Fire-damaged concrete structures: how do we know when to fix or rebuild a concrete structure after a fire?

Generally, when concrete is exposed to intense fire, materials in the concrete can decompose, and consequently there is a reduction in strength. Nevertheless, there is not a widely accepted method for evaluating this damage, making the choice between repair and demolition difficult.

Various techniques are introduced in research papers, such as visual observation, compression test, UV spectrum, oxygen measurement, but none of these can give a scientific basis on whether the structure in fire scenes should be replaced or repaired. This is because their results are not always accurate, not re-producible and thereby not applicable to actual fire scenes.

Now, a team of researchers, led by Dr Youngsun Heo of the Korean Institute of Civil Engineering and Building Technology (KICT), have developed the Fire Forensic Investigation of Structure (F2IS) tool that can answer the question: “how do we know when to fix or rebuild a concrete structure after a fire?”

“After fire exposure, service life of concrete structure can drop within two weeks, depending on the damage level,” says Heo. “The higher the volume of pores in concrete arising from fire, the faster is the dramatic reduction of life expectancy. If the structure is not going to be rebuilt, immediate diagnosis and subsequent repairing work should be proceeded even when there is minor damage.”

By taking tiny 1-2g samples for every 10mm of depth of fire-damaged concrete, F2IS can predict the impacts of the fire – such as temperature, length of time spent in the heat and how heat diffused through the structure – with 80% accuracy.

Using this data and deep learning, the tool assesses which key features to address. The whole process takes less than two weeks to support continuation of housing and businesses.

It also has the extra benefit of simulating scenarios for fire forensic specialists to investigate when and how the fire started.

The patent for F2IS was approved in August. The team plans to develop a rehabilitation system that can chemically cure the decomposed hydration products to fill in the cracks and help the structure recover.