same technique used in hospitals to monitor growing foetuses in the womb.
One of the systems being developed builds up quasi-3D images of the interiors of concrete structures.
Many were put up in the 50s and 60s and some are already approaching the end of their design lives.
But the technology could also have a potential application in police investigations.
Since the late 1980s, Cambridge Ultrasonics has been working on ways of using ultrasound to inspect concrete structures for signs of corrosion.
A version of its technology, licensed by UK firm Sonatest, seeks to generate images from interiors.
It uses an array of up to six transducers to fire sound waves into the concrete from different angles. The transducers then collect echo-waves returning from within.
Software then helps build the raw data into a pseudo-3D image of the interior.
Initial signs of deterioration in concrete often present as hairline cracks. Sonatest's technology, which is still at the research and development stage, sorts out genuine structural flaws from "noise" generated by concrete's lumpy constitution.
"Shooting from many angles, if it's part of the aggregate you would see it from only one viewpoint. But a crack would probably appear as a linear defect as you turn the image," Wayne Woodhead, Sonatest managing director, told BBC News.
Ultrasound could monitor for changes in structural integrity
Dr David Andrews, director at Cambridge Ultrasonics, explained: "The design life of many concrete structures is 50-120 years. A lot were put up in the 50s, the 60s and some in the 70s.
"They are getting older all the time. Some are deteriorating faster than expected."
Of the possible use of ultrasound in police investigations, Mr Woodhead said: "If there was a body in concrete from 60 years ago, it would probably break down, leaving a void.
"If you scanned the area, you could find the void, but whether it would look like a big hole or would be person-shaped is anyone's guess."
David Andrews says police officers approached his company about using ultrasound for this purpose several years ago. Their enquiry concerned disappearances allegedly linked to gang activity in the 1960s.
It was rumoured bodies could have been deposited in wet concrete used to build vertical struts for a road bridge. But the technology was not at a sufficient stage of development for Dr Andrews to provide a mobile version.
Murderers have, in the past found it convenient to dispose of the bodies of their victims in concrete. For example, five sets of remains were found buried under the concrete cellar belonging to Gloucester serial killer Fred West.
Radar can also be used to scan concrete, but it is hampered if water has penetrated the structure.
Cambridge Ultrasonics has developed a sensor system, also based on ultrasound, which could be attached at points along a concrete structure to provide regular, automated monitoring for signs of corrosion.
Each sensor in the Cambridge Monitoring System has a "neural network" which can be trained to compensate for daily and seasonal temperature changes that could confuse readings.
Data from all the neural networks is combined to give a "probability of significant structural change".
Of particular concern are the tendons, which act as the skeleton of the structure. Corrosion leading to failure of one or a few tendons can lead to collapse of major parts or all of the structure.