Impact of hemp shiv surface treatments on the mechanical and hygrothermal behavior of hemp concrete

The use of bio-based materials in the construction sector is becoming more widespread around the world. This is due to their potential to reduce the use of fossil resources and lower energy costs. These materials are particularly valued for their good hygrothermal properties. However, in terms of mechanical properties, they are much weaker than ordinary concrete. This limits their range of applications. Their low strength can negatively affect adhesion and, consequently, the long-term durability of the material. To better balance hygrothermal and mechanical performance to be able to consider the extension of potential applications, the impact of several parameters was studied. Among the key factors, influencing hempcrete properties are the surface treatment and particle size of the hemp shiv. These two factors have a crucial role in the porosity scale. In this study, the effect of two types of treatment was analyzed: caustic soda (NaOH), applied to large hemp shiv particles, and a plant-based epoxy resin, applied to both large and small particles. The treatment effect on the hemp shiv is significant in altering either mechanical or hygrothermal properties, depending on the type of treatment applied, whereas no notable effect was observed from particle size variation in this study. • Improvement of hemp concrete mechanical performance with hemp shiv treatments. • Surface treatments of hemp shives significantly influence hempcrete’s hygrothermal and mechanical performance over time. • Resin epoxy treatment of hemp shives enhances mechanical adhesion but reduces hygroscopic performance. • Fine shiv-based formulations exhibit poor durability due to inadequate matrix–aggregate adhesion and suboptimal mix ratios.