Agriculture Reference
In-Depth Information
17.4.4 Hygrothermic performance
and humiditiy regulation
Trials are currently under way to evaluate
various formulations of hemp concrete as part
of the European Eureka Research Programme.
These performances will be compared with
those of other building materials.
Initial results show that the hemp cement's
porous nature allows faster and easier air
exchange, performing better than other materials
with a similar porosity. The resulting comfort is
therefore greater.
It is now widely accepted that one of the essen-
tial conditions contributing to the interior com-
fort of buildings relates to their management of
water and water vapour. For reasons of energy
conservation, building materials have been
developed in order to produce confined spaces.
The atmosphere thus created is far from opti-
mal in terms of sanitation. We are now pre-
sented with a promising new possibility:
materials that contribute to the regulation of
living spaces.
Water, in the form of water vapour, is
naturally present in ambient air; the propor-
tion will vary as a function of atmospheric
conditions, temperature and pressure,
together with natural or forced ventilation
and exchanges taking place across the shell
of the building. The exchange between
ambient air and the material of which the
shell is constructed is important. While the
physics regulating this exchange is very
complex, it is important to remember the
key role played by the material's permeabil-
ity, the size of its pores, the nature of its
constituents and their temperature. Figure
17.14 illustrates the significant ability of
hemp, the key ingredient of hemp cement,
to hold water (over 30% of its mass) under
different conditions, with relative humidity
(RH) both increasing (sorption curve) and
decreasing (desorption curve).
A wood-based material that does not burn
The integration of plant materials into con-
struction leads to questions concerning the fire
resistance of such products. It should first be
noted that wood is an integral part of construc-
tion and has a wide range of uses. It is viewed
by experts as a material that performs well
with regard to fire.
4
As we have seen already, hemp cement is
made from hemp coated with a matrix of lime.
This composition allows it to resist fire, because
of lime's excellent fire-resistant properties and
ability to preserve mechanical function. On its
part, hemp burns very slowly, as the oxygen
necessary for combustion is not present in sig-
nificant quantity in this composite material.
Conclusions
Cements and mortars that incorporate hemp
bring together two materials with very different
properties that can be mixed in different
0.4
isothermal line of absorption,
minimum water content
isothermal line of desorption,
maximum water content
0.3
0.2
0.1
0.0
0
0.2
0.4
0.6
0.8
1
Relative air humidity
Fig. 17.14.
Isothermal lines of absorption and desorption for hurds at 20°C.
