Hempcrete or Hemplime is bio-composite material, a mixture of hemp hurds (shives) and lime (possibly including natural hydraulic lime,sand, pozzolans) used as a material for construction and insulation. It is marketed under names like Hempcrete, Canobiote, Canosmose, and Isochanvre. 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. The result is a lightweight insulating material ideal for most climates as it combines insulation and thermal mass.
Like other plant products, hemp absorbs CO2 from the atmosphere as it grows. Furthermore the carbonation of the lime during curing adds to this effect as lime turns to limestone.
Hempcrete is one of the best performing, non-toxic, ecological and renewable materials available. It has a negative CO2 footprint thus alleviating the Greenhouse effect. It improves air quality, energy consumption for heating and cooling providing a comfortable and healthy living environment. It's cool in summer and warm in winter.
The typical compressive strength is around 1 MPa, around 1/20 that of residential grade concrete. It is a low density material and resistant to crack under movement thus making it highly 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 density is 15% that of traditional concrete.
Modern day building materials are either mined from the earth or harvested from centuries old forests. Hemp crops can be harvested annually in perpetuity. One acre of hemp provides as much paper as 4.1 acres of trees. Considering the trees take decades to grow and hemp takes about 4 months, the advantages become clear. In some areas of the US, you can grow more than one crop of hemp a year.
One ton of manufactured cement (1400–1450 °C) releases 850 kg of carbon dioxide into the atmosphere! This is a consequence of the chemical reaction and cannot be reduced by energy saving. The use of lime instead of cement will save approximately 80% of the CO2 release compared to ordinary cement. One single residence will save between 5,000 and 10,000 lbs of CO2 emissions.
The one drawback is that hempcrete takes a long time to cure, so is not good to use for load bearing walls. To make up for this, companies started making hempcrete bricks. There are quite a few companies that make hempcrete bricks. They manufacture them in a way that it takes a lot less time to cure than just putting the slurry into the wall cavity. There are various ways they are made, some put the slurry into wooden forms and left to dry, some are pressed in machines some forming a brick, then left to cure. Some companies put supporting structures such as 2×2’s in them so you can use them for load bearing walls immediately. After they are suitably cured, they are able to be stacked just like normal bricks although they are usually a few inches thicker than regular cinder blocks they are a lot lighter. With these bricks, the need for a wooden frame is practically zero, and since they eventually turn to petrified rock they will last for hundreds of years.
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