The Advanced Dry Recovery (ADR) technology was developed in an earlier European research programme. It involves crushing concrete and sieving the remains after other materials such as asbestos, glass, metals, and bricks have been removed from the demolition site. ADR typically produces 60% of course material (diameter 4-12 millimetre) and 40% fine material (diameter smaller than 4 mm). Although the course material can be reused in concrete, the fine material could only be reused in low-grade road base constructions.
A new process called HAS (Heating Air classification System) separates the fine ADR output into the finest material (diameter smaller than 0.25 mm) consisting mainly of fine cement particles and course sand (over 0.25 mm in diameter). “Separating sand and cement makes it possible to reuse and sell both materials,” says Dr. Francesco Di Maio, project coordinator at the Faculty of Civil Engineering and Geo Sciences. “Adding value to 40% of the ADR output makes recycling concrete more profitable.” Di Maio and his colleagues of the Resources & Recycling Group hope that their technology will make concrete recycling economically viable.
The process is being patented, so the researchers are reticent on details. The broad picture, however, is this: the fine ADR material is filled from the top into the reactor where it is heated to 300-400 degrees Celsius. As the material descends through the reactor, it also comes into contact with powerful air streams. This causes the course material to drop out of the bottom, while the finest material is blown out of the top.
The degree of separation depends on the details of the reactor’s construction, the placements of the air vents and the velocities of the air streams. Dr. Abraham Gebremariam (in collaboration with Dr. Somi Lotfi) is currently fine-tuning these parameters in a simulation.
Researchers are preparing to scale up the current lab scale set up into a prototype of an economically viable system that can process three tonnes of end-of-life concrete fines per hour.
From waste to concrete (video)