Influence of the shives orientation on selected hygro-thermal properties of hemp-magnesium composite

Abstract

Magnesium binder is an alternative to lime binder in the technology of hemp-based composites. The advantage of using this binder is an increase in mechanical strength compared to those based on lime. These composites are mainly used as an insulating wall material, as a filling of a wooden frame structure. During compaction of the mixture, hemp shives tend to lay with fibers perpendicular to the compaction direction. The direction of the fibers in the shives, as well as the direction of the capillary pores affect the properties of the composite. The performance characteristics of a building partition insulated with a composite will vary depending on the direction of the shives in relation to the direction of the external factor. The outer wall is exposed to heat flow and water transport, e.g. by capillary action. The article presents the results of tests of the thermal conductivity and capillary rise of a composite densified in the direction perpendicular and parallel to the heat flux and moisture flow. Composites samples with a bulk density of about 370 kg/m3 were tested. Compaction of the mixture in the direction parallel to the heat flow decreased the thermal conductivity. Due to the reduced value of the thermal conductivity of the composite compacted parallel to the heat flux, such a technique can be used in prefabrication, e.g. in the production of wall blocks. This direction of compaction - perpendicular to the wall surface, and thus to the direction of capillary rise, also reduced the amount of uptaken up water and changed the course of water rising over time.