Effect of compaction on mechanical and thermal properties of hemp ...

Effect of compaction on mechanical and thermal properties of hemp concrete Tai Thu Nguyen* — Vincent Picandet* — Patrick Carre* Thibaut Lecompte* — Sofiane Amziane** — Christophe Baley* * Laboratoire d’Ingénierie des MATériaux de Bretagne (LIMATB) Université de Bretagne Sud, Centre de Recherche de Saint-Maudé BP 92116, F-35631 Lorient cedex ** Laboratoire de Mécanique et Ingénieries (EA 3867 - FR TIMS/CNRS 2856) Université Blaise Pascal 24, avenue des Landais, BP 206, F-63174 Aubière cedex ABSTRACT.

Some preliminary studies, dealing with the process optimisation of pre-cast building elements made of Lime and Hemp Concrete (LHC), have shown that compression during casting lead to significant improvements: better mechanical characteristics and facing. However, this compaction leads to an increase of the weight to volume ratio and to a decrease in porous volume. Thus, the amount of entrapped air inside material, which contributes to decrease the thermal conductivity, is lower. Our data actually show a slight increase in thermal conductivity when compactness increases. The goal of this study is to compare the effect of compaction during casting on both mechanical and thermal characteristics of hardened specimens in order to evaluate the relevance of such a process. RÉSUMÉ. Une étude sur l’optimisation du procédé de préfabrication d’éléments de construction composés de béton de chanvre, mélange chaux-chanvre, a montré que leur compactage à l’état frais conduisait à une amélioration notable de leur qualité : meilleures caractéristiques mécaniques et qualité de parement. Toutefois ce compactage conduit à une augmentation du poids volumique du matériau et par conséquent à une diminution de sa porosité. Le volume d’air occlus conférant une faible conductivité thermique au matériau y est donc plus réduit. Nos mesures montrent effectivement une légère augmentation de la conductivité thermique du matériau avec sa compacité. Cette étude a donc pour objectif de confronter les effets du compactage lors de la mise en œuvre sur les caractéristiques à la fois mécaniques et thermiques d’éprouvettes durcies et d’évaluer la pertinence d’un tel procédé pour leur élaboration. KEYWORDS: hemp, lime, sustainable building, green materials, thermal insulation, mechanical behaviour. MOTS-CLÉS : chanvre, chaux, comportement mécanique.

écoconstruction,

écomatériaux,

isolation

thermique,

DOI:10.3166/EJECE.14.545-560 © 2010 Lavoisier, Paris

EJECE. Volume 14 – No. 5/2010, pages 545 to 560

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EJECE. Volume 14 – No. 5/2010

1. Introduction The awareness of the environmental impact of building has lead to a focus on green or alternative materials creating a context in which Lime and Hemp Concrete, LHC, has many assets. This product has the advantage of presenting a weaker ecological impact during its life cycle (Boutin et al., 2005); its energy balance, emission of CO2 or pollutants is significantly lower than traditional building materials, based on Portland cement in particular. This is an important point as building activities need 25 to 40% of the totality of the energy produced in OECD (OECD, 2003) (Constatinos et al., 2007). This industry also produces a third of carbon dioxide emissions in the atmosphere (Diana et al., 2007; IPCC, 2000; Price et al., 2006). Due to the low density and high porosity of the hemp shives, the combination of hemp and a cementitious binder creates a building material with properties that differ from those of conventional concrete. It has a lower density and lower thermal conductivity. Generally it ranges from 0.06 to 0.19 (W.m-1.K-1) for dry apparent densities between 200 and 840 kg/m3 (Arnaud, 2000) (Cérézo, 2005). However, its strength is very low compared to usual building materials. Currently, the compressive strength of this material is less than 2 MPa (Bütschi, 2004; Eires et al., 2005; Elfordy et al., 2008). The low compressive strength in combination with the low Young’s modulus of the LHC mixtures, approximately 20 MPa (Association construire en chanvre, 2007), indicates that the material in its present form cannot be used as a load bearing material. More rigidity and higher compressive strength are needed (Bruijn et al., 2009). Currently, LHC is mainly used in combination with a load bearing wooden framework or to make an additional layer on a traditional load bearing wall to ensure thermal and/or acoustic insulation. Depending on its composition, it can also be used in floors and roofs (Cérézo, 2005). Moreover, most of the research work in this area has been focused on thermal and hydrothermal properties of the LHC. However, mechanical properties have also been measured (Cérézo, 2005; Eires et al., 2005; Elfordy et al., 2008; Bruijn et al., 2009). The compressive strength of LHC ranges from 0.2 to 0.9 MPa, depending on the mix design and the binder used. According to (Bouloc et al., 2006), the low compressive strength of LHC is probably due to the high flexibility of aggregates, and to the imperfect arrangement of these particles. LHC walls can be made on site. The material is poured in a framework and is tamped manually, or it is sprayed using a projection process (Elfordy et al., 2008). These processes do not achieve high compactness or precise control of conditions of material maturation. LHC can also be used to make bricks, or hollow blocks, but very few data are available on the effect of compactness on mechanical or thermal properties (Cérézo, 2005; Bütschi, 2004).

Lime and hemp concrete

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Previous work (Nguyen et al., 2009) has shown that the compaction of fresh material can significantly increase the compressive strength of hemp concrete by reducing the volume of voids within the material. Such a process can significantly increase the mechanical strength of the produced material, while using lower binder contents. It can also particularly magnify the strain capacity before collapse. However, it does induce a decrease in the volume of entrapped air, which contributes to reducing the thermal conductivity of the hardened material. In the present work, LHC is designed to make pre-cast load bearing elements (bricks or hollow blocks) using a compacting process during casting. These elements should have a structural or load-bearing function, while keeping good thermal insulation properties. The goal of this study is to compare the effect of compaction during casting on both mechanical and thermal characteristics of hardened specimens to evaluate the relevance of such a process. Our measurements indeed show a slight increase in thermal conductivity, but it is clearly less significant than the improvement of mechanical strength of the material obtained using the compacting process. The influence of binder nature and of mix design (binder to hemp ratio, water to binder ratio) is also studied. The effect of particle orientation, induced during the process, on thermal conductivity is also presented. The presented results, in the case of a given casting process, forward more indepth knowledge on hemp concrete. Various improvement methods for this building material can be then identified. 2. Characterization of based materials 2.1. Aggregate Inside the stem of the hemp plant is its woody core, the shive. The hemp fibre, located near the external surface of the stem, is the most valuable product. It is used in cellulose pulp, paper, insulation materials and bio-composite for automotive parts. Fibres can be totally or partially separated from shives using a complex mechanical grinding process. In this study, the shives used contain no fibres (Figure 1a). This aggregate is characterized by very low bulk density (103 kg/m3) because of its highly porous structure. Figure 1b and 1c show the porous structure of the hemp shive particle. Capillaries are oriented in the stem axis and their size ranges from 10 to 50 µm while their average length is about 80 µm. This aggregate exhibits a high water absorption capacity: up to 406% of its own mass, after 48h immersion (Nguyen et al., 2009).

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b

a

c

Figure 1. Hemp shives (CP) in bulk (1a) and scanning electron microscope (SEM) pictures with different magnifications of longitudinal section (1b) and cross section (1c) of a hemp shive particle 2.2. Binder A lime based binder, called Tradical PF 70, was used. It consists of 75% of hydrated lime Ca(OH)2, 15% of hydraulic lime and 10% pozzolana. Mechanical behaviour in compression is studied with 110×220 mm cylindrical specimens of hardened binder pastes made with Water to Binder mass ratio (W/B) equal to 0.5. It is brittle, similar to those of cement paste, with lower rigidity and strength (about 4 GPa and 10 MPa respectively). However, the yield strain is higher (3.10-3 compared to 2.10-3 for cement paste). Table 1. Thermal conductivities and compressive strength of hardened binder pastes after 28 days made with a Water to Binder ratio W/B = 0.5 (dry density about 1200 kg/m3) Binder PF70 NHL 3.5Z NHL 2

Thermal conductivity (W.m-1.K-1) 0.373 0.37 0.363

Compressive strength (MPa) 10 5.9 3.9

Moreover, other binders (hydraulic lime NHL-2 and NHL-3.5Z) were used to highlight the effect of the binder composition on the compressive strength and


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thermal conductivity of the LHC produced. For the same W/B, Tradical PF70 has the highest compressive strength and NHL 2 the lowest (Table 1). The thermal conductivity of binder pastes was measured on dry samples of 10×10×3 cm3 using a stationary method called guarded hot plate. For a dry density about 1200 kg/m3, the thermal conductivities of the different binders are very close (Table 1). 3. Mix proportioning and material fabrication 3.1. Mix proportioning Based on a preliminary study (Nguyen et al., 2009), an experimental field has been defined and based on three parameters: initial density (ρinitial), binder (B) to hemp (H) mass ratio (B/H), and water (W) to binder mass ratio (W/B). Table 2. Parameters studied and their levels

1 2 3

Factor Binder to Hemp ratio B/H Initial density initiale (kg/m3) Water to Binder ratio W/B

Low (A) 1.11 684 0.55

Medium (B) 2.15 899 0.86

High (C) 3.48 963 0.93

Three levels have been assigned to each parameter (Table 2): low (A), medium (B) and high (C). Thereafter, the medium configuration LHC, when the three parameters are equal to their medium level, is used as a reference to study the binder effect (see Subsection 5.1). The 27 possible combinations of these parameters were not all tested. Figure 2 summarizes the experimental plan. In the case of highest density and lower B/H ratio the force needed to achieve the targeted initial density ( initial) was beyond the load capacity of the device used. Also in the case of highest density and medium B/H ratio, a small amount of paste (few cm3) was ejected from the final volume during the compaction process leading to an initial density slightly lower than that expected. Overall, fourteen mixes were prepared with the binder Tradical PF70, one with NHL 2 and one with NHL 3.5-Z. For each mix, two specimens are devoted to mechanical testing (compression) at 28 days and one to thermal testing (see Subsection 3.3).

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Factor 3 : (W/B) 0.93 (A)

Legend: Perfomed specimen

0.86 (B)

Specimen needing a compacting force beyond mold capacity Specimen with slight loss of paste during the compacting process

0.55 (C)

1.11 (A)

Factor 2 : (Density)

2.15 (B) 3.48 (C) 684 (A)

899 (B)

963 (C)

Factor 1 : (B/H)

Figure 2. Design of experiments for compression tests and measurements of thermal conductivity 3.2. Compaction of fresh material The process of mixing is identical for each batch and is detailed in a previous study (Nguyen et al., 2009). The compaction device is shown in Figure 3. It consists of a cylinder, the PVC tube (1) reinforced by clamping rings (2) & (3), a removable bottom (4) and a piston (5) moving down during loading. The initial apparent volume of the mixture poured in the cylinder is divided by a factor up to 3. The specimens were first left in the moulds for the first 48 h and then they were extracted and stored in an air-conditioned room at 20°C and 75% Relative Humidity (RH) until testing. A relatively high RH was selected in order to reduce competition between desiccation and hydration of hydraulic lime at an early age, while allowing for a gradual evaporation of the excess water remaining or produced during the carbonation of the hydrated lime. The mechanical tests were performed at 28 days. 3.3. Sample preparation for measurement of thermal conductivity Thermal conductivity tests are carried out with prismatic samples 60 × 60 × 30 mm3 taken from 100 × 200 mm cylindrical specimens. Figure 4 shows the location of the four prismatic samples inside the cylindrical specimen. Samples are cut in both axial and radial orientations, to evaluate the anisotropic properties of thermal conductivities, due to the preferential orientation of particles induced by the


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compacting process. Furthermore, due to the friction of the material along the cylindrical mould during the compacting process, an axial gradient of compactness is usually observed inside the specimen. The density of the material located close to the piston, (upper part of the cylinders) is then higher than those in the lower part. The four samples are cut from different heights, to evaluate the gradient of density of the cylindrical specimen and its effect on thermal conductivity.

Direction of compaction

4

30

4

60

ρ4

4

200

3

ρ3

3

3

30

1

60

2

2

1

1

2

ρ2

ρ1

100

Figure 3. Compacting device

Figure 4. Location of samples cut from a cast cylindrical specimen, and direction of thermal conductivities

During the thermal conductivity test, the heat flow cross over the prismatic sample according the perpendicular direction to the long side (square face 60×60 mm²). The measures will therefore be made by considering a heat flow in two directions: axial and radial or perpendicular to the axis of the cylindrical specimen (Figure 4): – Direction of compaction (axial or vertical direction), for samples n° 1 and n° 4. The thermal conductivities measured are named 1 and 4 respectively. The average value of these two measures will be considered as the axial or vertical thermal conductivity v , (i.e. parallel to the compaction direction). – Perpendicular to the direction of compaction (horizontal), for samples n° 2 and no3. The thermal conductivities measured are named 2 and 3 respectively. The average value of these two measures will be considered as the horizontal thermal conductivity v (i.e. perpendicular to the compaction direction).

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4. Experimental methods 4.1. Measurement of thermal conductivity The thermal conductivity of material is measured at a mean temperature close to 20°C, using a stationary heat flow method, known as guarded hot plate (De Ponte & Klarsfeld, 2002) (Figure 5). The device used was developed in the laboratory (Carré, Le Gall, 1990). The measuring cell consists of a cold plate (C), a heating element (H), and a rear guard (G) which prevents heat dissipation from H. Consequently, the totality of the heat flux generated by H is then goes up, through the tested sample. To ensure a good homogeneity of temperature, elements C and G are machined from solid copper. The heating element (H) consists of a heating film stuck on a copper plate 2 mm thick. It is insulated from the rear guard with 8 mm of insulation (I). This experimental device can test rectangular samples: up to 130 mm square based and different thicknesses. The heat flux through the sample is deduced from the electrical intensity which supplies the 60 × 60 mm2 heating element (H). It is relative to the joule heat dissipated.

Cold fluid Cold plate (C)

Sample

Heating element (H) of measurement area

Insulation (I) Hot plate (G) Hot fluid

Figure 5. Device for measuring thermal conductivity - guarded hot plate A 3D model of temperature inside the sample is computed to define the range of boundary temperatures inducing a mono directional flux with a negligible error. Moreover, the temperatures of (C) and (G) are close to the ambient temperature (± 5°C), respectively, to limit outlet heat flows. The thermal conductivity is then expressed in W.m-1.K-1 according to the following equation [1]:

λ=−

P / S W.m-1.K-1 dT dx

[1]


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The measurement uncertainties (± 0.5 mm in sample thicknesses, ± 1mm in lateral dimensions, ± 0.5°C in temperature measurements and ± 0.2 mW in dissipated or inlet power) lead to a thermal conductivity uncertainty of 7% (Carré, Le Gall, 1990). The thermal conductivity was measured with 60 x 60 x 30 mm3 samples cut from dry cylindrical specimens after 28 days (see Subsection 3.3). They are dried at 80°C until constant weight (for 7 days at least). 4.2. Compressive test and mechanical properties Two specimens per batch are tested at 28 days. The rate of displacement is controlled and set at 0.1 mm/s while the compressive load is monitored. A monotonic loading is applied on one specimen, and a cyclic loading is applied on the second one (figure 6). The two curves fit well, and good repeatability is generally observed. 30

Load (kN)

120 monotic loading

Load (kN)

100

25

cyclical loading

80

20

60

15

40

10 5

20

BBC, 28 days

BBB, 28 days

0 0

20 40 60 80 Longitudinal displacement (mm)

0 100

Figure 6. Typical force– displacement curve of a compression test

-0.1 -0.05 Radial strain

0

0.05

0.1 0.15 Longitudinal strain

Figure 7. Radial and longitudinal strain versus load

The high strains induced in the specimen required to measure and monitor the radial strain of the cylinder during testing (Figure 7) in order to deduce the compressive stress, and to draw the stress-strain curve as shown in Figure 8. The LHC studied exhibit a noticeable ductile behaviour. There is no sharp peak of load or abrupt collapse. Beyond the onset of the inelastic strain, the longitudinal strain does not lead to a fracture of the loaded specimen, but a continuous increase of stress. In most cases, a significant mechanical strength is still observed until 50 % of relative strain. Thereafter, our study focuses on mechanical behaviour in moderate relative strain, less than 15 %. This strain is rather important considering the building materials, but it could be conceivable for a particular design adapted to a light weight structure. To compare the materials, two longitudinal strains of reference are considered: 1.5 % and 7.5 %. The maximum stresses applied to the specimen until these two reference strains are then named fc0.015 and fc0.075 as shown in figure 8, in case of

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LHC specimen with medium parameter levels. Young’s modulus E is calculated according to the higher increase of the stress/strain rate recorded at the beginning of loading (Figure 8). Although the samples are ground true before the test, a brief period of contact must sometimes be corrected. Thereafter, fc0.015, fc0.075 and E are deduced from at least two tests for each configuration, and are considered as the average values.

Compressive stress (MPa)

3 2.5

fc0.075

2 1.5 fc0.015

1 0.5

E

BBB, 28 days

0 0

1.5

5

7.5 Strain (%)

10

15

Figure 8. Mechanical parameters studied (LHC at 28 days with medium parameter levels) 5. Results and discussion 5.1. Influence of binder In the case of LHC under loading, hemp shives deform as opposed to traditional Portland where mineral aggregates make a rigid skeleton. Thus, the binder gives cohesion between the deformable aggregates but material stiffness depends essentially on the binder paste. The mechanical strength of the binder used, if there is enough available water to completely hydrate it, has a great influence on the global mechanical behaviour of LHC. Figure 9 shows the wide-ranging differences observed on mechanical parameters (fc0.015, fc0.075 and E) of LHC made with the same mass proportion of components. Globally, the more pozzolana content is, the higher mechanical strength is. The binder NHL 3.5-Z and Tradical PF70 contain more pozzolana which can activate fast carbonation even in the bulk material to achieve higher mechanical strength at 28 days. However, no significant change on thermal conductivity of LHC is observed. This result could be expected since the thermal conductivities of binder paste are closed (Table 1). Consequently, comparing NHL 2 and PF70, a 70% increase of


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fc0,075 is observed while only a 16% increase in global thermal conductivity λv is induced in medium configuration LHC (see Subsection 3.1). Thereafter, only LHC made with the PF70 binder are studied.

1.8

0.096

1.2

0.092

0.6

0.088

L2 NH

70 PF

.5Z L3 NH Binder

0

150 v E

0.104

120

0.1

90

0.096

60

0.092

30

0.088

L2 .5Z NH L3 NH Binder

70 PF

Young's modulus (MPa)

0.1

v

2.4

(W.m -1.K-1)

0.108

Thermal conductivity

0.104

3 v fc0.075 fc0.015

Compressive strength (MPa)


v

(W.m -1 .K-1)

0.108

0

Figure 9. Influence of binder on the compressive strength, Young’s modulus and thermal conductivity of LHC with medium parameter levels 5.2. Variation of density in a compacted specimen Measurements of the apparent dry density of samples cut from cylindrical specimens at different heights (Figure 4) are presented in Figure 10. A density gradient can be observed. This gradient is very low on the upper part and is more significant on the lower part. Sample

CP3-ABB

4

CP1-BBB

Specimen height

CP4-CBB CP9-BAC

3

2

1

200

400

600

800

Apparent dry density (kg/m3)

Figure 10. Density according to height of the cylinder

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During the compacting process, the mix is poured in a 600 mm height cylinder. The compaction divided the initial height by a factor ranging from 2 to 3. Friction along walls induces a tangential stress. This tangential stress is opposed to the axial compression stress. Therefore, the lower part of the sample, close to the fixed bottom, undergoes a lower stress state than in the upper part, close to the moving piston. Then, apparent dry density of compacted LHC is higher, and more homogeneous, in the upper part of the compacted specimens than in the lower one. 5.3. Effect of particle orientation and anisotropy of thermal conductivity The effect of particle orientation, induced during the process, on thermal conductivity is also presented. The size distribution of particles using the image analysis method (Nguyen et al., 2009) revealed a mean aspect ratio (length/width) of hemp particles of about 5. Particles are anisotropic due to the capillary structure of the woody core part of the stem from which they are cut (Figures 1b and 1c). For instance, the longitudinal thermal conductivity inside wood (parallel to the capillaries) is higher than the cross one (Carré, Le Gall, 1990; Suleiman et al., 1999). Inside a hemp shive particle, the thermal conductivity is also probably higher in longitudinal direction (parallel to the stem axis) than in transversal direction. Due to the significant strain applied on the initially isotropic mix poured in the cylindrical mould, the compacting process induces a preferential orientation according to the cross section, in the perpendicular plan to the direction of compaction. The observation of vertical sections confirms this point (figure 11). Direction of compaction

Composition CP3-ABB Figure 11. Vertical sections of compacted material


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Thermal conductivity (W.m-1.K-1)

0.180 v h

0.150 0.120 0.090 0.060 0.030

BAC

CBB

ABB

BBB

0.000

Figure 12. Comparison between λh and λv The particle orientation tends to make a stratified structure. The main heat conductor, the binder matrix (see Subsection 2.2), is discontinuous according to the vertical or axial direction. Consequently, thermal conductivity v is lower than h. The v/ h ratio is approximately equal to 2/3 in the specimen tested (Figure 12). 5.4. Influence of compaction level during casting 0.2 -1

1.6

-1

Compressive strength (MPa)

fc0.015

1.2 B/H=1.11 ; W/B=0.86 B/H=2.15 ; W/B=0.55 B/H=2.15 ; W/B=0.86 B/H=2.15 ; W/B=0.93 B/H=3.48 ; W/B=0.55 B/H=3.48 ; W/B=0.86 B/H=3.48 ; W/B=0.93

0.8 0.4 0.0 450

Thermal conductivity (W.m .K )

2.0

550

650

750

850 3

Apparent density (kg/m )

Figure 13. Influence of density on the compressive strength

0.16 0.12 0.08 (Cérézo, 2005)

0.04

Thermal conductivity h Thermal conductivity v

0 300

400 500 600 3 Apparent dry density (kg/m )

700

Figure 14. Influence of apparent dry density on the thermal conductivity

Globally, the compaction level is relative to the apparent dry density of specimen, reducing the volume of air voids or porosity inside LHC (Nguyen et al., 2009). The mechanical strength increases when density becomes higher (Figure 13).

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It also tends to increase when the B/H ratio is low (i.e., the hemp content is high). However, this reduction in porosity also induces an increase in thermal conductivity No matter the mix used, v and h measured in our study are close to the thermal conductivity measured according to apparent dry density of LHC (Cérézo, 2005) (Figure 14). The relationship between the compressive strength and the thermal conductivity, of specimens are presented in Figures 15 and 16. Globally, the comparison between lower and higher compacting levels shows that the compacting process is able to induce a significant gain of mechanical strengths; fc0.015 (Figure 15) and fc0.075 (Figure 16) can be multiplied by a factor ranging from 2 to 7, while only a moderate increase in thermal conductivities is observed, lower than 40%.

-1

(W.m .K )

0.15 -1

0.12

v

0.09 0.06 0.03 0

B/H=2.15 ; W/B=0.86 B/H=2.15 ; W/B=0.93 B/H=3.48 ; W/B=0.93 B/H=3.48 ; W/B=0.55

0 0.5 1 1.5 2 Compressive strength fc0.015 (MPa)

Figure 15. Correlation between compressive strength fc0,015 and thermal conductivity v



v

(W.m-1.K-1)

0.15

0.12 0.09 0.06 0.03

B/H=2.15 ; W/B=0.86 B/H=2.15 ; W/B=0.93 B/H=3.48 ; W/B=0.93 B/H=3.48 ; W/B=0.55

0 0 1 2 3 Compressive strength fc0.075 (MPa)

Figure 16. Correlation between compressive strength fc0.075 and thermal conductivity v

6. Conclusions The effects of compaction on the mechanical and thermal properties of LHC are studied. In addition, the influence of the binder used is also discussed. The analysis of our results highlights the following points: – The compacting process clearly improves the compressive strength of LHC. The relative increase in thermal conductivity of LHC is less significant. However it reduces the volume of entrapped air, which contributes to reducing the thermal conductivity. Indeed, the data measurements show a slight increase in thermal conductivity, but it is definitely less sensitive than the improvement of mechanical strength. This process constitutes, therefore, an interesting way to develop the use of such materials. – The thermal conductivity increases with the apparent dry density of LHC. Measurements show that our results are consistent with those found in the literature.


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– The choice of the lime based binder is a key parameter since it has a great influence on the mechanical strength and almost no influence on the thermal conductivity of the LHC produced, for a same mix design. – Anisotropic properties of compacted LHC induce a lower axial (or vertical) thermal conductivity. In perpendicular direction of compaction, the thermal conductivity can be 50% higher for a given apparent dry density. – Due to friction of material along the inner surface of the cylindrical mould during the compacting process, the apparent dry density is always slightly higher near the piston in the upper part of the specimen than in the bottom part. The presented results, in the case of a given casting process, show that LHC can still be improved in many ways, and that it has great potential. 7. References Arnaud L., “Mechanical and thermal properties of hemp mortars and wools: experimental and theoretical approaches”, Bioresource Hemp 2000 & other Fibre Crops, Wolfsburg, 2000. Association construire en chanvre, Règles professionnelles d’exécution, 2007. Bouloc P., Allegret S., Arnaud L., Le chanvre industriel : production et utilisations, Paris, France agricole, 2006. Boutin M.P., Flamin C., Quinton S., Gosse G., Etude des caractéristiques environnementales du chanvre par l’analyse de son cycle de vie, ministère de l’Agriculture et de la Pêche, 2006. Bruijn P.B., Jeppsson K.H., Sandin K., Nilsson C., “Mechanical properties of lime – hep concrete containing shives and fibres”, Biosystems Engineering, vol. 103, 2009, p. 474-494. Bütschi P.-Y., Utilisation du chanvre pour la préfabrication d’éléments de construction, Thèse de génie civil, Faculté d’ingénieurs, université de Moncton, Canada, mai 2004. Carré P., Le Gall R., “Définition et détermination des conductivités thermiques dans la structures multicouches C.V.R. – balsa”, Revue générale de thermique, vol. 340, 1990. Cérézo V., Propriétés mécaniques, thermiques et acoustiques d’un matériau à base de particules végétales : approche expérimentale et modélisation théorique, Thèse de génie cvil, Institut national des sciences appliquées de Lyon, 2005. Constatinos A.B., Athina G.G., Elena G., Sevastianos M., Yiannis S., Dimitris P.L., “European residential buildings stock, energy consumption, emissions and potential energy savings”, Building and environment, vol. 42, 2007, p. 1298-1314. De Ponte F., Klarsfeld S., “Conductivité thermique des isolants”, R2 930, 2002. Diana Ü.-V., Aleksandra N., “Potentials and cost of carbon dioxide mitigation in the word’s buildings”, Energy Policy, vol. 36, 2000, p. 642-661. Elfordy S., Lucas F., Tancret F., Scudeller Y., Goudet L., “Mechanical and thermal properties of lime and hemp concrete (hempconcrete) manufactured by a projection process”, Construction and Building Materials, vol. 22, n° 1, 20080, p. 2116-2123.

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Eires R., Nunes P., Fangueiro R., Jalali S., Cameos A., “New eco-friendly hybrid composite materials for Civil construction”, European Conference on Composite Materials, Biarritz, 2006. IPCC (Intergovernmental Panel on Climate Change), Special Report on Emissions Scenarios, Cambridge University Press, Cambridge, 2000. Nguyen T.-T., Picandet V., Amziane S., Baley C.,“Influence of compactness and hemp hurd characteristics on the mechanical properties of lime and hemp concrete”, European Journal of Environmental and Civil Engineering, vol 13, n° 9, 2009, p. 1039-1050. OECD (Organisation for Economic Co-operation and Devolopement), “Environmentally sustainable buildings: Challenges and Policies”, OCDE Publishing, 2003. Price L., De la rue du Can S., Sinton J., Worrell E., Sectoral Trends in Global Energy Use and GHG Emissions, Lawrence Berkeley National Laboratory, Berkeley, CA, 2006. Suleiman B.M., Larfeldt J., Leckner B., Gustavsson M. “Thermal conductivity and diffusivity of wood”, Wood Science and Technology, vol. 33, 1999, p. 465-473.