A cement-free building material, its preparation method and application

Abstract

This invention belongs to the field of construction, specifically disclosing a cementless building material, its preparation method, and its application. The building material includes a waste matrix, the raw materials for which are construction waste and waste soil are used. The mass ratio of construction waste to waste soil is (0.1~9):1. The waste matrix is ​​prepared by mixing materials including construction waste and waste soil and then heat-treating and curing them at ≥1100℃. The waste matrix contains at least one of silicon dioxide, cubic aluminosilicate spinel, and γ-alumina spinel. The building material of this invention uses construction waste and waste soil as raw materials, which are widely available and inexpensive. Furthermore, the heat treatment and curing of construction waste and waste soil, along with the chemical reaction, improves the compressive strength of the resulting building material and reduces the heat treatment curing temperature, thus increasing production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of building technology, and specifically relates to a cement-free building material, its preparation method, and its application. Background Technology

[0002] Concrete, composed of cement and natural aggregates, is a commonly used material for constructing various engineering structures, including buildings, road surfaces, and retaining walls. However, cement production is also highly energy-intensive and generates significant carbon emissions because it requires heating raw materials to near 1400°C to form calcium silicates, which, upon hydration, bind with aggregates to impart strength to the material. Clay bricks are also an important building material. They are produced by heating clay containing hydrated aluminosilicates, alumina, and silicon to approximately 1200°C. Globally, over 3 billion cubic meters of clay are consumed annually to produce about 1.5 trillion bricks. The production of both cement and clay bricks generates substantial carbon dioxide emissions, burdening the environment. Developing new technologies for sustainable materials applicable to various applications, particularly in the construction sector, is essential for moving towards carbon neutrality.

[0003] Besides greenhouse gas emissions from material production, the disposal of building materials after use also poses serious environmental problems. During construction processes such as demolition, renovation, land leveling, and road paving, building materials are broken down into construction waste, which typically includes crushed concrete, broken rock, and broken bricks. Most construction waste is disposed of through landfill rather than incineration, as incineration produces toxic gases. However, landfilling construction waste hinders urban development, and the chemicals in the waste may be released, polluting soil and groundwater. On the other hand, waste soil, especially discarded bentonite and dredged marine sediments, is another major type of construction waste. It is generally defined as unwanted soil generated due to geological engineering and industrial processes. Typically, discarded bentonite is generated during construction as temporary supports and impermeable layers, while dredged marine sediments are formed from soil removed for land reclamation and waterway construction. Bentonite itself is also a problematic soil requiring foundation remediation. Therefore, new solutions are needed to address not only carbon emissions during material production but also waste management to achieve sustainable development. Ideally, different types of construction waste should be recycled and reused in the production of building materials to achieve sustainability.

[0004] To integrate sustainability into the production of building materials, researchers are exploring the use of construction waste to replace some of the natural aggregates in concrete. Extensive research has been conducted to determine the mechanical properties of concrete made using aggregates from construction waste (such as crushed concrete and waste soil). These methods still require the addition of carbon-intensive cement to bind these waste aggregates. In the production of clay bricks, some raw materials, especially clayey soil, have been replaced by industrial waste, including red mud, sewage sludge, recycled glass, fly ash, and steel slag. Organic waste from non-edible plant parts, such as nut shells, distiller's grains, fruit seeds, and rice husk ash, has also been used in brick production. Recently, there have been attempts to mix natural bentonite with recycled glass to produce lightweight glass-ceramic foam; simultaneously, there have been proposals to mix waste bentonite with incinerator bottom ash and sinter it to create ceramic filters for wastewater treatment. These developments suggest that using waste soil to replace clayey soil in the production of clay bricks is feasible. However, existing methods for producing sustainable building materials cannot recycle multiple types of construction waste in one go. Building materials made from construction waste generally have low strength and cannot meet usage requirements, which severely limits their industrial application. Furthermore, current technologies still cannot produce completely binder-free sustainable building materials by heating various types of construction waste. Summary of the Invention

[0005] In order to overcome at least one of the technical problems existing in the prior art, one of the objectives of the present invention is to provide a cement-free building material.

[0006] The second objective of this invention is to provide a method for preparing the above-mentioned cement-free building material.

[0007] The third objective of this invention is to provide the application of the above-mentioned cement-free building materials in the fields of walls, bridges, road surfaces, ceramic products, filters, wastewater treatment, landscaping, or prefabricated components.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of the present invention provides a cementless building material comprising a waste matrix, wherein the raw materials for preparing the waste matrix include construction waste and waste soil; the mass ratio of the construction waste to waste soil is (0.1~9):1; The waste matrix is ​​prepared by mixing materials including construction waste and waste soil and then heat-treating and solidifying them at ≥1100℃. The waste matrix contains at least one of silicon dioxide, cubic aluminum silicon spinel, and γ-alumina spinel.

[0009] In some embodiments of the present invention, the heat treatment curing temperature is 1100-1200°C.

[0010] In some embodiments of the present invention, the construction waste includes at least one of concrete waste, asphalt waste, waste stone powder, aggregate waste, and brick waste.

[0011] In some embodiments of the present invention, the construction waste contains minerals; the minerals include at least one of alkali metal oxides, alkaline earth metal oxides, alkaline earth metal hydroxides, alkaline earth metal inorganic acid salts, iron oxides, iron hydroxides, and iron inorganic acid salts.

[0012] In some embodiments of the present invention, the waste soil includes at least one of waste bentonite, marine sediments, waste quartz soil, red mud, sewage sludge, tailings, and loose fill.

[0013] In some embodiments of the present invention, the waste soil contains at least one mineral component selected from boron oxide, aluminum carbonate, aluminum oxide, aluminum hydroxide, aluminum silicate, iron oxide, iron hydroxide, iron carbonate, silicon dioxide, magnesium oxide, magnesium hydroxide, magnesium carbonate, and magnesium silicate.

[0014] In some embodiments of the present invention, the waste matrix does not contain cement.

[0015] In some embodiments of the present invention, the cement-free building material further includes a coating; the coating is disposed on at least one surface of the waste substrate; the coating includes at least one layer of a waterproof coating and a radiation cooling coating.

[0016] In some embodiments of the present invention, the material of the waterproof coating includes a silicon-based compound.

[0017] In some embodiments of the present invention, the material of the radiation cooling coating includes at least one of silicone containing metal oxides and silicone containing radiation cooling coating.

[0018] In some embodiments of the present invention, the metal oxide is selected from at least one of magnesium oxide, aluminum oxide, titanium oxide, and silicon oxide.

[0019] In some embodiments of the present invention, the mass ratio of the metal oxide to the silicone is 1:(1~19).

[0020] In some embodiments of the present invention, the radiation cooling coating includes at least one of titanium dioxide, barium sulfate, and polyvinylidene fluoride-hexafluoropropylene copolymer.

[0021] In some embodiments of the present invention, the mass ratio of the radiation cooling coating to the silicone is (0.1~9):1.

[0022] The second aspect of the present invention provides a method for preparing the cement-free building material described in the first aspect of the present invention, comprising the following steps: By mixing materials including construction waste, waste soil, and water, a waste mixture is obtained. The waste mixture is shaped and then heat-treated at a temperature ≥1100℃ to cause a chemical reaction and harden the waste mixture, resulting in a waste matrix. Optionally, a coating is prepared on the surface of the waste matrix to obtain the final product.

[0023] In some embodiments of the present invention, the heat treatment curing temperature is 1100-1200°C.

[0024] In some embodiments of the present invention, the heat treatment curing time is 1-8 hours.

[0025] In some embodiments of the present invention, the heat treatment curing is performed in air, a vacuum environment, or a protective atmosphere.

[0026] In some embodiments of the present invention, the heat treatment curing is carried out in a furnace, oven, kiln, or environmental test chamber.

[0027] In some embodiments of the present invention, the mass of the water is 5-50% of the total mass of the construction waste and waste soil.

[0028] In some embodiments of the present invention, the waste mixture is formed by compacting the waste mixture under a pressure of 0.5-50 MPa and then drying it.

[0029] In some embodiments of the present invention, the construction waste and / or the waste soil are dried and then crushed before use.

[0030] The third aspect of the invention provides the application of the cementless building materials described in the first aspect of the invention in the fields of walls, bridges, road surfaces, ceramic products, filters, wastewater treatment, landscaping, or prefabricated components.

[0031] The beneficial effects of this invention are as follows: The cement-free building material of this invention uses construction waste and waste soil as raw materials. The raw materials are widely available and inexpensive. Furthermore, the construction waste and waste soil undergo heat treatment and solidification, as well as a chemical reaction, which improves the compressive strength of the cement-free building material and reduces the heat treatment and solidification temperature during preparation, thereby increasing production efficiency. The resulting building material does not contain cement and can replace traditional high-carbon emission building materials, including concrete and clay bricks, achieving energy saving and carbon emission reduction. A detailed analysis follows: (1) The present invention reuses a variety of construction wastes to produce economically viable and sustainable materials without using new raw materials, such as cement and natural aggregates; (2) This invention improves the production efficiency of cement-free building materials by heat treatment curing, because the main components of waste soil and other construction waste cooperate with each other during the heating process, which can promote the occurrence of chemical reactions; (3) By surface treatment of waste substrate, the performance of the produced building materials can be improved, so that the produced building materials have effects such as radiation cooling and waterproofing, thereby increasing their application range; (4) This invention reduces reliance on high-carbon-emission building materials and lowers carbon dioxide emissions from the construction industry in order to achieve sustainable development and carbon neutrality goals.

[0032] The preparation method in this invention is the first developed method to produce economically viable and sustainable building materials using only different types of construction waste and waste soil, without the need to add new cement and natural aggregates. The produced materials can be used in a variety of engineering applications, especially in the construction industry. This helps to reuse urban solid waste and reduce the production of common carbon-intensive building materials such as concrete and clay bricks. Attached Figure Description

[0033] Figure 1 The diagram shows the unconfined compressive strength test results of the building materials prepared at different heat treatment curing temperatures in Examples 1, 1, and 3.

[0034] Figure 2 The unconfined compressive strength test diagrams are shown for the building materials prepared with different mass ratios of construction waste materials and waste soil materials in Examples 1-2 and Comparative Example 2. Detailed Implementation

[0035] The specific implementation of the present invention will be further described in detail below with reference to the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that any processes not specifically described in detail below are those that can be implemented or understood by those skilled in the art by referring to the prior art. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0036] In some embodiments of the present invention, the present invention provides a cementless building material comprising a waste matrix, wherein the raw materials for preparing the waste matrix include construction waste and waste soil; the mass ratio of construction waste to waste soil is (0.1~9):1; The waste matrix is ​​prepared by mixing materials including construction waste and soil and then heat-treating and curing them at ≥1100℃. The waste matrix contains at least one of silicon dioxide, cubic aluminum silicon spinel, and γ-alumina spinel.

[0037] In this invention, construction waste and waste soil undergo a chemical reaction during heat treatment and solidification to form a composite material selected from at least one of silica, cubic aluminosilicate spinel, and γ-alumina spinel, which then solidifies to form the building matrix. In some embodiments of this invention, the raw materials for preparing the waste matrix do not include cement. The building materials in this invention do not contain cement; instead, they utilize construction waste and waste soil materials as raw materials, thereby achieving the recycling of construction waste and waste soil, and realizing sustainability and carbon neutrality.

[0038] In some embodiments of the present invention, the mass ratio of construction waste to waste soil is any value or a range formed by any two of the following: 0.1:1, 1:9, 1:3, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1.

[0039] In some embodiments of the present invention, the heat treatment curing temperature is 1100-1200°C. In some embodiments of the present invention, the heat treatment curing temperature is any value or a range formed by any combination of 1100°C, 1110°C, 1120°C, 1130°C, 1140°C, 1150°C, 1160°C, 1170°C, 1180°C, 1190°C, and 1200°C, for example, 1100-1150°C. During the heat treatment curing process, the waste mixture (i.e., waste soil and construction waste) forms chemical bonds and hardens, thereby becoming a sustainable material with the mechanical strength required for cement-free building materials. The alkali metal oxides and alkaline earth metal oxides contained in the construction waste can also improve heating efficiency, thereby increasing the production efficiency of cement-free building materials.

[0040] In some embodiments of the present invention, the raw materials for preparing the waste matrix further include water; in some embodiments of the present invention, the raw materials for preparing the waste matrix are construction waste, waste soil and water; in some embodiments of the present invention, the mass of water is 5-50% of the total mass of construction waste and waste soil.

[0041] In some embodiments of the present invention, the water content in the raw materials for preparing the waste matrix is ​​any value or a range formed by any combination of 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, and 50% of the total mass of construction waste and waste soil, for example, 10-20%, 5-10%, etc. The role of water is to improve the molding efficiency of the waste mixture.

[0042] In some embodiments of the present invention, construction waste refers to any useless and broken materials generated during the construction process, including but not limited to waste generated during demolition, renovation, ground leveling, and road paving. These construction wastes have strong inert properties and mainly include, but are not limited to, concrete, asphalt, gravel, construction debris, crushed stone blocks, rocks, aggregates, stones, broken glass, tiles, bricks, concrete fragments, gypsum board, and mixtures of the above materials. In some embodiments of the present invention, construction waste includes at least one of concrete waste, asphalt waste, waste stone powder, aggregate waste, and brick waste.

[0043] In some embodiments of the present invention, the construction waste contains minerals; the minerals include at least one of alkali metal oxides, alkaline earth metal oxides, alkaline earth metal hydroxides, alkaline earth metal inorganic acid salts, iron oxides, iron hydroxides, and iron inorganic acid salts. The minerals in the construction waste can act as fluxes and promote chemical reactions among substances in the waste soil.

[0044] In some embodiments of the present invention, the alkali metal oxide includes at least one of lithium oxide (Li2O), sodium oxide (Na2O), potassium oxide (K2O), rubidium oxide (Rb2O), and cesium oxide (Cs2O).

[0045] In some embodiments of the present invention, the alkaline earth metal oxide includes at least one of beryllium oxide (BeO), magnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO), and barium oxide (BaO).

[0046] In some embodiments of the present invention, the alkaline earth metal hydroxide includes at least one of calcium hydroxide and magnesium hydroxide.

[0047] In some embodiments of the present invention, the alkaline earth metal inorganic acid salt includes at least one of calcium carbonate, magnesium carbonate, magnesium silicate, and calcium silicate.

[0048] In some embodiments of the present invention, the iron oxide includes at least one of ferrous oxide (FeO), ferric oxide (Fe2O3), and ferric oxide (Fe3O4).

[0049] In some embodiments of the present invention, the hydroxide of iron is iron hydroxide.

[0050] In some embodiments of the present invention, the inorganic acid salts of iron include at least one of ferric carbonate, ferric chloride, and ferric sulfate. In some embodiments of the present invention, waste soil refers to any abandoned soil generated due to geological engineering, construction activities, and industrial processes, including but not limited to waste soil generated from land reclamation, slope improvement projects, infrastructure construction, site formation, excavation, waterway construction, mining, and wastewater treatment. Waste soil includes, but is not limited to, waste bentonite, dredged marine sediments, red mud, sewage sludge, tailings, loose fill, and mixtures thereof. In some embodiments of the present invention, waste soil includes at least one of waste bentonite, marine sediments, waste quartz soil, red mud, sewage sludge, tailings, and loose fill. The marine sediments in the present invention are derived from marine sediments such as marine sludge generated during marine dredging.

[0051] In some embodiments of the present invention, the waste soil contains at least one of metal oxides, metal hydroxides, metal carbonates, and silicon-based compounds. The metal oxides and silicon-based compounds in the waste soil of the present invention can undergo chemical reactions, thereby increasing the strength of the resulting cement-free building materials.

[0052] In some embodiments of the present invention, the waste soil contains at least one mineral component selected from boron oxide, aluminum carbonate, aluminum oxide, aluminum hydroxide, aluminum silicate, iron oxide, iron hydroxide, iron carbonate, silicon dioxide, magnesium oxide, magnesium hydroxide, magnesium carbonate, and magnesium silicate.

[0053] In some embodiments of the present invention, the raw materials for preparing the waste matrix are concrete waste and waste bentonite / marine sediment; the mass ratio of concrete waste to waste bentonite / marine sediment is 1:3, 1:1, or 3:1.

[0054] In some embodiments of the present invention, the raw materials for preparing the waste matrix are concrete waste, waste bentonite, and marine sediments; the mass ratio of concrete waste, waste bentonite, and marine sediments is 1:2:1, 1:1:2, or 2:1:1.

[0055] In some embodiments of the present invention, the waste mixture (i.e., construction waste and waste soil) contains hydrated aluminosilicate, alumina, and silica, allowing various types of construction waste and waste soil to be mixed in any mass ratio. The mass ratio of waste soil to construction waste can be 1:9 to 1:3, 1:9 to 2:3, 1:9 to 1:1, 1:9 to 3:2, 1:9 to 3:1, 1:3 to 3:1, 2:3 to 3:1, 1:1 to 3:1, or 3:2 to 3:1.

[0056] In some embodiments of the present invention, the mass of the waste soil is at least 10%, at least 25%, at least 40%, at least 50%, at least 60%, or at least 75% of the total mass of waste soil and construction waste. In some embodiments, the mass of the waste soil is 10%-25%, 10%-40%, 10%-50%, 10%-60%, 10%-75%, 25%-75%, 40%-75%, 50%-75%, 60%-75%, 25%-60%, 25%-50%, 25%-40%, or 40%-50% of the total mass of waste soil and construction waste. In some embodiments of the present invention, the mass of the waste soil is 10%, 25%, 40%, 50%, 60%, or 75% of the total mass of waste soil and construction waste.

[0057] In some embodiments of the present invention, the construction waste is concrete waste.

[0058] In some embodiments of the present invention, the construction waste includes brick fragments, concrete fragments, and gravel; in some embodiments of the present invention, the ratio of the mass of concrete fragments and gravel to the mass of brick fragments is (1-5):7; in some embodiments of the present invention, the ratio of the mass of concrete fragments and gravel to the mass of brick fragments is any value of 1:7, 2:7, 3:7, 4:7, 5:7, or a range formed by any two of them.

[0059] In some embodiments of the present invention, concrete aggregate and crushed stone can be mixed in any ratio, for example, 1:(0.1-10).

[0060] In some embodiments of the present invention, the waste soil includes waste bentonite and sand; in some embodiments of the present invention, the mass ratio of waste bentonite to sand in the waste soil is (1-15):1; in some embodiments of the present invention, the mass ratio of waste bentonite to sand in the waste soil is any value or a range formed by any two of the following: 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1.

[0061] In this invention, waste materials can undergo chemical reactions during heating (e.g., waste soil) and act as fluxes (e.g., crushed recycled concrete).

[0062] In some embodiments of the present invention, the waste matrix does not contain cement.

[0063] In some embodiments of the present invention, the cement-free building material further includes a coating; the coating is disposed on at least one surface of the waste substrate; the coating includes at least one layer of a waterproof coating and a radiation cooling coating.

[0064] In some embodiments of the invention, the material of the waterproof coating includes a silicon-based compound. The silicon-based compound can be sprayed or coated onto the surface of a waste substrate to achieve hydrophobicity and radiative cooling effects.

[0065] This waterproof coating can be any waterproof coating well known to those skilled in the art. In some embodiments of the present invention, the waterproof coating comprises a silicon-based compound, which includes silicones, silanes, and silicate compounds. In some embodiments of the present invention, the silicon-based compound includes, but is not limited to, silicones (e.g., polyalkylsiloxanes, polydimethylsiloxanes, etc.), silanes (e.g., dichlorodimethylsilane), silicates (e.g., potassium methylsilicate), and silicate compounds (e.g., sodium silicate, potassium silicate, sodium silicate, potassium methylsilicate, etc.).

[0066] In some embodiments of the present invention, the radiation cooling layer can be any radiation cooling layer known to those skilled in the art. In some embodiments of the present invention, the radiation cooling layer is a silicon-based compound; in some embodiments of the present invention, the radiation cooling layer can be coated onto the material surface by spraying a silicon-based compound (i.e., silicone).

[0067] In some embodiments of the present invention, the material of the radiation cooling coating includes at least one of silicone containing metal oxides and silicone containing radiation cooling coatings. The present invention further improves the radiation cooling effect by introducing metal oxides or radiation cooling coatings into the silicone.

[0068] In some embodiments of the present invention, the radiative cooling layer is improved by mixing silicone with metal oxides (including but not limited to magnesium oxide, aluminum oxide, titanium oxide, silicon oxide, and mixtures thereof). In some embodiments of the present invention, the mass ratio of metal oxide to silicone is 1:(1~19). In some embodiments of the present invention, the mass ratio of metal oxide to silicone should not exceed 50%, and is preferably 5%.

[0069] In some embodiments of the present invention, the coating is prepared by first applying a radiation cooling coating to the surface of the waste substrate, and then spraying a silicon-based compound to further enhance the cooling effect.

[0070] In some embodiments of the present invention, the metal oxide is selected from at least one of magnesium oxide, aluminum oxide, titanium oxide, and silicon oxide.

[0071] In some embodiments of the present invention, the radiation cooling coating includes at least one of titanium dioxide, barium sulfate, and polyvinylidene fluoride-hexafluoropropylene copolymer.

[0072] In some embodiments of the present invention, the mass ratio of radiation cooling coating to silicone is (0.1~9):1.

[0073] The cement-free building materials of this invention can be used in a wide range of projects, such as structural walls, retaining walls, partition walls, bridges, road surfaces, ceramic products, filters, wastewater treatment, landscaping, and prefabricated components.

[0074] The present invention also provides a method for preparing the above-mentioned cement-free building material, comprising the following steps: By mixing materials including construction waste, waste soil, and water, a waste mixture is obtained. The waste mixture is shaped and then heat-treated at a temperature ≥1100℃ to cause a chemical reaction and harden the waste mixture, resulting in a waste matrix. Optionally, a coating is prepared on the surface of the waste matrix to obtain the final product.

[0075] In some embodiments of the present invention, the coating is prepared by mixing the raw materials used to prepare the coating into a slurry, and then coating the slurry onto the surface of the waste substrate.

[0076] In some embodiments of the present invention, the heat treatment curing temperature is 1100-1200°C. In some embodiments of the present invention, the heat treatment curing temperature is any value or a range formed by any combination of 1100°C, 1110°C, 1120°C, 1130°C, 1140°C, 1150°C, 1160°C, 1170°C, 1180°C, 1190°C, and 1200°C, for example, 1100-1150°C. The molded waste mixture should be cured at a certain temperature during the process that allows some of the mixture to undergo a chemical reaction to form a bond and harden.

[0077] In some embodiments of the present invention, the heat treatment curing time is 1-8 hours; in other embodiments, the heat treatment curing time is any value or a range formed by any two of 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, and 8 hours, such as 1-7 hours, 1-6 hours, 1-5 hours, 1-4 hours, 2-4 hours, 3-4 hours, 2-3 hours, etc. The time required to cure the waste mixture should be sufficient for a portion of the waste mixture to undergo a chemical reaction and form a high-strength cement-free building material.

[0078] In some embodiments of the present invention, heat treatment curing is performed in air, vacuum, or a protective atmosphere.

[0079] In some embodiments of the present invention, the protective atmosphere is at least one gas selected from nitrogen, carbon dioxide, helium, neon, and argon.

[0080] The waste mixture should be cured in a temperature-controlled environment. In some embodiments of the invention, heat treatment curing is carried out in a furnace, oven, kiln, or environmental test chamber.

[0081] In some embodiments of the present invention, the mass of water is 5-50% of the total mass of the waste mixture. The mass percentage of water is any value or a range formed by any combination of 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, and 50%, for example: 5%-50%, 5%-40%, 5%-30%, 5%-20%, 10%-20%, 15%-20%, 5%-15%, 10%-15%, or 5%-10%, etc. The role of water is to improve the molding efficiency of the waste mixture.

[0082] In some embodiments of the present invention, the waste mixture is formed by compacting it under a pressure of 0.5-50 MPa and then drying it. In some embodiments of the present invention, the specific steps of forming the waste mixture are: filling the waste mixture into a mold, then compacting it under a pressure of 0.5-50 MPa, and then drying it.

[0083] In some embodiments of the invention, the waste mixture can be molded into any shape that can be formed by a mold to meet the intended application requirements of cement-free building materials. The shaped waste mixture can be spherical, cubic, cuboid, cylindrical, hollow, conical, pyramidal, sheet-like, tubular, etc.

[0084] In some embodiments of the present invention, the compacted axial stress is any value or a range formed by any two of the following: 0.5 MPa, 1 MPa, 5 MPa, 10 MPa, 15 MPa, 20 MPa, 25 MPa, 30 MPa, 35 MPa, 40 MPa, 45 MPa, and 50 MPa, for example, 0.5-50 MPa, 0.5-40 MPa, 0.5-30 MPa, 0.5-25 MPa, 0.5-20 MPa, 0.5-10 MPa, 0.5-5 MPa, 5-50 MPa, 10-50 MPa, 20-50 MPa, 25-50 MPa, 30-50 MPa, 40-50 MPa, 10-40 MPa, 10-25 MPa, 10-20 MPa, or 20-25 MPa. The waste mixture can be compressed by applying axial stress to assist the molding process. Methods for compressing waste mixtures can employ a variety of known equipment, including hammers, hydraulic presses, pneumatic motors, water-air mixers, hot presses, tampers, vibratory rammers, vibratory plate compressors, drums, and / or other compression techniques.

[0085] In some embodiments of the present invention, the drying of the waste mixture after compaction can be carried out by natural air drying or drying at 40-150°C, for example, drying can be carried out at temperatures of 60-150°C, 80-150°C, 90-150°C, 90-130°C, 90-110°C, 40-110°C, 60-110°C, and 80-110°C.

[0086] In some embodiments of the present invention, construction waste is dried and then pulverized before use. In other embodiments of the present invention, construction waste is dried, then pulverized and sieved before use to reduce its particle size and increase its surface area, thereby promoting increased strength of the prepared cement-free building material upon heating.

[0087] In some embodiments of the present invention, construction waste can be dried by natural air drying or at a temperature of 40-150°C, for example, at temperatures of 60-150°C, 80-150°C, 90-150°C, 90-130°C, 90-110°C, 40-110°C, 60-110°C, or 80-110°C.

[0088] In some embodiments of the present invention, construction waste is sieved using a 75μm-5mm sieve after being crushed; in some embodiments of the present invention, construction waste can be sieved using a 5mm, 4mm, 2mm, 1mm, 500μm, 100μm or 75μm sieve after being crushed.

[0089] In some embodiments of the invention, construction waste may be crushed and screened to reduce its particle size. Smaller particle size increases the surface area of ​​the construction waste, thereby improving the efficiency of heating the waste mixture. Several known methods can be used to control the particle size of construction waste, such as mechanical methods for reducing size, including screening, cutting, impact, compression, abrasion, tearing, crushing, grinding, pulverizing, spray milling, hammer milling, compression milling, and drum milling, or other size reduction techniques. In some embodiments of the invention, the particle size of the construction waste may be reduced first, and then screened through screens of sizes including, but not limited to, 10 mm, 5 mm, 4 mm, 3 mm, 2.36 mm, 2 mm, 1.18 mm, 1 mm, 600 μm, 300 μm, 150 μm, and 75 μm, to make the waste more uniform.

[0090] In some embodiments of the present invention, the waste soil is dried and then pulverized before use. In other embodiments of the present invention, the waste soil is dried, then pulverized and sieved before use to reduce its particle size and increase its surface area, thereby promoting increased strength of the prepared cementless building material upon heating.

[0091] In some embodiments of the present invention, the waste soil can be dried by natural air drying or at a temperature of 40-150°C, for example, at temperatures of 60-150°C, 80-150°C, 90-150°C, 90-130°C, 90-110°C, 40-110°C, 60-110°C, or 80-110°C.

[0092] In some embodiments of the present invention, the waste soil is sieved using a 75μm-5mm sieve after crushing; in some embodiments of the present invention, the waste soil can be sieved using a 5mm, 4mm, 2mm, 1mm, 500μm, 100μm or 75μm sieve after crushing.

[0093] The specific implementation of the present invention will be further described in detail below with reference to specific embodiments and comparative examples: Example 1 This example provides a method for preparing cement-free building materials, the specific steps of which are as follows: (1) The construction waste and waste soil were baked at 100°C for 24 hours to remove the moisture. Then they were crushed by a grinder and filtered through a 2 mm sieve to increase the surface area and improve the uniformity of the particles, thus obtaining construction waste material and waste soil material. The construction waste used in this example consists of the following materials by mass percentage: 70% brick fragments, 30% a mixture of concrete fragments and gravel, wherein the mass ratio of concrete fragments to gravel is 1:3. The waste soil used in this example is composed of the following materials by mass percentage: 90% waste bentonite and 10% sand.

[0094] Construction waste was taken from Shenzhen Huwei Environmental Protection Building Materials Co., Ltd.; the waste soil was taken from the public filler bank under the Civil Engineering and Development Department of Hong Kong, which was generated from old bentonite and sand recovered from the department's highway construction projects, after screening, filtration and dewatering.

[0095] (2) The screened construction waste materials and waste soil materials were mixed together at a mass ratio of 1:1 to obtain a waste mixture. To facilitate the molding of the waste mixture, deionized water was added evenly to the waste mixture, with the weight of the deionized water being 5% of the weight of the waste mixture. The moistened mixture was then placed in a metal mold and compacted using a hydraulic press. An axial stress of 25 MPa was applied during compaction. Afterward, the waste specimen was removed from the metal mold, and three duplicate samples were prepared. The diameter of the specimen was 50 mm and the height was 100 mm.

[0096] (3) Dry the waste specimens in an oven at 100°C for 24 hours. Then, transfer all specimens to a furnace, fill the furnace with air, and heat-treat and cure them at a high temperature. The heat treatment curing temperature is 1150°C, and the heating process lasts for 4 hours. After the heating process is completed, remove the specimens for testing.

[0097] Example 2 This example provides a method for preparing cement-free building materials, which differs from Example 1 only in that: in this example, construction waste materials and waste soil materials are mixed together in a mass ratio of 1:3.

[0098] Comparative Example 1 The only difference between the preparation method of the cement-free building material in this example and that in Example 1 is that the heat treatment curing temperature in this example is 800℃.

[0099] Comparative Example 2 This example provides a method for preparing cement-free building materials, which differs from Example 1 only in that: in this example, construction waste materials and waste soil materials are mixed together at a mass ratio of 1:0.

[0100] Comparative Example 3 The only difference between the preparation method of the cement-free building material in this example and that in Example 1 is that the heat treatment curing temperature in this example is 1000℃.

[0101] Performance testing: The strength of the building material specimens prepared in Examples 1-2 and Comparative Examples 1-3 was tested using unconfined compression tests. During the tests, the specimens were sheared at a rate of 1 mm per minute, and the axial stress and axial deformation of the specimens were measured using a load cell and a linear variable differential transformer. The obtained peak stress was defined as the strength of the building material specimen. Each test group was repeated three times, and the average strength data (± standard error) of the three repeated tests was calculated. The unconfined compressive strength test results of the cement-free building materials prepared in Example 1 and Comparative Examples 1 and 3 are as follows: Figure 1 As shown. The unconfined compressive strength test results of the cement-free building materials prepared in Examples 1-2 and Comparative Example 2 are as follows. Figure 2 As shown in Table 1, the strength test results of the building material specimens prepared in Examples 1-2 and Comparative Examples 1-3 are shown in Table 1 below.

[0102] Table 1 Strength test results of cement-free building materials

[0103] Depend on Figure 1As shown in Table 1, the unconfined compressive strength of the prepared building materials increases with increasing heat treatment curing temperature. The strengths after heat treatment curing at 800℃, 1000℃, and 1150℃ are 2.2 ± 0.08 MPa, 2.9 ± 0.11 MPa, and 22.1 ± 0.27 MPa, respectively. Compared to heat treatment curing at 800℃, the strengths of the building materials prepared by heat treatment curing at 1000℃ and 1150℃ are increased by 32% and 905%, respectively. During heat treatment curing at 800℃, the main processes involved in the waste mixture (i.e., construction waste and soil) are evaporation of physically adsorbed water and dehydroxylation. When the heat treatment curing temperature increases to 1000℃, chemical compounds, including cubic aluminosilicate spinel and γ-alumina spinel, are formed in the waste mixture, thereby improving the material strength. Until the heat treatment curing temperature reaches 1150℃, the minerals in the waste mixture are mainly transformed into amorphous silica with an interconnected crystalline network, thereby significantly improving the material strength. Figure 1 The test results demonstrate that the preparation method of this invention has been shown to recycle construction waste and soil through heating to produce sustainable cement-free building materials. The preparation method of this invention does not require the addition of new raw materials (such as cement and natural aggregates), which further reduces carbon emissions during the material production process. More importantly, after heating at 1150°C, the strength of the waste mixture exceeds the minimum strength requirements for building bricks, pedestrian bricks, and lightweight traffic paving bricks (ASTM C62-17 Standard Specification for Building Bricks; ASTM C902-22 Standard Specification for Pedestrian and Lightweight Traffic Paving Bricks). According to the American Society for Testing and Materials (ASTM) standards, the minimum strength requirement for building bricks is 10.3 MPa, while the strength requirement for pedestrian bricks and lightweight traffic paving bricks is 20.7 MPa. This indicates that the sustainable building materials prepared by the method of this invention are suitable for various engineering applications, especially for building construction including structural walls, retaining walls, partition walls, and road paving.

[0104] Depend on Figure 2As shown in Table 1, Example 2, using construction waste and waste soil at a mass ratio of 1:3 as raw materials, produced a building material with an unconfined compressive strength approximately 902% higher than that of Comparative Example 2. This indicates that the mixing of construction waste and waste soil effectively enhances the chemical reaction during the high-temperature heat treatment curing process, thereby increasing the strength of the building material after heating. Comparing Examples 1-2, it is evident that adding too much construction waste to the waste soil reduces the unconfined compressive strength of the prepared building material. Although the strength of the building material produced at a higher mass ratio (i.e., a 1:1 mass ratio of construction waste to waste soil) is somewhat reduced, it is still higher than the strength required for building bricks, pedestrian bricks, and lightweight traffic paving bricks (ASTM C62-17 Standard Specification for Building Bricks; ASTM C902-22 Standard Specification for Pedestrian and Lightweight Traffic Paving Bricks). This demonstrates that different proportions of construction waste and waste soil can be used to prepare cement-free sustainable materials that meet the quality standards required for various applications. Therefore, this provides greater flexibility for the reuse of construction waste and waste soil and material production.

[0105] The water absorption rate of the building materials prepared in Examples 1-2 was tested according to the following test method: First, the building materials were dried in an oven at 100°C for 24 hours, and their mass m0 was recorded. Then, the building materials were soaked in water for 24 hours, and after being taken out, the surface water was wiped dry, and their mass m1 was recorded. The water absorption rate was calculated as: water absorption rate = (m1-m0) / m0 × 100%. The water absorption rates of the building materials prepared in Examples 1-2 were all less than 20%, which is similar to that of traditional clay bricks.

[0106] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A cement-free building material, characterized in that: The cement-free building material includes a waste matrix, the raw materials for preparing the waste matrix include construction waste and waste soil; the mass ratio of the construction waste and waste soil is (0.1~9):1; The waste matrix is ​​prepared by mixing materials including construction waste and waste soil and then heat-treating and solidifying them at ≥1100℃. The waste matrix contains at least one of silicon dioxide, cubic aluminum silicon spinel, and γ-alumina spinel.

2. The cement-free building material according to claim 1, characterized in that: The construction waste includes at least one of concrete waste, asphalt waste, waste stone powder, aggregate waste, and brick waste; And / or, the construction waste contains minerals; the minerals include at least one of alkali metal oxides, alkaline earth metal oxides, alkaline earth metal hydroxides, alkaline earth metal inorganic acid salts, iron oxides, iron hydroxides, and iron inorganic acid salts; And / or, the waste soil includes at least one of the following: waste bentonite, marine sediments, waste quartz soil, red mud, sewage sludge, tailings, and loose fill. And / or, the waste soil contains at least one mineral component selected from boron oxide, aluminum carbonate, aluminum oxide, aluminum hydroxide, aluminum silicate, iron oxide, iron hydroxide, iron carbonate, silicon dioxide, magnesium oxide, magnesium hydroxide, magnesium carbonate, magnesium silicate, and other minerals.

3. The cement-free building material according to claim 1, characterized in that: The waste matrix does not contain cement.

4. The cement-free building material according to claim 1, characterized in that: The cement-free building material further includes a coating; the coating is disposed on at least one surface of the waste substrate; the coating includes at least one layer of a waterproof coating and a radiation cooling coating.

5. The cement-free building material according to claim 4, characterized in that: The waterproof coating material includes silicon-based compounds; And / or, the material of the radiation cooling coating includes at least one of silicone containing metal oxides and silicone containing radiation cooling coatings.

6. The cement-free building material according to claim 5, characterized in that: The metal oxide is selected from at least one of magnesium oxide, aluminum oxide, titanium oxide, and silicon oxide; And / or, the mass ratio of the metal oxide to the silicone is 1:(1~19). And / or, the radiation cooling coating includes at least one of titanium dioxide, barium sulfate, and polyvinylidene fluoride-hexafluoropropylene copolymer; And / or, the mass ratio of the radiation cooling coating to the silicone is (0.1~9):

1.

7. The method for preparing the cement-free building material according to any one of claims 1-6, characterized in that: Includes the following steps: By mixing materials including construction waste, waste soil, and water, a waste mixture is obtained. The waste mixture is shaped and then heat-treated at a temperature ≥1100℃ to cause a chemical reaction and harden the waste mixture, resulting in a waste matrix. Optionally, a coating is prepared on the surface of the waste matrix to obtain the final product.

8. The method for preparing cement-free building materials according to claim 7, characterized in that: The heat treatment curing temperature is 1100-1200℃; And / or, the heat treatment curing time is 1-8 hours; And / or, the heat treatment curing is performed in air, a vacuum environment, or a protective atmosphere; And / or, the heat treatment curing is carried out in a furnace, oven, kiln, or environmental test chamber.

9. The method for preparing cement-free building materials according to claim 7, characterized in that: The mass of the water is 5-50% of the total mass of the construction waste and soil.

10. The application of the cement-free building material according to any one of claims 1-6 in the fields of walls, bridges, road surfaces, ceramic products, filters, wastewater treatment, landscaping, or prefabricated components.

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