Hempcrete is a bio-composite non-structural healthy building material that is made up of sand, lime and hemp hurds. It is also known as Hemplime.
The density of hempcrete is 300 to 900 kg/m3 and compressive strength is about 1 MPa.
Hempcrete is derived from hemp and concrete ( i.e. lime is used as binding material, sand is used as fine aggregate and hemp hurd is used as a coarse aggregate).
( Note: Hemp is the fibre of the Cannabis Sativa plant. It is one of the fastest-growing annual crop plants. It has high tensile strength thus mostly used as a construction material. )
Hempcrete is mostly used as a construction and insulating material.
Industrial hemp is legally allowed to use as a raw material for the manufacture of hempcrete (because industrial hemp is not marijuana species of cannabis party). Only 0.3% of marijuana is present in industrial hemp.
As at the ancient time, industrial hemp was stored for centuries and still had strength and durability. People observed this and decided to use as hempcrete for constructing buildings. In France; 6th-century hempcrete was discovered in a bridge abutment.
1.1. Features of Hempcrete
Some features of hempcrete are:
a. It has high moisture storing capacity from the surrounding.
b. It has a low compressive strength of about 1 MPa. Thus, it is used in minor structural construction such as lightweight wall framing members.
c. It is not fire-resistant as it contains polyester type woody fibre.
d. The R-value of hempcrete is 2.4 to 3 per inch according to American standard. R-value determines the heat flow in hempcrete walls. Hempcrete has thermal mass(mass having inertia with thermal capacity). Thus, it is not suitable as thermal material but good as an insulating material with thermal mass.
e. As hempcrete has breathability, it should be only painted with lime-based paints which are expensive though.
f. Hempcrete foundation walls are stronger and elastic than concrete walls.
g. After a certain period of times, hempcrete hardens like petrified rocks. Its durability and strength give soundproof and bulletproof properties.
h. It is mixed at a site of construction.
i. It smells like the pungent smell of dead skunk.
1.2. Construction of Hempcrete
Hempcrete is made at the site by mixing raw materials like lime, sand, water and industrial hemp in certain proportion by a motor mixer with a horizontal and vertical shaft. This mixture takes 7-8 minutes to be properly mixed to gain binding property.
The mixture is then filled in the mould for casting purpose and compacted properly to avoid air voids from it. Then, it is left for sometimes for curing. Now, hempcrete is ready to use.
1.3. Price of Hempcrete
Hempcrete has efficient energy and durable properties. Although, it is more expensive than other building material. It has a high demand in the market. It’s price differ from place to place according to the availability of hemp and thickness of hempcrete used for the construction.
The fixed price for hempcrete materials is approximately $135 per square metre based on a 300 mm thick wall. If labour is subcontracted out to an installation team, the owner can expect to pay between $230 and $265 per square metre. This makes the overall cost (labour and materials) between $365 and $400 per square metre.
1.4. Advantages of Hempcrete
a. It is an eco-friendly carbon-reducing building material.
b. It needs less maintenance and repair.
c. Its plastering is waterproof and soundproof.
d. It is insulating and temperature maintaining building material.
e. It can be used in the construction of retaining walls, floors and roofs.
f. It is lighter than concrete.
g. It has high moisture handling capacity.
h. It can also be used for decorating purpose.
1.5. Disadvantages of Hempcrete
a. In some country, even industrial hemp is not permissible to use as it also contains 0.3% of hemp. Thus, legal permission is important to use it for construction of hempcrete. It is a long process.
b. It is an expensive building material.
c. It is hygroscopic. It has a high moisture handling capacity. Thus, it cannot be used for underground or marine works.
d. It takes nearly (7-8) weeks to dry and also it can be affected by weather change.
f. It has low mechanical properties to be used in heavy load bearing works due to low elastic modulus.
g. Materials used for hempcrete is not abundant.
1.6. Applications of Hempcrete
a. Hempcrete is usually used for the construction of minor load-bearing structures.
b. It is also used for plastering work.
c. It is used for the construction of floor slab insulation. and roof insulation.
d. It is used in the preparation of hempcrete blocks and bricks.
e. It is used for creating an air-tight seal around the home.
|Read Also: Types of Concrete|