Foamed concrete based on micro-expansion effect of ettringite and its preparation method

Abstract

The present application relates to the technical field of foam concrete preparation, in particular to foam concrete based on ettringite micro-expansion effect and a preparation method thereof, the preparation method comprising the following steps: S1. preparation of modified ettringite; S2. dry material premixing; S3. preparation of additives; S4. concrete forming. The modified ettringite and modified calcium sulfate synergize to significantly improve the interfacial bonding strength of aggregate-matrix, so that the early and medium-term compressive strength of the composite system is improved; at the same time, the improved pore structure forms a triple action mechanism of "ettringite reinforcement-pore optimization-stress buffering": ettringite improves the interfacial bonding and shrinkage compensation capacity, the dissolution space of aggregate absorbs the volume deformation stress, the pore structure optimization reduces the humidity diffusion gradient, and the strength-shrinkage synergistic control is realized.

Description

Technical Field

[0001] This invention relates to the field of foamed concrete preparation technology, specifically to foamed concrete based on the micro-expansion effect of ettringite and its preparation method. Background Technology

[0002] With advancements in the construction industry, advanced green building methods such as prefabricated construction have gradually improved and are being widely applied. The construction area of ​​prefabricated buildings in my country surged from 160 million square meters in 2017 to 1.24 billion square meters in 2022. Currently, highly integrated modular construction is commonly used in prefabricated buildings. However, the design, production, transportation, and hoisting of prefabricated building modules are limited by their weight. Reducing the weight of the modules can effectively increase their integration, greatly improving the construction efficiency, building height, wind resistance, and earthquake resistance of prefabricated buildings.

[0003] Currently, the methods for reducing the weight of prefabricated building modules include: (1) using graded lightweight concrete for all concrete pouring structures, and using 2000 kg / m² for load-bearing structures in low-rise buildings that need to withstand more pressure. 3 For high-rise structures with relatively low load-bearing requirements, concrete with a strength of 1600-1800 kg / m³ is used. 3 This lightweight, high-strength concrete solution can effectively reduce the overall weight by 30%, to 1600-1800 kg / m³. 3 Lightweight high-strength concrete generally uses nano-glass cenosphere concrete to reduce weight, which leads to extremely high cost of this type of concrete. Its use in prefabricated buildings will greatly increase construction costs, and its application space in ordinary civil buildings is very low. (2) Lightweight design of the enclosure structure. Compared with the first scheme, this scheme is more economical: 500-900 kg / m² of lightweight concrete is used for the enclosure structure and various non-load-bearing enclosure structures in the building. 3 Lightweight concrete, such as steam-pressed concrete and foamed concrete, is used in prefabricated buildings. Foamed concrete has a highly porous internal structure, giving it lightweight properties and good thermal insulation and soundproofing performance. Its use in prefabricated buildings can effectively reduce the weight of individual modules while significantly improving the building's sound insulation and thermal insulation performance, raising the building's energy efficiency rating, and reducing carbon emissions. Furthermore, foamed concrete uses less cement and other binding materials than ordinary concrete, resulting in lower costs and carbon emissions, making it an ideal lightweight building envelope material.

[0004] However, due to the porous nature of foamed concrete, it has a large specific surface area and rapid water loss. The porous structure also tends to have more capillaries, which easily create negative pressure during water loss, leading to shrinkage. In engineering applications, foamed concrete is often used as large components. Uneven distribution of shrinkage deformation in large-volume components, coupled with constraints from reinforcing steel and other structures, easily leads to stress concentration. When the maximum tensile stress exceeds the tensile strength of the foamed concrete, cracking occurs. Cracking of foamed concrete components reduces their usability and durability. When used as wall cladding, stress can propagate to fireproofing, insulation, and decorative coatings, further degrading the building's performance. Therefore, reducing foamed concrete shrinkage, increasing its strength, and minimizing cracking are essential for improving the usability of foamed concrete in various spaces. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide foamed concrete based on the micro-expansion effect of ettringite and its preparation method.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] The preparation method of foamed concrete based on the micro-expansion effect of ettringite includes the following preparation steps:

[0008] S1. Preparation of modified ettringite:

[0009] S11. Mix aluminate cement and dihydrate gypsum at a mass ratio of 1:1.3-1.5, with a water-cement ratio of 0.45-0.5. After stirring for 3-5 minutes, pour the mixture into a mold and cure at a constant temperature of 23-25℃ for 20-24 hours. Then crush and grind the mixture through a 600-mesh sieve to obtain the ettringite precursor.

[0010] S12. By weight, add 4-6 parts of the modifier and 1-1.2 parts of sodium pyrophosphate to 180-200 parts of deionized water, and stir for 8-10 minutes at a speed of 300-350 r / min under a water bath at 38-42℃ to obtain the modifier.

[0011] S13. Add the modifier obtained in step S12 to the ettringite precursor, ultrasonically disperse it at a frequency of 40kHz for 25-30min, dry it under vacuum, and grind it through a 200-mesh sieve to obtain modified ettringite.

[0012] S2. Dry material premixing: Mix 45-50 parts cement, 19-23 parts slag, 6-8 parts glass cenospheres, and 5-6 parts modified calcium sulfate, and stir at a speed of 200-250 r / min for 2-4 min;

[0013] S3. Preparation of additives: Add 0.01-0.05 parts of hydroxypropyl methylcellulose, 0.2-0.3 parts of polycarboxylate superplasticizer, and 2-5 parts of modified ettringite to 25-30 parts of water, and stir at 200-300 r / min until dissolved;

[0014] S4. Concrete forming: Mix the dry materials with the additives and add 0.7-1.5 parts of polypropylene fiber and foam. Stir at 200-250 r / min for 1-3 min to obtain foamed concrete.

[0015] Preferably, the preparation of the modified additive includes the following steps:

[0016] S121. By mass, add 0.8-1 parts KH-560, 0.5-0.8 parts sodium gluconate, and 1-1.5 parts borax to 100-110 parts deionized water, and stir for 10-15 minutes in a water bath at 38-42℃ to obtain a preliminary mixture.

[0017] S122. Slowly add 1.3-1.5 parts of nano-silica powder to the preliminary mixture while dispersing it with ultrasound at a frequency of 20kHz. After the addition is completed, continue to sonicate for 10-15 minutes to obtain a suspension.

[0018] S123. The suspension is shaken and matured at 38-40℃ and 200-250r / min for 25-30min to obtain the modified additive.

[0019] Preferably, the preparation of modified calcium sulfate includes the following steps:

[0020] S21. By weight, add 0.6-0.8 parts of trisodium citrate, 0.4-0.6 parts of ammonium polyacrylate, and 1.2-1.5 parts of nano-alumina to 80-100 parts of deionized water and stir for 20-25 minutes;

[0021] S22. Mix 80-100 parts of anhydrous calcium sulfate with the mixture obtained in step S21, and then ball mill it at a speed of 300-400 r / min for 3-4 h. After that, vacuum dry it at 65-70℃ for 4-5 h and pass it through a 400-mesh sieve to obtain modified calcium sulfate.

[0022] Preferably, the foam in step S4 is obtained by diluting the foaming agent and water at a mass ratio of 1:300 and passing it through an air compressor, controlling the foam density to be 40±10g / L, and adding an amount of 0.5-1.5 times the total volume of dry material and additives.

[0023] Preferably, the mold size in step S11 is 40×40×160mm.

[0024] Preferably, the vacuum drying temperature in step S13 is 58-60℃ and the time is 3-4h.

[0025] Preferably, the stirring speed in step S121 is 300-350 r / min.

[0026] Preferably, the particle size of the nano-silicon powder is 50 nm.

[0027] Preferably, the stirring speed in step S21 is 450-500 r / min.

[0028] Foamed concrete based on the micro-expansion effect of ettringite was prepared by the above-mentioned preparation method.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1. The modified ettringite and modified calcium sulfate of this invention work synergistically to significantly improve the interfacial bonding strength between aggregate and matrix, thereby enhancing the early and mid-term compressive strength of the composite system. At the same time, the improved pore structure forms a triple mechanism of "ettringite reinforcement - pore optimization - stress buffering": ettringite enhances interfacial bonding and shrinkage compensation capabilities, aggregate dissolution space absorbs volumetric deformation stress, and pore structure optimization reduces the humidity diffusion gradient, thus jointly achieving synergistic control of strength and shrinkage.

[0031] 2. The foamed concrete slurry based on the micro-expansion effect of ettringite has good fluidity and stability. In actual use, it can increase the construction performance and the effective radiation radius of the mixing plant, help the matrix form an early transition pore structure, improve the later strength of the matrix, and reduce drying shrinkage. Attached Figure Description

[0032] Figure 1 This is a process flow diagram of the preparation process of foamed concrete based on the micro-expansion effect of ettringite according to the present invention;

[0033] Figure 2 This is a schematic diagram of the foamed concrete flowability mold used for flowability testing according to the present invention;

[0034] Figure 3 These are flowability curves of foamed concrete slurry in Embodiment 1 and Comparative Examples 1-4 of the present invention.

[0035] Figure 4 These are the stability curves of foamed concrete slurry in Embodiment 1 and Comparative Examples 1-4 of the present invention;

[0036] Figure 5 The drying density curves of the hardened foamed concrete matrix in Example 1 and Comparative Examples 1-4 of this invention are shown.

[0037] Figure 6The water absorption rate curves of foamed concrete in Embodiment 1 and Comparative Examples 1-4 of this invention are shown.

[0038] Figure 7 The bar chart shows the compressive strength of foamed concrete in Embodiment 1 and Comparative Examples 1-4 of this invention.

[0039] Figure 8 The XRD patterns of foamed concrete in Example 1 and Comparative Examples 1-4 of this invention on day 7;

[0040] Figure 9 The XRD patterns of foamed concrete in Example 1 and Comparative Examples 1-4 of this invention on day 14;

[0041] Figure 10 The XRD patterns of foamed concrete in Example 1 and Comparative Examples 1-4 of this invention on day 28;

[0042] Figure 11 The TG-DTG curves of foamed concrete in Example 1 and Comparative Examples 1-4 of this invention on day 7;

[0043] Figure 12 The TG-DTG curves of foamed concrete in Example 1 and Comparative Examples 1-4 of this invention on day 14;

[0044] Figure 13 The TG-DTG curves of foamed concrete in Example 1 and Comparative Examples 1-4 of this invention on day 28;

[0045] Figure 14 These are schematic diagrams of the scanning cross-sections of foamed concrete test blocks in Embodiment 1 and Comparative Examples 1-4 of the present invention;

[0046] Figure 15 This is a schematic diagram of the hole structure of foamed concrete under a microscope in Embodiment 1 of the present invention;

[0047] Figure 16 This is a bar chart showing the pore size distribution of foamed concrete in Embodiment 1 of the present invention. Detailed Implementation

[0048] The present invention will now be clearly and completely described in conjunction with embodiments thereof. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0049] Please see Figure 1-16 The present invention provides a technical solution:

[0050] Example 1

[0051] Preparation method of foamed concrete based on the micro-expansion effect of ettringite:

[0052] Before preparing foamed concrete based on the micro-expansion effect of ettringite, the modifying additives and modified calcium sulfate are prepared first:

[0053] The preparation of modified additives includes the following steps:

[0054] S121. Add 0.8g KH-560, 0.5g sodium gluconate and 1g borax to 100ml deionized water, and stir at 300r / min for 10min in a water bath at 38℃ to obtain a preliminary mixture;

[0055] S122. Slowly add 1.3g of nano-silicon powder (particle size 50nm) to the initial mixture while ultrasonically dispersing at a frequency of 20kHz. After the addition is completed, continue ultrasonic treatment for 10min to obtain a suspension.

[0056] S123. The suspension was shaken and matured at 38℃ and 200r / min for 25min to obtain the modified additive;

[0057] The preparation of modified calcium sulfate includes the following steps:

[0058] S21. Add 0.6g trisodium citrate, 0.4g ammonium polyacrylate, and 1.2g nano alumina to 80g deionized water and stir at 450r / min for 20min.

[0059] S22. Mix 80g of anhydrous calcium sulfate with the mixture obtained in step S21, and then ball mill it at 300r / min for 3h. After that, vacuum dry it at 65℃ for 4h and pass it through a 400-mesh sieve to obtain modified calcium sulfate.

[0060] S1. Preparation of modified ettringite:

[0061] S11. Aluminate cement and dihydrate gypsum are mixed at a mass ratio of 1:1.3 and a water-cement ratio of 0.45. After stirring for 3 minutes, the mixture is poured into a 40×40×160mm mold and cured at a constant temperature of 23℃ for 20 hours. The mixture is then crushed, ground, and passed through a 600-mesh sieve to obtain the ettringite precursor.

[0062] S12. Add 4g of the modifier and 1g of sodium pyrophosphate to 180g of deionized water, and stir at 300r / min for 8min in a 38℃ water bath to obtain the modifier.

[0063] S13. Add the modifier obtained in step S12 to the ettringite precursor, ultrasonically disperse it at a frequency of 40kHz for 25min, then vacuum dry it at 58℃ for 3h, grind it through a 200-mesh sieve to obtain modified ettringite.

[0064] S2. Dry material premixing: Mix 45g cement, 19g slag, 6g glass cenospheres and 5g modified calcium sulfate, and stir at 200r / min for 2min;

[0065] S3. Preparation of additives: Add 0.01g hydroxypropyl methylcellulose, 0.2g polycarboxylate superplasticizer and 2g modified ettringite to 25g water and stir at 200r / min until dissolved;

[0066] S4. Concrete Forming: The dry materials and additives are mixed, and 0.7g of polypropylene fiber and foam (obtained by diluting foaming agent and water at a mass ratio of 1:300 and passing it through an air compressor, controlling the foam density to 30g / L, with the addition amount being 0.5 times the total volume of the dry materials and additives) are added. The mixture is stirred at 200r / min for 1min to obtain foamed concrete. In this embodiment, the modified calcium sulfate content is 5%, and this embodiment is further named CAS5.

[0067] Example 2

[0068] Preparation method of foamed concrete based on the micro-expansion effect of ettringite:

[0069] Before preparing foamed concrete based on the micro-expansion effect of ettringite, the modifying additives and modified calcium sulfate are prepared first:

[0070] The preparation of modified additives includes the following steps:

[0071] S121. Add 1g KH-560, 0.8g sodium gluconate and 1.5g borax to 110ml deionized water, and stir at 350r / min for 15min in a water bath at 42℃ to obtain a preliminary mixture;

[0072] S122. Slowly add 1.5g of nano-silicon powder (particle size 50nm) to the initial mixture while dispersing it with ultrasound at a frequency of 20kHz. After the addition is completed, continue to sonicate for 15min to obtain a suspension.

[0073] S123. The suspension was shaken and matured at 40℃ and 250r / min for 30min to obtain the modified additive;

[0074] The preparation of modified calcium sulfate includes the following steps:

[0075] S21. Add 0.8g trisodium citrate, 0.6g ammonium polyacrylate, and 1.5g nano alumina to 100ml deionized water and stir at 500r / min for 25min.

[0076] S22. Mix 100g of anhydrous calcium sulfate with the mixture obtained in step S21, and then ball mill it at a speed of 400r / min for 4h. After that, vacuum dry it at 70℃ for 5h and pass it through a 400-mesh sieve to obtain modified calcium sulfate.

[0077] S1. Preparation of modified ettringite:

[0078] S11. Aluminate cement and dihydrate gypsum are mixed at a mass ratio of 1:1.5 and a water-cement ratio of 0.5. After stirring for 5 minutes, the mixture is poured into a 40×40×160mm mold and cured at a constant temperature of 25℃ for 24 hours. The mixture is then crushed, ground, and passed through a 600-mesh sieve to obtain the ettringite precursor.

[0079] S12. Add 6g of modifying additive and 1.2g of sodium pyrophosphate to 200ml of deionized water, and stir at 350r / min for 10min in a 42℃ water bath to obtain the modifier;

[0080] S13. Add the modifier obtained in step S12 to the ettringite precursor, ultrasonically disperse it at a frequency of 40kHz for 30min, then vacuum dry it at 60℃ for 4h, grind it through a 200-mesh sieve to obtain modified ettringite.

[0081] S2. Dry material premixing: Mix 50g cement, 23g slag, 8g glass cenospheres and 6g modified calcium sulfate, and stir at 250r / min for 4min;

[0082] S3. Preparation of additives: Add 0.05g hydroxypropyl methylcellulose, 0.3g polycarboxylate superplasticizer and 5g modified calcite to 30ml of water and stir at 300r / min until dissolved;

[0083] S4. Concrete forming: Mix the dry materials and additives, and add 1.5g of polypropylene fiber and foam (diluted with foaming agent and water at a mass ratio of 1:300, and obtained by passing through an air compressor, controlling the foam density to 50g / L, and adding 1.5 times the total volume of dry materials and additives). Stir at 250r / min for 3min to obtain foamed concrete.

[0084] Example 3

[0085] Preparation method of foamed concrete based on the micro-expansion effect of ettringite:

[0086] Before preparing foamed concrete based on the micro-expansion effect of ettringite, the modifying additives and modified calcium sulfate are prepared first:

[0087] The preparation of modified additives includes the following steps:

[0088] S121. Add 0.9g KH-560, 0.6g sodium gluconate and 1.6g borax to 112ml deionized water, and stir at 320r / min for 11min in a water bath at 40℃ to obtain a preliminary mixture;

[0089] S122. Slowly add 1.4g of nano-silicon powder (particle size 50nm) to the initial mixture while ultrasonically dispersing at a frequency of 20kHz. After the addition is completed, continue ultrasonic treatment for 11min to obtain a suspension.

[0090] S123. The suspension was shaken and matured at 39℃ and 220r / min for 26min to obtain the modified additive;

[0091] The preparation of modified calcium sulfate includes the following steps:

[0092] S21. Add 0.7g trisodium citrate, 0.5g ammonium polyacrylate, and 1.3g nano alumina to 90ml of deionized water and stir at 470r / min for 22min.

[0093] S22. Mix 90g of anhydrous calcium sulfate with the mixture obtained in step S21, and then ball mill it at a speed of 320r / min for 3.5h. After that, vacuum dry it at 66℃ for 4.5h and pass it through a 400-mesh sieve to obtain modified calcium sulfate.

[0094] S1. Preparation of modified ettringite:

[0095] S11. Aluminate cement and dihydrate gypsum are mixed at a mass ratio of 1:1.4 and a water-cement ratio of 0.46. After stirring for 4 minutes, the mixture is poured into a 40×40×160mm mold and cured at a constant temperature of 24℃ for 21 hours. The mixture is then crushed, ground, and passed through a 600-mesh sieve to obtain the ettringite precursor.

[0096] S12. Add 5g of modifying additive and 1.1g of sodium pyrophosphate to 190g of deionized water, and stir at 320r / min for 9min in a 40℃ water bath to obtain the modifier;

[0097] S13. Add the modifier obtained in step S12 to the ettringite precursor, ultrasonically disperse it at a frequency of 40kHz for 26min, then vacuum dry it at 59℃ for 3.5h, grind it through a 200-mesh sieve to obtain modified ettringite.

[0098] S2. Dry material premixing: Mix 46g cement, 20g slag, 7g glass cenospheres and 5.3g modified calcium sulfate, and stir at 220r / min for 3min;

[0099] S3. Preparation of additives: Add 0.02g hydroxypropyl methylcellulose, 0.25g polycarboxylate superplasticizer and 3g modified ettringite to 26g water and stir at 220r / min until dissolved;

[0100] S4. Concrete forming: Mix the dry materials and additives, and add 0.9g of polypropylene fiber and foam (obtained by diluting foaming agent and water at a mass ratio of 1:300 and passing it through an air compressor, controlling the foam density to 40g / L, and adding 0.8 times the total volume of dry materials and additives). Stir at 220r / min for 2min to obtain foamed concrete.

[0101] Example 4

[0102] Preparation method of foamed concrete based on the micro-expansion effect of ettringite:

[0103] Before preparing foamed concrete based on the micro-expansion effect of ettringite, the modifying additives and modified calcium sulfate are prepared first:

[0104] The preparation of modified additives includes the following steps:

[0105] S121. Add 0.95g KH-560, 0.7g sodium gluconate and 1.4g borax to 108ml deionized water, and stir at 340r / min for 14min in a water bath at 41℃ to obtain a preliminary mixture;

[0106] S122. Slowly add 1.45g of nano-silicon powder (particle size 50nm) to the initial mixture while ultrasonically dispersing at a frequency of 20kHz. After the addition is completed, continue ultrasonic treatment for 14min to obtain a suspension.

[0107] S123. The suspension was shaken and matured at 39℃ and 240r / min for 28min to obtain the modified additive;

[0108] The preparation of modified calcium sulfate includes the following steps:

[0109] S21. Add 0.75g trisodium citrate, 0.55g ammonium polyacrylate, and 1.4g nano alumina to 95g deionized water and stir at 480r / min for 24min.

[0110] S22. Mix 94g of anhydrous calcium sulfate with the mixture obtained in step S21, and then ball mill it at a speed of 380r / min for 3.5h. After that, vacuum dry it at 69℃ for 4.5h and pass it through a 400-mesh sieve to obtain modified calcium sulfate.

[0111] S1. Preparation of modified ettringite:

[0112] S11. Aluminate cement and dihydrate gypsum are mixed at a mass ratio of 1:1.45, with a water-cement ratio of 0.48. After stirring for 4.5 min, the mixture is poured into a 40×40×160 mm mold and cured at a constant temperature of 24℃ for 22 h. The mixture is then crushed, ground, and passed through a 600 mesh sieve to obtain the ettringite precursor.

[0113] S12. Add 5.5g of modifying additive and 1.15g of sodium pyrophosphate to 195ml of deionized water, and stir at 340r / min for 9min in a 41℃ water bath to obtain the modifier;

[0114] S13. Add the modifier obtained in step S12 to the ettringite precursor, ultrasonically disperse it at a frequency of 40kHz for 28min, then vacuum dry it at 59℃ for 3.5h, grind it through a 200-mesh sieve to obtain modified ettringite.

[0115] S2. Dry material premixing: Mix 49g cement, 22g slag, 7.5g glass cenospheres and 5.6g modified calcium sulfate, and stir at 240r / min for 3.5min;

[0116] S3. Preparation of additives: Add 0.04g hydroxypropyl methylcellulose, 0.28g polycarboxylate superplasticizer and 4g modified calcite to 28ml of water and stir at 280r / min until dissolved;

[0117] S4. Concrete forming: Mix the dry materials and additives, and add 1.3g of polypropylene fiber and foam (diluted with foaming agent and water at a mass ratio of 1:300, and obtained by passing through an air compressor, controlling the foam density to 45g / L, and adding 1.3 times the total volume of dry materials and additives). Stir at 240r / min for 2.5min to obtain foamed concrete.

[0118] Comparative Example 1

[0119] The only difference between Comparative Example 1 and Example 1 is that modified calcium sulfate was not added. The remaining steps are exactly the same in Comparative Example 1 and Example 1. This Comparative Example is further named Ref.

[0120] Comparative Example 2

[0121] The only difference between Comparative Example 2 and Example 1 is that the amount of modified calcium sulfate is controlled at 1%. The remaining steps are exactly the same in Comparative Example 2 and Example 1. This Comparative Example is further named CAS1.

[0122] Comparative Example 3

[0123] The only difference between Comparative Example 3 and Example 1 is that the amount of modified calcium sulfate is controlled at 10%. The remaining steps are exactly the same in Comparative Example 3 and Example 1. This comparative example is further named CAS10.

[0124] Comparative Example 4

[0125] The only difference between Comparative Example 4 and Example 1 is that the amount of modified calcium sulfate is controlled at 15%. The remaining steps are exactly the same in Comparative Example 4 and Example 1. This comparative example is further named CAS15.

[0126] Performance testing:

[0127] 1. Flowability test

[0128] The test was conducted according to the "Technical Specification for Application of Foamed Concrete" (JGJ / T 341—2014), using a copper mold with an inner diameter of 80mm and a height of 80mm. (Attached) Figure 2 This is a schematic diagram of the foamed concrete flowability mold used for flowability testing according to the present invention. Fresh foamed concrete slurry from Example 1 and Comparative Examples 1-4, mixed in a mixer, is poured into a flowability mold placed vertically on a plastic plate. The mold is tapped with a scraper to fully fill it, and then gently leveled with the scraper. The mold is slowly lifted, and the maximum horizontal diameter of the slurry is measured after 1 minute of even spreading. This process is repeated three times, and the average value is calculated. (See attached diagram.) Figure 3 The graphs show the flowability curves of foamed concrete slurry in Example 1 and Comparative Examples 1-4 of this invention. As shown in the graphs, the addition of calcium sulfate initially increases and then decreases the flowability of the foamed concrete slurry. At a modified calcium sulfate content of 5%, the slurry flowability reaches a maximum of 329 mm, a 4.1% increase compared to 316 mm in the Ref group (Comparative Example 1). It is generally believed that in the early stages of cement hydration, tricalcium aluminate (C3A) in the mineral phase rapidly hydrates in a saturated calcium hydroxide solution to form C4AH. 13 This is a very dense structure; excessive formation can lead to rapid setting or false setting in concrete paste. Modified calcium sulfate can improve paste fluidity because it can react with C4AH... 13 The rapid reaction produces ettringite, reducing C4AH. 13 Accumulation increases the fluidity of the slurry, but when the modified calcium sulfate content is further increased to 10% or 15%, the fluidity of the foamed concrete slurry decreases. This may be due to two reasons: Firstly, higher supersaturation can lead to the early formation of excessive ettringite that adheres to the surface of the cementitious material, forming a structure that reduces the fluidity of the foamed concrete. Secondly, in groups with higher modified calcium sulfate content, there is some undissolved calcium sulfate, which forms gypsum and creates a flaky structure in the slurry, resulting in reduced slurry fluidity.

[0129] 2. Stability test of foamed concrete slurry

[0130] Settlement of freshly mixed foamed concrete slurry in Examples 1 and Comparative Examples 1-4 was tested using a laser displacement sensor (Hepu GC02T-30, range 26-34mm, accuracy 0.002mm). Fresh slurry from the mixer was placed into a 50mL test tube, tapped to ensure complete filling, and the center of the test tube was placed under the laser. The sensor was adjusted to its range, connected to a computer, and data was recorded every 0.02s for 90 minutes. (Appendix) Figure 4 The figures show the slurry stability curves of foamed concrete in Example 1 and Comparative Examples 1-4 of this invention. Similar to fluidity, as the modified calcium sulfate content increases, the settlement distance of the freshly mixed foamed concrete slurry within 90 minutes first decreases and then increases, with the lowest settlement distance in the 5% content group, indicating that the foamed concrete slurry reaches its most stable state at this point. In the 1-5% content groups, the modified calcium sulfate reacts with the aluminum phase in cement and slag to generate an appropriate amount of ettringite. This ettringite, along with CSH and C-(A)-SH cementitious materials, forms structural links with cement stone, slag, and other cementitious materials, encapsulating the air bubbles and forming an early transition structure, increasing the dispersibility and stability between foams. In the 10% and 15% high-dosage calcium sulfate experimental groups, on the one hand, the excessive ettringite in the early matrix encapsulated slag and cement particles, slowing down the formation rate and amount of other hydration products, which was not conducive to the formation of transitional structures. On the other hand, there may have been excessive modified calcium sulfate in the high-dosage experimental groups. This modified calcium sulfate would consume the slurry water, leading to unstable foam and a large number of foam breakages. The slurry in the CAS15 experimental group showed a very large settling. The settling distance of all experimental groups showed a trend of first settling, then expanding, and then settling again. This was because there was unstable foam in the early stage, which disproportionated and floated in the slurry, causing the liquid surface to expand at 30 minutes.

[0131] 3. Dry density and water absorption rate

[0132] The true volume of the foamed concrete blocks in Example 1 and Comparative Examples 1-4 was calculated using the drainage method. The test was conducted three times to obtain the volume. Three 100mm × 100mm × 100mm foamed concrete blocks were placed in a 40℃ forced-air drying oven and dried for 4 hours until the mass change did not exceed 1g. The dry density of the foamed concrete was obtained by comparing the measured mass to volume.

[0133] Take 100mm×100mm×100mm foamed concrete specimens from Examples 1 and Comparative Examples 1-4, and dry them in a 60℃ forced-air drying oven until the mass change is less than 1g after 4 hours. Record the mass of the foamed concrete at this point. After cooling to room temperature, place them in a water tank at 20±5℃, add water to 1 / 3 of the specimen, and keep for 24 hours. Then add water to 2 / 3 of the specimen and keep for 24 hours. After pressing a grid on the specimen, add water to 30mm above the top surface and keep for 24 hours. Record the mass at this point and calculate using the following formula:

[0134]

[0135] In the formula:

[0136] —Water absorption rate of hardened foamed concrete test block (kg);

[0137] —Mass of foamed concrete after water absorption (kg);

[0138] —Dried mass of foamed concrete (kg).

[0139] The dry density curves of the hardened foamed concrete matrix in Example 1 and Comparative Examples 1-4 are attached. Figure 5 As shown, with the increase of modified calcium sulfate, the dry density of the hardened foamed concrete matrix gradually increases, with the highest dry density appearing in group CAS15 with 15% modified calcium sulfate content, reaching 782 kg / m³. 3 Compared to Ref group 757kg / m 3 Increased by 3.3%. As the supersaturation of sulfate increases, aluminum and iron ions dissolve more rapidly, accelerating the formation of more ettringite, making the matrix denser and reducing mass loss during the drying process. In foamed concrete with high dosage of modified calcium sulfate, there may be some undissolved modified calcium sulfate, which absorbs water and hydrates in the highly alkaline environment of cement to form gypsum, increasing the drying density.

[0140] The water absorption rate curves of foamed concrete in Example 1 and Comparative Examples 1-4 are attached. Figure 6 As shown, corresponding to the dry density, the content of modified calcium sulfate gradually decreased from 20% in the Ref group to 14.6% in the CAS15 group. This is because as the dry density of the foamed concrete dry matrix gradually increases, the pores and channels inside the hardened foamed concrete matrix decrease, the matrix gradually becomes denser, and the water absorption rate is reduced.

[0141] 4. Mechanical properties

[0142] Foamed concrete specimens of 100 mm × 100 mm × 100 mm from Example 1 and Comparative Examples 1-4 were dried in a 60°C forced-air drying oven until the mass change was less than 1 g over a 4-hour interval, and then loaded at a rate of 1.5 kN / s until failure. (See attached image) Figure 7 The bar charts shown are of the compressive strength of foamed concrete in Example 1 and Comparative Examples 1-4 of this invention. The experimental results show that with the increase of modified calcium sulfate content, the overall compressive strength of the foamed concrete first decreases, then increases, and then decreases again, reaching its optimal value at a 5% content. At lower content, the volume effect caused by the transformation of modified ettringite generated in the early stages of hydration into monosulfide-type hydrated calcium sulfoaluminate may lead to a decrease in compressive strength. At a 5% content, an appropriate amount of modified ettringite forms a transitional structure, optimizing the matrix structure. Furthermore, the sulfate ions provided by modified calcium sulfate induce matrix crystallization, consuming ions in the slurry and increasing the degree of hydration of the cementitious material, thus strengthening the matrix and gradually increasing its strength during hydration. The overall mechanical properties of the CAS5 experimental group exceed those of the Ref group.

[0143] To balance the paste density, the dosage of modified calcium sulfate was further increased, while the dosage of cement and slag was reduced by 8.7% and 12.4%, respectively, resulting in a decrease in the overall hydration products of the matrix. Excessive ettringite coated the cementitious particles, disrupting the stability of the transition structure and thus failing to compensate for the strength reduction caused by the decrease in hydration products. Excessive sulfate ions also induced the continued hydration of the matrix in later stages, producing ettringite that caused internal expansion of the matrix, damaging the pore structure and reducing the compressive strength of the hardened foamed concrete matrix in the later stages.

[0144] 5. XRD diffraction pattern analysis

[0145] The foamed concrete compressive strength test blocks from Examples 1 and Comparative Examples 1-4 were crushed, and the middle fragments were soaked in isopropanol solution for 24 h to stop hydration. They were then removed and dried in a 40 °C forced-air drying oven to constant weight. The test blocks were ground into powder using an agate mortar and pestle, and passed through a 200-mesh sieve. The powder was then scanned using a Mini Flex 600 XRD diffractometer with a scanning angle of 3-70°, a step size of 0.02°, and a scanning speed of 5 ° / min. (See attached image.) Figure 8-10 The XRD patterns of foamed concrete from Examples 1 and Comparative Examples 1-4 are shown on days 7, 14, and 28. In the figures, E represents ettringite, G represents gypsum, P represents calcium hydroxide, A represents tricalcium silicate, and K represents sulfoaluminate minerals. The main crystalline phase hydration products in the Ref group are monosulfide-type hydrated calcium sulfoaluminate (AFm) and calcium hydroxide. The sulfate ions in the Ref group mainly originate from gypsum added during cement production and are present in low concentrations. During hydration, sulfate ions and C4AH... 13After the reaction produces ettringite, it immediately reacts with aluminum ions to form AFm. In the CAS1 experimental group, with the incorporation of some sulfate ions, some ettringite is generated in the early stage of hydration of the foamed concrete. However, the sulfate ion concentration is insufficient, and as the hydration process continues, it cannot exist stably in the matrix. Instead, it reacts with subsequent hydration products to form AFm. It can be observed that the diffraction peak of ettringite weakens with age, while the diffraction peak of AFm gradually strengthens.

[0146] In the CAS5 experimental group, obvious XRD diffraction peaks of ettringite appeared in the foamed concrete. This indicates that as the sulfate ion concentration increases, sulfate ions continuously react with aluminum ion groups generated during the hydration of the cementitious material to form ettringite, which on the one hand reduces C4AH... 13 The amount of modified ettringite corresponds to the increase in fluidity; on the one hand, as the concentration of sulfate ions increases, the state of modified ettringite in the foamed concrete matrix remains stable and does not react with subsequent hydration products to transform into AFm. Etringite is generated in the slurry stage, providing a transitional structure in the early stages, reducing sedimentation before initial setting, and increasing the stability of the early-stage foamed concrete slurry. In the hardened matrix, modified ettringite optimizes the pore structure and the growth state of subsequent hydration products, improving the later-stage compressive strength of the foamed concrete. At a modified calcium sulfate content of 10%, the main crystalline phase hydration products in the foamed concrete are ettringite and CH4. No obvious diffraction peaks of modified calcium sulfate and gypsum were observed. In group CAS10, modified calcium sulfate was not excessive; calcium sulfate reacted with the Al(OH)4 group of aluminum ions to generate ettringite in the foamed concrete matrix. The decrease in various performance characteristics in group CAS10 mainly comes from the excess ettringite compared to group CAS5. The excessive amount of ettringite reduces the stability of the slurry in the early stage, and causes expansion and separation stress between the pore structures. If this stress continues to occur after the slurry hardens, it may also lead to matrix cracking, which is detrimental to the subsequent strength development.

[0147] The main crystalline phase hydration products in the foamed concrete of CAS15 are calcium hydroxide, ettringite, and gypsum. The appearance of gypsum diffraction peaks indicates that the modified calcium sulfate in the CAS15 experimental group was in excess, which became active in the alkaline environment of the cement paste, hydrating to form gypsum. The gypsum diffraction peaks gradually weakened between 7 and 28 days. As hydration progressed, the gypsum was gradually consumed to generate other hydration products. The ettringite generated later would affect the structure of the matrix, leading to a decrease in the compressive strength of the foamed concrete in the later stages.

[0148] 6. Thermogravimetric analysis (TG-DTG)

[0149] The foamed concrete compressive strength test blocks from Examples 1 and Comparative Examples 1-4 were crushed, and the middle fragments were soaked in isopropanol solution for 24 hours to stop hydration. They were then removed and dried in a 40°C forced-air drying oven to constant weight. The test blocks were ground into powder using an agate mortar and pestle, passed through a 200-mesh sieve, and tested using an SDT650 and STA449F3 simultaneous thermal analyzer under a nitrogen atmosphere, at temperatures ranging from 30 to 1000°C, with a heating rate of 10°C / min. (Appendix) Figure 11-13 The TG-DTG curves of foamed concrete in Example 1 and Comparative Examples 1-4 at 7 days, 14 days, and 28 days are shown.

[0150] The DTG curves of all samples showed weight loss peaks at 85–150 °C and 350–550 °C, respectively, indicating the weight loss due to the dehydration and decomposition of modified ettringite and calcium hydroxide. In the CAS15 experimental group, the characteristic weight loss peak of gypsum appeared at 100–150 °C. Combined with XRD qualitative analysis, it can be concluded that in the CAS15 group, anhydrous calcium sulfate was in excess. This excess anhydrous calcium sulfate was activated and hydrated to form gypsum. The formation of this gypsum consumes water during the process, slowing down the hydration of cement slag and resulting in slow strength development.

[0151] 7. Pore Structure Analysis

[0152] The pore structure of the foamed concrete in Example 1 was scanned using a hardened foamed concrete pore structure analyzer of Jianyan Huace HC-457. A 40 mm × 40 mm cross-section of the center of the test block was taken. The cross-section of the test block was first covered with black ink, and then the pore structure was filled with ultrafine barium sulfate. The number of wires per scan frame was set to 5, and the pore diameter of the foamed concrete cross-section was scanned.

[0153] Appendix Figure 14 These are schematic diagrams of scanned cross-sections of foamed concrete specimens from Embodiment 1 and Comparative Examples 1-4 of the present invention. The cross-sections are taken from the middle portion of the complete hardened foamed concrete matrix. To ensure image resolution under a pore structure microscope, and considering the porous nature of foamed concrete, the surface was first coated with black ink, then repeatedly smoothed with barium sulfate to enhance resolution under the microscope. A 25mm × 25mm area from the center of the cross-section was scanned. (See attached diagram.) Figure 15 This is a schematic diagram of the pore structure of foamed concrete under a microscope in Embodiment 1 of the present invention. It can be seen that the pore structure is clearly visible after being filled.

[0154] Appendix Figure 16This is a bar chart showing the pore size distribution of foamed concrete in Example 1 of the present invention. In the chart, the pore size of most experimental groups is below 0.5 mm. Combined with the analysis of slurry stability tests, as slurry stability increases, the proportion of small-sized air bubbles increases. An appropriate amount of modified calcium sulfate induces the cementitious material to hydrate in the early stages of hydration, generating ettringite that links the cementitious material particles on the foam surface, forming a structurally stable foam. This prevents the merging and rupture of air bubbles, resulting in a more uniform distribution of pores in the matrix and optimizing the pore structure of the hardened foamed concrete.

[0155] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing foamed concrete based on the micro-expansion effect of ettringite, characterized in that, The preparation steps include the following: S1. Preparation of modified ettringite: S11. Mix aluminate cement and dihydrate gypsum at a mass ratio of 1:1.3-1.5, with a water-cement ratio of 0.45-0.

5. After stirring for 3-5 minutes, pour the mixture into a mold and cure at a constant temperature of 23-25℃ for 20-24 hours. Then crush and grind the mixture through a 600-mesh sieve to obtain the ettringite precursor. S12. By weight, add 4-6 parts of the modifier and 1-1.2 parts of sodium pyrophosphate to 180-200 parts of deionized water, and stir for 8-10 minutes at a speed of 300-350 r / min under a water bath at 38-42℃ to obtain the modifier. S13. Add the modifier obtained in step S12 to the ettringite precursor, ultrasonically disperse it at a frequency of 40kHz for 25-30min, dry it under vacuum, and grind it through a 200-mesh sieve to obtain modified ettringite. S2. Dry material premixing: Mix 45-50 parts cement, 19-23 parts slag, 6-8 parts glass cenospheres, and 5-6 parts modified calcium sulfate, and stir at a speed of 200-250 r / min for 2-4 min; S3. Preparation of additives: Add 0.01-0.05 parts of hydroxypropyl methylcellulose, 0.2-0.3 parts of polycarboxylate superplasticizer, and 2-5 parts of modified ettringite to 25-30 parts of water, and stir at 200-300 r / min until dissolved; S4. Concrete forming: Mix the dry materials with the additives and add 0.7-1.5 parts of polypropylene fiber and foam. Stir at a speed of 200-250 r / min for 1-3 minutes to obtain foamed concrete. The preparation of the modified additive includes the following steps: S121. By mass, add 0.8-1 parts KH-560, 0.5-0.8 parts sodium gluconate, and 1-1.5 parts borax to 100-110 parts deionized water, and stir for 10-15 minutes in a water bath at 38-42℃ to obtain a preliminary mixture. S122. Slowly add 1.3-1.5 parts of nano-silica powder to the preliminary mixture while dispersing it with ultrasound at a frequency of 20kHz. After the addition is completed, continue to sonicate for 10-15 minutes to obtain a suspension. S123. The suspension is shaken and matured at 38-40℃ and 200-250r / min for 25-30min to obtain the modified additive; The preparation of the modified calcium sulfate includes the following steps: S21. By weight, add 0.6-0.8 parts of trisodium citrate, 0.4-0.6 parts of ammonium polyacrylate, and 1.2-1.5 parts of nano-alumina to 80-100 parts of deionized water and stir for 20-25 minutes; S22. Mix 80-100 parts of anhydrous calcium sulfate with the mixture obtained in step S21, and then ball mill it at a speed of 300-400 r / min for 3-4 h. After that, vacuum dry it at 65-70℃ for 4-5 h and pass it through a 400-mesh sieve to obtain modified calcium sulfate.

2. The method for preparing foamed concrete based on the micro-expansion effect of ettringite according to claim 1, characterized in that, The foam in step S4 is obtained by diluting the foaming agent and water at a mass ratio of 1:300 and passing it through an air compressor. The foam density is controlled at 40±10g / L, and the amount added is 0.5-1.5 times the total volume of dry material and additives.

3. The method for preparing foamed concrete based on the micro-expansion effect of ettringite according to claim 1, characterized in that, The mold dimensions in step S11 are 40×40×160mm.

4. The method for preparing foamed concrete based on the micro-expansion effect of ettringite according to claim 1, characterized in that, In step S13, the vacuum drying temperature is 58-60℃ and the time is 3-4 hours.

5. The method for preparing foamed concrete based on the micro-expansion effect of ettringite according to claim 1, characterized in that, The stirring speed in step S121 is 300-350 r / min.

6. The method for preparing foamed concrete based on the micro-expansion effect of ettringite according to claim 1, characterized in that, The particle size of the nano-silicon powder is 50 nm.

7. The method for preparing foamed concrete based on the micro-expansion effect of ettringite according to claim 1, characterized in that, The stirring speed in step S21 is 450-500 r / min.

8. Foamed concrete based on the micro-expansion effect of ettringite, characterized in that, The foamed concrete based on the micro-expansion effect of ettringite is prepared by the preparation method described in any one of claims 1-7.

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