Cheap nano-sensors could be embedded in buildings to give early warning of defects that make them more vulnerable to earthquakes, researchers have suggested.
Scientists embedded two types of nano-sensors — micro-electromechanical systems (MEMS) and carbon nanotube sensors -— into concrete blocks and beams, which they then tested under different environmental and load conditions.
The MEMS device monitored internal temperature and moisture while the nanotube detected cracks forming inside the concrete. The data from these sensors were transmitted wirelessly to a receiver connected to a laptop computer.
The scientists, from US universities and the National Institute of Applied Sciences in Tunisia, found that they could track the unfolding effects of freezing and thawing inside the concrete.
"The sensors can help developing countries keep bridges, water systems and roads in good shape," said Mohamed Saafi, from North Dakota State University in the United States, lead author of the study, which was published in the International Journal of Materials and Structural Integrity.
"The cost of these sensors will be pretty cheap compared with other available systems like fibre optic and acoustic emission sensors or conventional inspection methods."
Once the sensors are developed beyond the feasibility stage, he expects them to cost US$5–10.
"One of the problems in the construction industry is that there exist few methods to assess building integrity once the structure is complete," commented a prominent seismologist.
"Contractors and builders attempting to maximise profits can hide bad concrete frame construction behind a layer of plaster or paint.
"Embedded sensors capable of monitoring assembly integrity, strength of materials, and response to wind and vibration loads, would serve to remind contractors that their assembly methods can be checked in-situ.
"The cost of nano-sensors is trivial compared to the cost of a building," he added.
Dean Neikirk, professor of electrical and computer engineering from the University of Texas at Austin, United States, who has been researching nano-sensors for the past ten years, said: "I think the important issue in developing countries is that initial construction be done to a proper standard, up to 'code' — and that critically includes the quality of the original concrete mix used in the structure — rather than worrying about adding cost to monitor for damage after the structure is completed.
"When properly designed and constructed many concrete structures are really pretty hard to damage and, when the damage occurs, you don't need a nano-sensor to see it," he added.
International Journal of Materials and Structural Integrity doi: 10.1504/IJMSI.2010.032494 (2010)