Influence of hemp and straw fibres on the mechanical and rheological properties of a clay-based binder

Abstract

This thesis aims to investigate the influence of hemp and straw fibres on the mechanical and rheological properties of a clay-based binder. Density, length, aspect ratio and water absorption of the fibres are measured and fibre mixes with different proportions of straw and hemp are produced. Their compacity is measured and shows that when the fibre mix is composed by more than 50% of hemp, the compacity does not increase anymore. Slump tests are performed to study the influence of the fibres on rheology and find a mix with a good workability. They reveal that the spread diameter decreases with lower water to clay ratio or a higher fibre factor. Finally, a mix with a relative packing fraction of 25% and a water to clay ratio of 0.69 is used to produce clay blocks. The relative packing fraction is kept constant and the proportion of hemp and straw composing the fibre part are varied. The shrinkage of these samples is measured but no influence of straw and hemp proportions is found. The flexural, compressive and tensile strength of clay blocks is also measured. Fibre mixes with a high percentage of straw fibres optimize the flexural and tensile strength because they have a higher aspect ratio. The compressive strength instead, is maximized with a fibre mix containing a high part of hemp, since it has a higher density. These results underline the importance of the fibres on the mechanical properties of the clay-based binder.