Recycling Concrete from Buildings That are No Longer Needed Requires Long-Term Thinking at the Building’s Inception
Urban mining is increasingly being taken seriously by industry because it gives access to materials—such as expensive metals used in electronics—that are buried in waste tips and landfills. However, there is a new kid on the block—literally. Concrete buildings, when demolished, can serve as an excellent source of new building materials. “Instead of transporting aggregates from far away, we can use local buildings as a source for aggregates,” says Francesco Di Maio, a researcher in waste separation and recycling technology at the Technical University of Delft in the Netherlands. He is also the coordinator of the EU-funded project called C2CA.
Concrete consists mainly of two components: cement, in the form of calcium silicates, and an aggregate, which can consist of sand, pebbles and small rocks of up to about 2 centimetres across. The recycling of concrete involves recuperating these two components. “The main aim of C2CA is to recycle the aggregates contained in the concrete into new aggregates that can be used to make new mortar and new concrete,” Di Maio tells youris.com. The second component to be recycled, cement, is fed back into the kiln. The advantage of recycling the cement component is that it does not release CO2 into the atmosphere. “When you reintroduce the calcium silicates into the kiln, the CO2 is already released,” says Di Maio.
Although this scheme looks simple, there are still obstacles to the recycling of concrete. One is the cost of separating the aggregates from the concrete. “We wanted to develop a process, which is attractive economically, [as] washing is too expensive,” says Di Maio. The technique they developed, called Advanced Dry Recovery, separates the aggregates into three components using a ballistic effect. “The materials are subjected to an acceleration of up to 1,000 G, which separates the sand and dust from the stones, with the heaviest stones flying the furthest,” explains Di Maio.
Ironically, their biggest competitor in the Netherlands is the very cheap virgin aggregate obtained from the dredging of the Maas river. Also, doubts about the purity of the aggregate are still an obstacle for the acceptance of the recycled material. “Our customers would not like to see a small piece of wood sticking out of a concrete wall,” Di Maio tells youris.com. Although they are perfecting the detection of impurities using optical techniques, tests have shown that the concrete made from recycled aggregate has better mechanical properties than concrete made using virgin aggregates, explains Di Maio.
Source: Phys.org
By Alexander Hellemans