High-anti-cracking and low-shrinkage ready-mixed concrete and preparation method thereof

Abstract

The application belongs to the technical field of concrete, and particularly relates to high-anti-cracking and low-shrinkage ready-mixed concrete and a preparation method thereof. The high-anti-cracking and low-shrinkage ready-mixed concrete is prepared from, by weight, 80-100 parts of medium-heat Portland cement, 65-75 parts of silane-modified fly ash, 50-60 parts of acrylate graft-modified zeolite, 10-15 parts of polypropylene fiber, 260-320 parts of fine aggregate, 300-400 parts of coarse aggregate, 2-3.5 parts of water reducing agent, 4-6 parts of magnesium oxide expanding agent, 1-1.5 parts of non-ionic surfactant and 60-80 parts of water. The application effectively improves the defect that a large amount of mineral admixtures easily lead to concrete shrinkage and cracking, improves the anti-cracking grade of concrete, reduces the shrinkage rate of concrete and improves the durability of concrete.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology, specifically relating to a high crack-resistant, low-shrinkage ready-mixed concrete and its preparation method. Background Technology

[0002] With the ongoing large-scale infrastructure construction in my country, concrete, as the most important civil engineering material, is widely used in industrial and civil buildings, water conservancy projects, underground engineering, highways, railways, airports, bridges, and national defense construction. Commonly used mineral admixtures such as fly ash and ground granulated blast furnace slag are important cementitious materials in concrete. The use of mineral admixtures reduces the amount of cement used in concrete, lowers costs, and improves various properties of concrete, resulting in significant technical and economic benefits.

[0003] However, the use of large amounts of mineral admixtures can easily lead to shrinkage cracking in concrete, thereby reducing its durability. Patent publication number CN 111943583 A discloses a low-shrinkage, high-crack-resistance, high-durability, long-life concrete, comprising the following components by weight: 100 parts of medium-heat silicate cement, 48-56 parts of fly ash, 32-37 parts of natural zeolite powder, 4.2-6.4 parts of magnesium oxide expanding agent, 13-18 parts of limestone powder, 428-440 parts of sand, 599-607 parts of crushed stone, 85-92 parts of water, 1.7-2.1 parts of water-reducing agent, and 0.1-0.2 parts of defoamer. The use of medium-heat silicate cement with low heat of hydration reduces the risk of temperature cracks in large-volume concrete structures, improves the expansion performance of magnesium oxide, improves the pore structure of the matrix, makes the concrete structure denser, reduces the risk of shrinkage cracking, and improves the durability of the concrete.

[0004] The applicant found that although the above-mentioned patent reduced the risk of shrinkage cracking in concrete and improved the crack resistance of concrete, the mass ratio of medium-heat silicate cement, fly ash and natural zeolite powder was 100:(48~56):(32~37), and the amount of mineral admixture was not high. Summary of the Invention

[0005] In order to improve the defect that large amounts of mineral admixtures can easily lead to shrinkage cracking in concrete, this application provides a high-crack-resistant, low-shrinkage ready-mixed concrete and its preparation method.

[0006] In the first aspect, this application provides a high-crack-resistant, low-shrinkage ready-mixed concrete, which is achieved by the following technical solution:

[0007] A type of high crack resistance and low shrinkage ready-mixed concrete, by weight, comprises 80-100 parts of medium-heat silicate cement, 65-75 parts of silane-modified fly ash, 50-60 parts of acrylate-grafted modified zeolite, 10-15 parts of polypropylene fiber, 260-320 parts of fine aggregate, 300-400 parts of coarse aggregate, 2-3.5 parts of water-reducing agent, 4-6 parts of magnesium oxide expanding agent, 1-1.5 parts of nonionic surfactant, and 60-80 parts of water.

[0008] By adopting the above technical solution, the reaction contact area of ​​silane-modified fly ash is large, and the large number of Si-O-Si bonds on the surface of silane-modified fly ash improves the chemical activity of fly ash, making the concrete structure more compact, reducing the risk of concrete shrinkage cracking, and improving the durability of concrete.

[0009] Acrylic-grafted zeolite improves the compatibility between zeolite and polypropylene fibers, increases the tensile strength of concrete, and reduces the risk of shrinkage cracking. The porous structure of acrylic-grafted zeolite facilitates water absorption and exhibits excellent water retention, helping to reduce moisture loss and shrinkage in concrete, thus enhancing its crack resistance. Therefore, even at high dosages, silane-modified fly ash and acrylic-grafted zeolite, as mineral admixtures, are unlikely to cause shrinkage cracking in concrete.

[0010] The combined action of magnesium oxide expansive and nonionic surfactant can significantly reduce the shrinkage rate of concrete and improve its crack resistance. This may be because the nonionic surfactant is adsorbed on the gas-liquid interface where the air and the capillary solution of high-performance concrete come into contact, significantly reducing the surface tension of the gas-liquid interface, slowing down the rate of internal humidity reduction, increasing the hydration degree of magnesium oxide, improving the expansion performance of magnesium oxide, improving the pore structure of the matrix, making the concrete structure denser, reducing the risk of shrinkage cracking in concrete, and improving the durability of concrete.

[0011] Medium-heat silicate cement has advantages such as low heat of hydration and low drying shrinkage, which can reduce the shrinkage rate of concrete and improve the crack resistance of concrete.

[0012] Preferably, the method for preparing the silane-modified fly ash includes the following steps:

[0013] S1. Mix fly ash and activator, grind them to obtain ground fly ash;

[0014] S2. Mix the ground fly ash, dispersant, water and ethanol to obtain a mixed system;

[0015] S3. Stir the mixture and gradually add a mixed solution of 3-aminopropyltriethoxysilane and ethanol. React at 50-85℃ for 5-8 hours. Filter, wash, and dry to obtain silane-modified fly ash.

[0016] The mass ratio of fly ash, 3-aminopropyltriethoxysilane and ethanol in step S3 is 1:(0.1-0.15):(5-8).

[0017] By adopting the above technical solution, the activator can act as a catalyst in the cement hydration process, improving the chemical activity of fly ash. Grinding the activated fly ash breaks down the protective film on the glassy surface, increasing the reaction contact area and improving the surface condition of the fly ash. Then, a dispersant is used to disperse the fly ash, improving its dispersibility and allowing it to fully react with 3-aminopropyltriethoxysilane. The fly ash surface is extensively grafted with 3-aminopropyltriethoxysilane, mitigating the low strength problem caused by slow hydration when directly adding fly ash, thus improving the defect of high fly ash admixtures leading to concrete shrinkage cracking.

[0018] Preferably, the dispersant is a mixture of dodecyl glucoside and polyvinyl alcohol in a mass ratio of (3-4):1.

[0019] By adopting the above technical solution, dodecyl glucoside and polyvinyl alcohol, which possess hydroxyl groups, can interact with the amino groups in 3-aminopropyltriethoxysilane, further increasing the grafting amount of 3-aminopropyltriethoxysilane on the fly ash surface, which is beneficial for reducing the shrinkage rate of concrete. This may be because the hydrophilic groups of dodecyl glucoside can adsorb some water, reducing water evaporation, increasing the internal humidity of concrete, and further reducing shrinkage; at the same time, polyvinyl alcohol can improve the dispersibility and flowability between fly ash and coarse and fine aggregates, reducing the water-cement ratio, and polyvinyl alcohol binds and fills the microcracks and pores between aggregate particles with cementitious materials, improving the density of concrete.

[0020] Preferably, the mass ratio of fly ash, dispersant, water and ethanol in step S2 is 1:(0.1-0.15):(3-5):(5-8).

[0021] By adopting the above technical solution, fly ash exhibits good dispersibility.

[0022] Preferably, the mass ratio of fly ash to activator is 1:(0.0002-0.0003).

[0023] By adopting the above technical solution, the activation effect of fly ash is good.

[0024] Preferably, the activator is a mixture of triethanolamine and sodium hexametaphosphate in a mass ratio of (5-7):1.

[0025] By adopting the above technical solution, the combination of triethanolamine and sodium hexametaphosphate not only has a better activation effect on fly ash and can act as a catalyst in the cement hydration process, but also has an expansion effect, which can improve the pore structure of concrete, increase the density and structural strength of concrete, and reduce the shrinkage rate of concrete.

[0026] Preferably, the preparation method of the acrylate-grafted modified zeolite includes the following steps:

[0027] S1. Mix zeolite, aluminate coupling agent and ethanol, react at 50-80℃ for 3-4 hours, wash and dry to obtain aluminate coupling agent modified zeolite.

[0028] S2. Aluminate coupling agent modified zeolite, methyl methacrylate, initiator and water are mixed evenly at a ratio of 1:(0.6-0.8):(0.004-0.005):(5-8), and reacted at 70-90℃ for 3-4 hours. After post-treatment, acrylate grafted modified zeolite is obtained.

[0029] By adopting the above technical solution, the aluminate coupling agent has a coupling effect, which improves the affinity and binding force between zeolite and polymethyl methacrylate, which is conducive to the polymerization of methyl methacrylate on the zeolite surface. The resulting acrylate-grafted modified zeolite has good compatibility with polypropylene fibers, which improves the tensile strength of concrete and reduces the risk of concrete shrinkage cracking.

[0030] Preferably, the mass ratio of the zeolite to the aluminate coupling agent is 1:(0.08-0.1).

[0031] By adopting the above technical solution, the zeolite is evenly dispersed, which is beneficial for the grafting and polymerization of methyl methacrylate on the zeolite surface.

[0032] Preferably, the nonionic surfactant is a mixture of dehydrated sorbitan fatty acid ester and fatty acid polyoxyethylene ester in a mass ratio of (0.8-1.2):1.

[0033] By adopting the above technical solution, the nonionic surfactant compounded from dehydrated sorbitan fatty acid ester and fatty acid polyoxyethylene ester has a significant shrinkage reduction effect, reduces the shrinkage stress of concrete, reduces the evaporation of concrete moisture, increases the internal humidity of concrete, and further reduces shrinkage.

[0034] Secondly, this application provides a method for preparing high-crack-resistant and low-shrinkage ready-mixed concrete, which is achieved by the following technical solution:

[0035] A method for preparing high-crack-resistant, low-shrinkage ready-mixed concrete includes the following steps:

[0036] Magnesium oxide expanding agent, acrylate grafted modified zeolite, polypropylene fiber, water reducing agent, nonionic surfactant and water are mixed evenly to obtain mixture A;

[0037] Mixture B is prepared by dry mixing of medium-heat silicate cement, silane-modified fly ash, fine aggregate, and coarse aggregate.

[0038] Mix mixture A and mixture B thoroughly to obtain high crack resistance and low shrinkage ready-mixed concrete.

[0039] In summary, this application has the following beneficial effects:

[0040] 1. This application uses silane-modified fly ash. The Si-O-Si bonds on the surface enhance the chemical activity of the fly ash, making the concrete structure denser, reducing the risk of concrete shrinkage cracking, and improving the durability of the concrete.

[0041] 2. This application uses acrylate-grafted zeolite, which improves the compatibility between zeolite and polypropylene fiber, increases the tensile strength of concrete, and reduces the risk of concrete shrinkage cracking.

[0042] 3. The magnesium oxide expanding agent and nonionic surfactant of this application work together to significantly reduce the shrinkage rate of concrete and improve the crack resistance of concrete.

[0043] 4. This application uses silane-modified fly ash obtained by activation, grinding, dispersion and reaction with 3-aminopropyltriethoxysilane, which improves the problem of low strength caused by slow hydration of directly added fly ash, thereby improving the defect that high-volume fly ash easily leads to shrinkage cracking in concrete.

[0044] 5. This application uses a dispersant composed of dodecyl glucoside and polyvinyl alcohol, which can better disperse fly ash and further reduce the shrinkage rate of concrete.

[0045] 6. This application uses a compound activator of triethanolamine and sodium hexametaphosphate, which can better activate fly ash and further reduce the shrinkage rate of concrete.

[0046] 7. This application uses a nonionic surfactant compounded from sorbitan fatty acid ester and fatty acid polyoxyethylene ester, which has a significant shrinkage reduction effect, reduces the shrinkage stress of concrete, reduces the evaporation of concrete moisture, increases the internal humidity of concrete, and further reduces shrinkage. Detailed Implementation

[0047] The present application will be further described in detail below with reference to the embodiments.

[0048] Preparation Example

[0049] Preparation Examples 1-11 provide a silane-modified fly ash. The following description uses Preparation Example 1 as an example.

[0050] The preparation steps for the silane-modified fly ash provided in Example 1 are as follows:

[0051] S1. Mix 100kg fly ash and 0.02kg triethanolamine, grind, dry ball mill and pass through a 100-mesh sieve to obtain ground fly ash;

[0052] S2. Mix the ground fly ash prepared in S1, 10 kg of polyvinyl alcohol 2488, 300 kg of water and 500 kg of ethanol, and stir evenly to obtain a mixed system.

[0053] S3. Mix 10 kg of 3-aminopropyltriethoxysilane and 500 kg of ethanol to obtain a mixed solution of 3-aminopropyltriethoxysilane and ethanol. Stir the mixture prepared in S2 for 30 min, and gradually add the mixed solution of 3-aminopropyltriethoxysilane and ethanol. React at 50 °C for 8 h. Filter the solid and wash it three times with 0.1 mol / L sodium hydroxide solution and water, respectively. Dry the solid to obtain silane-modified fly ash.

[0054] Preparation Example 2 differs from Preparation Example 1 only in that the reaction temperature in step S3 is 85°C and the reaction time is 5 hours.

[0055] Preparation Examples 3-5 differ from Preparation Example 2 only in that the quality of each raw material is different, as detailed in Table 1.

[0056] Table 1. Mass of raw materials for each preparation example 2-5 (kg)

[0057]

[0058] Preparation Example 6 differs from Preparation Example 5 only in that triethanolamine is replaced by sodium hexametaphosphate in equal mass.

[0059] Preparation Example 7 differs from Preparation Example 5 only in that: the same mass of triethanolamine is replaced with a mixture of triethanolamine and sodium hexametaphosphate, with a mass ratio of triethanolamine to sodium hexametaphosphate of 5:1.

[0060] Preparation Example 8 differs from Preparation Example 7 only in that the mass ratio of triethanolamine to sodium hexametaphosphate is 7:1.

[0061] Preparation Example 9 differs from Preparation Example 8 only in that polyvinyl alcohol 2488 is replaced by dodecyl glucoside in equal mass.

[0062] Preparation Example 10 differs from Preparation Example 8 only in that: the same mass of polyvinyl alcohol 2488 is replaced with a mixture of dodecyl glucoside and polyvinyl alcohol 2488, with a mass ratio of dodecyl glucoside to polyvinyl alcohol 2488 of 3:1.

[0063] Preparation Example 11 differs from Preparation Example 10 only in that the mass ratio of dodecyl glucoside and polyvinyl alcohol 2488 is 4:1.

[0064] Preparation Examples 12-15 provide an acrylate-grafted modified zeolite, and the following description uses Preparation Example 12 as an example.

[0065] The acrylate-grafted modified zeolite provided in Example 12 is prepared by the following steps:

[0066] S1. Mix 100 kg of zeolite, 8 kg of aluminate coupling agent UP-801 and 500 kg of ethanol, react at 50 °C for 4 h, wash and dry to obtain aluminate coupling agent modified zeolite.

[0067] S2. The aluminate coupling agent modified zeolite prepared in S1, 60 kg of methyl methacrylate, 0.4 kg of azobisisobutyronitrile and 500 kg of water were mixed evenly and reacted at 70 °C for 4 h. After the reaction was completed, the product was removed and dried under vacuum at 50 °C for 24 h. It was then extracted with ethyl acetate as solvent for 8 h, dried at 110 °C for 8 h, ground and passed through a 100-mesh sieve to obtain acrylate grafted modified zeolite. The aluminate coupling agent UP-801 was purchased from Nanjing Youpu Chemical Co., Ltd.

[0068] Preparation Examples 13-14 differ from Example 12 only in that the quality of each raw material is different, as detailed in Table 2.

[0069] Table 2 Mass / kg of each raw material used in preparation examples 12-14

[0070]

[0071] Preparation Example 15 differs from Example 14 only in that: the reaction temperature in step S1 is 80°C and the reaction time is 3 hours; the reaction temperature in step S2 is 90°C and the reaction time is 3 hours.

[0072] Preparation of comparative examples

[0073] Comparative Examples 1-2 provide a silane-modified fly ash.

[0074] The silane-modified fly ash prepared in Comparative Example 1 differs from that in Preparation Example 1 only in that triethanolamine was not added in step S1.

[0075] The silane-modified fly ash prepared in Comparative Example 2 differs from that in Preparation Example 1 only in that polyvinyl alcohol 2488 was not added in step S2.

[0076] Example

[0077] Examples 1-23 provide a high crack resistance and low shrinkage ready-mixed concrete. The following description uses Example 1 as an example.

[0078] The high crack resistance and low shrinkage ready-mixed concrete provided in Example 1 is prepared by the following steps:

[0079] S1. Mix 4 kg of magnesium oxide expanding agent, 50 kg of acrylate grafted modified zeolite, 10 kg of polypropylene fiber Hongyao HY-426, 2 kg of BASF water reducing agent RHEOPLUS 412, 1 kg of dehydrated sorbitan fatty acid ester S-60 and 60 kg of water evenly to obtain mixture A.

[0080] S2. Mix 80 kg of medium-heat silicate cement, 65 kg of silane-modified fly ash, 260 kg of sand and 300 kg of crushed stone dry to obtain mixture B;

[0081] S3. Mix the mixture A prepared in S1 and the mixture B prepared in S2 evenly to obtain high crack resistance and low shrinkage ready-mixed concrete.

[0082] Among them, the acrylate-grafted modified zeolite was derived from Preparation Example 12;

[0083] The strength grade of the medium-heat silicate cement is 42.5.

[0084] The silane-modified fly ash was derived from Preparation Example 1.

[0085] Examples 2-5 differ from Example 1 only in that the quality of each raw material used in the preparation of ready-mixed concrete is different, as detailed in Table 3.

[0086] Table 3. Mass of each raw material used in the preparation of ready-mixed concrete in Examples 1-5 (kg)

[0087]

[0088] Example 6 differs from Example 2 only in that: the sorbitan fatty acid ester S-60 is replaced by polyoxyethylene laurate LAE-9.

[0089] Example 7 differs from Example 2 only in that: the sorbitan fatty acid ester S-60 is replaced by a mixture of sorbitan fatty acid ester S-60 and polyoxyethylene laurate LAE-9, with a mass ratio of sorbitan fatty acid ester S-60 to polyoxyethylene laurate LAE-9 of 0.8:1.

[0090] Example 8 differs from Example 7 only in that the mass ratio of sorbitan fatty acid ester S-60 to polyoxyethylene laurate LAE-9 is 1.2:1.

[0091] Examples 9-20 differ from Example 8 only in that the source of the silane-modified fly ash is different, as detailed in Table 4.

[0092] Table 4. Sources of silane-modified fly ash in Examples 8-20

[0093]

[0094] Examples 21-23 differ from Example 18 only in that the acrylate-grafted zeolite is different, as detailed in Table 5.

[0095] Table 5. Sources of acrylate-grafted zeolite in Examples 18, 21-23

[0096]

[0097] Comparative Example

[0098] Comparative Example 1 differs from Example 5 only in that the silane-modified fly ash is replaced by unmodified fly ash at the same mass.

[0099] Comparative Example 2 differs from Example 5 only in that the acrylate-grafted modified zeolite is replaced with unmodified zeolite.

[0100] Comparative Example 3 differs from Example 5 only in that the mass of dehydrated sorbitan fatty acid ester S-60 is replaced with magnesium oxide expander.

[0101] Comparative Example 4 differs from Example 5 only in that the magnesium oxide expanding agent is replaced by an equal mass of dehydrated sorbitan fatty acid ester S-60.

[0102] Performance testing

[0103] The following performance tests were conducted on the high crack resistance and low shrinkage ready-mixed concrete prepared in Examples 1-23 and Comparative Examples 1-4 of this application.

[0104] 1. Crack resistance performance: The crack resistance performance of the high crack resistance and low shrinkage ready-mixed concrete specimens prepared in Examples 1-23 and Comparative Examples 1-4 were tested according to the standard in 3.0.4 of JGJ / T 193-2009 "Standard for Testing and Evaluation of Concrete Durability". The test results of crack resistance grade are shown in Table 6.

[0105] 2. Shrinkage performance: Shrinkage tests were conducted on the specimens of high crack resistance and low shrinkage ready-mixed concrete prepared in Examples 1-23 and Comparative Examples 1-4 according to the non-contact shrinkage standard in 8.1 of GB / T50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete". The test results of shrinkage rate are shown in Table 6.

[0106] Table 6 Test Results

[0107] Crack resistance level 180-day shrinkage rate (%) Example 1 LV <![CDATA[3.21×10 -4 ]]> Example 2 LV <![CDATA[3.12×10 -4 ]]> Example 3 L-IV <![CDATA[3.28×10 -4 ]]> Example 4 L-IV <![CDATA[3.35×10 -4 ]]> Example 5 L-IV <![CDATA[3.43×10 -4 ]]> Example 6 LV <![CDATA[3.14×10 -4 ]]> Example 7 LV <![CDATA[2.91×10 -4 ]]> Example 8 LV <![CDATA[2.88×10 -4 ]]> Example 9 LV <![CDATA[2.87×10 -4 ]]> Example 10 LV <![CDATA[2.82×10 -4 ]]> Example 11 LV <![CDATA[2.80×10 -4 ]]> Example 12 LV <![CDATA[2.76×10 -4 <!-- 7 -->]]> Example 13 LV <![CDATA[2.77×10 -4 ]]> Example 14 LV <![CDATA[2.69×10 -4 ]]> Example 15 LV <![CDATA[2.65×10 -4 ]]> Example 16 LV <![CDATA[2.66×10 -4 ]]> Example 17 LV <![CDATA[2.60×10 -4 ]]> Example 18 LV <![CDATA[2.59×10 -4 ]]> Example 19 LV <![CDATA[3.08×10 -4 ]]> Example 20 LV <![CDATA[3.02×10 -4 ]]> Example 21 LV <![CDATA[2.53×10 -4 ]]> Example 22 LV <![CDATA[2.49×10 -4 ]]> Example 23 LV <![CDATA[2.47×10 -4 ]]> Comparative Example 1 L-III <![CDATA[4.94×10 -4 ]]> Comparative Example 2 L-III <![CDATA[4.91×10 -4 ]]> Comparative Example 3 L-III <![CDATA[4.83×10 -4 ]]> Comparative Example 4 L-III <![CDATA[4.87×10 -4 ]]>

[0108] The following section details this application based on the test data in Table 6.

[0109] As can be seen from the test data of Example 5 and Comparative Example 1, compared with unmodified fly ash, the silane-modified fly ash used in this application can improve the crack resistance of concrete and reduce the shrinkage rate of concrete under the condition of high doping amount of fly ash.

[0110] As can be seen from the test data of Example 5 and Comparative Example 2, compared with unmodified zeolite, the acrylate-grafted zeolite used in this application can improve the crack resistance of concrete and reduce the shrinkage rate of concrete even with a high amount of zeolite doping.

[0111] The test data from Example 5 and Comparative Examples 3-4 show that the combined action of magnesium oxide expansive agent and nonionic surfactant can significantly reduce the shrinkage rate of concrete and improve its crack resistance.

[0112] The test data from Examples 1-5 show that the concrete in Example 2 has a lower shrinkage rate and a crack resistance grade of LV; while the concrete in Example 5 has a crack resistance grade of L-IV and a higher shrinkage rate.

[0113] The test data from Examples 2, 6 and Examples 7-8 show that Examples 7-8 use a nonionic surfactant compounded from sorbitan fatty acid ester and fatty acid polyoxyethylene ester, while Examples 2 and 6 use only sorbitan fatty acid ester or fatty acid polyoxyethylene ester. The shrinkage rate of the concrete corresponding to Examples 7-8 is significantly lower than that of the concrete corresponding to Examples 2 and 6.

[0114] The test data from Examples 8 and 19-20 show that the silane-modified fly ash obtained by Triethanolamine activation followed by grinding, dispersion, and reaction with 3-aminopropyltriethoxysilane in Example 8 has a lower shrinkage rate in the corresponding concrete.

[0115] The test data from Examples 8 and 20 show that the silane-modified fly ash obtained in Example 8 through activation, grinding, dispersion with polyvinyl alcohol 2488, and reaction with 3-aminopropyltriethoxysilane has a lower shrinkage rate in the corresponding concrete.

[0116] The test data from Examples 12-13 and 14-15 show that Example 14-15 uses a combination of triethanolamine and sodium hexametaphosphate to activate fly ash, while Examples 12 and 13 use either triethanolamine or sodium hexametaphosphate to activate fly ash alone. The shrinkage rate of the concrete corresponding to Example 14-15 is lower than that of the concrete corresponding to Example 12-13.

[0117] The test data from Examples 15-16 and 17-18 show that Examples 17-18 used a composite dispersion of dodecyl glucoside and polyvinyl alcohol 2488 to disperse fly ash, while Examples 15 and 16 used either dodecyl glucoside or polyvinyl alcohol 2488 to disperse fly ash alone. The shrinkage rate of the concrete corresponding to Examples 17-18 was lower than that of the concrete corresponding to Examples 15-16.

[0118] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment 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 high-crack-resistant, low-shrinkage ready-mixed concrete, characterized in that, By weight, the raw materials for its preparation include 80-100 parts of medium-heat silicate cement, 65-75 parts of silane-modified fly ash, 50-60 parts of acrylate-grafted zeolite, 10-15 parts of polypropylene fiber, 260-320 parts of fine aggregate, 300-400 parts of coarse aggregate, 2-3.5 parts of water-reducing agent, 4-6 parts of magnesium oxide expanding agent, 1-1.5 parts of nonionic surfactant, and 60-80 parts of water. The method for preparing the silane-modified fly ash includes the following steps: S1. Mix fly ash and activator, grind them to obtain ground fly ash; S2. Mix the ground fly ash, dispersant, water and ethanol to obtain a mixed system; S3. Stir the mixture and gradually add a mixed solution of 3-aminopropyltriethoxysilane and ethanol. React at 50-85℃ for 5-8 hours. Filter, wash, and dry to obtain silane-modified fly ash. The mass ratio of fly ash, 3-aminopropyltriethoxysilane, and ethanol in step S3 is 1:(0.1-0.15):(5-8). The preparation method of the acrylate-grafted modified zeolite includes the following steps: S1. Mix zeolite, aluminate coupling agent and ethanol, react at 50-80℃ for 3-4 hours, wash and dry to obtain aluminate coupling agent modified zeolite. S2. Mix aluminate coupling agent modified zeolite, methyl methacrylate, initiator and water in a ratio of 1: (0.6-0.8): (0.004-0.005): (5-8) until homogeneous, react at 70-90℃ for 3-4 hours, and then perform post-treatment to obtain acrylate grafted modified zeolite.

2. The high crack resistance and low shrinkage ready-mixed concrete according to claim 1, characterized in that, The dispersant is composed of dodecyl glucoside and polyvinyl alcohol in a mass ratio of (3-4):

1.

3. The high crack resistance and low shrinkage ready-mixed concrete according to claim 1, characterized in that, The mass ratio of fly ash, dispersant, water and ethanol in step S2 is 1:(0.1-0.15):(3-5):(5-8).

4. The high crack resistance and low shrinkage ready-mixed concrete according to claim 1, characterized in that, The mass ratio of fly ash to activator is 1:(0.0002-0.0003).

5. The high crack resistance and low shrinkage ready-mixed concrete according to claim 1, characterized in that, The activator is a mixture of triethanolamine and sodium hexametaphosphate in a mass ratio of (5-7):

1.

6. The high crack resistance and low shrinkage ready-mixed concrete according to claim 1, characterized in that, The mass ratio of the zeolite to the aluminate coupling agent is 1:(0.08-0.1).

7. The high crack resistance and low shrinkage ready-mixed concrete according to claim 1, characterized in that, The nonionic surfactant is composed of dehydrated sorbitan fatty acid ester and fatty acid polyoxyethylene ester mixed in a mass ratio of (0.8-1.2):

1.

8. A method for preparing high-crack-resistant, low-shrinkage ready-mixed concrete according to any one of claims 1-7, characterized in that, Includes the following steps: Magnesium oxide expanding agent, acrylate grafted modified zeolite, polypropylene fiber, water reducing agent, nonionic surfactant and water are mixed evenly to obtain mixture A; Mixture B is prepared by dry mixing of medium-heat silicate cement, silane-modified fly ash, fine aggregate, and coarse aggregate. Mix mixture A and mixture B thoroughly to obtain high crack resistance and low shrinkage ready-mixed concrete.

Images