Assessment of the contaminants level in recycled aggregates and alternative new technologies for contaminants recognition and removal

One of the main challenging problems associated with the use of Recycled Aggregates (RA) is the level of mixed contaminants. For utilizing RA in high-grade applications, it is essential to monitor and minimise the content of the pollutants. To this extent the C2CA concrete recycling process investigates a combination of smart demolition, followed by new innovative technologies to produce high-grade secondary aggregates with low amount of contaminants. This paper firstly reports the level of contaminants in different fractions of recycled aggregates coming from a real case study. Results show that the wood content of 4-16 mm recycled aggregates is well within the strictest limit of the EU standard. However, there are still large visible pieces of wood and plastic in the +16 mm RA fraction which, albeit within the standards, does not satisfy the users. In order to solve this problem the feasibility of applying two existing technologies (near infrared sensor sorting and wind sifting) to remove contaminants, is studied. Furthermore, two types of online quality control sensors (hyper spectral imaging and laser induced breakdown spectroscopy) are introduced and a summary of their recent developments towards the quality control of RA are presented.