Utilisation of Post-Consumer Disposable Diaper Waste in Civil Engineering Applications: A Systematic Review of the Literature

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.