Experimental investigations on lime mortars reinforced with hemp braids

The need of experimenting sustainable components for building products is underlined by the prominent energy and raw material consumptions and carbon dioxide emissions for which the construction industry is responsible. Natural fibres, particularly hemp fibres, are worth of mention thanks to their acceptable mechanical properties and environmental advantages. The research aims to experiment two types of lime-based plasters reinforced with hemp braids, having different diameters, added in the mixture with different percentages. Two pre-mixed Natural Hydraulic Lime (NHL) mortars of M5 and M15 types, and three diameters of hemp braids (0.4 mm, 1 mm and 2.2 mm) in percentage by lime weight from 0.25% to 3% were considered. A first phase of the research consisted in physical tests to assess the amount of water absorbed by the hemp fibres to evaluate the plaster workability. Afterwards, only the mixtures with acceptable workability values were subjected to mechanical tests. The results of the laboratory tests showed that hemp braids produce a decrease in the workability of the plasters, that remains acceptable for low percentages of fibres. Compared to the unreinforced plaster, the braids allowed an increase in the flexural strength and a decrease of the compressive strength. In both mechanical tests it was evident the sewing and confinement effect of the fibres that led to a more ductile behavior of the mortar.