Exploring oat husks as construction material in Portland-cement composites

In recent decades, the construction industry has increasingly embraced the use of plant-based materials derived from agricultural waste, aligning with global sustainability goals and climate change initiatives. Within this trend, questions arise about the potential of oat husks—an abundant, local, and underexplored agricultural by-product—as a sustainable alternative for use in Portland cement-based composites as a construction material. This study employed an experimental approach to address this question, adopting research strategies previously applied to other plant-based resources. The first approach aimed to investigate the calcination temperature range (400-700 °C) required to extract silica-rich reactive ashes from oat husks for use as a natural pozzolan and partial binder replacement. The second approach focused on utilising husks directly as particles, examining their impact on the matrix's properties, including optimising extractive removal through washing and studying the effects of extractives on cement matrix hydration. Additionally, surface treatments of these particles, including linseed oil, water washing, and a cement-pozzolan binder, were investigated to assess extractive leaching retention, degradability, and performance as aggregates or reinforcement in cement mortars. Lastly, the thermal conductivity of husk particles and their potential use as fillers in the composite's dispersed phase were examined. The pioneering conclusions of this study, exploring oat husks and their ashes, confirm that under specific calcination conditions, oat husks can act as a limited source of reactive silica. However, their use as particles is constrained by the presence of extractives, which adversely affect matrix hardening and overall strength. Regarding the strategy of particle treatment, coating—particularly with linseed oil—delays particle degradation over 28 days, thereby enhancing composite mechanical strength. Nevertheless, the husks do not effectively serve as reinforcements or aggregates. However, when used as fillers, the husks exhibit low thermal conductivity, improving the thermal resistivity of denser cement composites and demonstrating their potential as construction materials.