Physical foaming agent suitable for autoclaved aerated concrete as well as preparation method and application of physical foaming agent

Abstract

The invention relates to the field of concrete, and particularly discloses a physical foaming agent suitable for autoclaved aerated concrete as well as a preparation method and application of the physical foaming agent. The physical foaming agent is composed of a phase A and a phase B which are used in cooperation with each other, and the phase A comprises an anionic surfactant, a 5-8% ampholytic surfactant, lauroyl diethanolamine, polyacrylamide and water; the phase B is prepared from nano silicon dioxide, nano calcium silicate hydrate, a polycarboxylic acid water reducing agent and water. The physical foaming agent is mixed with slurry through a pre-foaming technology, accurate control over the foam structure is achieved, meanwhile, the physical foaming agent has the advantages of being resistant to high temperature, easy to mix and excellent in foam stability, and the problems of suffocation, sedimentation and mold collapse caused by the fact that the foaming speed of a traditional chemical foaming agent (such as aluminum powder and hydrogen peroxide) is not matched with the thickening speed of the slurry can be effectively solved.

Description

Technical Field

[0001] The present application relates to the field of concrete, and more specifically, to a physical foaming agent suitable for autoclaved aerated concrete, and a preparation method and application thereof. Background Art

[0002] Autoclaved aerated concrete (AAC) is a key building material. Its porous structure imparts excellent properties such as lightweight, thermal insulation, and sound insulation. It is widely used in modern architecture and has played a positive role in promoting energy conservation, environmental protection, and sustainable development in the construction industry. As the construction industry's performance requirements for AAC continue to increase, ensuring the stability of its pore structure and the reliability of its products has become a key research topic.

[0003] In traditional autoclaved aerated concrete production, there's a mismatch between aluminum fume gas generation and slurry thickening. This mismatch can lead to multiple problems: ① Pore structure degradation, such as bubbles merging to form interconnected pores or large localized pores, reducing compressive strength; ② Body defects, such as insufficient gas generation height, subsidence, or shrinkage cracks; and ③ Decreased process stability, manifested as bubbling, boiling, and even mold collapse, seriously impacting yield.

[0004] Aluminum powder, a gas-generating agent, reacts in alkaline slurries to generate hydrogen and form bubbles. The gas generation rate is affected by factors such as the aluminum powder particle size, surface coating process (such as the amount of stearic acid added), slurry temperature, and alkalinity. For example, if the aluminum powder is too fine, it will generate gas prematurely, with large amounts of gas produced during the mixing phase, forming large bubbles or overflowing. If the aluminum powder is too coarse, gas generation will be delayed, with gas generation continuing even after the slurry enters the thickening phase, causing gas holding or bubbling. Slurry thickening relies on the hydration reaction of lime and cement to form a gelled structure, and its rate is controlled by factors such as lime activity (effective calcium oxide content), digestion temperature, water-to-cement ratio, and mixing time. If the lime digests too quickly or is used in excessive amounts, the slurry will thicken prematurely, hindering bubble expansion, leading to gas holding, insufficient mold filling, or surface cracks. Conversely, if the thickening is too slow, bubbles cannot be fixed in time, causing mold collapse or pore collapse.

[0005] To address the mismatch between aluminum powder gassing and slurry thickening, various approaches are often employed. For one thing, the gassing rate is adjusted by optimizing the aluminum powder particle size, for example, by selecting aluminum powder of appropriate coarseness and fineness to avoid premature or delayed gassing. Furthermore, the lime ratio is adjusted, with the amount of lime used determined based on factors such as lime activity and digestion temperature, thereby controlling the slurry thickening rate. Furthermore, the mixing process is controlled, with precise control of parameters such as mixing time and water-to-cement ratio to achieve a certain balance between gassing and thickening. These approaches can improve the performance of autoclaved aerated concrete within certain limits, but they are complex to implement and require strict control of multiple variables.

[0006] At the same time, these traditional methods have significant drawbacks. When raw material properties fluctuate frequently, the slurry thickening time also fluctuates frequently, making it difficult to align aluminum powder gassing with the slurry thickening time. This can lead to deterioration of the pore structure, causing bubbles to merge to form interconnected pores or large localized pores. This can also cause embryo defects such as insufficient gassing height, sinking, or shrinkage cracks. Furthermore, it can reduce process stability, manifesting as bubbling, boiling, and even mold collapse, seriously affecting product yield and quality. Summary of the Invention

[0007] To address the aforementioned issues of air stagnation, sedimentation, and mold collapse caused by the mismatch between aluminum powder gasification and slurry thickening in autoclaved aerated concrete, this application provides a physical foaming agent suitable for autoclaved aerated concrete, as well as its preparation method and application. This foaming agent is mixed with the slurry through a pre-foaming process, achieving precise control of the foam structure. It also exhibits high-temperature resistance, easy mixing, and excellent foam stability, while also reducing waste generation.

[0008] This application adopts the following technical solutions: In a first aspect, the present application provides a physical foaming agent suitable for autoclaved aerated concrete, which consists of a phase A and a phase B used in conjunction with each other: The phase A comprises, by weight percentage, 22-38% of anionic surfactant, 5-8% of amphoteric surfactant, 2-5% of lauryl diethanolamine, 0.5-1.0% of polyacrylamide, and the balance is water; The phase B comprises, by weight percentage, 3-5% of nano silicon dioxide, 10-15% of nano calcium silicate hydrate, 2-5% of polycarboxylate water reducer, and the balance is water.

[0009] Furthermore, in the above-mentioned physical foaming agent, the mass ratio of phase A to phase B is 1:3-7.

[0010] Furthermore, the anionic surfactant includes at least two of sodium fatty alcohol polyoxyethylene ether carboxylate, sodium α-olefin sulfonate and sodium dodecylbenzene sulfonate.

[0011] Furthermore, the above-mentioned anionic surfactant includes sodium fatty alcohol polyoxyethylene ether carboxylate, sodium α-olefin sulfonate and sodium dodecylbenzene sulfonate. In the phase A, the mass percentage of sodium fatty alcohol polyoxyethylene ether carboxylate is 12-18%, the mass percentage of sodium α-olefin sulfonate is 5-10%, and the mass percentage of sodium dodecylbenzene sulfonate is 5-10%.

[0012] Furthermore, the above-mentioned amphoteric surfactant is dodecyl dimethyl amine oxide.

[0013] Furthermore, the particle size of the nano-calcium silicate hydrate is 50-100 nm, and the nano-calcium silicate hydrate is modified by hexadecyltrimethylammonium bromide.

[0014] Furthermore, the modification method of the nano-calcium silicate hydrate includes: First, pre-disperse nano-calcium silicate hydrate in water, add 0.02-0.03wt% cetyltrimethylammonium bromide solution, and perform ultrasonic mixing; The obtained mixture is then placed at 28-32° C. and stirred for 40-80 minutes to perform electrostatic self-assembly, and then washed and freeze-dried to obtain modified nano-hydrated calcium silicate.

[0015] In a second aspect, the present application provides a method for preparing the above-mentioned physical foaming agent suitable for autoclaved aerated concrete, which comprises: The anionic surfactant, the amphoteric surfactant and water are mixed in proportion, stirred and dissolved to form a base liquid; lauryl diethanolamine and polyacrylamide are added to the base liquid, stirred and dispersed evenly to obtain phase A; Mix nano-silica, nano-calcium silicate hydrate, polycarboxylate water reducer and water in proportion, and stir to form a homogeneous suspension to obtain phase B; The phase A and phase B are mixed with water and uniformly stirred, and then a high-pressure foaming machine is used to generate uniform foam with a pore size of ≤0.5 mm.

[0016] Furthermore, the mass ratio of the above-mentioned phase A, phase B and water is 1:3-7:40-50.

[0017] In a third aspect, the present application provides an application of the above-mentioned physical foaming agent suitable for autoclaved aerated concrete, which comprises: Adding the foam formed by the physical foaming agent into autoclaved aerated concrete slurry to obtain a mixed slurry, wherein the foam accounts for 2-8 wt% of the autoclaved aerated concrete slurry; The mixed slurry was stirred at 200-400 rpm for 3-6 minutes until uniform, and a vibrating rod was used to eliminate large bubbles; After pouring, wait for 2-4 hours, and then autoclave and cure at 190-210℃ for 6-8 hours.

[0018] In summary, this application has the following beneficial effects: 1. The physical foaming agent provided in this application is composed of a phase A and a phase B that are used in conjunction with each other. Phase A is a foaming and stabilizing base liquid, and phase B is a high-temperature resistant and enhanced dispersed phase. The foam of this physical foaming agent gradually secretes water and the foam pore size increases over time. Under high temperature conditions, the slurry thickens quickly, allowing the pore structure to be quickly fixed, ensuring sufficient gas height and excellent pore structure. Moreover, this physical foaming avoids the uncontrollable chemical gasification rate and reduces air holding and sedimentation.

[0019] 2. Phase A of the physical foaming agent in this application contains lauroyl diethanolamine and polyacrylamide, which stabilize foam, allowing the resulting foam to remain free of water for 25 minutes. Since autoclaved aerated concrete typically thickens in 30-40 minutes, the addition of this physical foaming agent maintains a good pore structure, reducing the risk of excessive settlement or even collapse caused by a short foam stabilization time.

[0020] 3. In the physical foaming agent phase B of this application, nano-silica fills voids and participates in the hydration reaction to enhance strength. Nano-calcium silicate hydrate rapidly hydrates at high temperatures to form a calcium silicate network, enhancing foam wall strength and improving high-temperature resistance. Furthermore, nano-calcium silicate hydrate acts as a crystal nucleation agent, accelerating the hydration reaction and shortening downtime, facilitating production turnover.

[0021] 4. In a preferred embodiment of the present application, the nano-calcium silicate hydrate is modified with cetyltrimethylammonium bromide. This modified nano-calcium silicate hydrate, due to the surface modification with cetyltrimethylammonium bromide, not only increases steric hindrance, preventing nanoparticle aggregation, but also enhances interfacial bonding with the slurry, improving reactivity in high-temperature environments. DETAILED DESCRIPTION

[0022] The embodiments of the present invention will be described in detail below with reference to the examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Specific conditions not specified in the examples are carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without indicating the manufacturer are all conventional products that can be purchased commercially.

[0023] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention. Example

[0024] Example 1 This embodiment provides a physical foaming agent suitable for autoclaved aerated concrete, and the preparation method thereof is as follows: (1) Prepare materials according to the recipe: Component A: 14.3% sodium fatty alcohol polyoxyethylene ether carboxylate, 5.2% sodium α-olefin sulfonate, 6.0% sodium dodecylbenzenesulfonate, 2.3% lauryl diethanolamine, 5.5% dodecyl dimethyl ammonium oxide, 0.6% polyacrylamide, and 66.1% water.

[0025] Component B: nano silicon dioxide 4.0%, nano calcium silicate hydrate 13.0%, water reducer 3.0%, water 80%.

[0026] (2) Preparation of phase A and phase B: Phase A: Mix sodium fatty alcohol polyoxyethylene ether carboxylate, sodium α-olefin sulfonate, and sodium dodecylbenzene sulfonate with water in appropriate proportions, and stir to dissolve to form a base liquid; add lauroyl diethanolamine and polyacrylamide to the base liquid, and stir to disperse uniformly to obtain Phase A; Phase B: Mix nano-silica, nano-calcium silicate hydrate, polycarboxylate water reducer and water in proportion, and stir to form a homogeneous suspension to obtain phase B; (3) Preparation of foam: Phase A, phase B and water were stirred and mixed in a mass ratio of 1:5:44, and uniform foam with a pore size of ≤0.5 mm was generated by a high-pressure foaming machine.

[0027] Examples 2-4 The difference between this embodiment and embodiment 1 lies in the formulation of phase A, as shown in Table 1: Table 1. Examples 5-6 The difference between this embodiment and embodiment 1 lies in the formulation of phase B, as shown in Table 2: Table 2. Example 7 The difference between this embodiment and embodiment 1 is that the nano-calcium silicate hydrate is modified with hexadecyltrimethylammonium bromide; The preparation method of the modified nano-hydrated calcium silicate comprises: (1) preparing a cetyltrimethylammonium bromide solution with a concentration of 0.02-0.03 wt%; (2) pre-dispersing nano-calcium silicate hydrate with a particle size of 50-100 nm in water, adding a 0.02-0.03 wt% hexadecyltrimethylammonium bromide solution, and performing ultrasonic mixing; (3) The resulting mixture was stirred at 28-32° C. for 40-80 minutes to perform electrostatic self-assembly, and the resulting reaction product was centrifuged and washed three times with a 50% ethanol solution to remove physically adsorbed hexadecyltrimethylammonium bromide.

[0028] (4) The washed reaction product is pre-frozen at -20°C and then freeze-dried to obtain loose powdered modified nano-hydrated calcium silicate.

[0029] Example 8 The difference between this embodiment and embodiment 1 is that: (4) Preparation of foam: Phase A, phase B and water were stirred and mixed in a mass ratio of 1:2:44, and uniform foam with a pore size of ≤0.5 mm was generated by a high-pressure foaming machine.

[0030] Example 9 The difference between this embodiment and embodiment 1 is that: (4) Preparation of foam: Phase A, phase B and water were stirred and mixed in a mass ratio of 1:9:44, and uniform foam with a pore size of ≤0.5 mm was generated by a high-pressure foaming machine.

[0031] The foam density and standing time without water bleeding provided in the above examples or comparative examples were statistically analyzed, and the results are shown in Table 3: Table 2. As can be seen from Table 3: The foam density of the foam liquid provided in Examples 1-9 after foaming is 28-43 kg / m 3 The foam exhibits good uniformity and fluidity, and does not bleed after being allowed to stand for approximately 25 minutes. This indicates that it matches the thickening time of autoclaved aerated concrete, maintaining a good pore structure and reducing the risk of excessive settlement or even formwork collapse due to a short foam stabilization time. At the same time, the foam density should not be too low, and the viscosity should not be too high. Otherwise, the uniformity and fluidity of the foam after mixing with the slurry will be poor, leading to a deterioration in the pore structure of the autoclaved aerated concrete and a reduction in its compressive strength.

[0032] Combining Example 1 with Comparative Examples 1-2, it can be seen that the compounding of lauroyl diethanolamine and polyacrylamide in phase A can synergistically stabilize the foam and prolong the time that the foam can stand without water secretion.

[0033] Combining Example 1 with Comparative Examples 3-5, it can be seen that the addition of nano-silicon dioxide and nano-calcium silicate hydrate into phase B has little effect on the density of the foam and the standing time without water seepage.

[0034] Application Examples The foam formed by the physical foaming agent obtained in Examples 1 and 7 and Comparative Examples 1-5 was added to the autoclaved aerated concrete slurry to obtain a mixed slurry, in which the foam accounted for 5 wt% of the autoclaved aerated concrete slurry; the mixed slurry was stirred at 300 rpm for 5 minutes until uniform, and a vibrating rod was used to eliminate large bubbles; after pouring, it was allowed to stand for 3 hours and then autoclaved and cured at 200°C for 6 hours.

[0035] At the same time, the traditional aluminum powder gasification process was used as a control. After pouring, it was left to stand for 3-4 hours and then autoclaved and cured at 200℃ for 6 hours.

[0036] The thickening time, static dwell time, settlement height after pouring, and the compressive strength of the finished product after autoclaving for 6 hours were calculated. The results are shown in Table 4: Table 2. As can be seen from Table 2: Compared with the traditional aluminum powder gasification process, the autoclaved aerated concrete of Example 1 of this solution has reduced large pores, improved bubble uniformity, shortened the static time by 17.5%, reduced the settlement height by 80%, and reduced the dry density by 55kg / m 3 , the compressive strength is increased by 0.2MPa.

[0037] Combining Example 1 with Comparative Examples 1-2, it can be seen that the combination of lauroyl diethanolamine and polyacrylamide synergistically enhances the effect, helps stabilize bubbles, matches the thickening time, enables the autoclaved aerated concrete to maintain a good pore structure, and obtains higher compressive strength while reducing the dry density.

[0038] Combining Example 1 with Comparative Examples 3-5, it can be seen that adding an appropriate amount of nano-silica and nano-calcium silicate hydrate can increase the thickness of the cell wall, improve the high temperature resistance of the foam, and enable it to maintain a good pore structure in autoclaved aerated concrete; at the same time, it can increase the skeleton density and increase the pore wall thickness, thereby improving the compressive strength.

[0039] Combining Example 1 with Example 7, it can be seen that after surface modification of nano-calcium silicate hydrate, the hydration reaction can be further accelerated, the static time can be reduced, and the compressive strength can be improved, indicating that the modified nano-calcium silicate hydrate can enhance the interfacial bonding with the slurry and improve the reaction activity in a high temperature environment.

[0040] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A physical foaming agent suitable for autoclaved aerated concrete, characterized in that: It consists of phase A and phase B that work together: The phase A comprises, by weight percentage, 22-38% of anionic surfactant, 5-8% of amphoteric surfactant, 2-5% of lauryl diethanolamine, 0.5-1.0% of polyacrylamide, and the balance is water; The phase B comprises, by weight percentage, 3-5% of nano silicon dioxide, 10-15% of nano calcium silicate hydrate, 2-5% of polycarboxylate water reducer, and the balance is water.

2. The physical foaming agent suitable for autoclaved aerated concrete according to claim 1, characterized in that: In the physical foaming agent, the mass ratio of phase A to phase B is 1:3-7.

3. The physical foaming agent suitable for autoclaved aerated concrete according to claim 1, characterized in that The anionic surfactant includes at least two of sodium fatty alcohol polyoxyethylene ether carboxylate, sodium α-olefin sulfonate and sodium dodecylbenzene sulfonate.

4. The physical foaming agent suitable for autoclaved aerated concrete according to claim 3, characterized in that: The anionic surfactant includes sodium fatty alcohol polyoxyethylene ether carboxylate, sodium α-olefin sulfonate and sodium dodecylbenzene sulfonate. In the phase A, the mass percentage of sodium fatty alcohol polyoxyethylene ether carboxylate is 12-18%, the mass percentage of sodium α-olefin sulfonate is 5-10%, and the mass percentage of sodium dodecylbenzene sulfonate is 5-10%.

5. The physical foaming agent suitable for autoclaved aerated concrete according to claim 1, characterized in that: The amphoteric surfactant is dodecyl dimethyl amine oxide.

6. The physical foaming agent suitable for autoclaved aerated concrete according to any one of claims 1 to 5, characterized in that The particle size of the nano calcium silicate hydrate is 50-100 nm, and the nano calcium silicate hydrate is modified by using hexadecyltrimethylammonium bromide.

7. The physical foaming agent suitable for autoclaved aerated concrete according to claim 6, characterized in that: The modification method of the nano-calcium silicate hydrate comprises: pre-dispersing the nano-calcium silicate hydrate in water, adding a 0.02-0.03 wt % hexadecyltrimethylammonium bromide solution, and performing ultrasonic mixing; The obtained mixture is then placed at 28-32° C. and stirred for 40-80 minutes to perform electrostatic self-assembly, and then washed and freeze-dried to obtain modified nano-hydrated calcium silicate.

8. A method for preparing a physical foaming agent suitable for autoclaved aerated concrete according to any one of claims 1 to 7, characterized in that: It includes: The anionic surfactant, the amphoteric surfactant and water are mixed in proportion, and stirred to dissolve to form a base liquid; Add lauroyl diethanolamine and polyacrylamide to the base liquid, stir and disperse them evenly to obtain phase A; Mix nano-silica, nano-calcium silicate hydrate, polycarboxylate water reducer and water in proportion, and stir to form a homogeneous suspension to obtain phase B; The phase A and phase B are mixed with water and uniformly stirred, and then a high-pressure foaming machine is used to generate uniform foam with a pore size of ≤0.5 mm.

9. The method for preparing a physical foaming agent suitable for autoclaved aerated concrete according to claim 8, characterized in that: The mass ratio of phase A, phase B and water is 1:3-7:40-50.

10. Use of the physical foaming agent suitable for autoclaved aerated concrete according to any one of claims 1 to 7, characterized in that: It includes: Adding the foam formed by the physical foaming agent into autoclaved aerated concrete slurry to obtain a mixed slurry, wherein the foam accounts for 2-8wt% of the autoclaved aerated concrete slurry; The mixed slurry was stirred at 200-400 rpm for 3-6 minutes until uniform, and a vibrating rod was used to eliminate large bubbles; After pouring, wait for 2-4 hours, and then autoclave and cure at 190-210℃ for 6-8 hours.

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