Anti-crack concrete with high stone powder content and preparation method of anti-crack concrete
By combining modified wheat straw fiber with air-entraining and foam-stabilizing components, the problem of early cracking caused by excessive stone powder content in concrete was solved, improving the workability, strength, and durability of concrete and achieving efficient utilization of stone powder.
Patent Information
- Application Number
- CN202511424152.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-30
- Publication Date
- 2025-12-16
AI Technical Summary
Excessive stone powder content in concrete leads to poor workability, reduced strength, and decreased durability, with a significant increase in early cracking. Furthermore, traditional fiber materials are expensive and difficult to disperse, limiting their application in concrete.
Modified wheat straw fiber is used. The wheat straw fiber is modified by alkali activation, triethoxysilane and acrylic polymer emulsion. Combined with air-entraining and foam-stabilizing components, a uniform network structure is formed between the modified wheat straw fiber and the concrete matrix, which enhances the bonding force and adhesion and reduces the risk of early cracking.
This method enables the high-volume application of high-stone-powder-content concrete, improving workability, strength, and durability, reducing early cracking, and providing a new approach to the high-value utilization of stone powder. Moreover, the preparation method is simple and low-cost.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the technical field of building materials, and particularly relates to a high-stone-powder-content anti-cracking concrete and a preparation method thereof. BACKGROUND
[0002] With the sustained and rapid development of the construction industry, the demand for concrete materials is increasing, and the production of machine-made sand is also gradually increasing. In order to protect the environment and water resources, the proportion of dry sand making process in the production of machine-made sand is gradually increasing, which leads to a large amount of stone powder as a byproduct in the production process. A large number of studies have shown that stone powder can be added as an inert admixture to concrete, which has a certain improvement effect on the cohesiveness and strength of concrete at a certain dosage.
[0003] However, too high a dosage of stone powder can cause problems such as poor workability of concrete, reduced strength, and poor durability, especially significantly increased early cracking. This is because too high a dosage of stone powder increases the amount of concrete slurry, and the rough surface of stone powder has poor free water retention and can accelerate the hydration of cementitious materials, causing the water loss in the concrete to be too fast, the capillary pore negative pressure to grow too fast, the early shrinkage to increase, and the early cracking to increase. In view of the above problems, the dosage of stone powder in concrete usually cannot be too high, and the single dosage is generally not more than 50 kg, which can cause a large amount of stone powder to be stored as a byproduct in the sand making process of aggregate production enterprises, causing pressure on the environment and enterprise operation.
[0004] It has been proven that adding fiber materials to improve early cracking of concrete is an effective method, but traditional fibers are expensive, and some fibers also have the problems of dispersion difficulty and poor bonding performance with cement-based materials, which limits their use in ordinary concrete. Wheat straw fiber extracted from plant materials has a relatively low price and high economic benefit. However, wheat straw fiber has a large number of polar groups on its surface, and the fiber tends to agglomerate in the concrete matrix, which limits the effective application of this type of fiber material in concrete. SUMMARY
[0005] The main purpose of the present application is to solve the problems and deficiencies of the prior art, and to provide an anti-cracking concrete with high stone powder content, which can realize high dosage application of stone powder in concrete, and also effectively reduce early cracking of concrete and other problems, and improve the workability, strength, and durability of concrete.
[0006] To achieve the above purpose, the technical scheme adopted by the present application is as follows: A high stone powder content anti-cracking concrete, each raw material and the weight percentage thereof include: cement 180-230 parts, fly ash 40-80 parts, mineral powder 30-70 parts, stone powder 60-120 parts, coarse aggregate 1000-1200 parts, fine aggregate 800-1000 parts, water 170-190 parts, water reducing agent 5-15 parts, modified wheat straw fiber 2-8 parts, water retaining component 0.5-2 parts, air entraining-stable bubble component 0.1-0.5 parts; the modified wheat straw fiber is obtained by sequentially alkali activating, triethoxysilane and acrylic polymer emulsion modification of the wheat straw fiber.
[0007] In the above scheme, the cement is ordinary portland cement, P.O42.5 grade or above, the specific surface area is 300-350 m 2 / kg, and the 28d strength is greater than 45 MPa; the fly ash is selected as grade II fly ash, the specific surface area is 300-450 m 2 / kg, and the 28d activity index is greater than 80%; the mineral powder is S95 mineral powder, the specific surface area is 350-500 m 2 / kg, and the 28d activity index is greater than 95%.
[0008] In the above scheme, the stone powder is a dust collection stone powder of a dry sand making process, the 45 μm sieve residue is less than 8%, the specific surface area is 350-550 m 2 / kg, and the MB value is less than 0.5.
[0009] In the above scheme, the coarse aggregate is 5-16 and 16-31.6 mm crushed stone matched in a mass ratio of (5:5)-(3:7), the water absorption and the silt content are both less than 1%; the fine aggregate is 0-5 mm machine-made sand, the fineness modulus is 2.6-3.0, the MB value is less than 0.75, and the stone powder content is 5-8%.
[0010] In the above scheme, the water reducing agent is a polycarboxylic acid water reducing agent, and the water reducing rate is 10-25%.
[0011] In the preparation process of the modified wheat straw fiber in the above scheme, the main raw materials and the weight percentage thereof include: wheat straw fiber 30-60 parts, vinyl triethoxysilane 3-8 parts, and acrylic polymer emulsion 0.1-0.5 parts.
[0012] Further, the wheat straw fiber has a length of 2-10 mm and an average diameter of 0.05-0.1 mm.
[0013] Further, the acrylic polymer emulsion has a pH value of 8-9 at room temperature, a viscosity of 100-350 mPa﹒s, and a solid content of 40-50%.
[0014] Further, the alkali activation modification step comprises soaking the wheat straw fiber in a sodium hydroxide solution for 4-8 hours; then adding glacial acetic acid under stirring to adjust the pH value to 3-6, and continuing stirring for 0.5-2 hours.
[0015] Further, in the alkali activation modification step, the raw materials and their weight fractions include: wheat straw fiber 30-60 parts, sodium hydroxide 5-10 parts, and glacial acetic acid 5-10 parts.
[0016] Further, the introduced glacial acetic acid can adjust the pH value and promote and accelerate the hydrolysis of the wheat straw fiber, and improve the activity of Si-O bond.
[0017] Further, the triethoxysilane and acrylic polymer emulsion modification step comprises: first adding vinyl triethoxysilane and 2-mercaptobenzothiazole to the product obtained by alkali activation, and performing a first stirring reaction under stirring and water bath heating; adjusting the pH value of the obtained solution system to neutral, adding an acrylic polymer emulsion, and performing a second stirring reaction under stirring and water bath heating to obtain a modified wheat straw fiber flocculation mixture; adding an alcohol solvent, stirring, standing, obtaining a modified wheat straw fiber flocculation precipitate, filtering, washing with water, and drying to obtain the modified wheat straw fiber.
[0018] Further, in the triethoxysilane and acrylic polymer emulsion modification step, the raw materials and their weight fractions include: anhydrous ethanol 20-30 parts, vinyl triethoxysilane 3-8 parts, 2-mercaptobenzothiazole 0.5-2 parts, and acrylic polymer emulsion 0.1-0.5 parts.
[0019] Further, the first stirring reaction is performed at a rotation speed of 200-400 r / min, a temperature of 50-70°C, and for a time of 1-3 hours.
[0020] Further, the second stirring reaction is performed at a rotation speed of 50-100 r / min, a temperature of 60-80°C, and for a time of 0.5-1 hour.
[0021] Further, the stirring treatment is performed at a rotation speed of 10-50 r / min for a time of 10-30 minutes.
[0022] Further, the standing time is 1-2 hours.
[0023] Further, the drying temperature is 60-70°C.
[0024] Further, the water-retaining agent can be selected from one or more of fatty alcohol alkanolamide, fatty amine polyoxyethylene ether, and phosphated di-starch phosphate.
[0025] Further, the mass ratio of the fatty alcohol alkanolamide, the fatty amine polyoxyethylene ether and the phosphated distarch phosphate is (0-5):(0-10):(0-6); and the three components are not simultaneously 0.
[0026] Further, the fatty alcohol alkanolamide, the fatty amine polyoxyethylene ether and the phosphated distarch phosphate are mixed uniformly by magnetic stirring for 0.3-1h.
[0027] Further, the air entraining-stable bubble component comprises an air entraining component and a stable bubble component, wherein the air entraining component can be selected from one or more of potassium azodicarboxylate, p-toluenesulfonyl hydrazide and triazene triazene; and the stable bubble component can be selected from one or more of fatty acid diethanolamine, silicone amide and polyoxypropylene glycol.
[0028] Further, the mass ratio of the air entraining component and the stable bubble component is (1-5):1. Both are mixed uniformly by magnetic stirring for 0.5-1h.
[0029] Further, in the air entraining component, the mass ratio of potassium azodicarboxylate, p-toluenesulfonyl hydrazide and triazene triazene is (1-5):(1-8):(2-5).
[0030] Further, in the stable bubble component, the mass ratio of fatty acid diethanolamine, silicone amide and polyoxypropylene glycol is (1-3):(1-5):(3-8).
[0031] The application also provides a preparation method of the high-stone-powder-content anti-cracking concrete. 1) The weighed cement, fly ash, mineral powder, stone powder and fine aggregate are uniformly stirred (30-60s), the modified wheat straw fiber, the water retention component, the air entraining-stable bubble component and part of the water reducing agent are uniformly stirred (60-120s), the coarse aggregate and the remaining water reducing agent are continuously stirred (60-120s) to obtain a high-stone-powder-content anti-cracking concrete mixture. 2) The obtained mixture is poured into a corresponding mold, and is layered, vibrated and compacted, and then is covered and cured to different ages to obtain the high-stone-powder-content anti-cracking concrete.
[0032] In the above scheme, 1 / 4~2 / 3 of the water reducing agent is added first in step 1).
[0033] The principle of the application comprises: This invention targets relatively inexpensive wheat straw fiber materials. First, it involves alkali-activated modification. Then, vinyltriethoxysilane combined with a 2-mercaptobenzothiazole accelerator is used to further modify the alkali-activated wheat straw fibers. Finally, acrylic polymer emulsion is used as a surface modifier to prepare modified wheat straw fibers. The modification method described in this invention can appropriately reduce fiber size, increase the degree of fibrillation, increase the number of microfibrils, increase the fiber specific surface area, enhance surface energy, and improve strength. Simultaneously, the accelerator helps expose more active groups during the modification process, improving the modification effect and reducing fiber agglomeration. The introduced surface modifier increases the surface tension and adhesion of the fibers, thereby promoting increased adhesion and compatibility between the modified fibers and the concrete matrix, and facilitating the formation of a cross-linked network structure in the concrete matrix, enhancing the strength of the concrete material. When concrete shrinks during hardening, the uniformly distributed network structure of the modified fibers can offset the tensile stress generated during shrinkage, thereby minimizing the formation and further propagation of microcracks and achieving the goal of reducing early-stage cracking in concrete.
[0034] Compared with the prior art, the beneficial effects of the present invention are: 1) This invention targets wheat straw fiber and sequentially performs alkali activation, vinyltriethoxysilane modification, and acrylic polymer emulsion surface modification, which can effectively enhance the strength of the obtained modified fiber and its adhesion to the interface of concrete materials. This is beneficial to forming a uniformly distributed network structure in concrete, effectively offsetting the tensile stress generated during shrinkage, and achieving the purpose of reducing early cracking of concrete. 2) The water-retaining component introduced in this invention can form a spatial network structure with water molecules through hydrogen bonds, which can slow down the evaporation rate of water in concrete to a certain extent, reduce the humidity gradient difference between the concrete surface and the interior, reduce the negative pressure of the concave liquid surface caused by water loss in the surface capillaries, thereby reducing the formation and propagation of microcracks and achieving the purpose of inhibiting early cracking.
[0035] 3) In the air-entraining and foam-stabilizing component introduced in this invention, the air-entraining component can introduce micro-bubbles into the internal interface of concrete to counteract the negative pressure of capillary pores after water loss, reduce shrinkage tensile stress, and thus reduce early cracking; the foam-stabilizing component can reduce the surface tension of the air-entraining component, enabling it to generate a large number of small bubbles, and control the uniform distribution of small bubbles, automatically repairing the weak points of the bubble walls, preventing them from breaking, and extending their existence time; based on the above effects, the introduced bubbles can also play a ball bearing lubrication role, reducing the internal flow resistance of concrete and improving workability to a certain extent.
[0036] 4) This invention enables the high-volume application of stone powder in concrete, achieving a good crack-inhibiting effect while maintaining good workability, mechanical strength, and durability. It provides a new approach for the high-value utilization of stone powder.
[0037] 5) The preparation method involved in this invention is relatively simple and low in cost, and is suitable for widespread application. Specific Implementation To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.
[0039] Example 1 A crack-resistant concrete with high stone powder content is prepared by the following steps: 1) Weighing of raw materials; The weight composition of each raw material is as follows: 200 parts of ordinary Portland cement, 50 parts of fly ash, 60 parts of mineral powder, 60 parts of stone powder, 1000 parts of ordinary coarse aggregate, 900 parts of ordinary fine aggregate, 170 parts of water, 5 parts of water-reducing agent, 2 parts of modified wheat straw fiber, 0.5 parts of water-retaining component, and 0.1 parts of air-entraining and foam-stabilizing component; The cement used is P.O42.5 grade ordinary Portland cement, the fly ash is Grade II fly ash, the mineral powder is S95 mineral powder, and the stone powder is limestone dry sand making dust collection powder with a 45μm sieve residue of 4.7% and a specific surface area of 385m². 2 / kg, MB value 0.25; The coarse aggregate used is limestone crushed stone with a particle size of 5-16 and 16-31.6 mm in a 4:6 ratio, with a water absorption rate of 0.8% and a mud content of 0.5%; the fine aggregate is 0-5 mm manufactured sand with a fineness modulus of 2.8, an MB value of less than 0.75, and a stone powder content of 8%; the water-reducing agent is polycarboxylate water-reducing agent with a solid content of 10% and a water reduction rate of 20%.
[0040] The wheat straw fibers used had an average length of 5 mm and an average diameter of 0.1 mm. The raw materials used to prepare the modified wheat straw fibers included 40 parts wheat straw fibers, 6 parts sodium hydroxide, 5 parts glacial acetic acid, 20 parts anhydrous ethanol, 4 parts vinyltriethoxysilane, 0.5 parts 2-mercaptobenzothiazole, and 0.1 parts acrylic polymer emulsion (styrene-acrylate copolymer emulsion; solid content 40%, viscosity at 30℃ 200 mPa·s, pH 7.5, minimum film-forming temperature 23℃). The preparation method of the modified wheat straw fiber is as follows: Step 1: Soak the weighed wheat straw fiber in a 10wt% sodium hydroxide solution for 4 hours; Step 2: While stirring, add glacial acetic acid and test the pH with a pH tester to adjust the pH to 3. Continue stirring for 0.5 hours. Step 3: Add vinyltriethoxysilane and 2-mercaptobenzothiazole, and stir and react for 1 hour under magnetic stirring (300 r / min) and 55°C water bath conditions; Step 4: Adjust the pH to neutral with sodium hydroxide solution (concentration of 0.1 mol / L), then add acrylic polymer emulsion, and stir at 60 r / min in a 65℃ water bath for 0.5 h to obtain modified wheat straw fiber flocculant; Step 5: Add anhydrous ethanol and continue stirring at 20 r / min for 15 min. Then let it stand for 1 h to obtain modified wheat straw fiber flocculent precipitate. Filter the precipitate, wash it with distilled water, and dry it in an oven at 60℃ to a constant weight to obtain modified wheat straw fiber.
[0041] The water-retaining components were prepared by mixing fatty alcohol alkanolamide, fatty amine polyoxyethylene ether, and phosphorylated distarch phosphate in a mass ratio of 1:3:4 in a magnetic stirrer for 0.5 hours until homogeneous.
[0042] The air-entraining and foam-stabilizing components were prepared by mixing the air-entraining component (potassium azoformamide formate, p-toluenesulfonyl hydrazine, and trinitrosomethylenetriamine in a mass ratio of 1:2:3) with the foam-stabilizing component (diethanolamine of fatty acids, silicone amide, and polyoxypropylene glycol in a mass ratio of 1:2:5) in a 1:1 mass ratio on a magnetic stirrer for 0.5 hours.
[0043] 2) Concrete preparation; First, weigh the cement, fly ash, mineral powder, stone powder and fine aggregate into the mixer and mix for 40 seconds. Then, add the modified wheat straw fiber, water-retaining agent, air-entraining and foam-stabilizing component and half of the water-reducing agent and mix for 80 seconds. Finally, add the coarse aggregate and the remaining water-reducing agent and continue mixing for 90 seconds to obtain a crack-resistant concrete mixture with high stone powder content. The concrete is poured into the corresponding mold according to the application location, compacted in layers by vibration, and then covered with a film for curing at different ages to harden it, thus obtaining the crack-resistant concrete.
[0044] Example 2 A crack-resistant concrete with high stone powder content is prepared in a manner largely the same as in Example 1, except that: 1) The weight composition of each raw material is as follows: 190 parts ordinary silicate cement, 40 parts fly ash, 60 parts mineral powder, 80 parts stone powder, 1000 parts ordinary coarse aggregate, 900 parts ordinary fine aggregate, 175 parts water, 8 parts water-reducing agent, 4 parts modified wheat straw fiber, 1 part water-retaining component, and 0.2 parts air-entraining and foam-stabilizing component. 2) The raw materials used to prepare modified wheat straw fiber include 50 parts wheat straw fiber, 8 parts sodium hydroxide, 6 parts glacial acetic acid, 25 parts anhydrous ethanol, 5 parts vinyltriethoxysilane, 1 part 2-mercaptobenzothiazole, and 0.2 parts acrylic polymer emulsion. The preparation method of the modified wheat straw fiber is as follows: Step 1: Soak the weighed wheat straw fiber in a 10wt% sodium hydroxide solution for 5 hours; Step 2: While stirring, add glacial acetic acid and test the pH with a pH tester to adjust the pH to 4. Continue stirring for 1 hour. Step 3: Add vinyltriethoxysilane and 2-mercaptobenzothiazole, and stir for 2 hours under magnetic stirring (350 r / min) and a 60°C water bath. Step 4: Adjust the pH to neutral with sodium hydroxide solution (concentration of 0.1 mol / L), then add acrylic polymer emulsion, and stir at 70 r / min in a 70℃ water bath for 0.6 h to obtain modified wheat straw fiber flocculant; Step 5: Add anhydrous ethanol and continue stirring at 30 r / min for 20 min. Then let it stand for 1.5 h to obtain modified wheat straw fiber flocculent precipitate. Filter the precipitate, wash it with distilled water, and dry it in an oven at 60℃ to a constant weight to obtain modified wheat straw fiber.
[0045] The water-retaining components were prepared by mixing fatty alcohol alkanolamide, fatty amine polyoxyethylene ether, and phosphorylated distarch phosphate in a ratio of 2:5:5 in a magnetic stirrer for 0.5 hours until homogeneous.
[0046] The air-entraining and foam-stabilizing components were prepared by mixing the air-entraining component (potassium azoformamide formate, p-toluenesulfonyl hydrazine, and trinitrosomethylenetriamine in a mass ratio of 2:4:4) and the foam-stabilizing component (diethanolamine of fatty acids, silicone amide, and polyoxypropylene glycol in a mass ratio of 2:3:6) in a 2:1 mass ratio on a magnetic stirrer for 0.8 hours.
[0047] Example 3 A crack-resistant concrete with high stone powder content is prepared in a manner largely the same as in Example 1, except that: 1) 180 parts ordinary Portland cement, 40 parts fly ash, 50 parts mineral powder, 100 parts stone powder, 1000 parts ordinary coarse aggregate, 900 parts ordinary fine aggregate, 180 parts water, 10 parts water-reducing agent, 6 parts modified wheat straw fiber, 1.5 parts water-retaining component, and 0.3 parts air-entraining and foam-stabilizing component. 2) The raw materials used to prepare modified wheat straw fiber include 60 parts wheat straw fiber, 10 parts sodium hydroxide, 8 parts glacial acetic acid, 30 parts anhydrous ethanol, 6 parts vinyltriethoxysilane, 1.5 parts 2-mercaptobenzothiazole, and 0.3 parts acrylic polymer emulsion. The preparation method of the modified wheat straw fiber is as follows: Step 1: Soak the weighed wheat straw fiber in a 10wt% sodium hydroxide solution for 6 hours; Step 2: While stirring, add glacial acetic acid and test the pH with a pH tester to adjust the pH to 5. Continue stirring for 1.5 hours. Step 3: Add vinyltriethoxysilane and 2-mercaptobenzothiazole, and stir for 2.5 h under magnetic stirring (400 r / min) and 65 °C water bath conditions; Step 4: Adjust the pH to neutral with sodium hydroxide solution (concentration of 0.1 mol / L), then add acrylic polymer emulsion, and stir at 80 r / min in a 75℃ water bath for 1 h to obtain modified wheat straw fiber flocculant. Step 5: Add 30 parts of anhydrous ethanol, continue stirring at 40 r / min for 25 min, and then let stand for 1.5 h to obtain modified wheat straw fiber flocculent precipitate. Filter, wash the obtained precipitate with distilled water, and put it in an oven to dry at 60℃ to a constant weight to obtain modified wheat straw fiber.
[0048] The water-retaining components were prepared by mixing fatty alcohol alkanolamide, fatty amine polyoxyethylene ether, and phosphorylated distarch phosphate in a ratio of 3:6:5 in a magnetic stirrer for 0.6 hours until homogeneous.
[0049] The air-entraining and foam-stabilizing components were prepared by mixing the air-entraining component (potassium azoformamide formate, p-toluenesulfonyl hydrazine, and trinitrosomethylenetriamine in a mass ratio of 3:5:4) and the foam-stabilizing component (diethanolamine of fatty acids, silicone amide, and polyoxypropylene glycol in a mass ratio of 3:4:6) in a 3:1 mass ratio on a magnetic stirrer for 1 hour until homogeneous.
[0050] Example 4 A crack-resistant concrete with high stone powder content is prepared in a manner largely the same as in Example 1, except that: 1) The weight composition of each raw material is as follows: 180 parts ordinary silicate cement, 30 parts fly ash, 40 parts mineral powder, 120 parts stone powder, 1000 parts ordinary coarse aggregate, 900 parts ordinary fine aggregate, 185 parts water, 12 parts water-reducing agent, 8 parts modified wheat straw fiber, 2 parts water-retaining component, and 0.4 parts air-entraining and foam-stabilizing component.
[0051] 2) The raw materials used to prepare modified wheat straw fiber include 60 parts wheat straw fiber, 10 parts sodium hydroxide, 8 parts glacial acetic acid, 30 parts anhydrous ethanol, 8 parts vinyltriethoxysilane, 2 parts 2-mercaptobenzothiazole, and 0.4 parts acrylic polymer emulsion. The preparation method of the modified wheat straw fiber is as follows: Step 1: Soak the weighed wheat straw fiber in a 10wt% sodium hydroxide solution for 8 hours; Step 2: While stirring, add glacial acetic acid and test the pH with a pH tester to adjust the pH to 6. Continue stirring for 2 hours. Step 3: Add vinyltriethoxysilane and 2-mercaptobenzothiazole, and stir for 3 hours under magnetic stirring (300 r / min) and a 70°C water bath. Step 4: Adjust the pH to neutral with sodium hydroxide solution (concentration of 0.1 mol / L), then add acrylic polymer emulsion, and stir at 100 r / min in an 80℃ water bath for 1 h to obtain modified wheat straw fiber flocculant. Step 5: Add 30 parts of anhydrous ethanol, stir at 50 r / min for 30 min, and then let stand for 2 h to obtain modified wheat straw fiber flocculent precipitate. Filter, wash the obtained precipitate with distilled water, and dry it in an oven at 60℃ to a constant weight to obtain modified wheat straw fiber.
[0052] The water-retaining components were prepared by mixing fatty alcohol alkanolamide, fatty amine polyoxyethylene ether, and phosphorylated distarch phosphate in a mass ratio of 4:8:5 in a magnetic stirrer for 1 hour until homogeneous.
[0053] The air-entraining and foam-stabilizing components were prepared by mixing the air-entraining component (potassium azoformamide formate, p-toluenesulfonyl hydrazine, and trinitrosomethylenetriamine in a mass ratio of 4:7:5) and the foam-stabilizing component (diethanolamine of fatty acids, silicone amide, and polyoxypropylene glycol in a mass ratio of 3:5:8) in a 5:1 mass ratio on a magnetic stirrer for 1 hour until homogeneous.
[0054] Comparative Example 1 A crack-resistant concrete with high stone powder content is prepared in a manner largely the same as in Example 1, with the only difference being: Wheat straw fiber was conventionally modified using KH-550 silane coupling agent. The specific steps included: mixing 40 parts of wheat straw fiber with 6 parts of 0.1 mol / L sodium hydroxide solution and stirring at room temperature for 1-2 hours; adjusting the pH to neutral with acetic acid; washing, filtering, and drying to obtain alkalized fiber; adding 4 parts of the modifier isopropanol; stirring evenly and reacting at 60℃ for 1.5 hours to obtain etherified wheat straw fiber; adding the etherified wheat straw fiber to a container containing an ethanol solution of KH-550 silane coupling agent (containing 0.5 parts of KH-550 silane coupling agent); adjusting the pH to neutral with glacial acetic acid; and soaking at room temperature for 2 hours to obtain silane coupling agent modified wheat straw fiber.
[0055] Comparative Example 2 A crack-resistant concrete with high stone powder content is prepared in a manner similar to that of Example 2, except that no corresponding water-retaining component is introduced.
[0056] Comparative Example 3 A crack-resistant concrete with high stone powder content is prepared in a manner similar to that of Example 3, except that the corresponding air-entraining and foam-stabilizing component is replaced with a fatty alcohol alkanolamide that has both air-entraining and foam-stabilizing functions.
[0057] Comparative Example 4 A crack-resistant concrete with high stone powder content is prepared in a manner similar to that of Example 3, except that it does not use wheat straw fiber, water-retaining agent, or functional additives.
[0058] Standard 150mm cube specimens were prepared from Examples 1-4 and Comparative Examples 1-4, respectively. After standard curing, the compressive strength of the concrete at 7d and 28d was tested. Then, the concrete freeze-thaw resistance (rapid freezing method), chloride ion migration coefficient (RCM method) and early crack resistance (plate method) were tested according to GB / T50082 to characterize the durability and crack resistance of the concrete. The results are shown in Table 1.
[0059] Table 1. Performance test results of concrete obtained in Examples 1-4 and Comparative Examples 1-4
[0060] As shown in the table above, this invention enables concrete to maintain high workability, compressive strength, durability, and good crack resistance even with high stone powder content. The introduced wheat straw fiber, after modification, better bonds to the concrete matrix interface, enhancing interfacial properties. It also better counteracts early shrinkage stress in concrete, increasing strength, slowing early cracking, and improving durability. The introduced water-retaining agent slows down the rate of water migration in concrete, reduces the rate of surface water evaporation, delays capillary negative pressure caused by surface water loss, reduces the formation of surface microcracks, and decreases cracking. Excess free water increases the workability of the concrete. The introduced air-entraining and foam-stabilizing component, by introducing micro-air pockets into the concrete, can to some extent counteract the concave liquid surface pressure after capillary water loss, reducing the plastic shrinkage pressure caused by insufficient strength in the early stages of concrete, delaying crack formation, thereby reducing cracking and improving durability. Simultaneously, the introduced air bubbles also act as ball bearing lubricants, reducing internal viscous resistance in concrete, further promoting improved workability, and simultaneously improving concrete density and strength.
[0061] The embodiments of the present invention disclosed above are merely illustrative of the invention. These embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Those skilled in the art, after reading this specification, may make modifications to these embodiments without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.
Claims
1. A crack-resistant concrete with high stone powder content, characterized in that, The raw materials and their respective weight percentages include: 180-230 parts cement, 40-80 parts fly ash, 30-70 parts mineral powder, 60-120 parts stone powder, 1000-1200 parts coarse aggregate, 800-1000 parts fine aggregate, 170-190 parts water, 5-15 parts water-reducing agent, 2-8 parts modified wheat straw fiber, 0.5-2 parts water-retaining component, and 0.1-0.5 parts air-entraining and foam-stabilizing component; the modified wheat straw fiber is obtained by sequentially alkali activation, triethoxysilane, and acrylic polymer emulsion modification of wheat straw fiber.
2. The crack-resistant concrete according to claim 1, characterized in that, In the preparation process of the modified wheat straw fiber, the main raw materials and their weight percentages include: 30-60 parts wheat straw fiber, 3-8 parts vinyltriethoxysilane, and 0.1-0.5 parts acrylic polymer emulsion.
3. The crack-resistant concrete according to claim 1, characterized in that, The wheat straw fibers are 2-10 mm in length and have an average diameter of 0.05-0.1 mm.
4. The crack-resistant concrete according to claim 1, characterized in that, The steps for modifying triethoxysilane and acrylic polymer emulsions include: Vinyltriethoxysilane and 2-mercaptobenzothiazole were added to the product obtained by alkali activation, and a stirring reaction was carried out once under stirring and water bath heating conditions. The pH value of the resulting solution system was adjusted to neutral, acrylic polymer emulsion was added, and a second stirring reaction was carried out under stirring and water bath heating conditions to obtain the modified wheat straw fiber flocculent mixture. The modified wheat straw fiber was obtained after post-treatment.
5. The crack-resistant concrete according to claim 1, characterized in that, The cement is ordinary Portland cement with a specific surface area of 300-350 m². 2 / kg, 28-day strength greater than 45MPa; the specific surface area of the fly ash is 300-450m². 2 / kg, with an activity index greater than 80% after 28 days; the specific surface area of the mineral powder is 350-500 m² / kg. 2 / kg, with an activity index greater than 95% after 28 days.
6. The crack-resistant concrete according to claim 1, characterized in that, The stone powder has a 45μm sieve residue of less than 8% and a specific surface area of 350-550m². 2 / kg, MB value less than 0.
5.
7. The crack-resistant concrete according to claim 1, characterized in that, The water-retaining agent is one or more of fatty alcohol alkanolamide, fatty amine polyoxyethylene ether, and phosphorylated distarch phosphate.
8. The crack-resistant concrete according to claim 1, characterized in that, The air-entraining-foam-stabilizing component comprises an air-entraining component and a foam-stabilizing component, wherein the air-entraining component is one or more of potassium azoformamide formate, p-toluenesulfonyl hydrazine, and trinitrosomethylenetriamine; and the foam-stabilizing component is one or more of fatty acid diethanolamine, silicone amide, and polyoxypropylene glycol.
9. The crack-resistant concrete according to claim 8, characterized in that, The mass ratio of the air-entraining component to the foam-stabilizing component is (1-5):
1.
10. A method for preparing crack-resistant concrete with high stone powder content as described in any one of claims 1 to 9, characterized in that, Includes the following steps: 1) Weigh out the cement, fly ash, mineral powder, stone powder and fine aggregate and mix them evenly. Add the modified wheat straw fiber, water-retaining component, air-entraining and foam-stabilizing component and part of the amount of water-reducing agent and mix evenly. Add the coarse aggregate and the remaining water-reducing agent and continue to mix evenly to obtain a crack-resistant concrete mixture with high stone powder content. 2) The resulting mixture is poured, vibrated to compact, and then covered with a film for curing at different ages to obtain crack-resistant concrete with high stone powder content.