Mechanical Properties of Pre-Compressed Hemp-Lime Concrete

To answer different problems set by the 21st century, European Union is constantly updating the old and adapting new directives and regulations. One of these directives is 2010/31/EU as a piece of Energy package which sets forth a goal to reduce primary energy use by 20% and to achieve 20% reduction in greenhouse gas emissions by 2020. It also sets a task for all buildings built after 2020 to be zeroenergy buildings. To achieve these goals, next to existing building materials, a new, innovative, and more sustainable materials needs to be studied and implemented. One of these possible materials is lime-hemp concrete – a self-bearing thermal insulation material that consist of lime and hemp shives. Its mechanical properties seem promising, and thermal conductivity below 0,08 W/m*K is significant result for a material that sequesters more CO2 then is created in its life cycle. In the paper an effect of pre-compressed of hemp-lime mix before curing is studied. Two different binders were chosen (dolomitic lime and dolomitic lime with metakaolin) and three different compaction ratios – 50, 25 and 0 %. As expected, the compaction has a direct impact on compressive strength, as well as flexural. The elevated densities also have a negative effect on thermal conductivity, yet not as much if the same density would be achieved with addition of more binder. This method could help to produce lime-hemp concrete materials with better strength/thermal conductivity ratio. A further research of improved drying techniques is needed, as the samples had softer inner part, due to excess moisture during curing.


Introduction
Electronic version available www.sace.ktu.ltThis material uses inner part of the hemp stalk -hemp shives -a byproduct of hemp fiber manufacture as a filler and hydraulic lime as binder, it is known as lime-hemp concrete (LHC as referred in this article), hempcrete, hemp-lime and green concrete (Bruijn and Johansson 2014).It is mostly used as a self-bearing wall thermal insulation material in combination with structural timber frame.Developed in France in late 80`s (Walker and Pavía 2014) has now spread to other European countries like UK (Evrard et al 2014), Ireland, Poland, but have not yet acquired a significant amount of recognition.To understand the advantages of this material it will be reviewed through the prism of EU regulation N305/2011 (REGULATION (EU) No 305/2011) which sets forth 7 basic requirements for construction works and building materials: _ MECHANICAL RESISTANCE AND STABILITY -it has much higher mechanical resistance as typical thermal insulation materials, as it does not need any extra layers with materials and a plaster can be applied straight on the surface (Elfordy et al 2008).
_ SAFETY IN A CASE OF FIRE -the addition of mineral binders can improve hemp fire resistance up to class B by EN 13501-1 (Sassonia et al 2014) compared to typical E class of natural fiber insulation materials without mineral binder (Kyma and Sjo 2008).
_ HYGIENE, HEALTH AND THE ENVIRONMENT -LHC does not contain VOC`s or any other harmful substances.It also has great moisture buffering capabilities, which improves indoor air quality by preventing fungus and mold growth -which is a cause for allergic diseases (Lea et al 2010, Bruijn andJohansson 2014).
_ SAFETY AND ACCESSIBILITY IN USE -no major advantages/disadvantages.
_ PROTECTION AGAINST NOISE -due to its porous and fiber structure yet higher density than regular insulation materials, LHC insulates sound with both absorption and reflection providing better sound insulation at equal thickness (Carezo 2005).
_ ENERGY ECONOMY AND HEAT RETENTION -LHC has a relatively good thermal insulation properties -λ below 0,08 (W/m*K) which makes it compatible with other insulation materials (Sassonia et al 2014, Benfratello et al 2013) .
_ SUSTAINABLE USE OF NATURAL RESOURCES -it has been proven by several researchers that the whole manufacture process of LHC sequester more CO 2 then is released into the atmosphere, as the hemp plant takes up carbon dioxide in growing process and lime also gathers CO 2 in its hardening process.The amount of carbon dioxide sequestered is around 35 kg for 260 (Ip and Miller 2012) or 300 (Shea et al 2012) mm thick LHC wall.
As can be seen from the review, the LHC could be rather appropriate material to answer the challenges of the modern society.Yet it is not fully researched and tested in different environments, and the technologies regarding its manufacture, testing and disposal can also be improved.The goal of this research is to establish the effect of pre-compression of ready-mixed LHC material at different ratios and to test the correlation between density/thermal conductivity/ compressive strength/ flexural strength.The material will be compressed at three different ratios (0%, 25% and 50% from initial height) and two distinct binders will be used.The aim is to achieve better thermal conductivity/strength ratios than could be achieved by adding additional amounts of binder.

Materials
The hemp shives were not specially treated at laboratory, but were obtained from hemp processing plant in Kraslava, Latvia, as by-products of hemp fiber production.Shives are not fully separated from dust and some fiber, which has a negative effect on LHC properties.Granulometry of hemp shives can be seen in Fig. 1 and also other characteristics in Table 1.  is to establish the effect of pre-LHC material at different ratios ion between density/thermal trength/ flexural strength.The at three different ratios (0%, eight) and two distinct binders is to achieve better thermal than could be achieved by binder.
ere not specially treated at from hemp processing plant in ucts of hemp fiber production.ted from dust and some fiber, effect on LHC properties.s can be seen in Fig. 1 and also 1.
f used hemp shives Value

Sample preparation and curing
The proportion between hemp and binder was also elaborated during previous tests, so a 0.375/0.625hemp/binder ratio by mass proportion were used, binder/water ratio -0.66:1.Laboratory drum mixer was used to mix the ingredients.First, the hemp shives were put in the mixer along with a half of water necessary and mixed for 3 minutes, then the binder were put in, mixed for another 2 minutes, and then the rest of the water followed and the preparation continued for 3 minutes.After this process the binder had been uniformly distributed and was covering the surface of the shives.
Afterwards the ready mix were put in specially made moulds, which were designed to apply constant pressure to LHC defined by the ratio of height between uncompressed and compressed specimen.Mould is made out of 30 mm thick waterproof plywood, dimensions of uncompressed sample -350*350*120 mm (see Fig. 2).In all corners there are threaded rods with nuts which when tightened compress the sample by maximum 60 mm, which gives maximum compressive ratio of 50%.In this particular test three different ratios for both binders were used -0% (K3 and K6), 25% (K2 and K5) and 50% (K1 and K4).tural resources -it has been researchers that the whole LHC sequester more CO 2 then osphere, as the hemp plant takes growing process and lime also dening process.The amount of red is around 35 kg for 260 (Ip 0 (Shea et al 2012) mm thick the review, the LHC could be to answer the challenges of the t fully researched and tested in the technologies regarding its isposal can also be improved.
is to establish the effect of pre-LHC material at different ratios tion between density/thermal trength/ flexural strength.The d at three different ratios (0%, eight) and two distinct binders is to achieve better thermal than could be achieved by f binder.
ere not specially treated at d from hemp processing plant in ucts of hemp fiber production.ted from dust and some fiber, effect on LHC properties.s can be seen in Fig. 1 and also 1.

Sample preparation and curing
The proportion between hemp and binder was also elaborated during previous tests, so a 0.375/0.625hemp/binder ratio by mass proportion were used, binder/water ratio -0.66:1.Laboratory drum mixer was used to mix the ingredients.First, the hemp shives were put in the mixer along with a half of water necessary and mixed for 3 minutes, then the binder were put in, mixed for another 2 minutes, and then the rest of the water followed and the preparation continued for 3 minutes.After this process the binder had been uniformly distributed and was covering the surface of the shives.
Afterwards the ready mix were put in specially made moulds, which were designed to apply constant pressure to LHC defined by the ratio of height between uncompressed and compressed specimen.Mould is made out of 30 mm thick waterproof plywood, dimensions of uncompressed sample -350*350*120 mm (see Fig. 2).In all corners there are threaded rods with nuts which when tightened compress the sample by maximum 60 mm, which gives maximum compressive ratio of 50%.In this particular test three different ratios for both binders were used -0% (K3 and K6), 25% (K2 and K5) and 50% (K1 and K4).

Fig. 2. Moulds for compression
Before the ready mix was put, the moulds were covered with oil, to prevent the sticking of LHC to the mould.The samples of 0% compressive ratio were put in the moulds, slightly tamped and covered.When making the 25% and 50% samples, the mould were filled with the mix, and then The first binder (samples K1 -K3) used is formulated lime that has been elaborated during previous tests (Sinka et al 2013), it consists of 60% by mass DL60 dolomitic lime, produced by "Saulkalne" Ltd. and 40% metakaolin, obtained by burning kaolin clay at 800 0 C.In binder/sand ratio 1:3 it can obtain compressive strength as high as 10 MPa.Second binder (samples K4 -K6) is pure dolomitic lime which has also showed promising properties with hemp shives.

Sample preparation and curing
The proportion between hemp and binder was also elaborated during previous tests, so a 0.375/0.625hemp/binder ratio by mass proportion were used, binder/water ratio -0.66:1.Laboratory drum mixer was used to mix the ingredients.First, the hemp shives were put in the mixer along with a half of water necessary and mixed for 3 minutes, then the binder were put in, mixed for another 2 minutes, and then the rest of the water followed and the preparation continued for 3 minutes.After this process the binder had been uniformly distributed and was covering the surface of the shives.
Afterwards the ready mix were put in specially made moulds, which were designed to apply constant pressure to LHC defined by the ratio of height between uncompressed and compressed specimen.Mould is made out of 30 mm thick waterproof plywood, dimensions of uncompressed sample -350*350*120 mm (see Fig. 2).In all corners there are threaded rods with nuts which when tightened compress the sample by maximum 60 mm, which gives maximum compressive ratio of 50%.In this particular test three different ratios for both binders were used -0% (K3 and K6), 25% (K2 and K5) and 50% (K1 and K4).
Before the ready mix was put, the moulds were covered with oil, to prevent the sticking of LHC to the mould.The samples of 0% compressive ratio were put in the moulds, slightly tamped and covered.When making the 25% and 50% samples, the mould were filled with the mix, and then

Table 2
Density and thermal conductivity of the samples Table 3 Mechanical properties the nuts were tightened and the both sides of the mould closed in on each other by 30 and 60 mm.
The applied compression were removed after three days of curing in laboratory conditions (55±10 % RH and 20±2 0 C).After six days from the fabrication the samples were completely demoulded and placed vertically for quicker drying.The specimens were then allowed to dry in the same conditions and periodic weighting of the samples were done, to see if the drying process still continues.The evaporation of the water for all samples ended after two months, then the testing started.

Testing
Before the thermal conductivity test, the density of the samples were calculated by measuring the dimensions and weighting the samples.The thermal conductivity were measured in guidance of EN 12667 and EN 12939, using hot-plate method and FOX500 heat-flow measurer.
To test the compressive and flexural strength, the samples were sawed in necessary dimensions.The dimensions were 100*100*(height) mm cubic forms for compressive tests -three parallel and two crosswise to the tamping direction, one 100*250*height mm piece for each flexural strength.Mechanical tests were performed on ZWICK Z100 universal testing machine.The pressure applied -6 mm/min and a force-deformation diagram were recorded in the process.For compressive strength a stress at 10% deformation were recorded, for compressive crosswise and flexuraluntil failure.

Results
When the samples ceased to show any signs of drying, the density of the samples were calculated by measuring and weighting the samples.Afterward a thermal conductivity test on FOX500 were performed, the results of test can be seen in Table 2.The first thing that was observed when working with the samples -that the back side of the sample, is not so hard as the front side, as from the plates with no compression applied there were even some small bits that were crumbling of the back side.
When the samples were sawed into pieces, the problem revealed was even bigger, as the material had a strong layer only at the outside surface, the inner part of the LHC plate was softer.
For the samples without compression the inner part was too soft for a flexural strength prism to be sawed off, lime was in a form of powder.
During the compressive strength test parallel to the direction of compaction none of the samples showed any particular breaking point and deformed evenly.bserved when working with of the sample, is not so hard plates with no compression mall bits that were crumbling When the samples were sawed into pieces, the problem revealed was even bigger, as the material had a strong layer only at the outside surface, the inner part of the LHC plate was softer.For the samples without compression the inner part was too soft for a flexural strength prism to be sawed off, lime was in a form of powder.During the compressive strength test parallel to the direction of compaction none of the samples showed any particular breaking point and deformed evenly.In Fig. 5. a force-deformation diagram for the K1 three samples for compressive test can be seen.
It was observed that after removal of the pressure K1 and K4 samples most notably showed elastic deformation.These samples also displayed the best stress resistance and was removed from the testing machine in one piece, whilst the other samples failed.
It must be noted, that compressive test crosswise compaction direction shows a distinctive breaking point in the diagram, also the material itself failed and crumbled In Fig. 3. a force-deformation diagram for the K1 three samples for compressive test can be seen.
It was observed that after removal of the pressure K1 and K4 samples most notably showed elastic deformation.These samples also displayed the best stress resistance and was removed from the testing machine in one piece, whilst the other samples failed.
It must be noted, that compressive test crosswise compaction direction shows a distinctive breaking point in the diagram, also the material itself failed and crumbled completely.The value is about 1/3 of the compressive strength.
The material showed flexural deformation pattern similar of rigid materials -steady force-deformation line, then a forming of a Fig. 3 Force-deformation diagram for K1 in compression Fig. 4 Thermal conductivity/ density correlation crack in the middle of the sample and a failure.Flexural strength was there times lower than crosswise flexural strength, because material had soft inner core and rigid surface, which could withstand the applied force much better when positioned parallel to the force.
Firstly, as can be seen from Table 2. -compaction has a direct effect on density, yet the compaction coefficient and density doesn't correlate precisely, as , for example, the difference between K1 and K3 should be 0,5, yet it is 0,61.This is due to fact that the densities of samples before compression need to be similar, but it was not controlled, material was freely put in to moulds without tamping before compaction, but the K4 and K6 samples were tamped slightly.To evade this error in future, density of the samples need to be measured before compaction and similar results must be achieved.

Discussion
Secondly, the correlation between density and thermal conductivity can be seen from Table 2 and Fig. 4. and as expected -the thermal conductivity rises as the material becomes denser, because there are less air and better conducting lime particles are closer together.But on other hand -the increase in the density doesn't correlate with the available information in literature, where for the same amount of shives, different quantities of lime were added (Bruijn and Johansson 2014) but for similar densities much higher thermal conductivity was obtained.It can be explained by the fact that in this particular experiment the shives fill the empty air pores in compression process, not only lime, which worsens the thermal conductivity of LHC.
The material showed flexural deformation pattern similar of rigid materials -steady force-deformation line, then a forming of a crack in the middle of the sample and a failure.Flexural strength was there times lower than crosswise flexural strength, because material had soft inner core and rigid surface, which could withstand the applied force much better when positioned parallel to the force.

Discussion
Firstly, as can be seen from Table 2. -compaction has a direct effect on density, yet the compaction coefficient and density doesn't correlate precisely, as , for example, the difference between K1 and K3 should be 0,5, yet it is 0,61.This is due to fact that the densities of samples before compression need to be similar, but it was not controlled, material was freely put in to moulds without tamping before compaction, but the K4 and K6 samples were tamped slightly.To evade this error in future, density of the samples need to be measured before compaction and similar results must be achieved.
Secondly, the correlation between density and thermal conductivity can be seen from Table 2 and Fig. 4. and as expected -the thermal conductivity rises as the material becomes denser, because there are less air and better conducting lime particles are closer together.But on other hand -the increase in the density doesn't correlate with the available information in literature, where for the same amount of shives, different quantities of lime were added (Bruijn and Johansson 2014) but for similar densities much higher thermal conductivity was obtained.It can be explained by the fact that in this particular experiment the shives fill the empty air pores in compression process, not only lime, which worsens the thermal conductivity of LHC.From the chart (Fig. 4) it can also be seen that K4-K6 shows slightly lower density and thus also lower thermal The average thermal conductivity/density ratio for particular materials is about 0,005 W/m*K for every 50 kg/m 3 .Although lime is considerable a rigid material, forcedeformation diagram acquired from Zwick z100 and showing K1 samples [Fig.3.], calls for rethinking.Because it was observed that the inner part of the LHC slab is not fully hardened, it is safe to say that the inner part of the slab worked in elastic phase, while the outer part remained intact.This can be affirmed by the fact, that when removing some of the samples from the testing machine, they were virtually intact, contrary of the samples which were created in previous experiments and crumbled after the tests.
It can be seen from Table 3. and Figure 5. that density also has direct correlation with compressive strength -as the density rises, the compressive strength also rises.This can also be explained by the shorter distances between shives which provides more contact zone.The compressive strength loss with decreasing density is exhibited by both binders, although pure DL lime (K4-K6) binder showed poorer performance, which was expected, as the binder itself has a smaller compressive strength (Sinka et al 2013).
From Table 3. there can also be seen that compressive strength for LHC materials crosswise of the compaction direction are significantly lower than in parallel direction.This is due to the fact that without compression of the samples in this direction there are more open and empty spaces between shives, so a smaller contact zone and more voids to be filled by breaking shives.Compressive strength crosswise is around 4 -6 times lower than the regular compressive strength.
For flexural strength test only K1, K2, K4 and K5 prisms were sawed (Table 3.), as K3 and K6 samples were too soft and broke in the preparation process.The values of From the chart (Fig. 4) it can also be seen that K4-K6 shows slightly lower density and thus also lower thermal conductivity.This could possibly be only a technological error, as it is hard to achieve identical density of the material when it is put into the molds before compaction process.The average thermal conductivity/density ratio for particular materials is about 0,005 W/m*K for every 50 kg/m3.
Although lime is considerable a rigid material, force-deformation diagram acquired from Zwick z100 and showing K1 samples [Fig.3.], calls for rethinking.Because it was observed that the inner part of the LHC slab is not fully hardened, it is safe to say that the inner part of the slab worked in elastic phase, while the outer part remained intact.This can be affirmed by the fact, that when Fig. 5 Compressive strength/ density correlation 1 A correlation of LHC between density and thermal conductivity were confirmed, it is around 0,005 W/m*K for every 50 kg/m3 gained.Yet these observations don't match with results from previous test, so it is possible to assume that the inner voids were filled with more shives then in previous tests, which allowed to improve the thermal conductivity.
2 For the most compacted samples, the material in compression works in partly elastic defor- mation phase, as the most deformations are exhibited by the inner part of the slab and rigid outer layers didn't get invertibly compressed.
The material showed flexural deformation pattern similar of rigid materials -steady force-deformation line, then a forming of a crack in the middle of the sample and a failure.Flexural strength was there times lower than crosswise flexural strength, because material had soft inner core and rigid surface, which could withstand the applied force much better when positioned parallel to the force.

Discussion
Firstly, as can be seen from Table 2. -compaction has a direct effect on density, yet the compaction coefficient and density doesn't correlate precisely, as , for example, the difference between K1 and K3 should be 0,5, yet it is 0,61.This is due to fact that the densities of samples before compression need to be similar, but it was not controlled, material was freely put in to moulds without tamping before compaction, but the K4 and K6 samples were tamped slightly.To evade this error in future, density of the samples need to be measured before compaction and similar results must be achieved.
Secondly, the correlation between density and thermal conductivity can be seen from Table 2 and Fig. 4. and as expected -the thermal conductivity rises as the material becomes denser, because there are less air and better conducting lime particles are closer together.But on other hand -the increase in the density doesn't correlate with the available information in literature, where for the same amount of shives, different quantities of lime were added (Bruijn and Johansson 2014) but for similar densities much higher thermal conductivity was obtained.It can be explained by the fact that in this particular experiment the shives fill the empty air pores in compression process, not only lime, which worsens the thermal conductivity of LHC.From the chart (Fig. 4) it can also be seen that K4-K6 shows slightly lower density and thus also lower thermal conductivity.This could possibly be only a technological error, as it is hard to achieve identical density of the material when it is put into the molds before compaction process.
The average thermal conductivity/density ratio for particular materials is about 0,005 W/m*K for every 50 kg/m 3 .Although lime is considerable a rigid material, forcedeformation diagram acquired from Zwick z100 and showing K1 samples [Fig.3.], calls for rethinking.Because it was observed that the inner part of the LHC slab is not fully hardened, it is safe to say that the inner part of the slab worked in elastic phase, while the outer part remained intact.This can be affirmed by the fact, that when removing some of the samples from the testing machine, they were virtually intact, contrary of the samples which were created in previous experiments and crumbled after the tests.
It can be seen from Table 3. and Figure 5. that density also has direct correlation with compressive strength -as the density rises, the compressive strength also rises.This can also be explained by the shorter distances between shives which provides more contact zone.The compressive strength loss with decreasing density is exhibited by both binders, although pure DL lime (K4-K6) binder showed poorer performance, which was expected, as the binder itself has a smaller compressive strength (Sinka et al 2013).
From Table 3. there can also be seen that compressive strength for LHC materials crosswise of the compaction direction are significantly lower than in parallel direction.This is due to the fact that without compression of the samples in this direction there are more open and empty spaces between shives, so a smaller contact zone and more voids to be filled by breaking shives.Compressive strength crosswise is around 4 -6 times lower than the regular compressive strength.
For flexural strength test only K1, K2, K4 and K5 prisms were sawed (Table 3.), as K3 and K6 samples were too soft and broke in the preparation process.The values of flexural strength tests can be seen in Table 3.They were greatly influenced by the softer inner part of the slab as only the both outer crusts of the material worked in compression and strain.If obtained results are compared with similar studies (Walker et al 2014) then it can be seen that the inner removing some of the samples from the testing machine, they were virtually intact, contrary of the samples which were created in previous experiments and crumbled after the tests.
It can be seen from Table 3 and Figure 5 that density also has direct correlation with compressive strength -as the density rises, the compressive strength also rises.This can also be explained by the shorter distances between shives which provides more contact zone.The compressive strength loss with decreasing density is exhibited by both binders, although pure DL lime (K4-K6) binder showed poorer performance, which was expected, as the binder itself has a smaller compressive strength (Sinka et al 2013).
From Table 3 there can also be seen that compressive strength for LHC materials crosswise of the compaction direction are significantly lower than in parallel direction.This is due to the fact that without compression of the samples in this direction there are more open and empty spaces between shives, so a smaller contact zone and more voids to be filled by breaking shives.Compressive strength crosswise is around 4 -6 times lower than the regular compressive strength.
For flexural strength test only K1, K2, K4 and K5 prisms were sawed (Table 3), as K3 and K6 samples were too soft and broke in the preparation process.The values of flexural strength tests can be seen in Table 3.They were greatly influenced by the softer inner part of the slab as only the both outer crusts of the material worked in compression and strain.If obtained results are compared with similar studies (Walker et al 2014) then it can be seen that the inner softer part of the samples negatively influenced the performance.The flexural strength needed to be around ¼ of compressive strength, which is the approximate result of flexural strength crosswise.

Conclusions
Journal of Sustainable Architecture and Civil Engineering 2014/3/8 98 3 The insufficient hardening of the inner parts of the slabs is considered to be partly because of the excess moisture that couldn't evaporate fast enough through hardly compressed samples.This could be prevented in future with controlled and excessive drying of the samples.Also the relatively high density makes it harder for lime to carbonate, as this process can take even years for dense materials, such as mortars.
Fig. 1Size and shape of hemp particles

Fig. 1 .
Fig. 1.Size and shape of hemp particles for were then allowed to dry in ic weighting of the samples process still continues.The all samples ended after two ivity test, the density of the easuring the dimensions and thermal conductivity were 12667 and EN 12939, using heat-flow measurer.andflexural strength, the ecessary dimensions.The eight) mm cubic forms for lel and two crosswise to the 0*height mm piece for each tests were performed on ing machine.The pressure e-deformation diagram were mpressive strength a stress at d, for compressive crosswise to show any signs of drying, calculated by measuring and ard a thermal conductivity ed, the results of test can be

Table 3 .
Mechanical properties