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Such structures could also last for three-times as long using the new technique, according to the research team at the Korea Institute of Civil Engineering and Building Technology (KICT).
Carbon fibre sheets can be applied to the surface of deteriorated or structurally deficient concrete structures that need strengthening. This is typically done with organic adhesives, however, which are susceptible to fire and cannot be applied to wet surfaces. These carbon fibre sheets can detach and fall from structures if they are exposed to moisture.
The team, led by Dr Hyeong-Yeol Kim, developed an alternative that is reportedly effective and efficient. The new method uses thin, precast, textile-reinforced mortar (TRM) panels, made of a carbon textile grid and a thin layer of cement mortar. The TRM strengthening method can be applied in the form of cast-in-place construction. Using the method, 20mm-thick TRM panels are attached to the surface of the existing structure, and then the space between the existing structure and the panels is filled with cement grout, with the cement grout serving as the adhesive.
Both the carbon textile and cement mortar are non-combustible materials with high resistance to fire, meaning they can strengthen concrete buildings that may be exposed to fire hazards. The method can also be applied to wet surfaces, and the panels reportedly stay on even in the event of water ingress. Unlike steel reinforcing bars the carbon textile does not corrode, so it could be used in roads, multi-storey car parks and offshore structures that are exposed to a chloride-rich environment.
A failure test conducted at KICT indicated that the failure load of concrete structures strengthened with the TRM panels increased by at least 1.5 times compared to non-strengthened structures.
A durability test and analysis of the 1m x 2m TRM panels indicated a lifespan of more than 100 years. The researchers said the increase could be attributed to the cement mortar, developed by KICT, which contains 50% ground granulated blast furnace slag, an industrial by-product generated at ironworks. The cement mortar, which has a higher fire resistance than conventional cement mortar, is also reportedly half the cost of conventional mortar. Overall, the researchers said the new method can reduce construction costs by about 40% compared to existing carbon sheet attachment methods.
The researchers aim to complete performance tests of the method by the end of 2020.
The work was published in Materials.
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