EP4720423A1

EP4720423A1 - Thermal insulation material comprising biochar for filling hollow building elements, method of its production and its use

Info

Publication number: EP4720423A1
Application number: EP25749598.6A
Authority: EP
Inventors: Petr Stehlík
Original assignee: Intecores SRO
Current assignee: Intecores SRO
Priority date: 2024-06-17
Filing date: 2025-06-16
Publication date: 2026-04-08
Also published as: WO2025261543A1; CZ2024246A3; CZ310607B6

Abstract

The present invention generally relates to the field of construction, and in particular to hollow building elements. Specifically, it relates to a thermal insulation material that comprises biochar and is suitable for filling hollow building elements. The material comprising biochar is either in a loose state or is mixed with a binder in a semi-liquid to liquid form. A preferred loose thermal insulation material comprises biochar in the form of particles with a size of 2.0-11.2 mm, or 2.8-11.2 mm. A preferred semi-liquid thermal insulation material comprises biochar and a binder, which is preferably gypsum or cement. In the semi-liquid material with a binder, biochar in the form of particles with a size of 0-2.0 mm can be advantageously used. Furthermore, the invention relates to improving the thermal insulation properties of hollow building elements and a hollow building element, at least one cavity of which is filled with a thermal insulation material comprising biochar.

Description

Thermal insulation material comprising biochar for filling hollow building elements, method of its production and its use

Technical field

The present invention generally relates to the field of construction, and in particular to hollow building elements. Specifically, it relates to a thermal insulation material that comprises biochar and is suitable for filling hollow building elements. The material comprising biochar is either in a loose state or is mixed with a binder in a semi-liquid to liquid form. Furthermore, the invention relates to improving the thermal insulation properties of the hollow building elements.

Prior art

Hollow building elements, such as bricks/blocks in particular, have long been used in construction, the air in the cavities serves as a thermal insulator. It is known and has been implemented in practice for many years to improve the thermal insulation properties of these building materials by filling the cavities with expanded polystyrene or mineral wool, for large- volume cavities e.g. vacuum insulation panels (vacuum-packed silica fibre aerogel). At least experimentally, filling the cavities with perlite, polyurethane (Pavlik, Z. et al., MONITORING THERMAL PERFORMANCE OF HOLLOW BRICKS WITH DIFFERENT CAVITY FILLERS IN DIFFERENCE CLIMATE CONDITIONS. Int. J. Thermophys. 36, 557-568, 2015) or straw (Hou, S. et al., COUPLED HEAT AND MOISTURE TRANSFER IN HOLLOW CONCRETE BLOCK WALL FILLED WITH COMPRESSED STRAW BRICKS. Energy and Buildings 135, 74-84, 2017) has been tested. Utility model CZ30951U1 described a ceramic shaped building blocks where large-volume cavities were filled with textile fibres (polyester, cotton) in a vacuum package. Polystyrene, which is commonly used as a thermal insulation material, is very difficult to separate after the demolition of a building, for example, and there is a risk of its introduction into nature. Another commonly used material, such as mineral wool, is fibrous and is dusty during demolition, releasing fine fibres that are harmful to the human health. Recently, there have been considerations and attempts to use an interesting material - biochar - in the construction industry with the aim of improving the carbon balance of the construction industry - reducing the carbon footprint and permanently storing carbon. Biochar as such permanently stores carbon that the plant has drawn from the atmosphere in the form of CO2 during its growth. When biochar is deposited, for example, into a building material, carbon/CCb is permanently removed. For example, concrete (so-called carbon-negative or climate-neutral concrete) have been prepared, especially lightweight porous concrete, where biochar replaced sand and/or partly cement (e g. Chen, L. et al., BIOCHAR-AUGMENTED CARBONNEGATIVE CONCRETE. Chemical Engineering Journal, 431 (1), 2022). Concrete with a biochar content of up to 50 % was described in patent application CN 107586081 A. Concrete with a biochar content of up to 30 %, where the biochar is obtained by pyrolysis of pig waste, was described in patent US11104611B2. Patent application US20230002276A1 described carbon-negative concrete, where up to 26 % of the cement is replaced by biochar. Plasters (e.g. CN115784702A) containing biochar admixture have also been prepared. These materials show lower thermal conductivity compared to the same material without biochar admixture. Materials with biochar are often also economically advantageous. Biochar is a material similar to charcoal, obtained by pyrolysis of organic material at temperatures of 400-700 °C and without access of the air. Classic charcoal also falls into the category of biochar, which is broader in the sense that it uses not only wood as the starting material, but also various organic materials, often waste materials (straw, chaff, bagasse from sugar cane, litter from large-scale poultry farming). Biochar with standard properties can be obtained by pyrolysis of wood, preferably from fastgrowing woody species. The advantage of biochar, compared to polystyrene or mineral wool, is that it is harmless to health, it can be buried in the ground without any problems after the end of the building's service life, for example, and thus improve its sorption and retention of moisture and nutrients. Another positive aspect is a certain degree of absorption of some pollutants from the environment, its speed depends on the internal surface area of the biochar, which, among other things, depends on the method of its production.

Biochar has not yet been used to improve the thermal insulation properties of hollow building elements, e.g. bricks or blocks with cavities. However, at the same time, there is a continuing need to improve the thermal insulation properties of building elements due to the need for good thermal insulation of buildings in respect to energy savings for heating or cooling the interior of buildings. In addition, solutions are currently being sought that reduce the carbon footprint in the construction industry.

Summary of the Invention

The present invention relates to a thermal insulation material comprising biochar. It further relates to a method of producing a thermal insulation material comprising biochar, the use of this material for filling cavities in building elements, and finally to building elements filled with a thermal insulation material comprising biochar. Thus, the present invention solves the problem of improving the thermal insulation properties of hollow building elements and at the same time contributes to solving the problem of the high carbon footprint of the construction industry, in particular the production of concrete and concrete materials, towards the use of materials that allow long-term storage of carbon and thus reduce the carbon footprint.

Biochar for use in the present invention was obtained by pyrolysis of wood mass and further processed by crushing and/or grinding. The starting material was softwood (density 500-600 kg/m³), represented here by willow and spruce wood, and also hardwood (density 700-800 kg/m³), represented here by beech and oak wood. Willow biochar was obtained by conventional pyrolysis at 600-700 °C without access of the air. Beech-oak biochar is charcoal from a mixture of beech and oak wood obtained by pyrolysis at 400-800 °C without access of the air.

Both prior art publications and preliminary experiments performed by the inventor have shown that the properties of biochar are to some extent dependent on two basic parameters, namely the type of wood species that is the source of the starting material, and the method of biochar production. But further experiments by the inventor have shown that the thermal insulation properties depend mainly on the subsequent processing of biochar, crushing or grinding, or rather on the size of the particles thus obtained. Biochar from lighter wood species, e.g. willow or poplar, generally has better thermal insulation properties, while biochar from hard wood species, e.g. oak or beech, stores more carbon per volume unit. The method of production of biochar can largely influence its properties - e.g. density and internal structure.

Biochar for thermal insulation material can be prepared advantageously from soft wood of fastgrowing wood species, e.g. willow or some poplars, these wood species have a good yield. Spruce wood can also be used, and also other deciduous wood species such as linden, poplar, aspen and others. The use of wood material from Japanese poplar plantations will be advantageous.

For examples of the use of biochar according to the invention, biochar was prepared by pyrolysis of wood from willow, spruce, beech and oak. The biochar was further crushed/grinded and 4 fractions with different particle sizes were separated; fraction 1 : 0-2.0 mm, fraction 2: 2.0-2.8 mm, fraction 3: 2.8-11.2 mm and fraction 4: over 11.2 mm. By measuring the heat transfer of the individual fractions, it was found that fraction 1 has worse thermal insulation properties, while fractions 2 and 3 have essentially the same thermal insulation properties, better than fraction 1. The fraction with particles over 11.2 mm had the worst thermal insulation properties and was not used for the preparation of materials (it was crushed again into fractions with smaller particles).

By crushing/grinding biochar, its properties are essentially homogenized regardless of the type of original biomass. Crushing removes larger cavities (their size and quantity depend on the type of original biomass). Crushed biochar then has very similar properties regardless of the original biomass source.

In addition to crushing, it is possible to use directly for pyrolysis a material with a certain specific "particle" structure, for example sawdust or shavings from wood processing. For example, spruce sawdust (from a cross cut with a chainsaw) was processed, which after pyrolysis provided needle-shaped particles with a very small proportion of fine particles. After pyrolysis, the sawdust retained its needle-shaped shape and a very small proportion of fine particles was formed. Biochar structured in this way will be advantageous in materials with a large proportion of biochar, where it will contribute to higher cohesion (analogous, for example, to ceramic materials filled with fireclay chips).

Thermal insulation material comprising biochar is advantageously used to fill hollow building elements, or cavities of these hollow building elements. A hollow building element is here understood to mean any building elements, especially ceramic and concrete, comprising at least one cavity, such as bricks and shaped blocks (concrete blocks), ceiling systems of the “miako” or “hurdis” type, but also ceramic and concrete lintels that comprise one or more cavities. The term cavity is understood to mean any hollow space in the above-mentioned building elements. The cavity of a building element within the meaning of the invention also includes hollow spaces created during 3D printing of buildings or construction spaces for filling floors and ceilings.

Loose thermal insulation material comprising biochar

A loose thermal insulation material comprising crushed/ground biochar was prepared and this material was used to fill a hollow building element, in an exemplary embodiment of a concrete block. A material comprising fractions 2 and 3 (2.0-11.2 mm) of willow biochar and fraction 3 (2.8-11.2 mm) of beech-oak biochar appeared to be a preferred thermal insulation material. Regardless of the fraction used, the block with loose biochar filling showed better thermal insulation properties than the control block without filling (i.e. only with air in the cavity).

One of the aims of the present invention was to prepare a material that could replace polystyrene or mineral wool, which are standardly used in the state of the art for filling cavities. In the experiments performed, biochar did not achieve such high thermal insulation values as mineral wool in all embodiments, but biochar of fraction 2.0-11.2 mm from willow or biochar of fraction 2.8-11.2 from beech-oak used as a filler for hollow blocks showed values identical to mineral wool.

Filling the cavities of building elements with loose thermal insulation material comprising biochar can be carried out in the following ways:

A) Filling at the manufacturer, when during production a hollow building element, e.g. a brick or other shaped piece, is filled and shaken on a vibrating machine, and then it is filled so that the filler no longer settles.

B) Filling directly during construction, when biochar of the required fraction is poured into the cavities using a hopper. This method is particularly suitable for filling vertical cavities. It can also be used to fill floor cavities and other cavities where it is possible to pour loose material.

Various methods can be used to fix the filling in the cavities, for example, the cavity openings can be covered on both sides with a binder that performs the function of a "plug", in which case binders based on gypsum, cement, lime, polymers, etc. can be used. A polymer is any polymer suitable for construction, e.g. polyurethane, MS polymer, etc. The binder can optionally be mixed with biochar, thereby reducing the thermal bridge of the fixation layer. It seems advantageous to cover the openings of the filled cavities with a mesh, where the mesh ensures that when connecting the building elements, the applied binder reaches directly onto the supporting part of the product. To fix the mesh, adhesives based on gypsum, cement, lime, but also organic-based adhesives can be used.

C) Another advantageous option is to fill the cavities with biochar coated with a binder before filling the cavity. The selected fraction of biochar is coated in a pre-prepared binder, and then poured into the cavity, after hardening it is firmly held in the cavity and does not spill out. Therefore, there is no need to use any fixing covering of the cavities. Gypsum, cement, lime, polymer and other organic and inorganic binders can be used as a binder. Lime milk or cement milk is preferable. The coating is carried out in a conventional manner known to the persons skilled in the field of building materials.

With all of the above filling methods, it is possible to press or ram the loose biochar or coated biochar into the cavities. In this case, the insulation properties will slightly decrease, but on the other hand, the amount of stored carbon per unit volume of the material will increase.

Liquid/semi-liquid thermal insulation material comprising biochar

Furthermore, a liquid/semi-liquid thermal insulation material comprising biochar was prepared, which comprises a selected fraction of biochar particles and a binder, whereby a liquid to semiliquid mixture is created, which is suitable for filling the cavities of building elements, where it solidifies into a solid mass. Such a mixture can be advantageously poured into the cavities. The binder is, for example, gypsum, cement, lime, polymer, preferably gypsum or cement. Any fraction or fractions of crushed/ground biochar can be used for the thermal insulation filling comprising biochar, preferably the finest fractions can be utilized in this way.

When crushing biochar, a fine fraction of 0-2.0 mm (fraction 1) is formed in a considerably large proportion, which can represent up to % of the weight of the crushed biochar. This fine fraction, which is not very suitable in the loose state for direct filling of the cavities, can be advantageously used in a mixture with a binder. Fine biochar can represent up to 35 % in a mixture with gypsum and water. When combining fine and coarse biochar (in a ratio of 1 : 1), biochar constituted up to 44 % in a mixture with gypsum and water. The material comprising 27 % of fine fraction of beech-oak biochar, 20 % of gypsum and 1 % of water glass (+ 52 % of water) was suitable for pouring into cavities, after hardening it was solid, had good thermal insulation properties and a relatively low density (490 kg/m³). Even a very low binder content, 12-17 %, led to the formation of a solid thermal insulation material after hardening.

Similar to gypsum, mixtures of biochar and cement were prepared. Even at the lowest biochar content (28 %), the thermal conductivity of the material was significantly lower than that of the pure binder (cement). The density of the cement materials comprising fine biochar was comparable to gypsum materials. One of the advantageous materials comprising fine biochar was a material comprising 33 % of biochar, 17 % of cement and 50 % of water. Very interesting materials were created if the biochar was predominantly or exclusively coarse biochar (from spruce sawdust, uncrushed, particle size up to 5.0 mm in length). These materials had good thermal insulation properties, and in addition, they had a very low density (230-330 kg/m³) approaching the density of perlite (amorphous volcanic glass with high water content) (200 kg/m³).

An interesting material was created by mixing fine biochar (fraction 0-2.0 mm) and coarse biochar (0-5.0 mm, prepared from sawdust) with water (in a ratio of 1 : 1 :2) without any binder. After solidification (drying), an essentially solid, well-cohesive mass was created, which has good thermal insulation properties and is suitable as a filling for hollow building elements.

The present invention relates to a thermal insulation material for filling hollow building elements, which comprises crushed or ground biochar from wood mass. The preferred biochar is prepared by conventional pyrolysis of wood mass at a temperature of 300-700 °C without access of the air.

The preferred thermal insulation material comprises biochar in the form of particles with a size of 0-11.2 mm, preferably 2.0-11.2 mm.

Another preferred thermal insulation material, in addition to biochar, further comprises a binder, which can be gypsum, cement, lime or polymer, and water. This material in another preferred embodiment comprises biochar in the form of particles of size 0-2.0 mm.

A preferred thermal insulation material for filling hollow building elements comprises 25-35 wt. % of biochar in the form of particles of size 0-2.0 mm, 15-25 wt. % of gypsum and 40-60 wt. %. of water. Another preferred thermal insulation material for filling hollow building elements comprises 33-44 wt. % of biochar, 12-23 wt. % of gypsum and 33-55 wt. % of water, whereby half of the amount of biochar is in the form of fine particles of size 0-2.0 mm and half of the amount of biochar is in the form of coarse particles of size 0-40 mm.

Another preferred thermal insulation material for filling hollow building elements comprises 33 wt. % of biochar in the form of particles of size 0-2.0 mm, 17 wt. % of cement and 50 wt. % of water. And yet another thermal insulation material for filling hollow building elements comprises 33 wt. % of biochar in the form of particles of size 0-5.0 mm, 17 wt. % of cement and 50 wt. % of water.

The present invention further relates to the use of crushed and/or ground biochar made from wood mass for filling hollow building elements.

And further, the invention relates to a method of producing a thermal insulation material for filling hollow building elements, which comprises the steps of a) preparing biochar by pyrolysis of wood mass at a temperature of 300-700 °C without access of the air; b) crushing and/or grinding the biochar from step a); c) preparing selected fraction(s) from the crushed/ground biochar from step b); d) optionally mixing one or more fractions with a binder and water.

The present invention also relates to a method of improving the thermal insulation properties of a hollow building element, in which the cavity or cavities of the building element is/are filled with the thermal insulation material described above.

And the invention also relates to a hollow building element in which at least one cavity is filled with the thermal insulation material described above.

Description of the drawings

Fig. 1. Electron microscopic image of a cross-section of biochar from oak wood (magnification 750x)

Fig. 2. Electron microscopic image of a cross-section of biochar from oak wood (magnification 7500x) Fig. 3. Electron microscopic image of a longitudinal section of biochar from oak wood (magnification 750x)

Fig. 4. Electron microscopic image of a longitudinal section of biochar from oak wood (magnification 7500x)

Fig. 5. Concrete block used as an exemplary hollow building element.

Fig. 6. Concrete block used as an exemplary hollow building element - mouth of the cavity.

Embodiments of the invention

Example 1

Biochar and its production

Biochar was prepared in a smaller amount sufficient for verification experiments by conventional pyrolysis of wood mass from willow, spruce, beech and oak in a muffle furnace (the inventor's own design), without access of the air, at a temperature of 500 - 700 °C. The properties of biochar from oak and beech practically did not differ from the properties of biochar available commercially. This commercially available biochar (charcoal for barbecue, prepared by pyrolysis of a mixture of oak and beech wood in a retort without air access, at 300 -700 °C, brand: Barbecue charcoal, manufacturer: Servis Les, Deblice-lesy, s.r.o., Dymokury, Czech Republic) was used in the experiments on a larger scale. Spruce wood was pyrolyzed in the form of sawdust (from a cut with a chainsaw).

From the point of view of the thermal conductivity of biochar, its important property is porosity. Biochar, especially biochar obtained from woody biomass, contains pores of various sizes, from micropores (diameter less than 1 nm) to macropores (diameter greater than 50 nm). Macropores are usually a remnant of the original structure of plant tissue (vessels), smaller pores, especially micropores, are mostly formed as a result of gas evolved during pyrolysis. Fig. 1 and 2 show an electron microscope image of a cross-section of a “block” of biochar prepared from oak wood (see above), Fig. 3 and 4 show a longitudinal section. The images demonstrate the “tubular” structure of biochar with pores of various sizes. For further use, the biochar was further crushed in a roller crusher (the inventor's own design) or, to obtain finer fractions, in a ball mill (Jizerska porcelanka s.r.o., Desna v Jizerske horach I, Czech Republic, grinding mill of the author's own design, internal volume of the mill approx. 61, grinding balls diameter 20-30 mm, material of the mill and balls - technical porcelain). From the crushed/ground biochar, 4 fractions with different particle sizes were separated using analytical sieves; fraction 1 : 0-2.0 mm, fraction 2: 2.0-2.8 mm, fraction 3: 2.8-11.2 mm and fraction 4: over 11.2 mm. The fraction with particles over 11.2 mm had the worst thermal insulation properties in preliminary tests and was not further used for the preparation of thermal insulation materials (it was re-crushed into fractions with smaller particles).

The following table 1 shows the characteristics of the fractions of biochar prepared from different sources.

Table 1: Properties of biochar from different sources, softwood - willow, hardwood - a mixture of beech, and oak and spruce sawdust

Table 1 shows that the finest fraction is heavier, has a higher bulk and tapped density compared to fractions 2 or 3 for all types of wood. All fractions of hardwood biochar (beech-oak) are significantly “denser” than the corresponding fraction of softwood biochar. In a preliminary experiment, it was found that for willow and beech-oak biochar there was no significant difference in thermal transfer between fractions 2 and 3. However, fraction 1 showed worse thermal insulation properties. The bulk density of different types of biochar lies between the density of perlite (200 kg/m³) and “keramzif ’ (expanded clay) (600 kg/m³), in some cases it is even significantly lower (especially spruce-sawdust).

Example 2

Insulation properties of a building element filled with loose biochar

A concrete block (so-called lost formwork, DITON s.r.o., Stfitez, Czech Republic) with external dimensions of 500 mm x 250 mm x 100 mm with a single cavity (see Fig. 5) was used, where the cavity (slightly conical) has dimensions (area) of 425 mm x 30 mm at one end and 435 mm x 37 mm at the other end of the block (see Fig. 6).

The cavity was filled with loose biochar, specifically with a certain fraction (see Tables 2 and 3) by pouring and shaking (or by adding biochar and repeating the shaking until the filling no longer settled), the biochar was fixed in the cavity with jute fabric soaked in liquid plaster (the cavities of the control blocks were closed in the same way). The control samples were an empty block (i.e. with the air in the cavity) and a block filled with standard compacted mineral wool (ISOVER ORSIK, Saint-Gobain Construction Products CZ a.s.).

The block was placed with its side wall on an electrically heated metal (copper) plate (the inventor's own design) and using a temperature sensor (type K thermocouple, MAX6675 Module, with a recorder of inventor's own design) placed on the opposite wall of the block, the temperature of this wall was measured over the course of 24 hours. The plate was heated to a temperature of 87 °C ± 3 °C, the room temperature during the experiment was 20 °C ± 2 °C. The measurement results are given in Table 2 and 3.

The results showed that the best thermal insulation properties were possessed by biochar of fraction 2.0-11.2 mm (fraction 2+3) from willow (see Table 2) and biochar of fraction 2.8-11.2 (fraction 3) from beech-oak (see Table 3), these fillings were essentially identical in terms of heat transfer. Biochar of fraction 0-11.2 (i.e. fraction 1+2+3, without separation of the finest fraction 1) from willow and biochar of fraction 2.0-2.8 mm (fraction 2) from beech-oak were worse, however, not significantly. A coarse fraction was also prepared from biochar of willow, which contained particles up to 40 mm in size, but the fine fraction was not removed, i.e. the particle size was in the range of 0-40 mm. This fraction of willow biochar showed the worst thermal insulation properties (but still better than air filling), probably due to too large and interconnected air spaces. Surprisingly, the filling of fractions 0-2.0 mm (fraction 1, the finest) of beech-oak biochar behaved similarly.

In all tested cases, the thermal insulation properties of the block filled with loose biochar were significantly better than those of the block without filling and (depending on the fraction) very close to or identical to those of the block filled with mineral wool.

Table 2. Filling of the block with willow biochar. Temperature profile of the outer wall of the block opposite the heated wall over 20 hours. For each variant, the left column shows the temperature (°C) of the wall, the right column shows the temperature (°C) of the heating plate. The control block was filled with mineral wool (control 1) or had no filling (control 2). Table 3. Filling of the block with beech-oak biochar. Temperature profile of the outer wall of the block opposite the heated wall over 20 hours. For each variant, the left column shows the temperature (°C) of the wall, the right column shows the temperature (°C) of the heating plate. The control block was filled with mineral wool (control 1) or had no filling (control 2).

Example 3

Filling building elements with loose biochar

A. Filling with biochar during the production of a building element

During production, a hollow brick/block or other shaped element can be filled with loose biochar and shaken on a vibrating machine, and filled in such a way that the filling no longer settles. It is also possible to fill cavities that are in a horizontal position after the assembly of the building element, for example, ceiling panels and shaped elements of the “miako” and “hurdis” type, but also other shaped elements with internal cavities such as panels and others.

Several methods can be used to fix the filling in the cavities. a) Covering the holes on both sides with a binder that performs the function of a "plug", binders based on gypsum, cement, lime, polymers, etc. can be used. A fine fraction (0- 2.0 mm) of biochar can also be mixed into the binder, thereby reducing the thermal bridge of the fixation layer. An example of a suitable mixture for sealing loose biochar filling is a mixture of 20 % of fraction 1 biochar, 30 % of gypsum and 50 % of water (% are by weight). b) Another option is to cover the filled holes with mesh. The mesh is chosen so that high- quality joints are formed and the binder reaches the supporting part of the building element. This is especially true when using textile mesh or paper mesh. For ecological reasons, the preferred mesh material is a biodegradable material such as textile, paper, but glass fabric or mesh made of other fibres can also be used. The mesh size should be smaller than the size of the filled biochar fraction. To fix the mesh, binders/adhesives based on gypsum, cement, lime, but also organic-based adhesives can be used. An example of a suitable mesh is jute fabric in combination with gypsum or cement-based adhesive. c) Another option is to press or ram the filling into the cavity of the building element. When compacting biochar, the thermal insulation properties may deteriorate, but on the other hand, the amount of stored carbon per unit volume of the resulting material increases. The finer fraction 1 (0-2.0 mm) is more suitable for pressing. To improve cohesion, wetting of biochar can be used, or wetting of biochar with the addition of a binder. For example, water glass (i.e. sodium silicate) can be used advantageously. d) Biochar can be provided with a binder before filling the cavity. Biochar is coated in a pre-prepared binder, and then poured into the cavity. After hardening, it holds firmly in the cavity and does not spill out. Gypsum, cement, lime, polymer, and other organic and inorganic binders can be used as binders.

B. Filling building elements with biochar directly during construction

The selected fraction of biochar is poured into the cavities using a hopper. It is recommended to use the coarser fraction and omit the finest fraction 1, which is dusty and does not improve the thermal insulation properties of biochar. During the filling of the cavity, compaction can be used at the same time, both mechanical and vibratory. In the case of filling bricks or shaped blocks, the filling is followed by cleaning the contact surfaces, applying mortar or other binding material, and then laying another brick or shaped block, which will be filled again in the same way. This method is suitable for filling vertical cavities. Furthermore, floor cavities and other cavities where it is possible to pour loose material can be filled in a similar way.

Example 4

Preparation of an insulating material comprising biochar and a binder

When crushing biochar, a large proportion of fine fraction 0-2.0 mm (fraction 1) is formed, up to % of the weight of crushed biochar. This fine fraction can be advantageously used for the preparation of a thermal insulation material comprising biochar and a binder.

To prepare a thermal insulation material, fraction 1 biochar (or other fractions) is mixed with a binder, for example gypsum, cement, lime and others, and this liquid/semi-liquid mixture is poured into the cavities. There is a certain disadvantage in the longer drying of the filling, because a larger amount of distribution water must be used here, but on the other hand, the advantage is that after the water dries, a porous material is formed that has better thermal insulation properties. The proportion of biochar to the binder can to some extent control the thermal insulation properties and hardness of the resulting material.

For the preparation of the insulating material, Almond LC gypsum (Saint Gobain Formula) and “fine biochaf’, i.e. fraction 1 of beech-oak biochar (ground in a ball mill, fraction 0 -2.0 mm) and “coarse” biochar (from spruce sawdust, uncrushed, particle size up to 5.0 mm in length) were used.

In combination with gypsum, a wide range of biochar contents from 0.1 % (wt.) to 75 % relative to gypsum was tested, the preferred ratio was 50-67 % of biochar relative to gypsum. The addition of approximately 50 % of water relative to the weight of the dry biochar + gypsum mixture was best suited for mixing. A higher water content resulted in a more fluid mixture, but less solid after hardening, and a lower water content resulted in a mixture that could no longer be poured, but could be filled into cavities and tamped. Examples of mixtures that showed good properties while maintaining the highest possible biochar content are given in Table 4.

The preferred composition of the mixture, where only the fine fraction of biochar was present, was as follows (all wt. %): fine biochar 25-35 %, gypsum 15-25 % and water 40-60 %. The largest amount of biochar incorporated was used in a combination of fine and coarse biochar, in the range of 33-44 % of biochar (fine and coarse fractions together), 12-23 % of gypsum and 33-55 % of water (see samples 1 and 2 in Table 4). The amount of gypsum less than 10 % provided a mixture that set poorly and was very soft.

Table 4. Insulation material comprising biochar and a binder - gypsum.

Furthermore, mixtures comprising biochar, gypsum and water glass were tested, where the addition of water glass led to a harder mixture (see Table 5).

Table 5. Insulating material comprising biochar, gypsum and water glass. All the mixtures mentioned were suitable for filling cavities. Measurement of the thermal insulation properties (the same method as in Example 2) of the block filling from the materials listed in the Tables 4 and 5 showed that even at the lowest biochar content (17-20 %) the thermal conductivity was significantly lower than that of the pure binder (gypsum). A higher biochar content in the mixture clearly led to a decrease in thermal conductivity, i.e. an improvement in thermal insulation properties. The worst thermal conductivity was shown by the sample with a biochar content of 44 % (sample 3 in Table 4).

The density of the preferred materials (samples 3 and 4 in Table 5) is 490-500 kg/m³, which is a value higher than, for example, the value given for perlite (200 kg/m³), but lower than the value for “keramzit” (expanded clay) (600 kg/m³), and is approximately comparable to, for example, “heraclif ’ board (boards made of wood wool bonded with cement) (450 kg/m³).

Similar mixtures as with gypsum were also mixed with cement (Cement Portland- Kalksteinzement CEM II/A-LL 42.55 N, manufacturer SCHWENK, Ulm, Germany) as a binder. Measurement of thermal insulation properties (same method as in Example 2) showed that even at the lowest biochar content (28 %) the thermal conductivity was significantly lower than that of the pure binder (cement). With increasing biochar content in the mixture, the thermal conductivity of the material clearly decreased. The density of the cement materials comprising fine biochar was comparable to gypsum materials. One of the preferred materials comprising fine biochar contained 33 % of biochar, 17 % of cement and 50 % of water. Very interesting materials were created if the biochar was predominantly or exclusively coarse biochar (from spruce sawdust, uncrushed, particle size up to 5 mm in length). These materials had good thermal insulation properties, and in addition had a very low density (230-330 kg/m³) approaching the density perlite (200 kg/m³).

Table 6. Insulation material comprising biochar and a binder - cement.

Mixtures with lime as a binder were also mixed. These mixtures are also usable in principle, but their disadvantage is a long setting time.

Another interesting material was created by mixing fine and coarse biochar (see Table 7) with water without any binder. After setting (drying), a solid mass with good cohesion was essentially created, which has good thermal insulation properties and is suitable as a filling for hollow building elements.

Table 7. Solid insulation material comprising only biochar

Gypsum and cement proved to be the optimal binders for thermal insulation materials comprising biochar and binder. The resulting materials comprising biochar and gypsum or cement showed good thermal insulation properties and a specific gravity within the range of some commonly used insulation materials. From an economic point of view, cement, which is cheaper than gypsum, appears to be a more suitable binder. On the other hand, gypsum is more environmentally friendly because it is processed at lower temperatures and therefore produces less CO2 due to heating of the raw material. In addition, during the production of cement, a large amount of CO2 is released from the raw material itself, while gypsum only releases water during the production of gypsum. The optimal option would therefore be to use gypsum from the cheapest source, which can be, for example, waste gypsum, the so-called energy gypsum produced during desulfurization in coal-fired power plants.

Claims

PATENT CLAIMS

1. Thermal insulation material for filling hollow building elements, characterized in that it comprises crushed or ground biochar prepared from wood mass.

2. Thermal insulation material for filling hollow building elements according to claim 1, characterized in that the biochar was prepared by conventional pyrolysis of wood mass at a temperature of 300-700 °C without access of the air.

3. Thermal insulation material for filling hollow building elements according to claim 1 or 2, characterized in that the biochar is in the form of particles with a size of 0- 11.2 mm, preferably 2.0-11.2 mm.

4. Thermal insulation material for filling hollow building elements according to claim 1 or 2, characterized in that it further comprises a binder, which is gypsum, cement, lime or polymer, and water.

5. Thermal insulation material for filling hollow building elements according to claim 4, characterized in that the biochar is in the form of particles of size 0-2.0 mm.

6. Thermal insulation material for filling hollow building elements according to claim 5, characterized in that it comprises 25-35 wt. % of biochar, 15-25 wt. % of gypsum and 40-60 wt. % of water.

7. Thermal insulation material for filling hollow building elements according to claim 4, characterized in that it comprises 33-44 wt. % of biochar, 12-23 wt. % of gypsum and 33-55 wt. % of water, wherein half of the amount of biochar is in the form of fine particles of size 0- 2.0 mm and half of the amount of biochar is in the form of coarse particles of size 0-40 mm.

8. Thermal insulation material for filling hollow building elements according to claim 4, characterized in that it comprises 33 wt. % of biochar in the form of particles of size 0-2.0 mm, 17 wt. % of cement and 50 wt. % of water.

9. Thermal insulation material for filling hollow building elements according to claim 4, characterized in that it comprises 33 wt. % of biochar in the form of particles of size 0-5.0 mm, 17 wt. % of cement and 50 wt. % of water.

10. A use of crushed and/or ground biochar prepared from wood mass for filling hollow building elements.

11. Method for producing thermal insulation material according to any one of the claims 3 to 9, characterized in that it comprises the steps of a) preparing biochar by pyrolysis of wood mass at a temperature of 300-700 °C without access of the air; b) crushing and/or grinding the biochar from step a); c) preparing the selected fraction(s) from the crushed/ground biochar from step b); d) optionally mixing one or more fractions with a binder and water.

12. A method of improving the thermal insulation properties of a hollow building element, characterized in that the cavity or cavities of the building element are filled with a thermal insulation material according to any one of claims 1 to 9.

13. A hollow building element, characterized in that at least one of its cavities is filled with a thermal insulation material according to any one of claims 1 to 9.