High-aggregate low-shrinkage concrete, preparation method and preparation method of prefabricated part

Abstract

The invention discloses high-aggregate low-shrinkage concrete, a preparation method and a preparation method of a prefabricated component, the high-aggregate low-shrinkage concrete in the application comprises the following components in parts by weight: 140-160 parts of water, 340-400 parts of cement, 30-80 parts of mineral powder, 50-80 parts of fly ash, 500-600 parts of natural sand, 80-100 parts of machine-made sand, 800-900 parts of pebbles of 5-25 mm, 200-300 parts of pebbles of 5-20 mm and 2-6 parts of a water reducing agent, the machine-made sand is dry-process calcium machine-made sand, and the dry-process calcium machine-made sand is dry-process calcium machine-made sand. 200-300 parts of 5-20 mm stones are uniformly mixed with other materials and then are put into the mixture in batches. The preparation method of the prefabricated part comprises the steps that high-aggregate low-shrinkage concrete is poured into a prefabricated part mold in batches and then vibrated till the whole prefabricated part mold is filled with the concrete, and a certain amount of 5-20 mm stones are scattered on the concrete in the vibrating process. On the premise of not introducing new materials, the effect of low shrinkage and creep is achieved by increasing the proportion of coarse aggregate in the prefabricated part concrete, and the effect of improving the appearance quality of the prefabricated part concrete is achieved.

Description

Technical Field

[0001] This invention relates to the field of concrete technology, and in particular to a high-aggregate low-shrinkage concrete, its preparation method, and a method for preparing precast components. Background Technology

[0002] In the production and application of precast components, especially prestressed precast components, shrinkage and creep of concrete are key factors leading to the deterioration of component performance. Significant shrinkage and creep not only significantly increase the risk of cracking in the component itself, affecting the structure's durability, but also cause stress relaxation in the prestressing tendons, resulting in prestress loss and directly jeopardizing the structure's load-bearing capacity. Furthermore, long-term cumulative deformation can cause substantial dimensional deviations during construction and installation, making precise assembly of the overall structure difficult. Therefore, how to effectively suppress concrete shrinkage and creep has always been a hot topic of continuous attention and research for those in this field.

[0003] Currently, most solutions proposed by the technical community to reduce concrete shrinkage and creep focus on the material composition level. For example, Chinese patent application CN202110123855.3 discloses an early-strength, low-shrinkage concrete for precast components, the core of which lies in using biomass incineration ash as an internal curing material to reduce the drying shrinkage of concrete through continuous internal hydration. Another Chinese patent application CN202010499032.6 proposes using an air-entraining organic salt as a regulator to optimize the pore structure of concrete, thereby reducing its later drying shrinkage.

[0004] Furthermore, controlling shrinkage and creep by finely adjusting the concrete mix proportions is a well-known technical approach, and empirical models exist to illustrate the influence of each component on deformation performance. However, this method has inherent limitations: the concrete mix proportion is a complex multi-objective optimization system, and the dosage of each component (such as cementitious materials, water, admixtures, etc.) not only affects shrinkage and creep but also directly determines the core properties of concrete, such as compressive strength, workability (flowability, cohesiveness, etc.), and long-term durability. Therefore, making minor adjustments only within the existing mix design framework often results in very limited reductions, frequently leading to a "whack-a-mole" engineering dilemma, making it difficult to achieve breakthrough improvements. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this application provides a high-aggregate, low-shrinkage concrete, its preparation method, and a method for preparing precast components. This aims to solve the technical problems of large shrinkage and creep, and poor appearance quality in precast concrete components in existing technologies.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] A high-aggregate, low-shrinkage concrete comprises the following raw materials by weight: 140-160 parts water, 340-400 parts cement, 30-80 parts mineral powder, 50-80 parts fly ash, 500-600 parts natural sand, 80-100 parts manufactured sand, 800-900 parts 5-25mm aggregate, and 2-6 parts water-reducing agent, wherein the manufactured sand is dry-process calcareous manufactured sand.

[0008] In one embodiment, the cement is P·Ⅱ52.5 cement; the fly ash is Grade II fly ash with a 28-day activity index ≥70%; and the mineral powder is S95 mineral powder with a 28-day activity index ≥95%.

[0009] In one embodiment, the natural sand is natural medium sand; the gravel is natural crushed stone with a crushing index ≤20%.

[0010] In one embodiment, the water-reducing agent is a polycarboxylate superplasticizer with a water reduction rate >25%.

[0011] In one embodiment, the high-aggregate, low-shrinkage concrete has a strength grade of C55 to C60.

[0012] This application also provides a method for preparing high-aggregate low-shrinkage concrete, wherein the high-aggregate low-shrinkage concrete is the aforementioned high-aggregate low-shrinkage concrete, comprising the following steps:

[0013] S1. Weigh out 340-400 parts cement, 30-80 parts mineral powder, 50-80 parts fly ash, 500-600 parts natural sand, 80-100 parts manufactured sand, and 800-900 parts 5-25mm gravel by weight. The manufactured sand is dry-process calcareous manufactured sand. Add the 5-25mm gravel, natural sand, manufactured sand, cement, fly ash, and mineral powder into the mixer in sequence and mix for a period of time to ensure that the solid raw materials are evenly mixed.

[0014] S2. Weigh 140-160 parts of water and 2-6 parts of water-reducing agent by weight, and mix the water and water-reducing agent evenly to obtain solution A.

[0015] S3. Add solution A to the mixer in S1 and stir for a period of time to make the mixture of solution A and the mixture obtained in S1 uniformly to obtain concrete.

[0016] This application also provides a method for preparing the above-mentioned precast concrete component, comprising the following steps:

[0017] S1. Pour the high-aggregate, low-shrinkage concrete into the precast component mold in batches. After each batch is poured into the precast component mold, use a vibrator to compact it. During the compaction process, sprinkle a certain amount of 5-20mm aggregate on the concrete.

[0018] S2. Repeat step S1 until the high-aggregate low-shrinkage concrete fills the entire precast component mold. Continue to add small amounts of high-aggregate low-shrinkage concrete or 5-20mm stones until there is no obvious laitance or exposed stones on the surface of the precast component.

[0019] S3. After curing the precast components for 1 day, remove the formwork and cure them under the specified conditions to obtain the precast components.

[0020] In one embodiment, an overflow screen is provided on the top side of the precast component mold, the mesh size of the overflow screen is 5mm, the vibrator includes an attached vibrator and an immersion vibrator, the attached vibrator and the immersion vibrator work together, and the working time of the vibrator is 2 to 5 minutes; after each batch of concrete is poured into the precast component mold in S1, the concrete pouring height increases by 0.5 to 1m.

[0021] Compared with the prior art, this application has at least the following beneficial effects:

[0022] 1. The present invention includes calcareous dry-process manufactured sand in the raw materials of concrete to replace part of the natural sand. The limestone powder in the calcareous dry-process manufactured sand reacts with C3A and C4AF in the cement to accelerate the hydrolysis process. The products will increase the latency time in cement hydration, thereby reducing the early shrinkage after initial setting and reducing the risk of early cracking of precast components.

[0023] 2. This invention achieves low shrinkage and creep by increasing the proportion of coarse aggregate in the concrete of precast components. At the same time, this invention reserves some aggregate in the mix proportion to be added during the molding of precast components, so as to improve the reduced workability of concrete caused by the increase in the proportion of coarse aggregate, thereby improving the production efficiency of precast components.

[0024] 3. This invention effectively improves the problems of insufficient density, uneven distribution of stones, and surface laitance in precast components by means of molding processes such as vibration, batch spreading of 5-20mm stones, and setting up overflow screens. It can reduce the shrinkage and creep of precast components and improve their appearance quality. This application does not introduce new materials and will not significantly change the existing production system of precast components. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described below through specific embodiments. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0026] The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The singular forms “a,” “the,” and “the” as used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0027] It should be understood that although the terms first, second, third, etc., may be used in this disclosure to describe various information, such information should not be limited to these terms and should not be construed as indicating or implying relative importance. These terms are used only to distinguish information of the same type from one another. For example, without departing from the scope of this disclosure, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0028] In the description of this invention, unless otherwise specified and limited, it should be noted that the terms "installation", "connection" and "linking" should be interpreted broadly. For example, they can refer to mechanical connection or internal connection between two components. They can be direct connection or indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0029] To better understand the technical solution of the present invention, the present invention will be described in detail below with reference to embodiments and comparative examples.

[0030] Example 1:

[0031] Weigh out the following ingredients by weight: 150kg water, 340kg cement, 56kg mineral powder, 74kg fly ash, 515kg natural sand, 100kg manufactured sand, 841kg 5-25mm gravel, 300kg 5-20mm gravel, and 2.8kg water-reducing agent.

[0032] Preparation of high-aggregate, low-shrinkage concrete:

[0033] Step 1: Put 5-25mm gravel, natural sand, calcareous dry-process manufactured sand, cement, fly ash and mineral powder into a forced mixer and mix for 1 minute until evenly mixed.

[0034] Step 2: Mix water and water-reducing agent evenly to obtain solution A;

[0035] Step 3: Add solution A to a forced mixer and mix it with the mixture obtained in Step 1 for 3 minutes to obtain concrete.

[0036] Prefabricated concrete components:

[0037] Step 1: Pour the freshly mixed concrete obtained above into the precast component mold in batches. After each batch is poured in, use an attached vibrator and an immersion vibrator to vibrate for 3 minutes. During this time, evenly spread 5-20mm crushed stone. An overflow screen with a mesh size of 5mm is set on the top side of the precast component mold.

[0038] Step 2: Repeat the above operation until the concrete fills the entire mold. Continue to add small amounts of concrete or gravel and vibrate until there is no obvious laitance or exposed gravel on the surface of the precast component.

[0039] Step 3: After curing the precast components obtained from the above steps for 1 day, remove the formwork and place them in a water tank for curing for 28 days to obtain a low-shrinkage creep precast component with a strength grade of C55.

[0040] Comparative Example 1:

[0041] Weigh out the following ingredients by weight: 150kg water, 340kg cement, 56kg mineral powder, 74kg fly ash, 615kg natural sand, 1141kg 5-25mm gravel, and 2.8kg of other materials.

[0042] Concrete preparation:

[0043] Step 1: Put 5-25mm gravel, natural sand, calcareous dry-process manufactured sand, cement, fly ash and mineral powder into a forced mixer and mix for 1 minute until evenly mixed.

[0044] Step 2: Mix water and water-reducing agent evenly to obtain solution A;

[0045] Step 3: Add solution A to a forced mixer and mix it with the mixture obtained in Step 1 for 3 minutes to obtain concrete.

[0046] Prefabricated concrete components:

[0047] Step 1: Pour the freshly mixed concrete obtained above into the precast component mold in batches. After each batch is poured, use an attached vibrator and an immersion vibrator to vibrate for about 30 seconds. Repeat the above operation until the concrete fills the entire mold.

[0048] Step 2: After curing the precast components obtained from the above steps for 1 day, remove the formwork and place them in a water tank for curing for 28 days to obtain a common precast component with a strength grade of C55.

[0049] Example 2:

[0050] Weigh out the following ingredients by weight: 150kg water, 380kg cement, 40kg mineral powder, 60kg fly ash, 571kg natural sand, 110kg manufactured sand, 803kg 5-25mm gravel, 280kg 5-20mm gravel, and 3.84kg water-reducing agent.

[0051] Preparation of high-aggregate, low-shrinkage concrete:

[0052] Step 1: Put 5-25mm gravel, natural sand, calcareous dry-process manufactured sand, cement, fly ash and mineral powder into a forced mixer and mix for 1 minute until evenly mixed.

[0053] Step 2: Mix water and water-reducing agent evenly to obtain solution A;

[0054] Step 3: Add solution A to a forced mixer and mix it with the mixture obtained in Step 1 for 3 minutes to obtain concrete.

[0055] Prefabricated concrete components:

[0056] Step 1: Pour the freshly mixed concrete obtained above into the precast component mold in batches. After each batch is poured, use an attached vibrator and an immersion vibrator to vibrate for 4 minutes. During this time, evenly spread 5-20mm crushed stone. An overflow screen with a mesh size of 5mm is set on the top side of the precast component mold.

[0057] Step 2: Repeat the above operation until the concrete fills the entire mold. Continue to add small amounts of concrete or gravel and vibrate until there is no obvious laitance or exposed gravel on the surface of the precast component.

[0058] Step 3: After curing the precast components obtained from the above steps for 1 day, remove the formwork and place them in a water tank for curing for 28 days to obtain a low-shrinkage creep precast component with a strength grade of C60.

[0059] Comparative Example 2:

[0060] Weigh out the following ingredients by weight: 150kg water, 380kg cement, 40kg mineral powder, 60kg fly ash, 681kg natural sand, 1083kg 5-25mm gravel, and 3.84kg water-reducing agent.

[0061] Concrete preparation:

[0062] Step 1: Put 5-25mm gravel, natural sand, calcareous dry-process manufactured sand, cement, fly ash and mineral powder into a forced mixer and mix for 1 minute until evenly mixed.

[0063] Step 2: Mix water and water-reducing agent evenly to obtain solution A;

[0064] Step 3: Add solution A to a forced mixer and mix it with the mixture obtained in Step 1 for 3 minutes to obtain concrete.

[0065] Prefabricated concrete components:

[0066] Step 1: Pour the freshly mixed concrete obtained above into the precast component mold in batches. After each batch is poured, use an attached vibrator and an immersion vibrator to vibrate for about 30 seconds. Repeat the above operation until the concrete fills the entire mold.

[0067] Step 2: After curing the precast components obtained from the above steps for 1 day, remove the formwork and place them in a water tank for curing for 28 days to obtain a common precast component with a strength grade of C60.

[0068] The concrete and precast components prepared in Examples 1 and 2, and Comparative Examples 1 and 2 were tested, and the test results are shown in the table below.

[0069]

[0070] As can be seen from the table, the compressive strength of the concrete in Examples 1 and 2 both meet the requirements, and the early shrinkage of the precast component prepared in Example 1 is lower than that in Comparative Example 1, while the early shrinkage of the precast component prepared in Example 2 is lower than that in Comparative Example 2.

[0071] This application does not start from the perspective of component chemistry, but from the physical principle of dense skeleton, and creatively proposes a method for preparing low-shrinkage and low-creep precast components with high aggregate and low paste content. By optimizing the skeleton structure of concrete, the amount of cement paste that leads to shrinkage and creep is minimized, thereby fundamentally and significantly reducing the long-term deformation of the component while ensuring its mechanical properties.

[0072] 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 preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A high-aggregate, low-shrinkage concrete, characterized in that, The mixture comprises the following raw materials by weight: 140-160 parts water, 340-400 parts cement, 30-80 parts mineral powder, 50-80 parts fly ash, 500-600 parts natural sand, 80-100 parts manufactured sand, 800-900 parts 5-25mm gravel, 200-300 parts 5-20mm gravel, and 2-6 parts water-reducing agent. The manufactured sand is dry-process calcareous manufactured sand. The 200-300 parts 5-20mm gravel are added to the mixture in batches after being evenly mixed with the other materials.

2. The high-aggregate, low-shrinkage concrete according to claim 1, characterized in that, The cement is P·Ⅱ52.5 cement; the fly ash is Grade II fly ash with a 28-day activity index ≥70%; the mineral powder is S95 mineral powder with a 28-day activity index ≥95%.

3. The high-aggregate, low-shrinkage concrete according to claim 1, characterized in that, The natural sand is natural medium sand; the gravel is natural crushed stone with a crushing index ≤20%.

4. The high-aggregate, low-shrinkage concrete according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate high-efficiency water-reducing agent with a water reduction rate of >25%.

5. The high-aggregate, low-shrinkage concrete according to claim 1, characterized in that, The strength grade of the high aggregate low shrinkage concrete is C55 to C60.

6. A method for preparing high-aggregate low-shrinkage concrete, wherein the high-aggregate low-shrinkage concrete is the high-aggregate low-shrinkage concrete according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Weigh out 340-400 parts cement, 30-80 parts mineral powder, 50-80 parts fly ash, 500-600 parts natural sand, 80-100 parts manufactured sand, and 800-900 parts 5-25mm gravel by weight. The manufactured sand is dry-process calcareous manufactured sand. Add the 5-25mm gravel, natural sand, manufactured sand, cement, fly ash, and mineral powder into the mixer in sequence and mix for a period of time to ensure that the solid raw materials are evenly mixed. S2. Weigh 140-160 parts of water and 2-6 parts of water-reducing agent by weight, and mix the water and water-reducing agent evenly to obtain solution A. S3. Add solution A to the mixer in S1 and stir for a period of time to make the mixture of solution A and the mixture obtained in S1 uniformly to obtain concrete.

7. A method for preparing high-aggregate, low-shrinkage precast concrete components, characterized in that, Includes the following steps: S1. The high aggregate low shrinkage concrete as described in any one of claims 1-5 is poured into the precast component mold in batches. After each batch is poured into the precast component mold, it is vibrated with a vibrator. During the vibration process, a certain amount of 5-20mm stones are sprinkled on the concrete. S2. Repeat step S1 until the high-aggregate low-shrinkage concrete fills the entire precast component mold. Continue to add high-aggregate low-shrinkage concrete or 5-20mm stones until there is no obvious laitance or exposed stones on the surface of the precast component. S3. After curing the precast components for 1 day, remove the formwork and cure them under the specified conditions to obtain the precast components.

8. The high-aggregate, low-shrinkage concrete according to claim 7, characterized in that, An overflow screen is provided on the top side of the precast component mold. The mesh size of the overflow screen is 5mm. The vibrator includes an attached vibrator and an immersion vibrator. The attached vibrator and the immersion vibrator work together. The working time of the vibrator is 2 to 5 minutes. After each batch of concrete is poured into the precast component mold in S1, the concrete pouring height increases by 0.5 to 1m.

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