The alkali treatment increased slightly the density of the reinforced mortar.No significant difference could be noticed between the bulk densities of all mortar groups after wet/dry cycles compared to those of their non-aged counterparts.The difference of NaOH concentration by the fibres treatment does not significantly influence the physical properties of the fibre reinforced fly ash-based alkali-activated mortars.The reason for that is that even the lowest NaOH concentration was enough to separate the fibres from a fibre bundle.The increased NaOH concentration does not lead to more efficient fibres separation.This leads to no difference by the composites mixing and leads to similar composites structure formation.After the addition of the fibres,the compressive strength of the mortar decreases.It can be seen that at the age of 28 days,46% higher compressive strength is achieved in the plain mortar than in the non-treated fibre reinforced one.The addition of fibres leads to increased porosity and decreased density ,which consequently leads to a lower strength of the mortar.However,since the alkali treatment of fibres refines the fibre mortar’s pore structure,lowers the total pore volume and slightly increases the density of fibrereinforced mortars ,it consequently results in increasing their compressive strength.Additionally,the alkali treatment eliminates the fibrous filaments on the surface of hemp fibres as well as cleans the surface and separates the fibre bundles into fibrils ,which results in a better fibre dispersion within the matrix.Thisprovides better homogeneity of the composite,which in turn results in enhanced compressive strength.The concentration of the sodium itself in the fibres treatment proved to have no significant influence on the compressive strength of mortars.A similar trend but less pronounced was reported in fibre reinforced cementitious mortars after the fibres were treated with sodium hydroxide solutions.Jo et al.showed that 5 mm-long jute fibre treated with 0.5% sodium hydroxide increased the compressive strength of the fibre reinforced cement-based mortar by ca.5%.Yan et al.used 50 mm-long coir fibre to reinforce the cement-based specimens.After the fibre treatment with 5% sodium hydroxide solution,the compressive strength increased by only 0.8%.After the wet/dry cycles,cannabis grow racks the plain mortar shows 75% higher compressive strength than non-treated fibre reinforced mortar.
The drop of the strength after the fibres’ addition is related to the higher porosity of the fibre reinforced mortar.In addition to this,the hemp fibres are hydrophilic,so during the wet/dry cycles,they absorb water and swell.This can introduce micro-cracks in the matrix and lead to fibre–matrix debonding,thus preventing an optimal stress transfer within the matrix.However,the alkali-treated fibres significantly reduce the strength loss.It is shown that up to 50% higher compressive strength of the fibre reinforced mortar could be achieved after the wet/dry cycles when fibres are previously treated with 6% sodium hydroxide.Even more important is that 6% sodium hydroxide-treated fibre reinforced mortars experienced no loss of compressive strength after the wet/dry cycles.Without the fibre treatment,fibrereinforced mortars lose 20% of their strength when compared the result after wet/dry cycles to the non-aged mortar’ result.TG-DTA plots of the mortar samples are illustrated in Figs.13 and 14.The bound water in the gel-like binder phase and the heat of reaction required for its decomposition are reported in Table 5.A higher heat of reaction in the plain mortar compared to the fibre reinforced mortar groups indicates a larger amount and a better-incorporated binder phase in the formed alkali-activated matrix,characterized by a binding potential.Mortars show a broad endothermic peak in the temperature range of 100 ◦C to 300 ◦C,especially those without hemp fibres.The observed weight losses can be related to the bound water loss.It is shown that there is more bound water in the plain mortar than in the fibre reinforced mortars.This could be an indicator of the pore sizes of the binder gel since the bound water is tightly held only in very small pores.The more bound water,the more small-size pores appear.This correlates to the porosity obtained by the MIP.The plain mortar results in a more pronounced amount of the smallest pores than fibre reinforced mortars.However,the alkali-treated fibre reinforced mortars result in slightly enhanced bounded water content in their gel-like matrices and the more optimal pore sizes distribution than the nontreated fibre reinforced mortar.This consequently leads to their higher compressive strength.The flexural strength of the mortars follows the same trend as their compressive strength.The addition of fibres decreases the flexural strength of mortars.The flexural strength of the plain mortar is 34% higher than the one of non-treated fibre-reinforced mortar,tested at the age of 28 days.This is the result of increased porosity and decreased density after fibres addition,which consequently leads to a lower strength of the mortar.Even though the flexural strength is mostly influenced by the matrix itself,it is noticed that with the fibre treatment,the flexural strength of the fibre reinforced mortar increases.The difference in the concentrations of the applied sodium hydroxide influenced only slightly the flexural strengths of the mortars.A similar trend but less pronounced was reported in fibre reinforced cementitious mortars after the fibres were treated with sodium hydroxide solutions.Jo et al.showed that 5 mm-long jute fibre when treated with 0.5% sodium hydroxide,increased the flexural strengths of fibre reinforced cementbased mortars by 3.6%.Yan et al.used 50 mm-long coir fibre to reinforce the cementbased specimens.After fibre treatment with 5% sodium hydroxide solution,the flexural strength increased by 6.5%.After the wet/dry cycles,the plain mortar shows 46% higher flexural strength than the non-treated fibre reinforced mortar.This results from the hydrophilic nature of hemp fibres and their ability to absorb water and swell during wet/dry cycles.This could cause microcracks in the matrix and lead to fibre–matrix debonding,which decreases the flexural strength of a mortar.
The alkali-treated fibres could reduce the strength loss,by reducing the water absorption capacity of the fibres themselves.On average 23% higher flexural strengths are achieved after the wet/dry cycles.The flexural strength of all mortars after wet/dry cycles was on average 33% lower in comparison to their non-aged counterparts.In the fibre reinforced mortar groups,this difference is even lower in the case of 6%- and 9% sodium hydroxide-treated fibre reinforced mortar.These mortar groups show almost the same flexural strength drop as plain mortars.The most important contribution of fibre reinforcement in the mortar matrix is in the prolongation of crack initiation in the pre-cracked state and in the slowdown of crack propagation in the cracked state which results in enhanced energy absorption capacity under flexure.The presence of fibres in the matrix changes the mortars’ behaviour from quasi-brittle toward a more ductile one dependent on the type,geometry and dosage of the fibres.Plain mortars have almost no deformation capacity after the maximal flexural force is reached,indicating a negligible energy absorption capacity in the post-peak region.On the other hand,hemp fibre reinforced mortars have a significantly higher deformation capacity in the post-peak region,indicating a much higher energy absorption capacity than plain mortar.With the fibres treatment the energy absorption capacity can be increased even more.The fibre-bundles separation leads to better fibre dispersion through the matrix.In addition to this,the fibres treatment increases the roughness of the fibre surface resulting in a stronger fibre–matrix bond,which could be seen by the higher number of matrix particles attached to the treated fibres after 3PBT.The alkali pretreatment of hemp fibres leads to their surface fraying effect due to the degradation of the hemp components – hemicellulose and lignin.This chemical process could cause an improvement in interaction at the interface of the binding alkali-activated matrix and hemp fibers.At the age of 28 days,3% sodium hydroxide-treated fibre reinforced mortar has a higher energy absorption capacity than the nontreated fibre reinforced mortar.The further increase of the sodium hydroxide concentration in the fibres’ treatment slightly decreases a mortar’s energy absorption capacity ,keeping it still higher than the one of the non-treated fibre reinforced mortar.The enhancement of the energy absorption capacity with alkali treatment of fibres was also reported in cementitious materials.Jo et al. showed that the energy absorption of the jute fibre reinforced cement-based mortar increased by 6.5% when the fibres were treated with 0.5% sodium hydroxide solution,whereas Yan et al.reported an increase by 8.7% of the coir fibre reinforced cement-based mortar’s energy absorption when the fibres were previously treated with 5% sodium hydroxide solution.
When specimens undergo wet/dry cycles,the results show that nontreated fibre reinforced mortar has 343% higher energy absorption capacity than plain mortar.In the case of alkali-treated fibres,the energy absorption capacity of the non-treated fibre reinforced mortar increases even more,i.e.by 8%,19% and 15% for 3%-,6%- and 9% sodium hydroxide-treated fibre reinforced mortars,respectively.It seems that the higher concentration of the sodium hydroxide results in less hemicellulose in the fibres which leads to lower water absorption.This prevents the swelling of fibres,which causes micro-cracks in the matrix around the fibres and leads to fibre–matrix debonding.When comparing the results of the specimens after wet/dry cycles to those tested at the age of 28 days,it is seen that the addition of nontreated fibres to the matrix can significantly reduce the decrease of the energy absorption capacity of the plain mortar.With the alkali-treated fibres,cannabis grow system the decrease could be reduced even more.The energy absorption capacity of the mortar shows the lowest decrease after the wet/dry cycles when the fibres are treated with 9% sodium hydroxide.The fibres in that case reduce their water absorption capacity mostly.Besides,it could be seen that 3% sodium hydroxide treated fibre reinforced mortar before the wet/dry cycles has a higher percentage share of the energy absorption capacity in the later post-peak part of the force–displacement curve than after the wet/dry cycles.On the other hand,9% sodium hydroxide treated fibre reinforced mortar contributes more to the percentage share of energy absorption capacity in the post-peak part after the wet/dry cycles than it does before the aging.The reason could be that after the heat during the drying cycles,mortars continue with the further development of their system and increase the formation of mineral products while decreasing the amount of entrained pores.Including the higher fibres roughness after 3% sodium hydroxide treatment,this could lead to strong fibre–matrix bonds.The strong fibre–matrix bond leads consequently to a more pronounced fibres break after the failure of the matrix,which does not increase the post-peak part of the force–displacement curves.Therefore,in terms of the energy absorption capacity of the mortars when exposed to wet/dry cycles,9% sodium hydroxide concentration is considered as the most optimal fibre treatment.Hemp is an industrial crop that is commonly used in the textile,pharmaceutical,and paper industries.Hemp seeds are a by-product of hemp processing and contain 25–30% oil,20–30% protein and other nutritional substances.
Hemp seed oil contains more than 80% unsaturated fatty acids and a high content of functional components,including linoleic acid ,linolenic acid and other essential fatty acids,as well as tocopherols,vitamin A,minerals,etc.,which have a positive impact on cardiovascular,mental and immune diseases and can be added to foods as functional fats.HSO contains low levels of the psychoactive compound tetrahydrocannabinol in compliance with European Union and American standards.THC is a polyphenol with high antioxidant properties,which enhances the antioxidant properties of the product.Therefore,encapsulating HSO in emulsions can improve its bioavailability,avoid oxidation reactions,and broaden its application scope.Mikulcov´ a et al.prepared HSO oil-in-water emulsion with emulsifier Tween to improve its stability and antimicrobial activity.Jarzebski et al.used pea protein as a stabilizer for HSO emulsions and the emulsions showed good results in terms of particle size and encapsulation efficiency.Proteins with amphiphilic properties can be used as emulsifiers,and similarly,hemp seed proteins can be used to stabilize HSO emulsions.Compared to common high-quality proteins ,HPI is hypoallergenic,highly digestibility,has a good composition of essential amino acids.This means a more nutritionally superior amino acid pattern.In addition,its solubility is low,and its emulsification ability can be affected by external factors such as pH during treatment.HPI-stabilized sunflower oil emulsions were prepared by Dapˇcevi´cHadnađevd et al.It was found that the interaction between HPIs affected the transient flocculation network and contributed to the emulsion stabilization,and the emulsification activity of HPIs was similar to the protein solubility curve.Tang et al.have compared the functional properties of different proteins,where HPI has lower emulsifying activity and emulsifying stability than soybean protein,rice protein and pea protein.Therefore,external more energy efficient means or devices are needed to assist in the preparation of stable emulsions,such as ultrasonic,microwave,microjet,etc.High-intensity ultrasonic is an emerging processing method with frequencies typically in the range of 20–100 kHz and intensities in the range of 10–1000 W/cm2.