Greater quality control for C&D waste recyclers within reach?

Germany – Currently upwards of 461 million tons per year of increasingly complex construction and demolition waste are generated in the European Union. Modern-day sorting techniques are said to provide a good solution to this quickly growing waste stream.

The worldwide construction market is expected to reach over US$ 1 trillion by 2020. ‘There are a lot of new structures and roads in development, which will add to the already sizeable waste flow of the international construction and demolition market,’ observed Roberta Palmieri of Rome University at the recent Sensor-Based Sorting & Control Conference in Aachen, Germany.

‘The good thing is that this waste is being reused or recycled more and more. Of course, recycled aggregates must be competitive with natural aggregates,’ she said. Palmieri affirmed that the advantages of a hyperspectral imaging-based quality control approach are ‘considerable’, describing the technique as ‘objective, fast and non-destructive, allowing to continuously perform a low-cost analysis’.

She and her team at Rome University applied this method to distinguish recycled aggregates from contaminants, such as bricks, plastic and wood, while also separating mortar paste from aggregate particles. A goal of this work was to boost high-value "green concrete" production.

The researchers received a bulk quantity of C&D waste test samples from nearby recycling plants as well as partners in the Netherlands. This material was fed through a system equipped with a HSI sensor with a short-wave infrared range of 1000-2500 nm.

Then, the samples were sorted into seven different categories, namely: aggregate, brick, foam, gypsum, mortar paste, plastic and wood.

‘Classification was successful, with one exception; aggregate particles were sometimes mistaken for mortar paste,’ the researcher stated. Reasons were stated to be light scattering and dirt.

On the whole, though, the innovative method was found to be suitable for identifying the presence of a great variety of pollutant materials in the C&D waste stream, thus enabling ‘greater quality control’ for recycling firms operating in this sector.