Abstract
Organic admixtures based on polysaccharides are used in construction for modifying the properties of mortars and concretes. Gum arabic is an example of a polysaccharide-based biopolymer. The aim of the article was to investigate the possibilities of improving the strength parameters of a binder paste based on hydrated lime and metakaolin. The paste was modified with powdered gum arabic at 1%, 3% and 5% (by mass) as a partial replacement for the binder mix. The influence of the admixture on the pore size distribution as well as flexural and compressive strength was investigated. The admixture enhanced the total porosity of the paste, increasing the pore diameter compared with the reference formulation. The increase in porosity, in turn, did not reduce the mechanical strength. Conversely, the admixture in the amount of 3% and 5% caused a significant increase in the flexural (by about 300% in relation to reference paste) and compressive strengths (by 25% and 60%, respectively). The tested pastes were used as a binder in a composite based on hemp shives. The influence of binder modification on the water absorption and compressive strength of hemp concrete was tested. The strength of the composite soaked in water was also tested. The modification of the binder with gum arabic in the amount of 3% and 5% increased the compressive strength of hemp concrete (not soaked in water) by 53% and 92%, respectively and reduced the mass absorptivity by 6.6% and 10.4%, respectively.
Highlights
Hemp concrete is mainly used as insulation filling in timber frame wall structures
It consists of hemp shives and a binder based on hydrated lime
Larger amounts of metakaolin were applied in other works [9,28], it was decided to use the lesser amount, expecting that the admixture of gum arabic will provide an additional increase in strength
Summary
Hemp concrete (hemp-lime composite) is mainly used as insulation filling in timber frame wall structures It consists of hemp shives and a binder based on hydrated lime. This type of lime is used to produce mortars or other composites, presently this is mostly in a powdered form but in the past was primarily in the form of lime putty [1]. This binder hardens very slowly in the carbonation process, i.e., calcium hydroxide binds carbon dioxide in the air in the presence of moisture. Due to the slow setting and hardening process of lime, for practical reasons, this binder is modified with additives or admixtures that speed up setting, improve strength, and enhance frost and water resistance
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