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Concrete structure lifespan extended by carbon textile

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Researchers in Korea have developed an effective structural strengthening method using a non-combustible carbon textile grid and cement mortar.

According to its creators at the Korea Institute of Civil Engineering and Building Technology (KICT), this new method can double the load-bearing capacities of structurally deficient concrete structures and increase their usable lifespan threefold.

More than 90 per cent of infrastructures in South Korea such as bridges and tunnels, as well as residential buildings, were initially constructed out of concrete. For deteriorated or structurally deficient concrete structures in need of structural strengthening, carbon-fibre sheets are typically applied to the surface of the concrete structure using organic adhesives. 

However, organic adhesives are susceptible to fire and cannot be applied to structures with wet surfaces. These carbon-fibre sheets may detach and fall from the structure if they are exposed to moisture. To tackle these issues, a team at KICT, led by Dr Hyeong-Yeol Kim, developed an effective and efficient strengthening method for deteriorated concrete structures, deploying thin, precast, textile-reinforced mortar (TRM) panels, which are made of a carbon textile grid and affixed with a thin layer of cement mortar.

Furthermore, the TRM strengthening method can be applied in the form of cast-in-place construction. As part of KICT’s method, 20mm-thick TRM panels are attached to the surface of the existing structure, with the space between the existing structure and the panels then filled with cement grout, with the cement grout serving as the adhesive.

The researchers said that both the carbon textile and cement mortar are non-combustible materials that have a high resistance to fire, meaning that they can be effectively used to strengthen concrete buildings that may be exposed to fire hazards. It can also be applied to wet surfaces, as well as during the winter, and the panels do not fall off even in the event of water ingress. 

Additionally, unlike steel reinforcing bars, the carbon textile does not corrode. This, therefore, means it can be effectively used to strengthen highway facilities and parking buildings, where de-icing agents are often used, as well as to strengthen offshore concrete structures that are exposed to a chloride-rich environment, the team said.

“For easier production and shipping, the TRM panels are manufactured in a relatively small size of 1m x 2m and must be connected at the construction site,” said Dr Kim. “A method for effectively connecting the panels is currently being developed and performance tests of the method will be conducted by the end of 2020.”

A failure test conducted at KICT found that the failure load of concrete structures strengthened with the TRC panel increased by at least 1.5 times compared to that of an unstrengthened structure. Furthermore, the chloride resistance of the TRM panel has been evaluated in order to assess its service life in a chloride-rich environment.

The durability test and analysis of the TRM panel suggested that the lifespan of the panel is more than 100 years. This increase can be attributed to the cement mortar, developed by KICT, which contains 50 per cent ground granulated blast furnace slag, an industrial byproduct generated at ironworks.

The researchers added that the cement mortar, which has a higher fire resistance than conventional mortar, is also more suitable because the cost is half that of conventional mortar. Regarding economic efficiency, the new method could also reduce construction costs by about 40 per cent compared to existing carbon sheet attachment methods, the researchers said. 

Furthermore, they said the strengthening method advantage of using thin TRM panels is that they are very versatile and can be used for building facades, repair and strengthening materials, and in other applications. In the future, the team said if the panels can be fabricated with thermal insulators, it is expected that they will replace building insulation materials that are susceptible to fires.

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