Performance of hempcrete in a building - The Hempcrete Topic: Designing and Building with Hemp-lime - page 132

The flexibility and porosity of the hemp shiv also contributes interesting and useful qual-
ities in terms of elasticity and flexural strength (the ability of a material to bend under a
load without tearing). However, these same properties mean that hempcrete is not suitable
in load-bearing applications.
The combination of the flexible hemp shiv particles with the rigid-setting binder produces
a material which, in contrast to other building materials, also shows a high deformability
under stress, a lack of fracturing and the ability to sustain significant changes in shape
without breaking, even after the full mechanical strength of the binder has been reached.
These properties, together with the significant improvement in racking strength that hemp-
crete brings to a frame (see opposite), have clear possibilities for seismic design, which
aims to produce safe buildings in earthquake-prone areas: structures that are capable of
withstanding the shock of earth tremors without collapsing. Further research in this area
is likely to accompany the wider adoption of hempcrete in countries such as the USA and
New Zealand, for example, where building with hempcrete is only just beginning to gain
popularity.
Perhaps the most interesting thing about the mechanical behaviour of hempcrete is the way
in which it can be easily manipulated by altering the ratio of binder to hemp shiv in the
mix, which enables us to formulate different hempcretes tailored to specific applications.
For example, a roof-insulation hempcrete requires a low-density mix, i.e. with relatively
little binder, since the thermal properties are more important than the mechanical integrity
of the cast material. Under a microscope, such a mix looks almost like a matrix of hemp
particles with bridges of binder connecting them.
Walls require a more binder-rich mix, and floor slabs, which need to withstand the load of
people walking on them, require a hempcrete with a much higher proportion of binder -
a higher-density mix, in which the composite resembles a continuous binder matrix with
particles of hemp buried inside it. Even these binder-rich mixes, however, retain the qual-
ities of deformability and resistance to cracking, which are lacking in a mineral concrete
floor slab.
Structural qualities
A large number of studies have looked into the structural properties of hempcrete, in a
range of applications and using a variety of testing methods. Perhaps unsurprisingly, the
results show a wide range of values for the structural performance achieved.