A process for disintegrating waste concrete into its various components using bolts of lightning could help to make concrete a truly recyclable building material.
When it's recycled at all, waste concrete is typically ground down into smaller pieces, a process that not only produces lots of dust, but because of its limited efficiency, turns out a product mostly used as a road base material. That process is more akin to simple reuse than to true recycling, and it only accounts for a small percentage of the waste concrete produced every year.
But if there was a process that could break down the concrete into its constituent components, which could then be used again in new products, then the rate for waste concrete recycling could jump by a factor of ten, according to research being done in Germany.
Researchers at the Fraunhofer Institute for Building Physics IBP are using a process known as electrodynamic fragmentation to selectively separate concrete in their lab. The method was originally developed by Russian scientists in the 40s, but it wasn't until recently that the technology was improved to the level that could make large-scale use feasible.
The fragmentation system, also known as "pulsed power processing", uses electrical pulses forced through the materials, which are submerged underwater:
“When the pulses strike the rock, in this case the concrete, the pre-discharges always follow the path of least resistance – along grain boundaries." - Dr. Volker Thome
Once the pre-discharges have weakened the rock along its grain boundaries, shock waves then disintegrate the concrete by pulling it apart into its individual components with great force:
"The force of this shock wave is comparable to that of a TNT explosion." - Thome
Once the components have been dried and screened, they can potentially be reused as raw materials, such as gravel aggregate in cement production. With the hundreds of millions of pounds of waste concrete generated around the world each year, being able to recycle even some of it would reduce not only the need for new mineral extractions, but would also lessen the loads of landfills.
Mining companies currently use the fragmentation process to separate valuable minerals from the surrounding rock without destroying them, and this new advancement could also be developed into applications for recycling carbon fiber reinforced polymers and reclaiming municipal solid waste incineration (MSWI) bottom ash, according to the researchers.