Waste is not only made up of soda bottles thrown away or discarded newspaper. People are continually changing the environment to suit new purposes or needs. Buildings are thus being put up, torn down or renovated at a constant rate, resulting in many tons of building waste.
Concrete waste, not so long ago, was only useful as a base layer in road construction. However, research in the Fraunhofer Institute for Building Physics has showed a better way, that is, by using lightning to divide waste concrete into its fundamental and reusable parts.
Concrete is quite adaptable, and as such is the most widely used building material in the world. It is simply made by mixing water, aggregate and cement, with stone particles like limestone or gravel in differing sizes, and is therefore affordable as well.
These advantages come at a cost, as the Fraunhofer Institute explains, “the production of one ton of burned cement clinker of limestone and clay releases 650 to 700 kilograms of carbon dioxide.” This implies that concrete manufacture contributes to the yearly global CO2 production by as much as 8 to 15 percent.
In order to recycle concrete and help reduce these carbon emissions, the key is to divide concrete waste into its basic components which can thus be mixed to form new concrete. The researchers in the Fraunhofer Institute who devised the procedure use electrodynamic fragmentation, that is, extremely short pulses of artificial lightning to divide the concrete into gravel and cement materials.
When the lightning hits the concrete waste, the force travels along the path of minimum resistance, that is, the bond between the constituents, such as the cement stone and gravel. First though, initial impulses called pre-discharges are generated and cause the debris to weaken mechanically.
This was explained at the Concrete Technology Group located in Holzikirchen by Volker Thome of the Fraunhofer Institute for Building Physics IBP as follows, “The pre-discharge which reaches the counter-electrode in our fragmentation plant at first, then causes an electrical breakdown. At this instant a plasma channel is formed in the concrete which grows within a thousandth of a second, like a pressure wave from the inside outwards.”
The ensuing explosion releases a force which rapidly and efficiently disintegrates the concrete in a time that is only a fraction of conventional methods. The researchers aim towards a target of 20 tons per hour, which according to them, is possible in about two years.
