The technique involves use of a hand-held radar device that can "see" through the fiberglass-polymer wrapping often used to strengthen aging concrete columns to detect damage behind the wrapping not visible to the naked eye. Such damage can occur on the concrete itself, or to areas where layers of the wrapping have come loose from one another or even debonded from the concrete.
The new noninvasive technique can be used onsite from a distance of more than 10 meters (30 feet) and requires no dismantling or obstruction of the infrastructure. It provides immediate, onsite feedback.
Called FAR-NDT (far-field airborne radar nondestructive testing), the technique could prove especially advantageous for bridges that span rivers or highways, which can prove inaccessible for other inspection techniques. The MIT researchers first reported the technique in the proceedings of the International Conference on Structural Faults and Repair held in Edinburgh, Scotland, last year.
"The use of radar for detecting hidden defects and deterioration behind covered surfaces offers great potential for wide-range use in assessing the safety of bridges and buildings that have been retrofitted with composite materials," said Professor Oral Buyukozturk of the Department of Civil and Environmental Engineering (CEE), who developed the technique with CEE graduate student Tzu-Yang Yu and Dennis Blejer of MIT Lincoln Laboratory, where prototype radar measurements were made.
Fiberglass-polymer jacketing--shiny, textured fabric in black or ivory often seen wrapped around concrete columns--is widely used to upgrade existing concrete structures so they can carry a greater load or sustain additional earthquake impact. The wrap is also commonly used to retrofit structures that are damaged or deteriorating from weather or other wear.
Techniques presently available for inspecting these fiberglass-polymer jacketing systems require the inspector to come in direct or close contact with the structure. Some actually require removal of a physical sample, which itself could create a safety issue. The advantage of the new technique is that it allows a rapid inspection from a distance and provides computerized visualization of the internal damages.
"This technique would allow the engineers to perform reliable, in-situ inspection for visualizing and characterizing hidden damages from distances without having to endanger the structure by taking specimens from it, and at the same time, without disturbing the traffic or service," said Yu, whose Ph.D. thesis will focus on this research. "The project is an excellent example of bridging fundamental science and engineering applications."
The researchers have demonstrated the validity and potential of the new technique through experiments and computer simulations by sending and receiving radar signals using a "horn" antenna to inspect bridge piers from distances of more than 10 meters. In their experiments, a horn antenna transmits a radar signal to a fiber-wrapped concrete specimen, which reflects the signal back to the antenna. The collected data are then converted by an imaging algorithm into a visualization of the interior of the specimen, including any damage.
The researchers say that the concept has been validated by their initial experimental results using an existing prototype radar system and by computer simulations. Future development of appropriate portable radar equipment for onsite use is necessary before the system can be placed in widespread use by industry.
Source: MIT
Related stories:
What a sleep study can reveal about fibromyalgia
Research engineers and sleep medicine specialists from two Michigan universities have joined technical and clinical hands to put innovative quantitative analysis, signal-processing technology and computer algorithms to work in the sleep lab. One of their recent findings is that a new approach to analyzing sleep fragmentation appears to distinguish fibromyalgia patients from healthy controls.
Efficient technique enables thinking
(PhysOrg.com) -- Nerve cells constantly create new contact points to their neighbouring cells. This is how the basic structure of our brain develops. In adults, new contact makes learning and memory possible. However, not all contact between cells is useful - most of it is dismantled again very quickly. Scientists at the Max Planck Institute for Neurobiology in Martinsried near Munich have now described a completely new technique with which nerve cells can evaluate the quality of the cells they contact in a very time- and energy-saving way. (
Neuron, July 31, 2008)
A Telescope Made of Moondust
A gigantic telescope on the Moon has been a dream of astronomers since the dawn of the space age. A lunar telescope the same size as Hubble (2.4 meters across) would be a major astronomical research tool. One as big as the largest telescope on Earth—10.4 meters across—would see far more than any Earth-based telescope because the Moon has no atmosphere. But why stop there? In the Moon's weak gravity, it might be possible to build a telescope with a mirror as large as 50 meters across, half the length of a football field—big enough to analyze the chemistry on planets around other stars for signs of life.
Synthetic molecules emulate enzyme behavior for the first time
When chemists want to produce a lot of a substance -- such as a newly designed drug -- they often turn to catalysts, molecules that speed chemical reactions. Many jobs require highly specialized catalysts, and finding one in just the right shape to connect with certain molecules can be difficult. Natural catalysts, such as enzymes in the human body that help us digest food, get around this problem by shape-shifting to suit the task at hand.
New technology may help Olympic sailing
A team of researchers at the Ocean University of China has developed and tested a mobile lidar (light detection and ranging) station that can accurately measure wind speed and direction over large areas in real time -- an application useful for aviation safety, weather forecasting and sports.
Space radar to improve miners' safety
Advanced ground penetration radar, originally developed to investigate the soil structure on the Moon and other planets on ESA planetary missions, is now being used in Canadian mines to spot hidden cracks and weaknesses in mine roofs.
NASA Scientists Pioneer Method for Making Giant Lunar Telescopes
Scientists working at NASA’s Goddard Space Flight Center in Greenbelt, Md., have concocted an innovative recipe for giant telescope mirrors on the Moon. To make a mirror that dwarfs anything on Earth, just take a little bit of carbon, throw in some epoxy, and add lots of lunar dust.
LIDAR imaging detector could build 'super road maps' of planets and moons
Technology that could someday “MapQuest” Mars and other bodies in the solar system is under development at Rochester Institute of Technology’s Rochester Imaging Detector Laboratory (RIDL), in collaboration with Massachusetts Institute of Technology’s Lincoln Laboratory.
