Scientists in Germany, along with researchers at the University of Glasgow, are working towards certifying a technique known as muography for detecting faults in concrete.
As reported by the Financial Times, concrete is one of the most used materials on the planet – over 10 billion tonnes of concrete are produced every year, and around 70% of humans live in structures made from reinforced concrete.
However, concrete can decay and crack over time. Cables and metal supports embedded in the concrete can corrode or snap without being seen from the outside, leading to structural failure. This puts countless buildings and bridges at risk, not to mention human lives.
It’s not just economically impossible to drill test holes in concrete structures to examine them, but it would also damage them and potentially cause structural failure anyway. There needs to be a way to look inside concrete pillars without damaging them.
This is where muography comes in, with the potential to identify faults inside concrete before they fail, possibly preventing structural collapse.
Muons are energetic particles with short lives, which are generated through cosmic ray collisions in the upper atmosphere. Travelling at almost the speed of light, they can penetrate deeply into the surface of the Earth – meaning they can pass through human-made structures with ease.
However, muons have a harder time passing through denser materials, such as steel rebar inside less dense concrete. Blocking or scattering of muons would indicate that a denser object is present.
The Muon Imaging for Mining and Archaeology (MIMA) equipment is a relatively small metal cube on a stand containing electronic muon detectors. Using complex mathematical modelling software, the data it collects can be used to calculate and visualise what the muons passed through.
This then produces images that look like grey-toned early photography, or modern photocopies. Currently, muography makes pieces of steel rebar and evidence of damage visible at a centimetre-scale resolution – and it’s likely to become as precise as a few millimetres in the next few years.
The machinery only requires about the same energy to run as a regular light bulb, meaning it can be left running for several days on a battery pack or even use solar power. The downside is that you have to set it up and leave it for a while to collect the data, because it can take a long time for enough muons to pass through to create a coherent image of a building.
When it comes to concrete, there are several non-destructive ways to inspect it for fatigue and corrosion. The problem is that those methods are too limited. Radar can’t penetrate more than a couple of metres, and ultrasound produces too much visual ‘noise’.
X-rays would be ideal for providing crisp images, but – being a form of radiation – they pose a health risk to anyone exposed. This makes X-raying a large structure in the middle of a city practically impossible. It could be done, but not without completing a lot of complicated paperwork, applying for safety permits, and evacuating the entire area first.
Now, there is an alternative option – a small, unobtrusive detection system that uses the natural cosmic rays already here to gather data for physicists to collate with their advanced software. Muography could revolutionise structural imaging technology within the next decade.
This technology has already been incredibly useful in the field of archaeology since the 1960s, helping researchers to map underground mines, tombs, and natural chambers and landforms. It can also be used to monitor changes in the magma chambers of volcanoes, possibly detecting an imminent volcanic eruption with enough time to evacuate and save many lives.
In terms of the technology’s new application in detecting faults in concrete infrastructure, there are plenty of examples where this equipment could have saved lives.
One such case is the partial collapse of a 12-storey block of apartments in Miami in 2021, which killed 98 people. The investigation found that the shattered concrete pillars appeared to have insufficient steel rebar supports, suggesting that corners were cut during construction, leading to the building being overloaded for years until it eventually collapsed.
If muography was widely used in regular inspections of concrete structures, this is one of many disasters that could have been avoided.
Muography will allow building inspections of concrete infrastructure in populated areas without causing any disruption or risk to life.
This relatively straightforward technique could help inspectors to check the condition of structural components such as metal rebar, and identify problems before they become so advanced that they cause a collapse. This would then give the relevant authorities time to reinforce the structure.
Currently, the experts are still in the process of intensive work on the testing and certification of their muography equipment, which could transform from a physics tool to a commercial product. It will take a few more years of proving the technology’s accuracy and reliability before standards can be created and investments made for the wider manufacture and sale of this equipment.
The more data that muography can gather on structural defects in concrete, the more architects and engineers can use this knowledge to improve their own work in designing structures. Better buildings and bridges are good news for everyone – and the economy, since taxpayers won’t have to spend as much on maintaining crumbling public infrastructure.
While it’s adapted from an old and slow technology that isn’t terribly exciting to look at, developments in muography could really change the future of the construction industry.
In the meantime, as research continues, builders and buyers alike should continue to invest in insurance policies for their buildings. Setting up a building warranty from the start of construction ensures that regular structural inspections will take place throughout, minimising the risk of defective materials or workmanship going unnoticed.
As the saying goes, prevention is better than cure – so always make sure that new builds have comprehensive surveys during construction and protect them into the future with a warranty.
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