3D printing concrete method and wall

Abstract

Disclosed is a method of 3D printing a concrete wall. The method comprises steps of: a) obtaining a supply of a concrete composition, the concrete composition comprising a coarse aggregate with an average particle size of greater than about 4 mm, the concrete composition comprising a retarding admixture; and b) depositing a plurality of deposited layers of the concrete composition using a 3D printer; wherein an accelerating admixture is added to the concrete composition.

Description

[0001] 3D Printing Concrete Method and Wall

[0002] This invention relates to a method for 3D printing concrete and a 3D printed concrete wall.

[0003] Background

[0004] 3D printing processes involve depositing material in layers so as to build up a 3D structure. 3D printing may be used for constructing buildings, such as houses. 3D printing may be used to construct the walls of a building. The walls may be built up from layers of material.

[0005] During the 3D printing process, the building material must stay fluid, so that the building material can be easily deposited by the 3D printer. 3D printing can take a long period of time to print an entire wall or building. During the printing time, the building material can start to set. Additionally, if the building material is mixed offsite, and transported to the building site, this adds to the time before the building material is deposited. This gives even less time onsite before the building material sets. If the building material sets before it is deposited, it may be wasted. The set building material may also damage the 3D printer, and associated components such as piping.

[0006] Mortar has previously been used to 3D print houses. Mortar is well suited as a building material for the 3D printing process. Mortar can be mixed onsite. Mixing the mortar onsite may maximise the amount of time that mortar can be used for printing before it sets.

[0007] However, using mortar as a building material can have limitations in terms of the strength, and the durability of the walls. Concrete may be preferred as a building material. However, concrete is generally mixed offsite, and transported to the building site, which adds to the time before the building material is deposited. Concrete may begin to set during the printing process. Thus, concrete may not generally be well suited as a building material for the 3D printing process.

[0008] It is desirable for an improved concrete composition which may be used for 3D printing. It is also desirable for an improved 3D printing method which allows concrete to be used as a building material.

[0009] Most walls are made using a cavity wall system. In a cavity wall system, two wall leaves are located beside one another, often with a layer of insulation sandwiched in a cavity in between. The two wall leaves may only need to be thin to meet the required building standards. It is also possible to make a wall out of a single wall leaf. In the case of a single leaf wall, the wall may need to be thicker to meet the required building standards.

[0010] As described herein, using mortar as a building material can have limitations in terms of the strength, and the durability of the walls. In particular, using mortar as a building material can limit the width that the walls can be printed. If mortar-based walls are too wide, then the walls may not meet the required building standards. Therefore, mortarbased walls may not be suitable for single leaf walls.

[0011] It is also desirable for an improved building material for wider 3D printed single leaf walls.

[0012] It is an object of the invention to alleviate some of the above detailed problems.

[0013] Summary

[0014] According to a first aspect of the present invention there is provided a method of 3D printing a concrete wall, the method comprising steps of: a) obtaining a supply of a concrete composition, the concrete composition comprising a coarse aggregate with an average particle size of greater than about 4 mm, the concrete composition comprising a retarding admixture; and b) depositing a plurality of deposited layers of the concrete composition using a 3D printer; wherein an accelerating admixture is added to the concrete composition. The use of a retarding admixture and an accelerating makes concrete a viable building material for 3D printing by overcoming the technical challenges associated with transporting and / or using concrete in 3D printing. In some implementations, the 3D printer may comprise a nozzle through which the concrete composition passes during deposition. The nozzle may provide a controlled deposition of the concrete composition. In some implementations, the accelerating admixture may be added to the concrete composition prior to the concrete composition passing through the nozzle. The concrete composition may then start to set as it is deposited, allowing for subsequent layers of composition to be deposited on top of the previous layer. In some implementations, the accelerating admixture may be added to the concrete composition no more than about 30 minutes prior to the concrete composition passing through the nozzle, preferably between about 30 seconds and about 20 minutes prior to the concrete composition passing through the nozzle. These time ranges may provide the correct setting rate for printing.

[0015] In some implementations, the accelerating admixture may be added by spraying the accelerating admixture on to the concrete composition. Spraying may allow the accelerating admixture to be quickly incorporated in the concrete composition.

[0016] In some implementations, the 3D printer may comprise a vessel through which the concrete composition passes before deposition. In some implementations, the accelerating admixture may be added to the concrete composition in the vessel. In some implementations, the accelerating admixture may be sprayed on to the concrete composition in the vessel. Spraying in the vessel may contain the application of the accelerating admixture to the concrete composition.

[0017] In some implementations, the concrete composition may pass through the vessel prior to passing through the nozzle. This may allow the accelerating admixture to be incorporated into the concrete composition before it is deposited.

[0018] In some implementations, the accelerating admixture and the concrete composition may be mixed in the vessel. In this way, the accelerating admixture may be dispersed through the concrete composition so as to evenly accelerate the setting throughout the concrete. In some implementations, the retarding admixture may comprise a citric acid, a lignosulfonate, a sulfonated naphthalene-formaldehyde condensate, a sulfonated melamine-formaldehyde condensate, a sulfonated vinyl copolymer, a polycarboxylate, a hydroxylated carboxylic acid, a sugar, a carbohydrate derivative, a phosphorous acid, a phosphoric acid, a salt of any thereof, or a combination of two or more thereof, preferably a phosphorous acid, a phosphoric acid, a lignosulfonate, a chloride-based sugar, a salt of any thereof, or a combination of two or more thereof, preferably a sodium salt of a phosphorous acid or a sodium salt of a phosphoric acid or a combination of two or more thereof. These retarding admixtures may allow the retarding action to be at least partially reversed such that it is possible for 3D printed concrete to be set, without needing to wait until the effect of the retarder wears off.

[0019] In some implementations, the concrete composition may comprise between about 0.05 wt% and about 5 wt% of the retarding admixture. This retarding admixture range has been found to have a good balance between increased transportation / printing time and faster printing. In some implementations, the concrete composition may comprise between about 0.1 wt% and about 1 wt% of the retarding admixture. This narrower retarding admixture range has been found to have an optimised balance between increased transportation / printing time and faster printing.

[0020] In some implementations, the accelerating admixture may comprise calcium dinitrate, calcium stearate, calcium chloride, sodium nitrate, sodium silicate, magnesium hydroxide, magnesium oxide, magnesium chloride, magnesium nitrate, triethylamine (TEA), triisopropanolamine (TIPA), an aluminium compound or a mixture of two or more thereof, preferably calcium dinitrate, calcium chloride, an aluminium compound or a combination of two or more thereof, preferably calcium dinitrate, aluminium sulphate or a combination thereof. These admixtures have been found to be particularly effective in accelerating the setting of the concrete composition

[0021] In some implementations, the accelerating admixture is added in an amount of about 0.05% to about 5% based on the weight of the concrete composition. This accelerating admixture range has been found to have a good balance between faster printing and risk of early setting. In some implementations, the accelerating admixture is added in an amount of about 0.1 % to about 3% based on the weight of the concrete composition. This narrower accelerating admixture range has been found to have an optimised balance between faster printing and risk of early setting.

[0022] In some implementations, the obtaining a supply of concrete may comprise pumping the concrete composition from a reservoir to the nozzle. This may allow the supply of concrete to be moved from a storage unit to the nozzle for printing.

[0023] In some implementations, the obtaining a supply of concrete may comprise pumping the concrete composition from the reservoir via the vessel to the nozzle. This may allow the accelerating admixture to be added on route between the storage unit and the nozzle for printing.

[0024] In some implementations, the obtaining a supply of concrete may comprise transporting the supply of the concrete composition from a concrete production plant to a construction site, preferably in a concrete truck. This may allow the supply of concrete to be moved from an offsite production plant to the site for printing. In some implementations, the 3D printer may be located at the construction site.

[0025] In some implementations, the initial concrete setting time of the concrete composition, prior to adding the accelerating admixture may be at least about 2 hours, This time may provide sufficient time for the concrete to be transported to site and to be printed. In some implementations, the initial concrete setting time of the concrete composition, prior to adding the accelerating admixture may be between about 3 to about 14 hours. This time may provide sufficient time for the concrete to be transported to site and to be printed while setting quick enough for subsequent concrete layers to be printed on previous layers. In some implementations, the initial concrete setting time of the concrete composition, prior to adding the accelerating admixture may be between about 3 to about 12 hours. This time may provide sufficient time for the concrete to be transported to site and to be printed while setting quick enough for subsequent concrete layers to be printed on previous layers more quickly. In some implementations, the initial concrete setting time of the concrete composition, prior to adding the accelerating admixture may be between about 4 hours and about 8 hours. This time may provide sufficient time for the concrete to be transported to site and to be printed while setting quick enough for subsequent concrete layers to be printed on previous layers much more quickly.

[0026] In some implementations, the initial concrete setting time of the concrete composition, after adding the accelerating admixture may be less than about 30 minutes, preferably about 2 minutes to about 30 minutes, preferably about 5 minutes to about 20 minutes. This use of the accelerating admixture may significantly reduce the setting time such that as the concrete composition leaves the nozzle the setting time enables fast and efficient 3D printing.

[0027] In some implementations, depositing the concrete composition using a 3D printer may comprise depositing a plurality of layers. In this way, the deposition may allow a wall to be build up layer by layer.

[0028] In some implementations, each of the layers may comprise a height of about 25mm to about 75mm. This layer height range has been found to have a good balance between deposition speed and setting time.

[0029] In some implementations, each of the layers may comprise a width between about 50mm and about 250mm. This layer width range has been found to have a good balance between compressive strength and waste material.

[0030] In some implementations, each of the layers may comprise a width between about 50mm and about 150mm. This layer width range has been found to provide a wall thickness suitable for double leaf walls.

[0031] In some implementations, each of the layers may comprise a width between about 100mm and about 250mm. This layer width range has been found to provide a wall thickness suitable for single leaf walls.

[0032] In some implementations, the concrete composition may further comprise a fine aggregate, a binder and water. This may provide suitable durability to the concrete composition. In some implementations, the binder comprises Portland cement and / or a supplementary cementitious material. This may provide suitable durability and reduced carbon footprint.

[0033] In some implementations, the flow of the concrete composition may be in the range of about 300 mm to about 550 mm, preferably about 350 mm to about 500 mm. This range of flow may provide an efficiency deposition for the 3D printing.

[0034] In some implementations, the concrete composition may be uncured concrete. In some implementations, the concrete composition may be 3D printed and then cured. The composition of the concrete may be measured before curing.

[0035] According to a second aspect of the present invention there is provided a 3D printed concrete wall comprising a plurality of cured deposited layers of a concrete composition, the wall being made by the method as described herein. The use of a retarding admixture and an accelerating makes concrete a viable building material for 3D printing by overcoming the technical challenges associated with transporting and / or using concrete in 3D printing.

[0036] According to a third aspect of the present invention there is provided a 3D printed concrete wall comprising a plurality of deposited layers of a concrete composition, the wall being made by: obtaining a supply of concrete composition, the concrete composition comprising a coarse aggregate with an average particle size of greater than about 4mm, the concrete composition comprising a retarding admixture; and depositing the concrete composition using a 3D printer; wherein an accelerating admixture is added to the concrete composition. The use of a retarding admixture and an accelerating makes concrete a viable building material for 3D printing by overcoming the technical challenges associated with transporting and / or using concrete in 3D printing.

[0037] In some implementations, each of the deposited layers comprise a width between about 100 mm and about 250 mm. This layer width range has been found to provide a wall thickness suitable for single leaf walls. According to a fourth aspect of the present invention there is provided a single leaf 3D printed concrete wall comprising a plurality of deposited layers of concrete composition, the concrete composition comprising a coarse aggregate with an average particle size of greater than about 4 mm, wherein each of the deposited layers comprise a width between about 100 mm and about 250 mm. This layer width range has been found to provide a wall thickness suitable for single leaf walls.

[0038] In some implementations, each of the deposited layers may comprise a width between about 150mm and about 200mm. This narrower layer width range has been found to provide an optimal wall thickness suitable for single leaf walls which also reduces waste material.

[0039] In some implementations, the wall may comprise a height between about 1 m and about 5 m. This may provide a wall height suitable for buildings, including houses.

[0040] In some implementations, each of the layers may comprise a height of about 25 mm to about 75 mm. This layer height range has been found to have a good balance between deposition speed and setting time.

[0041] In some implementations, each of the layers may comprise a width to height ratio of about 1 .5 to about 2.5, preferably about 1 .9 to about 2.1 . has been found to result in a good balance between setting time and the compressive strength of the layers.

[0042] In some implementations, the wall may comprise an insulation layer on a first major surface of the wall. The insulation layer may improve the insulation of the wall.

[0043] In some implementations, the wall may comprise a rendering layer on a major surface of the insulation layer. The rendering layer may improve the waterproofing of the wall. The rendering layer may reduce the amount of moisture entering the wall. The rendering layer may improve the sound proofing of the wall. The rendering layer may improve the surface finish of the outside of the wall. The rendering layer may provide a flat surface to the outside of the wall. The rendering layer may improve the appearance of the outside of the wall. The rendering layer may allow paint and other decoration to be applied to the outside of the wall. The rendering layer may allow fittings and other structure to be applied to the outside of the wall.

[0044] In some implementations, the wall may comprise a drylining layer on a second major surface of the wall. The drylining layer may improve the waterproofing of the wall. The drylining layer may improve the sound proofing of the wall. The drylining layer may improve the surface finish of the inside of the wall. The drylining layer may provide a flat surface to the inside of the wall. The drylining layer may improve the appearance of the inside of the wall. The drylining layer may allow paint and other decoration to be applied to the inside of the wall. The drylining layer may allow plaster and other structure to be applied to the inside of the wall.

[0045] In some implementations, the wall may comprise a plaster layer on a major surface of the drylining layer. The plaster layer may improve the sound proofing of the wall. The plaster layer may improve the surface finish of the inside of the wall. The plaster layer may provide a flat surface to the inside of the wall. The plaster layer may improve the appearance of the inside of the wall. The plaster layer may allow paint and other decoration to be applied to the inside of the wall.

[0046] According to a fifth aspect of the present invention there is provided a building comprising one or more walls as described herein. This layer width range has been found to provide a wall thickness suitable for single leaf walls.

[0047] According to a sixth aspect of the present invention there is provided a building comprising one or more single leaf 3D printed concrete walls comprising a plurality of deposited layers of concrete composition, the concrete composition comprising a coarse aggregate with an average particle size of greater than about 4mm, wherein each of the deposited layers comprise a width between about 100mm and about 250mm. This layer width range has been found to provide a wall thickness suitable for single leaf walls.

[0048] According to a seventh aspect of the present invention there is provided a method of 3D printing a single leaf 3D printed concrete wall as described herein. This layer width range has been found to provide a wall thickness suitable for single leaf walls. According to an eighth aspect of the present invention there is provided a method of 3D printing a single leaf 3D printed concrete wall comprising a plurality of deposited layers of concrete composition, the concrete composition comprising a coarse aggregate with an average particle size of greater than about 4mm, wherein each of the deposited layers comprise a width between about 100mm and about 250mm. This layer width range has been found to provide a wall thickness suitable for single leaf walls.

[0049] An advantage of the invention is that the use of an accelerating admixture makes it technically and commercially possible to use concrete in 3D printing as described below.

[0050] Brief Description

[0051] The present invention will now be described by way of example with reference to the accompanying drawings. In the drawings:

[0052] Figure 1 illustrates the steps of a method of 3D printing of a concrete wall of an embodiment of the invention.

[0053] Figure 2 schematically illustrates an apparatus for 3D printing concrete walls of an embodiment of the invention.

[0054] Figure 3a schematically illustrates a 3D printed concrete wall from a side view of an embodiment of the invention. Figure 3b schematically illustrates a 3D printed concrete wall cross section of a first embodiment of the invention. Figure 3c schematically illustrates a 3D printed concrete wall cross section of a second embodiment of the invention. Figure 3d schematically illustrates a 3D printed building plan view of an embodiment of the invention.

[0055] Detailed Description The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art.

[0056] The general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

[0057] The present invention relates to a method for 3D printing concrete and a 3D printed concrete wall.

[0058] Concrete Composition

[0059] A concrete composition may be used in 3D printing concrete walls. The concrete composition may form the walls. The concrete composition may form the bulk of the material in the walls. The concrete composition may provide the main load bearing structure of the walls.

[0060] The method of printing the concrete wall from the concrete composition may be as described herein, for example with reference to Figure 1. The apparatus used for printing the concrete wall from the concrete composition may be as described herein, for example with reference to Figure 2. The structure of the concrete wall may be made from the concrete composition may be as described herein, for example with reference to Figures 3a-c.

[0061] The concrete composition may also be used in 3D printing components other than walls. For example, the concrete composition may be used to print, foundations, tiles, bricks, blocks, fittings, and any other building component. The concrete composition may also be used for printing aesthetic components, such as statues. The composition of the concrete may be defined by the percentage content of each component. The percentage content is the percentage weight of the total mix weight.

[0062] The concrete composition comprises between about 5 wt% and about 50 wt% of a coarse aggregate. The coarse aggregate may preferably comprise gravel. Particles of the coarse aggregate may preferably comprise different sizes. The average particle size of the coarse aggregate is greater than about 4 mm. A composition may be defined as concrete if the coarse aggregate has an average particle size greater than about 4 mm. Having an average particle size greater than about 4 mm may be advantageous. Having an average particle size of greater than about 4 mm may provide sufficient compressive strength such that the concrete wall meets required building standards. Preferably, the coarse aggregate has an average particle size of at least about 6 mm. Preferably, the coarse aggregate has an average particle size between about 4 mm and about 20 mm, preferably between about 6 mm and about 15 mm. It is an advantage of the invention that coarse aggregate can be used in 3D printing to improve the compressive strength of the concrete compared to mortar.

[0063] Preferably the average particle size can be measured by laser diffraction or sieving, preferably by laser diffraction.

[0064] The concrete composition may preferably comprise a coarse aggregate in an amount of between about 5% and about 50% by weight of the composition. Depending on the requirements, the amount of coarse aggregate may preferably be greater than about 5 wt%, about 10 wt%, about 25 wt%, about 30 wt%, about 35 wt%, about 40 wt% or about 45 wt%. Depending on the requirements, the amount of coarse aggregate may preferably be less than about 10 wt%, about 25 wt%, about 30 wt%, about 35 wt%, about 40 wt%, about 45 wt%, or about 50 wt%. Increasing the content of coarse aggregate can increase the compressive strength of the concrete wall. Reducing the content of the coarse aggregate can improve the flow of the concrete during deposition by the 3D printer, as there are less particles which may get stuck. A balance between compressive strength and an improved flow is advantageous. A coarse aggregate content of between 5% and 50% by weight of the composition has been found to have a good balance between compressive strength and an improved flow. Preferably, the coarse aggregate content is greater than about 20 wt% to provide sufficient compressive strength. Preferably, the coarse aggregate content is less than about 30 wt% to provide improved flow. More preferably, the coarse aggregate content is about 25 wt%.

[0065] The concrete composition comprises a fine aggregate. The fine aggregate preferably comprises sand. Particles of the fine aggregate may preferably comprise different sizes. The average particle size of the fine aggregate is preferably less than about 4 mm, preferably less than about 3 mm.

[0066] The concrete composition comprises a fine aggregate in an amount of between about 30% and about 70% by weight of the composition. Depending on the requirements, the amount of fine aggregate may preferably be greater than about 30 wt%, about 35 wt%, about 40 wt%, about 45 wt%, about 50 wt%, about 55 wt%, about 60 wt%, or about 65 wt%. Depending on the requirements, the amount of fine aggregate may preferably be less than about 35 wt%, about 40 wt%, about 45 wt%, about 50 wt%, about 55 wt%, about 60 wt%, about 65 wt% or about 70 wt%. Increasing the content of fine aggregate can increase the density of the concrete wall, which may reduce voids which can cause defects. Reducing the content of the fine aggregate can improve the flow of the concrete during deposition by the 3D printer, as there are less particles which may get stuck. A balance between density and an improved flow is advantageous. A fine aggregate content of between 30% and 70% by weight of the composition has been found to have a good balance between density and an improved flow. Preferably, the fine aggregate content is greater than 45% to provide sufficient density. Preferably, the fine aggregate content is less than 55% to provide improved flow.

[0067] The concrete composition comprises a binder. The binder preferably comprises cement. The binder preferably comprises Portland cement. The binder preferably comprises a supplementary cementitious material. Use of a supplementary cementitious material may reduce the carbon footprint of the concrete composition. A combination of different binders, such as Portland cement and a supplementary cementitious material may be used. The composition of the combination may be varied depending on the requirements for the concrete composition, including the binder strength and the carbon levels. The concrete composition comprises a binder content of between about 8% and about 25% by weight of the composition. Depending on the requirements, the binder content may preferably be greater than about 8 wt%, about 10 wt%, about 12 wt%, about 14 wt%, about 16 wt%, about 18 wt%, about 20 wt%, about 22 wt% or about 24 wt%. Depending on the requirements, the binder content may preferably be less than about 10 wt%, about 12 wt%, about 14 wt%, about 16 wt%, about 18 wt%, about 20 wt%, about 22 wt%, about 24 wt%, or about 25 wt%. Increasing the content of binder can improve the binding and durability of the concrete. Reducing the content of the binder can reduce the carbon footprint of the concrete. A balance between durability and a lower carbon footprint is advantageous. A binder presenting an amount of between 8% and 25% by weight of the composition has been found to have a good balance between durability and a lower carbon footprint. Preferably, the amount of binder is greater than about 10 wt% to provide sufficient durability. Preferably, the amount of binder is less than about 15 wt% to provide reduced carbon levels.

[0068] The concrete composition comprises water. The water may be from a local water supply. The water may comprise natural impurities.

[0069] The concrete composition comprises between about 2 wt% and about 10 wt% of water. Depending on the requirements, the amount of water may preferably be greater than about 2 wt%, about 4 wt%, about 6 wt%, or about 8 wt%. Depending on the requirements, the amount of water may preferably be less than about 4 wt%, about 6 wt%, about 8 wt% and about 10 wt%. Increasing the content of water can improve the binding and durability of the concrete. Reducing the content of the water can improve compressive strength of the concrete. A balance between durability and compressive strength is advantageous. A water content of between 2% and 10% by weight of the composition has been found to have a good balance between durability and compressive strength. Preferably, the amount of water is greater than 5% to provide sufficient durability. Preferably, the amount of water is less than 7% to provide sufficient compressive strength.

[0070] The concrete composition comprises a retarding admixture. The use of a retarding admixture in the concrete composition increases the operating window to use the concrete before it sets. It is important for 3D printing to be able to control the setting time of the building material. As a result, 3D printing of walls and buildings has typically used mortar which can be made on the 3D printing site, however mortar requires a higher amount of binder than concrete to achieve the required strength and even high binder content may not be sufficient. Production of binder, such as Portland cement produces large amounts of carbon dioxide and as a result is undesirable to use in building products.

[0071] It has been a particular problem to make concrete at one site and transport it for use in 3D printing at a second site. Often, concrete has an operating window of around 2 hours, and this gives a limited window to make, transport and use the concrete. It limits the use of concrete for 3D printing to sites which are close to a concrete production site. Even if the concrete is produced close to the building site, this does not overcome the problems with 3D printing concrete as the operating window of around 2 hours does not give sufficient time to use the concrete and handle any of the delays that arise in 3D printing. For example, the 3D printing is a process which needs to be carefully monitored and adjusted to ensure the correct location of the building material and to ensure the building material has set enough for a subsequent layer to be applied. Additionally, it is necessary to pause printing to allow items such as wall ties and insulation materials to be attached to the wall. Typically, material to be 3D printed needs to be transported in pipes to a nozzle for printing. If concrete were to set in the pipes or any part of the 3D printer, this would cause waste of material and costly delays to clean or replace the pipes and equipment.

[0072] As described herein, the use of a retarding admixture makes concrete a viable building material for 3D printing by overcoming the technical challenges associated with transporting and / or using concrete in 3D printing. The retarding admixture increases the operating window of the concrete to allow it to be made at one site and then transported to a second site to be printed. This increased operating window compared to typical concrete allows for transportation and 3D printing delays which gives an operationally viable product to use in 3D printing. If the concrete composition sets before it is deposited, it may be wasted. The set concrete composition may also damage the 3D printer, and associated components, such as piping. Preferably the retarding admixture is a reversible retarding admixture. This allows the concrete composition to retain fluidity prior to being 3D printed and then the concrete composition can set to allow enough strength to develop to allow a subsequent layer of concrete to be printed. This allows the hydration reaction in the concrete to be controlled.

[0073] Preferably, in use the hydration reaction in the concrete composition can be increased by reversing and / or reducing the retarding action of the retarding additive.

[0074] The retarding admixture preferably comprises a citric acid, a lignosulfonate, a sulfonated naphthalene-formaldehyde condensate, a sulfonated melamineformaldehyde condensate, a sulfonated vinyl copolymer, a polycarboxylate, a hydroxylated carboxylic acid, a sugar, a carbohydrate derivative, a phosphorous acid, a phosphoric acid, a salt of any thereof, or a combination of two or more thereof, preferably a phosphorous acid, a phosphoric acid, a lignosulfonate, a chloride-based sugar, a salt of any thereof, or a combination of two or more thereof, preferably a sodium salt of a phosphorous acid or a sodium salt of a phosphoric acid or a combination of two or more thereof. These admixtures have been found to be particularly effective in delaying the setting of the concrete composition. The composition of the retarding admixture may be varied depending on the requirements for the concrete composition, including the setting time required. Such retarding admixtures are preferably used as the retarding action may be at least partially reversed. This means that it is possible for 3D printed concrete to be set, without needing to wait until the effect of the retarder wears off. This has the advantage of the concrete having the desired fluidity until it is printed and then allows the concrete to set after 3D printing to allow subsequent layers to be printed.

[0075] The concrete composition comprises between 0.05 wt% and about 5 wt% of the retarding admixture, preferably between about 0.1 wt% and about 1 wt% of the retarding admixture. Depending on the requirements, the amount of retarding admixture may preferably be greater than about 0.05 wt%, about 0.1 wt%, about 0.25 wt%, about 0.5 wt%, about 1 wt%, about 2 wt%, about 3 wt%, or about 4 wt%. Depending on the requirements, the amount of retarding admixture may preferably be less than about 0.1 wt%, about 0.25 wt%, about 0.5 wt%, about 1 wt%, about 2 wt%, about 3 wt%, about 4 wt%, or about 5 wt%. Increasing the content of retarding admixture can increase the concrete setting time, which gives more time for transporting and printing the concrete. Reducing the content of the retarding admixture can decrease the concrete setting time, which may allow subsequent layers to be printed more quickly. For example, it may be that a 3D printed layer needs to set before a subsequent layer can be printed on top. This is because previous layer may need to support the subsequent layer. A balance between increased transportation / printing time and faster printing is advantageous. A retarding admixture in an amount of between about 0.05 wt% and about 5wt % has been found to have a good balance between increased transportation / printing time and faster printing. Preferably, the retarding admixture amount is greater than 0.1 about wt% to provide sufficient setting time. Preferably, the retarding admixture amount is less than about 1 wt% to provide fast printing time.

[0076] Concrete may generally have an initial setting time of about 2 hours. The retarding admixture may preferably delay the initial setting time by 1 to 12 hours. This would increase the setting time to 3 to 14 hours. Preferably, the setting time may be increased to by 1 to 4 hours. This would increase the setting time to 3 to 6 hours. The composition retarding admixture, and the content of the admixture in the concrete composition, may be varied depending on the requirements for the concrete composition, including the setting time required. For example, if the concrete is mixed on site, a 3 hour setting time may be suitable. However, if the concrete is mixed offsite, a 6+ hour setting time may be more suitable.

[0077] Preferably, the initial concrete setting time of the concrete composition is at least about 3 hours, preferably between about 3 to about 14 hours, preferably between about 3 to about 12 hours, preferably between about 4 hours and about 8 hours. The initial concrete setting time can be measure in accordance with ASTM ZC403M-08.

[0078] Preferably, the retarding admixture acts as a water reducing admixture. A water reducing admixture may reduce the amount of water required to mix the concrete composition. By having less water, this may improve the compressive strength of the concrete, and reducing the setting time of the concrete. The concrete composition preferably comprises an accelerating admixture. The accelerating admixture may increase the rate at which the concrete composition sets. As described herein, during 3D printing a layer of concrete composition may be deposited on a previous layer. The previous layer may need to set quickly so that is has sufficient strength for the subsequent layer to be printed on top of it. Using an accelerating admixture can reduce the setting time of the previous layer, allowing the subsequent layer to be deposited more quickly. This may increase the overall printing speed. The accelerating admixture may be added to the concrete composition during the deposition of the concrete composition.

[0079] The accelerating admixture preferably comprises calcium dinitrate, calcium stearate, calcium chloride, sodium nitrate, sodium silicate, magnesium hydroxide, magnesium oxide, magnesium chloride, magnesium nitrate, triethylamine (TEA), triisopropanolamine (TIPA), an aluminium compound or a mixture of two or more thereof, preferably calcium dinitrate, calcium chloride, an aluminium compound or a combination of two or more thereof, preferably calcium dinitrate, aluminium sulphate or a combination thereof. These admixtures have been found to be particularly effective in accelerating the setting of the concrete composition. The composition of the accelerating admixture may be varied depending on the requirements for the concrete composition, including the setting time required.

[0080] The concrete composition preferably comprises between about 0.05 wt% and about 5 wt% of an accelerating admixture content. Depending on the requirements, the amount of accelerating admixture may preferably be greater than about 0.1 wt%. Depending on the requirements, the amount of accelerating admixture may preferably be less than about 3 wt%. Increasing the content of accelerating admixture can reduce the concrete setting time, reducing the overall print time. Reducing the content of the accelerating admixture can increase the concrete setting time, which may avoid the risk of concrete setting in the nozzle. A balance between faster printing and risk of early setting is advantageous. An accelerating admixture amount of between about 0.05 wt% and about 5 wt% has been found to have a good balance between faster printing and risk of early setting. Preferably, the amount of accelerating admixture is greater than about 0.1 wt% to provide fast printing time. Preferably, the amount of accelerating admixture is less than about 3 wt% to provide a reduced risk of early setting.

[0081] Preferably, the flow of the concrete composition is in the range of about 300 mm to about 550 mm, preferably about 350 mm to about 500 mm. Preferably, the flow of the concrete is measure in accordance with BS EN 12350-5, Testing fresh concrete. Flow table test. This allows the concrete composition to be 3D printed in layers and retain its structure when subsequent layers are deposited.

[0082] Preferably, the concrete composition is uncured concrete. This allows the concrete composition to be 3D printed. Preferably, the concrete composition is 3D printed and then cured.

[0083] The cured concrete composition has a compressive strength. The compressive strength may be measured once the wall is printed, and the concrete composition has cured. The concrete composition may cure after about 28 days. The compressive strength may be measured after about 28 days. Preferably, the compressive strength of the concrete wall may be between 10 MPa and 65 MPa. More preferably, the compressive strength of the concrete wall may be between 35 MPa and 60 MPa. Preferably, the compressive strength is measure at 28 days. A compressive strength within these ranges may meet the required building standards. The content and composition of the components of the concrete composition described herein may be varied so as to meet these compressive strength levels.

[0084] The following tables include the results of compressive strength testing carried out on compositions which fall within the ranges outlined herein.

[0085] Table 2 includes trials carried out in the lab. In the lab, the concrete composition was mixed and left to set in normal inside room conditions. The mix column indicates different mixes. The 24hr column indicates the compressive strength MPa after 24hrs.

[0086] The 7 Day column indicates the compressive strength MPa after 7 days. The 28 Day column indicates the compressive strength MPa after 28 days.

[0087] Table 3 includes trials carried out onsite. Onsite, the concrete composition was mixed, printed using a 3D printer, and left to set outdoor conditions (Irish summertime). The mix column indicates different mixes. The 7 Day column indicates the compressive strength MPa after 7 days. The 28 Day column indicates the compressive strength MPa after 28 days.

[0088] As shown in the tables, the compressive strength is generally lower in outside conditions after 3D printing when compared to the lab. This may be due to pores created during 3D printing, and sub-optimal setting conditions outside. However, the mixes still meet the requirements for strength outlined herein.

[0089] Method of 3D Printing

[0090] Figure 1 illustrates the steps of a method 100 of 3D printing of a concrete wall of an embodiment of the invention.

[0091] The method 100 may use the concrete composition as described herein. The method 100 may use the apparatus as described herein, for example with reference to Figure 2. The method 100 may make structure of the concrete wall as described herein, for example with reference to Figures 3a-c.

[0092] The method 100 may also be used in 3D printing components other than walls. For example, the method 100 may be used to print, foundations, tiles, bricks, blocks, fittings, and any other building component. The method 100 may also be used for printing aesthetic components, such as statues.

[0093] A supply of concrete composition may be obtained. The concrete composition may comprise the composition as described herein. The obtaining of the supply of concrete may comprise different steps depending on the implementation.

[0094] Obtaining the concrete composition may comprise a step of mixing 101 the concrete composition. The composition may comprise the components as described herein. The components may be mixed together to form the concrete composition. The components may be mixed in a single mix. Alternatively, the components may be added in a certain order. For example, the dry components (aggregates, binder, solid admixture(s)) may be added first, and wet components (water, liquid admixture(s)) may be added later, or vice versa. The concrete composition may be mixed offsite. The concrete composition may be mixed at a concrete production site. Alternatively, the concrete composition may be mixed onsite. The concrete composition may be mixed at the construction site.

[0095] During the mixing 101 step, a retarding admixture may be added. The retarding admixture may delay the setting of the supply of concrete during the following steps. The retarding admixture may comprise the features as described herein.

[0096] Obtaining the concrete composition may comprise a step of delivering 102 the supply of concrete. In the case that the concrete composition is mixed offsite, the supply of concrete may be transported from the concrete production site to the construction site. The supply of concrete may be transported in a truck, such as a mixer truck, such as a concrete truck. For a standard 3-bed house, approximately four trucks of concrete may be needed. This may correspond to 32 meters of concrete. The supply of concrete may be delivered to a reservoir for storing the concrete onsite. Alternatively, the obtaining the concrete composition may not comprise a step of delivering 102 the supply of concrete (as outlined by the dashed line in Figure 1 ). In this case, the concrete is mixed onsite. The supply of concrete may be mixed and put into the reservoir for storing the concrete onsite. The 3D printer and the reservoir may both be located at the construction site.

[0097] Obtaining the concrete composition may comprise pumping 103 the supply of concrete. The supply of concrete may be pumped from the reservoir to the 3D printer. The 3D printer may comprise a nozzle. The supply of concrete may be pumped from the reservoir to the nozzle.

[0098] An accelerating admixture may be added 104 to the concrete. The admixture may reduce the setting time of the concrete composition. If a retarding admixture is used in the supply of concrete, the accelerating admixture may counteract the retarding admixture. Reducing the setting time of the concrete composition may be advantageous during 3D printing. The accelerating admixture may comprise the features as described herein.

[0099] The accelerating admixture preferably comprises calcium chloride, calcium dinitrate, calcium stearate, sodium nitrate, sodium silicate, magnesium hydroxide, magnesium oxide, magnesium chloride, magnesium nitrate, triethylamine (TEA), triisopropanolamine (TIPA), or a mixture of two or more thereof. These admixtures have been found to be particularly effective in reducing the setting of the concrete composition. The composition of the accelerating admixture may be varied depending on the requirements for the concrete composition, including the setting time required.

[0100] The concrete composition may be deposited 105. The concrete composition may be deposited using the 3D printer. The concrete composition may be deposited using the nozzle of the 3D printer. The concrete composition may pass through the nozzle during deposition. The concrete composition may be deposited layer by layer to build up the wall.

[0101] The accelerating admixture may be added to the concrete composition during the deposition of the concrete composition. In this way, setting of the concrete composition may be accelerated as soon as it is deposited.

[0102] The accelerating admixture may be added to the concrete composition at the nozzle. In this way, the concrete composition setting may be accelerated as it leaves the nozzle during deposition. The accelerating admixture may be sprayed on to the concrete composition. In this way, the accelerating admixture may be quickly incorporated in the concrete composition.

[0103] The accelerating admixture is added to the concrete composition prior to the concrete composition passing through the nozzle. The accelerating admixture may be added to the concrete composition no more than about 30 minutes prior to the concrete composition passing through the nozzle. Preferably between about 30 seconds and about 20 minutes prior to the concrete composition passing through the nozzle. The 3D printer may comprise a vessel. The nozzle may be fluidly connected to the vessel. The concrete composition may pass through the vessel before passing through the nozzle. Obtaining the supply of concrete may comprise pumping the concrete composition from the reservoir via the vessel to the nozzle. The accelerating admixture may be sprayed on to the concrete composition when the concrete composition is passing through the vessel. In this way, the application of the accelerating admixture to the concrete composition may be contained. Additionally, the accelerating admixture and the concrete composition may be mixed in the vessel. In this way, the accelerating admixture may be dispersed through the concrete composition so as to evenly accelerate the setting throughout the concrete.

[0104] Taking the method as a whole: using a retarding admixture in the supply of the concrete composition may provide more time for transporting / storing / pumping / depositing the concrete composition; and using an accelerating admixture may provide a fast-setting concrete composition for deposition. This may be a key enabler in the use of concrete in 3D printing. The retarding admixture reduces the time constraints on the transporting / storing / pumping / depositing times. The accelerating admixture improves the speed / compressive strength of the 3D printing.

[0105] 3D Printing Apparatus

[0106] Figure 2 schematically illustrates an apparatus 200 for 3D printing concrete walls of an embodiment of the invention.

[0107] The apparatus 200 may use the concrete composition as described herein. The apparatus 200 may use the method 100 of printing the concrete wall as described herein, for example with reference to Figure 1 . The apparatus 200 may make structure of the concrete wall as described herein, for example with reference to Figures 3a-c.

[0108] The apparatus 200 may also be used in 3D printing components other than walls. For example, the apparatus 200 may be used to print, foundations, tiles, bricks, blocks, fittings, and any other building component. The apparatus 200 may also be used for printing aesthetic components, such as statues. The apparatus 200 illustrated in Figure 2 outlines the components which may be located on the construction site. A software program may operate and control the components of the apparatus 200. The software program may be automated. The software program may be controllable by an operator.

[0109] The apparatus 200 may comprise a reservoir 201 . A supply of concrete composition 211 may be put in the reservoir. The supply of concrete composition 211 may have been mixed offsite, and delivered to the reservoir. Alternatively, the supply of concrete 211 may have been mixed onsite, and put into the reservoir. The supply of concrete composition 211 may be stored in the reservoir 201 . The use of a retarding admixture may allow the supply of concrete composition 211 to be stored in the reservoir 201 for longer without setting. The retarding admixture may comprise the features as described herein.

[0110] The apparatus 200 may comprise piping 202. The piping 202 may link the reservoir 201 to the 3D printer. The piping 202 may be around 70m long. Different piping 202 lengths may be used on different sites. The apparatus 200 may comprise a pump 203. The pump 203 may be configured to pump the supply of concrete 211 from the reservoir 201 to the 3D printer. The 3D printer may comprise a nozzle 207. The supply of concrete 211 may be pumped from the reservoir 201 to the nozzle 207. The use of a retarding admixture may allow the supply of concrete composition 211 to be passed through the piping 202, which can be very long, without setting.

[0111] The concrete composition may be deposited. The concrete composition may be deposited using the 3D printer. The concrete composition may be deposited using the nozzle 207 of the 3D printer. The concrete composition may pass through the nozzle 207 during deposition. The concrete composition may be deposited in layers 213, 214 to build up the wall. The first layer 214 may be deposited on a base plate 210. The base plate 210 may comprise a foundation, such as a concrete foundation. The base plate 210 may comprise the ground. The base plate 210 may comprise any other suitable printing surface, such as a metal plate. Subsequent layers 213, 214 may be printed on top of the first layer 214. The current layer 213 may be printed on the previous layers. Once the layers 214 are deposited, they begin to set. This is illustrated by the darked material in Figure 2.

[0112] The nozzle 7 may be sized to produce the required layer 214 sizes. The width of the nozzle 7 may be sized to produce a certain width of layer 214. The height of the nozzle 7 may be sized to produce a certain height of layer 214. The nozzle 7 may produce a layer 214 width between 50mm and 250mm. Preferably, for a single leaf wall 500, the nozzle 7 may produce a layer 214 width between 100mm and 250mm. Preferably, for a double leaf wall 400, the nozzle 7 may produce a layer 214 width between 50mm and 150mm. The nozzle 7 may produce a layer 214 height between 25mm and 75mm. The nozzle 7 may produce a layer 214 width to height ratio between 1.5 to 2.5. Preferably, the width to height ratio of the layer 214 is between 1.9 to 2.1. More preferably, the width to height ratio of the layer 214 is about 2.

[0113] The nozzle 207 may be mounted onto a frame 208. The nozzle 207 may be mounted onto the frame 208 by a support 209. The nozzle 207 and optionally the support 209, may be controlled to move relative to the frame 208. Moving horizontally allows the nozzle 207 to deposit a layer 213, 214 of the wall. The nozzle 207 may move continuously around a plan of the walls to deposit the walls. For example, if the nozzle 207 moves in a square, then a square plan wall will be printed. To deposit the next layer, the support 209 may move the nozzle 207 up. The distance the nozzle 207 moves up my dictate the height of each layer 213, 214.

[0114] An accelerating admixture may be added 104 to the concrete. The admixture may reduce the setting time of the concrete composition 211. If a retarding admixture is used in the supply of concrete 211 , the accelerating admixture may counteract the retarding admixture. Reducing the setting time of the concrete composition 211 may be advantageous during 3D printing.

[0115] The accelerating admixture may comprise an acid. The accelerating admixture may comprise calcium dinitrate, calcium stearate, calcium chloride, sodium nitrate, sodium silicate, magnesium hydroxide, magnesium oxide, magnesium chloride, magnesium nitrate, triethylamine (TEA), triisopropanolamine (TIPA), an aluminium compound or a mixture of two or more thereof, preferably calcium dinitrate, calcium chloride, an aluminium compound or a combination of two or more thereof, preferably calcium dinitrate, aluminium sulphate or a combination thereof. These admixtures have been found to be particularly effective in reducing the setting of the concrete composition 211 . The composition of the accelerating admixture may be varied depending on the requirements for the concrete composition, including the setting time required. The accelerating admixture may comprise the features as described herein.

[0116] The accelerating admixture may be added to the concrete composition during the deposition of the concrete composition. In this way, setting of the concrete composition may be accelerated as soon as it is deposited.

[0117] The accelerating admixture may be added to the concrete composition at the nozzle 207. In this way, the concrete composition setting may be accelerated as it leaves the nozzle 207 during deposition.

[0118] The accelerating admixture is added to the concrete composition prior to the concrete composition passing through the nozzle 207. The accelerating admixture may be added to the concrete composition no more than about 30 minutes prior to the concrete composition passing through the nozzle 207. Preferably between about 30 seconds and about 20 minutes prior to the concrete composition passing through the nozzle 207.

[0119] The 3D printer may comprise a vessel 204. The nozzle 207 may be fluidly connected to the vessel 204. The concrete composition may pass through the vessel 204 before passing through the nozzle 207. Obtaining the supply of concrete may comprise pumping the concrete composition from the reservoir 201 via the vessel 204 to the nozzle 207. The concrete composition may pass through the vessel 204 before deposition. The accelerating admixture may be applied to the concrete composition 211 in the vessel 204. In this way, the application of the accelerating admixture to the concrete composition 211 may be contained.

[0120] The vessel 204 may comprise a spraying device 205. The spraying device 205 may spray additives onto the concrete composition. The additives may be sprayed on to the concrete composition 211 when the concrete composition 211 is passing through the vessel 204. The accelerating admixture may be sprayed on to the concrete composition 211 when the concrete composition 211 is passing through the vessel 204. The spraying device 205 may spray the accelerating admixture. In this way, the accelerating admixture may be quickly incorporated in the concrete composition 211 .

[0121] Additionally, the vessel 204 may comprise a mixer 206. For example, the mixer 206 may be a screw. The additives and the concrete composition 211 may be mixed in the vessel 204. The accelerating admixture and the concrete composition 211 may be mixed in the vessel 204. The mixer 206 may mix the accelerating admixture and the concrete composition 211. In this way, the accelerating admixture may be dispersed through the concrete composition so as to evenly accelerate the setting throughout the concrete.

[0122] Once the accelerating admixture is applied to the concrete composition 211 , the concrete composition 211 may be deposited through the nozzle 207.

[0123] Concrete Wall

[0124] Figure 3a schematically illustrates a 3D printed concrete wall 300 from a side view of an embodiment of the invention. Figure 3b schematically illustrates a 3D printed concrete wall 400 cross section of a first embodiment of the invention. Figure 3c schematically illustrates a 3D printed concrete wall 500 cross section of a second embodiment of the invention. Figure 3d schematically illustrates a 3D printed building 600 plan view of an embodiment of the invention.

[0125] The 3D printed concrete wall 300, 400, 500 may use the concrete composition as described herein. The 3D printed concrete wall 300, 400, 500 may be made using the method 100 of printing as described herein, for example with reference to Figure 1. The 3D printed concrete wall 300, 400, 500 may be made using the apparatus 200 as described herein, for example with reference to Figure 2.

[0126] As described herein, the concrete composition may be deposited in layers 214. A plurality of layers 214 may be deposited on top of one another to form a wall 300, 400, 500. Figure 3a illustrates a concrete wall 300 from the side. A plurality of layers 214 on top of one another may form the wall 300. The layers 214 may be deposited directly on top of one another. This may form a vertically straight wall 300. This may provide the highest compressive strength. Alternatively, one or more of the layers 214 may be deposited out of line with the previous layer. This may provide the ability to print vertically curved or vertically angled walls. For example, it may be possible to print a dome. This may provide a lower compressive strength than a vertically straight wall. That said, the compressive strength my still met the required building standards.

[0127] The path of the deposition of each layer 214 may be straight. This may provide a horizontally straight wall 300. Alternatively, the path of the deposition of each layer 214 may not be straight, for example curved or angled. This may provide the ability to print horizontally curved or horizontally angled walls.

[0128] Figures 3a-c illustrate a vertically straight and horizontally straight wall. The features described in relation to Figure 3a-c may equally be applied to vertically curved / angled and horizontally curved / angled walls.

[0129] Figure 3b illustrates a cross section of a wall 400 of a first embodiment. The wall 400 may comprise a plurality of leaves 301 , 302. The wall 400 may comprise two leaves 301 , 302. This may be known as a double leaf 301 , 302 wall 400, or a ‘cavity wall’ 400. A first leaf 301 may be the inner leaf of the wall 400, with respect to the building 600. The second leaf 302 may be the outer leaf of the wall 400, with respect to the building 600.

[0130] Each of the leaves 301 , 302 may comprise layers 214 of deposited concrete composition. Each leaf 301 , 302 may be formed by depositing a plurality of concrete composition layers 214. Each leaf 301 , 302 may be formed separately. The 3D printer may deposit a layer 214 of a first leaf 301 , followed by a corresponding layer 214 of a second leaf 302. This may be repeated until all of the layers 214 of each leaf 301 , 302 are deposited. Alternatively, a double nozzle may be used, and the first leaf 301 and the second leaf 302 may be deposited together. Alternatively, the first leaf 301 may be entirely deposited before the second leaf 302 is deposited. The two leaves 301 , 302 may provide the required compressive strength for the wall 400 to meet building standards. The two leaves 301 , 302 may be thinner than if a single leaf 301 was used. One or more of the layers 214 in the leaves 301 , 302 may comprise a width between 50mm and 250mm. Each of the layers 214 in the leaves 301 , 302 may comprise a width between 50mm and 250mm. Preferably, for a double leaf wall 400, one or more of the layers 214 may comprise a width between 50mm and 150mm. The compressive strength of the double leaf wall 400 may be higher than a single leaf wall 400 so that individually thicker leaves 301 , 302 are not required. Thinner leaves 301 , 302 are preferred, so as not to waste material. A thickness between 50mm and 150mm for a double leaf wall 400 has been found to have a good balance between compressive strength and waste material. More preferably, one or more of the layers 214 may comprise a width between 75mm and 125mm.

[0131] If each of the layers 214 comprise the same thickness, then the leaf 301 , 302 may comprise a constant thickness. However, the thickness of individual layers 214 may be varied. For example, layers 214 may become progressively thinner as the layers 214 are built up. This may be preferable for compressive strength and / or waste material

[0132] One or more of the layers 214 may comprise a height between 25mm and 75mm. Each of the layers 214 may comprise a height between 25mm and 75mm. Layers 214 with a smaller height may be quicker to deposit, but may take more time to set. A height between 25mm and 75mm for a double leaf wall 400 has been found to have a good balance between deposition speed and setting time. Each of the layers 214 comprise the same height. Alternatively, the thickness of individual layers 214 may be varied. For example, layers 214 may become progressively thinner as the layers 214 are built up. This may be preferable, as higher layers may need to set more quickly so that further layers 214 can be deposited.

[0133] If the layers 214 are very wide compared to height, then setting time can be quick, but structural issues can occur. Similarly, if the layers 214 are very narrow compared to height, then setting time can be quick, but structural issues can occur. This may be due to the lack of binding in thin or narrow layers 214. The width to height ratio of the layer 214 is preferably between 1.5 to 2.5. This has been found to result in a good balance between setting time and the compressive strength of the layers 214. Preferably, the width to height ratio of the layer 214 is between 1.9 to 2.1. More preferably, the width to height ratio of the layer 214 is about 2. This has been found to provide an optimum balance between setting time and the compressive strength of the layers 214.

[0134] The height of the wall 400 may be varied by the number of layers 214 deposited. The height of the wall may be between 1 m and 5m. The height of the wall 400 may be one storey. The height of the wall 400 may be two storeys. The height of the wall 400 may be varied depending on the building 600 being built.

[0135] A cavity may be formed between the two leaves 301 , 302. The leaves 301 , 302 may be deposited a distance apart from one another. This may form the cavity between the two leaves 301 , 302. The cavity may comprise air. The air in the cavity may improve the insulating properties of the wall 400. The cavity may be open at the top of the wall 400.

[0136] The wall 400 may comprise an insulation layer 303. The insulation layer 303 may be positioned inside of the outermost leaf 302. The insulation layer 303 may improve the insulation of the wall 400. The cavity may comprise the insulation layer 303. The insulation layer 303 may be located in between the first leaf 301 and the second leaf 302. The insulation layer 303 may fill a part, or all of, the cavity. This may improve the insulation between the two leaves 301 , 302. The cavity may be open at the top above the insulation layer 303. The insulation layer 303 may be on an outer major surface of the first leaf 301 . The insulation layer 303 may be on an inner major surface of the second leaf 302. The insulation layer 303 may be applied to the outer major surface of the first leaf 301 . The insulation layer 303 may be applied to the inner major surface of the second leaf 302. The insulation layer 303 may cover part, or all, of the outer major surface of the first leaf 301 . The insulation layer 303 may cover part, or all, of the inner major surface of the second leaf 302. The more surface area of the leaves 301 , 302 that are covered by the insulation layer 303, the better the insulation of the wall 400 may be. The insulation layer 303 may be located in the cavity after both leaves 301 , 302 have been deposited. This may simplify the manufacturing process. The insulation layer 303 may comprise one or more of fibreglass, cellulose, mineral wool, and spray foam. In the case of spray foam, the insulation layer 303 may be sprayed into the cavity.

[0137] The wall 400 may comprise one or more ties 307. The ties 307 may link the first leaf 301 to the second leaf 302. The ties 307 may improve the compressive strength of the wall 400. The ties 307 may share load between the first leaf 301 and the second leaf 302. The ties 307 may be inserted in between layers 214. The tie may be inserted on top of one layer 214 before a subsequent layer 214 is then deposited on top of the tie 307. This may secure the ties 307 to the leaves 301 , 302. The ties 307 may be dispersed vertically and horizontally in the wall 400. Figure 3b illustrates vertical dispersion of the ties 307. Similar arrangements may apply to horizontal dispersion of the ties 307.

[0138] The wall 400 may comprise a rendering layer 306. The rendering layer 306 may be positioned outside of the outermost leaf 302. The rendering layer 306 may improve the waterproofing of the wall 400. The rendering layer 306 may reduce the amount of moisture entering the leaves 301 , 302. The rendering layer 306 may improve the sound proofing of the wall 400. The rendering layer 306 may improve the surface finish of the outside of the wall 400. The rendering layer 306 may provide a flat surface to the outside of the wall 400. The rendering layer 306 may improve the appearance of the outside of the wall 400. The rendering layer 306 may allow paint and other decoration to be applied to the outside of the wall 400. The rendering layer 306 may allow fittings and other structure to be applied to the outside of the wall 400. The rendering layer 306 may be on an outer major surface of the second leaf 302. The rendering layer 306 may be applied to the outer major surface of the second leaf 302. The rendering layer 306 may cover part, or all, of the outer major surface of the second leaf 302. The more surface area of the leaf 302 that is covered by the rendering layer 306, the better the properties of the wall 400 may be. The rendering layer 306 may comprise one or more of cement render, acrylic render, silicone render, mineral render, lime render, or monocouche render.

[0139] The wall 400 may comprise a drylining layer 305. The drylining layer 305 may be positioned inside of the innermost leaf 301 . The drylining layer 305 may improve the waterproofing of the wall 400. Moister transferring through the leaves 301 , 302 may be prevented from transferring into the building 600 by the drylining layer 305. The drylining layer 305 may improve the sound proofing of the wall 400. The drylining layer 305 may improve the surface finish of the inside of the wall 400. The drylining layer 305 may provide a flat surface to the inside of the wall 400. The drylining layer 305 may improve the appearance of the inside of the wall 400. The drylining layer 305 may allow paint and other decoration to be applied to the inside of the wall 400. The drylining layer 305 may allow plaster and other structure to be applied to the inside of the wall 400. The drylining layer 305 may be on an inner major surface of the first leaf 301 . The drylining layer 305 may be applied to the inner major surface of the first leaf 301 . The drylining layer 305 may cover part, or all, of the inner major surface of the first leaf 301 . The more surface area of the leaf 301 that is covered by the drylining layer 305, the better the properties of the wall 400 may be. The drylining layer 305 may comprise plasterboard.

[0140] The wall 400 may comprise a plaster layer 304. Alternatively, or in addition to, the drylining layer 305, the wall 400 may comprise a plaster layer 304. The wall 400 may comprise the drylining layer 305 and / or the plaster layer 304. Figure 3c illustrates both the drylining layer 305 and the plaster layer 304. The plaster layer 304 may be positioned inside of the innermost leaf 301. The plaster layer 304 may improve the sound proofing of the wall 400. The plaster layer 304 may improve the surface finish of the inside of the wall 400. The plaster layer 304 may provide a flat surface to the inside of the wall 400. The plaster layer 304 may improve the appearance of the inside of the wall 400. The plaster layer 304 may allow paint and other decoration to be applied to the inside of the wall 400. The plaster layer 304 may be on an inner major surface of the first leaf 301 . The plaster layer 304 may be applied to the inner major surface of the first leaf 301 . The plaster layer 304 may cover part, or all, of the inner major surface of the first leaf 301 . The more surface area of the leaf 301 that is covered by the plaster layer 304, the better the properties of the wall 400 may be. Alternatively, the plaster layer 304 may be on an inner major surface of the drylining layer 305. The plaster layer 304 may be applied to the inner major surface of the drylining layer 305. The plaster layer 304 may cover part, or all, of the inner major surface of the drylining layer 305. The more surface area of the drylining layer 305 that is covered by the plaster layer 304, the better the properties of the wall 400 may be. The plaster layer 304 may comprise liquid plaster.

[0141] Figure 3c illustrates a cross section of a wall 500 of a second embodiment. The wall 500 may comprise a single leaf 301 . The wall 500 may comprise only one leaf 301 . This may be known as a single leaf 301 wall 500. A single leaf 301 wall 500 comprises only a single leaf 301 , and does not comprise any further leaves.

[0142] The leaf 301 may comprise layers 214 of deposited concrete composition. The leaf 301 may be formed by depositing a plurality of concrete composition layers 214.

[0143] The single leaf 301 may provide the required compressive strength for the wall 500 to meet building standards. That said, the single leaf 301 may need to be thicker than if two leaves 301 , 302 were used. One or more of the layers 214 in the leaf 301 may comprise a width between 50mm and 250mm. Each of the layers 214 in the leaf 301 may comprise a width between 50mm and 250mm. Preferably, for a single leaf wall 500, one or more of the layers 214 may comprise a width between 100mm and 250mm. The compressive strength of the single leaf wall 500 may be lower than a double leaf wall 400 with the same thickness leaves. As such thicker a thicker leaf 301 is required. That said, thinner walls are preferred, so as not to waste material. A thickness between 100mm and 250mm for a single leaf wall 500 has been found to have a good balance between compressive strength and waste material. More preferably, one or more of the layers 214 may comprise a width between 150mm and 200mm.

[0144] If each of the layers 214 comprise the same thickness, then the leaf 301 may comprise a constant thickness. However, the thickness of individual layers 214 may be varied. For example, layers 214 may become progressively thinner as the layers 214 are built up. This may be preferable for compressive strength and / or waste material.

[0145] As described herein, using mortar as a building material can have limitations in terms of the strength, and the durability of the walls. In particular, using mortar as a building material can limit the width that the walls can be printed. If mortar-based walls are too wide, then the walls may not meet the required building standards. Therefore, mortar- based walls may not be suitable for single leaf walls 500. The concrete composition, as described herein, may be suitable for making single leaf walls 500. The coarse aggregate in the concrete composition, which is not present in mortar, may allow the thicker layers 214 to be deposited to form the thicker single leaf wall 500. Thus, using a concrete composition may allow the single leaf wall 500 to be 3D printed.

[0146] One or more of the layers 214 may comprise a height between 25mm and 75mm. Each of the layers 214 may comprise a height between 25mm and 75mm. Layers 214 with a smaller height may be quicker to deposit, but may take more time to set. A height between 25mm and 75mm for a single leaf wall 500 has been found to have a good balance between deposition speed and setting time. Each of the layers 214 comprise the same height. Alternatively, the thickness of individual layers 214 may be varied. For example, layers 214 may become progressively thinner as the layers 214 are built up. This may be preferable, as higher layers may need to set more quickly so that further layers 214 can be deposited.

[0147] If the layers 214 are very wide compared to height, then setting time can be quick, but structural issues can occur. Similarly, if the layers 214 are very narrow compared to height, then setting time can be quick, but structural issues can occur. This may be due to the lack of binding in thin or narrow layers 214. The width to height ratio of the layer 214 is preferably between 1.5 to 2.5. This has been found to result in a good balance between setting time and the compressive strength of the layers 214. Preferably, the width to height ratio of the layer 214 is between 1.9 to 2.1. More preferably, the width to height ratio of the layer 214 is about 2. This has been found to provide an optimum balance between setting time and the compressive strength of the layers 214.

[0148] The height of the wall 500 may be varied by the number of layers 214 deposited. The height of the wall may be between 1 m and 5m. The height of the wall 500 may be one storey. The height of the wall 400 may be two storeys. The height of the wall 400 may be varied depending on the building 600 being built.

[0149] The wall 500 may comprise an insulation layer 303. The insulation layer 303 may be positioned outside of the leaf 301 . The insulation layer 303 may improve the insulation of the wall 500. This may improve the insulation between the outside air and the leaf 301 . The insulation layer 303 may be on an outer major surface of the leaf 301 . The insulation layer 303 may be applied to the outer major surface of the leaf 301 . The insulation layer 303 may cover part, or all, of the outer major surface of the leaf 301 . The more surface area of the leaf 301 that is covered by the insulation layer 303, the better the insulation of the wall 500 may be. The insulation layer 303 may comprise one or more of fibreglass, cellulose, mineral wool, and spray foam. In the case of spray foam, the insulation layer 303 may be sprayed onto the leaf 301 .

[0150] The wall 500 may comprise a rendering layer 306. The rendering layer 306 may be positioned outside of the leaf 301. The rendering layer 306 may improve the waterproofing of the wall 500. The rendering layer 306 may reduce the amount of moisture entering the leaf 301. The rendering layer 306 may improve the sound proofing of the wall 500. The rendering layer 306 may improve the surface finish of the outside of the wall 500. The rendering layer 306 may provide a flat surface to the outside of the wall 500. The rendering layer 306 may improve the appearance of the outside of the wall 500. The rendering layer 306 may allow paint and other decoration to be applied to the outside of the wall 500. The rendering layer 306 may allow fittings and other structure to be applied to the outside of the wall 500. The rendering layer 306 may be on an outer major surface of the leaf 301 . The rendering layer 306 may be applied to the outer major surface of the leaf 301 . The rendering layer 306 may cover part, or all, of the outer major surface of the leaf 301 . If an insulation layer 303 is present (as shown in Figure 3c), the rendering layer 306 may be on an outer major surface of the insulation layer 303. The rendering layer 306 may be applied to the outer major surface of the insulation layer 303. The rendering layer 306 may cover part, or all, of the outer major surface of the insulation layer 303. The more surface area of the leaf 301 or insulation layer 303 that is covered by the rendering layer 306, the better the properties of the wall 500 may be. The rendering layer 306 may comprise one or more of cement render, acrylic render, silicone render, mineral render, lime render, or monocouche render.

[0151] The wall 500 may comprise a drylining layer 305. The drylining layer 305 may be positioned inside of the leaf 301. The drylining layer 305 may improve the waterproofing of the wall 500. Moister transferring through the leaf 301 may be prevented from transferring into the building 600 by the drylining layer 305. The drylining layer 305 may improve the sound proofing of the wall 500. The drylining layer 305 may improve the surface finish of the inside of the wall 500. The drylining layer 305 may provide a flat surface to the inside of the wall 500. The drylining layer 305 may improve the appearance of the inside of the wall 500. The drylining layer 305 may allow paint and other decoration to be applied to the inside of the wall 500. The drylining layer 305 may allow plaster and other structure to be applied to the inside of the wall 500. The drylining layer 305 may be on an inner major surface of the leaf 301 . The drylining layer 305 may be applied to the inner major surface of the leaf 301 . The drylining layer 305 may cover part, or all, of the inner major surface of the leaf 301 . The more surface area of the leaf 301 that is covered by the drylining layer 305, the better the properties of the wall 500 may be. The drylining layer 305 may comprise plasterboard.

[0152] The wall 500 may comprise a plaster layer 304. Alternatively, or in addition to, the drylining layer 305, the wall 500 may comprise a plaster layer 304. The wall 500 may comprise the drylining layer 305 and / or the plaster layer 304. Figure 3c illustrates both the drylining layer 305 and the plaster layer 304. The plaster layer 304 may be positioned inside of the leaf 301 . The plaster layer 304 may improve the sound proofing of the wall 500. The plaster layer 304 may improve the surface finish of the inside of the wall 500. The plaster layer 304 may provide a flat surface to the inside of the wall 500. The plaster layer 304 may improve the appearance of the inside of the wall 500. The plaster layer 304 may allow paint and other decoration to be applied to the inside of the wall 500. The plaster layer 504 may be on an inner major surface of the leaf 301 . The plaster layer 304 may be applied to the inner major surface of the leaf 301 . The plaster layer 304 may cover part, or all, of the inner major surface of the leaf 301 . The more surface area of the leaf 301 that is covered by the plaster layer 304, the better the properties of the wall 500 may be. Alternatively, the plaster layer 304 may be on an inner major surface of the drylining layer 305 (as illustrated in Figure 3c). The plaster layer 304 may be applied to the inner major surface of the drylining layer 305. The plaster layer 304 may cover part, or all, of the inner major surface of the drylining layer 305. The more surface area of the drylining layer 305 that is covered by the plaster layer 304, the better the properties of the wall 500 may be. The plaster layer 304 may comprise liquid plaster. Figure 3d schematically illustrates a 3D printed building 600 plan view of an embodiment of the invention. The building 600 may comprise one or more walls 300, 400, 500. Figure 3d shows four walls 300, 400, 500 arranged in a rectangular shape. The building 600 may be formed by separate walls 300, 400, 500 which are later connected. Alternatively, the building 600 may be formed by a single deposition which forms all the walls 300, 400, 500 continuously.

[0153] The walls 300, 400, 500 may comprise one or more leaves 301 , 302. Figure 3d shows both the first leaf 301 and the second leaf 302. Figure 3d shows a double leaf wall 400. Alternatively, the wall 500 may comprise only the first leaf 301 . In which case, the wall 500 would comprise a single leaf wall 500.

[0154] The terms ‘inner’ and ‘outer’ used herein are with respect to the building 600. The inner surface is the surface facing the inside of the building 600. The outer surface is the surface facing the outside of the building 600. The term ‘major surface’ used herein refers to the largest surfaces of the walls 300, 400, 500. For example, the inner and outer surface of the walls 300, 400, 500 are significantly larger than the top, bottom and two end surfaces of the walls. The inner and outer surfaces of the walls 300, 400, 500 are the major surfaces.

[0155] The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention. Within this specification, the term "about" means plus or minus 20%, more preferably plus or minus 10%, even more preferably plus or minus 5%, most preferably plus or minus 2%.

[0156] Within this specification, the term "substantially" means a deviation of plus or minus 20%, more preferably plus or minus 10%, even more preferably plus or minus 5%, most preferably plus or minus 2%.

[0157] Within this specification, reference to “substantially” includes reference to “completely” and / or “exactly”. That is, where the word substantially is included, it will be appreciated that this also includes reference to the particular sentence without the word substantially.

[0158] Within this specification, reference to “comprises” includes “consists essentially of” and / or “consists of’ and / or “is”. Where the word “comprises” is used, it will be appreciated that this also includes reference to “consists essentially of’ and / or “consists of” and / or “is”.

[0159] It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications are covered by the appended claims.

[0160] In this disclosure, when the subject of a phrase is described as being "configured to" or “arranged to”, followed by a term defining a condition or function, this is used to indicate that the subject of the phrase is in a state in which it has that condition, or is able to perform that function, without the subject being modified or further configured.

[0161] Some implementations may be described using the expressions “one / an embodiment” or “one / an example”, along with their derivatives. These terms mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Moreover, unless otherwise noted the features described above are recognized to be usable together in any combination. Thus, any features discussed separately may be employed in combination with each other unless it is noted that the features are incompatible with each other.

[0162] The foregoing description of example embodiments has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the present disclosure to the precise forms disclosed. Many modifications and variations are possible in light of this disclosure. It is intended that the scope of the present disclosure be limited not by this detailed description, but rather by the claims appended hereto. Future filed applications claiming priority to this application may claim the disclosed subject matter in a different manner and may generally include any set of one or more limitations as variously disclosed or otherwise demonstrated herein.

[0163] Within this specification embodiments have been described in a way which enables a clear and concise specification to be written, but it is intended and will be appreciated that embodiments may be variously combined or separated without parting from the invention. For example, it will be appreciated that all preferred features described herein are applicable to all aspects of the invention described herein and vice versa. For example, all preferred features of the composite apply to all aspects of the invention.

[0164] The following clauses form part of the disclosure:

[0165] 1 . A method of 3D printing a concrete wall, the method comprising steps of: a) obtaining a supply of a concrete composition, the concrete composition comprising a coarse aggregate with an average particle size of greater than about 4 mm, the concrete composition comprising a retarding admixture; and b) depositing a plurality of deposited layers of the concrete composition using a 3D printer; wherein an accelerating admixture is added to the concrete composition.

[0166] 2. A method according to clause 1 , wherein the 3D printer comprises a nozzle through which the concrete composition passes during deposition, preferably wherein the accelerating admixture is added to the concrete composition prior to the concrete composition passing through the nozzle, preferably wherein the accelerating admixture is added to the concrete composition no more than about 30 minutes prior to the concrete composition passing through the nozzle, preferably between about 30 seconds and about 20 minutes prior to the concrete composition passing through the nozzle.

[0167] 3. A method according to clause 1 or 2, wherein the accelerating admixture is added by spraying the accelerating admixture on to the concrete composition.

[0168] 4. A method according to any preceding clause, wherein the 3D printer comprises a vessel through which the concrete composition passes before deposition, and wherein the accelerating admixture is added to the concrete composition in the vessel, preferably wherein the accelerating admixture is sprayed on to the concrete composition in the vessel.

[0169] 5. A method according to clause 4, wherein the concrete composition passes through the vessel prior to passing through the nozzle.

[0170] 6. A method according to clause 4 or 5, wherein the accelerating admixture and the concrete composition are mixed in the vessel.

[0171] 7. A method according to any preceding clause, wherein the retarding admixture comprises a citric acid, a lignosulfonate, a sulfonated naphthalene-formaldehyde condensate, a sulfonated melamine-formaldehyde condensate, a sulfonated vinyl copolymer, a polycarboxylate, a hydroxylated carboxylic acid, a sugar, a carbohydrate derivative, a phosphorous acid, a phosphoric acid, a salt of any thereof, or a combination of two or more thereof, preferably a phosphorous acid, a phosphoric acid, a lignosulfonate, a chloride-based sugar, a salt of any thereof, or a combination of two or more thereof, preferably a sodium salt of a phosphorous acid or a sodium salt of a phosphoric acid or a combination of two or more thereof; and / or wherein the concrete composition comprises between about 0.05 wt% and about 5 wt% retarding admixture, preferably between about 0.1 wt% and about 1 wt% of the retarding admixture. 8. A method according to any preceding clause, wherein the accelerating admixture comprises calcium dinitrate, calcium stearate, calcium chloride, sodium nitrate, sodium silicate, magnesium hydroxide, magnesium oxide, magnesium chloride, magnesium nitrate, triethylamine (TEA), triisopropanolamine (TIPA), an aluminium compound or a mixture of two or more thereof, preferably calcium dinitrate, calcium chloride, an aluminium compound or a combination of two or more thereof, preferably calcium dinitrate, aluminium sulphate or a combination thereof; and / or wherein the accelerating admixture is added in an amount of about 0.05% to about 5% based on the weight of the concrete composition, preferably in an amount of about 0.1 % to about 3% based on the weight of the concrete composition.

[0172] 9. A method according to any preceding clause, wherein obtaining a supply of concrete comprises pumping the concrete composition from a reservoir to the nozzle.

[0173] 10. A method according to any of clauses 4 to 9, wherein obtaining a supply of concrete comprises pumping the concrete composition from the reservoir via the vessel to the nozzle.

[0174] 11. A method according to any preceding clause, wherein obtaining a supply of concrete comprises transporting the supply of the concrete composition from a concrete production plant to a construction site, preferably in a concrete truck.

[0175] 12. A method according to clause 11 , wherein the 3D printer is located at the construction site.

[0176] 13. A method according to any preceding clause, wherein the initial concrete setting time of the concrete composition, prior to adding the accelerating admixture is at least about 2 hours, preferably between about 3 to about 14 hours, preferably between about 3 to about 12 hours, preferably between about 4 hours and about 8 hours.

[0177] 14. A method according to any preceding clause, wherein the initial concrete setting time of the concrete composition, after adding the accelerating admixture is less than about 30 minutes, preferably about 2 minutes to about 30 minutes, preferably about 5 minutes to about 20 minutes.

[0178] 15. A method according to any preceding clause, wherein depositing the concrete composition using a 3D printer comprises depositing a plurality of layers.

[0179] 16. A method according to clause 15, wherein each of the layers comprise a height of about 25mm to about 75mm.

[0180] 17. A method according to clause 15 or 16, wherein each of the layers comprise a width between about 50mm and about 250mm.

[0181] 18. A method according to clause 17, wherein each of the layers comprise a width between about 50mm and about 150mm.

[0182] 19. A method according to clause 17, wherein each of the layers comprise a width between about 100mm and about 250mm.

[0183] 20. A method according to any preceding clause, wherein the concrete composition further comprises a fine aggregate, a binder and water, preferably wherein the binder comprises Portland cement and / or a supplementary cementitious material.

[0184] 21. A method according to any preceding clause, wherein the flow of the concrete composition is in the range of about 300 mm to about 550 mm, preferably about 350 mm to about 500 mm.

[0185] 22. A method according to any preceding clause, wherein the concrete composition is uncured concrete.

[0186] 23. A method according to any preceding clause wherein the concrete composition is 3D printed and then cured.

[0187] 24. A 3D printed concrete wall comprising a plurality of cured deposited layers of a concrete composition, the wall being made by the method of any preceding clause. 25. A 3D printed concrete wall comprising a plurality of deposited layers of a concrete composition, the wall being made by: obtaining a supply of concrete composition, the concrete composition comprising a coarse aggregate with an average particle size of greater than about 4mm, the concrete composition comprising a retarding admixture; and depositing the concrete composition using a 3D printer; wherein an accelerating admixture is added to the concrete composition.

[0188] 26. A wall according to clause 24 or 25, wherein each of the deposited layers comprise a width between about 100 mm and about 250 mm.

[0189] 27. A single leaf 3D printed concrete wall comprising a plurality of deposited layers of concrete composition, the concrete composition comprising a coarse aggregate with an average particle size of greater than about 4 mm, wherein each of the deposited layers comprise a width between about 100 mm and about 250 mm.

[0190] 28. A wall according to clause 27, wherein each of the deposited layers comprise a width between about 150mm and about 200mm.

[0191] 29. A wall according to any of clauses 27 or 28 wherein the wall comprises a height between about 1 m and about 5 m.

[0192] 30. A wall according to any of clauses 27 to 29, wherein each of the layers comprise a height of about 25 mm to about 75 mm.

[0193] 31 . A wall according to any of clauses 27 to 30, wherein each of the layers comprise a width to height ratio of about 1 .5 to about 2.5, preferably about 1 .9 to about 2.1 .

[0194] 32. A wall according to any of clauses 27 to 31 , wherein the wall comprises an insulation layer on a first major surface of the wall.

[0195] 33. A wall according to clause 32, wherein the wall comprises a rendering layer on a major surface of the insulation layer. 34. A wall according to any of clauses 27 to 32, wherein the wall comprises a drylining layer on a second major surface of the wall.

[0196] 35. A wall according to clause 34, wherein the wall comprises a plaster layer on a major surface of the drylining layer.

[0197] 36. A building comprising one or more walls according to any of clauses 24 to 35.

[0198] 37. A building comprising one or more single leaf 3D printed concrete walls comprising a plurality of deposited layers of concrete composition, the concrete composition comprising a coarse aggregate with an average particle size of greater than about 4mm, wherein each of the deposited layers comprise a width between about 100mm and about 250mm.

[0199] 38. A method of 3D printing a single leaf 3D printed concrete according to any of clauses 27 to 35.

[0200] 39. A method of 3D printing a single leaf 3D printed concrete wall comprising a plurality of deposited layers of concrete composition, the concrete composition comprising a coarse aggregate with an average particle size of greater than about 4mm, wherein each of the deposited layers comprise a width between about 100mm and about 250mm.

[0201] 40. A wall according to any of clauses 24 to 35, a building according to clause 36 or 37, or a method according to clause 38 or 39, further comprising the feature of any of clause 1 to 23.

Claims

Claims1 . A method of 3D printing a concrete wall, the method comprising steps of: a) obtaining a supply of a concrete composition, the concrete composition comprising a coarse aggregate with an average particle size of greater than about 4 mm, the concrete composition comprising a retarding admixture; and b) depositing a plurality of deposited layers of the concrete composition using a 3D printer; wherein an accelerating admixture is added to the concrete composition.

2. A method according to claim 1 , wherein the 3D printer comprises a nozzle through which the concrete composition passes during deposition, preferably wherein the accelerating admixture is added to the concrete composition prior to the concrete composition passing through the nozzle, preferably wherein the accelerating admixture is added to the concrete composition no more than about 30 minutes prior to the concrete composition passing through the nozzle, preferably between about 30 seconds and about 20 minutes prior to the concrete composition passing through the nozzle.

3. A method according to claim 1 or 2, wherein the accelerating admixture is added by spraying the accelerating admixture on to the concrete composition; and / or wherein the 3D printer comprises a vessel through which the concrete composition passes before deposition, and wherein the accelerating admixture is added to the concrete composition in the vessel, preferably wherein the accelerating admixture is sprayed on to the concrete composition in the vessel; and optionally wherein the concrete composition passes through the vessel prior to passing through the nozzle; and optionally wherein the accelerating admixture and the concrete composition are mixed in the vessel.

4. A method according to any preceding claim, wherein the retarding admixture comprises a citric acid, a lignosulfonate, a sulfonated naphthalene-formaldehyde condensate, a sulfonated melamine-formaldehyde condensate, a sulfonated vinylcopolymer, a polycarboxylate, a hydroxylated carboxylic acid, a sugar, a carbohydrate derivative, a phosphorous acid, a phosphoric acid, a salt of any thereof, or a combination of two or more thereof, preferably a phosphorous acid, a phosphoric acid, a lignosulfonate, a chloride-based sugar, a salt of any thereof, or a combination of two or more thereof, preferably a sodium salt of a phosphorous acid or a sodium salt of a phosphoric acid or a combination of two or more thereof; and / or wherein the concrete composition comprises between about 0.05 wt% and about 5 wt% retarding admixture, preferably between about 0.1 wt% and about 1 wt% of the retarding admixture.

5. A method according to any preceding claim, wherein the accelerating admixture comprises calcium dinitrate, calcium stearate, calcium chloride, sodium nitrate, sodium silicate, magnesium hydroxide, magnesium oxide, magnesium chloride, magnesium nitrate, triethylamine (TEA), triisopropanolamine (TIPA), an aluminium compound or a mixture of two or more thereof, preferably calcium dinitrate, calcium chloride, an aluminium compound or a combination of two or more thereof, preferably calcium dinitrate, aluminium sulphate or a combination thereof; and / or wherein the accelerating admixture is added in an amount of about 0.05% to about 5% based on the weight of the concrete composition, preferably in an amount of about 0.1 % to about 3% based on the weight of the concrete composition.

6. A method according to any preceding claim, wherein the initial concrete setting time of the concrete composition, prior to adding the accelerating admixture is at least about 2 hours, preferably between about 3 to about 14 hours, preferably between about 3 to about 12 hours, preferably between about 4 hours and about 8 hours; and / or wherein the initial concrete setting time of the concrete composition, after adding the accelerating admixture is less than about 30 minutes, preferably about 2 minutes to about 30 minutes, preferably about 5 minutes to about 20 minutes.

7. A method according to any preceding claim, wherein the concrete composition further comprises a fine aggregate, a binder and water, preferably wherein the binder comprises Portland cement and / or a supplementary cementitious material.

8. A 3D printed concrete wall comprising a plurality of cured deposited layers of a concrete composition, the wall being made by the method of any preceding claim.

9. A 3D printed concrete wall comprising a plurality of deposited layers of a concrete composition, the wall being made by: obtaining a supply of concrete composition, the concrete composition comprising a coarse aggregate with an average particle size of greater than about 4mm, the concrete composition comprising a retarding admixture; and depositing the concrete composition using a 3D printer; wherein an accelerating admixture is added to the concrete composition.

10. A single leaf 3D printed concrete wall comprising a plurality of deposited layers of concrete composition, the concrete composition comprising a coarse aggregate with an average particle size of greater than about 4 mm, wherein each of the deposited layers comprise a width between about 100 mm and about 250 mm.

11. A wall according to claim 10, wherein each of the deposited layers comprise one or more of: a width between about 150mm and about 200mm; a height of about 25 mm to about 75 mm; and a width to height ratio of about 1 .5 to about 2.5, preferably about 1 .9 to about 2.1 .

12. A building comprising one or more walls according to claim 10 or 11 .

13. A building comprising one or more single leaf 3D printed concrete walls comprising a plurality of deposited layers of concrete composition, the concrete composition comprising a coarse aggregate with an average particle size of greater than about 4mm, wherein each of the deposited layers comprise a width between about 100mm and about 250mm.

14. A method of 3D printing a single leaf 3D printed concrete wall according to any of claims 15 to 17.

15. A method of 3D printing a single leaf 3D printed concrete wall comprising a plurality of deposited layers of concrete composition, the concrete composition comprising a coarse aggregate with an average particle size of greater than about 4mm, wherein each of the deposited layers comprise a width between about 100mm and about 250mm.

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