Natural Fibers in Composite Materials for Sustainable Building: A State-of-the-Art Review on Treated Hemp Fibers and Hurds in Mortars

In recent years, natural-fiber composite building materials have experienced a revival and have become an important area of interest for the international building and scientific community as a sustainable solution for new constructions and restoration interventions. Natural fibers are obtained from renewable sources and are thus environmentally friendly, while at the same time they do not harm human health, as they do not contain toxic substances. Furthermore, natural reinforced composites present enhanced thermal and acoustic properties. However, the variety of components, the presence of hydroxyl groups, and the surface impurities which plant fibers possess, create a series of issues related to the design of composite materials, as they affect their final properties. Aiming to optimize the physical and chemical characteristics of fibers, several treatments have been applied. International research focuses mainly on hemp fibers, which are considered particularly durable and have thus been extensively studied. This literature review discusses the properties of hemp fibers and hurds, treatments which have been applied up to today, and their effect on the fiber and hurds, as well as the composite materials and discusses future trends. Mortars reinforced with treated hemp present mechanical benefits in most of the cases, such as higher flexural and tensile strength. Also, the improved adhesion between hemp and mortar matrices is commonly accepted by researchers.