A simple numerical model was set up to investigate the hydraulic behaviour of a regional dyke to improve understanding of the response under variable atmospheric conditions. The unsaturated hydraulic properties of the dyke body and the relevant foundation layers were calibrated either on the results of laboratory tests or on a national database, namely the Staringreeks, compiled for typical Dutch soils. The boundary conditions were imposed according to the weather history at the top, and to the pore pressures measured in the field at the bottom of the representative soil column. The results indicate that a simple 1D model is able to accurately reproduce the suction time history in the dyke core, provided the hydraulic conductivity and soil water retention properties are properly calibrated. The optimised hydraulic conductivities are typically two orders of magnitude higher than the saturated hydraulic conductivity from the laboratory tests, but comparable to the ones suggested in the database developed on field data. The work highlights that cautious evaluation of laboratory data is needed for field applications, and that direct information from the field should be used to validate numerical models in the presence of organic soils.

@en

An innovative route for plastics recycling is proposed, based on a combination of a logarithmic sorting process and colour plus high-resolution near-infrared (NIR) sensors. Although counterintuitive, it is shown that such a technology could sort clean flakes from rigid packaging waste into a very large number of different plastic grades with modest sorter capacity, provided that the chosen sensor is able to differentiate correctly between any two grades of plastics in the waste. Tests with high-resolution NIR on single pixels of transparent flakes from different types and brands of packaging show that this is indeed the case for a selection of 20 different packaging items bought from shops. Moreover, the results seem to indicate, in line with previous research, that high-resolution NIR data can be linked to important physical plastic properties like the melt flow viscosity and tensile strength. The attraction of deep sorting of waste plastics with relatively cheap sensors and modest sorter capacity is that the present industrial practice of tuning plastic grades to specific applications could coexist with commercial high-grade recycling at high levels of circularity and low carbon footprint. Therefore, advanced recycling technology is likely to be a societal alternative to phasing out plastics for rigid applications.

@en

Efficient mechanical and sensor-based separation of mixed solid waste into valuable secondary materials is a critical step in recycling and in the preservation of primary resources. To position the associated research field, we discuss backgrounds and links to societal and political developments within and outside the classical waste chain. An encompassing theory detailing separation processes is briefly introduced and explained using appealing examples. The roles of science and industry in the development of innovative technologies is clarified, finishing with examples of physical principles that are behind many contemporary separation technologies. Throughout, scientific challenges and technological advances are identified.@en

Automated optic inspection of concrete aggregates for pollutants (e.g. wood, plastics, gypsum and brick) is required to establish the suitability for reuse in new concrete products. Inspection is more efficient when directly sampling the materials on the conveyor belt instead of feeding them in a sampled stream to the sensor system. However, this does not reveal the true volume contents if the concrete and pollutants have segregated. Moreover, even if the concrete was homogenous, the relation between the number of visible pollutants and those in the volume varies depending on the size of the pollutants relative to the size of the concrete. A few fundamental issues must be investigated and technically resolved before this improved way of automated inspection becomes possible. First we investigated if it is possible to feed concrete at a high rate in a homogenous volume to a conveyor belt using batches of several tonnes. Second we investigated the surface-volume numbers for specified pollutants. Progress in the first part was a promising method of feeding that appears to produce not a true homogenous volume, but at least a volume with a mild and most of all reproducible degree of segregation for the different pollutants. This suggests the segregation could be corrected for in the data using a model. As a follow-up, a theory was developed that predicted accurately how thin plastic flakes of different sizes correlate with the number of visible flakes on the surface of a granular matrix. This theory is now extended and tested successfully in the laboratory using batches of 2-8 mm dry and moist river gravel with added 1% plastic flakes. @en

Optical inspection of a thick layer of granules for foreign particles does not directly reveal their true number and the more so if the layer is not homogenous. This raises questions such as “how do I know if the layer is homogenous?” and “what is the relation between the observable particles and the true number?” In this work a theory is proposed for granules with a minority of flat plates that explains their statistical properties under the homogenous condition. Moreover, it offers a simple test for homogeneity or, vice-versa, a way to calculate the true contents in a thick homogenous layer from surface observations of the number of plates. The theory is tested successfully on a uniform ball batch and on dry and moist 2-8 mm gravel batches. The latter served as scaled labsimulations of a concrete demolition waste stream. @en