Characteristics of low density hemp-lime building materials

Hemp-lime is a sustainable low-carbon composite building material that combines renewably sourced hemp shiv (a coproduct of hemp fibre crop production) with formulated lime-based binders. To date, its primary use has been to form solid external walls in timber-framed buildings. This paper reports on the testing of 54 hemp-lime cylinders to compare their strength and stiffness properties at three different densities and at different ages up to 180 days. Three different and widely used formulated lime binders were studied. Phenolphthalein staining was used to map development of the carbonation front across specimen cross-sections. The strength and stiffness properties of the hemp-lime are comparable with other rigid insulation materials such as woodfibre board. The strength of hemp-lime increases with mix density and age. However, the strength of hemp-lime is not directly related to the individual strength of the binder, but rather is a function of complex and dynamic interactions between the hemp and the binder matrix, as well as the density and the percentage of wet binder mix at fabrication.