However, there is also a by-product from the waste plastics’ recycling process – a heterogeneous mix of plastics with poor mechanical properties. In general, the most common way of handling this by-product is incinerating or landfilling it. Another more environmentally-friendly option is using it as a raw material for manufacturing lightweight construction material, something that the project NUMIX (High performance lightweight aggregate for concrete from recycling of plastic waste) is highly involved with. This three-year project has been funded by the European Union through CIP programme, a public grant funding for demonstration programme, and will come to an end in 2012.
The by-product of mixed plastic waste can be processed into two types of products; flakes and granules, and the aforementioned project aims to promote these two products and its production processes. The different steps of the production process include segregating, grinding and cleaning the mixed plastic waste. The further densification, cooling and physical separating (sieving) of the material results in a product called Densified Flakes. These flakes are used as aggregate for concrete and mortar and are also the raw material for creating the other product, Expanded Granules.
The Expanded Granules are produced through a foaming process, extruding granules from flakes using gypsum powder as blowing agent. The obtained granules are used as an aggregate for lightened structural and non-structural concrete. The two products can be used separately or together in the same construction materials.
The testing processes within the project have been conducted in a number of plants to improve the extrusion line and the production capacity. To evaluate process sustainability, environmental indicators were calculated through Life Cycle Analysis (LCA) and tests for CE marking were carried out. Characterization and validation tests proved that the new aggregates can be successfully used for production of bricks, screed coats and other products where thermal insulation is a critical issue as the aggregates showed a decrease in thermal conductivity of 25 % compared to the traditional material expanded clay. More specifically, the tests showed that the Expanded Granules can be a valuable substitution for the expanded clay that, besides the improved insulating properties, is giving main achievable improvements of weight reduction and mixing water control (i.e. decreasing variability in water content). The extensive testing also gave indications on how the physical and chemical properties of these aggregates can be obtained in the long term and the results have been included in the design of industrial processes and equipment.
As the final products have been realised, the technology readiness level of the two products is estimated to be a 9 on the TRL scale. On-going work within the project is now focusing on market establishment through development of demonstration products that will include both the flakes and granules in bricks to demonstrate their thermic and acoustic capabilities. The Densified Flakes have already been introduced to the market and are now being sold in small scale by one of the consortium partners in Italy.