Hempcrete or hemplime is
biocomposite
A biocomposite is a composite material formed by a matrix (resin) and a reinforcement of natural fibers.
Environmental concern and cost of synthetic fibres have led the foundation of using natural fibre as reinforcement in polymeric composites ...
material, a mixture of hemp hurds (
shives
Shives, also known as shoves, boon or hurd, are the wooden refuse removed during processing flax, hemp, or jute, as opposed to the fibres ( tow). Shives consist of "the woody inner portion of the hemp stalk, broken into pieces and separated from ...
) and
lime
Lime commonly refers to:
* Lime (fruit), a green citrus fruit
* Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide
* Lime (color), a color between yellow and green
Lime may also refer to:
Botany ...
,
sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...
, or
pozzolan
Pozzolans are a broad class of Silicon_dioxide, siliceous and aluminium oxide, aluminous materials which, in themselves, possess little or no cementitious value but which will, in finely divided form and in the presence of water, react chemically ...
s, which is used as a material for construction and
insulation
Insulation may refer to:
Thermal
* Thermal insulation, use of materials to reduce rates of heat transfer
** List of insulation materials
** Building insulation, thermal insulation added to buildings for comfort and energy efficiency
*** Insulated ...
. It is marketed under names like Hempcrete, Canobiote, Canosmose, Isochanvre and IsoHemp.
Hempcrete is easier to work with than traditional lime mixes and acts as an insulator and moisture regulator. It lacks the
brittleness
A material is brittle if, when subjected to stress, it fractures with little elastic deformation and without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Bre ...
of
concrete
Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wi ...
and consequently does not need
expansion joint
An expansion joint, or movement joint, is an assembly designed to hold parts together while safely absorbing temperature-induced expansion and contraction of building materials, and vibration, or to allow movement due to ground settlement or seis ...
s.
The result is a lightweight insulating material ideal for most climates as it combines insulation and
thermal mass
In building design, thermal mass is a property of the mass of a building that enables it to store heat and provide inertia against temperature fluctuations. It is sometimes known as the thermal flywheel effect. The thermal mass of heavy structura ...
.
Mixture materials
Hempcrete is developed from a mixture of
hemp
Hemp, or industrial hemp, is a botanical class of ''Cannabis sativa'' cultivars grown specifically for industrial or medicinal use. It can be used to make a wide range of products. Along with bamboo, hemp is among the fastest growing plants o ...
shives, and a lime based binder.
The lime-based binder typically consists of either hydrated lime or natural hydraulic lime.
Hydrated lime is made from pure
limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
and sets through the absorption of CO
2 during the carbonation process.
When dealing with time constraints, hydraulic binders are used in combination with regular hydrated lime because the set time for hempcrete will be less than that of regular limes (about two weeks to a month to gain adequate strength).
For example, a small fraction of cement and/or pozzolanic binder is added to speed up the setting time as well.
The overall process creates a mixture that will develop into a solid, but light and durable product.
The typical production process of hempcrete is contained in a few steps.
At the manufacturing location,
hemp
Hemp, or industrial hemp, is a botanical class of ''Cannabis sativa'' cultivars grown specifically for industrial or medicinal use. It can be used to make a wide range of products. Along with bamboo, hemp is among the fastest growing plants o ...
is stored in a storage room, and the lime is stored in silos. The
hemp
Hemp, or industrial hemp, is a botanical class of ''Cannabis sativa'' cultivars grown specifically for industrial or medicinal use. It can be used to make a wide range of products. Along with bamboo, hemp is among the fastest growing plants o ...
and lime are added to water and thus mixed.
The mixture then travels through a conveyor belt where a machine shapes it into blocks.
The blocks are then taken to an area to cure.
Once cured, the blocks are separated into 2 m
3 batches and loaded on pallets.
They are wrapped up with polyethylene packaging film and polypropylene straps to be transported to a construction site.
Applications and specifications
Hempcrete has been used in
France
France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...
since the early 1990s, and more recently in
Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
, to construct non-weight bearing insulating infill walls, as hempcrete does not have the requisite strength for constructing
foundation
Foundation may refer to:
* Foundation (nonprofit), a type of charitable organization
** Foundation (United States law), a type of charitable organization in the U.S.
** Private foundation, a charitable organization that, while serving a good cause ...
and is instead supported by the frame.
Hempcrete was also used to renovate old buildings made of stone or lime.
France continues to be an avid user of hempcrete, and it grows in popularity there annually. Canada has followed France's direction in the organic building technologies sector, and hempcrete has become a growing innovation in
Ontario
Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central Ca ...
and
Quebec
Quebec ( ; )According to the Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is one of the thirtee ...
. There are two primary construction techniques used right now for implementing hempcrete. The first technique consists of using forms to cast or spray hempcrete directly in place on the construction site.
The second technique consists of stacking prefabricated blocks that are delivered to the project site similar to masonry construction.
Once hempcrete technology is implemented between timber framing, drywall or plaster is added for aesthetics and increased durability.
The typical
compressive strength
In mechanics, compressive strength or compression strength is the capacity of a material or structure to withstand loads tending to reduce size (as opposed to tensile strength which withstands loads tending to elongate). In other words, compre ...
is around 1 MPa,
around 5% that of residential grade
concrete
Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wi ...
. It is a low density material and resistant to cracking under movement, thus making it suitable for use in earthquake-prone areas. Hempcrete walls must be used together with a frame of another material that supports the vertical load in building construction, as hempcrete's
density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...
is 15% that of traditional concrete. Studies in the UK indicate that the
performance gain between and walls is insignificant. Hempcrete walls are fireproof, transmit humidity, resist mould, and have excellent acoustic performance. Limecrete, Ltd. (UK) reports a fire resistance rating of 1 hour per British/EU standards.
In the United States, a permit is needed for the use of
hemp
Hemp, or industrial hemp, is a botanical class of ''Cannabis sativa'' cultivars grown specifically for industrial or medicinal use. It can be used to make a wide range of products. Along with bamboo, hemp is among the fastest growing plants o ...
in building.
Hempcrete's
R-value (its resistance to heat transfer) can range from to , making it an efficient insulating material (the higher the R-value, the better the insulation). The porosity of hempcrete falls within the range of 71.1% to 84.3% by volume.
The average
specific heat capacity
In thermodynamics, the specific heat capacity (symbol ) of a substance is the heat capacity of a sample of the substance divided by the mass of the sample, also sometimes referred to as massic heat capacity. Informally, it is the amount of heat t ...
of the hempcrete ranges from 1000 J/kg K to 1700 J/kg K.
The dry
thermal conductivity
The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa.
Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...
of hempcrete ranges from 0.05 W/mK to 0.138 W/mK.
The low
thermal diffusivity
In heat transfer analysis, thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure. It measures the rate of transfer of heat of a material from the hot end to the cold end. It has the SI ...
(1.48 x 10
−7 m
2/s) and effusivity (286 J/m
2Ks
-1/2) of hempcrete influence longer times for temperature change and create a warm sensation on the touch.
Low thermal diffusivity directly relates to increased thermal comfort within the building.
Benefits and constraints
Hempcrete provides high vapor permeability because of the mixture's ability to easily absorb or release water vapor from the air.
In frame structures, hempcrete mixtures can be used as filling materials in infill walls. Increasing the density of the mixture allows the production of roof or floor insulation hempcrete materials.
Decreasing the density allows the production of indoor and outdoor plasters.
Hempcrete block walls can be laid without any covering or can be covered with finishing plasters.
This latter uses the same hempcrete mixture but in different proportions.
The fact that the mixture contains a plant-based compound introduces the caution against water and rising damp levels.
Hempcrete walls need to be built with a joint between the wall and the ground in order to avoid capillary rising as well as water runoff at the wall base.
Moreover, hempcrete block can only be installed above the ground level.
External walls need to avoid rotting of shives by implementing protection by the rain gale with sand and lime plaster.
The exterior of a hempcrete based assembly needs these protections, but the interior side of an assembly can stay exposed.
Life cycle effects
Just like any crop,
hemp
Hemp, or industrial hemp, is a botanical class of ''Cannabis sativa'' cultivars grown specifically for industrial or medicinal use. It can be used to make a wide range of products. Along with bamboo, hemp is among the fastest growing plants o ...
absorbs CO
2 from the atmosphere while growing, so hempcrete is considered a
carbon-storing material.
Accordingly, this CO
2 will be stored in the hempcrete block after fabrication and for the duration of the block's life allowing positive environmental benefits.
The specific amount of carbonates in the blocks actually increases with the age of the block.
The amount of CO
2 capture within the net life cycle CO
2 emissions of hempcrete is estimated to be between -1.6 to -79 kg CO
2e/m
2.
There is a correlation that increasing the mass of the binder which increases the mixture density will increase the total estimated carbon uptake via carbonation.
The main cause of the environmental footprint for hempcrete comes from the production of the binder. Reports have estimated that 18.5% - 38.4% of initial emissions from binder production can be recovered through the carbonation process.
The binder is produced by the calcination of lime which takes place in kilns at very high temperatures.
The transport phase poses an
embodied energy
Embodied energy is the sum of all the energy required to produce any goods or services, considered as if that energy was incorporated or 'embodied' in the product itself. The concept can be useful in determining the effectiveness of energy-produ ...
footprint since it involves the consumption of diesel.
The diesel consumption also occurs due to the functioning of machineries used for
hemp
Hemp, or industrial hemp, is a botanical class of ''Cannabis sativa'' cultivars grown specifically for industrial or medicinal use. It can be used to make a wide range of products. Along with bamboo, hemp is among the fastest growing plants o ...
shives production.
Abiotic depletion is caused from the consumption of lead and cadmium in the electricity generation process, which is largest in the manufacturing of the hempcrete block inside the company.
See also
*
Fiber-reinforced concrete
Fiber-reinforced concrete or fibre-reinforced concrete (FRC) is concrete containing fibrous material which increases its structural integrity. It contains short discrete fibers that are uniformly distributed and randomly oriented. Fibers inclu ...
References
Further reading
*
External links
Hemcrete application datafrom Limetechnology
{{cannabis
Appropriate technology
Building materials
Concrete
Hemp products
Masonry