Hempcrete or hemplime is biocomposite material, a mixture of hemp hurds (shives) and lime, [1] sand, or pozzolans, which is used as a material for construction and insulation. [2] It is marketed under names like Hempcrete, Canobiote, Canosmose, Isochanvre, and IsoHemp. [3] Hempcrete is easier to work with than traditional lime mixes and acts as an insulator and moisture regulator. It lacks the brittleness of concrete and consequently does not need expansion joints. [3]
Typically, hempcrete has good thermal and acoustic insulation capabilities, but low mechanical performance, specifically compressive strength. [4] When used in prefabricated blocks, hempcrete acts as a carbon sink throughout its lifetime. [5] [6] The result is a lightweight, insulating material, finishing plaster, or a non-load bearing wall, ideal for most climates, since it combines insulation and thermal mass while providing a positive impact on the environment.
Hempcrete is made of the inner woody core of the hemp plant (hemp shives), a lime-based binder, and water. [6] The binder consists of either hydrated lime, or natural hydraulic lime. [7] Hydrated lime is made from pure limestone and sets through the absorption of CO2 during the carbonation process. [7] 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 (e.g., about two weeks to a month, to gain adequate strength). [7]
A small amount of cement and/or pozzolanic binder is added to speed up the setting time. [6] The overall process creates a mixture that will develop into a solid, light, and durable product. [6]
Hempcrete has been used in France since the early 1990s, and more recently in Canada, to construct non-weight bearing insulating infill walls, as hempcrete does not have the requisite strength for constructing foundation and is instead supported by the frame. [8] Hempcrete was also used to renovate old buildings made of stone or lime. [9] France continues to be an avid user of hempcrete, and it grows in popularity there annually. [10] Canada has followed France's direction in the organic building technologies sector, and hempcrete has become a growing innovation in Ontario and Quebec. [11]
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. [7] The second technique consists of stacking prefabricated blocks that are delivered to the project site similar to masonry construction. [7] Once hempcrete technology is implemented between timber framing, drywall or plaster is added for aesthetics and increased durability. [7] Hempcrete can be used for a number of purposes in buildings, including roof, wall, slab, and render insulation, each of which has its own formulation and dosages of the various constituents respectively. [12] [13] [14] [15]
Typically, hempcrete has a low mechanical performance. Hempcrete is a fairly new material and is still being studied. Several items affect the mechanical properties of hempcrete such as aggregate size, type of binder, proportions within the mixture, manufacturing method, molding method, and compaction energy. [4] All studies show variability within hempcrete properties and determine that it is sensitive to many factors. [4]
A study was conducted that focuses on the variability and statistical significance of hempcrete properties by analyzing two sizes of hempcrete columns with hemp from two different distributors under a normal distribution. The coefficient of variance (COV) indicates the dispersion of experimental results and is important in understanding the variability among hempcrete properties. [4] Young's modulus continually has a high COV across multiple experiments. The Young's modulus of hempcrete is 22.5 MPA. [4] Young's modulus and compressive strength are two mechanical properties that are correlated. [4]
The compressive strength is typically around 0.3 MPA. [4] Due to the lower compressive strength, hempcrete cannot be used for load-bearing elements in construction. Density is affected by drying kinetics, with a larger specific area the drying time decreases. [4] The size of the specimen and the hemp shives should be accounted for when determining the density. [4] In the model, the density of hempcrete is 415 kg/m3 with an average coefficient of variance (COV) of 6.4%. [4]
Hempcrete's low density material and resistance to cracking under movement make it suitable for use in earthquake-prone areas. [16] Hempcrete walls must be used together with a frame of another material that supports the vertical load in building construction, as hempcrete's density is 15% that of traditional concrete. [17] Studies in the UK indicate that the performance gain between 230 mm (9 in) and 300 mm (12 in) walls is insignificant.[ clarification needed ] Hempcrete walls are fireproof, transmit humidity, resist mould, and have excellent acoustic performance. [18] Limecrete, Ltd. (UK) reports a fire resistance rating of 1 hour per British/EU standards. [19]
Hempcrete's R-value (its resistance to heat transfer) can range from 0.67/cm (1.7/in) to 1.2/cm (3.0/in) , making it an efficient insulating material (the higher the R-value, the better the insulation). [20] [21] [22] The porosity of hempcrete falls within the range of 71.1% to 84.3% by volume. [23] The average specific heat capacity of the hempcrete ranges from 1000 to 1700 J/(kg⋅K). [23] The dry thermal conductivity of hempcrete ranges from 0.05 to 0.138 W/(m⋅K). [23] The low thermal diffusivity (1.48×10−7 m2/s) and effusivity [286 J/(m2⋅K⋅s−1/2)] of hempcrete reduce the ability of hempcrete to activate the thermal mass.
Hemp concrete has a low thermal conductivity, ranging from 0.06 to 0.6 W m−1 K−1, [24] [15] [25] a total porosity of 68–80% [24] [26] and a density of 200 kg /m3 to 960 kg/m3. [15] [27] Hemp concrete is also an aerated material with high water vapour permeability and its total porosity very close to open porosity allowing it to absorb significant amounts of water. [28] The water vapour diffusion resistance of hemp concrete ranges from 5 to 25. [24] [29] Furthermore, between 2 and 4.3 g/ (m2%RH), it is considered an excellent moisture regulator. [28] [30] It can absorb relative humidity when there is a surplus in the living environment and release it when there is a deficit. [31] [32] [33] It is important to note that these properties depend on the composition of the material, the type of binder, temperature and humidity. Due to its latent heating effects, which are the results of its high thermal ability and comprehensive moisture control, hemp concrete exhibits phase change material properties. [5]
Due to the large variety of hemp, the porosity differs from one type to another, therefore its thermal insulating abilities vary too. [34] The lower the density, the lower the heat transfer coefficient, a characteristic of insulating materials. [34] On three cubic samples of hempcrete after 28 days of drying the heat transfer coefficient was measured using ISOMET 2114, a portable system for measuring the heat transfer of properties. [34] Hempcrete has a coefficient of heat transfer of 0.0652 W/(m⋅K) and a specific weight of 296 kg/m3. [34] Attention should be paid to mixing the hempcrete, as it influences the properties of the material. Further testing needs to be conducted in correlation to specimen size to determine the influence that size has on the properties of hempcrete.
In the United States, a permit is needed for the use of hemp in building. [35]
Hempcrete has a high silica content, which makes it more resistant to biological degradation than other plant products. [36]
Hempcrete materials are a product of a type of binder and hemp shives size and quality, and the proportions in the mixture can greatly affect its properties and performance. [6] The most notable limiting factor with hempcrete is the low mechanical performance. [4] Due to low mechanical performance, the material should not be used for load-bearing structures.
Although it is not known for its strength, hempcrete provides a high vapor permeability that allows for better control of temperature in an indoor environment. [6] It can also be used as a filling material in frame structures and be used to make prefabricated panels. [6] Altering the density of hempcrete mixtures also affects its use. Higher-density hempcrete mixtures are used for floor and roof insulation, while lower-density mixtures are used for indoor insulation and outdoor plasters. [6]
Hempcrete block walls can be laid without any covering or can be covered with finishing plasters. [6] This latter uses the same hempcrete mixture but in different proportions. Since hempcrete contains a plant-based compound, walls need to be built with a joint in between the wall and ground to prevent capillary rising of water and runoff, blocks need to be installed above ground level and exterior walls should be protected with sand and plasters to avoid rotting shives. [6]
Just like any crop, hemp absorbs CO2 from the atmosphere while growing, so hempcrete is considered a carbon-storing material. [6] A hempcrete block continually stores CO2 during its entire life, from fabrication to end-of-life, creating positive environmental benefits. [6] Through a life cycle assessment (LCA) of hempcrete blocks using research and X-ray Powder Diffraction (XRPD), it was found that the blocks store a large quantity of carbon from photosynthesis during plant growth and by carbonation during the use phase of the blocks. [6]
The LCA of hempcrete blocks considers seven unit processes: hemp shives and production, binder production, transport of raw materials to the manufacturing company, hempcrete blocks production processes, transport of hempcrete blocks to the construction site, wall construction, and the use phase. [6] The impact assessment of each process was analyzed using the following impact categories: abiotic depletion (ADP), fossil fuel depletion (ADP Fossil), global warming over a time interval of 100 years (GWP), ozone depletion (ODP), acidification (AP), eutrophication (EP), and photochemical ozone creation (POCP). [6]
The binder production provides the largest environmental impact while the transport phases are the second. [6] During binder production in the lime calcination and clinker creation portion, the emissions are the most notable. [6] A large amount of diesel consumption in the transport phases and during the manufacturing of hemp shives created a large portion of the cumulative energy demand and along with the calcination of lime which takes place in kilns, is a main source of fossil fuel emissions. [6] Abiotic depletion is mostly attributed to the electricity used during binder production and although minimal, also during the block production processes. [6] It is important to focus on the water content in a hempcrete mixture, because too much water can cause slow drying and create a negative impact, preventing lime carbonation. [34]
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. [7] The specific amount of carbonates in the blocks actually increases with the age of the block. [6] During the growth of hemp the plant absorbs CO2, the binder begins to absorb CO2 after the mixing process, and the wall absorbs CO2 counteracting the greenhouse emissions, by acting as a carbon sink. [6] A hempcrete block will continue to store carbon throughout its life and can be crushed and used again as a filler for insulation. [6] The amount of CO2 capture within the net life cycle CO2 emissions of hempcrete is estimated to be between -1.6 to -79 kg CO2e/m2. [7] 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. [7]
The impacts arising from indirect land use changes of hemp cultivation, maintenance work, and end-of-life need to be studied to create a full cradle-to-grave environmental impact profile of hempcrete blocks. To counteract the negative environmental impacts that hempcrete blocks have on the environment the transport distances should be shortened as much as possible. Since hempcrete is not typically load-bearing, ratios should be explored to possibly completely remove the cement from the mixture. [6]
Hempcrete is a fairly new natural building material whose usage has increased throughout European countries in recent years and is gaining traction within the United States. The Hemp Building Foundation submitted paperwork to the International Residential Codes (IRC) in February 2022 to certify the material as a national building material, allowing the construction industry to gain more familiarity with the material. [37]
Hempcrete is a construction building material that uses hemp shives, aggregate, water, and a type of binder to act as non-bearing walls, insulators, finishing plasters, and blocks. The material has low mechanical properties and low thermal conductivity, making it ideal for insulation material. Hempcrete blocks have a low carbon footprint and are effectively carbon sinks. Widespread codes and specifications still need to be developed for the widespread usage of hempcrete, but it shows promise to replace current non-bearing construction materials that negatively impact the environment.
Concrete is a composite material composed of aggregate bonded together with a fluid cement that cures to a solid over time. Concrete is the second-most-used substance in the world after water, and is the most widely used building material. Its usage worldwide, ton for ton, is twice that of steel, wood, plastics, and aluminium combined.
A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement mixed with fine aggregate produces mortar for masonry, or with sand and gravel, produces concrete. Concrete is the most widely used material in existence and is behind only water as the planet's most-consumed resource.
Engineered wood, also called mass timber, composite wood, man-made wood, or manufactured board, includes a range of derivative wood products which are manufactured by binding or fixing the strands, particles, fibres, or veneers or boards of wood, together with adhesives, or other methods of fixation to form composite material. The panels vary in size but can range upwards of 64 by 8 feet and in the case of cross-laminated timber (CLT) can be of any thickness from a few inches to 16 inches (410 mm) or more. These products are engineered to precise design specifications, which are tested to meet national or international standards and provide uniformity and predictability in their structural performance. Engineered wood products are used in a variety of applications, from home construction to commercial buildings to industrial products. The products can be used for joists and beams that replace steel in many building projects. The term mass timber describes a group of building materials that can replace concrete assemblies.
Straw-bale construction is a building method that uses bales of straw as structural elements, building insulation, or both. This construction method is commonly used in natural building or "brown" construction projects. Research has shown that straw-bale construction is a sustainable method for building, from the standpoint of both materials and energy needed for heating and cooling.
Building material is material used for construction. Many naturally occurring substances, such as clay, rocks, sand, wood, and even twigs and leaves, have been used to construct buildings and other structures, like bridges. Apart from naturally occurring materials, many man-made products are in use, some more and some less synthetic. The manufacturing of building materials is an established industry in many countries and the use of these materials is typically segmented into specific specialty trades, such as carpentry, insulation, plumbing, and roofing work. They provide the make-up of habitats and structures including homes.
Hemp, or industrial hemp, is a plant in the botanical class of Cannabis sativa cultivars grown specifically for industrial and consumable use. It can be used to make a wide range of products. Along with bamboo, hemp is among the fastest growing plants on Earth. It was also one of the first plants to be spun into usable fiber 50,000 years ago. It can be refined into a variety of commercial items, including paper, rope, textiles, clothing, biodegradable plastics, paint, insulation, biofuel, food, and animal feed.
Natural building or ecological building is a discipline within the more comprehensive scope of green building, sustainable architecture as well as sustainable and ecological design that promotes the construction of buildings using sustainable processes and locally available natural materials.
Lime is an inorganic material composed primarily of calcium oxides and hydroxides. It is also the name for calcium oxide which is used as an industrial mineral and is made by heating calcium carbonate in a kiln. Calcium oxide can occur as a product of coal-seam fires and in altered limestone xenoliths in volcanic ejecta. The International Mineralogical Association recognizes lime as a mineral with the chemical formula of CaO. The word lime originates with its earliest use as building mortar and has the sense of sticking or adhering.
Hydraulic lime (HL) is a general term for a variety of lime different from calcium oxide (quicklime), that sets by hydration and consists of calcium silicate and calcium aluminate, compounds that can harden in contact with water. This contrasts with calcium hydroxide, also called slaked lime or air lime that is used to make lime mortar, the other common type of lime mortar, which sets by carbonation (re-absorbing carbon dioxide (CO2) from the air). Hydraulic lime provides a faster initial set and higher compressive strength than air lime, and hydraulic lime will set in more extreme conditions, including under water.
Concrete recycling is the use of rubble from demolished concrete structures. Recycling is cheaper and more ecological than trucking rubble to a landfill. Crushed rubble can be used for road gravel, revetments, retaining walls, landscaping gravel, or raw material for new concrete. Large pieces can be used as bricks or slabs, or incorporated with new concrete into structures, a material called urbanite.
Building insulation materials are the building materials that form the thermal envelope of a building or otherwise reduce heat transfer.
Earthen plaster is made of clay, sand and often mixed with plant fibers. The material is often used as an aesthetically pleasing finish coat and also has several functional benefits. This natural plaster layer is known for its breathability, moisture-regulating ability and ability to promote a healthy indoor environment. In the context of stricter indoor air quality regulations, earthen plaster shows great potential because of its properties as a building material.
Argonoxygen decarburization (AOD) is a process primarily used in stainless steel making and other high grade alloys with oxidizable elements such as chromium and aluminium. After initial melting the metal is then transferred to an AOD vessel where it will be subjected to three steps of refining; decarburization, reduction, and desulfurization.
Alternative natural materials are natural materials like rock or adobe that are not as commonly used as materials such as wood or iron. Alternative natural materials have many practical uses in areas such as sustainable architecture and engineering. The main purpose of using such materials is to minimize the negative effects that built environments can have on the planet, while increasing the efficiency and adaptability of the structures.
Concrete is produced in a variety of compositions, finishes and performance characteristics to meet a wide range of needs.
The environmental impact of concrete, its manufacture, and its applications, are complex, driven in part by direct impacts of construction and infrastructure, as well as by CO2 emissions; between 4-8% of total global CO2 emissions come from concrete. Many depend on circumstances. A major component is cement, which has its own environmental and social impacts and contributes largely to those of concrete.
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 the fiber in the processes of breaking and scutching" and "correspond to the shives in flax, but are coarser and usually softer in texture". Shives are a by-product of fiber production.
Geopolymer bonded wood composite (GWC) are similar and a green alternatives to cement bonded wood composites. These products are composed of geopolymer binder, wood fibers/ wood particles. Depending on the wood and geopolymer ratio in the material, the properties of the wood-geopolymer composite material vary.
Cork thermal insulation refers to the use of cork as a material to provide thermal insulation against heat transfer. Cork is suitable as thermal insulator, as it is characterized by lightness, elasticity, impermeability, and fire resistance. In construction, cork can be applied in various construction elements like floors, walls, roofs, and lofts to reduce the need for heating or cooling and enhance energy efficiency. Studies indicate that cork's thermal insulation performance remains unaffected by moisture absorption during rainy seasons, making it suitable for diverse climates. Additionally, research on cork-based composites, such as cork-gypsum structures, suggests a substantial improvement in energy efficiency for buildings.
Bio-based building materials incorporate biomass, which is derived from renewable materials of biological origin such as plants,, animals, enzymes, and microorganisms, including bacteria, fungi, and yeast.
This article incorporates text by S. Bourbia1, H. Kazeoui, R. Belarbi available under the CC BY 4.0 license.