A waterproofing admixture for autoclaved aerated concrete and its preparation method

Abstract

The application discloses an inner-mixing waterproof material for autoclaved aerated concrete, which comprises a mixture A and a mixture B in a mass ratio of 1:4, and a dispersing agent less than 0.5 wt% of the total mass of the mixture A and the mixture B; the mixture A comprises 5 wt% fine flaky expanded graphite, 5-10 wt% earthy graphite and 85-90 wt% aerated concrete waste; and the mixture B comprises 80-85 wt% modified light calcium carbonate, 10-15 wt% quicklime and 5 wt% silica powder. The application further discloses a preparation method of the inner-mixing waterproof material for autoclaved aerated concrete. The waterproof material has good compatibility with raw materials and bubbles of the autoclaved aerated concrete, the modified light calcium carbonate can improve the foaming of aerated concrete slurry, the pore diameter of the green body is fine and uniform, the green body collapse is reduced, and the influence on the batching scheme, the process condition, the pouring stability, the product quality is small.

Description

Technical Field

[0001] This invention relates to the field of wall material technology, specifically to a waterproofing material for autoclaved aerated concrete and its preparation method. Background Technology

[0002] Autoclaved aerated concrete (AAC) has advantages such as a wide availability of raw materials, resource conservation, waste utilization, and low transportation costs. However, AAC itself has high porosity and large surface free energy, which often leads to reduced strength and thermal insulation performance, as well as decreased frost resistance and durability due to water absorption. After absorbing water, the product is prone to large shrinkage during drying, resulting in reduced bonding strength with the finishing mortar during construction. This can cause problems such as hollow walls, mold, cracking, and large-area peeling, affecting the aesthetics of the building walls and shortening their service life.

[0003] Currently, the main methods for waterproofing autoclaved aerated concrete (AAC) are matrix structure optimization and modification using waterproofing agents. Matrix structure optimization improves the waterproofing performance of AAC by adjusting material formulations and process parameters to improve the pore structure and the crystal-to-colloid ratio of the pore walls. Reducing the water-to-material ratio is a common method. While a low water-to-material ratio helps reduce the water absorption of AAC, its improvement effect is limited in practical applications and may affect the stability of casting, the structure of pores, and the thickening and hardening speed of the green body, easily leading to unstable product quality or even product defects. Waterproofing agents are typically applied to AAC through surface coating or internal modification. Surface-coated waterproofing agents lose their waterproofing effect once the surface is damaged, while internally added waterproofing agents retain their waterproofing effect even after surface abrasion during transportation. Commonly used organic waterproofing agents include organosilicon waterproofing agents, fatty acid salt waterproofing agents, paraffin emulsion waterproofing agents, and water-based crystalline waterproofing agents. Inorganic waterproofing agents include chlorides, inorganic aluminates, and zirconates, which generally show good results when used in concrete. However, aerated concrete differs from ordinary concrete. The static curing process and steam curing process are crucial to ensuring the quality of aerated concrete. Ordinary waterproofing agents can affect the gasification, thickening, hardening, and steam curing processes of the slurry during static curing, or cause problems such as uneven pore structure, unqualified density, excessive static curing time, or excessive steam curing time.

[0004] Patent CN105036677A discloses an autoclaved aerated concrete (AAC) block or slab and its preparation method. This invention incorporates chlorides, organosilicon waterproofing agents, water-reducing agents, and calcined gypsum to reduce the water absorption rate of the blocks and improve their durability. However, in AAC production, the gas generation process of aluminum powder after pouring is slow, typically lasting 10-30 minutes. The addition of water-reducing agents lowers the water-to-material ratio, while chlorides accelerate the hydration of C3A in the cement. The calcium hydroxide formed by chlorides and cement hydration generates calcium chlorate, which is not easily soluble in water, reducing the alkalinity of the slurry. Furthermore, calcined gypsum reacts with fly ash and other ingredients to form ettringite, significantly increasing the slurry viscosity. In this alkaline environment, the aluminum powder reacts more slowly, and the gas generation resistance increases, potentially leading to insufficient gas generation height and making it difficult to meet the technical requirements for cutting the green body, not to mention the significantly increased density. Therefore, solving the compatibility problem between waterproofing agents and AAC raw materials and air bubbles is an urgent research issue.

[0005] Currently, ultrafine particles, such as nano-calcium carbonate, are used to fill the pores inside aerated concrete to improve its mechanical and durability properties. However, nano-calcium carbonate particles are small and prone to agglomeration, leading to high slurry consistency and high gas generation resistance in practical applications. Although the strength is improved, the bulk density also increases. Modifying lightweight calcium carbonate with calcium stearate can improve its agglomeration. At the same time, calcium stearate can improve the foaming of aerated concrete slurry, resulting in fine and uniform pore size and reducing green body collapse. The self-lubricating properties of earthy graphite powder can improve the fluidity of the slurry, and its filling of pores and microcracks can also increase mechanical properties. Fine-flake expanded graphite has a loose porous structure and easily forms a hydrophobic structure.

[0006] This invention utilizes calcium stearate to modify calcium carbonate. The modified calcium carbonate, together with earthy graphite and fine-flake expanded graphite, exhibits enhanced hydrophobicity. The addition of a certain amount of silica fume and aerated concrete waste improves the fluidity of the slurry and reduces gas generation resistance. The amorphous silicon and ultrafine powder in the slurry react with Ca(OH)2 to generate CSH gel, which reduces the calcium-silicon ratio in the green body, ensuring the cutting strength of the green body. The fine silica fume particles react more easily to generate tobermorite crystals during steam curing, providing crystal guidance and resulting in a better internal mineral structure and higher mechanical properties in the aerated concrete. Summary of the Invention

[0007] The purpose of this invention is to provide a waterproofing material for autoclaved aerated concrete and its preparation method, thereby solving the technical problems of high water absorption and poor durability of autoclaved aerated concrete.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A waterproofing material for autoclaved aerated concrete (AAC) comprises a mixture A and a mixture B in a mass ratio of 1:4, and a dispersant comprising less than 0.5 wt% of the total mass of mixture A and mixture B. Mixture A comprises, by mass ratio: 5 wt% fine flake expanded graphite, 5-10 wt% earthy graphite, and 85-90 wt% AAC waste. Mixture B comprises, by mass ratio: 80-85 wt% modified lightweight calcium carbonate, 10-15 wt% quicklime, and 5 wt% silica fume.

[0010] Furthermore, the fine-flake expanded graphite is obtained by oxidation, acidification intercalation, and high-temperature calcination of fine-flake graphite with a particle size of 0.075-0.1 mm;

[0011] Preferably, the fine-flake expanded graphite is obtained by oxidation and acidification intercalation using potassium permanganate, perchloric acid, glacial acetic acid, and nitric acid. 细鳞片石墨 ∶m 高锰酸钾 ∶V 高氯酸 ∶V 冰乙酸 ∶V 硝酸 = 5g∶1.7g∶10mL∶3.5mL∶3mL, the reaction environment temperature is 40℃ and the reaction time is 30min, and then the fine flake expanded graphite is obtained by expansion at 600℃. The expansion volume of the fine flake expanded graphite is 190mL / g.

[0012] Furthermore, the aerated concrete waste is one or more of sand aerated concrete waste, fly ash aerated concrete waste, and slag aerated concrete waste;

[0013] Preferably, the type of aerated concrete waste is the same as that of autoclaved aerated concrete. That is, if the autoclaved aerated concrete is fly ash aerated concrete, the aerated concrete waste used should be fly ash aerated concrete waste to prevent changes in the color of the aerated concrete product and the proportion of the steam-cured products.

[0014] Furthermore, the moisture content of the aerated concrete waste is not higher than 2 wt%; the aerated concrete waste is obtained by crushing aerated concrete blocks, and the particle size of the aerated concrete waste is 1-5 mm.

[0015] Furthermore, the earthy graphite has a carbon content of ≥95wt% and a particle size of 0–0.045μm.

[0016] Furthermore, the modified light calcium carbonate is made by modifying calcium carbonate. The specific operation is as follows: Weigh light calcium carbonate and calcium stearate at a mass ratio of 1:0.015, mix them evenly, and then grind them in a vibratory mill for 2-5 minutes to obtain modified light calcium carbonate.

[0017] Furthermore, the quicklime has a CaO content ≥80wt% and a particle size of 10-30mm.

[0018] Furthermore, the silica fume is a byproduct of smelting ferrosilicon alloys or silicon metal in an electric arc furnace, and has an SiO2 content of ≥90wt%.

[0019] Furthermore, the dispersant is a cement grinding aid.

[0020] This invention utilizes calcium stearate to modify calcium carbonate to obtain modified light calcium carbonate. The modified light calcium carbonate works synergistically with earthy graphite and fine flake expanded graphite, resulting in stronger hydrophobicity. The addition of a certain amount of silica fume and aerated concrete waste improves the fluidity of the slurry and reduces the gas generation resistance. The amorphous silicon and ultrafine powder react with Ca(OH)2 to generate CSH gel, which reduces the calcium-silicon ratio in the green body, ensuring the cutting strength of the green body. The fine silica fume particles are more likely to react and generate tobermorite crystals during steam curing, providing crystal guidance and resulting in a better internal mineral structure and higher mechanical properties in aerated concrete.

[0021] This invention also provides a method for preparing waterproofing materials for autoclaved aerated concrete, comprising the following steps:

[0022] S1. Weigh out fine flake expanded graphite, earthy graphite and aerated concrete waste according to the mass ratio, grind and mix them evenly to obtain mixture A;

[0023] S2. Weigh the modified light calcium carbonate, quicklime and silica fume according to the mass ratio, grind and mix them evenly to obtain mixture B;

[0024] S3. Weigh mixture A and mixture B at a mass ratio of 1:4, then add a dispersant of less than 0.5 wt% of the total mass of mixture A and mixture B, and grind and mix until the residue on a 45 μm sieve is ≤8% to obtain the internally added waterproof material.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The waterproof material of this invention has good compatibility with the raw materials and air bubbles of autoclaved aerated concrete. Calcium stearate can improve the foaming of autoclaved aerated concrete slurry, resulting in fine and uniform pore size in the green body, reducing green body collapse, and having little impact on the batching scheme, process conditions, casting stability, and product quality.

[0027] 2. The waterproof material of the present invention is applied in autoclaved aerated concrete. Modified lightweight calcium carbonate and silica powder can be filled into the aerated concrete structure to improve the overall strength. Modified nano-calcium carbonate, together with earthy graphite and fine flake expanded graphite, can easily form a hydrophobic layer, which can reduce the water absorption rate of the product and improve the durability of aerated concrete. Moreover, the waterproof material is internally modified, so there is no concern that the water absorption of the material will be affected after the surface of the blocks is worn. Detailed Implementation

[0028] 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. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0029] Example 1

[0030] As a preferred embodiment of the present invention, this embodiment discloses an internal waterproofing material for autoclaved aerated concrete, comprising a mixture A and a mixture B in a mass ratio of 1:4, and a dispersant comprising 0.1 wt% of the total mass of mixture A and mixture B.

[0031] The mixture A comprises the following components by mass ratio: 5 wt% fine flake expanded graphite, 10 wt% earthy graphite, and 85 wt% aerated concrete waste; the mixture B comprises the following components by mass ratio: 85 wt% modified light calcium carbonate, 10 wt% quicklime, and 5 wt% silica fume.

[0032] In this embodiment, the preparation method of waterproof material admixture for autoclaved aerated concrete includes the following steps:

[0033] S1. Weigh 5wt% fine flake expanded graphite, 5wt% earthy graphite and 90wt% aerated concrete waste, grind and mix them evenly to obtain mixture A;

[0034] S2. Weigh 80wt% modified light calcium carbonate, 15wt% quicklime and 5wt% silica fume, grind and mix them evenly to obtain mixture B;

[0035] S3. Weigh mixture A and mixture B at a mass ratio of 1:4, then add 0.1wt% of dispersant (triethanolamine) of the total mass of mixture A and mixture B, and grind and mix until the residue on a 45μm sieve is ≤8% to obtain the waterproof material with internal admixture.

[0036] In this embodiment, the fine flake expanded graphite is obtained by oxidation, acidification intercalation, and high-temperature calcination of fine flake graphite with a particle size of 0.075-0.1 mm.

[0037] In this embodiment, the aerated concrete waste has a moisture content of 1.5 wt% and a particle size of 1-5 mm.

[0038] In this embodiment, the aerated concrete waste is sand-based aerated concrete waste.

[0039] In this embodiment, the earthy graphite has a carbon content of 95 wt% and a particle size of 0–0.045 μm.

[0040] In this embodiment, the modified light calcium carbonate is obtained by modifying calcium carbonate. The specific operation is as follows: light calcium carbonate and calcium stearate are weighed at a mass ratio of 1:0.015, mixed evenly, and then ground in a vibratory mill for 5 minutes to obtain modified light calcium carbonate.

[0041] In this embodiment, the quicklime has a CaO content of 82wt% and a particle size of 10-30mm.

[0042] In this embodiment, the silica ash is a byproduct of smelting ferrosilicon alloys or silicon metal in an electric arc furnace, and the SiO2 content is 93wt%.

[0043] Example 2

[0044] As a preferred embodiment of the present invention, this embodiment discloses an internal waterproofing material for autoclaved aerated concrete, comprising a mixture A and a mixture B in a mass ratio of 1:4, and a dispersant comprising 0.1 wt% of the total mass of mixture A and mixture B.

[0045] The mixture A comprises the following components by mass ratio: 5 wt% fine flake expanded graphite, 5 wt% earthy graphite, and 90 wt% aerated concrete waste; the mixture B comprises the following components by mass ratio: 80 wt% modified light calcium carbonate, 15 wt% quicklime, and 5 wt% silica fume.

[0046] In this embodiment, the preparation method of waterproof material admixture for autoclaved aerated concrete includes the following steps:

[0047] S1. Weigh 5wt% fine flake expanded graphite, 10wt% earthy graphite and 85wt% aerated concrete waste, grind and mix them evenly to obtain mixture A;

[0048] S2. Weigh 85wt% modified light calcium carbonate, 10wt% quicklime and 5wt% silica fume, grind and mix them evenly to obtain mixture B;

[0049] S3. Weigh mixture A and mixture B at a mass ratio of 1:4, then add 0.1wt% of dispersant (triethanolamine) of the total mass of mixture A and mixture B, and grind and mix until the residue on a 45μm sieve is ≤8% to obtain the waterproof material with internal admixture.

[0050] In this embodiment, the fine flake expanded graphite is obtained by oxidation, acidification intercalation, and high-temperature calcination of fine flake graphite with a particle size of 0.075-0.1 mm.

[0051] In this embodiment, the aerated concrete waste has a moisture content of 1.5 wt% and a particle size of 1-5 mm.

[0052] In this embodiment, the aerated concrete waste is sand-based aerated concrete waste.

[0053] In this embodiment, the earthy graphite has a carbon content of 95 wt% and a particle size of 0–0.045 μm.

[0054] In this embodiment, the modified light calcium carbonate is obtained by modifying calcium carbonate. The specific operation is as follows: light calcium carbonate and calcium stearate are weighed at a mass ratio of 1:0.015, mixed evenly, and then ground in a vibratory mill for 5 minutes to obtain modified light calcium carbonate.

[0055] In this embodiment, the quicklime has a CaO content of 82wt% and a particle size of 10-30mm.

[0056] In this embodiment, the silica ash is a byproduct of smelting ferrosilicon alloys or silicon metal in an electric arc furnace, and the SiO2 content is 93wt%.

[0057] Example 3

[0058] As a preferred embodiment of the present invention, this embodiment discloses an internal waterproofing material for autoclaved aerated concrete, comprising a mixture A and a mixture B in a mass ratio of 1:4, and a dispersant comprising 0.1 wt% of the total mass of mixture A and mixture B.

[0059] The mixture A comprises the following components by mass ratio: 5 wt% fine flake expanded graphite, 5 wt% earthy graphite, and 90 wt% aerated concrete waste; the mixture B comprises the following components by mass ratio: 80 wt% modified light calcium carbonate, 15 wt% quicklime, and 5 wt% silica fume.

[0060] In this embodiment, the preparation method of waterproof material admixture for autoclaved aerated concrete includes the following steps:

[0061] S1. Weigh 5wt% fine flake expanded graphite, 8wt% earthy graphite and 87wt% aerated concrete waste, grind and mix them evenly to obtain mixture A;

[0062] S2. Weigh 82wt% modified light calcium carbonate, 13wt% quicklime and 5wt% silica fume, grind and mix them evenly to obtain mixture B;

[0063] S3. Weigh mixture A and mixture B at a mass ratio of 1:4, then add a dispersant (triethanolamine) accounting for 0.05 wt% of the total mass of mixture A and mixture B, and grind and mix until the residue on a 45 μm sieve is ≤8% to obtain the waterproof material with internal admixture.

[0064] In this embodiment, the fine flake expanded graphite is obtained by oxidation, acidification intercalation, and high-temperature calcination of fine flake graphite with a particle size of 0.075-0.1 mm.

[0065] In this embodiment, the aerated concrete waste has a moisture content of 1.5 wt% and a particle size of 1-5 mm.

[0066] In this embodiment, the aerated concrete waste is fly ash aerated concrete block waste.

[0067] In this embodiment, the earthy graphite has a carbon content of 95 wt% and a particle size of 0–0.045 μm.

[0068] In this embodiment, the modified light calcium carbonate is obtained by modifying calcium carbonate. The specific operation is as follows: light calcium carbonate and calcium stearate are weighed at a mass ratio of 1:0.015, mixed evenly, and then ground in a vibratory mill for 5 minutes to obtain modified light calcium carbonate.

[0069] In this embodiment, the quicklime has a CaO content of 82wt% and a particle size of 10-30mm.

[0070] In this embodiment, the silica ash is a byproduct of smelting ferrosilicon alloys or silicon metal in an electric arc furnace, and the SiO2 content is 93wt%.

[0071] The waterproofing material prepared in Example 1 was added to the aerated concrete block mix at 0.3% of the dry mass of the raw materials of autoclaved aerated concrete. The mixture was then stirred, poured, allowed to stand, steam-cured, and cut to obtain aerated concrete block 1.

[0072] The waterproofing material prepared in Example 2 was added to the aerated concrete block mix at 0.5% of the dry mass of the raw materials of autoclaved aerated concrete. The mixture was then stirred, poured, allowed to stand still, steam-cured, and cut to obtain aerated concrete block 2.

[0073] The waterproofing material prepared in Example 3 was added to the fly ash concrete block mix at 0.5% of the dry mass of the raw materials for autoclaved aerated concrete. The mixture was then stirred, poured, allowed to stand, steam-cured, and cut to obtain autoclaved concrete blocks 3.

[0074] Comparative Example 1

[0075] Without adding any waterproofing materials, the aerated concrete blocks 4 are obtained by mixing, pouring, static curing, steam curing, and cutting according to the cement-quicklime-sand aerated concrete block batching method.

[0076] Comparative Example 2

[0077] Without adding any waterproofing materials, the aerated concrete blocks 5 are obtained by mixing, pouring, static curing, steam curing, and cutting according to the cement-quicklime-fly ash aerated concrete block batching method.

[0078] According to GB 11969-2020, the compressive strength, water absorption, drying shrinkage value, and frost resistance of aerated concrete blocks 1 to 5 were tested. The water absorption test was conducted on the saturated water absorption rate after 72 hours. The test results are shown in Table 1.

[0079] Table 1. Test results of mechanical and durability properties of the blocks.

[0080]

[0081] As shown in Table 1, the control group without the waterproof material of the present invention had poor mechanical properties and frost resistance, and high 72h saturated water absorption rate and drying shrinkage value, which were on the verge of being qualified. The experimental group with the waterproof material of the present invention showed significantly improved mechanical properties, reduced 72h saturated water absorption rate, and improved drying shrinkage value and frost resistance as the saturated water absorption rate decreased. This indicates that the waterproof material of the present invention improves the performance of the blocks.

[0082] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention used to illustrate the technical solutions of the present invention, and are not intended to limit the invention, nor are they intended to limit the patent scope of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. That is to say, any changes or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but whose technical problems are still consistent with the present invention, should be included within the protection scope of the present invention. In addition, the direct or indirect application of the technical solutions of the present invention to other related technical fields are similarly included within the patent protection scope of the present invention.

Claims

1. An internal waterproofing material for autoclaved aerated concrete, characterized by, The mixture A and the mixture B are mixed in a mass ratio of 1:4, and the dispersant is less than 0.5wt% of the total mass of the mixture A and the mixture B; the mixture A comprises the following components in a mass ratio: The mixture B comprises the following components in a mass ratio: modified light calcium carbonate 80~85wt%, quicklime 10~15wt%, and silicon powder 5wt%. The fine flake expanded graphite is obtained by oxidizing, acidizing, and intercalating fine flake graphite with a particle size of 0.075~0.1mm and high-temperature calcination. The fine flake expanded graphite is prepared by using potassium permanganate, perchloric acid, glacial acetic acid and nitric acid for oxidation and acidification intercalation, m 细鳞片石墨 ∶m 高锰酸钾 ∶V 高氯酸 ∶V 冰乙酸 ∶V 硝酸= 5g∶1.7g∶10m L∶3.5m L∶3m L, the reaction environment temperature is 40 DEG C, the reaction time is 30 min, and then the fine flake expanded graphite is prepared by high temperature expansion at 600 DEG C, and the expansion volume of the fine flake expanded graphite is 190 mL / g.

2. The internal waterproofing material for autoclaved aerated concrete according to claim 1, characterized by, The aerated concrete waste is one or more of sand aerated concrete waste, fly ash aerated concrete waste, and slag aerated concrete waste.

3. The internal waterproofing material for autoclaved aerated concrete according to claim 2, characterized in that, The aerated concrete waste is consistent with the type of autoclaved aerated concrete.

4. The internal waterproofing material for autoclaved aerated concrete according to claim 1, characterized by, The water content of the aerated concrete waste is not higher than 2wt%, and the aerated concrete waste is obtained by crushing aerated concrete blocks, and the particle size of the aerated concrete waste is 1~5mm.

5. The internal waterproofing material for autoclaved aerated concrete according to claim 1, characterized in that, The carbon content of the earthy graphite is ≥95wt%, and the particle size is 0~0.045μm.

6. The internal waterproofing material for autoclaved aerated concrete according to claim 1, characterized by, The modified light calcium carbonate is obtained by modifying calcium carbonate, and the specific operation is as follows: light calcium carbonate and calcium stearate are weighed in a mass ratio of 1:0.015, mixed uniformly, and then vibrated and ground for 2~5min to obtain the modified light calcium carbonate.

7. The internal waterproofing material for autoclaved aerated concrete according to claim 1, characterized in that, The CaO content of the quicklime is ≥80wt%, and the particle size is 10~30mm.

8. The internal waterproofing material for autoclaved aerated concrete according to claim 1, characterized in that, The silicon powder is a byproduct obtained during the smelting of ferrosilicon alloy or silicon metal by an electric arc furnace, and the SiO2 content is ≥90wt%.

9. The internal waterproofing material for autoclaved aerated concrete according to claim 1, characterized in that, The dispersant is a cement grinding aid.

10. The method for preparing an internal waterproofing material for autoclaved aerated concrete according to any one of claims 1 to 9, characterized in that, The method comprises the following steps: S1, fine flake expanded graphite, earthy graphite, and aerated concrete waste are weighed in a mass ratio, and then ground and mixed uniformly to obtain a mixture A; S2, modified light calcium carbonate, quicklime, and silicon powder are weighed in a mass ratio, and then ground and mixed uniformly to obtain a mixture B; S3, the mixture A and the mixture B are weighed in a mass ratio of 1:4, and then a dispersant is added, which is less than 0.5wt% of the total mass of the mixture A and the mixture B, and then ground and mixed until the 45μm sieve residue is ≤8% to obtain an internally doped waterproof material.

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