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Bioclimatic envelopes made of lime and hemp concrete

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Building envelopes are designed to regulate dynamic flows between interior and exterior environment. The paper presents a new type of sustainable building material made of rich lime and hemp chips and focuses on a particular mixture used to fill timber framed structures. Most of material's hygrothermal parameters were measured in the Fraunhofer-Institut for Building Physics in Holzkirchen and its specific behaviour under transient conditions is studied through simulations with WUFI ® 4.0 software. Three case studies were defined to point out its thermal and hygric inertia. According to bioclimatic principles, these effects can help architects and designers to combine comfort feelings and low energy demand. Results are compared to other materials and future works are discussed. RESUME L'enveloppe des bâtiments est conçue pour réguler les flux dynamiques qui s'établissent entre les ambiances intérieure et extérieure. L'article suivant présente un nouveau type de matériau de construction "durable" composé de chaux aérienne et de particules de chanvre, et plus particulièrement sur le mélange utilisé pour habiller les constructions à ossature de bois. Les principaux paramètres hygrothermiques du matériau furent mesurés au Fraunhofer-Institut für Bauphysik de Holzkirchen et son comportement spécifique en régime transitoire est étudié à travers des simulations réalisées avec le logiciel WUFI ® 4.0. Trois études de cas ont été définies pour mettre en évidence son inertie thermique et hydrique. D'après les principes de l'architecture bioclimatique, ces effets peuvent aider les architectes et concepteurs à combiner le sentiment de confort à une demande en énergie réduite. Les résultats sont comparés à ceux obtenus pour d'autres matériaux et les recherches futures sont discutées.
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BIOCLIMATIC ENVELOPES MADE OF LIME AND HEMP CONCRETE
A. Evrard *; A. De Herde*
* Architecture et Climat – Université catholique de Louvain (UCL)
1, Place du Levant ; B-1348 Louvain-la-Neuve
A
BSTRACT
Building envelopes are designed to regulate dynamic flows between interior and exterior
environment. The paper presents a new type of sustainable building material made of rich
lime and hemp chips and focuses on a particular mixture used to fill timber framed structures.
Most of material’s hygrothermal parameters were measured in the Fraunhofer-Institut for
Building Physics in Holzkirchen and its specific behaviour under transient conditions is
studied through simulations with WUFI 4.0 software. Three case studies were defined to
point out its thermal and hygric inertia. According to bioclimatic principles, these effects can
help architects and designers to combine comfort feelings and low energy demand. Results
are compared to other materials and future works are discussed.
R
ESUME
L’enveloppe des bâtiments est conçue pour réguler les flux dynamiques qui s’établissent entre
les ambiances intérieure et extérieure. L’article suivant présente un nouveau type de matériau
de construction "durable" composé de chaux aérienne et de particules de chanvre, et plus
particulièrement sur le mélange utilisé pour habiller les constructions à ossature de bois. Les
principaux paramètres hygrothermiques du matériau furent mesurés au Fraunhofer-Institut für
Bauphysik de Holzkirchen et son comportement spécifique en régime transitoire est étudié à
travers des simulations réalisées avec le logiciel WUFI 4.0. Trois études de cas ont été
définies pour mettre en évidence son inertie thermique et hydrique. D’après les principes de
l’architecture bioclimatique, ces effets peuvent aider les architectes et concepteurs à combiner
le sentiment de confort à une demande en énergie réduite. Les résultats sont comparés à ceux
obtenus pour d’autres matériaux et les recherches futures sont discutées.
I
NTRODUCTION
Many sustainable aspects of using lime and hemp concrete to fill timber framed structures
could be discussed since assessments on the life cycle of this “inorganic matrix composite”
seems to very positive. Hemp chips were first introduced into buildings in France in the
beginning of the nineties to lighten concrete mixtures. Practitioners started in using cement
binder, but very few decisive results were obtained. Numerous building experiments showed
that rich lime is more appropriate for this kind of use. The main reason is that slow
carbonatation process of rich lime is more compatible with the fast water uptake of the chips
compared to reactions of hydraulic binder as cement. High pH of lime also protects hemp
chips for a long time from mould or bacteria attack, and its mechanical flexibility allows
slight distortion without cracking and good toughness against shocks. In addition, its density
and thermal conductivity is lower than cements. A high quality rich lime for building purpose
is however sometimes hard to find and its chemical transformation is quite slow compared to
what is expected nowadays in building process. This rich lime basis gives thus better results if
a small part of hydraulic and puzzolanic binders are added. Specific additives can also help to
enhance desired properties: water repellency, air availability during chemical reactions,
surface covering of hemp chips, etc. The pre-formulated lime Tradical pf 70 corresponds to
this special binder mixture even if it was first developed to be used in old buildings masonry.
This binder was chosen to realize the samples first because its properties are uniform and then
to allow comparison with other laboratory measurements [1] made on the same material using
this binder. The hemp chips Chanvribat were used for the same reasons.
In 2002, an important synthesis of laboratory experiments made on lime and hemp concrete
has been done [2]. The document gathers what was considered as the “state of the art” and
described four mixtures used by practitioners and studied in [1]. The name of the mixture is
linked with the use they will fulfil: build a “wall”, cover a “floor”, insulate a “roof” or to
realize a “plaster”. These uses can be found either in new or in renovated buildings. Samples
submitted to measurements correspond to “wall” mixture: one cubic meter is obtained with
130 kg of hemp chips, 220 kg of binder and approximately 350 litres of water. The samples
were made three years before the measurements and binder’s carbonatation and drying were
considered as completed. Mechanical properties [1] of “wall” mixture are not high enough to
consider this particular concrete as a structural material. It should then fill or cover a structure
with sufficient load capacity like a timber frame structure. Thermal properties are detailed
here after, but lime and hemp concrete should be at least a 25 to 30cm layer for an exterior
wall, and must be protected inside and outside. Figure 1 illustrates the two main types of
exterior wall when using “wall” mixture: both are with rich lime plaster inside, one is with
hydraulic lime plaster outside and the other is with wood cladding.
Figure 1: “Wall” mixture in two types of wall made of hemp and lime concrete
This paper presents first steps of a research realised with Lhoist R&D s.a. (B) partnership and
with financial support of Waloon Region (B) and European Social Found.
H
YGROTHERMAL PARAMETERS
Dry density and porosity
Dry state was obtained with an oven at 40°C, with recycled dry air, when loss of mass of
samples was smaller than 0,1% during 24 hours. Mean dry density is 480 kg/m3 (Table 1). A
very high total porosity of 71,1% was measured on those dry samples with helium
pycnometer. With this single value, it is not possible to differentiate “microscopic porosity”,
in the matrix (~1µm) or in the hemp chips (~10µm), from “macroscopic porosity” (~1mm)
which is obvious when looking at the samples (Figure 2). Future measurements will define
pore size distribution with Mercury and Nitrogen Intrusion Porosimetry.
Figure 2: Macroscopic porosity of lime and hemp concrete – “wall” mixture
Sorption
Three different sorption regions can be defined. Water content of “wall” mixture in the first
one, the “hygroscopic region” (Figure 3), was studied in placing dry samples (~20 grams),
into different climate rooms at 23°C, with relative humidity going from 32 to 93%. As
expected, there mass starts to climb up due to increasing water content. Equilibrium water
content was measured when gain of mass during 24 hours was smaller than 0,1% of dry mass.
The time needed for this stabilisation was quite long, usually more than two weeks for thin or
broken samples. Future researches will study these retarded sorption effects in details. Mean
value of the results are relatively high, as presented in Table 1.
The second region starts when “capillary condensation” becomes prevalent compared to
hygroscopic phenomenon (Figure 4). It is considered to begin where the slope of isotherms
starts to rise much faster, generally around 80%, and goes until saturation (RH=100%).
Results from Pressure Plate experiments will soon give more details on the real edges of the
“capillary region” that seems to start in this case after 93% of relative humidity. Until then, it
is assumed that water content rise linearly from the value obtained at 93% to free saturation.
The high value of 596 kg/m3 can be used for free saturation of the “wall” mixture (575 kg/m3
for wood and 250 kg/m3 for lime plaster). It has been measured on samples placed under
water until their mass was stable. The last region, called “sursaturated region” (Figure 5), is
usually not taken into account in buildings physics. However, we can assume that the
maximal water content of the material is reached when all the pores are filled of water.
Maximal water content of “wall” mixture is then presumably 711 kg/m3.
Figure 3: Hygroscopic region Figure 4: Capillary region Figure 5: Sursaturated region
Storage parameters
Thermal capacity was measured into an adiabatic surrounding. Samples were dried and heated
to 100°C and were put into water at 22°C (room temperature). From the thermal capacity of
water, the mass of water and the mass of the sample, the measure of the resulting temperature
allows to determine thermal capacity of “wall” mixture. As presented in Table 1, the mean
measured dry value was c= 1550 [J/kgK]. The method was validated with measurement on
aluminum sample (920 [J/kgK]).
The slope of sorption’s isotherm is called hygric capacity ξφ. In the hygroscopic region,
sorption isotherm at 23°C is almost linear, hygric capacity takes then a single value: 10,2 [%].
Moisture transfer parameters
Water vapour permeability of “wall” mixture was measured following EN ISO 12572 with
dry cup (RH=3% in the cup, 50% in the room) and wet cup (RH=93% in the cup, 50% in the
room) methods. Results were respectively a coefficient of vapour diffusion resistance of µs=
4,84 [-] and an apparent coefficient of vapour diffusion µ*= 4,51 [-]. But µ* will not be use
since the difference is due to liquid transport, expressed with liquid transport coefficient.
Water absorption coefficient was measured following DIN 52 617. Its value is A= 7,5.10-2
[kg/m2.s]. The liquid transport coefficient for absorption Dws and for redistribution Dww were
approximated from this value using Künzel method. Measurement with Nuclear Magnetic
Resonance will soon give results closer from reality. Liquid transport in lime and hemp
concrete is expected to have a certain time dependency (non fickian behavior) similarly to
what is observed in wood, cellular concrete or clay bricks.
Heat transfer parameters
Dry thermal conductivity λ is estimated on the basis of other research (especially [1]). Until
new measurement, it is assumed in the following simulations that its dry value is 0,11 W/mK
rising linearly with relative humidity until maximal water content with a increase of 1,515 %
per additional % of masse content. Table 1 presents its dependency to water content as well as
two other useful thermal parameters. First is the thermal diffusivity α [m2/s], calculated by the
ratio: λ/ρc. Then is the thermal “Effusivity” ξff [J/m2Ks] witch is calculated by (λρc)1/2.
RH
[%]
w
[kg/m³]
ρ
ρ ρ
ρ
[kg/m³]
c
[J/kgK]
λ
λ λ
λ
[W/mK]
α
α α
α
[10-7m²/s]
ξ
ξξ
ξff
[J/m²K
s]
0
0
480
1550
0,11
1,48
286
32
15,24
495,24
1631
0,115
1,43
305
50
22,31
502,31
1667
0,118
1,41
314
65
30,78
510,78
1708
0,121
1,38
325
80
36,48
516,48
1735
0,123
1,37
332
93
45,40
525,40
1777
0,126
1,35
343
100
596
1076
3005
0,317
0,98
1012
Table 1: Water content dependency of different parameters for lime and hemp concrete
C
ASE STUDY
Case 1: Thermal shock
This theoretical situation was defined to show that permanent transfer is not immediately
obtained when one side of an element is submitted to thermal variations. Initial temperature is
20°C (RH50%) on both sides and through the 25cm elements of plain material. From the first
time step, temperature on left side is lowered to 0°. The induced effect on relative humidity is
not discussed here but will be analyzed in detail in future works. Figure 6 shows that linear
temperature distribution through the element is barely obtained after 48h in lime and hemp
concrete. Wood has almost the same behaviour. For cellular concrete, it took approximately
24h, for cement concrete less than 10 hours and for mineral wool around 5 hours. Referring to
Table 2, it can be noticed that linear temperature distribution is thus obtained faster with high
thermal diffusivity material.
Figure 6: Thermal shock propagation Figure 7: Evolution of heat flux
in 25cm of lime and hemp concrete through right surface (25cm)
Figure 7 shows the evolution of heat flux through opposite surface (right) for these materials.
Negative value means the flux is going from right to left. It appears that approximate
permanent transfer takes longer to set up in materials with high thermal Effusivity: more than
48h in lime and hemp concrete or wood; around 36 hours for cellular concrete; and less than
12 hours in mineral wool (and it was not installed after 96h in the cement concrete element).
Table 2 also presents surface temperatures Tsurf [°C] on right side after 96h. In addition, the
amount of energy given to the elements from right side environment after 24h, Q24h [kJ/m2],
appears lower for lime and hemp concrete or wood, than for other material.
Case 2: Thermal cycles
Once again, this situation is theoretical. It was defined to illustrate that materials have a very
different response when they are submitted to cyclic thermal variations. Initial temperature is
10°C (RH50%) on both side and through elements of 1m of thickness. From the first time
step, temperature on left side starts to vary following a sinus curve with maximum at 20°C,
minimum at 0°C (amplitude θinit=10°C). Those cycles have a 24 hours period. The induced
effect on relative humidity is not discussed in this case either but future works will detail
them. Figure 8 shows that in lime and hemp concrete the wave is almost totally dampened at
25cm of depth. Dampening factor νx [-] of thermal wave amplitude at a depth of x [cm] can
be defined by νx= 1-(θx/θinit). In addition, Figure 8 also shows that at this depth, maximal
temperature is reach after the minimal temperature has been reached on left surface affected
by the harmonic variation. Time discrepancy ηx [h] can be defined by the time difference
between the maximum (or minimum) of corresponding cycle, on the surface submitted to
thermal variation and at a depth of x [cm]. Table 2 present results obtained at 25cm for lime
and hemp concrete and for other materials. Low νx and low ηx is obtained when α is high.
Figure 8: Propagation of thermal wave Figure 9: Water content of a 25cm element
in a lime and hemp concrete element when humidity on right side is lowered
Case 3: Hygric shock
This case was defined to show that hygric equilibrium is much slower to install than thermal’s
one and that envelope materials can contribute to regulate relative humidity of inside air.
Initial conditions were set to a relative humidity of 80% outside and 50% inside with a linear
distribution through the 25cm elements of plain material. From the first time step, relative
humidity on right side is lowered to 40%. The boundary temperatures are constant and fixed
to 20°C. Thermal effect induced by moisture transfers will be discussed in future works.
As figure 9 shows, constant water content, and thus permanent transfer conditions, in the lime
and hemp concrete element are reached only about 9 months after the hygric shock. In table 2,
this time lapse is represented by τ. When permanent flow is reached, there is gv
τ
= 0,5 g/m2 per
hour of vapour going through the lime and hemp concrete element from left to right (NB:
there is no plasters in this case !).
To precisely assess the quantity of moisture given by the element to right side environment
Wt [kg/m2] on a certain time period t, moisture flux going out of right surface lowered by the
flux entering from left one should be integrated on the time period. In this case, Wt was
approximated by the loss of mass of the element during the time period. Nine months after
hygric shock, lime and hemp concrete element gave 600 g/m2 to the right side environment.
After 3 months, it already gave 550 g/m2, corresponding to 91,7% of final value.
Table 2 gives corresponding values for other materials. It shows that, in the hygroscopic
region, materials with a low moisture transfer parameter (coefficient of vapour diffusion
resistance µs) and low moisture storage parameter (water content at RH80% gives a good idea
if hygric capacity ξφ is high or low) are getting faster to their hygric equilibrium. Besides, the
amount of moisture exchanged with the environment Wτ during the time lapse τ needed to get
constant water content is higher for materials with higher moisture storage parameter. Lime
and hemp concrete has a very specific behaviour due to its very low resistance to vapour
diffusion combined with quite pronounced hygroscopic uptake. Future works will define
combined parameters corresponding to thermal diffusivity and Effusivity for hygric transfers.
Case
Lime and hemp
concrete Wood
Cellular
concrete Mineral
wool CEM
concrete
α
αα
α
[10-7m²/s]
- ~1,4
~1,35
~3
13,3
~6
ξ
ξξ
ξff
[J/m²K
s]
- ~320
~350
~330
35
~1700
T
surf
[°C]
1 18,92
19,04
18,85
19,62
11,98
Q
24h
[kJ/m2]
1 187
146
410
229
3163
ν
νν
ν
25cm
[%]
2 98,5
98,8
95
77,5
89,5
η
ηη
η
25cm
[h]
2 15
16
10,5
6
7
w
80%
[kg/m³]
- 36,48
60
9,8
(0)
85
µ
µµ
µ
s
[−]
[−] [−]
[−]
- 4,84
200
8
1,3
180
τ
ττ
τ
3 9 months
8 years
4 months
(7 days)
45 years
g
v
τ
ττ
τ
[g/m2h]
3 0,5
0,06
0,34
1,95
0,02
W
3m
[g/m2]
3 550
160
190
(35)
130
W
3m
/W
τ
ττ
τ
[%]
3 91,7
32
97,4
(100)
15,3
Table 2: Results from case 1, 2 and 3 for lime and hemp concrete and other materials
C
ONCLUSION
As introduced, sustainable nature of hemp and lime concrete could still be studied in many
ways. After presenting main hygrothermal parameters of this new insulation material, the
paper defined three theoretical case studies to enable comparison with other material, and to
point out its specific behaviour. Bioclimatic architecture takes in account the dynamic reality
of climate, and it appears that transient performances of such a wall element are definitely
higher than what permanent transfer calculations would assess. This conclusion is often
observed in wood or earth constructions. Combined parameters can be defined on the basis of
material’s transfer and storage parameters to help architects and designers to choose materials
when they wish to optimized comfort feelings and low energy demand of their buildings.
R
EFERENCES
1. Arnaud, L., Cérézo, V.: Qualification physique des matériaux de construction à base de
chanvre, Rapport final CNRS 0711462, ENTPE, France, 2001.
2. Evrard, A.: Bétons de chanvre : Synthèse des propriétés physiques, Association Construire
en Chanvre, France, 2003.
... For instance, the thermal conductivities of hempcrete mixtures with densities ranging from 220 to 627 kg/m 3 were reported in the range of 0.06-0.14 W/m K [17,18]. Furthermore, the specific heat capacities of hempcrete mixtures with densities ranging from 381 to 627 kg/m 3 were reported in the range of 1000-1590 J/kg K [17,18,19]. ...
... W/m K [17,18]. Furthermore, the specific heat capacities of hempcrete mixtures with densities ranging from 381 to 627 kg/m 3 were reported in the range of 1000-1590 J/kg K [17,18,19]. Moreover, studies show that low thermal diffusivity, ranging from 1.48 × 10 -7 m 2 /s in the dry state to 0.98 × 10 -7 m 2 /s in the fully saturated condition, and high specific heat capacity of hempcrete, can provide better thermal performance than suggested by its thermal transmittance [15]. ...
... This research focuses on maximizing the hemp hurd ratio within the hempcrete mixture to improve its thermal properties while reducing its carbon footprint and price. Hence, the ratio used in the preparation of the hempcrete sample was 1:1 of hemp hurds and binders with a density adequate for wall applications between 300 and 500 kg/m 3 [17,18]. The binders' ratio was 50% hydrated lime and 50% metakaolin by weight. ...
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Biocomposite materials offer the potential to reduce the embodied energy in the construction of buildings significantly. This study develops a new low-carbon heat storage material composed of hempcrete and microencapsulated phase change material (MPCM) that is capable of reducing energy consumption and improving indoor thermal comfort in buildings. Eight hempcrete-MPCM (HPCM) composites were created using: (a) two MPCM types, (b) four MPCM melting temperatures, and (c) two MPCM concentrations. A set of experiments enabled thermophysical and microstructural characterization of MPCM, hempcrete, and HPCM samples. Furthermore, numerical simulations allowed the extension of the experimental results by comparing the performance of timber-frame walls made of hempcrete and HPCM infills with different MPCM concentrations. The findings show that, on the one hand, the developed HPCM formulas have superior heat storage potential compared to the hempcrete owing to their 35% to 85% higher maximum specific heat capacity than hempcrete. On the other hand, HPCM formulas, on average, have lower thermal conductivity than hempcrete due to the low thermal conductivity of MPCMs. As a result, HPCM wall types achieve approximately 5% to 16% and 1% to 36% higher heating and cooling energy savings, respectively, compared to the hempcrete wall. However, the results also indicate that an increase in the percentage share of MPCMs from 9% to 18% in the hempcrete mixture reduces total energy savings and, in particular cooling savings. Therefore, there is a need for a thorough consideration of the operating temperature and percentage share of MPCMs within the hempcrete concerning the specific application and performance objectives. The optimal integration of HPCMs into building envelope might also require changes in the operation of heating and cooling systems.
... Ces phénomènes, étudiés par de nombreux auteurs (Barsotti et al., 2020;T. Colinart et al., 2016;Collet et al., 2008Collet et al., , 2013A Evrard & Herde, 2005;Shea et al., 2012), sont représentés par des courbes associées (Figure 1.11) qui traduisent l'évolution de la teneur en eau d'un matériau en fonction de la valeur de l'humidité relative de l'air en équilibre à une température constante. A partir des courbes de sorption, il est possible de définir le coefficient [kg/m 3 ] correspondant à la capacité de stockage d'humidité. ...
... On observe une hystérésis entre les isothermes d'adsorption et de désorption. Cette différence entre les courbes d'adsorption et de désorption a déjà été étudiée dans le béton de chanvre (Collet & Pretot, 2012;A Evrard & Herde, 2005;Shea et al., 2012), dans le bois (Merakeb et al., 2009), dans les films d'amidon de sagoutier (Bajpai et al., 2011), dans le béton (Baroghel-Bouny, 2007) et dans la bentonite (Mihoubi & Bellagi, 2006). L'évolution de la capacité de stockage d'humidité en fonction de l'humidité relative des 5 bétons est présentée à la Figure 2.11 pour la méthode DVS. ...
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... In this regard, hempcrete is a non-structural material used with a load-bearing frame that offers a beneficial compromise between thermal conductivity and thermal inertia, thus enabling a passive control of the indoor building environment [33]. For example, low thermal diffusivity of hempcrete, ranging from 1.48 × 10 −7 m 2 /s in the dry state to 0.98 × 10 −7 m 2 /s in the fully saturated condition, and its high specific heat capacity from 1000 to 1590 J/(kg K) [34][35][36][37] can provide better thermal performance than suggested by its thermal transmittance in the range of 0.06-0.14 W/(m K) [35,36,38]. ...
... For example, low thermal diffusivity of hempcrete, ranging from 1.48 × 10 −7 m 2 /s in the dry state to 0.98 × 10 −7 m 2 /s in the fully saturated condition, and its high specific heat capacity from 1000 to 1590 J/(kg K) [34][35][36][37] can provide better thermal performance than suggested by its thermal transmittance in the range of 0.06-0.14 W/(m K) [35,36,38]. Moreover, hempcrete envelopes can also meet building code requirements and simplify envelope construction [39]. ...
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Phase change material (PCM)-enhanced building envelopes can control indoor temperatures and save energy. However, PCM needs to undergo a phase change transition from solid to liquid and back to be fully effective. Furthermore, most previous research integrated PCM with high embodied energy materials. This study aims to advance the existing research on integrating PCM into carbon-negative wall assemblies composed of hempcrete and applying temperature control strategies to improve wall systems’ performance while considering the hysteresis phenomenon. Four hempcrete and hempcrete-PCM (HPCM) wall design configurations were simulated and compared under different control strategies designed to reduce energy demand while enhancing the phase change transition of the microencapsulated PCM. The HPCM wall types outperformed the hempcrete wall assembly through heating (⁓3–7%) and cooling (⁓7.8–20.7%) energy savings. HPCM walls also maintained higher wall surface temperatures during the coldest days, lower during the warmest days, and within a tighter range than hempcrete assembly, thus improving the thermal comfort. However, the results also show that the optimal performance of thermal energy storage materials requires temperature controls that facilitate their charge and discharge. Hence, applied control strategies reduced heating and cooling energy demand in the range of ⁓4.4–21.5% and ⁓14.5–55%, respectively.
... Ces phénomènes, étudiés par de nombreux auteurs (Barsotti et al., 2020;T. Colinart et al., 2016;Collet et al., 2008Collet et al., , 2013A Evrard & Herde, 2005;Shea et al., 2012), sont représentés par des courbes associées (Figure 1.11) qui traduisent l'évolution de la teneur en eau d'un matériau en fonction de la valeur de l'humidité relative de l'air en équilibre à une température constante. A partir des courbes de sorption, il est possible de définir le coefficient [kg/m 3 ] correspondant à la capacité de stockage d'humidité. ...
... On observe une hystérésis entre les isothermes d'adsorption et de désorption. Cette différence entre les courbes d'adsorption et de désorption a déjà été étudiée dans le béton de chanvre (Collet & Pretot, 2012;A Evrard & Herde, 2005;Shea et al., 2012), dans le bois (Merakeb et al., 2009), dans les films d'amidon de sagoutier (Bajpai et al., 2011), dans le béton (Baroghel-Bouny, 2007) et dans la bentonite (Mihoubi & Bellagi, 2006). L'évolution de la capacité de stockage d'humidité en fonction de l'humidité relative des 5 bétons est présentée à la Figure 2.11 pour la méthode DVS. ...
Thesis
In France, thermal regulations for buildings are changing to face the climatic challenges. The “Grenelle 2” law and the “Plan de Rénovation Energétique de l'Habitat” strategy establish requirements that motivate the search for innovative solutions for the insulation of buildings with high thermal losses. This is the case of national heritage, whose bio-energy retrofit is at the heart of this thesis project. In this context, the agroconcrete industry is currently experiencing an upturn driven by the economic and environmental benefits of the exploitation of agricultural waste and of the local production of resources. This work seeks to characterize lime-based concretes made from sunflower pith and maize pith, two agricultural by-products available in large quantities and whose properties have been scarcely studied. To this end, a study of the mechanical, hygrothermal and acoustical characteristics, compared to the properties of hemp concrete, is carried out, focusing on the impact of the binder-aggregate couples. This experimental campaign has the double objective of exploring new methods of characterization of macroscopic properties. In addition, a mathematical model, which considers the coupling of thermal and hygroscopic effects, is proposed in order to describe the hygrothermal response of the concretes studied at the wall scale. The experimental study has corroborated that lightweight pith concretes show relatively low mechanic characteristics, which place them in the limit of the threshold for “wall”-type applications according to the “Règles Professionnelles Construire en Chanvre” guideline. However, its interesting hygrothermal properties, whose variation with humidity was determined, make it suitable for use as interior insulation, which is the main application envisioned by the project. The campaign also highlighted the extent of the impact of the interactions between the pith and the binder on the properties and the importance of studying the compatibility between aggregates and binders when developing new concretes. During this campaign, a new device for measuring the thermal conductivity of walls was conceived. The cross study of the properties resulted in a contribution to the determination of thermal conductivity and water vapour permeability from acoustic measurements. On the other hand, the results of the numerical study underline the influence of climate on the response of the wall, which determines the choice of the insulating material, and revealed that the presence of pith does not guarantee a greater degree of hygroscopicity of the concrete than the presence of hemp shiv. This hygroscopicity has been proven to have a significant impact on surface heat flows. Lastly, the proposed numerical model is used to quantify the impact of the presence of several kinds of thermal flowmeters on the heat flow passing through a wall during a laboratory test under controlled hygrothermal solicitations.
... Thus, the wet state's thermal diffusivity k ρ C p is lower than that of the dry state (i.e., have higher thermal inertia than the dry samples.) Our results are slightly higher than the range of thermal diffusivity values reported in the literature, between 0.98 and 1.68 (m 2 /s) × 10 −7 [5,47]. A possible explanation might be the higher density values that previous studies used to calculate thermal diffusivity. ...
Article
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Hempcrete is a sustainable biocomposite that can reduce buildings' embodied energy while improving energy performance and indoor environmental quality. This research aims to develop novel insulating hemp-lime composites using innovative binder mixes made of recycled and low-embodied energy pozzolans. The characterization of composites' mechanical and hygrothermal properties includes measuring compressive strength, splitting tensile strength, thermal conductivity, specific heat capacity, and moisture buffer capacities. This study also investigates the impact of sample densities and water content on compressive strength at different ages. The findings suggest that mixes with a 1:1 binder to hemp ratio and 300−400 kg/m 3 density have hygrothermal and mechanical properties suitable for insulating infill wall applications. Hence, compressive strengths, thermal conductivity, and specific heat capacity values range from 0.09 to 0.57 MPa, 0.087 to 0.10 W/m K, and 1250 to 1557 J/kg K, respectively. The average moisture buffer value for all hempcrete samples of 2.78 (gm/m 2 RH%) indicates excellent moisture buffering capacity. Recycled crushed brick pozzolan can enhance the hygrothermal performance of the hemp-lime composites. Thus, samples with 10% crushed brick have the lowest thermal conductivity considering their density and the highest moisture buffer capacity. The new formulas of hydrated lime and crushed brick have mechanical properties comparable to metakaolin and hydraulic lime formulas.
Article
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Background: Environment-friendly materials attract attention whilst the construction sector causes excessive global energy consumption and emission of greenhouse gas. Renewable plant-based biomaterials, which have a low environmental impact, are very beneficial in order to prevent environmental pollution and to preserve natural resources. Hempcrete provides environment-friendly construction materials as well as thermal and hygroscopic properties. Objective: This paper presents a review of hempcrete research about understanding the environmental effects and construction methods of hempcrete; moreover, the benefits and innovations it has provided throughout its life cycle, have been investigated. Methods: For this purpose, experimental studies of hempcrete were compared to each other in all aspects in order to determine density, thermal conductivity, vapor permeability, hygrometric behavior, durability, acoustic absorption, mechanical properties and life cycle analysis. Moreover, binder characteristics, hemp shiv proportions, water content, curing conditions and results have been focused on to explain the benefits of hempcrete. Results: The results obtained show that hempcrete has high porosity and vapor permeability, medium-low density, low thermal conductivity, Young's modulus and compressive strength. Conclusion: Based upon the findings of the studies reviewed, hempcrete is an advantageous material in buildings with its extraordinary thermal and hygrometric behaviour. Hemp is also an eco-friendly and economical plant-based raw material for the construction industry.
Article
Full-text available
Background Environment-friendly materials attract attention whilst the construction sector causes excessive global energy consumption and emission of greenhouse gas. Renewable plant-based biomaterials, which have a low environmental impact, are very beneficial in order to prevent environmental pollution and to preserve natural resources. Hempcrete provides environment-friendly construction materials as well as thermal and hygroscopic properties. Objective This paper presents a review of hempcrete research about understanding the environmental effects and construction methods of hempcrete; moreover, the benefits and innovations it has provided throughout its life cycle, have been investigated. Methods For this purpose, experimental studies of hempcrete were compared to each other in all aspects in order to determine density, thermal conductivity, vapor permeability, hygrometric behavior, durability, acoustic absorption, mechanical properties and life cycle analysis. Moreover, binder characteristics, hemp shiv proportions, water content, curing conditions and results have been focused on to explain the benefits of hempcrete. Results The results obtained show that hempcrete has high porosity and vapor permeability, medium-low density, low thermal conductivity, Young’s modulus and compressive strength. Conclusion Based upon the findings of the studies reviewed, hempcrete is an advantageous material in buildings with its extraordinary thermal and hygrometric behaviour. Hemp is also an eco-friendly and economical plant-based raw material for the construction industry.
Chapter
The development and subsequent incorporation of the advanced materials and technologies in buildings, with a view to target energy savings, and to fulfill the energy requirements have been gaining impetus during the recent years. The inherent vision lying behind the state-of-the-art technological advancements taking place in the construction sector is to sustain the energy efficiency in both existing and newly developed buildings on a long run. Thermal energy storage (TES), achieved through the phase-change materials (PCMs), is one among a few energy-efficient technologies available. The energy demand at the end-user side can be greatly satisfied using the TES technologies. Using bio-based PCMs in buildings is considered to be an ever-growing as well as an emerging field of interest to wider scientific and engineering communities, worldwide. This chapter is devoted to provide an in-depth understanding of a variety of bio-based PCMs for accomplishing thermal storage and energy efficiency in buildings. The nucleus of this chapter is focused on the TES properties enhancement for a variety of bio-based PCMs through the incorporation of different functional materials thereby; energy efficiency in buildings can be achieved.
Chapter
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In “agro-concretes”, highly-porous plant-based particles are used, and 5 are responsible for massive water absorption.
Qualification physique des matériaux de construction à base de chanvre, Rapport final CNRS 0711462
  • L Arnaud
  • V Cérézo
Arnaud, L., Cérézo, V.: Qualification physique des matériaux de construction à base de chanvre, Rapport final CNRS 0711462, ENTPE, France, 2001.