Recycling

Waste electrical and electronic equipment (WEEE) represents a heterogeneous waste stream containing valuable non-ferrous metals, yet RGB-based characterization of pre-concentrated output fractions (6–10 mm) recovered from shredded WEEE remains underexplored. Therefore, in this study, we investigate the feasibility of particle-level instance segmentation and propose a process-oriented temporal assessment method. By linking end-to-end detection time (E2E) to particle residence time (PRT) within the sensor’s field of view, the method assesses the preliminary temporal suitability of deep learning (DL) models for future inline applications. For this reason, ten state-of-the-art DL-models (YOLO and Mask R-CNN) were evaluated on a novel particle-level WEEE benchmark dataset. In addition, we examine how visual material characteristics and input variability affect detection performance and the training process. Results demonstrate that YOLOv9 achieved an mAP@0.5 of 75.16% across all material classes, while E2E remained below the PRT, indicating inline feasibility for the investigated application. Replacing the ResNet-50 backbone of Mask R-CNN with VGG-16 reduced E2E from 26 ms to 21.1 ms (53.3%) and increased mAP@0.5 from 67.30% to 74.82%. Our work establishes groundwork for future inline applications, emphasizing the interaction between process constraints and detection time. Overall, these findings advance sensor-based real-time characterization of pre-concentrated fine fractions from shredded WEEE, contributing to future inline applications toward Recycling 4.0.

Crushed brick waste (CBW) is a major fraction of construction and demolition waste, yet design-oriented shear strength data for its reuse in earthworks remain scarce. This study examines CBW–soil mixtures within the block-in-matrix soil (Bimsoil) framework and quantifies their shear strength at large scale. The block-to-matrix contrast was checked through elastic modulus, friction angle, and unconfined compressive strength ratios. Large-scale multistage direct shear tests with a double shear-plane configuration were performed on one specimen per mixture, with the volumetric block proportion (VBP) ranging from 0% to 67%, and the failure point of every stage was defined with a single strain-based criterion. The friction angle increased from 21.3° to 38.3° with VBP, following a significant linear trend (R² = 0.94), whereas the apparent cohesion dropped from 29.1 kPa for the natural soil to 10.6–18.5 kPa for the mixtures, without a significant trend among them. For VBP ≥ 48%, the envelopes intersect that of the natural soil at 46–52 kPa, within the tested range, so the natural soil governs at lower and the mixtures at higher normal stresses. In illustrative 6 m high gabion- and geogrid-reinforced soil walls, VBP of 67% reduced the gabion weight and geogrid area by 44.4% and 59.1% and by 28–45% and 19–61% over the examined wall heights and surcharges. These results provide a material-specific basis for selecting CBW content in embankments and retaining-wall backfills.

Disposable post-consumer diaper (nappy) waste represents a growing and compositionally complex waste stream containing recoverable materials with considerable potential for civil engineering applications. This systematic review critically evaluates the utilisation of post-consumer disposable diaper waste and its recovered constituents across civil engineering applications, linking laboratory-scale research with emerging industrial recycling and material-recovery pathways. The review demonstrates that engineering performance is strongly dependent on the intended application, processing method, replacement level and recovered material fraction. Direct incorporation of processed nappy waste provides a relatively simple waste-diversion route but is frequently associated with reductions in mechanical strength, increased porosity and variability arising from material heterogeneity. In contrast, selective recovery enables superabsorbent polymers, cellulose fibres and polyolefin fractions to be utilised according to their distinct moisture-regulating, reinforcing and material-modifying properties. Applications in concrete, mortar and plaster, masonry products, and soil and geotechnical engineering demonstrate differing levels of technical feasibility, performance benefits and limitations. Importantly, this review integrates evidence from civil engineering applications with existing and emerging industrial nappy-recycling technologies, highlighting opportunities for component-based resource recovery within a circular-economy framework. Key priorities for future research and implementation include standardisation and characterisation of recovered materials, assessment of long-term durability and field performance, development of scalable and hygienically robust recovery processes, and comprehensive life-cycle environmental and economic evaluation.