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Hemp Concrete – A Traditional and Novel Green Building Material

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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
Advances in Construction Materials and Structures (ACMS-2018)
IIT Roorkee, Roorkee, Uttarakhand, India, March 7-8, 2018
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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IIT Roorkee, Roorkee, Uttarakhand, India, March 7-8, 2018
2
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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Advances in Construction Materials and Structures (ACMS-2018)
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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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Advances in Construction Materials and Structures (ACMS-2018)
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5
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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... Hempcrete and similar materials can be used to create a variety of building products, including bricks, natural mortar, thermal plaster, and thermal screed for flooring (Radogna et al. 2018). As described above, hemp-based construction materials have low-embodied energy, with each kilogram of hemp hurd sequestering roughly 1.6 to 1.8 kg of carbon dioxide (Jami et al. 2018). In theory, hempcrete could even have a negative carbon footprint if waste lime captured from other industries could be used as the mineral binder (Jami et al. 2018). ...
... As described above, hemp-based construction materials have low-embodied energy, with each kilogram of hemp hurd sequestering roughly 1.6 to 1.8 kg of carbon dioxide (Jami et al. 2018). In theory, hempcrete could even have a negative carbon footprint if waste lime captured from other industries could be used as the mineral binder (Jami et al. 2018). ...
... Binders (which range from clays to lime) serve to aggregate the hemp hurd and play an integral role in enhancing its strength, durability, hydroscopicity, pyrolysis threshold, resistance to insect damage, and acoustical and thermal performance. (Arizzi et al. 2015;Florentin et al. 2017;Jami et al. 2018). Hemp can absorb most of the water existing in the binder matrix. ...
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... The Aggregate size, binder's chemical composition and compaction are among the principal parameters affected compressive strength of hempcrete composites. The composites showed a clear proportionality between compressive strength and density [25]. The compressive strength of some hempcrete formulations was found to be equivalent to that of lightweight concrete and foam concrete [26]. ...
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Construction industry is one of the main sectors contributing for the growth of countries economy and also it is one of sector releasing huge amount of carbon emission in the atmosphere. Several measures are taken in this sector by adopting new trends in the construction industry with respect to the use of evolving material such as low carbon cement, fast setting concrete, Self-healing concrete and more, has left us with a high need for research in the area of sustainable materials. As most of the building material used in construction like concrete and cement are high carbon dioxide emitting material that can be a hazard (in a longer run) to the environment and people working in such buildings. To overcome this situation an alternative sustainable material has to be used for the construction of eco-friendly buildings. Hempcrete is a bio-composite material and also it is one of the prospective materials to reduce greenhouse gas emissions. It can be used in Construction and Insulation activities by Hemp hurds and lime. Hemp is the fastest growing plant and has one of the strongest plants fibers and due to its fastest and rapid growing nature it can lock up more carbon in it. This has been used in France since the 1990s for construction of non-weight bearing insulating infill walls. A meter cube of hempcrete has the capability to absorb 165 kg of carbon dioxide and has excellent fire resistance. Resistance to crack under movement being the core property of hempcrete makes it most appropriate for use in earthquake-prone areas. In this research, an initiative was taken up to check the feasibility of hempcrete as an alternative to conventional concrete. Few feasibility studies were carried to highlight application and access the properties of the same. The main aim to suggest the application of hempcrete with admixture like fine aggregate and testing of its strength under Universal Testing Machine (AIMIL) make. Though, Hempcrete does not have adequate strength as par with the conventional concrete but can be used for the construction of substructure. It can be concluded that it can be highly beneficial for non-load bearing structures for its property like lightweight breathability, energy efficiency etc.
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Research on the application of the Passive House standard both in warm and cold climates and with a focus on difficulties-failures that stem from this application, as well as the ecological/environmental aspect of this model, led to the idea of developing a house model in such a way that it can provide answers to the questions that arose throughout this study. The design of residences in accordance with the principles of Passive House should neither rule out, nor ignore the principles of Bioclimatic Design on Green Building as fundamental for designing houses that are friendly to the environment and the user. Τhe planning of buildings that aim at very low consumptions, as in the case of the German standard, should be inextricably linked with the implementation of Green Building principles on design, as well as the obvious use of materials that are friendly to the environment and the user. The extent to which a residence is ecological should be examined in parallel with the energy conservation that is achieved in the building, so that the discussion regarding environmental protection and human intervention has a substantial meaning. The architect is required to resolve all difficulties/obstacles that arise from this undertaking, in order that the architectural work is robust and eco-friendly with very low power consumptions. On the ground of this reasoning, the current postgraduate dissertation examines the combination of all aforementioned fundamental principles, which are essential to the formation of an environmental, sustainable architecture, with the aim of designing a building on an existent place, that is formed as a small residential area with defined limitations and a thorough examination, in order to produce a proper outcome. The primary aim throughout the conduction of this study was to design a residence from house materials that fulfils the principles of Passive House and incorporates the Green Building principles to the highest possible extent, without downgrading its architectural quality. The result indicates that this project is plausible and flexible, determined by the existent choices, and the outcome varies depending on the prioritization of the aforementioned principles at each case.
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Background: Environment-friendly materials attract attention whilst the construction sector causes excessive global energy consumption and emission of greenhouse gas. Renewable plant-based biomaterials, which have a low environmental impact, are very beneficial in order to prevent environmental pollution and to preserve natural resources. Hempcrete provides environment-friendly construction materials as well as thermal and hygroscopic properties. Objective: This paper presents a review of hempcrete research about understanding the environmental effects and construction methods of hempcrete; moreover, the benefits and innovations it has provided throughout its life cycle, have been investigated. Methods: For this purpose, experimental studies of hempcrete were compared to each other in all aspects in order to determine density, thermal conductivity, vapor permeability, hygrometric behavior, durability, acoustic absorption, mechanical properties and life cycle analysis. Moreover, binder characteristics, hemp shiv proportions, water content, curing conditions and results have been focused on to explain the benefits of hempcrete. Results: The results obtained show that hempcrete has high porosity and vapor permeability, medium-low density, low thermal conductivity, Young's modulus and compressive strength. Conclusion: Based upon the findings of the studies reviewed, hempcrete is an advantageous material in buildings with its extraordinary thermal and hygrometric behaviour. Hemp is also an eco-friendly and economical plant-based raw material for the construction industry.
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Background Environment-friendly materials attract attention whilst the construction sector causes excessive global energy consumption and emission of greenhouse gas. Renewable plant-based biomaterials, which have a low environmental impact, are very beneficial in order to prevent environmental pollution and to preserve natural resources. Hempcrete provides environment-friendly construction materials as well as thermal and hygroscopic properties. Objective This paper presents a review of hempcrete research about understanding the environmental effects and construction methods of hempcrete; moreover, the benefits and innovations it has provided throughout its life cycle, have been investigated. Methods For this purpose, experimental studies of hempcrete were compared to each other in all aspects in order to determine density, thermal conductivity, vapor permeability, hygrometric behavior, durability, acoustic absorption, mechanical properties and life cycle analysis. Moreover, binder characteristics, hemp shiv proportions, water content, curing conditions and results have been focused on to explain the benefits of hempcrete. Results The results obtained show that hempcrete has high porosity and vapor permeability, medium-low density, low thermal conductivity, Young’s modulus and compressive strength. Conclusion Based upon the findings of the studies reviewed, hempcrete is an advantageous material in buildings with its extraordinary thermal and hygrometric behaviour. Hemp is also an eco-friendly and economical plant-based raw material for the construction industry.
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This paper investigates some of the myriad collective action implications of geoengineering. Its two major components – carbon dioxide reduction and albedo modification – present diverse collective action and strategic aspects. Carbon dioxide reduction may be characterized by Prisoners’ Dilemma, threshold, or harmony games, depending on capture and sequestration procedures. In contrast, albedo modification may abide by chicken, coordination, or threshold games. Once deployed, albedo modification presents an addiction problem that makes current efforts difficult to alter, even by countries originally opposed to such modification. With its many procedures, geoengineering is tied to a host of collective action problems that may ensue prior, during, or after geoengineering deployment. For carbon dioxide reduction, governance concerns encouraging action, while for albedo modification, governance concerns inhibiting unilateral action. The latter may be a more difficult governance issue.
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The onset of heavy greenhouse gas (GHG) emissions from conventional construction practices has led to research on several plausible low-carbon dioxide footprint construction materials that are either carbon dioxide neutral or carbon dioxide negative. One such ‘green’ construction material is lime hemp concrete (LHC), hemp concrete or hempcrete, which are some of the many names of this novel construction material. Hemp concrete is essentially a composite made of lime and hemp shivs. This paper presents a literature review of the various studies carried out on hemp concrete to understand its properties, drawbacks and advantages in construction. The review dwells on discussion of hemp, use of lime as a binder material and the mechanical, thermal and hygric properties of LHC. The salient features of LHC with regard to mechanical, thermal and hygric properties and ecological impact are discussed in the paper. It is observed that further research on LHC is required to be able to establish mix design principles, improve the compressive and flexural strengths of LHC and its use as a load-bearing structural material for high-rise constructions and establish cradle-to-death GHG emissions, recyclability and reusability which seem to be promising propositions with hemp concrete.
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Experiments were carried out according to the Nordtest protocol to study the moisture buffer potential of hemp-lime walls with a range of different internal linings and surface treatments. It was observed that the moisture buffer value was ‘Excellent’ when the inner surface of hemp-lime was exposed. ‘Excellent’ moisture buffer values were also obtained for hemp-lime with lime plaster. All other assemblies demonstrated ‘Good’ moisture buffer value. Moisture buffer values of the assemblies, after application of paint on the upper surfaces, were also determined. It was observed that application of synthetic pigment based trade paint could reduce the moisture buffer performance of the assembly consisting of hemp-lime and lime-plaster from ‘Excellent’ to ‘Good’ while between 61 and 69% reduction of moisture buffer value was observed for the other assemblies. However, the reduced buffer values of the assemblies are still comparable with other moisture buffering building materials. It was further observed that moisture buffer performance was improved when clay based organic paint was used instead of trade paint.
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This article discusses about the possibility of using industrial hemp as a source of natural fibres for purpose of construction. The technical hemp (Cannabis Sativa) is the source of two types of fibres; bast fibres (used mainly in the paper and textile industries) and woody fibres - hurds. In recent decades hemp hurds have experienced a renaissance in use in the construction industry. This material is waste resulting from the processing of hemp stem on bast fibres. For the purposes of construction it has potential thanks to their exceptional thermal insulation, antiseptic, acoustic and mechanical properties. One of the aspects of using hemp products in building industry is that these materials are environmentally friendly in comparison to the used conventional materials (such as conventional insulating materials with polymer matrix or based on mineral wool). In this article, the lightweight composites based on hemp hurds (as a biomass) and nonconventional binders MgO-cement are tested. The physical and mechanical properties of the composites hardened in indoor condition (28, 60, 90, 180 days) are studied. The results of the obtained parameters (density, water content, compressive strength, thermal conductivity coefficient) of hardened composites are presented.
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Hemp is made of highly deformable particles. Depending on the water content, on the particle size distribution, and on many other material parameters such as initial porosity and retting of the processed stalks, the mechanical behaviour of shiv in bulk can change significantly. In a compaction process, the mass per volume of the raw material increases with the applied stress and some creep or relaxation effects occur as observed in wood based materials. Hence, the mechanical properties of the bulk impact the packaging of the raw material as the shiv density inside the final mix and the in-service properties of the composite material. In this way, the bulk compressibility is primarily useful to manage the building processes, from transport of the raw material, to mixing and casting.
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Hemp concrete is becoming a popular building construction material, as it has a low environmental impact and helps reducing the heat conductivity of walls. The generally used binder is lime, but in this study a prompt natural cement binder was used. The objective of this study was to analyse the behaviour of a hempcrete wall in realistic conditions. 2 test walls made of prefabricated hemp concrete blocks were built. Those walls were exposed to the outdoor climate on the one side, and to a controlled indoor climate on the other side. 2 different exterior coatings were applied. The experiment lasted one year. In addition, numerical simulations were carried out. The model was used to determine the material properties and to help understand the behaviour measured. The results show that an important humidification of the wall can occur if the coating is not well chosen. The exterior coating must be very permeable to water vapour, but it seems to be important to prevent the absorption of rain as well, otherwise, the humidity inside the wall can lead to degradations such as mould growth or increased thermal conductivity. Both numerical simulation and measurements show that applying a vapour permeable coating on the blocks does not slow down the drying process, the hempcrete itself being the limiting factor.
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Over half of the global raw materials are consumed in the construction of buildings and roads, their associated greenhouse gas emissions from excavation to final disposal are pivotal to the change in global climate. Hemp is a natural resource that has recently been used as a low environmental impact material in a number of composite products. In buildings, it is increasingly used with a lime base binder in wall constructions. There are limited data available to evaluate the environmental impact of this type of construction in the UK. This research aims to identify the processes and materials involved in the construction of hemp-lime walls and to establish their life cycle impact on climate change. The study follows assessment procedures and guidelines of international (ISO14040) and UK (PAS2050) standards. The functional unit defined for the hemp-lime wall construction is 1 m square in area, 300 mm thick with timber frame support inside. Primary data were collected for processes and materials that have no existing information. Other processes with impact data available from credible database were adapted in the assessment by taking into account the conditions and practice in the UK. Assessment was carried out using the SimaPro LCA tool over a lifetime of 100 years. Within the boundary and assumptions made, results showed the functional unit could sequestrate 82.7 kg of carbon dioxide with a net life cycle reduction of greenhouse gas emission of 36.08 kg CO2e. Crown Copyright