Performance of hempcrete in a building - The Hempcrete Topic: Designing and Building with Hemp-lime - page 145

thermal bridging, both of which have very positive implications for its overall thermal per-
formance in well-detailed buildings.
As discussed in Chapter 4 (see page 55 ) , hempcrete also has wider benefits in terms of
energy consumption over its whole 'lifecycle', which cannot be measured in thermal per-
formance tests, notably its low embodied energy and carbon sequestration.
Acoustic performance
The micro- and macro-porosity of hempcrete, as described earlier, are as beneficial for
hempcrete's acoustic performance as they are for its thermal performance. It appears that
these different levels of porosity within the material lead to an acoustic quality which is -
as with its other characteristics - unusual and distinct from that of conventional building
materials.
All three of the key factors outlined at the start of this chapter have the potential to alter
the acoustic properties of hempcrete. In particular, the choice of constituent materials, not
only the binder but also the type of hemp shiv and its particle size distribution, is import-
ant. The porosity of the material is the critical factor in the physical processes of sound
insulation and absorption. Additionally, the density of the finished material, according to
specific mix ratios used, and the casting technique can both play a significant part.
As our understanding of this aspect of the material's performance develops, Arnaud and
Amziane point out, the possibility emerges of producing a hempcrete that is designed to a
particular specification of acoustic performance for a given situation, by manipulating the
variables described above.
Perhaps equally interesting is the idea that - since the nature and particle size distribution
of the hemp shiv are such good predictors of acoustic performance - by inverting the data
recorded on the acoustic properties of a range of hempcrete materials we may be able to
devise an acoustic test to determine the characteristics (e.g. particle size, apparent density
and porosity) of different hemp aggregates. This is interesting because currently there are
few techniques available for assessing these characteristics. An acoustic measure would
make it possible to describe the characteristics of hemp shiv based on a sample volume
that is representative of a wall, rather than by microscopic analysis of individual particles.
Furthermore, this technique would offer the opportunity to assess the quality of finished
hempcrete in situ in a non-invasive way, by the analysis of its acoustic parameters.