Hempcrete or hemplime is biocomposite material, a mixture of hemp hurds (shives) and lime, sand, or pozzolans, which is used as a material for construction and insulation. 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 of concrete and consequently does not need expansion joints. Typically, hempcrete has good thermal and acoustic insulation capabilities, but low mechanical performance, specifically compressive strength. When used in prefabricated blocks, hempcrete acts as a carbon sink throughout its lifetime. The result is a lightweight, fireproof, 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.
History
There are some mentions of use of concrete building materials including hemp, like in India, 1727: "Puckah […] is a Composition of Brick-dust, Lime, Molasses, and cut Hemp, and when it comes to be dry, it is as hard and tougher than firm Stone or Brick."
Mixture of materials Hempcrete is made of the inner woody core of the hemp plant (hemp shives), a lime-based binder, and water. The binder consists of either hydrated lime or natural hydraulic lime. Hydrated lime is made from pure limestone and sets through the absorption of CO2 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 (e.g., about two weeks to a month, to gain adequate strength).
A small amount of cement, pozzolanic binder or both are added to speed up the setting time. The overall process creates a mixture that will develop into a solid, light, and durable product.
Applications 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. 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 and Quebec. 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. Hempcrete can be used for many purposes in buildings, including roof, wall, slab, and render insulation, each of which has its formulation and dosages of the various constituents respectively.
Properties
Mechanical properties 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. All studies show variability within hempcrete properties and determine that it is sensitive to many factors. 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. Young's modulus continually has a high COV across multiple experiments. The Young's modulus of hempcrete is 22.5 MPA. Young's modulus and compressive strength are two mechanical properties that are correlated. The compressive strength is typically around 0.3 MPA. 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. The size of the specimen and the hemp shives should be accounted for when determining the density. In the model, the density of hempcrete is 415 kg/m3 with an average coefficient of variance (COV) of 6.4%. Hempcrete's low density material and resistance to cracking under movement make 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 is 15% that of traditional concrete. Studies in the UK indicate that the performance gain between 230 mm (9 in) and 300 mm (12 in) 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.
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