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Making Fire Damage Assessment Concrete

EuroPhotonics
Mar 2017
AUTUM C. PYLANT, NEWS EDITOR, autum.pylant@photonics.com

Concrete, fire and lasers generally don’t go hand in hand. But suppose there was a way to incorporate all three — specifically, in a laser that could detect and assess fire damage on concrete.

Researchers at the University of Nottingham in England and its overseas campus, the University of Nottingham Ningbo, China (UNNC), are firing laser scanners at concrete bricks, some of which have been exposed to excessive temperatures, all in hopes of offering a nondestructive way to asses fire damage to concrete.

Equipped with two laser scanners — a Leica HDS7000 and a FARO Focus 120 — an M-Cam and an HP flatbed scanner, researchers have been investigating the effects of fire on concrete in a controlled environment. Concrete’s physical, chemical and mechanical properties break down when subjected to high temperatures; a significant loss in strength occurs when heated above 300 °C.

After a fire, structural safety assessments provide information needed to evaluate the residual bearing capacity and durability of damaged concrete structures. Conventional techniques include visual inspections of color change and invasive tests such as core drilling to help propose repair methods or decide if demolition is needed.

A team of researchers — Wallace Mukupa, a Ph.D. candidate at the Nottingham Geospatial Institute at UNNC; Gethin Roberts, professor of Geospatial Engineering at Nottingham; and Craig Hancock, assistant professor of Geospatial Engineering at UNNC — raised temperatures and assessed color change in the heated concrete by creating specimen images using the M-Cam attached to the Leica scanner

. Roberts told Photonics Media the study investigated the use of laser scanner intensity for post-fire assessment of concrete, which is a new area of research.

“The results demonstrated the feasibility of using terrestrial laser scanning as an approach to assessing levels of fire-damaged concrete and provide an understanding of the condition of concrete in relation to the strength changes of concrete when it is heated to elevated temperatures,” he said.

Lasers are not part of the equation right now, but Mukupa told Photonics Media the team’s research and findings could change that.

“The use of laser scanning technology for health assessment of fire-damaged concrete complements existing assessment techniques ... such as some manual onsite methods where hammers and chisels are used and even the more invasive lab-based tests,” he said.

During the experiments, the incidence angles for the concrete blocks was found to vary with distance. As the scanning distance increased, the incidence angle decreased and both scanners used showed the same trend. Laser intensity values of heated concrete showed a remarkable increase in the concrete exposure temperatures from 250 °C to 1000 °C, according to the researchers.

“Such a correlation between the intensity and the exposure temperature is of cardinal importance in assessing the condition and extent of damage to concrete,” said Mukupa. “This finding implies it could be possible to use laser intensity to detect the state of concrete, whether it has been heated or not.”

So the question remains: to use lasers or not to use lasers? The answer could come in the form of accessibility and timeliness, as scanning can be performed in a relatively short time and at a distance that improves safety. The team plans to extend its research outside of its own concrete walls very soon.

ConcretefirelasersUniversity of NottinghamNingboChinaEuropeAsia-PacificUNNCLeica HDS7000FARO Focus 120scannersWallace MukupaGethin RobertsCraig HancockM-CamPicture This

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