Eco-materials in the Building Sector

Eco-materials in the Building Sector



We at are really glad to inform the readers that eco-materials are making a comeback in the building sector. The natural materials like bamboo, linen, straw, hemp and plaster have been used in the construction works during the past. These are the materials with less ecological footprint. Also, these are known to reduce the energy consumption of your buildings. The benefits offered by these alternate materials are many. Let’s see in detail about this subject matter here…

Building and Energy Consumption:

Buildings are among the sectors that consume the highest energy. Not only this, the building sector is also known to account for almost 30% of greenhouse gasses. Therefore, if we want to want to overcome the challenges of sustainable development, we need to go for alternate building materials. The eco-materials are such alternatives that allow us to build eco-friendly homes that consume less energy.

1. Insulation with Straw and its Benefits:

Straw, which is the agricultural waste got after harvest, is quite old. Mixing with soil, this straw was used to make cob and/or to enhance the mixtures for making adobe. Straw in the form of bonded boots has always been good as a roofing material.

In the middle of the 19th century, the more efficient tools mechanized the agriculture. During the harvest, the combines associated with the baling machines seemed to condition the straw into parallel-piped boots of same size so as to make it easier to pile up.


Bale-Shaped Straw (Bales):

The straw bales thus produced were compressed. The resultant product was found to be effective as a construction material with better insulating properties (bales provide better insulation than mud) and was easy to use. These were the first forms of straw transformed into a building material in Nebraska, United States. After this, few initiatives were noted in the 1920s in France. The modern building materials with higher performance were able to quickly suppress this constructive channel. But, the new paradigms of sustainable development are found to be making this material attractive once again.

Straw is the residual stem of the following edible grasses:

          .  Wheat

          .  Rye

          .    Barley

          .   Oats

          .  Spelled rice

In general, straw is considered to be the agricultural waste. In agriculture, the uses of this straw are limited to litter for animals and for mulching only. Also, the quantity of straw required for these is very minimal when compared to the overall production.

The reconversion of this agricultural waste into building material demonstrates an integrated system with outstanding virtues. This insulation material, which absorbs CO2 during production, can supply the construction sites within the radius of < 30  miles.

Straw as a building material is regaining some attention these days. As such, straw processing has gradually increased pertaining to the industrialization of the straw manufacturing process. Currently, there are different construction techniques like straw carrier, GREB technique, and straw board. A majority of the current constructions that uses straw is found to be combining the straw boots and timber framing. The straw, which has got the insulating function, will be placed between the uprights of the frame. It’s to be noted that the constructive mode can be prefabricated. As such, the walls and roof panels will be prepared in the workshop. These are the ribbed boxes that are dimensioned in coordination with the dimensions of the boots. We can several constructive variations in this. The construction of a straw house will then require a protection through plaster to the ground or lime.

The thermal characteristics of the straw bundles are as follows:

For a median density of 5to 7.4 lb/ft3, the thermal conductivity coefficient would vary between 0.04 and 0.075 W/mK. Alternatively, the high density boots with the density of about 9 to 15 lb/ft3 will have a thermal conductivity coefficient between 0.06 and 0.12 W/mK.


Courtesy of  strawtec


Industrialization of the Process and Technical Tips:

The conversion of straw bales into blocks of uniform size and density is often proposed by the companies that have the industrialized process. For instance, the “Isopaille block” is got by pressing the straw previously examined. The hygrometry of the material will be tested through the entire process. The blocks will be held in shape and compression using two links. This system must be accompanied by a vapor barrier on the inner side and a rain guard on the outer side. The fire behavior of the two-storey façade containing a straw-insulated wooden frame that contains a coating will be checked. It has been found that these construction processes are complying with the fire safety regulations for public facilities for R + 2 curtain wall facades.


The GREB Technique:

This technique was designed by Patrick Déry at the “Batture Ecological Research Group” in Quebec during the mid-1990s. As per this technique, two lightweight wooden frames will be linked by metal strips and spaced apart by the breadth of a boot of straw. The fillings of the walls will contain a bed of boots of straw protected by a light mortar that is maintained by branches fastened to the framework. After twenty-four hours, you may go up to the next bed and so on. The light mortar that is being used will contain lime, cement, sand, and sawdust. This empirical construction technique proved resistant because the mortar that blends with straw assures of the bracing.

Nebraska Carrier or Technical Straw:

Construction with using load-bearing straw walls is called as the “Nebraska Technique”. In this, the walls will consist of straw bales backed in staggered rows and compressed between a smooth foundation and breakdown pits. These are being protected by a lime plaster. This technique is recommended in less wooded regions like England as some wood is needed.

Compressed Straw Panels:

In this technique, the compressed straw will be held by cardboard sheets and glued on both sides to make the self-supporting distribution partitions. The panels that are being placed on a low wooden railing will be held by fastening tabs on all the four sides. The special parts will ensure the connection between the plates. This process would then receive finish of any kind.

As such, the straw that is released and cleaned will be arranged regularly and will be subjected to compression between the heating plates at temperatures of about 180 to 200 degrees C. This compressed sheet of straw will then be covered on both sides using glued thick cardboard. The heating that is done will ensure the sterilization of the straw, as well as the polymerization of the glue.

2. Bamboo Thatch and its Benefits:

Bamboo has been in construction since the ancient times and we can say it is the oldest construction material. This is lightweight and hence, transportable. The thatched bamboo, which is the stem of the plant, can be used as a cane for producing lightweight structures. When slatted, these structures can be used to make panels. In particular, the resistant fibers of bamboo are used in composite materials.

Bamboo belongs to the grass family like our rice, wheat, and corn. This occurs naturally on all the world continents except that Europe. Basically, this plant is found to be enjoying warm and humid climates. It’s due to this reason that the most beautiful species of bamboo are found in the continents of Asia, South America, and Africa. But, it’s not that it can’t withstand cooler temperatures. Bamboo can thrive well even in -20 degrees. So, we can possibly cultivate it in Europe. Example: bamboo plantation in Anduze, France.

Bamboo is known to show a very rapid growth. Unlike the tree’s trunk, the stem of the bamboo plant (thatch) doesn’t grow on the plane of its section, but it grows like a telescopic cane. The plant would reach its final height in a season and it would achieve its maturity in four or five years. In the completely matured plant, the fibers would be woody. This development process would take place from the outside to the inner side and also from the foot to the top. The largest stubble could grow up to 115 foot high and 10 to 13 inchs in diameter.


Bamboo’s Composition:

Similar to woods, the bamboo plant is also composed of fibers being arranged in a longitudinal direction to the stem. The plant’s main components are cellulose, hemicellulose, and lignin. Due to the progressive lignification of the cells, the density of the walls will not be uniform. Thus, the plant is found to be denser on the periphery and on the foot.

The thatch of bamboo is found to be tubular and hollow and is covered on the outside with a protective layer, which appears like your varnish. The thatch is divided at the nodes. The morphology of the bamboo is making the plant light and resistant. However, the cylindrical shape of the plant makes the structural assemblies tough.

Physical Properties of Bamboo:

The walls of the bamboo have a median density of 37 lb/ft3 However, this value is found to be ranging from 31 to 50 lb/ft3 from the top to the foot of the stem. The median resistance strength of the bamboo thatch is found to be 200 MPa and its median compressive strength is found to be 70 MPa. Again, these values would also vary between the sections of the stem and will not be regular throughout. The tensile strength will be higher in those parts of the stem with a higher density (parts at the bottom). Bamboo is hydrophobic in nature and doesn’t rot. However, it’s susceptible to some kinds of biological attacks.


Bamboo Fiber, a Less-Studied Material:

The bamboo can be exploited with a simple cut without sawing. This lightness of the material is the key to transportation and makes it a very beneficial ecological material. Despite of this, bamboo remains a poorly exploited construction material due to the difficulty in assembling the fibers. To use in construction, this will be usually transformed into slats, fibers, or powders.

Similar to wood, bamboo can also be used to build frameworks with ligated assemblies. This way, it could be used in almost all the structural works like poles, walls, floors, and roofs. In addition, the slat flow would enable the production of tiles and braided walls. By removing the internal partitions of the rod, the tubular shape can be used to make pipes/water pipes.

Industrial Exploitation of Bamboo:

Bamboo fibers’ incredible mechanical strength, especially the tensile strength, was not fully utilized in traditional building works due to the difficulty in assembling the fibers. In fact, the drawing of these fibers would require a continuous flow of material in the assembly, which is not facilitated by the cylindrical section of the bamboo. In the contemporary process, the possibilities offered are the transformation of the matter into fibers.

Bamboo Slats:

The stubbles will be cut as lengthwise strips and their outer layers will be stripped off. Once dried, these lamellae will be planed and can be used according to our preferences. The slats that are pressed in the longitudinal or vertical directions would make it possible to produce panels, which can then be used in the composition of internal arrangements. These slats can also be compressed at high pressures and glued. The resultant product would have uniform characteristics than your natural bamboo. It will be harder and highly resistant.

Bamboo Fibers and Powders:

The defibration and shredding of bamboo rods would give us the bamboo fibers and powders that can be used in various materials. In the construction industry, these fibers are being used as reinforcement materials that are subjected to expansion just like the reinforcement of plaster, waterproofing, or the like.

It’s to be noted that these applications are recent and still in experimental stages. But, we could say that they are undergoing an important development in the section of ecological construction materials, which are called ‘biosourced materials’. The polymer manufacturing process is also exploiting products that are derived from bamboo. The pultruded or extruded tubes with bamboo fibers are offering an alternate approach to fiberglass and carbon-based manufacturing with similar strengths and with much lesser environmental impacts.

Thus, bamboo serves as a raw material with added value and can soon be seen in the fabrications too.

3. Hemp in Building Sector:

Hemp, which is an annual plant, is a plant of temperate climates. This is undemanding and grows on all soil types. The whole plant is found to be transforming from stems to seeds. Currently, this plant is being used in several industrial applications in the following sectors:

        .  Paper industry

        .    Textiles

        .    Hygiene

        .   Paints

        .    Sealants

        .    Food

In the building sector, this is serving as an insulation material and is also used to reinforce some materials like plastics.

Hemp, especially in France, is in cultivation for centuries for its solid fibers and oils of its seeds. Using this plant, various tissues, sails, ropes, oils, and pulps are made. Thus, it has several uses. However, the growth of materials like cotton and synthetic has limited the cultivation of hemp. In the 1960, the hemp production was prohibited by the international convention on narcotics. But, the cultivation of Cannabis sativa is allowed today because it’s free from psychotropic molecules. As per the regulation, to be cultivated, these molecules should not constitute more than 2% of the weight of the dry plant. Among all the European countries, France is the largest hemp producer and is representing about half of the continent’s total production.


Properties of Hemp:

Hemp is an herbaceous plant that could grow up to three meters in height. In general, hemp exhibits a rapid growth from May through September. An advantage of this short growth cycle is that it enables an easier crop rotation. The plant’s deep and branched root system is beneficial to the soil as well. The plant is resistant to external aggressions of all kinds and hence, they don’t require phytosanitary interventions. It’s for these reasons that the cultivation of hemp is marked as ecological.

The stems of the hemp plant are made of fibers at the periphery and of hemp at the heart. The seeds of the plant are called as hempen. The fibers are representing about 30 to 35% by weight of the plant. They are being used in those applications where their mechanical strength can be applied. The medullar part of the stem, which is called the hemlock is accounting for another 55% of the weight of the plant and is having a significant absorbing power.

Harvesting Hemp:

Usually, the straw will be mown during September when the plant has lost two to three of its leaves. Then, it will be packaged as bales and are stored in the shelter until the defibration process is done. During the defibration process, the fibers of the plant will be separated from the wood through a mechanical procedure that uses little energy and no chemical treatment. The defibration process will be carried out throughout the year according to the needs. In simple terms, we can say that all the parts of the hemp plant can be exploited.


Hemp Insulation:

Among all the eco-materials that are used in the building sector, the hemp is found to be having some excellent insulating properties. The hemp has the ability to develop insulation faster. The current insulation processes allow for various applications of hemp like insulating wool, aggregate or concrete.

In the construction industry, the fibers, as well as the hemp wood are being used to form the composition of materials. As such, the fibers are exploited in two different ways. One way is to transform the fibers to get insulating wool. The other way is to use the fibers as byproducts in the manufacturing of composite materials that are based on earth, lime, cement, or polymers. It’s to be noted here that the chénevotte is being used in aggregates while manufacturing the insulating structures. Finally, it should be noted that it is also being used as a raw material for biosourced plastics.

Insulating Wool:

The insulating wools are produced from mechanically cleaned fibers, which are then mixed with binder fibers (made of polyethylene). This mixture will contain about 85% hemp fibers and 15% binders. This will then be spread out in layers that are superimposed one on the other to form a mattress.

This set up will then be kept in the oven so as to enable the fibers to bind together. Some manufacturers are offering the insulating wools prepared solely from biosourced materials. In such cases, the binding fibers will be made of maize starch. The thermal conductivity coefficient of hemp wool is λ = 0.038 W / mK.


Hemp Aggregates:

The short fibers of the wood are being used in the form of chips to produce the insulating aggregates. In bulk, the chips will be used to isolate invisible entrances or attic spaces. As such, these chips can be used in the construction of masonry structures in order to get a distributed natural insulation.

The aggregates of hemp concretes are containing chénevotte and the aggregates for the coatings are containing a low percentage of fibers. The thermal conductivity coefficient of hemp aggregates is λ = 0.048 W / mK. These aggregates are broadly used in raw earth construction to enhance thermal efficiency. The hemp fibers are being used to enhance the mechanical efficiency.

Hemp Concrete:

The hemp concrete is produced using a blend of aerial lime, hydraulic lime, pozzolana, and chénevotte. This mixture will vary according to the application. In order to ensure the regulatory environment of hemp concrete structures, there are some professional rules available now. It is the performance guide to satisfy the requirements of compatibility between the binder and hemp aggregates and the performance levels for each application (threshold performance).

Each and every manufacturer should carry out the lab tests to verify the performance of its products. As such, the test procedures are devised by the CenC association. While some manufacturers are offering prefabricated hemp concrete walls that are dry-mountable, others are offering bricks based on hydraulic lime and hemp aggregates with a thermal conductivity coefficient of 0.07 W / mK. These products are constantly developing.


 Courtesy  picture from architects journal


4. Flax for Building Sector:

Flax, which is a sensitive plant, can be used as an eco-material for construction. Now, this is being used in ecological construction to a larger extent. Traditionally, the linen was providing fine and solid fibers for the fabric milling. But now, the situation is different. Almost all the parts of the plant can be exploited using the contemporary techniques.

Flax Cultivation:

The flax cultivation will be done on an annual cycle of hundred days. Sowing will be done from mid-March to mid-April. As mentioned above, flax is sensitive to the soil’s nature and climatic conditions. The plant is not resistant to strong heat and drought. Due to this reason, in France, flax is cultivated in the northern regions and in oceanic climate zones. The crop needs special attention due to the small size of the seeds that contain nutrient reserves. The growth of the plant requires a little nitrogen input. We should also watch out the weeds.

Harvesting Flax:

There are many steps in the harvesting of flax and the main ones are:

 .    Grubbing

  .    Grounding

 .    Bundling

When they are matured, that is when they are almost leafless; the plants with the seeds will tear off. Then, the plants will be deposited in regular sheaves on the ground where they are allowed for natural retting by the action of microorganisms. Thus, the stems will get rid of the filamentous bark which is surrounding them. These will then be placed in cylindrical bales after several turning and decapsulating operations to recover the seeds. These are done because they contain <15% moisture.

Flax Processing:

The stems of the plant are beaten well to separate the constituents. On one hand, the wood, which represents 50% of the plant, will be harvested. This substance is called flaxseed or flax sequin. On the other hand, two types of fibers (both short and long) are harvested. The long fibers are being used in the textile industry, while the short ones are used for manufacturing the insulation for the buildings. It is to be noted that the linen fiber is the natural fiber that exhibits best resist traction. It’s for this reason that these are used for the manufacturing of composite materials.