Vapothermal curing of hemp shives: Influence on some chemical and physical properties

Abstract

In a perspective of a sustainable development, a new generation of construction materials based on renewable plant resources has emerged to face environmental issues. However, the formulation of structural vegetal concretes (based on plant aggregates, a mineral binder and water) requires to enhance the compatibility of plant aggregates and binder.This paper presents an experimental study that evaluates the influence of vapothermal treatment, a promising method of cure under saturated water vapour pressure, on chemical composition and physical properties (loss of mass, absorption, and specific gravity) of hemp shives, entering in the composition of vegetal concrete. Indeed, developing bio-based concrete by vapothermal curing requires identifying the appropriate curing conditions both from the point of view of the hemp aggregates and the binder. In particular, these curing conditions must respect a compromise between the preservation of the physical and chemical properties of hemp shives and an efficient curing of the binder.Several levels of curing temperatures were defined between 150 and 230 °C (carbonization) and results of Treated Hemp Shives (THS) were compared with those of Raw Hemp Shives (RHS). The experimental results showed physical modifications explained by chemical transformations that affects the hemicellulose, cellulose and lignin composition of TSH and modifies the structure of hemp shives. The effect of vapothermal curing on hemp shives was determined through X-Ray Diffraction XRD and thermogravimetry TG. The loss of mass of THS increases as the curing temperature increases and specific gravity decreases. As for water absorption, which relates to the hydrophilic character of the treated hemp shives, it decreases slightly. This experimental study made it possible to assess the interest of a vapothermal curing in a prospect of using hemp shives in binder interaction in order to perform structural vegetal concrete.