Interaction of plant particles / fibres and alkali activated materials: Critical review, unsolved problems and future direction of research.

Alkali-activated materials (AAMs) combined with plant fibres (PFs) and/or plant particles (PPs) represent construction materials with significant future potential. From an environmental perspective, reducing the use of Portland clinker-based cement and utilising rapidly renewable raw materials is highly favourable. Research on this topic has intensified in recent years; however, significant knowledge gaps remain. Of particular importance are the interactions between AAMs and PFs/PPs, which have so far been examined in only a limited number of detailed studies. Analysis of the existing literature reveals that the mechanisms governing the formation of gel phases in AAMs influenced by the presence of PPs (or PFs) have not yet been fully elucidated. Furthermore, the mechanisms of ion exchange and the interconnection between the inorganic structure of AAMs and the cellular structure of PFs/PPs remain insufficiently understood. Many studies are also limited by inadequate preparation of representative samples for chemical, phase, and microstructural analyses. The key outcome of this review is a proposed kinetic scheme illustrating the parallel timelines of AAM synthesis and the degradation of lignocellulosic components, including their mutual interactions. The scheme indicates that the degradation of lignocellulosic components overlaps with critical stages of AAM formation, suggesting that these processes are interdependent and play a crucial role in determining composite performance. By integrating previously fragmented knowledge, the proposed framework provides an important reference for future research on AAM/PP composites and contributes to a better understanding of the fundamental phenomena governing their behaviour.