The effect of wheat starch addition on water transport by capillary action in acomposite based on clay and hemp shives

Abstract

One of the assumptions of sustainable construction is the use of low-processed materials and those with a propitious carbon footprint. An example of a material that is used in raw form is clay. Its binding process consists in drying the mixture developed on its basis, e.g. mortar. It can be successfully used in construction in an unfired form. In turn, an example of a material of plant origin is hemp shives, which, due to their porosity and hygroscopic properties, are used in construction, e.g. in hempcrete. Lightweight mixtures based on clay and plant filler (mainly straw) are also used as insulating filling of a frame wall. However, due to the content of plant components and the way the clay is bound, they are characterized by low mechanical strength and lack of resistance to water, which causes the clay to wash out. One way to improve the properties of clay related to water is to stabilize it with biopolymers. This work focuses on the assessment of the possibility of modifying a clay-hemp composite with the addition of wheat starch in the amount of 15 %, as aweight substitute for clay. Various methods of biopolymer processing or sample maturation conditions were taken into account. The developed composites were characterized in terms of their ability to capillary water absorption. Additionally, due to the anisotropy of the proposed material, the influence of the direction of water transport in relation to the direction of sample compaction was also investigated. The influence of the presence of biopolymer on the density, porosity and shrinkage of the composite was also assessed.