Measurements show that values of thermal conductivity coefficient for composites are in a range 0.125- 0.065 W·m-1·K-1.In the paper,it was reported,that the thermal conductivity coefficients of hardened composites based on MgO-cement and unmodified hemp shives of another origin were 0.111- 0.23 W·m-1·K-1 and comparable to other building materials such as aerated autoclaved concrete.The obtained values of absorbability of composites made with chemically treated hemp shives are higher than in the case of referential composite.According to the measurements,bulk density of composites was found to be in the range of 1220-1440 kg·m-3.As shown,only chemical treatment of hemp shives with NaOH leads to slightly higher density value of composite compared to composite based on unmodified hemp shives.In the case of composites with modified hemp shives,the highest value of compressive strength was recorded for composite made from hemp shives treated by Ca2.Decrease in compressive strength values for all samples with chemically treated hemp shives in comparison to referential composite was observed.This fact is contrary to previously published data on lime composites based chemically treated hemp fibres >23@.The obtained results are difficult to interpret.It is most likely that many factors could cause this phenomen.Various unfavourable factors acting when processing the hemp shives and mixture could be considered in clarifying of this fact,e.g.short time of hardening,content of crystalline cellulose,varying polymerization degrees of cellulose and degradation of hemp fibres surface,heterogeneity of hemp shive slices in comparison to fibres as well as used binder MgO-cement,grow cannabis in containers mainly the action of alkaline components combination.
Measurements show that values of thermal conductivity coefficient for composites are in a range 0.125- 0.065 W·m-1·K-1.In the paper,it was reported,that the thermal conductivity coefficients of hardened composites based on MgO-cement and unmodified hemp shives of another origin were 0.111- 0.23 W·m-1·K-1 and comparable to other building materials such as aerated autoclaved concrete.The obtained values of absorbability of composites made with chemically treated hemp shives are higher than in the case of referential composite.According to the measurements,bulk density of composites was found to be in the range of 1220-1440 kg·m-3.As shown,only chemical treatment of hemp shives with NaOH leads to slightly higher density value of composite compared to composite based on unmodified hemp shives.In the case of composites with modified hemp shives,the highest value of compressive strength was recorded for composite made from hemp shives treated by Ca2.Decrease in compressive strength values for all samples with chemically treated hemp shives in Maximum power consumption comes to building heating,which depends on the efficiency of building envelopes.Building sector energy consumption covers 50% of the total energy consumption.Reducing building energy cost it is necessary to increase the energy efficiency of complex elements in envelopes,both in their production and operational conditions.In order to build environmentally friendly,energy efficient and affordable buildings,it is appropriate to link the agricultural and construction industries.Environmentally friendly buildings can only be built when there is the use of renewable resources.Insulation materials are increasingly used in the production of renewable resources such as hemp,flax,jute straw,various kinds of wood.Hemp is one of the most rational plant because all of its parts are used in industry.Hemp seeds are used for the edible oil extraction and bio-diesel production,bast fibers are used in special paper production,cars,construction and other industries.Fiber is obtained by soaking the hemp stalks in order to separate the fibers and non-fibrous components called hurds.Hemp hurds are ligneous woody tissues,which are considered as fiber products obtained by secondary manufacturing.Although the usage of new hemp hurds is being developed,but most of them are used for animal litter and in construction only 5%.The hemp fiber insulation is made of composite materials.
Scientists investigated the material from hemp fibers,hurds and a binder,they exhibited low thermal conductivity which varied from 0.0393 W/ to 0.0486 W/,when density was from 40.3 kg/m3 to 77.9 kg/m3 respectively.Conducted analysis by Finnish scientists has showed that the thermal insulation materials made from hemp or hemp and flax fiber mixture with density varying from 5 kg/m3 to 100 kg/m3 have the thermal conductivity ranging from 0,033 W/ to 0.094 W/.Hemp hurds are suitable for the production of thermal insulation composites due to their porous structure consisting of small pores,and due to this good strength and thermal properties can be achieved.Hemp hurds are loose-fill material,so it can be characterized by two types of porosity,i.e.internal particles porosity and porosity of the particles formed between particles.By the method of 3D tomography foreign scientists had determined that porosity of hemp hurds was of 57%.The size of pores formed between the particles depends on the texture of hurds and it is about 1 mm.The inner porosity of hemp hurds consists of 15% of 70 μm sized pores and 85% of 400 μm pores.Foreign scientists studied hemp concrete,in which the binding material was lime.The results showed that compressive strength was from 0.2 to 1.2 MPa and the modulus of elasticity – from 3 to 90 MPa.Elford 2008 also investigated the thermal conductivity of hemp concrete with lime binder.The thermal conductivity of specimens with a density ranging from 417 kg/m3 to 551 kg/m3 varied from 0.179 W/ to 0.485 W/.Swedish scientists studied the mechanical properties of composite materials from hemp hurds,fibers and several different binding materials.Compressive strength of mixture of cement and lime and only cement,varied from 0.15 MPa to 0.83 MPa,and the modulus of elasticity varied from 12.6 MPa to 28.0 MPa respectively when the density of the specimens ranged from 587 kg/m3 to 733 kg/m3.Literature analysis has shown that lime is usually used as a binding material for tests of composites from hemp hurds.The usage of other binding materials has been barely studied,so the aim of this work is to figure out how to use binder in order to obtain omptimal strength and thermal insulating properties.Now-a-days,natural fibers reinforced composites exhibit the superior mechanical properties than synthetic fiber reinforced polymer composites due to its inherent properties.
The mechanical properties such as tensile strength,flexural and impact strengths of natural and synthetic fibers reinforced polymer composites with different fiber volume were evaluated by Ramesh et al..The result indicated that,there is the significant improvement in mechanical properties and the process of hybridization reduces the risks related to the environmental concern.Sapuan et al. fabricated the composites by using banana fiber is a waste product of banana cultivation and which is easily available in tropical countries like malaysia and south india.This fiber has many advantages and holding high mechanical strength when compared to the synthetic fibers.They have prepared three samples with different geometries and evaluated the maximum stress value and young’s modulus along two directions and found the maximum deflection under the maximum load conditions.Ramesh et al. carried out an experiment to evaluate the tensile and flexural properties of hybrid composites and the results are compared.Form the experiment,they found that the incorporation of natural fibers such as sisal/jute with glass fiber improve the tensile and flexural strength and these composites play a vital role in the field of engineering and technology.They suggested that these hybrid composites can be used for medium strength applications.Venkateshwaran et al. studied the mechanical properties such as tensile strength,flexural strength,impact strength and water absorption rate of sisal and banana fibers reinforced epoxy composite materials.They have observed that there is the significant improvement in mechanical strength and reduction in water absorption rate while hybridizing the sisal fiber up to 50% by weight with banana fiber reinforced epoxy composites.The banana and GFRP composites have good tensile property with minimum deflection when compared to the flax and GFRP composites.Also the banana and flax fiber reinforced composites holds more flexural and impact strengths when compared to the flax and glass fiber reinforced polymer composites.Natural fiber reinforced composites are renewable,biodegradable,environment friendly,light weight material when compared to the synthetic fiber reinforced composites.The potential applications of these composites are growing rapidly in many engineering fields especially the cost of the material is main factor and to improve erosive environment.The mechanical properties of sodium hydroxide treated natural fiber composites under saturation pressure can be improved without any major changes in mechanical behavior.Yuanjian and Isaac have investigated the impact and fatigue behavior of non-woven hemp fiber composites which is reinforced with polyester and found that there is the remarkable improvement in such properties.Li have evaluated and correlated the compressive strength,flexural strength,toughness,pot for cannabis specific gravity and water absorption rate of hemp fiber reinforced composites with different compositions.
The water absorbing ratio and the linear specific gravity of the composites are gradually reduced by adding the hemp fiber with concrete matrix.They have observed that the fiber content by weight is the important factor which affects the compressive and flexural strength of HFRC.Hemp fiber has superior reinforcement property while increasing tensile property and strong toughness in an alkali environment.Kobayashi et al. investigated the processing and characterization of hemp fiber textile composites with micro-braiding technique and found that the hemp fiber is suitable reinforcement for textile composites.Kabir et al. studied the mechanical property of chemically treated hemp fiber reinforced composites.They found that due to the rapid climate changes in environment,the physical and geometrical characteristics of natural fiber and synthetic fiber components are affected and the fibers are undergoes some irregularities and lose the maximum load carrying capacity of the materials in engineering applications.For better surface finish of the hemp fiber composites the chemical treatment process like alkali,acetyl and silane treatments are carried out.From this study they have found that the tensile strength of untreated fiber composites is much greater than the chemically treated fiber composites.The natural fiber reinforced composites were fabricated with hemp/paper/epoxy and flax/paper/epoxy by adding the paper on the both surfaces of hemp or flax unidirectional fibers and the composites are tested under tensile loading conditions.These tensile properties are compared with unidirectional composites with absence of paper between layers of composites.They found that the unidirectional natural fiber composite with one or two layers of thin paper holds the minimum variability in tensile strength and elastic modulus.The tensile strength and delamination properties of laminated composites with paper were improved when compared to without paper unidirectional composites and the modulus are slightly reduced when compared to epoxy composites.Banerjee et al. have conducted the micro-mechanics analysis of hybrid composites by using FEA software.The different hybrid laminates are prepared by using short carbon fibers and glass fibers which is reinforced with polypropylene.In this study,the elastic constant and strength properties have evaluated by using analytical formula and the results are compared with FEA results.They have observed that the negligible variability in elastic constants and longitudinal strength properties.They also found that the significant variability in transverse strength properties.Many researchers have reviewed the experimental data about hybrid composites and they observed that rule of hybrid mixtures is the prime factor to predict the mechanical properties of unidirectional interplay hybrid composites.In the present experimental study,the mechanical properties of banana–hemp–glass fiber reinforced composite materials are evaluated.The banana–hemp–glass fiber reinforced composite materials are fabricated by hand lay-up process.The properties such as tensile,flexural and impact strengths are studied and presented in detail.The results indicated that the addition of banana and hemp fibers in the glass fiber composite materials improve the mechanical properties.The base plate was cleaned of rust by scrubbing with an abrasive paper.Then the surface was allowed to dry after cleaning it with a thinner solution.After drying,the surface was coated with silicon gel.The surface was given a few minutes to get it set for the mold lay-up.The epoxy resin and the hardener are mixed in the proportion of 10:1.The curing time or the pot life,which is how it is usually notified in the laboratory charts,was 20 minutes once mixed.The care must be taken so that the resin does not cure in the curing pot itself.A constant watch over the blend in the pot was made with the aid of a stop watch.Initially the natural fibers are dried with sunlight for 3 to 5 hours.The first laminate is fabricated by using banana and glass fibers with epoxy resin over the base plate.This laminate consists of three layers glass fiber and two layers banana fiber was fabricated by hand lay process.The size of the fabricated laminate is restricted to 300×300×4 mm.The top,middle and bottom layers of each laminate are consist of glass fiber and the second and fourth layers are filled with natural fibers.Similarly the hemp-glass fiber and banana-hemp-glass fibers with epoxy resin laminates are prepared by same hand lay method.Then the three sets hybrid laminate was cured under the loaded condition for 12 hours with the help of the weight press.