Super-retarding concrete and preparation method thereof

Abstract

The invention provides super-retarded concrete and a preparation method thereof. The super-retarded concrete is prepared from the following raw materials in parts by weight: 250 to 350 parts of cement, 80 to 120 parts of fly ash, 60 to 100 parts of superfine slag powder, 600 to 800 parts of sand, 1000 to 1200 parts of stone, 150 to 200 parts of water, 3 to 5 parts of a high-efficiency water reducing agent, 8 to 12 parts of a composite retarder, 5 to 7 parts of an expanding agent and 32 to 45 parts of an anti-cracking agent, wherein the composite retarder is prepared from sodium gluconate, citric acid and sodium lignin sulfonate, and the mass ratio of the sodium gluconate to the citric acid to the sodium lignin sulfonate is (2.5 to 3.5) to (1.5 to 2.5) to (0.5 to 1.5). According to the super-retarding concrete, the setting time of the concrete can be remarkably prolonged, and the problems of long-time pouring of a building structure, 'cold joint 'in mass concrete construction, slump loss in summer construction and the like are well solved; meanwhile, the super-retarded concrete provided by the invention can reduce hydration heat and improve crack resistance, and can well meet the construction requirements of mass concrete.

Description

Technical Field

[0001] This invention relates to the field of concrete technology, and in particular to an ultra-retarded concrete and its preparation method. Background Technology

[0002] In modern construction engineering, when building structures require long pouring times, the initial setting time of ordinary concrete (6-10 hours) is insufficient to meet construction requirements. For example, in the construction of large-volume concrete structures, if the initial setting time is too short, the earlier poured sections will set before the later poured sections, resulting in "cold joints" in the structure. This leads to delamination and cracks in the concrete structure, severely affecting project quality and structural stability. Furthermore, during construction in high-temperature summer environments, ordinary concrete experiences rapid slump loss and has a short service life, making it difficult to ensure the continuity of construction and the workability of the concrete.

[0003] The construction of the ring slab foundation for a high-level cooling tower with high water collection capacity presents numerous complex challenges due to its large-volume concrete nature. Large-volume concrete construction is prone to excessive internal temperatures caused by the accumulation of cement hydration heat, leading to significant thermal stress and subsequent concrete cracking. Furthermore, the ring slab foundation construction requires strict control over construction time, temperature, and techniques. For example, the closure temperature must be around 10℃, and in summer, the concrete placement temperature must be strictly controlled to not exceed 25℃. Additionally, staggered placement construction, controlled construction joint treatment, and controlled temperature differences and cooling rates between the inner and outer surfaces are essential. Currently, ordinary concrete cannot meet the stringent requirements of high-level cooling tower ring slab foundation construction in terms of setting time, temperature control, and crack resistance. Therefore, there is an urgent need to develop an ultra-retarded setting concrete suitable for this project and its preparation method.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide an ultra-retarded concrete and its preparation method, which can significantly extend the setting time of concrete, while reducing the heat of hydration and improving crack resistance.

[0006] This invention provides an ultra-retarded concrete, comprising the following raw materials in parts by weight: 250-350 parts cement, 80-120 parts fly ash, 60-100 parts slag powder, 600-800 parts sand, 1000-1200 parts gravel, 150-200 parts water, 3-5 parts high-efficiency water-reducing agent, 8-12 parts composite retarder, 5-7 parts expansion agent, and 32-45 parts crack-resistant agent; wherein the composite retarder comprises sodium gluconate, citric acid, and sodium lignosulfonate, and the mass ratio between sodium gluconate, citric acid, and sodium lignosulfonate in the composite retarder is (2.5-3.5):(1.5-2.5):(0.5-1.5).

[0007] In this invention, the cement is ordinary Portland cement with a strength grade of not less than 42.5, and its quality should comply with the relevant provisions of the national standard GB175-2007 "General Portland Cement".

[0008] The fly ash is Class II fly ash, with a water requirement ratio not exceeding 105% and a loss on ignition not exceeding 8%. Its quality should meet the requirements of the national standard GB / T1596-2017 "Fly Ash for Cement and Concrete".

[0009] The specific surface area of ​​slag powder is not less than 400m². 2 / kg, with an activity index of not less than 95%, and its quality conforms to the national standard GB / T18046-2017 "Granulated blast furnace slag powder for use in cement, mortar and concrete".

[0010] The sand is medium sand with a fineness modulus of 2.3-3.0 and a mud content of no more than 3%.

[0011] The gravel is continuously graded crushed stone with a particle size of 5-25mm, a needle-like and flaky particle content of no more than 15%, and a mud content of no more than 1%.

[0012] The high-efficiency water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent with a water reduction rate of not less than 25%.

[0013] The expansive agent can be an ettringite-type expansive agent; specifically, UEA or CSA expansive agents can be used. The main components of ettringite-type expansive agents are calcium sulfoaluminate, calcium oxide, etc. These expansive agents react with cement hydration products to form ettringite crystals, resulting in moderate volume expansion (expansion rate is usually 0.02-0.05%). This can compensate for plastic shrinkage and drying shrinkage during the hardening process of concrete, reducing cracks caused by shrinkage, and is especially suitable for large-volume concrete structures. The quality of the expansive agent should comply with the national standard "Concrete Expansive Agent" (GB / T 23439-2017), limiting the expansion rate to not less than 0.025% in water after 7 days and not more than 0.010% in air after 21 days.

[0014] Crack-resistant agents can be composite crack-resistant agents; specifically, composite crack-resistant agents include polypropylene fibers and polyether derivatives; wherein, the length of the polypropylene fibers is 6-12 mm and the diameter is 20-50 μm; the polyether derivatives can be modified polyethers, polyglycol ethers, or polycarboxylic acid ethers, and the mass ratio of polypropylene fibers to polyether derivatives in the composite crack-resistant agent is (3-5):1. In the above-mentioned composite crack-resistant agents, polypropylene fibers can enhance the toughness of concrete through random distribution and inhibit the initiation and propagation of plastic cracks; polyether derivatives can reduce the surface tension inside the concrete and reduce drying shrinkage. In addition, SY-T composite fiber crack-resistant agent (Henan Zhonglu Juneng New Building Materials Co., Ltd.) can also be used. The performance of the crack-resistant agent should meet the following requirements: fiber content 0.9-1.2 kg / m³.3 At that time, the crack resistance grade of the concrete shall not be lower than L-II grade (tested according to the "Standard for Test Methods of Fiber Reinforced Concrete" GB / T 50081-2019).

[0015] In the composite retarder of the present invention, sodium gluconate has a dispersing and retarding effect; citric acid can regulate the hydration rate and reduce temperature stress concentration; sodium lignosulfonate can improve the cohesiveness of the paste; the three work synergistically to significantly improve the crack resistance of concrete.

[0016] The ultra-retarded concrete of this invention has a scientific and reasonable raw material ratio. It uses a specific proportion of basic raw materials such as cement, fly ash, and slag powder, and introduces a composite retarder composed of sodium gluconate, citric acid and sodium lignosulfonate. At the same time, it adds an appropriate amount of expansion agent and crack-resistant agent, which can significantly extend the setting time of concrete, reduce the heat of hydration and improve crack resistance, and can well meet the construction requirements of large volume concrete.

[0017] The present invention also provides a method for preparing the above-mentioned super-retarded concrete, comprising the following steps:

[0018] S1: Add cement, fly ash, slag powder, sand and gravel to the mixer according to the weight parts, and dry mix to ensure that all raw materials are fully and evenly mixed;

[0019] S2: Add the high-efficiency water-reducing agent, composite retarder, expansion agent and crack-resistant agent to water according to the weight parts, stir evenly to make a mixed solution;

[0020] S3: Under continuous stirring conditions, the mixed solution is slowly added to the mixer and stirred until it is uniformly mixed to obtain super-retarded concrete.

[0021] In step S1, the dry mixing time is 1-2 minutes; in step S3, the stirring time is 3-5 minutes.

[0022] The preparation method of this invention is scientifically sound and reasonable. By clearly specifying the specific steps and times for weighing raw materials, dry mixing, solution preparation, and stirring, it ensures that the concrete mixture is uniform and consistent, and guarantees the stable performance of the super-retarded concrete. Moreover, the preparation method is simple to operate and suitable for industrial production.

[0023] The implementation of this invention has at least the following advantages:

[0024] 1) By employing specific raw material ratios, especially the use of composite retarder, this invention significantly extends the setting time of concrete, with initial setting time reaching over 24 hours and final setting time reaching over 36 hours. This meets the special requirements for concrete setting time in long-term pouring of building structures, avoiding "cold joints" in large-volume concrete construction, and the construction of high-level cooling tower ring plate foundations, facilitating construction operation and control. In summer construction, it can also effectively reduce concrete slump loss, extend the service life of concrete, and ensure construction continuity.

[0025] 2) By adding fly ash and slag powder and designing a reasonable mix proportion, this invention effectively reduces the amount of cement used in concrete and reduces the generation of heat of hydration. At the same time, the composite retarder can delay the release of heat of hydration. Combined with the use of crack-resistant agent and expansion agent, it greatly improves the crack resistance of concrete and can meet the requirements of temperature control and crack resistance of large-volume concrete in the "Code for Construction of Mass Concrete" GB50496-2009, thus ensuring the engineering quality of large-volume concrete such as ring slab foundations.

[0026] 3) The preparation method of the present invention is simple and easy to implement, convenient to operate, suitable for industrial production, and can effectively improve production efficiency and reduce production costs. The concrete prepared by this method has stable performance, can effectively extend the setting time of the concrete, effectively delay the release of hydration heat, reduce the hydration heat, and improve the crack resistance of the concrete. It meets the special requirements of concrete setting time, temperature control, and crack resistance in the construction of the ring plate foundation of the high-level water collection cooling tower, and can effectively ensure the smooth progress of the construction of various related projects such as the ring plate foundation of the high-level water collection cooling tower. Detailed Implementation

[0027] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0028] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0029] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1

[0031] The super-retarded concrete of this embodiment comprises the following raw materials in parts by weight: 250 parts cement, 80 parts fly ash, 60 parts slag powder, 600 parts sand, 1000 parts gravel, 150 parts water, 3 parts polycarboxylate-based high-efficiency water-reducing agent, 8 parts composite retarder, 5 parts UEA expansion agent, and 32 parts composite crack-resistant agent; wherein, the composite retarder is composed of sodium gluconate, citric acid, and sodium lignosulfonate, with a mass ratio of sodium gluconate, citric acid, and sodium lignosulfonate of 3:2:1; the composite crack-resistant agent is composed of polypropylene fibers (6-12 mm in length and 20-50 μm in diameter) and polycarboxylate ether, with a mass ratio of polypropylene fibers to polycarboxylate ether of 5:1.

[0032] The method for preparing super-retarded concrete in this embodiment is as follows:

[0033] 1. Accurately weigh the above-mentioned raw materials according to the above weight proportions;

[0034] 2. Add cement, fly ash, slag powder, sand and gravel to the mixer and dry mix for 1 minute;

[0035] 3. Add polycarboxylate superplasticizer, composite retarder, UEA expansion agent and composite crack-resistant agent to water, stir evenly to make a mixed solution;

[0036] 4. While the mixer is continuously stirring, slowly add the mixed solution into the mixer and stir for 3 minutes to obtain super-retarded concrete.

[0037] The above-mentioned ultra-retarded concrete is used in the construction of the ring plate foundation of the high-level water collection cooling tower. The construction requirements are as follows:

[0038] 1) After the foundation treatment of the high-level tower is completed, it must pass inspection before the foundation construction can proceed. Excavation of the foundation pit is strictly prohibited in rainy weather. After excavation, the pit should be inspected immediately, and effective measures should be taken to prevent damage to the original structure and natural humidity of the foundation. Before excavating to the design elevation, a certain thickness of coating should be retained, which should be removed before the foundation is poured.

[0039] 2) Strictly control construction quality in accordance with the "Code for Construction of Mass Concrete" GB50496-2009. Construction should be scheduled for spring and autumn whenever possible, with the closure temperature controlled at around 10℃. Strengthen insulation measures during construction. In summer, strictly control the concrete's temperature upon placement in the formwork; under no circumstances should it exceed 25℃. Take cooling measures if necessary. Do not sprinkle water when the average temperature is below 5℃, and stop construction when it is below -5℃. After concrete pouring, cover and water it within 12 hours, and maintain the water for at least 14 days.

[0040] 3) Adopt skip-pour construction, with a pouring interval of more than 2 weeks, and strictly treat construction joints according to regulations to prevent cold joints.

[0041] 4) Contact the local meteorological department before construction to obtain recent weather information and formulate construction technical measures for special weather conditions (such as cold waves, low temperatures, strong winds, rain, snow, etc.). Stop high-altitude operations when winds exceed level six.

[0042] 5) When the average daily outdoor temperature is consistently below 5℃ for 5 consecutive days, winter construction methods shall be followed. If construction is necessary when the temperature is below -5℃, insulation measures shall be strengthened, and antifreeze shall be added if necessary (the amount added shall be determined by the construction unit according to the construction specifications). If winter approaches after the completion of the ring foundation construction, necessary protective measures shall be taken.

[0043] 6) During construction, strictly ensure the thickness of the concrete cover and strictly control the negative deviation of the cover; retain test blocks for compressive strength concrete, frost resistance concrete, and impermeability concrete as required by specifications; take appropriate protective measures when welding reinforcement for man-made columns and support piers in rainy, snowy, or windy weather; reserve reinforcement for the A-frame columns and supports during the construction of the ring foundation; embed the reinforcement for settlement monitoring during the pouring of the supports; embed lightning protection down conductors during the construction of the A-frame columns and supports; if special circumstances are encountered during construction (such as inconsistencies between geological conditions and survey boreholes), contact the survey and design unit in a timely manner to negotiate a solution; apply 300μm epoxy asphalt to the contact parts between the ring foundation, supports, and soil; for the natural foundation section of the ring foundation, set two layers of isolation, such as a 200mm crushed stone cushion layer or asphalt felt, between the ring foundation and the bearing layer.

[0044] The performance of the ultra-retarded concrete prepared in this embodiment was tested, and the results are as follows:

[0045] Initial setting time: 25 hours;

[0046] Final setting time: 37 hours;

[0047] 28-day compressive strength: 55 MPa (design strength grade is C50);

[0048] Crack resistance: Under simulated temperature control conditions during ring slab foundation construction, the probability of cracks appearing is significantly reduced;

[0049] Slump loss during summer construction: Under high temperature conditions, concrete slump loss is significantly reduced, effectively extending the service life.

[0050] Example 2

[0051] The super-retarded concrete of this embodiment comprises the following raw materials in parts by weight: 300 parts cement, 100 parts fly ash, 80 parts slag powder, 700 parts sand, 1100 parts gravel, 170 parts water, 4 parts polycarboxylate-based high-efficiency water-reducing agent, 10 parts composite retarder, 6 parts UEA expansion agent, and 38.4 parts composite crack-resistant agent; wherein, the composite retarder is composed of sodium gluconate, citric acid, and sodium lignosulfonate, and the mass ratio between sodium gluconate, citric acid, and sodium lignosulfonate is 2.5:2.5:1.5; the composite crack-resistant agent is composed of polypropylene fibers (6-12 mm in length and 20-50 μm in diameter) and polycarboxylate ether, and the mass ratio of polypropylene fibers to polycarboxylate ether is 3:1.

[0052] The method for preparing super-retarded concrete in this embodiment is as follows:

[0053] 1. Accurately weigh the above-mentioned raw materials according to the above weight proportions;

[0054] 2. Add cement, fly ash, slag powder, sand and gravel to the mixer and dry mix for 1.5 minutes;

[0055] 3. Add polycarboxylate superplasticizer, composite retarder, UEA expansion agent and composite crack-resistant agent to water, stir evenly to make a mixed solution;

[0056] 4. While the mixer is continuously stirring, slowly add the mixed solution into the mixer and stir for 4 minutes to obtain super-retarded concrete.

[0057] The above-mentioned ultra-slow-setting concrete was used in the construction of the ring plate foundation of the high-level water collection cooling tower. The construction requirements were the same as in Example 1.

[0058] The performance of the ultra-retarded concrete prepared in this embodiment was tested, and the results are as follows:

[0059] Initial setting time: 28 hours;

[0060] Final setting time: 40 hours;

[0061] 28-day compressive strength: 58 MPa (design strength grade is C50);

[0062] Crack resistance: Under simulated temperature control conditions during ring slab foundation construction, the probability of cracks appearing is significantly reduced;

[0063] Slump loss during summer construction: Under high temperature conditions, the slump loss of concrete is further reduced compared to Example 1, and the service time is extended by 1-2 hours compared to Example 1, which can better ensure the continuity of construction.

[0064] Example 3

[0065] The super-retarded concrete of this embodiment comprises the following raw materials in parts by weight: 350 parts cement, 120 parts fly ash, 100 parts slag powder, 800 parts sand, 1200 parts gravel, 200 parts water, 5 parts polycarboxylate-based high-efficiency water-reducing agent, 12 parts composite retarder, 7 parts CSA expansion agent, and 44.8 parts composite crack-resistant agent; wherein, the composite retarder is composed of sodium gluconate, citric acid, and sodium lignosulfonate, and the mass ratio between sodium gluconate, citric acid, and sodium lignosulfonate is 3.5:1.5:0.5; the composite crack-resistant agent is SY-T composite fiber crack-resistant agent (Henan Zhonglv Juneng New Building Materials Co., Ltd.).

[0066] The method for preparing super-retarded concrete in this embodiment is as follows:

[0067] 1. Accurately weigh the above-mentioned raw materials according to the above weight proportions;

[0068] 2. Add cement, fly ash, slag powder, sand and gravel to the mixer and dry mix for 2 minutes;

[0069] 3. Add polycarboxylate superplasticizer, composite retarder, CSA expansion agent and composite crack-resistant agent to water, stir evenly to make a mixed solution;

[0070] 4. While the mixer is continuously stirring, slowly add the mixed solution into the mixer and stir for 5 minutes to obtain super-retarded concrete.

[0071] The above-mentioned ultra-slow-setting concrete was used in the construction of the ring plate foundation of the high-level water collection cooling tower. The construction requirements were the same as in Example 1.

[0072] The performance of the ultra-retarded concrete prepared in this embodiment was tested, and the results are as follows:

[0073] Initial setting time: 29 hours;

[0074] Final setting time: 41 hours;

[0075] 28-day compressive strength: 60 MPa (design strength grade is C50);

[0076] Crack resistance: Under simulated temperature control conditions during ring slab foundation construction, the probability of cracks appearing is significantly reduced;

[0077] Slump loss during summer construction: Under high temperature conditions, the slump loss of concrete is further reduced compared to Example 1, and the service time is extended by 1-2 hours compared to Example 1, which can better ensure the continuity of construction.

[0078] Compare with Example 1

[0079] Except for the different composition of the composite retarder, everything else is the same as in Example 1.

[0080] The composite retarder in this comparative example is composed of sodium gluconate and citric acid, with a mass ratio of sodium gluconate to citric acid of 3:3.

[0081] The performance of the super-retarded concrete prepared in this comparative example was tested, and the results are as follows:

[0082] Initial setting time: 17 hours;

[0083] Final setting time: 25 hours;

[0084] 28-day compressive strength: 52 MPa (design strength grade is C50);

[0085] Crack resistance: Under simulated temperature control conditions during ring slab foundation construction, the probability of crack occurrence increased by 30-40% compared to Example 1;

[0086] Slump loss during summer construction: Under high temperature conditions, the slump of concrete can drop by 30-40% within 1 hour, shortening the working time to 4-5 hours. The retarding effect is insufficient, and the workability deteriorates rapidly under high temperature.

[0087] Compare with Example 2

[0088] Except for the different composition of the composite retarder, everything else is the same as in Example 1.

[0089] The composite retarder in this comparative example consists of sodium gluconate and sodium lignosulfonate, with a mass ratio of sodium gluconate to sodium lignosulfonate of 3:3.

[0090] The performance of the super-retarded concrete prepared in this comparative example was tested, and the results are as follows:

[0091] Initial setting time: 19 hours;

[0092] Final setting time: 27 hours;

[0093] 28-day compressive strength: 51 MPa (design strength grade is C50);

[0094] Crack resistance: Under simulated temperature control conditions during ring slab foundation construction, the probability of crack occurrence increased by 25-35% compared to Example 1;

[0095] Slump loss during summer construction: Under high temperature conditions, the slump of concrete decreases by 25-35% within 1 hour, and the usable time is shortened to 5-6 hours.

[0096] Compare with Example 3

[0097] Except for the different composition of the composite retarder, everything else is the same as in Example 1.

[0098] The composite retarder in this comparative example consists of citric acid and sodium lignosulfonate, with a mass ratio of citric acid to sodium lignosulfonate of 4:2.

[0099] The performance of the super-retarded concrete prepared in this comparative example was tested, and the results are as follows:

[0100] Initial setting time: 13 hours;

[0101] Final setting time: 21 hours;

[0102] 28-day compressive strength: 50 MPa (design strength grade is C50);

[0103] Crack resistance: Under simulated temperature control conditions during ring slab foundation construction, the probability of cracks appearing is 50-60% higher than in Example 1 (concentrated heat of hydration release, increased temperature stress, and high risk of cracks).

[0104] Slump loss during summer construction: Under high temperature conditions, concrete loses 40-50% of its slump within 1 hour, and its usability is only 3-4 hours (insufficient retarding ability, rapid loss of plasticity under high temperature).

[0105] Compare with Example 4

[0106] Except for the different composition of the super-retarded concrete (i.e., no fly ash and slag powder are added), it is the same as in Example 1.

[0107] The super-retarded concrete of this comparative example comprises the following raw materials in parts by weight: 390 parts cement, 600 parts sand, 1000 parts gravel, 150 parts water, 3 parts polycarboxylate-based high-efficiency water-reducing agent, 8 parts composite retarder, 5 parts UEA expansion agent, and 32 parts composite crack-resistant agent.

[0108] The performance of the super-retarded concrete prepared in this comparative example was tested, and the results are as follows:

[0109] Initial setting time: 11 hours;

[0110] Final setting time: 17 hours;

[0111] 28-day compressive strength: 53 MPa (design strength grade is C50);

[0112] Crack resistance: Under simulated temperature control conditions during ring slab foundation construction, the probability of cracks appearing increased by 60-70% compared to Example 1 (high heat of hydration, high temperature stress, and poor crack resistance);

[0113] Slump loss during summer construction: Under high temperature conditions, concrete slump loss is 50-60% within 1 hour, and the usable time is only 2-3 hours (cement paste has high viscosity and is prone to loss of plasticity at high temperatures).

[0114] Compare with Example 5

[0115] Except for the absence of UEA expansion agent and composite crack-resistant agent, it is the same as in Example 1.

[0116] The performance of the super-retarded concrete prepared in this comparative example was tested, and the results are as follows:

[0117] Initial setting time: 24 hours;

[0118] Final setting time: 35 hours;

[0119] 28-day compressive strength: 53 MPa (design strength grade C50);

[0120] Crack resistance: Under simulated temperature control conditions during ring slab foundation construction, the probability of crack occurrence increased by 80-90% compared to Example 1 (without expansion compensation and crack-resistant components, shrinkage cracks increased significantly);

[0121] Slump loss during summer construction: Under high temperature conditions, the slump loss of concrete is similar to that in Example 1.

[0122] Compare with Example 6

[0123] Except for replacing the composite crack-resistant agent of Example 1 with the polypropylene fiber of Example 1, the rest is the same as Example 1.

[0124] The performance of the super-retarded concrete prepared in this comparative example was tested, and the results are as follows:

[0125] Initial setting time: 24 hours;

[0126] Final setting time: 35 hours;

[0127] 28-day compressive strength: 53 MPa (design strength grade C50);

[0128] Crack resistance: Under simulated temperature control conditions during ring slab foundation construction, the probability of crack occurrence increased by 30-40% compared to Example 1;

[0129] Slump loss during summer construction: Under high temperature conditions, the slump loss of concrete is similar to that in Example 1.

[0130] Compare with Example 7

[0131] Except for replacing the composite crack-resistant agent of Example 1 with the polycarboxylic acid ether of Example 1, the rest is the same as Example 1.

[0132] The performance of the super-retarded concrete prepared in this comparative example was tested, and the results are as follows:

[0133] Initial setting time: 24 hours;

[0134] Final setting time: 35 hours;

[0135] 28-day compressive strength: 53 MPa (design strength grade C50);

[0136] Crack resistance: Under simulated temperature control conditions during ring slab foundation construction, the probability of crack occurrence increased by 25-35% compared to Example 1;

[0137] Slump loss during summer construction: Under high temperature conditions, the slump loss of concrete is similar to that in Example 1.

[0138] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; 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; and 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.

Claims

1. A super-retarded concrete, characterized in that, The raw materials include the following parts by weight: 250-350 parts cement, 80-120 parts fly ash, 60-100 parts slag powder, 600-800 parts sand, 1000-1200 parts gravel, 150-200 parts water, 3-5 parts high-efficiency water-reducing agent, 8-12 parts composite retarder, 5-7 parts expansion agent, and 32-45 parts crack-resistant agent; wherein, the composite retarder includes sodium gluconate, citric acid, and sodium lignosulfonate, and the mass ratio between sodium gluconate, citric acid, and sodium lignosulfonate in the composite retarder is (2.5-3.5):(1.5-2.5):(0.5-1.5).

2. The super-retarded concrete according to claim 1, characterized in that, The cement is ordinary Portland cement with a strength grade of not less than 42.

5.

3. The super-retarded concrete according to claim 1, characterized in that, The specific surface area of ​​slag powder is not less than 400m². 2 / kg, with an activity index of not less than 95%.

4. The super-retarded concrete according to claim 1, characterized in that, The sand is medium sand with a fineness modulus of 2.3-3.0 and a mud content of no more than 3%.

5. The super-retarded concrete according to claim 1, characterized in that, The gravel is continuously graded crushed stone with a particle size of 5-25mm, a needle-like and flaky particle content of no more than 15%, and a mud content of no more than 1%.

6. The super-retarded concrete according to claim 1, characterized in that, The high-efficiency water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent with a water reduction rate of not less than 25%.

7. The super-retarded concrete according to claim 1, characterized in that, The expanding agent used is an calcite-type expanding agent.

8. The super-retarded concrete according to claim 1, characterized in that, The crack-resistant agent is a composite crack-resistant agent, which includes polypropylene fiber and polyether derivatives. The mass ratio of polypropylene fiber to polyether derivative in the composite crack-resistant agent is (3-5):

1.

9. The method for preparing super-retarded concrete according to any one of claims 1-8, characterized in that, Includes the following steps: S1: Add cement, fly ash, slag powder, sand and gravel to the mixer according to the weight parts, and dry mix to ensure that all raw materials are fully and evenly mixed; S2: Add the high-efficiency water-reducing agent, composite retarder, expanding agent and crack-resistant agent to water according to the weight parts, stir evenly to make a mixed solution; S3: Under continuous stirring conditions, the mixed solution is slowly added to the mixer and stirred until it is uniformly mixed to obtain super-retarded concrete.

10. The preparation method according to claim 9, characterized in that, In step S1, the dry mixing time is 1-2 minutes; in step S3, the stirring time is 3-5 minutes.