Salt-precipitation-resistant hydrophobic baking-free brick based on all-solid-waste cementing material and preparation method of salt-precipitation-resistant hydrophobic baking-free brick

Abstract

The invention relates to a salting-out-resistant hydrophobic baking-free brick based on an all-solid waste cementing material and a preparation method, and relates to the technical field of solid waste resource utilization and building materials. Comprising the following components in parts by weight: 25 parts of an all-solid waste cementing material, 50 parts of recycled aggregate, 20 parts of recycled concrete micro powder, 15 parts of water, 1-5 parts of an alkali-resisting agent and 0.5-3 parts of a water repellent agent, the all-solid waste cementing material is prepared from slag, fly ash, steel slag, desulfurized gypsum and red mud according to the mass ratio of 60: 20: 10: 5: 5. According to the baking-free brick prepared through the method, the high strength is kept, meanwhile, the water absorption rate can be reduced to 5% or below, the baking-free brick is remarkably superior to that of a conventional product, the freeze-thaw resistance and the impermeability are also greatly improved, the optimal balance among high strength, low water absorption and salt precipitation resistance is achieved, and the service life in the severe environment is effectively prolonged.

Description

Technical Field

[0001] This invention relates to the fields of solid waste resource utilization and building materials technology, and in particular to a salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious materials and its preparation method. Background Technology

[0002] All-solid-waste non-fired bricks are a type of brick building material made from industrial solid waste. They are mainly formed through the polymerization reaction of cementitious materials and physical compaction, and have the advantages of low energy consumption and large solid waste usage. However, existing all-solid-waste non-fired bricks have two main problems in practical applications: First, the solid waste raw materials, especially steel slag, red mud, and desulfurized gypsum, often contain soluble alkali metal salts (such as K⁺, Na⁺) and sulfates. During the use of the bricks, internal moisture will carry these soluble salts to the surface. After the moisture evaporates, white salt crystals precipitate out, forming "frost," which not only affects the appearance of the bricks, but also generates stress inside the bricks during the crystallization process, leading to loose structure, reduced strength, and deterioration of durability.

[0003] Currently, common methods to address these issues include extending the curing period or pre-treating the raw materials. However, these methods increase energy consumption and costs, and their effectiveness is limited. While simply adding hydrophobic agents can reduce water absorption, if the internal soluble salts are not effectively consolidated, the salts, along with a small amount of water, will still migrate internally and may precipitate from weak points in the hydrophobic coating, leading to salt accumulation and damage. Therefore, there is an urgent need to develop a synergistic technology that can fundamentally inhibit salt precipitation and impart hydrophobic properties to the brick. Summary of the Invention

[0004] The purpose of this invention is to address the above-mentioned problems by providing a salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious materials and its preparation method.

[0005] The first aspect of this invention provides a salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious materials, employing the following technical solution:

[0006] A salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material comprises the following components by weight: 25 parts of all-solid waste cementitious material, 50 parts of recycled aggregate, 20 parts of recycled concrete powder, 15 parts of water, 1-5 parts of alkali-resistant agent, and 0.5-3 parts of hydrophobic agent.

[0007] By adopting the above technical solution, using industrial solid waste, recycled concrete aggregate, and recycled concrete powder as the main raw materials, the synergistic treatment and high-value utilization of various solid wastes are realized, which is in line with the green and low-carbon sustainable development strategy. Through the combined use of alkali-resistant agents and hydrophobic agents, the highly active aluminosilicate gel formed by the hydration of alkali-resistant agents provides abundant bonding sites for hydrophobic agents, enabling the hydrophobic film to be firmly anchored through -Si-O-Si / Al- covalent bonds, thereby improving its stability. At the same time, the hydrophobic layer performs in-situ hydrophobic modification on the hydration products, blocking the intrusion of external moisture and corrosive ions, creating a dry environment for the long-term stability of the solidified products. While reducing the water absorption rate of the brick, it effectively solidifies soluble salt ions, significantly enhances the durability of the system, thereby reducing the probability of salt precipitation and improving the strength and durability of the non-fired bricks.

[0008] Preferably, it comprises the following components by weight: 25 parts of solid waste cementitious material, 50 parts of recycled aggregate, 20 parts of recycled concrete powder, 15 parts of water, 3 parts of alkali-resistant agent, and 1.5 parts of hydrophobic agent.

[0009] Preferably, the all-solid-waste cementitious material comprises slag, fly ash, steel slag, desulfurized gypsum, and red mud, with the mass ratio of each component being slag:fly ash:steel slag:desulfurized gypsum:red mud = 60:20:10:5:5, and the specific surface area of ​​the all-solid-waste cementitious material is 500 m². 2 / kg.

[0010] Preferably, the particle size of the recycled aggregate is 4.75–9 mm.

[0011] Preferably, the specific surface area of ​​the recycled concrete powder is 300–400 m². 2 / kg.

[0012] Preferably, the alkali-resistant agent is sodium aluminate.

[0013] Preferably, the hydrophobic agent is a silane emulsion.

[0014] By adopting the above technical solution, sodium aluminate directly consumes and solidifies soluble K⁺ and Na⁺ in solid waste through chemical reaction, reducing the total amount of precipitable salts. The silane emulsion forms a strong hydrophobic layer on the pore walls, greatly blocking the intrusion and migration of water, thus forming a solid barrier to inhibit salt precipitation. The hydration reaction of sodium aluminate generates a large number of secondary minerals with large specific surface areas and rich in silanol and aluminum hydroxyl groups, such as nanoscale hydrated calcium aluminosilicate (CASH) gel, ettringite, and zeolite-like phases. These newly formed phases provide far more abundant chemical bonding sites for the silanols (-Si-OH) produced after the hydrolysis of organosilanes than ordinary hydrated calcium silicate (CSH) gels. The silanols undergo condensation reactions with the hydroxyl groups on these surfaces to form strong -Si-O-Si- or -Si-O-Al- covalent bonds, allowing the hydrophobic organic long chains to be more firmly and persistently grafted onto the pore wall surface. This significantly improves the stability and aging resistance of the hydrophobic layer, avoiding the risk of failure of purely physically adsorbed hydrophobic agents due to long-term water immersion or physical wear. The silane emulsion undergoes an interfacial condensation reaction with the pore wall and the surface of the hydration products, which is equivalent to an in-situ hydrophobic functionalization of the hydrophilic aluminosilicate network generated by the alkali-resistant agent reaction, changing its surface from hydrophilic to hydrophobic. Even if a small amount of water vapor breaks through the external defense, it is difficult to wet and penetrate these key salt fixation sites, thereby greatly improving the long-term stability of the curing reaction and thus improving the strength and durability of the non-fired bricks.

[0015] A second aspect of the present invention provides a method for preparing the above-mentioned salt-resistant, hydrophobic, non-fired bricks based on all-solid waste cementitious materials, comprising the following steps:

[0016] S1. Raw material premixing: Dry mix all solid waste cementitious materials, recycled aggregates, recycled concrete powder and alkali-resistant agent, and obtain dry mix after uniform mixing.

[0017] S2, Mixing: Disperse the hydrophobic agent in the total water to form solution A, add solution A to the dry mixture prepared in S1 and mix wet to obtain the mixture;

[0018] S3. Pressing and Curing: The mixture obtained in S2 is pressed to form a brick blank. The brick blank is cured with a film at room temperature and then demolded. After demolding, it is cured for a period of time to obtain a salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material.

[0019] Preferably, in the above preparation method, the pressing pressure in step S3 is 20 MPa.

[0020] Preferably, in the above preparation method, the curing time at room temperature in step S3 is 24 hours, and the curing time after demolding is 28 days.

[0021] In summary, this application includes at least one of the following beneficial technical effects:

[0022] 1. Using industrial solid waste (slag, fly ash, steel slag, desulfurized gypsum, red mud), recycled concrete aggregate, and recycled concrete micro powder as main raw materials, this method achieves the synergistic treatment and high-value utilization of various solid wastes, aligning with the green and low-carbon sustainable development strategy. Through the combined use of alkali-resistant and hydrophobic agents, the highly active aluminosilicate gel formed by the hydration of the alkali-resistant agent provides abundant bonding sites for the hydrophobic agent, enabling the hydrophobic film to be firmly anchored through -Si-O-Si / Al- covalent bonds, thus enhancing its stability. Simultaneously, the hydrophobic layer performs in-situ hydrophobic modification on the hydration products, blocking the intrusion of external moisture and corrosive ions, creating a dry environment for the long-term stability of the solidified products. While reducing the water absorption rate of the brick, it effectively solidifies soluble salt ions, significantly enhancing the durability of the system, thereby reducing the probability of salting out and improving the strength and durability of the non-fired bricks.

[0023] 2. By combining sodium aluminate with a silane emulsion, synergistic function and enhanced performance are achieved. The alkali-resistant agent reacts to form a zeolite phase structure that solidifies alkali metal ions; the hydrophobic agent forms a stable hydrophobic film within the pores through chemical bonding, effectively blocking moisture migration.

[0024] 3. The highly active aluminosilicate gel formed by hydration of alkali-resistant agents provides abundant bonding sites for organosilanes, enabling the hydrophobic film to be firmly anchored through -Si-O-Si / Al- covalent bonds, thus improving its stability. At the same time, the hydrophobic layer performs in-situ hydrophobic modification on the hydration products, blocking the intrusion of external moisture and corrosive ions, creating a dry environment for the long-term stability of the cured products, and significantly enhancing the durability of the system.

[0025] 4. The non-fired bricks prepared by this method maintain high strength while reducing water absorption to below 5%, which is significantly better than conventional products. The freeze-thaw resistance and impermeability are also greatly improved, achieving the optimal balance between high strength, low water absorption and salt precipitation resistance, effectively extending the service life in harsh environments. Attached Figure Description

[0026] Figure 1 These are physical comparison images of the non-fired bricks prepared in some embodiments and comparative examples of this application. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0028] The reagents and raw materials used in the following examples are as follows. Other specific conditions not specified shall be performed according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0029] The sources of raw materials and reagents in the embodiments and comparative examples of this application are as follows:

[0030] Slag: Originates from steel plants, with a specific surface area of ​​500–600 m². 2 / kg;

[0031] Fly ash: originates from power plants, with a specific surface area of ​​500–600 m². 2 / kg, residue on 80μm square hole sieve is less than 15%;

[0032] Steel slag: originates from steel plants, with a specific surface area of ​​450-550 m² / kg;

[0033] Desulfurized gypsum: derived from power plants, with a calcium sulfate dihydrate content of not less than 95% and a specific surface area of ​​500-600 m². 2 / kg;

[0034] Red mud: originates from alumina plants, with a specific surface area of ​​450–600 m² / kg;

[0035] Recycled aggregate: Recycled concrete aggregate, derived from building demolition, with a particle size of 4.75–9 mm.

[0036] Recycled concrete powder: derived from building demolition, with a specific surface area of ​​350–400 m². 2 / kg;

[0037] Sodium aluminate: industrial grade, effective content ≥95%.

[0038] Sodium aluminosilicate: chemical composition Na₂O·Al₂O₃·xSiO₂·yH₂O, is a white powder with a specific surface area ≥400 m² / g.

[0039] Silane emulsion: The active ingredient is n-octyltriethoxysilane, with a solid content of 50%.

[0040] Calcium stearate emulsion: 40% solids content, made by dispersing calcium stearate in water. Other products not specified are commercially available products that can be obtained by conventional means.

[0041] I. Implementation Examples

[0042] Example 1

[0043] A salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material comprises: 25 parts of all-solid waste cementitious material, 50 parts of recycled concrete aggregate, 20 parts of recycled concrete powder, 15 parts of water, 1 part of sodium aluminate as an alkali resistant agent, and 0.5 parts of silane emulsion as a hydrophobic agent. The all-solid waste cementitious material includes slag, fly ash, steel slag, desulfurized gypsum, and red mud, with the mass ratio of each component being slag:fly ash:steel slag:desulfurized gypsum:red mud = 60:20:10:5:5.

[0044] A method for preparing salt-resistant, hydrophobic, non-fired bricks based on all-solid waste cementitious materials includes the following steps:

[0045] S1. Raw material premixing: Dry mix the solid waste cementitious material, recycled concrete aggregate, recycled concrete powder and sodium aluminate until uniformly mixed to obtain dry mix.

[0046] S2. Mixing: Disperse the silane emulsion in total water to form solution A, then add solution A to the dry mixture prepared in S1 and mix it wet to obtain the mixture.

[0047] S3. Pressing and curing: The mixture obtained in S2 is pressed into shape under a pressure of 20 MPa to obtain a brick blank. The brick blank is cured with a film at room temperature for 24 hours and then demolded. It is then cured at room temperature for 28 days to obtain the whole solid waste salt-resistant hydrophobic non-fired brick.

[0048] Example 2

[0049] A salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material comprises: 25 parts of all-solid waste cementitious material, 50 parts of recycled concrete aggregate, 20 parts of recycled concrete powder, 15 parts of water, 1 part of sodium aluminate as alkali resistant agent, and 1.5 parts of silane emulsion as hydrophobic agent; the all-solid waste cementitious material includes slag, fly ash, steel slag, desulfurized gypsum, and red mud, with the mass ratio of each component being slag:fly ash:steel slag:desulfurized gypsum:red mud = 60:20:10:5:5.

[0050] The preparation method of a salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material is the same as that in Example 1, and will not be repeated here.

[0051] Example 3

[0052] A salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material comprises: 25 parts of all-solid waste cementitious material, 50 parts of recycled concrete aggregate, 20 parts of recycled concrete powder, 15 parts of water, 1 part of sodium aluminate as an alkali resistant agent, and 3 parts of silane emulsion as a hydrophobic agent; the all-solid waste cementitious material includes slag, fly ash, steel slag, desulfurized gypsum, and red mud, with the mass ratio of each component being slag:fly ash:steel slag:desulfurized gypsum:red mud = 60:20:10:5:5.

[0053] The preparation method of a salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material is the same as that in Example 1, and will not be repeated here.

[0054] Example 4

[0055] A salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material comprises: 25 parts of all-solid waste cementitious material, 50 parts of recycled concrete aggregate, 20 parts of recycled concrete powder, 15 parts of water, 3 parts of sodium aluminate as alkali resistant agent, and 0.5 parts of silane emulsion as hydrophobic agent; the all-solid waste cementitious material includes slag, fly ash, steel slag, desulfurized gypsum, and red mud, with the mass ratio of each component being slag:fly ash:steel slag:desulfurized gypsum:red mud = 60:20:10:5:5.

[0056] The preparation method of a salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material is the same as that in Example 1, and will not be repeated here.

[0057] Example 5

[0058] A salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material comprises: 25 parts of all-solid waste cementitious material, 50 parts of recycled concrete aggregate, 20 parts of recycled concrete powder, 15 parts of water, 3 parts of sodium aluminate as alkali resistant agent, and 1.5 parts of silane emulsion as hydrophobic agent; the all-solid waste cementitious material includes slag, fly ash, steel slag, desulfurized gypsum, and red mud, with the mass ratio of each component being slag:fly ash:steel slag:desulfurized gypsum:red mud = 60:20:10:5:5.

[0059] The preparation method of a salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material is the same as that in Example 1, and will not be repeated here.

[0060] Example 6

[0061] A salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material comprises: 25 parts of all-solid waste cementitious material, 50 parts of recycled concrete aggregate, 20 parts of recycled concrete powder, 15 parts of water, 3 parts of sodium aluminate as alkali resistant agent, and 3 parts of silane emulsion as hydrophobic agent; the all-solid waste cementitious material includes slag, fly ash, steel slag, desulfurized gypsum, and red mud, with the mass ratio of each component being slag:fly ash:steel slag:desulfurized gypsum:red mud = 60:20:10:5:5.

[0062] The preparation method of a salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material is the same as that in Example 1, and will not be repeated here.

[0063] Example 7

[0064] A salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material comprises: 25 parts of all-solid waste cementitious material, 50 parts of recycled concrete aggregate, 20 parts of recycled concrete powder, 15 parts of water, 5 parts of sodium aluminate as alkali resistant agent, and 0.5 parts of silane emulsion as hydrophobic agent; the all-solid waste cementitious material includes slag, fly ash, steel slag, desulfurized gypsum, and red mud, with the mass ratio of each component being slag:fly ash:steel slag:desulfurized gypsum:red mud = 60:20:10:5:5.

[0065] The preparation method of a salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material is the same as that in Example 1, and will not be repeated here.

[0066] Example 8

[0067] A salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material comprises: 25 parts of all-solid waste cementitious material, 50 parts of recycled concrete aggregate, 20 parts of recycled concrete powder, 15 parts of water, 5 parts of sodium aluminate as alkali resistant agent, and 1.5 parts of silane emulsion as hydrophobic agent; the all-solid waste cementitious material includes slag, fly ash, steel slag, desulfurized gypsum, and red mud, with the mass ratio of each component being slag:fly ash:steel slag:desulfurized gypsum:red mud = 60:20:10:5:5.

[0068] The preparation method of a salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material is the same as that in Example 1, and will not be repeated here.

[0069] Example 9

[0070] A salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material comprises: 25 parts of all-solid waste cementitious material, 50 parts of recycled concrete aggregate, 20 parts of recycled concrete powder, 15 parts of water, 5 parts of sodium aluminate as alkali resistant agent, and 3 parts of silane emulsion as hydrophobic agent; the all-solid waste cementitious material includes slag, fly ash, steel slag, desulfurized gypsum, and red mud, with the mass ratio of each component being slag:fly ash:steel slag:desulfurized gypsum:red mud = 60:20:10:5:5.

[0071] The preparation method of a salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material is the same as that in Example 1, and will not be repeated here.

[0072] II. Comparative Example

[0073] Comparative Example 1 (Blank Comparative Example)

[0074] A non-fired brick based on all-solid waste cementitious material differs from Example 1 in that it does not contain hydrophobic agents and alkali-resistant agents. It comprises 25 parts of all-solid waste cementitious material, 50 parts of recycled concrete aggregate, 20 parts of recycled concrete powder, and 15 parts of water. The all-solid waste cementitious material includes slag, fly ash, steel slag, desulfurized gypsum, and red mud, with the mass ratio of each component being slag:fly ash:steel slag:desulfurized gypsum:red mud = 60:20:10:5:5.

[0075] The difference between the preparation method of non-fired brick based on solid waste cementitious material and Example 1 is that S1 does not contain alkali-resistant agent, and in S2, water is directly poured into the dry mixture of S1 for mixing. The remaining steps are the same as in Example 1, and the product obtained is non-fired brick based on solid waste cementitious material.

[0076] Comparative Example 2

[0077] A non-fired brick based on all-solid waste cementitious material differs from Example 5 in that it does not contain a hydrophobic agent. It comprises 25 parts of all-solid waste cementitious material, 50 parts of recycled concrete aggregate, 20 parts of recycled concrete powder, 15 parts of water, and 3 parts of sodium aluminate as an alkali resistant agent. The all-solid waste cementitious material includes slag, fly ash, steel slag, desulfurized gypsum, and red mud, with the mass ratio of each component being slag:fly ash:steel slag:desulfurized gypsum:red mud = 60:20:10:5:5.

[0078] The difference between the preparation method of the non-fired brick based on solid waste cementitious material and Example 5 is that in S2, water is directly poured into the dry mixture in S1 for mixing, while the remaining steps are the same as in Example 5, and the product obtained is a non-fired brick based on solid waste cementitious material.

[0079] Comparative Example 3

[0080] A non-fired brick based on all-solid waste cementitious material differs from Example 2 in that it does not contain an alkali-resistant agent. It comprises 25 parts of all-solid waste cementitious material, 50 parts of recycled concrete aggregate, 20 parts of recycled concrete powder, 15 parts of water, and 1.5 parts of silane emulsion as a hydrophobic agent. The all-solid waste cementitious material includes slag, fly ash, steel slag, desulfurized gypsum, and red mud, with the mass ratio of each component being slag:fly ash:steel slag:desulfurized gypsum:red mud = 60:20:10:5:5.

[0081] The difference between the preparation method of the non-fired brick based on all-solid waste cementitious material and Example 2 is that S1 does not contain alkali-resistant agent, while the remaining steps are the same as in Example 1, and the product obtained is a non-fired brick based on all-solid waste cementitious material.

[0082] Comparative Example 4

[0083] A non-fired brick based on all-solid waste cementitious material differs from Example 5 in that the alkali-resistant agent used is sodium aluminosilicate. The brick comprises 25 parts of all-solid waste cementitious material, 50 parts of recycled concrete aggregate, 20 parts of recycled concrete powder, 15 parts of water, 3 parts of sodium aluminosilicate as the alkali-resistant agent, and 1.5 parts of silane emulsion as the hydrophobic agent. The all-solid waste cementitious material includes slag, fly ash, steel slag, desulfurized gypsum, and red mud, with a mass ratio of slag:fly ash:steel slag:desulfurized gypsum:red mud = 60:20:10:5:5.

[0084] The preparation method of a non-fired brick based on solid waste cementitious material is the same as that in Example 5, and will not be repeated here.

[0085] Comparative Example 5

[0086] A non-fired brick based on all-solid waste cementitious material differs from Example 5 in that the hydrophobic agent is calcium stearate emulsion, comprising 25 parts of all-solid waste cementitious material, 50 parts of recycled concrete aggregate, 20 parts of recycled concrete powder, 15 parts of water, 3 parts of sodium aluminate as alkali resistant agent, and 1.5 parts of calcium stearate emulsion as hydrophobic agent; the all-solid waste cementitious material includes slag, fly ash, steel slag, desulfurized gypsum, and red mud, with the mass ratio of each component being slag:fly ash:steel slag:desulfurized gypsum:red mud = 60:20:10:5:5.

[0087] The preparation method of a non-fired brick based on solid waste cementitious material is the same as that in Example 5, and will not be repeated here.

[0088] Comparative Example 6

[0089] A non-fired brick based on all-solid waste cementitious material differs from Example 5 in that the alkali-resistant agent is sodium aluminosilicate and the hydrophobic agent is calcium stearate emulsion. It comprises 25 parts of all-solid waste cementitious material, 50 parts of recycled concrete aggregate, 20 parts of recycled concrete powder, 15 parts of water, 3 parts of sodium aluminosilicate as the alkali-resistant agent, and 1.5 parts of calcium stearate emulsion as the hydrophobic agent. The all-solid waste cementitious material includes slag, fly ash, steel slag, desulfurized gypsum, and red mud, with a mass ratio of slag:fly ash:steel slag:desulfurized gypsum:red mud = 60:20:10:5:5.

[0090] The preparation method of a non-fired brick based on solid waste cementitious material is the same as that in Example 5, and will not be repeated here.

[0091] Comparative Example 7

[0092] A non-fired brick based on all-solid waste cementitious material differs from Example 5 in that it does not contain a hydrophobic agent and the alkali-resistant agent is sodium aluminosilicate. It includes 25 parts of all-solid waste cementitious material, 50 parts of recycled concrete aggregate, 20 parts of recycled concrete powder, 15 parts of water, and 3 parts of sodium aluminosilicate as the alkali-resistant agent. The all-solid waste cementitious material includes slag, fly ash, steel slag, desulfurized gypsum, and red mud, with the mass ratio of each component being slag:fly ash:steel slag:desulfurized gypsum:red mud = 60:20:10:5:5.

[0093] The difference between the preparation method of non-fired bricks based on solid waste cementitious materials and Example 5 is that water is directly poured into the dry mixture obtained in S1 in S2, while the remaining steps are the same as in Example 5, and will not be described in detail here.

[0094] Comparative Example 8

[0095] A non-fired brick based on all-solid waste cementitious material differs from Example 5 in that it does not contain alkali-resistant agents and the hydrophobic agent is calcium stearate emulsion. It includes 25 parts of all-solid waste cementitious material, 50 parts of recycled concrete aggregate, 20 parts of recycled concrete powder, 15 parts of water, and 1.5 parts of calcium stearate emulsion as the hydrophobic agent. The all-solid waste cementitious material includes slag, fly ash, steel slag, desulfurized gypsum, and red mud, with the mass ratio of each component being slag:fly ash:steel slag:desulfurized gypsum:red mud = 60:20:10:5:5.

[0096] The difference between the preparation method of the non-fired brick based on solid waste cementitious material and Example 5 is that there is no alkali-resistant agent in S1, while the remaining steps are the same as in Example 5, and will not be described in detail here.

[0097] III. Performance Test Experiments and Results

[0098] The non-fired bricks prepared in Examples 1-9 and Comparative Examples 1-8 were subjected to multiple tests under the same conditions.

[0099] To evaluate the inhibitory effect of the hydrophobic system on the overall water absorption behavior of bricks, the water absorption rate and compressive strength were tested using the full immersion method according to GB / T 2542-2012 "Test Methods for Masonry Bricks". The specific steps for determining the water absorption rate are as follows:

[0100] 1) Drying: Place the unfired brick samples with a molding and curing period of 28 days in an oven at 105±5℃ and dry them to constant weight (two consecutive weighings with an interval of 2 hours, and the mass change does not exceed 0.2%). Take them out and cool them to 20±5℃ at room temperature. Weigh the dried mass m0 of the sample, accurate to 0.01g.

[0101] 2) Immersion: Slowly place the sample into deionized water, ensuring the water level is at least 20 mm above the top of the sample, and let it stand for 24 hours at 20±2℃. To avoid severe erosion and damage to the hydrophobic layer, the sample should be slowly introduced into the water along an inclined plane to avoid direct impact of the water flow on the sample surface.

[0102] 3) Surface treatment and weighing: After soaking, take out the sample and let it stand at room temperature for 1 to 2 minutes. Quickly wipe away the free water adhering to the sample surface with a damp cloth (do not wipe repeatedly to avoid damaging the hydrophobic film on the surface). Immediately weigh the mass m1 at this time, accurate to 0.01g.

[0103] 4) Calculation: The water absorption rate of the sample is calculated using the following formula:

[0104]

[0105] Where W is the water absorption rate (%), m0 is the dry mass of the sample (g), and m1 is the mass of the sample after soaking in water for 24 h (g).

[0106] To evaluate the ability of unfired bricks to inhibit the migration and precipitation of soluble salts within the brick, the efflorescence (salting out) test method was based on the principles for surface salt efflorescence observation and grading in GB / T 2542-2012 "Test Methods for Masonry Bricks". The specific steps are as follows: Samples cured naturally for 28 days were dried to constant weight. After removing surface dust, they were placed upright in a shallow dish, and deionized water was added to the dish until the water level was 1 / 3 to 1 / 2 of the sample height. The samples were then left to stand at room temperature (20±5℃) for 7 days, maintaining a relatively constant water level. From the 7th day onwards, the surface moisture and soluble salt precipitation of the samples were observed and recorded daily. Curing continued for 3–4 days. Final evaluation was conducted when the efflorescence phenomenon stabilized. No salts were added to the medium during the test; the efflorescence phenomenon was entirely caused by the transport and crystallization of soluble salts such as K⁺ and Na⁺ contained within the brick to the surface under water-salt migration. Based on the distribution area and thickness of the surface salt bloom, the samples were classified into four levels: no bloom, slight bloom, obvious bloom, and severe bloom.

[0107] The test results for each group are shown in the table below:

[0108] Table 1. Comparison of performance of non-fired bricks in different groups

[0109] Group Compressive strength (MPa) Water absorption rate (%) Evaluation of efflorescence (salting out) Example 1 29.5 5.8 No frost Example 2 30.1 5.2 No frost Example 3 30.5 4.8 No frost Example 4 32.5 5.5 No frost Example 5 33.2 4.9 No blooming, surface is dry Example 6 32.8 4.5 No frost Example 7 31.0 5.4 No frost Example 8 31.8 5.0 No frost Example 9 31.5 4.5 No frost Comparative Example 1 22.1 14.5 Severe frost, covering the entire surface Comparative Example 2 28.5 12.8 There was virtually no bloom, but the surface was damp. Comparative Example 3 24.8 6.2 Mild spotting Comparative Example 4 29.8 5.5 No precipitation Comparative Example 5 30.5 7.8 Very slight frost Comparative Example 6 27.2 8.5 Very slight frost Comparative Example 7 27.0 13.5 Slight frost, surface damp Comparative Example 8 23.5 8.0 Noticeable frost

[0110] As shown in the table, the compressive strength, water absorption and salting-out index of the non-fired bricks prepared in Examples 1-9 are generally better than those in Comparative Examples 1-8. The overall performance of the comparative examples is generally deteriorated due to the lack of alkali-resistant agent / hydrophobic agent.

[0111] Regarding hydrophobic properties, water absorption rate is the core indicator for measuring the hydrophobicity of bricks. The lower the value, the stronger the hydrophobicity. The water absorption rate of the example groups ranged from 4.5% to 5.8%, while that of the comparative groups ranged from 5.5% to 14.5%. Only the water absorption rate of comparative example 4 was less than 6%. Comparative example 4 added both alkali-resistant agent and hydrophobic agent, only changing the type of alkali-resistant agent. This proves that the combination of alkali-resistant agent and hydrophobic agent can improve the hydrophobicity of non-fired bricks.

[0112] In terms of salt precipitation resistance, efflorescence is a phenomenon of powdering and peeling caused by the precipitation of soluble salts from the brick body. No efflorescence indicates excellent salt precipitation resistance.

[0113] Figure 1The figures and tables show a comparison of the physical samples from Examples 1 and 5, and Comparative Examples 1, 2, 3, and 6 of this application. As can be seen from the figures and tables, Examples 1-9 showed no efflorescence and consistent salt-leaching resistance. In the comparative examples, Comparative Example 1 (without alkali-resistant agent + without hydrophobic agent) showed severe efflorescence, with the surface completely covered; Comparative Example 2 (without hydrophobic agent) showed almost no efflorescence, but the surface was damp. This is because although sodium aluminate can react with K⁺ and Na⁺ ions to form an insoluble aluminosilicate network structure, solidifying alkali metal ions within the matrix and thus reducing soluble salt content to some extent, the product and the pore surface within the matrix are still inherently hydrophilic, unable to prevent the intrusion of external liquid water or moisture. Moisture can freely enter and exit, not only maintaining a high water absorption rate in the brick, making it prone to freeze-thaw damage, but also allowing residual salts that are not completely fixed or reaction products unstable under complex conditions to slowly migrate and precipitate under the carrier of moisture.

[0114] Comparative Example 3 (without alkali-resistant agent) showed slight spotting. This was due to the use of only silane emulsion, which forms a hydrophobic film on the capillary walls and significantly reduces water absorption through physical barriers. While this can cut off the main channel for liquid water to transport salt, under high ambient humidity or water vapor pressure, water molecules may still penetrate the hydrophobic film through diffusion or seep into the brick body through defects in the film. A single physical barrier cannot eliminate the soluble salts already present inside the brick body. The salts fixed inside will crystallize and precipitate at the pores near the surface or weak points of the hydrophobic film due to changes in internal humidity or temperature fluctuations, forming localized "frost". In some cases, the crystallization pressure may even cause the surface hydrophobic film to rupture, accelerating performance degradation.

[0115] Comparative Example 4 (alkali-resistant agent sodium aluminosilicate + hydrophobic agent silane emulsion) showed no precipitation; Comparative Example 5 (hydrophobic agent calcium stearate emulsion + alkali-resistant agent sodium aluminate) showed very slight blooming; Comparative Example 6 (alkali-resistant agent sodium aluminosilicate + hydrophobic agent calcium stearate emulsion) showed very slight blooming; Comparative Example 7 (no hydrophobic agent + alkali-resistant agent sodium aluminosilicate) showed slight blooming and a damp surface; Comparative Example 8 (no alkali-resistant agent + hydrophobic agent calcium stearate emulsion) showed obvious blooming. Therefore, it can be concluded that the combined use of alkali-resistant agent and hydrophobic agent can improve the salt precipitation resistance of non-fired bricks; the preferred alkali-resistant agent is sodium aluminate, and the preferred hydrophobic agent is silane emulsion.

[0116] Regarding compressive strength, which reflects the mechanical properties of the brick and briefly demonstrates the stability of the formula, the compressive strength of the example group is concentrated between 29.5 and 33.2 MPa, while the compressive strength of the comparative group is concentrated between 22.1 and 30.5 MPa. This indicates that the compressive strength of the example group is excellent, which indirectly verifies the stable synergistic effect of the alkali-resistant agent and the hydrophobic agent in the formula, providing a foundation for hydrophobicity and salt-leaching resistance.

[0117] In terms of overall performance, when the hydrophobic agent is fixed as silane emulsion, the sample using sodium aluminate as the alkali-resistant agent (Example 2) has a significantly higher compressive strength than the control group using sodium aluminosilicate (Comparative Example 4). When the alkali-resistant agent is fixed as sodium aluminosilicate, the sample using silane emulsion (Example 2) is significantly better than the control group using calcium stearate emulsion (Comparative Example 5) in terms of water absorption and salting-out inhibition. In addition, when an alternative combination (sodium aluminosilicate and calcium stearate emulsion, Comparative Example 7) is used simultaneously, its overall performance is the worst, further confirming the superiority of the combination of sodium aluminosilicate and silane emulsion.

[0118] Based on systematic dosage tests, the compressive strength and water absorption rate showed a clear regularity with the amount of admixture. When the amount of hydrophobic agent was fixed at 1.5 parts, the compressive strength first increased and then decreased with the increase of alkali-resistant agent, from 30.1 MPa at 1 part to 33.2 MPa at 3 parts, and then slightly decreased to 31.8 MPa at 5 parts. When the amount of alkali-resistant agent was fixed at 3 parts, the water absorption rate continued to decrease with the increase of hydrophobic agent, from 5.5% at 0.5 parts to 4.9% at 1.5 parts, and reached the lowest value of 4.5% at 3.0 parts. Through comprehensive consideration, Example 5 was determined to have a peak compressive strength of 33.2 MPa and a water absorption rate of 4.9%, and was therefore identified as the optimal formulation. Therefore, Example 5 is the optimal embodiment of this application.

[0119] In summary, this invention, through the compounding of sodium aluminate and silane emulsion, achieves functional integration from simple physicochemical reactions to the formation of chemical bonds at the microscopic level. The alkali-resistant agent reaction product provides a superior substrate for the hydrophobic agent, and the hydrophobic agent deeply protects and enhances the function of the cured product. This enables the prepared non-fired bricks to maintain high strength while maintaining a stable water absorption rate of approximately 5%, significantly better than conventional products. Freeze-thaw resistance and impermeability are also greatly improved, achieving an optimal balance between high strength, low water absorption, and salt precipitation resistance. This effectively extends the service life under harsh environments. Furthermore, since the main raw materials are industrial solid waste, it achieves the synergistic treatment and high-value utilization of various solid wastes, thus making non-fired bricks a high-performance, long-life green building material.

Claims

1. A salt-dissociation resistant hydrophobic non-sintered brick based on a total solid waste cementitious material, characterized in that: It includes the following components by weight: 25 parts of solid waste cementitious material, 50 parts of recycled aggregate, 20 parts of recycled concrete powder, 15 parts of water, 1-5 parts of alkali resistant agent, and 0.5-3 parts of hydrophobic agent.

2. The salt efflorescence resistant, hydrophobic, unfired brick based on a total solid waste cementitious material according to claim 1, characterized in that: It includes the following components by weight: 25 parts of solid waste cementitious material, 50 parts of recycled aggregate, 20 parts of recycled concrete powder, 15 parts of water, 3 parts of alkali-resistant agent, and 1.5 parts of hydrophobic agent.

3. The salt efflorescence resistant and hydrophobic unfired brick based on total solid waste cementitious material according to claim 1 or 2, characterized in that: The all-solid-waste cementing material includes slag, fly ash, steel slag, desulfurization gypsum and red mud, and the mass ratio of each component is slag:fly ash:steel slag:desulfurization gypsum:red mud = 60:20:10:5:5, and the specific surface area of the all-solid-waste cementing material is 500 m 2 / kg.

4. The salt efflorescence resistant, hydrophobic, unfired brick based on a total solid waste cementitious material according to claim 1, characterized in that: The recycled aggregate has a particle size of 4.75–9 mm.

5. The salt efflorescence resistant, hydrophobic, unfired brick based on a total solid waste cementitious material according to claim 1, characterized in that: The specific surface area of the recycled concrete micro powder is 300-400 m 2 / kg.

6. The salt efflorescence resistant, hydrophobic, unfired brick based on a total solid waste cementitious material according to claim 1, characterized in that: The alkali-resistant agent is sodium aluminate.

7. The salt efflorescence resistant, hydrophobic, unfired brick based on a total solid waste cementitious material according to claim 1, characterized in that: The hydrophobic agent is a silane emulsion.

8. A method for preparing a salt-lysis resistant hydrophobic non-burned brick based on a full-solid-waste cementitious material according to any one of claims 1-7, characterized in that: Includes the following steps: S1. Raw material premixing: Dry mix all solid waste cementitious materials, recycled aggregates, recycled concrete powder and alkali-resistant agent, and obtain dry mix after uniform mixing. S2, Mixing: Disperse the hydrophobic agent in the total water to form solution A, add solution A to the dry mixture prepared in S1 and mix wet to obtain the mixture; S3. Pressing and Curing: The mixture obtained in S2 is pressed to form a brick blank. The brick blank is cured with a film at room temperature and then demolded. After demolding, it is cured for a period of time to obtain a salt-resistant, hydrophobic, non-fired brick based on all-solid waste cementitious material.

9. The method of claim 8, wherein: The pressing pressure in S3 is 20 MPa.

10. The method of claim 8, wherein: The curing time for the film at room temperature in S3 is 24 hours, and the curing time after demolding is 28 days.

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