Researchers at Luleå University of Technology have discovered an environmentally friendly method for recycling old concrete.
By using metal balls and frictional heat, they make use of what was previously considered a waste product.
– In my eyes, this is a gold mine. There is so much cement sitting in piles of old concrete and not being used. But it could be used, says Andrzej Cwirzen, professor of building materials at Luleå University of Technology.
Concrete is one of the world’s most common building materials and consists of crushed stone bound together by water and cement. The binding agent cement, in turn, consists of limestone and clay that are heated to very high temperatures.
The process involves large carbon dioxide emissions. For every ton of cement produced, 700 kilograms of carbon dioxide is released, and cement production accounts for eight percent of global emissions.
Only recycles stone
Currently, recycling concrete, for example from old buildings, means recycling the crushed stone, but not the cement.
– The concrete is crushed in several different complicated steps and in the end there are particles of different sizes that can be used to make new concrete. But to make new concrete, you have to add new cement. So the only thing you recycle is basically crushed stone in different sizes, says Andrzej Cwirzen.
The new method provides major environmental benefits
When the concrete is crushed, a dust-like powder is formed. It is in the dust from the crushed concrete that researchers have now found a method to recycle cement from what was previously considered a residual product, and thus a problem.
By grinding the dust from recycled and crushed concrete together with metal balls, frictional heat is created which in turn reactivates the cement found in the powder. The process can be likened to heating up solidified glue so that it becomes sticky again.
– It is actually very simple. It’s about crushing and grinding. We have only optimized it and taken it one step further, says Andrzej Cwirzen.
Before concrete with only recycled cement is used in buildings, further tests need to be done and the regulatory framework for building materials needs to be changed. But the method would mean big environmental gains.
– If you use green electricity to drive the machines, this method does not emit any carbon dioxide. Imagine the amount of cement found in old concrete in the world. If we can recycle just a part of it, it would have a big effect on a global level, concludes Andrzej Cwirzen.