Hemp Concrete – A Traditional and Novel Green Building Material

Abstract

With the alarming global increase in carbon emissions and its implications, the need for carbon neutral or carbon negative technologies is of utmost importance and urgency. Cellulose aggregate concrete (CAC) or bio-aggregate concrete has not only the multi-benefits of low density, better thermal insulation and low embodied energy, it can also make use of industrial wastes such as fly ash, slag, etc. One such CAC is called hemp concrete, which is a composite made of hemp shiv and lime based binder. Hemp is one of the world's earliest cultivated crops and has a variety of applications including construction. This paper discusses various properties and applications of hemp and hemp concrete such as mechanical performance and durability, with a focus on its carbon sequestration ability and carbon negativity, and the current research interest as well as its possible contribution towards solution of climate change problems.

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International Conference on
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1
Hemp Concrete – A Traditional and Novel Green Building
Material
Tarun Jami1, S R Karade2 and L P Singh3
1Research Scholar, AcSIR, CSIR-Central Building Research Institute, Roorkee, tarunjami@gmail.com
2Sr. Principal Scientist, CSIR-Central Building Research Institute, Roorkee. srkarade@cbri.res.in
3Principal Scientist, CSIR-Central Building Research Institute, Roorkee, lpsingh@cbri.res.in
ABSTRACT
With the alarming global increase in carbon emissions and its implications, the need for carbon
neutral or carbon negative technologies is of utmost importance and urgency. Cellulose
aggregate concrete (CAC) or bio-aggregate concrete has not only the multi-benefits of low
density, better thermal insulation and low embodied energy, it can also make use of industrial
wastes such as fly ash, slag, etc. One such CAC is called hemp concrete, which is a composite
made of hemp shiv and lime based binder. Hemp is one of the world’s earliest cultivated crops
and has a variety of applications including construction. This paper discusses various properties
and applications of hemp and hemp concrete such as mechanical performance and durability,
with a focus on its carbon sequestration ability and carbon negativity, and the current research
interest as well as its possible contribution towards solution of climate change problems.
Keywords: Hemp Concrete; Carbon Negative; Carbon Sequestration; Green Building
Material; Sustainable Materials
INTRODUCTION
World leaders at the Paris Climate Accord, 2016 had committed to limit the global rise in
temperature to less than 1.5oC. Understandably that is a tall order as the global greenhouse gas
emissions are over 49.3 billion tonnes of CO2 equivalent (Olivier et al., 2017). Hence,
researchers and scientists have put forth a possible solution involving the deliberate and large-
scale modification of the Earth’s environment in an effort to negate some manifestations of
anthropogenic climate change, called geoengineering (Sandler, 2018). Geoengineering is not a
relatively new concept and has been a topic of discussion since early 2000s. Some strategies
that accomplish geoengineering are the large-scale removal of carbon dioxide from the earth’s
atmosphere, called Carbon Dioxide Reduction (CDR), and the large scale modification of the
earth’s atmosphere such as seeding large amounts of chemicals into the atmosphere in an
attempt to prevent solar warming of the earth’s surface, called Albedo Modification (AM)
(Sandler, 2018).
In effect, the world is currently at a stage where the human race is considering such a deliberate
large-scale anthropogenic intervention to the climate change problem that the use of “natural”
or bio-based products is freshly incentivised. A year 2014 study had shown that carbon dioxide
emissions (carbon emissions) from the manufacture of cement alone had amounted to 102
mega-tonnes of CO2 in India, forming a 4.4% component of the total 2.3 giga-tonnes of carbon
dioxide emitted (Olivier et al., 2015; Jami et al., 2016). Theoretically, the construction industry

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accounts for about 10% of the total carbon emissions. To counter the rising carbon dioxide
emissions, punctuated by the alarming rise in global warming and climate change, a fresh, new
perspective for a traditional building material has been put forth - the incorporation of plant-
derived biomass in a mineral binder matrix to form a productive building material with
desirable properties such as mechanical performance, durability and low carbon footprint,
called cellulose aggregate concrete (CAC). One such CAC is lime hemp concrete, also known
as hemp concrete or hempcrete.
Hempcrete is constituted of hemp shivs and lime based binder. Hemp is a collective name for
the high-growing varieties of the cannabis sativa plant used for industrial purposes such as
textiles, food, plastics, paper, etc. The success of hempcrete lies in the fact that it is carbon
negative due to its agricultural origin and the use of lime and other industrial wastes as the
mineral binders. It was found that every kilogram of hemp shivs sequesters about 1.6 to 1.8 kg
of carbon dioxide (Jami, 2016). Historically, a recent study had found that hemp was present
in the lime and clay plaster found in the Ellora Caves, over 1500 years old, fulfilling the
function of preventing insect activity (Rizwanullah, 2016). Consequently, due to its suitability
as a feedstock for various industries and applications ranging from food, clothing, shelter and
recreation to more sophisticated application such as Nano-technology, combined with its
excellent ability to sequester carbon dioxide rapidly; cultivation of the hemp plant for industrial
uses is a viable geoengineering mechanism.
Hemp shiv is one of the most widely used and studied plant particles for the manufacture of
building materials, and hemp concrete is one of the most widely studied bio-based concretes.
This paper apart from connecting geoengineering with industrial hemp, will also discuss the
various applications of hemp, mechanical properties of hemp concrete and its ability for carbon
sequestration.
APPLICATIONS OF HEMP
Hemp has found its use in about 25000 applications (Popular Mechanics, 1938) and has been
in use since as early as 8000 BCE (Allegret, 2013), making it one of the earliest cultivated
crops. Interestingly, the U.S. Declaration of Independence was written on a hemp paper. Some
of the many products refined from hemp that have been perfected over time are as following:
1. Hemp seed food
2. Hempseed edible oil
3. Oil, resin and wax for industrial applications such as lubricants, etc.
4. Medicines for various pains and psychological ailments, as well as cancer treatment
5. Personal care products derived from hempseed oil
6. Textiles products such as apparels and technical textiles,
7. Cordage
8. Biofuel
9. Cellulose plastics
10. Paper
11. Defence applications such as bullet-proof vests and bunkers

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12. Hemp concrete
13. Hemp composite boards for construction
With the rising popularity of hemp and its eco-friendly stature being recognised, more and
more researchers and private organisations are joining the bandwagon exploring various
applications for the products of this plant.
PROPERTIES OF HEMP CONRETE
Anatomy of Hemp Stalk
The hemp stalk/straw is majorly divided into 2 parts – (a) bast and (b) hurd. The bast fibres are
extracted from a retting process of the hemp straw and woven into textiles, cords, ropes, etc.
The hurd of the plant has hitherto been used for insulation, animal bedding, etc. However, for
the purpose of hemp concrete, it is the hurds, also known as shivs that are used as the cellulose
aggregates. Figure 1 shows the hemp stalk that is processed into its various forms for the
manufacture of hempcrete.
Figure 1 a. Retted hemp stalk without bast fibres; b. Process hemp shivs along with
bast fibres; c. hemp shivs for making high-density hemp concrete; d. hemp bast fibres
The retted hemp stalks as shown in Figure 1 are processed in a blade mill where the size of the
aggregates can be chosen and follow a definite size group. Large hemp industries that process
hemp stalks for bast fibres use a decorticator, which produces hemp shivs of random sizes from
the whole hemp straws.
Mechanical Properties of Hemp Concrete
Hemp concrete is a lightweight concrete that is currently only being used as an in-fill material
in non-structural applications (see Figure 2). In European countries it is normally cast in
between timber studs as an infill material, playing the double function of a wall and insulation.
Hence, mechanical performance was not a matter of major concern for hemp concrete, with
manufacturers focusing majorly on the thermal and hygrothermal properties. However, the
mechanical support provided by hempcrete infill to timber studs in weak-axis is an added
benefit, begotten unintentionally. A 2012 study at Queen’s University had shown that high
density as well as low-density hemp concrete infill had prevented weak axis buckling in timber
a.
b.
c.
d.

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walls, failing at more than twice the load as compared to unfilled timber walls (Mukherjee,
2012).
Density
Several researchers have published varying results for the density of hempcrete, ranging from
300 to 900 kg/m3 (Arnaud and Gourlay, 2011; Cerezo, 2005; Cigasova et al., 2014; Elfordy et
al., 2008; Evrard, 2003; Kioy, 2005; Nguyen et al., 2009; Piot et al., 2017). However, the
material has never lost its lightweight status always remaining well below the 1000 kg/m3
density mark. The large variation in the values of density of hemp concrete also bears testament
towards the material’s versatility in applications, within of course, the boundaries of non-
structural applications. The characteristic reason for the low density of hemp concrete lies in
the fact that hemp is a very lightweight material with an apparent density of about 112 kg/m3
(Picandet, 2017) and the use of lightweight binders such as lime (900 – 1000 kg/m3) and fly
ash.
Figure 2 Hemp concrete blocks made from hemp shivs and 90% hydrated lime
Compressive Strength
One of the most important parameters for a building material used as a walling material is
compressive strength. Researchers around the world that have worked with hemp concrete have
reported various values of hempcrete’s compressive strength ranging from 0.2 to 6.94 MPa
depending on the casting process (Arnaud and Gourlay, 2011; Cerezo, 2005; Cigasova et al.,
2014; Elfordy et al., 2008; Evrard, 2003; Kioy, 2005; Nguyen et al., 2009). The authors have
also discerned a clear proportional relationship between density and compressive strength.
Most hemp concrete mixes when manufactured without any compaction tend to have a low
young’s modulus and dimensional stability as compared to the compacted mixes. Also, it was
found that compaction increases the density as the compactness increases. Some other factors,
which affect the compressive strength of the hemp concrete mix, are aggregate size and
chemical composition of the binder.
Thermal Conductivity
One of the hallmark characteristics of hemp concrete is its excellent thermal behaviour. Past
research had shown that the thermal conductivity falls between 0.06 and 0.54 W/(m.K)
(Elfordy et al., 2008; Lawrence et al., 2012; Evrard et al., 2014). Much like compressive

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strength, the thermal conductivity of hemp concrete varies proportionally with density (see
Table 1). As the density of the mix increases, so does the thermal conductivity. This is because
of the reduction of the pore size and the porosity. As the density increases, the heat transfer
interface becomes more connected, thereby facilitating heat transfer. However, due to hemp
concrete’s high porosity and Moisture Buffer Value of 2 g/(m2.%RH) (Latif et al., 2015),
moisture gets entrapped within the many pores of the material resulting in the material gaining
thermal mass. This thermal mass prevents fluctuations in temperature of the indoor atmosphere
much like phase change materials (PCM).
Table 1. Thermal conductivities of various mixes of hemp concrete as reported by
various authors in published research
Author
Density: kg/m3
Thermal Conductivity: W/(m.K)
Lawrence et al., 2012
330
0.09 – 0.115
440
0.115
600 - 1000
0.14 – 0.27
Elfordy et al., 2008
417
0.179
475
0.421
496
0.542
Evrard et al., 2014
743
0.133
Durability
Durability signifies the longevity of the structure made from the material studied. Interestingly,
hemp concrete, because of the lime content undergoes carbonation across a span of several
years and turns into limestone, rendering strength to the structure and the micro bonds in the
binder matrix (Cultrone et al., 2005; Lawrence, 2006). This gain in strength over time could
possibly signify increasing durability with time. According to Walker et al. who had studied
the mechanical properties and durability of various hemp-lime mixes, hemp concrete behaves
poorly in freeze-thaw cycles because of the washout of mass. However, they had found that
hemp concrete is fairly resistant to sodium chloride salt exposure and biological deterioration
due to microbial attack (Walker et al., 2014). Contrarily, Piot et al., 2017 had reported the
growth of mould just beneath the surface of the coating they had applied to their test specimens.
They had tested their hemp concrete specimens for an entire year (Piot et al., 2017).
Carbon Negativity of Hemp Concrete
A study conducted by Jami, 2016 had shown that hemp shivs are composed of 45% carbon,
meaning 1 kg of hemp shivs sequester about 1.6 to 1.8 kg of carbon dioxide through
photosynthesis during the plant’s growth. A study conducted by Ip and Miller, 2012 indicated
that a functional wall unit of dimensions 1m x 1m x 0.3m had sequestrated 82.71 kg of carbon
dioxide, which not only compensated for the 46.43 kg of carbon dioxide emitted during
growing, manufacturing and construction processes such as manufacture of lime,
transportation of material, etc., but also enabled an additional 36.08 kg of carbon storage. This
means that structures made of hemp concrete essentially compensate for all of the carbon

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emissions made from all other processes related to constructing the structures. Hence, if the
goal is to achieve a carbon neutral building, hemp concrete must be used in a considerable
quantum to offset the carbon emissions.
CONCLUSION
With enough emphasis laid on the carbon negative nature and the various mechanical
properties of the material, it can be concluded that while hemp concrete has been in use since
several centuries ago, the traditional material has freshly acquired a futuristic status. However,
competing against technologies that enable rapid construction and reduce cost would mean that
considerable research efforts would need to be undertaken. Currently, only one variety of hemp
construction is being explored, which is the application of hemp concrete in combination with
timber studs in walls and columns. For wider distribution of the material, hemp concrete blocks
must be researched and developed that can be enabled to take larger loads. Hence
developmental studies for improve the mechanical properties such as compressive strength,
flexural strength and dimensional stability must be undertaken. Further, the durability issues
arising out of the mould growth must be addressed as it affects the health of the residents.
ACKNOWLEDGEMENTS
The authors would like to thank GreenJams Infrastructures LLP for sponsoring this research.
The authors would also like to thank the Director, CSIR – CBRI for permitting to present this
work.
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