## 3 Results and Discussion
### Antimicrobial Properties  
A different hemp adding method was employed in this study. Figure 7 presents the HC antimicrobial properties against tested microorganisms. Interestingly, the sample containing only lime as a binder (HC1) shows the best antimicrobial activity against all tested model microorganisms. After only 30 min, a total inactivation of Gram-negative _E. coli_, Gram-positive _S. epidermidis_ and mould fungi _A. niger_ occurred (Figure 7a-c).  
Figure 6: Compressive strength of HC after 28 days of curing.  
Our results showed that each evaluated hemp concrete displays antimicrobial action and causes a significant (from 3 to 6 log) reduction in the bacterial cell and fungal spores after 60 min. However, the poorer antimicrobial performance demonstrated materials based on cement binder (specimens HC0 and HC3). The method of adding the hemp to the concrete and the type of binder both play a vital role in the antimicrobial activity. We suggest that the porous structure of hemp fibre increases the antibacterial effect when combined with lime as a binder in concrete. It is well known that lime concrete has slightly higher values of water sorption coefficients. An increase in pH negatively affects bacterial viability, particularly Gram-negative bacteria _E. coli_[40; 41]. The above observation was confirmed in our studies (Figure 7a). The same effect was observed for _Aspergillus niger--moulds_ that colonies damp or water-damaged building materials and elements or ventilation systems. According to [29], hemp concrete shows slow mineralisation under the action of lime which makes the composite inert and reduces the risk of not and mould growth.  
It has been widely accepted that the _Camnabis sativa_ L plants produce various (over 560) chemical compounds. Many present antimicrobial actions (e.g., cannabinoids, alco-hols, simple aldehydes, simple ketones, simple esters, lactones, steroids, terpenes, non-cannabinoid phenols, and flavonoid glycosides) [42; 43]. The evaluation of the chemical composition of flax and hemp fibres confirmed that some of these biologically active sub-stances are also extracted from raw materials. The parameters of hemp fibres depend on many factors like the type of variety, the climatic conditions, and the applied retting method, which all affect the chemical composition of the fibres [44].  
The antibacterial activity of different hemp shiv powders has been proven against _E. coli_. The results of tests performed according to ASTM E2149-10 showed that hemp shiv powder heated at 160 \({}^{\circ}\)C for two hours causes 90% bacterial reduction after one hour. It was also found that the particle size of shiv powder has no evident impact on the anti-bacterial performance [42]. Hemp fibres were chemically modified to create a new strategy for designing materials characterised by improved antimicrobial activity. Grafted hemp fibres with quaternary ammonium groups (HF-GTA) [45] demonstrated antibacterial activity,  
Figure 7: Inactivation of microorganisms in tested HC (**a**) _Escherichia coli_ (**b**) _Staphylococcus ep-idermidis_ (**c**) _Aspergillus niger_.  
resulting from the positive charge carried by the quaternary ammonium group and the negative charge of the bacterial cell membranes. There is a lack of knowledge on hemp fibres' mechanisms of action. Nonetheless, the bacterial death caused by the release of cytoplasmic substances and depletion of the electrochemical potential on the cell membrane was offered to explain these phenomena [30; 45]. Studies based on using hemp to modify concrete for antibacterial application have been reported only by [46]. In these studies, the lime hemp concrete was inoculated repeatedly with a high concentration of a mixed culture of fungi Aspergillus sp. and Penicillium sp. and the Gram-positive bacteria Bacillus sp. within two years. It was shown that all microorganisms were killed within two months of the first inoculation. Moreover, the tested materials showed no deterioration and were resistant to biodeterioration.