Concrete product and methods of manufacture thereof

Abstract

The present invention relates to a composite concrete product and methods thereof. The product comprises one or more solid concrete (SC) outer layers; and an aerated concrete (AC) inner core that is bound to the one or more solid concrete outer layers, wherein the one or more solid concrete outer layers cover at least a portion of the surface of the AC inner core.

Description

[0001] CONCRETE PRODUCT AND METHODS OF MANUFACTURE THEREOF

[0002] Field of the invention

[0003] The invention relates to a composite concrete product comprising aerated concrete (AC) and solid concrete (SC).

[0004] Background to the invention

[0005] Solid concrete (SC) is a widely used building material, known for its strength and durability. Its liquid form, such as concrete slurry, offers high workability as it can be moulded and shaped into various construction articles without compromising quality. Despite these advantages, solid concrete’s weight presents handling challenges, and its production raises significant environmental concerns. Producing cement, a primary component of the concrete, emits a substantial amount of greenhouse gases. With each tonne of cement manufactured, approximately 500kg of carbon dioxide is released into the atmosphere. Consequently, there is a growing need to explore greener alternatives.

[0006] One such alternative is lightweight concrete. This variant typically has a volume of air or other gas (e.g. formed using foam) entrained in the concrete, replacing some of the aggregates and cement used in the solid concrete. The production and transportation of this type of concrete have a reduced environmental impact compared to solid concrete. Additionally, lightweight concrete is easier to handle due to its lighter weight; and it possesses desirable properties such as fire resistance, and thermal and acoustical insulation. Lightweight concrete is commonly used for insulating buildings, void filling, and manufacturing building blocks. Nevertheless, despite these merits, lightweight concrete is often weaker and less durable than solid concrete. Furthermore, some types may lack visual appeal due to their porous nature.

[0007] Hence, there persists a demand for concrete formulations that not only address environmental concerns but also offer enhanced strength, appearance and durability. This may involve one or more of: minimising greenhouse gas emissions, maintaining or improving appearance, reducing solid material usage, facilitating easier handling and transportation, and complying with load-bearing requirements.

[0008] It is in this context that the present invention has been made.

[0009] Summary of the invention

[0010] The present invention provides a composite concrete product comprising: one or more solid concrete (SC) outer layers and an aerated concrete (AC) inner core that is bound to the one or more SC outer layers, wherein the one or more SC outer layers cover at least a portion of the surface of the AC inner core.

[0011] The surface of the AC inner core refers to its outermost part (e.g. the surface of the AC that is exposed before covered by the SC layer). ‘Cover’ includes, but is not limited to, providing a skin over, veneering over, laminating over, providing an (outer) surface over, coating, shielding, masking, overlaying, enveloping, encasing, and cladding.

[0012] It will be understood that the composite concrete product comprises two types of concretes. Combining the AC and SC leverages the benefits of each concrete while compensating for their disadvantages, resulting in a composite product with superior performance and environmental credentials.

[0013] The inclusion of a SC outer layer provides visual appeal to the finished appearance, particularly for applications in landscaping and bespoke constructions such as kitchen worktops and steps for internal or external stairs. The SC also contributes to the structural robustness of the composite product. The AC, on the other hand, reduces the overall weight of the product, rendering it more manageable during handling, installation, and transportation, thus streamlining logistics. This also ensures that the composite product can be used in various contexts where load bearing could be an issue if solely solid concrete were used, such as in concrete pavers, seating elements, or planters for rooftop terraces.

[0014] The inclusion of an AC inner core makes the overall product lighter and reduces the usage of solid components (e.g. cement, aggregates) in the concrete product. This lowers the greenhouse gas emissions associated with production and logistics operations. More products can be efficiently transported on trucks with the same weight load, and less heavy lifting equipment is required for installation. The AC may possess lower impact resistance compared to the solid concrete but using the latter as an outer layer to cover at least a portion of the AC’s surface provides effective protection, thereby enhancing the overall strength of the product, making it suitable for demanding load-bearing applications in certain landscaping and constructions. The cover layer of the solid concrete may also prolong the lifespan of the AC and the resultant composite product.

[0015] Herein, concrete typically refers to a (hard and strong) material made by mixing at least cement and aggregate (which may comprise sand and optionally other solid materials) with sufficient water to cause the cement to set and bind the entire mass.

[0016] AC is a type of lightweight concrete, including deliberately introduced air or gas bubbles in the concrete to create a porous structure. Said porous structure is typically characterised by a network of air voids or gas voids throughout the AC. These voids may be achieved through chemical and / or mechanical means and can vary in size and distribution depending on the specific type of aerated concrete and the method used to generate the bubbles. Typically, AC is formed from a composition comprising water, cement, aggregate(s), and a gas-forming or foaming agent. After mixing, said composition sets and hardens into aerated concrete. Said agent may create air or gas bubbles throughout the concrete (e.g. bubbles entrained in the concrete), resulting in a porous structure (e.g. cellular structure) that reduces the density of the concrete. Typically, AC is lighter (less dense) than SC. It should be understood that air may be inadvertently entrapped within the concrete during mixing, transportation and placement such that solid concrete may also contain aeration. However, in the context of the present invention, solid concrete is different from aerated concrete. AC does not refer to concrete that only contains incidentally introduced air. It may be that a composition free from any gas-forming or foaming agent is not for forming aerated concrete. The AC may be selected from foam concrete, air-entrained concrete, cellular concrete (e.g. cellular lightweight concrete [CLC], autoclaved aerated concrete [AAC]), and mixtures thereof. Typically, the AC is cellular concrete (e.g. CLC, AAC). The AC may be CLC.

[0017] It may be that the density of the AC (after setting and / or hardening) is from 300kg / m3to 1800 kg / m3, or from 400kg / m3to 1600kg / m3, or from 500kg / m3to 800kg / m3, optionally determined according to ASTM C567 / C567M-19. It may be that the compressive strengths of the AC (after setting and / or hardening) range from 0.5MPa to 10MPa, or from 1 MPa to 8MPa, optionally determined according to ASTM C495 / 495M-12(2019). Due to its porous structure, the aerated concrete offers good thermal and sound insulation properties. Typically, the aerated concrete is cellular concrete such as CLC or AAC. The presence of the cellular structure provides added strength as well as flexibility. This shows up as an enhancement in compressive strength as well as flexural strength, compared to other types of aerated concrete.

[0018] The aerated concrete may contain open pores, closed pores, or mixtures thereof. Closed pores refer to pores that are not (inter)connected to each other and / or not connected to the exterior of the AC. The closed pores may provide isolated cavities in the AC. Open pores refer to pores that are (inter)connected. Open pores may provide one or more continuous networks in the AC. It may be that the CLC contains closed pores. It may be that the AAC contains open pores. In the CLC, the majority of the pores may be closed pores with reference to the total number of the pores in the CLC (i.e. at least 51 %, or at least 80%, or at least 90%, or at least 95%). In the AAC, the majority of the pores may be open pores, with reference to the total number of the pores in the AAC (i.e. at least 51%, or at least 80%, or at least 90%, or at least 95%). Since open pores may allow air and liquids to pass, an open pore structure is more permeable to water and can lead to higher water absorption rates. CLC may have a lower water absorption rate compared to AAC due to its closed pore structure. The water absorption rate of the CLC may be from 5% to 20% (e.g. 10%), optionally measured according to ASTM C642-21. This helps in maintaining the integrity and insulation properties of the product, especially in moisture conditions. Therefore, CLC is more suitable for applications in which water resistance and thermal insulation are crucial.

[0019] Solid concrete (SC) has a dense, solid structure throughout, typically referring to (dense) concrete that does not contain any air or gas network, cellular structure, foam, or intentionally introduced bubbles. Thus, SC referred to herein denotes ‘concrete’ according to its conventional or standard form, which is concrete which does not have an intentionally introduced aerated, porous or lightweight structure. However, this does not exclude air voids that may be inadvertently entrapped within the concrete during mixing, transportation and placement. The SC outer layer may comprise from 0.1 % to 10% volume percent of aeration, or from 0.5% to 5%, or from 1 % to 2%.

[0020] SC is typically formed from compositions comprising water, cement and aggregate(s). After mixing, the composition sets and hardens into a dense, solid mass (e.g. a solid concrete). The composition typically does not contain any gas-forming or foaming agent. It may be that the solid concrete has a greater density and / or compressive strength compared to AC. It may be that the density of the solid concrete (after setting and / or hardening) is from 2000kg / m3to 2800kg / m3, or from 2200kg / m3to 2500kg / m3, optionally measured according to ASTM C642-21. It may be that the compressive strengths of the solid concrete (after setting and / or hardening) range from 20MPa to 60MPa, or from 25MPa to 40MPa, optionally determined according to ASTM C39 / C39M-21. The absence of intentionally introduced air or gas bubbles in the SC structure results in denser and heavier concrete, which adds strength and durability to the composite concrete product according to the present invention.

[0021] It may be that the density of the composite concrete product (after setting and / or hardening) according to the present invention is from 1000 kg / m3to 1500 kg / m3(e.g. 1200 kg / m3), optionally measured according to ASTM C642-21 or other suitable methods (e.g. density = weight I volume).

[0022] According to the present invention, the AC inner core is bound to the solid concrete outer layer. This may involve physical and / or chemical binding. There is strong and secure connection between the two concretes such that they are at least very difficult to separate without deliberate effort. This enhances the structural integrity of the resultant concrete product, making it unified, stable and durable. As described hereinafter, the binding is achieved by method(s) involving adding AC slurry to SC slurry, or adding set or partially set AC composition to SC slurry, or adding AC slurry to set or partially set SC slurry.

[0023] The one or more solid concrete layers may be continuous layers. Said one or more layers may cover at least the majority of the surface area of the AC (i.e. at least 51%), or at least 60%, or at least 80%, or at least 90%, or 100%. In this way, a portion or the entirety of the AC is protected by the solid concrete layer(s). This enhances the overall strength of the composite concrete product as well as improves its appearance.

[0024] It may be that the one or more solid concrete layers partially or wholly encase the AC. It may be that said layers encase the AC. Said layers may be the outer layers of the concrete product, surrounding the AC which forms an inner core of said product. The surface of the AC may be partially or fully covered, optionally fully covered. Said layers may encapsulate or laminate over the AC. This configuration further enhances appearance and strength of the composite concrete product.

[0025] It may be that the one or more solid concrete layers defining a space therebetween and the AC being partially or wholly encased within said space. The volume provided by said space is at least 50% of the volume of the said layers, or at least 80%, or at least 100%, or at least 200%, or at least 300%, but more than 800%, or not more than 500%, or not more than 400%. Herein the volume of the said layers excludes said space but includes any air and gas voids that may be inadvertently entrapped within the solid concrete. It may be that the volume ratio of the AC inner core to the solid concrete layer(s) is at least 1 :10, or at least 1 :5, or at least 1 :2, or at least 1 : 1 , or at least 3:2, but not more than 20: 1 , or not more than 10:1 , or not more than 5: 1. The volume of the AC includes the air and gas bubbles entrapped within the AC.

[0026] It may be that the weight ratio of the AC inner core to the solid concrete layer(s) in the composite concrete product is at least 1 : 5, or at least 1 : 3, or at least 1 : 1 , but not more than 5: 1 , or not more than 3: 1 , or not more than 1.5:1.

[0027] Increasing the ratio of AC to SC (e.g. more aerated concrete, less solid concrete) can lead to a reduction in the amount of solid component used, resulting in a lighter composite product. This reduction in weight enables more efficient transportation, allowing for the delivery of up to 40% to 100% more product volume using trucks with the same load capacity. Additionally, the composite product uses less solid (e.g. cement, aggregate) per cubic meter compared to concrete product consisting of solid concrete (e.g. about 20%-30% less solid utilized per cubic meter). By significantly reducing the solid consumption, less quarrying is required, resulting in reduced transportation of heavy materials. This enhances the environmental credentials of the composite concrete product. However, as the ratio (e.g. volume and / or weight ratio) increases, there may be a decrease in the overall strength and durability of the composite product. Thus, the specified ratios represent the optimal ratio to achieve the desired balance between material and transportation efficiency, and product strength.

[0028] It may be that the thickness of the solid concrete layer ranges from 0.5cm to 10.0cm, or from 1.0cm to 8.0cm, or from 1.5cm to 5.0cm, or from 1.7cm to 2.1cm, or from 1.8cm to 2.0cm. The thin SC layers reduce the overall weight of the composite product, while the thick SC layers provide better protection to the AC inner core. The above thickness ranges strike the best balance between weight reduction and adequate protection.

[0029] It may be that the composite product comprises from 20% to 70% volume percent of aeration, or from 30% to 60%. It may be that the AC inner core comprises from 50% to 90% volume percent of aeration, or from 60% to 80%. It may be that in the composite concrete product, from 80% to 98% volume percent of the total aeration is comprised in the AC inner core, or from 90% to 98%. The aeration provides enhanced insulation and reduced weight. This leads to a lighter composite concrete product that is easier to handle and place. Further, this reduces the overall solid (e.g. cement) consumption, which, as previously mentioned, enhances the environmental credentials of the composite concrete product. However, too much aeration may reduce the structural integrity of the AC. The specified ranges strike the best balance. Herein, aeration may refer to air or gas bubbles, or the incorporation of air or gas bubbles within the relevant concrete.

[0030] It may be that the composite concrete product is set in the form of a construction article, optionally a pre-cast and / or pre-stressed construction article. The construction article may be selected from (a group consisting of) a panel, a board, a concrete masonry unit, a block, a paver, a tile, a column, a pillar, a beam, a slab, a step, a railing, a baluster, a kerb, an edging, a planter, a wall such as a retaining wall, a worktop, a benchtop, a seating, a water feature such as a cascade or a fountain or a pond, and combinations thereof, typically selected from (a group consisting of) a panel, a board, a concrete masonry unit, a block, a paver, a tile, a column, a slab, a step, a kerb, an edging, a worktop, a benchtop, a seating, and combinations thereof. The construction article may be configured for landscaping, building construction, interior design (e.g. kitchen worktops), and similar applications. Typically, the construction article is a kerb. The kerb may act as an edge for the roadway. The kerb may be configured to provide a barrier between a road and a pedestrian pathway. It may be that the height of the kerb is from 10cm to 30cm. It may be that the width of the kerb is from 5cm to 15cm. The kerb may be a tapered kerb (having a narrower top than bottom). The width of the bottom of the kerb may be greater than that of the top of the kerb. It may be that the length of the kerb is from 80cm to 150cm. The kerb may be a curved kerb or a straight kerb. The kerb may have one or more curved edges, such as a chamfered edge, or a bevelled edge.

[0031] It may be that the solid concrete outer layer is formed from a first concrete composition comprising a first concrete mixture and water, the first concrete mixture comprising cement and one or more aggregates. The first concrete composition may be shaped (e.g. moulded) and / or set in the form of a construction article, optionally the solid concrete outer layer as described herein. The concrete article may be as described hereinbefore. The solid concrete outer layer may comprise the first concrete composition. The solid concrete outer layer may comprise the first concrete mixture. The present application provides the first concrete composition. The present application provides the first concrete mixture. The first composition may be free from any gas-forming or foaming agent.

[0032] It may be that the AC inner core is formed from a second concrete composition comprising a second concrete mixture and water, the second concrete mixture comprising cement, one or more aggregates, and a gas-forming agent or foaming agent. The second concrete composition may be shaped (e.g. moulded) and / or set in the form of a construction article, optionally the AC inner core. The concrete article may be as described hereinbefore. The AC inner core may comprise the second concrete composition. The AC inner core may comprise the second concrete mixture. The present application provides the second concrete composition. The present application provides the second concrete mixture.

[0033] It may be that the first and / or the second concrete compositions are free from any airentraining agents (e.g. synthetic detergents, synthetic resins, and natural resins such as natural wood resins).

[0034] It will be understood that the first concrete composition is different from the second concrete composition; and that the first concrete mixture is different from the second concrete mixture. It may be that in the first and second concrete mixtures, the cement contains any type of Portland cement, optionally in the second mixture, the cement containing the same type of Portland cement as that in said first mixture, or a different type of Portland cement from that in said first mixture. Cement acts as a binder in the concrete, providing strength, durability, and stability. It should be understood that cement is not limited to Portland cement but may refer to binders in the concrete in general, such as calcium sulphoaluminate (CSA) cement, magnesium phosphate cement, natural pozzolans, alkali-activated cement or acid-activated cement (e.g. geopolymer), and mixtures thereof.

[0035] The cement in the concrete mixture (i.e. the first and / or the second concrete mixtures) may comprise (e.g. be) any type of Portland cement according to EN 197-1: 2011.

[0036] It may be that the types of Portland cement are as follows.

[0037] I Portland cement: Portland cement and up to 5% of one or more additional constituents.

[0038] II Portland-composite cement: Portland cement, and up to 35% of one or more constituent(s) optionally select from artificial pozzolans such as blast furnace slag, silica fume, fly ashes, natural pozzolans such as siliceous or siliceous aluminous materials, volcanic ash glasses, calcined clays, shales, and mixtures thereof.

[0039] III Blast furnace cement: Portland cement and higher percentages (e.g. from 40% to 90%) of blast furnace slag.

[0040] IV Pozzolanic cement: Portland cement and higher percentages (e.g. up to 55%) of pozzolanic constituent(s).

[0041] V Composite cement: Portland cement, blast furnace slag or fly ash and pozzolana. Pozzolana may refer to a siliceous or siliceous-aluminous material (e.g. volcanic ash) or the like which reacts with calcium hydroxide in the presence of water (to form a compound possessing cementitious properties).

[0042] The percentages referred to may be based upon the total weight of the relevant type of Portland cement. Where any one of type II to type V Portland cement is used, the composition of the Portland cement (clinker) and the other material may be calculated on the same weight basis as if they were added separately. In the first concrete mixture, the cement may be from 10% to 40% (e.g. 20% - 30%) of the total weight of said first mixture. In the SC outer layer, the cement may be from 10% to 40% (e.g. 20% - 30%) of the total weight of said outer layer.

[0043] In the second concrete mixture, the cement may be from 40% to 90% (e.g. 60%-80%) of the total weight of said second mixture. In the AC inner core, the cement may be from 40% to 90% (e.g. 60%-80%) of the total weight of said inner core.

[0044] Pozzolanic constituent(s) or Pozzolanic materials may include synthetic particulates such as (ground blast furnace slag), fly ash, fumed silica and natural pozzolans such as diatomaceous earth and calcined clays, shales, volcanic ash glasses, siliceous or siliceous aluminous materials. In the first concrete mixture, the pozzolanic material is preferably present in a concentration of from 10% to 80% by weight of the total mixture (e.g.40%-70%). Alternatively or additionally, the weight percentage of the pozzolans is the same in the second concrete mixture. The particle size distribution of pozzolanic material can vary widely depending on the process.

[0045] Typically, the first and / or the second concrete mixtures comprise one or more aggregates. The aggregates may be independently selected from sand, limestone, crushed stone, gravel, granite, blast furnace slag, fly ash, glass, silica, slate, clay, pumice, vermiculite, scoria, diatomite, expanded shale, expanded clay, expanded slag, fumed silica, pelletized aggregate, tuff, macrolite, coal cinders, recycled aggregates, and mixtures thereof, typically selected from sand, limestone, crushed stone, granite, gravel, recycled aggregates, expanded clay, expanded shale, slag, fly ash, and mixtures thereof, more typically the first and / or the second concrete mixtures comprising sand. It may be that the first concrete mixture comprises sand, and the second concrete mixture comprises sand and limestone. The aggregates provide bulk strength and stability, reduce shrinkage and cracking, and enhance workability of the concrete. Sand is particularly preferred as it can fill voids between particles to create a dense and durable structure.

[0046] In the first concrete mixture, the aggregates may be from 30% to 90% (e.g. from 60% to 80%) of the total weight of said first mixture. In the SC outer layer, the aggregates may be from 30% to 90% (e.g. 60% - 80%) of the total weight of said outer layer. In the second concrete mixture, the aggregates may be from 10% to 40% (e.g. 20%- 30%) of the total weight of said second mixture. In the AC inner core, the aggregates may be from 10% to 40% (e.g. 20%-30%) of the total weight of said inner core.

[0047] Optionally the weight ratio of the one or more aggregates to the cement in the first concrete mixture and / or in the SC outer layer is from 1 : 10 to 10: 1 , or from 1 :2 to 5: 1 , or from 2: 1 to 4: 1. Alternatively or additionally, the weight ratio of the one or more aggregates to the cement in the second concrete mixture and / or in the AC inner core is from 1 : 10 to 5: 1 , or from 1 : 5 to 1 : 1 , or from 2:5 to 4:5. It may be that the weight ratio of the aggregates to the cement in the first concrete mixture and / or in the SC outer layer is from 2:1 to 4: 1 , and the weight ratio of the aggregates to the cement in the second concrete mixture and / or in the AC inner core is from 2:5 to 4:5. There may be more cement than aggregates in the AC inner core (i.e. the weight percentage of the cement is greater than that of the aggregates). There may be more aggregates than cement in the SC outer layer (i.e. the weight percentage of the aggregates is greater than that of the cement). The weight ratio of the cement to the aggregates in the aerated concrete is typically greater than that in the solid concrete. This meets the higher strength requirements of the aerated concrete and improves the robustness of the final composite product. Additionally, in some instances, this addresses the need for the solid components to set up quickly around the bubbles when combined with an aerated composition (e.g. foam) to form the aerated concrete.

[0048] In the composite concrete product, the cement may be from 30% to 70% (e.g. 40%- 50%) of the total weight of said product. The aggregates may be from 20% to 60% (e.g. 45% to 55%) of the total weight of said product. In the composite concrete product, the cement may be from 10% to 50% (e.g. 20% to 30%) of the total volume of said product. The aggregates may be from 5% to 40% (e.g. 10% to 30%) of the total volume of said product. This represents a reduced solid consumption compared to traditional concrete which consists entirely of solid concrete. This reduction enhances the environmental credentials of the composite concrete product and eases its logistics operations.

[0049] It may be that the first and / or the second concrete mixtures comprise one or more fibers. The fibers may be independently selected from steel fibers, organic fibers, ceramic fibers, polypropylene fibers, polyvinyl alcohol (PV A) fibers, glass fibers, carbon fibers, polyester fibers, silicon carbide, aramid fibers, composite fibers, fiberglass, cellulose fibers, natural fibers, and mixtures thereof, typically the first and / or the second concrete mixtures comprising fiberglass, more typically shredded fiberglass. The average length of the (shredded) fiberglass may be from 5mm to 30mm, or from 6mm to 25mm, or from 8mm to 15mm.

[0050] Incorporating fiber (e.g. fiberglass) into the concrete helps distribute the stress more evenly across the concrete and increase resistance to impact and abrasion. This leads to a longer-lasting and more resilient structure. Using shredded fiberglass is particularly beneficial as it provides additional benefits of improving bonding within the concrete and enhanced flexibility. Further, it reduces the likelihood of microcracks and hairline cracks, hence contributing to the longevity of the composite concrete.

[0051] In the first concrete mixture, the fibers may be from 0.01% to 5% (e.g. from 0.05% to 0.5%) of the total weight of said first mixture. In the SC outer layer, the fibers may be from 0.01 % to 5% (e.g. from 0.05% to 0.5%) of the total weight of said outer layer.

[0052] In the second concrete mixture, the fibers may be from 1% to 10% (e.g. from 2% to 5%) of the total weight of said second mixture. In the AC inner core, the fibers may be from 1% to 10% (e.g. from 2% to 5%) of the total weight of said inner core. More fibers in the second concrete mixture provides additional strength, thereby improving the robustness of the AC and the composite concrete product.

[0053] In the composite concrete product, the fibers may be from 0.01 % to 8% of the total weight of said product, or from 0.1 % to 5%.

[0054] The second concrete mixture may comprise perlite. The perlite may be expanded perlite. Perlite is understood as a lightweight, volcanic glass material. Thus, the inclusion of perlite in the AC would not greatly increase the weight of the composite concrete product. The perlite typically has a porous structure. This leads to better air or gas network in the AC (e.g. the air or gas bubbles are stronger, more uniform and more evenly distributed). The inclusion of perlite therefore reduces the likelihood of cracking and shrinkage of the AC, leading to an improved composite concrete product. Overall, the AC and the composite concrete product are stronger, more resistant to stress.

[0055] The average particle size of the perlite may be from 1 mm to 1cm, or from 2 mm to 5mm, optionally determined in accordance with ASTM C136 / C136M-14. The perlite with specified particle size further improves the structure in the AC. It offers great surface area to bind the air or gas bubbles. Thus, the resultant AC and composite concrete product are even stronger.

[0056] In the second concrete mixture, the perlite may be from 5% to 55% (e.g. 10%-30%) of the total weight of said second mixture. In the AC inner core, the perlite may be from 5% to 55% (e.g. 10%-30%) of the total weight of said inner core.

[0057] Optionally, the weight ratio of the perlite to the cement in the second concrete mixture and / or in the AC inner core is from 1 : 100 to 60: 100, or from 5: 100 to 30: 100, or from 10: 100 to 20: 100.

[0058] The gas forming agent may be selected from aluminium powder, aluminium powder with calcium hydroxide, hydrogen peroxide, zinc powder, magnesium powder, sodium bicarbonate, hydrolyzed protein, sulphate-based compounds such as aluminium sulphate and ammonium sulphate, and mixtures thereof.

[0059] The foaming agent may be selected from alkaline salt, anionic surfactants such as sodium alkyl sulphate, non-ionic surfactants, synthetic resins such as polyvinyl alcohol (PVA) and polycarboxylate ether (PCE), fatty acids, fatty alcohol ethoxylates, polysorbates, fatty acid esters, sulphonated organic compounds, saponins, proteins, and mixtures thereof.

[0060] In the second concrete mixture, the gas forming agent or the foaming agent may be from 0.001% to 2% of the total weight of said second mixture. In the AC inner core, the gas forming agent or the foaming agent may be from 0.001 % to 2% of the total weight of said inner core.

[0061] It may be that the second concrete mixture comprises a hydroscopic agent typically glycerine. Optionally, the weight ratio of the hydroscopic agent to the gas-forming agent or foaming agent in the second concrete mixture and / or in the AC inner core is from 1 : 5 to 1 : 1 , or from 1 :3 to 1 :2. The inclusion of the hydroscopic agent (e.g. glycerine) is particularly beneficial because this component enhances the robustness of the air or gas bubbles in the AC, contributing to the overall strength of the AC. Additionally, the hydroscopic agent (e.g. glycerine) reduces the risk of slump during the curing process of the AC. The specified ratios further improve the manufacturing of the aerated concrete. When a foam generator is used in the process (to create an aerated composition such as a foam), these ratios allow sufficient time for the solid materials to set around the bubbles, without affecting the flow and / or stability of the aerated composition as it exits the foam generator.

[0062] It may be that the first and / or the second concrete mixtures further comprise one or more additives. The additives may be one or more of: plasticizer, shrinkage control agent, colouring agent, viscosity modifier, setting regulator and curing agent. In the first and / or second concrete mixtures, the total weight of the additives may be from 0.01 % to 10% (e.g. from 0.5% to 5%) of the total weight of said first and / or second mixtures, respectively. In the SC outer layer, the total weight of the additives may be from 0.01 % to 10% of the total weight of said outer layer. In the AC inner core, the total weight of the additives may be from 0.01 % to 10% of the total weight of said inner core. It may be that the first and / or second concrete mixtures comprise gypsum (as a setting regulator). Gypsum may be included at the level as described herein. This component typically slows down the hydration process of cement, allowing sufficient time for mixing, transporting and placing the concrete. Thus, gypsum helps improve the workability of the concrete mixtures.

[0063] The first concrete mixture and / or the SC outer layer may comprise the cement (e.g. any type of Portland cement), the one or more aggregates (e.g. sand), and the fiber (e.g. fiberglass), as described herein. Said concrete mixture and / or said outer layer may further contain one or more additives, as described herein. The percentages and ratios may be as described herein. The first concrete mixture may comprise, by weight of the total mixture: 20% to 30% cement, 60% to 80% aggregate(s), and 0.01 % to 5% fiber, wherein optionally the weight ratio of the aggregate(s) to the cement is from 2: 1 to 4: 1. Optionally, the first concrete mixture may be used to form an ultra-high- performance concrete. Said mixture may comprise cement, one or more cementitious materials (e.g. silica flume, fly ash, ground granulated blast-furnace slag, or mixtures thereof), one or more aggregates (e.g. sand), a plasticizer, and one or more fibers (e.g. steel fibers, synthetic fibers, fiberglass, or mixtures thereof).

[0064] Said first concrete mixture may be combined with water to form the first concrete composition (e.g. in the form of a slurry). The water in the first concrete composition may be from 10% to 40% by weight of the total composition. The weight ratio of the water to the first concrete mixture may be from 1 :9 to 1 : 1 , or from 1 :5 to 1 :2. The first concrete composition may comprise, by weight of the total composition: from 10% to 50% (e.g. 10% - 30%) cement, from 30% to 80% (e.g. 60%-80%) one or more aggregates, from 0.01 % to 5% fiber, and from 10% to 40% water, wherein optionally the weight ratio of the aggregate(s) to the cement is from 2: 1 to 4: 1 . The first concrete composition may be shaped (e.g. moulded) and set to provide the solid concrete, optionally the solid concrete in the form of a construction article, further optionally the SC outer layer. It will be understood that the set composition may be optionally cured. The construction article may be as described hereinbefore.

[0065] The second concrete mixture and / or the AC inner core may comprise the cement (e.g. any type of Portland cement), the one or more aggregates (e.g. sand), the fiber (e.g. fiberglass), the perlite, the gas-forming agent or foaming agent, as described herein. Said concrete mixture and / or said inner core may further contain a hydroscopic agent (e.g. glycerine), as described herein. Said concrete mixture and / or said inner core may further contain one or more additives, as described herein. The percentages and ratios may be as described herein. The second concrete mixture may comprise, by weight of the total mixture: 40% to 80% cement (e.g. 60%- 70%), 10% to 40% one or more aggregates( e.g. 20%-30%), 10% to 30% perlite (e.g. 10%-20%), 0.01 % to 10% fiber, and a gas-forming agent or foaming agent, wherein optionally the weight ratio of the aggregate(s) to the cement is from 2:5 to 3:5. Said mixture may further comprise a hydroscopic agent (e.g. glycerine), optionally weight ratio of the hydroscopic agent to the gas-forming agent or foaming agent being from 1 :5 to 1 : 1 , or from 1 :3 to 1 :2.

[0066] Said second concrete mixture may be combined with water to form the second concrete composition (e.g. in the form of a slurry). The water in the second concrete composition may be from 10% to 50% by weight of the total composition (e.g. 20%- 40%). The weight ratio of the water to the second concrete mixture may be from 1 :5 to 1 : 1 , or from 1 :2 to 3:5. The second concrete composition may comprise, by weight of the total composition: from 30% to 70% cement (e.g. from 30% - 40%), from 10% to 50% one or more aggregates (e.g. 10%-30%), from 0.01% to 5% fiber, from 10% to 30% perlite (e.g. 10%-20%), a gas-forming agent or foaming agent, from 10% to 50% water (e.g. 20%-40%), and optionally a hydroscopic agent. The weight ratio of the aggregate(s) to the cement is from 2:5 to 3:5. The weight ratio of the hydroscopic agent to the gas-forming agent or foaming agent may be from 1 : 3 to 1 :2. The second concrete composition may comprise aeration (e.g. foam). The volume of the aeration (e.g. foam) may be from 40% to 90% of the total volume of the second concrete composition, or from 50% to 80%. The second concrete composition may be shaped (e.g. moulded) and set to provide the acerated concrete, optionally the aerated concrete in the form of a construction article, further optionally the AC inner core. It will be understood that the set composition may be optionally cured. The construction article may be as described hereinbefore.

[0067] The present invention may provide the aerated concrete and / or the solid concrete, as described herein.

[0068] The present invention may provide a gas-forming or foaming composition, comprising: the gas-forming or foaming agent, water and optionally the hydroscopic agent (e.g. glycerine), as described herein. The gas-forming or foaming agent may range from 1% to 5% by volume of the total composition. The weight ratio of the hydroscopic agent to the gas-forming agent or foaming agent may be from 1 : 5 to 1 : 1 , or from 1 :3 to 1 :2. Said composition may be an aqueous composition.

[0069] The gas-forming or foaming composition may additionally comprise a plurality of bubbles. The gas-forming agent or foaming agent may range from 0.1% to 0.5% by volume of the total composition comprising bubbles. The weight ratio of the hydroscopic agent to the gas-forming agent or foaming agent may be from 1 : 5 to 1 :3, or from 1 :3 to 1 :2. Said composition may be an aerated composition (e.g. a foam). The density of the foam may be from 30kg / m3to 120kg / m3, or from 40kg / m3to 70kg / m3. The density of the foam may be from 30kg / m3to 50kg / m3, or from 80kg / m3to 120kg / m3. The density values may be determined by any suitable methods, such as by measuring the weight of a foam sample, measuring the volume of the same sample, and then calculating the density by dividing the weight by the volume.

[0070] The present invention may provide a method of forming the gas-forming or foaming composition, comprising: mixing the gas-forming agent or foaming agent, water and optionally the hydroscopic agent, to form the aqueous composition. The method may further comprise adding gas to the aqueous composition so that said composition comprises a plurality of bubbles. Said composition may be an aerated composition (e.g. a foam).

[0071] The present invention may provide a first method of forming a composite concrete product, comprising: (a) adding a first concrete composition to a mould to provide one or more layers within said mould, wherein optionally the first concrete composition is as described herein; (b) providing a second concrete composition to the one or more layers such that the one or more layers cover at least a portion of the surface of the second concrete composition, thereby obtaining the composite concrete product, wherein optionally the second concrete composition is as described herein; (c) optionally, setting the concrete product; and (d) optionally, curing the set concrete product. The first concrete composition is different from the second concrete composition. The composite concrete product may be as described herein. Adding the first concrete composition may refer to spraying the first concrete composition.

[0072] In step (a), the one or more layers within the mould may define a space therebetween to receive the second concrete composition. Step (a) may comprise adding (e.g. spraying) the first concrete composition to dispose a base layer on the base of the mould. The base layer may assume the shape of the moulding surface provided by the base of the mould. The base layer may be shaped to assume said shape. Step (a) may comprise adding (e.g. spraying) the first concrete composition to dispose one or more side layers on the side walls of the mould. The one or more side layers may assume the shape of the moulding surface provided by the side walls of the mould. Said side layers may be shaped to assume said shape. The base layer and the mould may define a space therebetween to receive the second concrete composition. The side layers and the mould may define a space therebetween to receive the second concrete composition. Step (a) may comprise adding (e.g. spraying) the first composition to dispose the base layer and the one or more side layers extending therefrom. The base and the one or more side layers may define a space therebetween to receive the second concrete composition. The thickness of the base layer may be from 1.5cm to 5cm. The thickness of the one or more side layers may be from 1.5cm to 5cm.

[0073] Step (b) may comprise filling said space with the second concrete composition and optionally allowing said composition to assume the shape of the space. Said composition may expand to assume the shape of the space. Said composition may be shaped to assume the shape of the space. The second concrete composition may be levelled off prior to setting the composite concrete product.

[0074] The weight ratio of the second concrete composition to the first concrete composition may be from 1 :5 to 5: 1 , or from 1 :3 to 3: 1 , or from 1 : 1 to 3:2. The volume ratio of the second concrete composition to the first concrete composition may be from 1 :2 to 20: 1 , or from 1 : 1 to 10: 1 , or from 3:2 to 5: 1 .

[0075] The first concrete composition may be a SC slurry. The first concrete composition may be formed by: providing the first concrete mixture as described herein and mixing said mixture with water to form the first concrete composition (e.g. the SC slurry). The weight ratio of water to the first concrete mixture may be from 1 :5 to 1 : 1.

[0076] The second concrete composition may be an AC slurry. The second concrete composition may be formed by: (i) mixing the second concrete mixture as described herein with water to form a slurry, wherein the second concrete mixture excludes the gas-forming agent, the foaming agent and the hydroscopic agent; (ii) mixing the gasforming agent or foaming agent, water and optionally the hydroscopic agent, to form an aqueous composition and adding gas to the aqueous composition to generate an aerated composition comprising a plurality of bubbles; and (iii) mixing the slurry with the aerated composition, to form the second concrete composition, wherein optionally the mixing ratio is from 0.5kg to 1kg of the slurry per 1L of the aerated composition. The aerated composition may be a foam. The density of the aerated composition (e.g. the foam) may be from 30kg / m3to 120kg / m3, or from 40kg / m3to 70kg / m3. The density of the slurry obtained in step (i) may be from 1500 kg / m3to 2500 kg / m3. The density of the AC slurry may be from 500 kg / m3to 1500 kg / m3. The density values may be determined by any suitable methods (e.g. density = weight I volume). In step (i), the weight ratio of water to the second concrete mixture may be from 1 :5 to 3:5. In step (ii), the weight ratio of the hydroscopic agent to the gas-forming agent or foaming agent may be from 1 : 5 to 1 :1 , or from 1 :3 to 1 :2. In step (ii), the weight ratio of the gas-forming agent or foaming agent to water may be from 1 : 100 to 1 : 20, or from 1 : 60 to 1 :30, or from 1 : 50 to 1 : 30. Step (ii) may be replaced by the method of forming the gas-forming or foaming composition. The method described herein may be suitable for forming a CLC slurry.

[0077] The second concrete composition (e.g. the AC slurry) may be alternatively formed by mixing the second concrete mixture as described herein with water to form the AC slurry. Further alternatively, the second concrete composition (e.g. the AC slurry) may be formed by: mixing the second concrete mixture described herein with water to form a slurry, wherein the second concrete mixture excludes the gas-forming agent, the foaming agent and the hydroscopic agent; and mixing the gas-forming agent or foaming agent with the slurry to generate a plurality of air or gas bubbles, thereby obtaining the second concrete composition comprising said bubbles. The weight ratio of water to the second concrete mixture may be from 1 :5 to 4:5, or from 3:5 to 4:5. The weight percentage of the gas-forming agent or foaming agent in the second concrete composition may be from 0.001% to 2%, or from 0.05% to 0.1%. The density of the obtained second concrete composition (e.g. the AC slurry) may be from 500kg / m3to 1200kg / m3, or from 600kg / m3to 1000kg / m3. The method may be suitable for forming an AAC slurry.

[0078] The second concrete composition (the AC slurry) may be set. The set slurry may be cured. If an AAC slurry (i.e. AAC composition) is used for forming the aerated concrete (SC), the method of setting and / or curing the AAC composition may comprise precuring the AAC composition, in which the AAC slurry is allowed to expand in a mould and at least partially set. The method may comprise cutting the at least partially set AAC (into the desired shape). The method may comprise autoclaving. Autoclaving may comprise: placing the (at least partially set) AAC composition in an autoclave, and subjecting the AAC composition to steam curing under pressure. The method may further comprise cooling the autoclaved AAC composition. The temperature during autoclaving may be from 160°C to 200°C. The pressure may be from 1.2MPa to 1.5MPa. The duration of autoclaving may be from 1.5 hours to 12 hours, or from 2 hours to 10 hours, or from 6 hours to 8 hours.

[0079] The first concrete composition (the SC slurry) may be set. The set slurry may be cured.

[0080] The present invention may provide a second method of forming a composite concrete product, comprising: (a)adding a first concrete composition to a mould to provide one or more layers within said mould, wherein optionally the first concrete composition is as described herein; (b) providing a second concrete composition to the one or more layers, said composition is at least partially set; (c) expanding the one or more layers of the first concrete composition, such that said layers at least partially encase the second concrete composition to form the concrete product; (d) optionally, covering any exposed surface of the second concrete composition with the first concrete composition; (e) optionally, setting the concrete product described in step (c) or (d); and (f) optionally, curing the set product described in step (e). The first concrete composition is different from the second concrete composition. The composite concrete product may be as described herein. The second concrete composition may be as described herein.

[0081] In step (b), the second concrete composition may be (fully) set. In step (b), the second concrete composition may be partially or fully cured. The method may comprise setting and curing the second concrete composition prior to providing it to the one or more layers. If an AAC composition is used, the second method may comprise setting and / or curing the AAC composition, as described herein. In step (c), the mould may be vibrated to sink the second concrete composition. The mould may be vibrated to expand the one or more layers. Sinking the second concrete composition may cause the one or more layers to expand.

[0082] In the second method, the volume ratio of the cured second concrete composition to the first concrete composition may be from 1 : 5 to 5:1 , or from 1 :2 to 2:1. The weight ratio of the cured second concrete composition to the first concrete composition may be from 1 :5 to 3: 1 , or from 1 :3 to 1 :2.

[0083] In the second method, the first concrete composition may be a SC slurry, obtainable as described herein. The (partially) set or cured second concrete composition (e.g. a cured AAC composition or a cured CLC composition) may be obtainable as described herein.

[0084] Step (a) in the second method may comprise adding the first concrete composition to provide a base layer, wherein optionally the base layer is disposed on the base of the mould. The base layer may assume the shape of the moulding surface provided by the base of the mould. Step (b) may comprise providing the (cured) second concrete composition to the base layer. Step (c) in the second method may comprise vibrating the mould to at least partially sink the (cured) second concrete composition into the provided layers (e.g. the base layer). In step (c), sinking the second concrete composition may force the one or more layers (e.g. the base layer) to expand and to lift up, thereby forming one or more side layers (to at least partially encase the [cured] second concrete composition). The (cured) second concrete composition may be at least partially encased by the base layer and the one or more side layers extending therefrom. The one or more side layers may extend from the base layer. The one or more side layers and the base layer may assume the shape of the moulding surface of the mould. The thickness of the base layer may be from 1.5cm to 5cm, or from 1.8cm to 2cm. The thickness of the one or more side layers may be from 1.5cm to 5cm, or from 1.8cm to 2cm.

[0085] In the second method, prior to step (d), the first and second concrete compositions may be levelled off. Prior to step (e), the first concrete composition used to cover the exposed surface may be levelled off. The present invention may provide a third method of forming a composite concrete product, comprising: (a) adding a first concrete composition to a mould, wherein said composition is partially set and mouldable; (b) moulding the first concrete composition in step (a) to provide one or more layers, wherein said layers define a space therebetween to receive a second concrete composition; c) filling said space with the second concrete composition such that the layers at least partially encase the second concrete composition, thereby obtaining the concrete product; (d) optionally, setting the concrete product; and (e) optionally, curing the set concrete product. The composite concrete product may be as described herein. The first and second concrete compositions may be as described herein. The first concrete composition is different from the second concrete composition.

[0086] In the third method, the first concrete composition may be obtainable as described herein. The first concrete composition in step (a) is partially set and mouldable. The first concrete composition may be in a plastic state. This state means the composition (e.g. a mouldable SC slurry) is still workable after mixing but before set and hardened. For a mouldable slurry, it may be that the slump ranges from 50 mm to 200mm, or from 75mm to 175mm, optionally determined according to ASTM C143 / C143M-12. The second concrete composition (e.g. an AC slurry) may be obtainable as described herein.

[0087] In the third method, the weight ratio of the second concrete composition to the first concrete composition may be from 1 :5 to 5: 1 , or from 1 :3 to 3: 1 , or from 1 : 1 to 3:2. The volume ratio of the second concrete composition to the first concrete composition may be from 1 :2 to 20: 1 , or from 1 : 1 to 10: 1 , or from 3:2 to 5: 1.

[0088] In the third method, step (a) may comprise adding the first concrete composition to dispose a base layer on the base of the mould. The mould mentioned in the third method may be a first mould (e.g. an outer mould). Step (b) of the method may comprising using a second mould (e.g. an inner mould) to expand the one or more layers (e.g. the base layer), urging said layers to assume the shape of the moulding surface of the first mould. The one or more layers may define a space therebetween. Said space may assume the shape of the moulding surface of the second mould. Accordingly, the first concrete composition may be moulded (between the first and second moulds) to provide a base layer and one or more side layers extending therefrom. The base layer and the one or more side layers may define a space therebetween to receive the second concrete composition. The base layer and the one or more side layers may assume the shape of the moulding surface of the first mould. The space may assume the shape of the moulding surface of the second mould. The thickness of the base layer may be from 1.5cm to 5cm, or from 1.8cm to 2cm. The thickness of the one or more side layers may be from 1.5cm to 5cm, or from 1.8cm to 2cm.

[0089] In the third method, step (c) may comprise filling said space with the second concrete composition and optionally allowing said composition to assume the shape of the space. Said composition may expand to assume the shape of the space. The second concrete composition may be levelled off prior to setting the composite concrete product in step (d). The second concrete composition may be an AC slurry, obtainable as described herein.

[0090] The present invention provides a mould apparatus for forming a composite concrete product, wherein optionally the product is as described herein. The mould apparatus may be configured to mould a first concrete composition and a second concrete composition to form said product, optionally according to any one of the methods described herein. The first and the second concrete compositions may be as described herein. The first concrete composition is different from the second concrete composition.

[0091] It may be that the mould apparatus comprises a first mould comprising a plurality of plates and one or more magnetic means, the plurality of plates configured to be (removably) secured together (via the one or more magnetic means) to form: a base; and one or more side walls extending therefrom; wherein the base is configured to be removably secured to the one or more side walls via the magnetic means, typically electromagnetic means.

[0092] The plates may be steel plates, typically cast steel plates, more typically galvanised steel plates or mild steel plates (in which the carbon content is up to 0.5% by weight of the total plate). The plates may be made from metal, typically sheet metal.

[0093] It may be that the plates configured to form the side walls of the mould are secured to each other by welding or bolting. It may be that the side walls of the mould are welded or bolted on their corners. Other attachment means or methods may also be used to secure said plates together, optionally selected from rivets, pins, adhesives, clamps, clips, screws, brazing, soldering, and suitable combinations thereof. Said side walls can be removably secured to the base via magnetic means (e.g. magnets), typically electromagnetic means. This design is suitable for the second and third methods of forming the composite concrete product. The mould is robust enough to withstand both the vibrating process and the compression pressure when moulding the first concrete composition between the first and second moulds.

[0094] It may be that the mould comprises multiple plates configured to form multiple side walls (e.g. the mould comprises multiple side walls). It may be that the side walls (e.g. the plates configured to form the side walls) are configured to be removably secured to each other via the magnetic means (e.g. magnets). Said side walls can be removably secured to the base via magnetic means (e.g. magnets), typically electromagnetic means. This design is suitable for the first method of forming the composite concrete product, wherein the pressure involved in said method is low and the magnets provide sufficient strength to sustain the load.

[0095] The shapes and dimensions of the plates can vary, allowing for versatility in assembly. The plates can be assembled (e.g. configured to be assembled) in multiple ways by the magnetic means, to form moulds of different shapes and sizes. This flexibility enables the production of various composite concrete products using the same mould apparatus. This eliminates the need to create a unique mould apparatus for each individual concrete product. As a result, a wide range of products can be produced with a single set of plates and magnetic means.

[0096] It may be that the mould apparatus comprises a second mould. The first and the second moulds may be configured to mould at least a portion of the first concrete composition therebetween to form one or more layers, said one or more layers defining a space therebetween to receive the second concrete composition. The first and the second compositions may be as described herein. The first mould may be an outer mould (e.g. female mould). The second mould may be an inner mould (e.g. male mould). This design is particularly suitable for the third method of forming the composite concrete product. The dimension and size of the moulding surface provided by the second mould may be smaller than those of the moulding surface provided by the first mould. The shape of the moulding surface provided by the second mould may correspond to (e.g. be substantially the same as, be the same as) that of the moulding surface provided by the first mould. The second mould (e.g. the inner mould) may be configured to at least partially fit within the mould cavity of the first mould (e.g. the outer mould). The second mould (e.g. the inner mould) may comprise one or more profiled edges. The edge may be rounded, curved, bevelled, chamfered, or tapered. The edge may be a fillet edge (e.g. a rounded edge), a chamfered edge, a bevelled edge, or a tapered edge, typically a chamfered edge. Said edge may extend along at least part of the periphery of the second mould. Said edge may extend along the periphery of the second mould. Said edge may extend along the periphery of the base of the second mould. Said edge may extend along the periphery of the side walls of the second mould. Said edge may extend between the adjacent side walls of the second mould. Said edge may extend between the side walls and the base of the second mould. Operably, said edge may face the corner formed by the base and the side walls of the first mould (e.g. the outer mould) with a gap therebetween. Operably, said edge may face the corner formed by the adjacent side walls of the first mould (e.g. the outer mould) with a gap therebetween. This specialized edge design reduces the likelihood of the second mould becoming stuck. It improves the release of the second mould (from the first mould), when moulding is complete. Thus, it enhances the overall operation of the mould apparatus.

[0097] Optional features described in relation to the first or second aspect of the invention are optional features of both the first and second aspects of the invention.

[0098] Example embodiments of the present invention will now be illustrated with reference to the following Figures in which:

[0099] Figure 1 shows a cross-sectional view of a composite concrete product according to an embodiment of the present invention;

[0100] Figures 2(a) and 2(b) show plan views of composite concrete products according to embodiments of the present invention;

[0101] Figures 3(a), (b), and (c) illustrate three moulds used to make concrete products of different shapes according to embodiments of the present invention;

[0102] Figure 4 shows a photograph of the three moulds in Figures 3(a)-(c);

[0103] Figure 5 shows a row of moulds used to make concrete products according to an embodiment of the present invention, in which the moulds are partially filled; Figure 6 shows the row of moulds in Figure 5, in which the moulds are fully filled;

[0104] Figures 7 (a) and 7(b) show a mould apparatus according to an embodiment of the present invention; and

[0105] Figures 8, 9 and 10 show flow charts of different methods of forming composite concrete products according to embodiments of the present invention.

[0106] Detailed Description of the Drawings

[0107] In detail, figure 1 shows a photograph of a cross-sectional view of a composite concrete product 1 according to an embodiment of the present invention. The product 1 is in the form of a composite concrete panel. The panel 1 comprises an inner core 2 which is made of cellular lightweight concrete (CLC, being an example of the aerated concrete). The inner core 2 contains perlites and bubbles 3 are formed around the perlites. The panel 1 further comprises an outer layer 4 which is made of solid concrete (SC). The SC outer layer 4 covers at least a portion of the surface of the CLC inner core 2.

[0108] Figures 2(a) and 2(b) show photographs of top views of composite concrete products 5 and 6 according to embodiments of the present invention. Product 5 is in the form of a rectangular concrete panel; and product 6 is in the form of a rectangular concrete board. Each of products 5 and 6 has a CLC inner core 2, which is partially encased by a SC outer layer 4. A portion of the surface of the inner core 2 is exposed (not covered by the SC outer layer 4).

[0109] Figures 3(a), (b), and (c) illustrate three moulds 7, 8 and 9 used to make concrete products of different shapes according to embodiments of the present invention. Each mould comprises a plurality of steel plates 10. In each figure, the steel plates 10 are removably held in place by magnet means 11 (e.g. magnets). In figure 3(a), the mould 7 has a rectangular configuration; in figure 3(b), the mould 8 has an isosceles trapezoidal configuration; and in figure 3(c), the mould 9 has a triangular configuration. Figure 4 shows a photograph of these three moulds 7, 8, and 9.

[0110] In figure 5, rectangular moulds 7 are used to prepare composite concrete products according to an embodiment of the present invention. In each mould 7, the steel plates 10 forming the side walls are welded or bolted on the corners. These side walls are then removably secured to a base steel plate 12 with electromagnets 13 to form the mould 7. Each mould7 is filled with semi-dry (i.e. partially set) solid concrete (SC) and said concrete is moulded to provide a continuous layer 14 in accordance with the inner shape of the mould 7. The layer 14 provides a space therebetween and said space is partially filled with the CLC slurry 15. In figure 6, the space is fully filled with the CLC slurry 15 and levelled off.

[0111] Figure 7(a) shows a mould apparatus suitable for forming the composite concrete product according to the third method of the present invention. The mould apparatus comprises a first mould 16 and a second mould 17. The first mould 16 is an outer mould and the second mould 17 is an inner mould. The first mould 16 is rectangular in shape. The second mould 17 has a similar shape but is smaller in dimensions such that the second mould 17 may fit into the moulding cavity 18 of the first mould 16. The plates forming the side walls of mould 16 are secured together by magnets 11. The moulds

[0112] 16 and 17 are configured to mould the semi-dry, solid concrete therebetween. The second mould 17 has a chamfered edge 19, which facilitates the release of the second mould 17 from the first mould 16 when moulding is completed. In figure 7(a), the chamfered edge 19 is indicated around the bottom edge of the mould 17. Additionally (not shown), the chamfered edge 19 may also be present along one or more vertical edges 20, preferably all of the vertical edges 20, of the mould 17. In other words, the chamfered edge 19 may also be present between the adjacent side walls of the mould

[0113] 17 (not shown). Figure 7(b) provides a sectional view of the moulds 16 and 17, with the second mould 17 disposed within the moulding cavity of the first mould 16.

[0114] Figure 8 shows a flow chart of forming a composite concrete product according to the first method of the invention. In step 801 , the first concrete composition is sprayed into a mould, to provide one or more layers. The first concrete composition may be the solid concrete (SC) slurry, obtainable as described herein. In step 802, the one or more layers of the first concrete composition is shaped to provide a space therebetween, to receive the second concrete composition. The second concrete composition may be the aerated concrete slurry (e.g. CLC slurry, AAC slurry), obtainable as described herein. The layers may be shaped to provide a base layer and one or more side layers extending therefrom. The base layer and the one or more side layers may define the space therebetween. The base layer and the one or more side layers may assume the shape of the moulding surface of the mould. In step 803, the space is filled with the second concrete composition, such that the layers cover at least a portion of the surface of the second concrete composition. The layers may at least partially encase the second concrete composition. The second concrete composition is levelled off in step 804, to obtain the composite concrete product. Said product is then set and cured in step 805.

[0115] Figure 9 shows a flow chart of forming a composite concrete product according to the second method of the invention. In step 901 , the first concrete composition (e.g. the SC slurry) is added to a mould to provide one or more layers (e.g. a base layer disposed on the base of the mould). The second concrete composition (e.g. the aerated concrete slurry) is set and cured. The cured composition is then provided to the one or more layers in step 902. In step 903, the mould is vibrated to sink the cured second concrete composition. The sinking and / or vibrating causes the one or more layers to expand to at least partially encase the cured second concrete composition. Sinking and / or vibrating urges the one or more layers (e.g. the base layer) to expand and to lift up, thereby forming one or more side layers. The one or more side layers may extend from the base layer. The cured second concrete composition may be at least partially encased by the base layer and the one or more side layers. Sinking and / or vibrating also urges the layers to assume the shape of the moulding surface of the mould. In step 904, any exposed surface (e.g. the top surface) of the cured second concrete composition is covered with the first concrete composition. The first concrete composition may be levelled off to obtain the composite concrete product. The product is then set and cured in step 905.

[0116] Figure 10 shows a flow chart of forming a composite concrete product according to the third method of the invention. In step 1001 , the first concrete composition (e.g. the SC composition) is added to a first mould. The composition is partially set and still mouldable. In step 1002, said composition is moulded, optionally compressed between the first and second moulds (e.g. the outer and the inner moulds), to provide one or more layers defining a space therebetween. The one or more layers may comprise a base layer and one or more side layers extending therefrom. Moulding urges the base layer and the side layers to assume the shape provided by the moulding surface of the first mould (e.g. outer mould), and the space to assume the shape provided by the moulding surface of the second mould (e.g. inner mould). In step 1003, the space is filled with the second concrete composition (e.g. the AC slurry). In this way, the second concrete composition is at least partially encased by the one or more layers. In step 1004, the second concrete composition is levelled off, to obtain the composite concrete product. The obtained product is then set and cured in step 1005. Examples

[0117] The following examples illustrate the invention without limiting it.

[0118] Example 1 : The first concrete composition may contain the following materials with the following concentration.

[0119] The Portland cement, the sand and the fiberglass were mixed with water to obtain a slurry. This slurry (i.e. wet SC composition) can be directly used to create the composite concrete product according to the present invention (as described in the first and second methods). Alternatively, the slurry can be allowed to partially set and hardened (i.e. the SC composition becomes semi-dry), and then the partially set SC composition can be used to create the composite concrete product according to the present invention (as described in the third method).

[0120] Example 2: An aqueous composition may contain the following materials with the following concentration.

[0121] The foaming agent, glycerine and water were mixed to obtain an aqueous composition. This composition was agitated into foam using a foam generator or a suitable mixer (e.g. a paint mixer). Gas was introduced into the aqueous composition during this foaming process. 30L- 50L aqueous composition resulted in about 650L foam (i.e. the aerated composition). The inclusion of glycerine is particularly beneficial because this component provides a robustness to the air bubbles, enhancing the overall strength of the resultant aerated concrete. Additionally, glycerine reduces the risk of slump during the curing process of the aerated concrete. The foam (i.e. the aerated composition) obtained may be used to create the second concrete composition, for example, the composition for the cellular lightweight concrete (CLC).

[0122] Example 3: A slurry for forming the second concrete composition (e.g. the CLC composition) may contain the following materials with the following concentration.

[0123] A slurry was created by mixing the Portland cement, sand, perlite, fiberglass and water. This slurry was then mixed with the foam obtained from Example 2 to form the CLC composition (i.e. the CLC slurry). CLC is a type of aerated concrete (AC). About 30kg slurry was mixed with about 30L- 40L foam to create the CLC composition. It is advantageous to have the mixing ratio at from 0.5kg to 1kg of the slurry per 1 L of the foam, typically 0.75kg to 1kg of the slurry per 1 L of the foam, more typically about 0.8kg of the slurry per 1 L of the foam. The specific mixing ratios not only enhance the strength of the CLC but also the overall durability of the composite concrete product.

[0124] The CLC composition (i.e. the CLC slurry) can be directly used to create the composite concrete product, as described in the first and third methods. Alternatively, the CLC composition (i.e. the CLC slurry) can be allowed to set and cured, and then the cured CLC composition can be used to create the composite concrete product, as described in the second method.

[0125] By way of another example, the second concrete composition may be a composition for autoclaved aerated concrete (AAC). The composition may comprise cement (Portland Cement type I), limestone, sand, a gas-forming agent (e.g. aluminium powder), and water. These components may be mixed to form a slurry (i.e the AAC slurry). The gas forming agent (e.g. aluminium powder) may react with limestone and water to produce gas (e.g. hydrogen gas), which creates bubbles in the slurry, resulting in the AAC. The AAC composition (i.e. the AAC slurry) may be allowed to set and cure. The AAC composition may go through an autoclaving process, in which the composition is placed in an autoclave, subjecting to steam under high pressure at temperatures ranging from 160°C to 200°C for several hours. The composition is then cooled down to room temperature. The cooled composition can be used to create the composite concrete product, as described herein.

[0126] Herein, terms such as ‘outer’, ‘inner’, ‘upward(ly)’, ‘downward(ly)’, ‘upwards', ‘downwards’, ’up’, ‘upper(most)’, ‘down’, ‘top’, ‘bottom’, ‘low’, ‘lower’, ‘below’, ‘above’, ‘beyond’, when employed in respect of objects such as the composite concrete product, the mould apparatus, the mould and their constituent parts or intermediate forms or preforms, unless specified otherwise, refer to when said object is in an upright orientation in its intended application. For example, the base is at the bottom of said object, an opening of the mould used for filling the concrete composition being at the top of said object. The term ‘outer surface’ or ‘outer layer’ or the likes denote the surface or layer positioned on the exterior of the inner part, thereby providing at least partial covering to the inner component when the object is in use, such as in building construction, landscaping, or other comparable contexts where applicable. The term 'inner' or 'inner core' or the likes refer to the interior of the object, opposite the outer surface or outer layer.

[0127] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to and do not exclude other components, integers, or steps. The word ‘comprise’ and variations thereof may also encompass the meaning of ‘consist of’ and variations. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. Features, integers, characteristics, or groups described in conjunction with a particular aspect, embodiment, or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. Numerical ranges expressed in the format ‘from x to y’ and ‘between x and y’ are understood to include x and y, unless specified otherwise. When for a specific feature multiple optional ranges are described, it is understood that all ranges combining the different endpoints are also contemplated. Except in the operating and comparative examples, or where otherwise explicitly indicated, all numbers in this description indicating amounts of material or conditions of reaction, physical properties or materials and / or use are to be understood as modified by the word ‘about’.

Claims

Claims1. A composite concrete product, comprising: one or more solid concrete (SC) outer layers; and an aerated concrete (AC) inner core that is bound to the one or more solid concrete outer layers, wherein the one or more solid concrete outer layers cover at least a portion of the surface of the AC inner core.

2. The composite concrete product according to claim 1 , wherein the one or more SC outer layers partially or wholly encase the AC inner core, and wherein optionally, said SC outer layers are continuous layers.

3. The composite concrete product according to claim 2, the one or more SC outer layers defining a space therebetween and the AC inner core being partially or wholly encased within said space, wherein the volume provided by said space is at least 100% of the volume of the one or more solid concrete outer layers, but not more than 400%.

4. The composite concrete product according to any one of the preceding claims, wherein said product comprises from 20% to 70% volume percent of aeration, or from 30% to 60%, and wherein optionally, the AC inner core comprises from 50% to 90% volume percent of aeration, or from 60% to 80%.5 The composite concrete product according to any one of the preceding claims, wherein the thickness of the one or more SC outer layers ranges from 1 ,7cm to 2.1cm.

6. The composite concrete product according to any one of the preceding claims, wherein the one or more SC outer layers are formed from a first concrete composition comprising a first concrete mixture and water, the first concrete mixture comprising cement and one or more aggregates, and the AC inner core is formed from a second concrete composition comprising a second concrete mixture and water, the second concrete mixture comprising cement, one or more aggregates, and a gas-forming agent or foaming agent, optionally the weight ratio of the one or more aggregates to the cement in the first concrete mixture being from 1 :2 to 5: 1 , and further optionally the weight ratio of the oneor more aggregates to the cement in the second concrete mixture being from 1 : 5 to 1 :1.

7. The composite concrete product according to claim 6, wherein the second concrete mixture comprises a perlite, the perlite being in an amount ranging from 10% to 30% by weight of the total second concrete mixture.

8. The composite concrete product according to claim 6 or claim 7, wherein the second concrete mixture comprises a hydroscopic agent typically glycerine, and wherein the weight ratio of the hydroscopic agent to the gas-forming agent or foaming agent is from 1 : 5 to 1 : 1 .

9. The composite concrete product according to any one of claims 6 to 8, wherein the first and / or the second concrete mixtures comprise one or more fibers, independently selected from steel fibers, organic fibers, ceramic fibers, polypropylene fibers, polyvinyl alcohol (PVA) fibers, glass fibers, carbon fibers, polyester fibers, silicon carbide, aramid fibers, composite fibers, fiberglass, cellulose fibers, natural fibers, and mixtures thereof, typically the first and / or the second concrete mixtures comprising fiberglass, more typically shredded fiberglass.

10. The composite concrete product according to any one of the preceding claims, wherein the product is set in the form of a construction article, selected from a panel, a board, a concrete masonry unit, a block, a paver, a tile, a column, a slab, a step, a kerb, an edging, a worktop, a benchtop, a seating, and combinations thereof.

11. A method of forming a composite concrete product, comprising:(a) adding a first concrete composition to a mould to provide one or more layers within said mould;(b) providing a second concrete composition to the one or more layers such that said layers cover at least a portion of the surface of the second concrete composition, thereby obtaining the composite concrete product, wherein the second concrete composition is different from the first concrete composition;(c) optionally, setting the composite concrete product; and(d) optionally, curing the set composite concrete product.

12. A method of forming a composite concrete product, comprising:(a) adding a first concrete composition to a mould to provide one or more layers within said mould;(b) providing a second concrete composition to the one or more layers, wherein the second concrete composition is different from the first concrete composition and is at least partially set;(c) expanding the one or more layers of the first concrete composition such that said layers at least partially encase the second concrete composition to form the composite concrete product;(d) optionally, covering any exposed surface of the second concrete composition with the first concrete composition;(e) optionally, setting the composite concrete product described in step(c) or (d); and(f) optionally, curing the set composite product described in step (e).

13. A method of forming a composite concrete product, comprising:(a) adding a first concrete composition to a mould, wherein said composition is partially set and mouldable;(b) moulding the first concrete composition in step (a) to provide one or more layers, wherein said layers define a space therebetween to receive a second concrete composition which is different from the first concrete composition;(c) filling said space with the second concrete composition such that the one or more layers at least partially encase the second concrete composition, thereby obtaining the composite concrete product;(d) optionally, setting the composite concrete product; and(e) optionally, curing the set concrete product.

14. The method according to any one of claims 11 to 13, further comprising forming the second concrete composition which comprises:(a) mixing the second concrete mixture as described in any one of claims 6 to 9 excluding the gas-forming agent, the foaming agent and the hydroscopic agent, with water to form a slurry;(b) mixing the gas-forming agent or foaming agent, the hydroscopic agent, and water to form an aqueous composition and adding gas to theaqueous composition to generate an aerated composition comprising a plurality of bubbles;(c) mixing the slurry obtained in step (a) with the aerated composition obtained in step (b), to form the second concrete composition, wherein the mixing ratio is from 0.5kg to 1 kg of the slurry per 1 L of the aerated composition;(d) optionally, setting the so-formed second concrete composition; and(e) optionally, curing the set second concrete composition.

15. A mould apparatus configured to form a composite concrete product, the mould apparatus comprising a first mould, said mould comprising a plurality of plates and one or more magnetic means, and the plurality of plates configured to be secured together to form: a base; and one or more side walls extending therefrom; wherein the base is configured to be removably secured to the one or more side walls via the magnetic means, typically electromagnetic means and wherein optionally, the mould comprises multiple side walls and said side walls are configured to be removably secured to each other via the magnetic means.

16. The mould apparatus according to claim 15, comprising a second mould, wherein the first and the second moulds are configured to mould at least a portion of a first concrete composition therebetween to form one or more layers, said one or more layers defining a space therebetween to receive a second concrete composition, and wherein the first concrete composition is different from the second concrete composition.

17. The method or the mould apparatus according to any one of claims 11 to 16, wherein the composite concrete product is according to any one of claims 1 to 10.

18. The method or the mould apparatus according to any one of claims 11 to 14 and 16, wherein the first concrete composition is as described in any one of claims 6 to 9, and the second concrete composition is as described in any one of claims 6 to 9.

19. The second concrete composition as described in any one of claims 7 to 9, shaped and set in the form of a construction article, wherein optionally theconstruction article is selected from a panel, a board, a concrete masonry unit, a block, a paver, a tile, a column, a slab, a step, a kerb, an edging, a worktop, a benchtop, a seating, and combinations thereof.

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