Agriculture Reference
In-Depth Information
was recognized. Satisfactory results were
obtained from the use of a binding agent that
hardened in air (
chaux
) mixed with hydraulic
and/or pozzolanic binding agents and a spe-
cially adapted adjuvant. These have led to a
number of patented methods. It is, however,
difficult to provide reliable recipes and the pro-
fessional code of the
Construction en Chanvre
requires that manufacturers produce binding
agents that correspond with, and meet the
technical specifications of, the end use intended
for the concrete. Different products are avail-
able on the market today.
The mixing of the binding agents with the
hurds, as seen below, allows mortars and
cements of very different nature to be produced
for speciality markets. Hemp mortars and
hemp cement are conglomerates made of a
plant aggregate (hurds) and a binding agent.
Variations in the ratio of hurds and binding
agent allow materials with different mechani-
cal, thermal and acoustic properties to be
developed for use in flooring, wall construc-
tion, rendering and roofing.
17.4.3 Performance
If we are interested in the performance of a
particular building material, it will often be lim-
ited to a single function. Thus, for the material
that assures the consolidation of mechanical
forces, it is easy to determine its mechanical
resistance. Current practices in the construc-
tion industry encourage the use of various
products (other materials) to those providing
mechanical strength, in order to provide ther-
mal and noise insulation. This tendency to
sandwich together these different materials is
rapidly reaching its limitations, both in terms of
function and performance. Let us, for exam-
ple, consider the control of humidity in a room
(or space) and its role in hygrothermic comfort.
This is a much overlooked issue and requires us
to factor in the performance of all the materi-
als used in order to evaluate the behaviour of
the space. This is never done. The juxtaposi-
tion of various materials also poses a number
of problems related to the amount of on-site
handling by different workmen, the chaotic
association of materials and the need to strike
compromises, all resulting in mediocre
performance.
It is becoming necessary today to recon-
sider the role and function of building materials
in order to evaluate better their overall per-
formance in providing the shell (or envelope)
for a home or other living space.
As a constitutive envelope for a building,
hemp concrete can provide thermal and sound
insulation while also regulating water exchange,
thus conditioning the comfort of the home
while contributing to the mechanical proper-
ties of the construction.
Hurds, as a plant material, produce granu-
lar particles with a highly porous structure that
confers a number of 'original' properties on
mortar and cement when compared with the
synthetic materials normally used:
17.4.2
Method of manufacture
The production of hemp-based mortars and
concrete does not present any particular diffi-
culties provided a few basic precautions are
taken: these relate to the aggregate and its abil-
ity to absorb large quantities of water rapidly.
The mixture should not contain any small
clumps and should be put together in a cement
mixer, vertical or horizontal paddle mixer,
cement lorry, or by hand (although this is more
difficult).
When using a cement mixer or mixer
truck, a mixing tank containing the entire vol-
ume of water and binding agent must prepared.
The hurds are then added gradually. This
method is not to be used with vertical and hori-
zontal axis mixers as the emptying traps are
generally not fully sealed. The latter type of
mixer does, however, produce a very uniform
mixture. In the case of these machines, the
binding agent and hurds will be mixed first
before spraying on the water. This allows well-
mixed cements to be produced with very low
water content.
•
The lightness of the particles, and therefore
of the material, results in a product that is
easy to install and work with and has a high
resistance relative to its density.
The compressibility/deformability of the
•
granules plays an essential role in the
mechanical behaviour of the matrix pro-
duced by the binding agent.
