Method of growing vegetation and construction element

Abstract

The disclosure relates to a method of growing vegetation, the method comprising: providing a composition comprising a binder and one or more aggregates, wherein the composition comprises biochar as an additive and / or an aggregate; forming a construction element using the composition; growing vegetation directly on the construction element. The disclosure further relates to construction elements suitable for the growth of vegetation thereon.

Description

[0001] Bioreceptive composition, method and construction element

[0002] The present invention relates to the general field of urban greening, in particular, but not exclusively, to vertical urban greening technologies such as so-called “green wall” or “green cladding” technologies. In particular, the present invention relates to a composition for forming bioreceptive construction elements, a method of growing vegetation, and a construction element for supporting vegetative growth.

[0003] High and increasing levels of pollution within cities and urban environments has been a severe problem for many years due to the detrimental effects caused to the environment and to public health. At the same time, increasing levels of development in cities and urban environments has significantly reduced the area available for green spaces. However, the beneficial effects of plants and other vegetation for establishing a stable environment and reducing levels of pollution is well known. Not only does such vegetation reduce levels of gases such as carbon dioxide and nitrogen dioxide (amongst others) within the atmosphere but also provide filtration of fine dust and other particulates. There is therefore a desire for creative solutions for increasing the amount of green space and vegetation within cities, without compromising the ability to develop the built environment.

[0004] So-called “green wall” or “green cladding” technologies are becoming increasingly common as a solution to the abovementioned problems. Such technologies utilise building surfaces such as roofs, facades, internal or external walls for the growth of vegetation. In addition to pollution abatement, green wall or green cladding technologies can also be used for temperature regulation of buildings, insulating buildings in colder environments and cooling in warmer environments. Such technologies further offer advantages such as contributing to the absorption of excess water (e.g. storm water run-off) and reducing the urban heat island effect. Green spaces are also proven to help with habitants' stress and wellbeing, and overall offer a holistic solution to many of the challenges faced by today's urban environment.

[0005] However, there remains a need for suitable systems for supporting the growth of vegetation on buildings that are effective for supporting vegetation, whilst also meeting strict safety regulations for the built environment. At the same time, there is also a desire to reduce the carbon footprint of construction materials.

[0006] The present invention arose in an attempt to provide robust construction materials and construction elements that can be used to passively support the growth of vegetation, requiring minimal maintenance and meeting necessary regulations.

[0007] In a first aspect, the present invention provides a method of growing vegetation, the method comprising:

[0008] - providing a composition comprising a binder and one or more aggregates, wherein the composition comprises biochar as an additive and / or an aggregate;

[0009] - forming a construction element using the composition; and

[0010] - growing vegetation directly on the construction element.

[0011] The present inventors have found that the use of biochar in a composition for the formation of a construction material improves the bioreceptivity of the construction material. Accordingly, it has been found that construction elements comprising a construction material formed of the composition of the present invention provide a suitable substrate for the direct growth of vegetation thereon. Such construction elements can therefore be used to introduce vegetation into the built environment.

[0012] The present invention is particularly beneficial for the growth of bryophytes. Bryophytes are a group of plants including liverworts, hornworts and mosses. Bryophytes have many advantages including low maintenance and excellent pollution absorption due to a high cation exchange capacity. Furthermore, bryophytes are non-vascular and thus bind to the material via rhizoids, allowing the plant to bind strongly to the substrate.

[0013] Biochar is a particularly beneficial component of the system for the following reasons:

[0014] 1 . Biochar acts as a nutrient source for vegetation supported by the construction material, supplying carbon, nitrogen, hydrogen, and some lower nutrient elements, such as potassium, calcium, sodium and magnesium. Moreover, biochar is a porous material having a high specific surface area, demonstrating an affinity for nutrients such as heavy metal ions, phosphates and nitrates. The biochar can thus be prepared in an appropriate nutrient formula to provide the desired nutrient profile in the material for a given application (e.g. a specific nutrient profile for the growth of a specific plant species).

[0015] 2. Biochar has an inherently large internal surface area. The biochar contained within the construction material therefore acts as a reservoir for moisture, which can be stored within the construction material and diffused to the vegetation to support growth. Additionally, the construction material itself can act as an effective water reservoir for the storage of excess rainwater. Not only does this make more efficient use of rainwater (avoiding the need to supply water to the construction material separately from a mains supply) but may also prevent damage to buildings by collecting excess water (for example, in the event of a storm). The large surface area also enhances the porosity of the construction material, allowing the diffusion of moisture through the construction material to the vegetation supported thereon.

[0016] 3. The porosity of biochar also has the ability to trap air within the construction material, thereby providing insulating properties to the construction elements (e.g. cladding panels) formed from the construction material.

[0017] 4. Biochar may also improve the overall strength of the construction material, thus providing the necessary strength combined with the porosity required to support vegetative growth. Natural silicates present in the biochar strengthen the binder by creating a calcium silicate hydrate phase in the hydraulic set, strengthening the final construction material..

[0018] 5. Biochar acts as a natural filter to remove pollutants from water, which may be a particular benefit in urban environments.

[0019] A further advantage of the use of biochar is the reduction of the overall carbon footprint of the construction material by capturing and storing atmospheric carbon in the form of biochar. Moreover, the storage of atmospheric carbon is permanent. This is a major advantage over other carbon storage methods such as cross laminated timber, which releases the carbon back into the environment at the end of the product lifetime by decomposition. The method of the present invention therefore additionally provides a means or method for carbon deposit, carbon storage or carbon sequestering, comprising forming a biochar and incorporating the biochar into a construction material.

[0020] The biochar source used for the composition of present invention is not particularly limited and may be any suitable organic material or biomass capable of forming a biochar by pyrolysis or gasification. It will be appreciated that different biochar sources may be used and / or combined to impart different properties on the construction material.

[0021] Biochar sources can be split into two groups: 1) municipal waste, and 2) crop-residue. Different sources carry different mineral groups, for example municipal-sourced biochars, e.g., sewage sludge, carry aluminosilicates beneficial to strength and calciumphosphates (beneficial to bioreceptivity). Crop-residue biochars e.g, hemp shiv, rice husk and agricultural waste will undergo decomposition before pyrolysis to establish optimal conditions to produce reactive silicates in the resulting biochar.

[0022] In particularly suitable embodiments, the biochar source comprises hemp shiv or rice husk, which are particularly effective for forming strong bonding to the binder and / or other aggregates due to their high natural silicate content.

[0023] The biochar source may alternatively or additionally comprise organic waste, such as sewage sludge, animal manures and / or other agricultural waste. Such organic waste materials are advantageous due to their high level of contained aluminosilicates, which improve the mechanical strength of the material, and calcium phosphates, which are beneficial to the bioreceptivity of the material. In other embodiments, the biochar source may comprise hardwood.

[0024] Moreover, the biochar source may comprise multiple different organic materials to provide a biochar ‘blend’. That is, the biochar may be formed by pyrolysis or gasification of a mixture of different organic materials.

[0025] The binder may comprise at least one component selected from the group consisting of: hydraulic lime (e.g. natural hydraulic lime); non-hydraulic lime; Portland cement; a geopolymer (alkali-activated material); and an organic binder. Suitably, the binder is a lime-based binder.

[0026] In embodiments, a mass ratio of biochar to binder is in the range 0.1 :1 to 10:1 . Suitably, a mass ratio of biochar to binder is in the range 0.1 :1 to 3:1 , more suitably in the range 0.1 :1 to 1 :1 , most suitably in the range 0.3:1 to 1 :1 , and may be approximately 0.6:1 in some embodiments. Such compositions have been found to provide a desirable balance of good support for vegetative growth, combined with good water storage and transport properties and good mechanical properties (e.g. flexural strength and compressive strength), whilst at the same time providing a level of carbon storage.

[0027] The one or more aggregates may be selected from the group consisting of: sand; gravel; crushed stone; and recycled concrete aggregate. The composition may alternatively or additionally comprise recycled glass or plastics, recycled brick, expanded clay and / or perlite as an aggregate. Suitably, the aggregate may comprise grit sand (also known as sharp sand). Grit sand has been found particularly beneficial for providing the desired combination of porosity and strength to the construction material due to the size and shape variation in the grain profile.

[0028] It is particularly preferred that the aggregate includes a recycled aggregate, such a recycled concrete (e.g. crushed concrete), recycled brick (e.g. crushed brick) or other recycled (e.g. crushed) materials that are stable, non-toxic and pH neutral. Incorporation of recycled aggregates further reduces the carbon footprint of the material by incorporating used construction materials. In particularly preferred embodiments, the aggregate comprises recycled concrete aggregate, which offers a suitable replacement for grit sand in terms of the mechanical properties of the composition.

[0029] In embodiments, a mass ratio of aggregate to binder is in the range 0.1 :1 to 4:1 . Suitably, a mass ratio of biochar to binder is in the range 1 :1 to 3:1 , more suitably 2:1 to 3:1 , and most suitably of approximately 2.5:1 .

[0030] The composition may comprise at least one additive selected from the group consisting of: a phosphorus source; a nitrogen source; a foaming agent; a pozzolanic material; and a fibrous material. The inclusion of a fibrous material is beneficial for increasing the tensile strength of the construction material forming the construction element. The fibrous material may preferably comprise polypropylene fibres.

[0031] The phosphorus source may comprise at least one source selected from the group consisting of: bone ash (e.g. Ca3(PO4)2); worm castings; composted manure; bone meal; foliar fish emulsion; and rock phosphate.

[0032] In embodiments, a mass ratio of the phosphorus source to binder is in the range 0.005:1 to 0.5:1 . Suitably, a mass ratio of the phosphorus source to binder is in the range 0.05:1 to 0.5:1 , more suitably in the range 0.1 :1 to 0.3:1 , more suitably in the range 0.1 :1 to 0.2:1 , and most suitably of approximately 0.15:1 .

[0033] The foaming agent acts to cause the composition to foam and thus enhance and control the porosity of the construction material formed using the composition. The foaming agent may be at least one agent selected from the group consisting of: aluminium powder; a surfactant; and hydrogen peroxide. Where a surfactant or a mixture of surfactants is used, any appropriate source may be used including readily available surfactant sources such as soaps, shampoos and detergents. A suitable foaming agent is EABASSOC foaming agent (available from Bayley-Edge Ltd, United Kingdom, t / a E-A-B Associates).

[0034] Where using a surfactant, in particular EABASSOC foaming agent, a foam is generated by mixing the surfactant with water, which foam is added to the composition. A quantity of the foam in the composition may be in the range 250 millilitres to 2 litres per kilogram of binder, more suitably in the range 500 millilitres to 1 .5 litres per kilogram of binder, and most suitably approximately 1 litre per kilogram of binder.

[0035] The pozzolanic material may comprise at least one material selected from the group consisting of a kaolinite clay fly ash; silica fume; burnt organic matter rich in silica; and a volcanic material. Suitably, the pozzolanic material comprises metakaolin.

[0036] In this regard, pozzolanic materials are to be understood as any material containing and suitable for providing pozzolans to the composition when mixed with water. Pozzolans are a class of alumina- and silica-based materials which, in the presence of water, react with calcium hydroxide (Ca(OH)2) to form calcium silicate hydrate (C-S-H) via the pozzolanic reaction.

[0037] In some embodiments, the pozzolanic material may be mechanically activated before addition to the composition in order to enhance the reactivity of the material. The pozzolanic material may be mechanically activated by grinding or milling, for example.

[0038] It has also been found that including a clay-containing soil in the biochar formation process (pyrolysis or gasification) can be particularly beneficial. After the biochar formation process, the residual soil has a high clay content. This clay provides pozzolans to the construction material, strengthening the resultant material by providing aluminas and silicas to create calcium silicate hydrate and calcium aluminate hydrate phases. A class of clays that provide such strength gains are kaolinite clays, an example of which is metakaolin. Incorporation of a clay-containing soil in the biochar formation process can achieve a particularly high clay content in the composition, for example as high as 50% of the weight of the binder. In particularly suitable embodiments, the clay content in the composition is approximately 10 % of the weight of the binder (e.g. Natural Hydraulic Lime).

[0039] Accordingly, in particular embodiments, the method comprises forming the biochar in the presence of a soil containing the pozzolanic material, preferably a clay-containing soil. For example, the method may comprise forming the biochar by pyrolysis or gasification of an organic material or biomass in the presence of a clay-containing soil, preferably a soil containing a kaolinite clay and most preferably a soil containing metakaolin.

[0040] In embodiments, a mass ratio of the pozzolanic material to binder is in the range 0.01 : 1 to 2 : 1 , suitably 0.05:1 to 1 :1 , more suitably 0.1 :1 to 0.5:1 , and most suitably 0.15:1 .

[0041] Suitably, the biochar has an average particle size in the range 5 microns to 50 mm.

[0042] In embodiments, the composition comprises biochar having an average particle size of 100 microns or less, preferably 50 microns or less, and most preferably 10 microns or less. It has been found that the inclusion of biochar having particle sizes in the above ranges, particularly in the range of 10 microns or less, provide enhanced strength to the construction material formed from the composition. Biochar having particle sizes of 10 microns or less may suitably be formed by gasification of an organic material or biomass, or by mechanical grinding or processing.

[0043] In embodiments, the composition comprises biochar having an average particle size in the range 1 mm to 15 mm, more suitably 2.5 mm to 5 mm. It has been found that the provision of larger biochar particles (chunks) with particle sizes in the above ranges enhance the insulative properties and water retention capability of the construction material by retaining the porous microstructure of the biochar (relative to smaller particle sizes). Biochar having particle sizes in the above range may suitably be formed by pyrolysis of an organic material or biomass. It will be appreciated that mixtures of biochar particles having different particles sizes may be used in appropriate proportions to provide both enhanced strength and surface area. For example, the composition may comprise a first biochar source comprising biochar having an average particle size of 100 microns or less, preferably 50 microns or less, and most preferably 10 microns or less, and a second biochar source comprising biochar having an average particle size in the range 1 mm to 15 mm, more suitably 2.5 mm to 5 mm. It will be appreciated that the composition of the present invention may comprise a variety of biochar ‘blends’, wherein a plurality of biochar sources having difference particles sizes are combined in appropriate proportions to impart different characteristics to the resultant construction material.

[0044] Suitably, the method further comprises forming a mixture of the composition with water, and subsequently curing the mixture to provide a construction material from which the construction element is formed.

[0045] Suitably, the mixture comprises a mass ratio of water to binder in the range 0.1 :1 to 3:1 , suitably 0.3:1 to 1 :1 , more suitably 0.5:1 to 0.8:1 , and most suitably approximately 0.6:1 .

[0046] Suitably, the curing step comprises carbon curing the mixture by placing the mixture in an atmosphere having:

[0047] - carbon dioxide in an amount greater than 1 % by volume, preferably greater than 75 % by volume, preferably greater than 90 % by volume, preferably greater than 95 % by volume and most preferably greater than 99 % by volume;

[0048] - a relative humidity in the range 50 to 100 %; and

[0049] - a temperature of 40 to 100 °C.

[0050] By curing the mixture under elevated concentrations of carbon dioxide, the pH of the construction material forming the construction element is reduced, thus enabling the material to support vegetative growth.

[0051] In embodiments, the mixture is placed into a mould prior to curing. Accordingly, a construction element comprising the construction material is formed directly upon curing of the mixture. In the present invention, the vegetation may be a bryophyte (e.g. a moss, a hornwort or a liverwort) or a lichen. The vegetation may comprise at least one moss selected from the group consisting of: Cushion mosses

[0052] Carpet mosses

[0053] Amblystegium serpens

[0054] Brachythecium rutabulum

[0055] Bryum Capillare

[0056] Bryum Argenteum

[0057] Ceratodon purpureus

[0058] Eurynchium sp.

[0059] Dicranum scoparium

[0060] Mnium hornum

[0061] Rhytidiadelphus squarrosus

[0062] Syntrichia ruraliformis

[0063] Rhynchostegium confertum

[0064] Hylocomnium splendens

[0065] Hypnum cupressiforme

[0066] Homalothecium sericeum

[0067] Polytrichum spp

[0068] In a second aspect, the present invention provides a composition for forming a construction material, the composition comprising a binder and one or more aggregates, wherein the composition comprises biochar as an additive and / or an aggregate. The composition may be the composition as described above in relation to the first aspect.

[0069] In a third aspect, the present invention provides a construction element comprising an outer surface having at least one bioreceptive region.

[0070] The bioreceptive region is a region of the outer surface of the construction element that is capable of supporting (and designed to support) vegetative growth thereon. The bioreceptive region has the ability to support or encourage the surface growth of plants and plant-like organisms. Preferably, the bioreceptive region is formed from a composition comprising a binder and one or more aggregates, wherein the composition comprises biochar as an additive and / or an aggregate, according to the second aspect of the present invention.

[0071] Suitably, the material of the bioreceptive region has a pH in the range 5.5 to 8.5. This pH range provides a substrate suitable for supporting vegetative growth. Measurement of surface pH can be carried out by a number of appropriate techniques that will be known to the skilled person. In one example, universal indicator is applied to the surface of the material via a pipette and the resulting colour is colour matched to a chart indicating the pH of the surface. In another example, a 3 mm cubic sample of material is crushed and added to 10 mL of distilled water. The sample is left overnight and the pH of the water is subsequently tested using a pH meter. Numerous alternative methods will be known to the skilled person.

[0072] Suitably, the construction element comprises vegetation supported directly on the or each bioreceptive region. The vegetation may be any suitable vegetation, including the examples described above.

[0073] Suitably, the construction element comprises a plurality of bioreceptive regions located discretely on the outer surface of the construction element. That is, each bioreceptive region is discontinuous with the other bioreceptive region(s) provided on the outer surface of the construction element. The outer surface of the construction element therefore has a plurality of bioreceptive “growth zones” which can support vegetation, and one or more “non-growth zones” extending between the growth zones, such that the growth of vegetation is limited to the discretely-formed growth zones. This arrangement is particularly important from a fire safety perspective. A significant problem associated with traditional ‘green wall’ arrangements is the continuous nature of the vegetative growth covering potentially large areas of a building structure. In the event of a fire, this creates the risk of fire spreading across a potentially large area of the building via the vegetation. This has hitherto limited the application of green wall structures over large areas e.g. on internal walls or facades of buildings. With the present arrangement, the vegetation is formed discretely, meaning that fire cannot spread between vegetation provided in the discrete bioreceptive regions (or “growth zones”). Accordingly, it is possible to provide the vegetative growth over much larger areas of a building structure, whilst still meeting strict fire safety standards. For the above purpose, the bioreceptive regions preferably form less than 99% of a surface area of the outer surface of the construction element, more preferably less than or equal to 80% of a surface area of the outer surface of the construction element, or in some embodiments less than or equal to 50% of a surface area of the outer surface of the construction element.

[0074] Suitably, the outer surface comprises a non-bioreceptive region separating and / or surrounding the bioreceptive regions. This ensures that vegetation does not spread between the bioreceptive regions.

[0075] The non-bioreceptive region is a region of the outer surface that is not bioreceptive. The non-bioreceptive region of the outer surface therefore lacks the ability to support or encourage the surface growth of plants and plant-like organisms. The non-bioreceptive region may be formed of a non-bioreceptive concrete. A suitable, non-limiting, example of a material for the formation of a non-bioreceptive region is Jesmonite (RTM) AC630, available from Jesmonite Ltd (Shropshire, United Kingdom).

[0076] The outer surface of the construction element preferably comprises a plurality of discrete, discontinuous bioreceptive regions, each being surrounded by a substantially continuous non-bioreceptive region.

[0077] Suitably, the non-bioreceptive region has a pH less than 5.5 or greater than 8.5. These conditions prevent the growth of vegetation in the non-bioreceptive region. In this regard, in the context of the present specification, the non-bioreceptive region can be defined at a fundamental level as a region of the outer surface having a pH less than 5.5 or greater than 8.5. It will be appreciated that other characteristics and properties of the material forming the non-bioreceptive region may be engineered to deter or prevent vegetative growth thereon.

[0078] The non-bioreceptive region preferably has a porosity that is lower than a porosity of the bioreceptive region(s). Even more desirably, the non-bioreceptive region is impermeable to liquid i.e. the non-bioreceptive region is sealed to have zero porosity. This can be applied via an additive process or by mechanically polishing the non-bioreceptive region. The non-bioreceptive region may have a maximum pore diameter of 100 nm. This ensures that the material forming the non-bioreceptive region is insufficiently porous to provide the necessary water storage and transport to support vegetative growth.

[0079] The biorecetive region may preferably comprise pores having a diameter of at least 500 nm. This ensures that the material forming the biorecetive region comprises pores that are sufficiently large for effective water storage and transport, thus enabling the material to support vegetative growth. It will be appreciated that the material forming the non- bioreceptive region may also comprise pores having a diameter of less than 500 nm. However, provided at least some pores are present having a diameter of at least 500 nm, the desired porosity can be achieved.

[0080] In this regard, the pore diameter of the material is measured by mercury intrusion porosimetry (MIP). In an exemplary test method, MIP measurements are performed using a Thermo Scientific Pascal 440 Series instrument. Specimens of the material forming the bioreceptive and / or non-bioreceptive regions are crushed into small pieces (about 1 g in mass). MIP is performed using an external pressure ranging from 0.10 MPa to 400 MPa. Values of mercury contact angle and surface tension of 140° and 0.48 N / m are used, respectively. The distribution of pore diameters is analysed to determine the maximum pore diameter present in the specimen and to determine the presence or absence of pore diameters within preferred ranges.

[0081] Suitably, the construction element comprises a base layer formed of a bioreceptive material, preferably formed of a composition in accordance with the aforementioned aspects of the present invention, and an outer layer formed of a non-bioreceptive material, the outer layer comprising one or more openings in which the non-bioreceptive material is absent, the or each opening exposing a region of the underlying base layer so as to define the bioreceptive region or a respective one of the bioreceptive regions. Each bioreceptive region is preferably recessed from an outer surface of the outer layer. The non- bioreceptive material forms a non-bioreceptive region of the outer surface, as described above.

[0082] The base layer preferably defines a continuous structure. Accordingly, the arrangement comprises a continuous base layer formed of a bioreceptive material, with an outer ‘skin’ formed of a non-bioreceptive material, wherein openings or gaps formed in the outer skin expose regions of the underlying base layer to define one or more of the bioreceptive regions, which are capable of supporting vegetative growth and through which water can enter to be absorbed by the base layer. This arrangement is particularly advantageous, especially where the non-bioreceptive material forming the outer skin has a porosity lower than that of the bioreceptive material forming the base layer, since moisture can be more reliably retained within the base layer (that is, the outer skin prevents evaporation of moisture from the construction element in the regions covered by the non-bioreceptive outer skin). Also, the arrangement controls diffusion of moisture within the base layer to be directed towards the bioreceptive regions, thus creating the humid conditions desirable for vegetative growth.

[0083] The base layer preferably has no openings extending from a front (outer) surface of the construction element to a rear (inner) surface of the construction element. This arrangement prevents the spread of fire from a front (outer) surface of the construction element to a rear (inner) surface of the construction element, as well as preventing the spread of fire across the outer surface as described above.

[0084] The construction element may be any element forming the construction of a building and for example may be a wall or a wall cladding.

[0085] The construction element may be modular. The construction element may preferably comprise a plurality of units arranged to interconnect with each other to form the construction element. In the arrangements described above, one or more of the bioreceptive regions may be formed wholly within a single unit. Alternatively, or additionally, one or more of the bioreceptive regions may be defined by two adjacent units. That is, one or more of the bioreceptive regions may bridge between adjacent units of the modular system.

[0086] The construction element preferably comprises a plurality of channels, preferably extending at an angle in the range of 10 to 80 degrees from vertical (in use), more preferably 20 to 70 degrees from vertical (in use). In a particularly preferred embodiments, the construction element comprises a substantially continuous bioreceptive layer formed of a bioreceptive material, preferably a bioreceptive concrete, wherein the channels extend through the bioreceptive layer. Accordingly, the channels allow for the supply of water to the bioreceptive layer. The porosity of the bioreceptive layer allows further dispersion of water throughout the continuous bioreceptive layer and to any flora or vegetation supported thereon.

[0087] The construction element may comprise an inlet port in fluid communication with one or more channels. The inlet port provides a fluid pathway from an exterior of the construction element to the internal channels of the construction element. The inlet port therefore allows connection to a water source, such as a water storage tank or mains water supply, for supplying water to the channels.

[0088] In preferred embodiments, wherein the construction element is modular, the channels are defined by mutually engaging edges of adjacent units. That is, each unit comprises an edge arranged to engage with a cooperating edge of an adjacent unit, so as to define a channel therebetween.

[0089] The construction element may further comprise one or more cavities formed within the base layer. The or each cavity can act as a reservoir for the storage of water. Suitably, the or each cavity is in fluid communication with the bioreceptive material of the base layer to allow for diffusion of water / moisture between the cavity and the bioreceptive material of the base layer. The or each cavity is preferably in fluid communication with a channel of the construction element.

[0090] In preferred embodiments, wherein the construction element is modular, each unit preferably comprises an inlet port arranged to be in fluid communication with one or more channels of the construction element, when assembled.

[0091] The or each bioreceptive region may comprise one or more grooves formed in an outer surface thereof. The grooves may have a maximum depth of at least 2mm, at least 3mm, at least 4mm, at least 5mm, at least 6mm, at least 7mm, at least 8mm, at least 9mm or at least 10mm relative to the outer surface of the bioreceptive region in which the grooves are formed. The grooves provide a base for roots or rhizoids of vegetation (e.g. moss rhizoids) to bind to and therefore provide a strong anchoring of the vegetation on the bioreceptive zone. The grooves may also allow for the build up of organic material such as soils, which can further support the growth of vegetation on the construction element. The construction element may comprise one or more protrusions arranged to extend outwardly from the outer surface of the construction element. The one or more protrusions may be arranged so as to provide solar shading to one or more of the bioreceptive regions. Preferably, a portion of the outer surface is arranged to protrude outwardly so as to provide solar shading to one or more bioreceptive region. That is, the or each protrusion is formed unitarily with the outer surface of the construction element. Where the construction element is modular, each unit may comprise a protrusion arranged to provide shading to a bioreceptive region of an adjacent unit located below the unit, in use. The profusion may be located, for example, at or near a lower edge of the unit.

[0092] Non-limiting embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0093] Figure 1 is a flow diagram illustrating an exemplary method of growing vegetation in accordance with the present invention;

[0094] Figure 2 is a front view of a construction element in accordance with the present invention;

[0095] Figure 3 is a cross sectional view of the construction element through line Ill-Ill shown in Figure 2;

[0096] Figure 4 is an enlarged view of the circled region A indicated in Figure 1 ;

[0097] Figure 5 is a front view of a further construction element;

[0098] Figure 6 is a cross-sectional view of the construction element through line VI-VI shown in Figure 5; and

[0099] Figure 7 is a perspective view of a further cladding element in accordance with the present invention.

[0100] Definitions

[0101] Herein, the term ‘aggregate’ refers to any particulate material that may be combined with a binder to form a composite material, such as concrete. Aggregates may be fine-grained, medium-grained or coarse-grained.

[0102] Herein, the term ‘binder’ refers to any material or that holds or draws other materials together to form a cohesive whole, mechanically or chemically, by adhesion or cohesion. Herein, the term ‘biochar’ refers to any organic material or biomass which has been carbonised by pyrolysis or gasification in a low or zero oxygen environment. Biochar is defined by the International Biochar Initiative as "the solid material obtained from the thermochemical conversion of biomass in an oxygen-limited environment".

[0103] Herein, the term ‘bioreceptive’ or ‘bioreceptivity’ refers to the ability of a material to support floral or vegetative growth. A bioreceptive material has the ability to support or encourage the surface growth of plants and plant-like organisms.

[0104] Herein, the term ‘construction element’ is not particularly limiting and refers to any element that may be used in the construction of the built environment. A construction element in accordance with the present invention may be any slab, panel (e.g. a cladding panel), brick, block or similar element (aesthetic or structural) that is used in the construction of the built environment. The present invention is envisaged for particular use in aesthetic construction elements such as external or internal cladding panels.

[0105] Composition and method for growth of vegetation

[0106] Example 1 - Fabrication of a construction element with biochar

[0107] Four compositions (Table 1) were prepared and used to fabricate construction elements. The suitability of each construction element for the growth of a moss was evaluated. Comparative examples 1 to 3 are example compositions not in accordance with the present invention, which were prepared for comparative purposes. Example 1 is a composition comprising biochar, in accordance with the present invention.

[0108] A flow diagram illustrating the method of growing vegetation is provided in Figure 1 .

[0109] Ground Granulate Blast-furnace slag supplied by Cemfree (Comparative Example 1) or Natural Hydraulic Lime (NHL 5) supplied by Saint-Astier (Comparative Examples 2 and 3; Example 1 ) was used as a binder.

[0110] Grit sand supplied by Jewsons was used as an aggregate. EABASSOC foaming agent supplied by Bayley-Edge Ltd (t / a E-A-B Associates) was used as a foaming agent.

[0111] Bone ash supplied by Bath Potters Supplies was used as an additive.

[0112] Biochar granules (2 to 8 mm) supplied by SoilFixer (United Kingdom) were used as a biochar source. To provide the desired granule size, the biochar granules were passed through an 8 mm mesh and retained by a 2 mm mesh. The biochar source was hardwood and the biochar was formed by pyrolysis in a low oxygen environment (step S1 - Figure 1).

[0113] The compositions were prepared (step S2 - Figure 1 ) by mixing components according to the ratios provided in Table 1 :

[0114] Table 1 : composition ratios

[0115] Binder, aggregate, biochar and additive (bone ash) were combined to form a dry mixture. Water was then added to the dry mixture in a ratio of approximately 0.5 : 1 to 1 : 1 water to binder, to achieve the desired consistency (step S3 - Figure 1 ). It will be appreciated that steps S2 and S3 may be carried out simultaneously. That is, components of the composition may be added sequentially to the cementitious mixture. In Comparative Example 3 and Example 1 , foaming agent was included in the composition. The foaming agent was first mixed with water to generate a foam. The foam was then added to the wet cementitious mixture in the quantities specified in Table 1 , and mixing continued to provide a homogenous wet mixture.

[0116] The cementitious mixture was placed in a mould, pressed with moderate pressure and excess mixture was removed from the top of the mould.

[0117] The moulds were placed in a sealed container for curing (step S4 - Figure 1). The container was purged with carbon dioxide (CO2) at regular intervals to maintain an atmospheric carbon dioxide content of approximately 60 to 90 %. The temperature of the container was maintained at approximately 40 to 60 °C.

[0118] The moulds were removed from the container once it was observed that curing was complete.

[0119] The cured samples were removed from the moulds, representing construction elements in accordance with the present invention. In this regard, in the Examples discussed herein, the construction elements were formed as small slabs of material for the purpose of testing and evaluation. However, it will be appreciated that the construction elements in accordance with the present invention may be moulded into any appropriate form suitable for use as a construction, such as in the form of a cladding panel for mounting to a wall of a building, or similar.

[0120] The construction elements were then evaluated for pore sizes, water storage and transportation, strength and suitability for growth of moss thereon.

[0121] Pore sizes were evaluated by mercury intrusion porosimetry. Peaks in the particle size distribution were recorded, as noted in Table 2:

[0122] Table 2: results

[0123] It was concluded that Example 1 offered suitable strength, porosity and capability to support moss growth for use as a construction element capable of supporting vegetative growth.

[0124] Cladding element Figures 2 to 4 show a construction element 1 in accordance with an embodiment of the present invention. The construction element 1 has an outer surface 2 comprising a plurality of discretely formed bioreceptive regions 4. The bioreceptive regions 4 are preferably formed using a bioreceptive biochar material as described above. However, it will be appreciated that alternative bioreceptive materials may also be used to form the bioreceptive regions 4.

[0125] As shown most clearly in Figure 3, the construction element 1 comprises a substantially continuous bioreceptive base layer 6 formed of the bioreceptive material and a ‘skin’ layer 8 formed of a non-bioreceptive material, defining a non-bioreceptive region 10 of the outer surface 2. The non-bioreceptive skin layer 8 covers the bioreceptive base layer 6 on an outer surface thereof. It will be appreciated that in embodiments of the present invention, the non-bioreceptive ‘skin’ layer may wrap fully around the bioreceptive base layer 6 (i.e. around the back and sides of the base layer 6) except in the region of the bioreceptive regions 4, in which the bioreceptive base layer 6 is exposed.

[0126] The non-bioreceptive region 10 of the outer surface 2 lacks the ability to support or encourage the surface growth of plants and plant-like organisms. The non-bioreceptive region 10 may be formed of a non-bioreceptive concrete. It will be appreciated that the material non-bioreceptive region 10 is not particularly limited and may comprise any material that is unsuitable for supporting vegetative growth. In embodiments, the non- bioreceptive region 10 may be formed of a concrete having a pH less than 5.5 or greater than 8.5. The non-bioreceptive region 10 may alternatively or additionally have a porosity lower than that of the bioreceptive regions, such that diffusion of water in the non- bioreceptive region (skin) is insufficient to support vegetative growth. Still further, the non- bioreceptive region 10 may be surface treated to deter the growth of vegetative thereon. For example, the surface of the non-bioreceptive region may be polished or sealed to reduce the roughness of the surface, so as to inhibit the attachment of roots or rhizoids thereto.

[0127] The non-bioreceptive region (skin) 10 comprises a plurality of openings 12 in which the non-bioreceptive material is absent. Each opening exposes a region of the underlying base layer 6 so as to define a respective one of the bioreceptive regions 4 of the outer surface 2. The non-bioreceptive region 10 is a continuous region that surrounds the bioreceptive regions 4 so as to separate the bioreceptive regions 4. With this arrangement, the bioreceptive regions 4 are formed discretely, such that growth of vegetation is limited to the areas of the outer surface 2 defined by the bioreceptive regions 4. By defining discrete, discontinuous growth zones, two main advantages are achieved.

[0128] Firstly, areas of vegetative growth are separated, meaning that in the event of a fire, the spread of fire between growth zones and therefore, across the outer surface of the construction element is inhibited. When a large area such as an internal or external wall is covered with the construction element, this arrangement advantageously prevents the spread of fire over a large area. Fire safety of the construction element is therefore improved.

[0129] Secondly, the non-bioreceptive skin prevents diffusion of water vapour from the base layer to the outer surface via the non-bioreceptive region. Moisture is thereby retained within the bioreceptive base layer and can diffuse through the base layer to provide moisture to the bioreceptive regions. Moreover, the present arrangement encourages diffusion of water to the bioreceptive regions formed on the outer surface of the construction element. Solar gains experienced by the construction element over a period of time will cause evaporation of water held within the base layer. Water vapour is therefore directed to the bioreceptive regions (growth zones) of the outer surface as indicated by arrows shown in Figure 3, thereby producing a humid environment at the bioreceptive regions to further encourage the growth of vegetation.

[0130] Each bioreceptive region 4 comprises a plurality of grooves 14 formed in an outer surface thereof (i.e. the outer surface of the bioreceptive region 4 exposed by the openings 12 of the non-bioreceptive region 10). The grooves 14 may have a maximum depth of at least 2mm, at least 3mm, at least 4mm, at least 5mm, at least 6mm, at least 7mm, at least 8mm, at least 9mm or at least 10mm relative to the outer surface 2 of the bioreceptive region 4 in which the grooves are formed. The depth of the grooves 14 may be constant or may vary along ethe length of each groove 14. The grooves 14 provide a base for roots or rhizoids of vegetation (e.g. moss rhizoids) to bind to and therefore provide a strong anchoring of the vegetation on the bioreceptive region 4. In the illustrated embodiment, the grooves 14 are arranged diagonally (relative to the vertical direction, in use), however alternative embodiments may comprise grooves formed in alternative orientations. The grooves may be linear or non-linear. Referring to Figure 2, the construction element 1 is a modular arrangement comprising a plurality of construction panels 16 arranged to interconnect with each other to form the construction element 1. The construction panels 16 may be arranged to interconnect in any appropriate manner. Side edges of adjacent panels 16 may be formed with mutually cooperating profiles so as to connect adjacent panels 16 together. Alternatively, the construction panels 16 may be individually mounted on a supporting element (e.g. mounted on a wall directly or indirectly) such that the adjacent edges of adjacent construction panels abut or are positioned close together.

[0131] In the illustrated embodiment, openings 12 in the non-bioreceptive region (skin) are formed at the edges of each panel 16. Accordingly, respective openings 12 of adjacent panels collectively define a single bioreceptive region 4 of the construction element. This is shown most clearly in Figure 4, which is an enlarged view of the circled area A shown in Figure 2. A first panel 16a comprises a first opening 12a formed in a side edge 18a of the first panel 16a, the first opening 12a exposing a region of the underlying bioreceptive base layer 6. A second panel 16b comprises a second opening 12b formed in a side edge 18b of the second panel 16b, the second opening 12b exposing a region of the underlying bioreceptive base layer 6. The two adjacent exposed regions define a bioreceptive region 4 of the construction element 1 .

[0132] It is noted in this regard that each individual construction panel 16 may also be considered to be a construction element within the context of the present invention, each construction panel comprising a bioreceptive base layer and a non-bioreceptive skin layer, wherein the non-bioreceptive skin layer defines a non-bioreceptive region of the outer surface of the cladding panel, and openings formed at the edges of the panel expose regions of the underlying bioreceptive base layer, so as to define bioreceptive regions of the outer surface of the construction panel.

[0133] Figure 5 shows a construction element 1 substantially as described above. The construction element is formed of two interconnecting panels 16a, 16b. A channel 20 is formed in the base layer 6, the channel 20 extending at an oblique angle in the range 10 to 80 degrees from vertical (in use). The channel 20 extends continuously between adjoining panels 16a, 16b. Each panel 16a, 16b comprises an inlet port 22 that is in fluid communication with the channel 20. This allows any of the panels 16a, 16b to be connected to a water source for the supply of water into the channel 20. The channel 20 allows for water transport throughout the base layer 6 of the construction element 1 and to the bioreceptive regions 4 formed by the exposed portion of the base layer 6.

[0134] Figure 6 is a cross-sectional view taken through line VI-VI shown in Figure 5. The channel 20 is formed in an upper edge of the panel 16b. Panel 16a has a corresponding upper edge profile, such that when the panels 16a, 16b are connected, the channel 20 extends between the panels 16a, 16b. It will also be appreciated that corresponding lower edges of vertically adjacent panels may also be profiled so as to engage with the upper edge of an adjacent panel, so as to define the channel therebetween.

[0135] The base layer 6 comprises a cavity 24 in fluid communication with the channel 20. The cavity 24 allows for transport of water / moisture from the channel to the bioreceptive material forming the base layer 6. This allows for storage of excess water within the structure of the construction element. It will be appreciated that the cavity may be formed in any appropriate location, depending on the constraints of the manufacturing process. For example, where the panels 16a, 16b are cast from a cementitious mixture, the cavity may be defined by mutually engaging recesses formed in the sides of adjoining panels.

[0136] Figure 7 shows a further embodiment of a construction element 100 in accordance with the present invention. The construction element 100 has an outer surface 102 comprising a plurality of discretely formed bioreceptive regions 104. The bioreceptive regions 104 are preferably formed using a bioreceptive biochar material as described above. However, it will be appreciated that alternative bioreceptive materials may also be used to form the bioreceptive regions 104.

[0137] The construction element 100 comprises a substantially continuous bioreceptive base layer 106 formed of a bioreceptive material and a ‘skin’ layer 108 formed of a non- bioreceptive material, defining a non-bioreceptive region 110 of the outer surface 2. The non-bioreceptive skin layer 108 covers the bioreceptive base layer 106 on an outer surface thereof. The non-bioreceptive region 110 may be formed as outlined above.

[0138] The non-bioreceptive region (skin) 110 comprises a plurality of openings in which the non-bioreceptive material is absent. Each opening exposes a region of the underlying base layer 106 so as to define a respective one of the bioreceptive regions 104 of the outer surface 102. The non-bioreceptive region 110 is a continuous region that surrounds the bioreceptive regions 104 so as to separate the bioreceptive regions 104. With this arrangement, the bioreceptive regions 104 are formed discretely, such that growth of vegetation is limited to the areas of the outer surface 102 defined by the bioreceptive regions 104.

[0139] The construction element 100 comprises a plurality of protruding portions 126 extending outwardly from the outer surface 102 of the construction element 100. In the illustrated embodiment, the protusions 126 are formed unitarily with the non-bioreceptive regions 110 of the outer surface 102. The protrusions 126 are located so as to provide solar shading to the bioreceptive regions 104.

[0140] The invention has been described above with reference to specific embodiments, given by way of example only. It will be appreciated that different arrangements of the system are possible, which fall within the scope of the appended claims.

Claims

Claims1 . A method of growing vegetation, the method comprising:- providing a composition comprising a binder and one or more aggregates, wherein the composition comprises biochar as an additive and / or an aggregate;- forming a construction element using the composition; and- growing vegetation directly on the construction element.

2. A method according to claim 1 , wherein a mass ratio of biochar to binder is in the range 0.1 : 1 to 10 : 1.

3. A method according to claim 25 or 2, wherein the binder comprises at least one component selected from the group consisting of: hydraulic lime; non-hydraulic lime; Portland cement; a geopolymer; and an organic binder.

4. A method according to any preceding claim, wherein the one or more aggregates are selected from the group consisting of: sand; gravel; crushed stone; recycled aggregate material; expanded clay; and perlite.

5. A method according to claim 4, wherein the recycled aggregate material comprises recycled concrete aggregate, recycled brick aggregate, recycled glass aggregate and / or recycled plastic aggregate.

6. A method according to any preceding claim, wherein a mass ratio of aggregate to binder is in the range 0.1 : 1 to 4 : 1 .

7. A method according to any preceding claim, further comprising at least one additive selected from the group consisting of: a phosphorus source; a nitrogen source; a foaming agent; a pozzolanic material; and a fibrous material.

8. A method according to claim 7, wherein the phosphorus source comprises at least one source selected from the group consisting of: bone ash; worm castings; composted manure; bone meal; foliar fish emulsion; and rock phosphate.

9. A method according to claim 8, wherein a mass ratio of the phosphorus source to binder is in the range 0.05 : 1 to 0.5 : 1 .

10. A method according to any one of claims 7 to 9, wherein the foaming agent comprises at least one agent selected from the group consisting of: aluminium powder; a surfactant; and hydrogen peroxide.1 1 . A method according to any one of claims 7 to 10, further comprising a step of forming the biochar in the presence of a soil containing the pozzolanic material.

12. A method according to any one of claims 7 to 11 , wherein the pozzolanic material comprises at least one kaolinite clay.

13. A method according to claim 12, wherein the pozzolanic material comprises metakaolin.

14. A method according to any one of claims 11 to 13, wherein a mass ratio of the pozzolanic material to binder in the composition is in the range 0.01 : 1 to 2 : 1 .

15. A method according to any preceding claim, wherein the biochar has an average particle size in the range 5 microns to 50 mm.

16. A method according to claim 15, wherein the composition comprises biochar having an average particle size of 100 microns or less, preferably 50 microns or less, and most preferably 10 microns or less.T117. A method according to any preceding claim, wherein the step of forming the construction material comprises forming a mixture of the composition with water, and subsequently curing the mixture to form the construction element.

18. A method according to claim 17, wherein the mixture comprises a mass ratio of water to binder in the range 0.1 :1 to 3:1 .

19. A method according to claim 17 or 18, wherein the curing step comprises carbon curing the mixture by placing the mixture in an atmosphere having:- carbon dioxide in an amount greater than 1 % by volume, preferably greater than 75 % by volume, preferably greater than 90 % by volume, preferably greater than 95 % by volume and most preferably greater than 99 % by volume;- a relative humidity in the range 50 to 100 %; and- a temperature of 40 to 100 °C.

20. A method according to any one of claims 17 to 19, wherein the mixture is placed into a mould prior to curing.21 . A construction element comprising an outer surface having at least one bioreceptive region, the bioreceptive region being formed from a composition comprising a binder and one or more aggregates, wherein the composition comprises biochar as an additive and / or an aggregate.

22. A construction element according to claim 21 , wherein the construction element comprises vegetation supported directly on the or each bioreceptive region.

23. A construction element according to claim 21 or 22, wherein the material of the bioreceptive region has a pH in the range 5.5 to 8.5.

24. A construction element comprising an outer surface having a plurality of bioreceptive regions located discretely on the outer surface of the construction element.

25. A construction element according to claim 24, wherein the construction element is a construction element according to any one of claims 21 to 23, wherein each one of the plurality of bioreceptive regions is formed from a composition comprising a binder and one or more aggregates, wherein the composition comprises biochar as an additive and / or an aggregate.

26. A construction element according to claim 24 or 25, wherein the bioreceptive regions form less than or equal to 80% of a surface area of the outer surface of the construction element.

27. A construction element according to any one of claims 24 to 26, wherein the outer surface comprises a non-bioreceptive region separating and / or surrounding the bioreceptive regions.

28. A construction element according to claim 27, wherein the non-bioreceptive region has a pH less than 5.5 or greater than 8.5.

29. A construction element according to claim 27 or 28, wherein the non-bioreceptive region has a porosity that is lower than a porosity of the or each bioreceptive region.

30. A construction element according to claim 29, wherein the non-bioreceptive region has a maximum pore diameter of 100 nm, and wherein the or each bioreceptive region comprises pores having a diameter of at least 500 nm.31 . A construction element according to any one of claims 21 to 30, comprising a base layer formed from a composition comprising a binder and one or more aggregates,wherein the composition comprises biochar as an additive and / or an aggregate, and an outer layer formed of a non-bioreceptive material, the outer layer comprising one or more openings in which the non-bioreceptive material is absent, the or each opening exposing a region of the underlying base layer so as to define the bioreceptive region or a respective one of the bioreceptive regions.

32. A construction element according to claim 31 , wherein the base layer defines a continuous structure.

33. A construction element according to claim 31 or 32, further comprising one or more cavities formed within the base layer, the or each cavity being arranged to provide a reservoir for the storage of water.

34. A construction element according to any one of claims 21 to 33, comprising a plurality of channels extending at an angle in the range of 10 to 80 degrees from vertical, in use.

35. A construction element according to claim 34, further comprising an inlet port in fluid communication with one or more of the channels, the inlet port being arranged to provide a fluid pathway from an exterior of the construction element to the channel or channels.

36. A construction element according to claim 34 or 35, wherein the construction element comprises a plurality of units arranged to interconnect with each other to form the construction element, and wherein the channels are defined by mutually engaging edges of adjacent units.

37. A construction element according to any one of claims 21 to 36, wherein a portion of the outer surface is arranged to protrude outwardly so as to provide solar shading to one or more bioreceptive region.

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