Hemp and Lime as a Building Material

Dinesh.

Contents:-IntroductionHistorical back groundHempLimeComposite materialsCombination of hemp and limeThe three mixesMethod of sample preparationLaboratary testsconclusions

Introduction:-The combination of hemp and lime is considered as an alternate structural building to other conventional materials. These materials are ‘environmentally friendly’ and have, overall, a low level of embodied energy. Hemp is a plant and thus utilizes carbon dioxide during its growth. Natural hydraulic lime produces less co2 in its production than cement and also absorbs co2 as it sets.

Historical backgroundThe first documented use of organic materials in construction dates back as the Mesopotamian civilization(2000 Bc), where buildings were discovered made from mud bricks reinforced with reeds. This tradition has continued through the ages and is now being revitalized in the in the 21st century through the increased building with cob (monolithic mud and straw), straw-bale houses and adobe(mud and straw bricks).

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Hemp There is much interest among both engineers

and architects in using hemp hurds as an aggregate with hydraulic lime binders, as they are both strong and light.

Throughout the world, hemp is cultivated commercially for its strong, valuable fibers and oil

These hurds are natural by-product after the plant has been used for other purposes.

Hemp plant does not require pesticides and requires less fertilizing.

One hectare of hemp produces 3.5 tons of hurds.

Lime Lime comes from lime stone

rock and has been used in building for thousands of years.

It was used in ancient times and in the roman empire.

The earliest traces of lime use in construction have been found in early Egyptian buildings

The blocks of pyramids, were bond using a lime motor.

The dome of the pantheon is made of lime concrete

Composite materialsA composite building material

consists of at least two different materials, neither of which is suitable for constricting buildings on its own but when combined, result in a strong and suitable material.

These materials have been used in buildings for thousands of years. Adobe mud huts made from a mixture of straw and clay have existed since the stone age.

In the last 40 years polymer composite materials have been developed.

Glass fiber mats and natural fiber like hemp fibers are the good composite mix

inner car door made of hemp fibers

Combination of hemp and Lime Hemp hurds can be used as an aggregate in the lime

mix to form a durable and lightweight material Currently, this is being used as an infill in timber

frame houses

Infill of timber frame structure with hemp hurds and lime

The three mixes1) Hemp and lime2) Hemp fibers (and hurds) and lime3) Hemp, lime and sand

volume proportions of materials in mix Hemp hurds: lime hemp fibers (and hurds):lime hemp hurds: lime: sand

0:1 0:1 3:1:0

1:1 1:1 3:1:1

2;1 2:1 3:1:2

3:1 3:1 3:1:3

4:1 no samples 3:1:4

5:1 5:1 no samples

• Three cubes and three cylinders were prepared so that an average strength could be calculated for each mix

The bulk density of each material was calculated

bulk density of materialHemp hurds hemp fibers(and hurds):lime Lime sand

92 kg/m3 106 kg/m3 636kg/m3 1027kg/m3

Method of sample preparation The dimensions of cubes used

were 100mmx100mmx100mm. The cylinders had a diameter of 100mm and were 200mm high. The moulds are lined with a cling film.

A known volume of lime was mixed with water until a workable state was reached. This water/lime ratio was kept constant during the experiments. To prevent hemp from absorbing water during mixing, hemp hurds was soaked in water for 10minutes in advance.

Mould lined with cling-film

• The materials were added gradually to a mixture. Slump test was carried out, for mixes with a slump less than 40mm a 2.5kg proctor hammer used for compacting.The samples were de-moulded after 24

hours and allowed to dry at room temperature. They are then placed in a carbonation tank with a concentration=10%. They are allowed to cure for 30 days.

Lime sets firstly with water and secondly with co2. The use of carbonation tank accelerated this process, as the normal combination of co2 in air is 0.03%

A test was conducted for the samples to know how much lime reacted with co2. The samples were sprayed with phenolphthalein after testing. The purple colour in photos shows phenolphthalein reacted with the un-carbonated region.

Laboratory tests The compressive and

tensile material strength of the different mixes was measured using cube compression tests.

The cubes did not fracture but deformed slowly due to the fibrous nature of the material. This displacement was limited to 10mm, and the maximum force was recorded

Determination of young's moduli for various mixesMix hurds[mpa] mix fibers[mpa] mix sand[mpa]

1:1 167 1:1 219 3:1:0 38 2:1 78 2:1 67 3:1:1 89 3:1 38 3:1 68 3:1:2 162 4:1 36 - - 3:1:3 77 5:1 24 5:1 22 3:1:4 38

Results of tensile tests for mixesHurd lime mix Hurd mix density[kg/m3] force[kn] tensile strength[n/m3]

1:1 1269.27 10.44 0.22

2:1 1094.23 10.70 0.23

3:1 865.57 7.10 0.15

4:1 714.17 5.75 0.12

5:1 652.33 5.68 0.12

Fiber lime mixMix density[kg/m3] force[kn] tensile strength[n/m3] 1:1 1331.90 11.98 0.25 2:1 1118.00 8.66 0.18 3:1 914.47 6.43 0.14 5:1 691.60 3.85 0.08

Hurd/lime/sand mixmix density[kg/m3] force[kn] tensile strength[n/mm2]3:1:1 1274.60 5.64 0.123:1:2 1708.83 7.82 0.173:1:3 1878.40 8.21 0.173:1:4 1877.37 4.71 0.10Advantages of hemp and lime as building material:-Low embodied energy –an ‘environmentally

friendly’ material.A structural and insulating building material.Durable and light weight.Provides a ‘breathable’ and porous building

membrane. This prevents moisture build-up and ensures a dry building.

conclusionsBuilding with this material uses less energy than

conventional methods and is a sustainable building solution for the future.

It is a material which both insulates and provides structural strength.

A 5:1hurd/lime mix was considered to be as optimum mix ratio with a compressive strength of 0.7N/mm2 and an estimated thermal conductivity of 0.11w/mk.

A 3:1 hurd/lime mix has the same strength as 5:1hurd/lime mix. This is a significant result as previously hurd/lime mixes used as infill in timber frames have been based on 3:1 mix by volume which uses the lime binder less efficiently and has a higher thermal conductivity.

EXAMPLES OF HEMP BUILDINGS

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