Preparation method and application of multi-doped concrete for adjusting solidification state of concrete

Abstract

The invention relates to the technical field of concrete, in particular to a preparation method and application of multi-doped concrete for adjusting the solidification state of the concrete. The preparation method of the multi-doped concrete for adjusting the setting state of the concrete comprises the following steps: adding a calcium sulfate expanding agent into an acid solution, carrying out ultrasonic treatment, filtering and drying, and then mixing and grinding with basalt nanofibers to obtain an expanding agent A; carrying out wet granulation on a calcium oxide expanding agent, a polycarboxylic acid plasticizer and silica fume, and finally drying to obtain an expanding agent B; after cement and gravel are subjected to dry mixing, the expanding agent A is added for stirring, finally, the expanding agent B, the fly ash, the water and the water reducing agent are added for secondary stirring, and the concrete is obtained. Through the synergistic effect of the composite expanding agent A and the composite expanding agent B, the shrinkage rate of the concrete is effectively reduced, the occurrence rate of cracks is reduced, and the anti-cracking performance of the structure is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of concrete technology, and specifically to a method for preparing and applying multi-doped concrete that adjusts the setting state of concrete. Background Technology

[0002] Concrete, as one of the most widely used building materials in engineering construction, plays a crucial role in bridges, high-rise buildings, water conservancy projects, and other fields. However, during the solidification process, concrete often cracks due to shrinkage deformation, leading to decreased structural durability, weakened load-bearing capacity, and even safety hazards.

[0003] To address this issue, existing technologies primarily compensate for concrete shrinkage by adding a single expansive agent (such as calcium oxide or calcium sulfoaluminate) or by using multi-component admixtures (such as fibers or mineral admixtures) to improve its performance. For example, while a single calcium oxide expansive agent can provide significant expansion force, its rapid hydration rate can easily lead to uncontrolled early expansion; calcium sulfoaluminate expansive agents, on the other hand, suffer from delayed expansion and poor compatibility with cement. Furthermore, some technologies attempt to combine multiple admixtures, but due to the lack of synergistic mechanisms between the components, imbalances in expansion and strength development, as well as inhomogeneous microstructure, often occur, making precise control of the concrete's setting state difficult. Simultaneously, existing multi-admixed concretes exhibit poor dispersion and weak interfacial bonding during preparation, resulting in limited improvements in crack resistance and durability, failing to meet the demands of large-scale, complex engineering projects for high-performance concrete. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for preparing and applying multi-doped concrete that adjusts the setting state of concrete. Through the synergistic effect of composite expansive agents A and B, this invention achieves gradient expansion compensation of concrete during the "early-mid-late" stages of setting. Calcium oxide in expansive agent B rapidly hydrates in the early stage to provide expansion force and compensate for plastic shrinkage, while calcium sulfate in expansive agent A continuously reacts in the mid-stage to generate ettringite, inhibiting autogenous shrinkage. This effectively reduces the shrinkage rate of concrete, decreases the incidence of cracks, and significantly improves the crack resistance of the structure.

[0005] Therefore, the present invention provides the following technical solution:

[0006] In a first aspect, the present invention provides, in optional embodiments, a method for preparing multi-doped concrete with adjusted concrete setting state, comprising the following steps:

[0007] S1: Add calcium sulfate expansion agent to acid solution, sonicate, filter and dry, then mix and grind with basalt nanofibers to obtain expansion agent A;

[0008] S2: Calcium oxide expander, polycarboxylate plasticizer and silica fume are wet granulated and then dried to obtain expander B;

[0009] S3: After dry mixing cement and sand, add the expansion agent A and stir. Finally, add expansion agent B, fly ash, water and water-reducing agent and stir again to obtain concrete.

[0010] In this invention, expansion agent A, composed of calcium sulfate and basalt nanofibers, provides mid-term expansion through the generation of ettringite (CaSO4·2H2O reacts with aluminate to form 3CaO·Al2O3·3CaSO4·32H2O), while the basalt fibers suppress early shrinkage cracks through physical constraint. Expansion agent B, composed of calcium oxide, polycarboxylic acid, and silica fume, provides early expansion through the hydration of calcium oxide to form Ca(OH)2, while the polycarboxylic acid slows down the hydration rate of calcium oxide, and the silica fume fills the pores and improves later strength. Early expansion agent B compensates for plastic shrinkage, and mid-term expansion agent A compensates for hardening shrinkage, forming a "time gradient expansion" that covers the entire curing cycle of concrete. Furthermore, this invention utilizes cavitation (i.e., ultrasonic treatment) to break down calcium sulfate particles (increasing specific surface area, accelerating the formation rate of ettringite, and simultaneously promoting the dispersion of basalt fibers, forming a "fiber-calcium sulfate" composite framework). Moreover, after wet granulation of calcium oxide and silica fume, the polycarboxylic acid encapsulation effect delays the contact between calcium oxide and water, avoiding structural damage caused by early and rapid expansion, thus achieving controllable expansion rate. In addition, calcium sulfate undergoes surface dissolution or ion exchange reactions in acidic solutions. For example, citric acid can react with Ca... 2+ It forms soluble complexes (such as calcium citrate), while dilute hydrochloric acid passes through H+. + With the OH groups on the surface of calcium sulfate - The reaction disrupts part of the crystal structure. After acidification, the content of hydroxyl (-OH) groups on the surface of calcium sulfate increases, the surface energy increases, and the interfacial bonding force is enhanced when mixed with basalt nanofibers, thus forming a more uniform distribution of expansion sources in concrete.

[0011] Preferably, in step S1, the acid solution is selected from citric acid or dilute hydrochloric acid, or a mixture of both, wherein the concentration of citric acid is 5-10% and the concentration of dilute hydrochloric acid is 3-5%; and / or, the mass ratio of the calcium sulfate expanding agent to the acid solution is 1:4-6. The ultrasonic treatment time is 10-30 min, the power is 200-500 W, and the frequency is 20-40 kHz; and / or, the drying temperature is 60-80℃, and the time is 4-8 h. The mass ratio of the basalt nanofibers to the calcium sulfate expanding agent is 0.005-0.02:1; and / or, the grinding speed is 300-500 r / min, and the time is 5-10 min.

[0012] Preferably, in step S2, the mass ratio of the calcium oxide expanding agent to the polycarboxylate plasticizer is 100:(0.5-2); and / or, the amount of silica fume added is 5-15% of the mass of the calcium oxide expanding agent. During the wet granulation, the mass ratio of water to the calcium oxide expanding agent is 1:0.15-0.25; and / or, the rotation speed during the wet granulation is 100-200 r / min. The drying temperature is 80-100℃; and / or, the drying time is 6-12 h.

[0013] Preferably, in step S3, the mass ratio of cement, sand, expansive agent A, expansive agent B, fly ash, water, and water-reducing agent is 100:(150-220):(3-8):(1-5):(10-30):(33-65):(0.55-2.6); and / or, the dry mixing time is 1-2 min, and the rotation speed is 60-100 r / min; and / or, the stirring time is 2-3 min, and the rotation speed is 80-120 r / min; and / or, the secondary stirring time is 3-5 min, and the rotation speed is 100-150 r / min.

[0014] Secondly, in an optional embodiment, the present invention provides a multi-doped concrete for adjusting the solidification state of concrete, which is prepared by the above-described preparation method.

[0015] Thirdly, in an optional embodiment, the present invention provides an application of the above-mentioned multi-doped concrete with adjusted concrete setting state in bridge engineering.

[0016] Compared with the prior art, the present invention has one of the following beneficial effects:

[0017] 1. This invention achieves gradient expansion compensation of concrete during the "early-middle-late" stage of the solidification process through the synergistic effect of composite expansive agents A and B. The calcium oxide in expansive agent B provides expansion force through rapid hydration in the early stage, compensating for plastic shrinkage. The calcium sulfate in expansive agent A continuously reacts in the middle stage to generate ettringite, inhibiting autogenous shrinkage. This effectively reduces the shrinkage rate of concrete, reduces the incidence of cracks, and significantly improves the crack resistance of the structure.

[0018] 2. This invention combines basalt nanofibers with calcium sulfate (expansion agent A), forming a three-dimensional network structure that bridges cracks and limits excessive expansion of the expansion agent. The granulation process using silica fume and calcium oxide (expansion agent B) delays calcium oxide hydration through the encapsulation effect of polycarboxylic acid, while the silica fume fills pores, working together with fly ash and other mineral admixtures to densify the microstructure. This multi-component synergistic mechanism reduces concrete porosity, improves impermeability, and significantly enhances durability.

[0019] 3. While ensuring the expansion compensation effect, this invention avoids the strength loss problem caused by a single expansion agent by reasonably controlling the dosage of each component. Basalt fiber enhances the toughness of concrete, thereby improving flexural strength; the pozzolanic effect of silica fume and fly ash promotes cement hydration, thereby improving compressive strength, achieving coordinated development of expansion performance and mechanical properties. Attached Figure Description

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 This is a schematic diagram of the process for preparing concrete according to Embodiment 1 of the present invention;

[0022] Figure 2 This is a photograph of the concrete prepared in Example 1 of the present invention;

[0023] Figure 3 This is a physical image of the raw materials used to prepare concrete in Example 1 of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0025] In the following examples and comparative examples, the water-reducing agent is a polycarboxylate water-reducing agent, purchased from Shandong Huangteng Building Materials Co., Ltd., model HT polycarboxylate high-performance water-reducing agent.

[0026] The technical solution of the present invention will be described below with reference to embodiments.

[0027] Example 1

[0028] See Figure 1 and Figure 3 This embodiment provides a method for preparing concrete, including the following steps:

[0029] S1: Weigh 500g of calcium sulfate expanding agent using an electronic balance (accuracy 0.01g). Pour 2500g of 5% citric acid solution into a 5L beaker. Slowly add calcium sulfate to the citric acid solution and stir until homogeneous. Then, place the beaker in a CNC ultrasonic cleaner for ultrasonic treatment. Set the power to 300W, the frequency to 30kHz, and the time to 20min. After ultrasonic treatment, use a Buchner funnel and a 0.2μm microporous membrane, along with a circulating water multi-purpose vacuum pump, to perform vacuum filtration to separate the solid and liquid. Transfer the filter residue to an electric heating drying oven and dry it at 70℃ for 6h. Weigh 5g of basalt nanofibers and place them together with the dried calcium sulfate in a planetary ball mill. Set the speed to 400r / min and grind for 8min to obtain expanding agent A.

[0030] S2: Weigh 1000g of calcium oxide expanding agent, 10g of polycarboxylate plasticizer, and 100g of silica fume using an electronic balance, pour them into a 5L plastic bucket, and manually stir to initially mix. Measure 200g of water and add it to the bucket. After stirring evenly, pour the mixture into a disc granulator, set the speed to 150r / min, and the granulation time to 20min to form particles with an average particle size of 3mm. Transfer the granulated particles to an electric thermostatic drying oven, set the temperature to 90℃, and dry for 8h to obtain expanding agent B.

[0031] S3: Using a single-shaft forced concrete mixer, first add 1000g of cement and 2000g of sand and gravel, set the speed to 80r / min and dry mix for 1.5min. Then add 50g of expansive agent A, adjust the speed to 100r / min and mix for 2.5min. Finally, add 30g of expansive agent B, 200g of fly ash, 450g of water, and 12g of water-reducing agent, set the speed to 120r / min and mix for 4min. Discharge to obtain concrete. See [link / reference]. Figure 2 .

[0032] Example 2

[0033] This embodiment provides a method for preparing concrete, including the following steps:

[0034] S1: Weigh 500g of calcium sulfate expanding agent using an electronic balance (accuracy 0.01g). Pour 3000g of 4% dilute hydrochloric acid solution into a 5L beaker. Slowly add calcium sulfate to the dilute hydrochloric acid solution and stir evenly. Then, place the beaker in a CNC ultrasonic cleaner for ultrasonic treatment. Set the power to 300W, the frequency to 30kHz, and the time to 20min. After ultrasonic treatment, use a Buchner funnel and a 0.2μm microporous filter membrane, along with a circulating water multi-purpose vacuum pump, to perform vacuum filtration to separate the solid and liquid. Transfer the filter residue to an electric heating blast drying oven and dry it at 70℃ for 6h. Weigh 5g of basalt nanofibers and place them together with the dried calcium sulfate in a planetary ball mill. Set the speed to 400r / min and grind for 8min to obtain expanding agent A.

[0035] S2: Weigh 1000g of calcium oxide expanding agent, 10g of polycarboxylate plasticizer, and 100g of silica fume using an electronic balance, pour them into a 5L plastic bucket, and manually stir to initially mix. Measure 200g of water and add it to the bucket. After stirring evenly, pour the mixture into a disc granulator, set the speed to 150r / min, and the granulation time to 20min to form particles with an average particle size of 3mm. Transfer the granulated particles to an electric thermostatic drying oven, set the temperature to 90℃, and dry for 8h to obtain expanding agent B.

[0036] S3: Using a single-shaft forced concrete mixer, first add 1000g of cement and 2000g of sand and gravel, set the speed to 80r / min and dry mix for 1.5min. Then add 50g of expansion agent A, adjust the speed to 100r / min and mix for 2.5min. Finally, add 30g of expansion agent B, 200g of fly ash, 450g of water and 12g of water-reducing agent, set the speed to 120r / min and mix for 4min. Discharge to obtain concrete.

[0037] Example 3

[0038] This embodiment provides a method for preparing concrete, including the following steps:

[0039] S1: Weigh 500g of calcium sulfate expanding agent using an electronic balance (accuracy 0.01g). Pour 2500g of 5% citric acid solution into a 5L beaker. Slowly add calcium sulfate to the citric acid solution and stir until homogeneous. Then, place the beaker in a CNC ultrasonic cleaner for ultrasonic treatment. Set the power to 300W, the frequency to 30kHz, and the time to 20min. After ultrasonic treatment, use a Buchner funnel and a 0.2μm microporous membrane, along with a circulating water multi-purpose vacuum pump, to perform vacuum filtration to separate the solid and liquid. Transfer the filter residue to an electric heating drying oven and dry it at 70℃ for 6h. Weigh 10g of basalt nanofibers and place them together with the dried calcium sulfate in a planetary ball mill. Set the speed to 400r / min and grind for 8min to obtain expanding agent A.

[0040] S2: Weigh 1000g of calcium oxide expanding agent, 10g of polycarboxylate plasticizer, and 100g of silica fume using an electronic balance, pour them into a 5L plastic bucket, and manually stir to initially mix. Measure 200g of water and add it to the bucket. After stirring evenly, pour the mixture into a disc granulator, set the speed to 150r / min, and the granulation time to 20min to form particles with an average particle size of 3mm. Transfer the granulated particles to an electric thermostatic drying oven, set the temperature to 90℃, and dry for 8h to obtain expanding agent B.

[0041] S3: Using a single-shaft forced concrete mixer, first add 1000g of cement and 2000g of sand and gravel, set the speed to 80r / min and dry mix for 1.5min. Then add 50g of expansion agent A, adjust the speed to 100r / min and mix for 2.5min. Finally, add 30g of expansion agent B, 200g of fly ash, 450g of water and 12g of water-reducing agent, set the speed to 120r / min and mix for 4min. Discharge to obtain concrete.

[0042] Example 4

[0043] This embodiment provides a method for preparing concrete, including the following steps:

[0044] S1: Weigh 500g of calcium sulfate expanding agent using an electronic balance (accuracy 0.01g). Pour 2500g of 5% citric acid solution into a 5L beaker. Slowly add calcium sulfate to the citric acid solution and stir until homogeneous. Then, place the beaker in a CNC ultrasonic cleaner for ultrasonic treatment. Set the power to 300W, the frequency to 30kHz, and the time to 20min. After ultrasonic treatment, use a Buchner funnel and a 0.2μm microporous membrane, along with a circulating water multi-purpose vacuum pump, to perform vacuum filtration to separate the solid and liquid. Transfer the filter residue to an electric heating drying oven and dry it at 70℃ for 6h. Weigh 2.5g of basalt nanofibers and place them together with the dried calcium sulfate in a planetary ball mill. Set the speed to 400r / min and grind for 8min to obtain expanding agent A.

[0045] S2: Weigh 1000g of calcium oxide expanding agent, 10g of polycarboxylate plasticizer, and 100g of silica fume using an electronic balance, pour them into a 5L plastic bucket, and manually stir to initially mix. Measure 200g of water and add it to the bucket. After stirring evenly, pour the mixture into a disc granulator, set the speed to 150r / min, and the granulation time to 20min to form particles with an average particle size of 3mm. Transfer the granulated particles to an electric thermostatic drying oven, set the temperature to 90℃, and dry for 8h to obtain expanding agent B.

[0046] S3: Using a single-shaft forced concrete mixer, first add 1000g of cement and 2000g of sand and gravel, set the speed to 80r / min and dry mix for 1.5min. Then add 50g of expansion agent A, adjust the speed to 100r / min and mix for 2.5min. Finally, add 30g of expansion agent B, 200g of fly ash, 450g of water and 12g of water-reducing agent, set the speed to 120r / min and mix for 4min. Discharge to obtain concrete.

[0047] Example 5

[0048] This embodiment provides a method for preparing concrete, including the following steps:

[0049] S1: Weigh 500g of calcium sulfate expanding agent using an electronic balance (accuracy 0.01g). Pour 2500g of 5% citric acid solution into a 5L beaker. Slowly add calcium sulfate to the citric acid solution and stir until homogeneous. Then, place the beaker in a CNC ultrasonic cleaner for ultrasonic treatment. Set the power to 300W, the frequency to 30kHz, and the time to 20min. After ultrasonic treatment, use a Buchner funnel and a 0.2μm microporous membrane, along with a circulating water multi-purpose vacuum pump, to perform vacuum filtration to separate the solid and liquid. Transfer the filter residue to an electric heating drying oven and dry it at 70℃ for 6h. Weigh 5g of basalt nanofibers and place them together with the dried calcium sulfate in a planetary ball mill. Set the speed to 400r / min and grind for 8min to obtain expanding agent A.

[0050] S2: Weigh 1000g of calcium oxide expanding agent, 10g of polycarboxylate plasticizer, and 150g of silica fume using an electronic balance, pour them into a 5L plastic bucket, and manually stir to initially mix. Measure 200g of water and add it to the bucket. After stirring evenly, pour the mixture into a disc granulator, set the rotation speed to 150r / min, and the granulation time to 20min to form particles with an average particle size of 3mm. Transfer the granulated particles to an electric thermostatic drying oven, set the temperature to 90℃, and dry for 8h to obtain expanding agent B.

[0051] S3: Using a single-shaft forced concrete mixer, first add 1000g of cement and 2000g of sand and gravel, set the speed to 80r / min and dry mix for 1.5min. Then add 50g of expansion agent A, adjust the speed to 100r / min and mix for 2.5min. Finally, add 30g of expansion agent B, 200g of fly ash, 450g of water and 12g of water-reducing agent, set the speed to 120r / min and mix for 4min. Discharge to obtain concrete.

[0052] Example 6

[0053] This embodiment provides a method for preparing concrete, including the following steps:

[0054] S1: Weigh 500g of calcium sulfate expanding agent using an electronic balance (accuracy 0.01g). Pour 2500g of 5% citric acid solution into a 5L beaker. Slowly add calcium sulfate to the citric acid solution and stir until homogeneous. Then, place the beaker in a CNC ultrasonic cleaner for ultrasonic treatment. Set the power to 300W, the frequency to 30kHz, and the time to 20min. After ultrasonic treatment, use a Buchner funnel and a 0.2μm microporous membrane, along with a circulating water multi-purpose vacuum pump, to perform vacuum filtration to separate the solid and liquid. Transfer the filter residue to an electric heating drying oven and dry it at 70℃ for 6h. Weigh 5g of basalt nanofibers and place them together with the dried calcium sulfate in a planetary ball mill. Set the speed to 400r / min and grind for 8min to obtain expanding agent A.

[0055] S2: Weigh 1000g of calcium oxide expanding agent, 10g of polycarboxylate plasticizer, and 50g of silica fume using an electronic balance, pour them into a 5L plastic bucket, and manually stir to initially mix. Measure 200g of water and add it to the bucket. After stirring evenly, pour the mixture into a disc granulator, set the speed to 150r / min, and the granulation time to 20min to form particles with an average particle size of 3mm. Transfer the granulated particles to an electric thermostatic drying oven, set the temperature to 90℃, and dry for 8h to obtain expanding agent B.

[0056] S3: Using a single-shaft forced concrete mixer, first add 1000g of cement and 2000g of sand and gravel, set the speed to 80r / min and dry mix for 1.5min. Then add 50g of expansion agent A, adjust the speed to 100r / min and mix for 2.5min. Finally, add 30g of expansion agent B, 200g of fly ash, 450g of water and 12g of water-reducing agent, set the speed to 120r / min and mix for 4min. Discharge to obtain concrete.

[0057] Comparative Example 1

[0058] This comparative example provides a method for preparing concrete, including the following steps:

[0059] S1: Weigh 1000g of calcium oxide expanding agent, 10g of polycarboxylate plasticizer, and 100g of silica fume using an electronic balance, pour them into a 5L plastic bucket, and manually stir to initially mix. Measure 200g of water and add it to the bucket. After stirring evenly, pour the mixture into a disc granulator, set the speed to 150r / min, and the granulation time to 20min to form particles with an average particle size of 3mm. Transfer the granulated particles to an electric thermostatic drying oven, set the temperature to 90℃, and dry for 8h to obtain expanding agent B.

[0060] S2: Using a single-shaft forced concrete mixer, first add 1000g of cement and 2000g of sand and gravel, set the speed to 80r / min and dry mix for 1.5min. Then add 50g of calcium sulfate expansion agent, adjust the speed to 100r / min and mix for 2.5min. Finally, add 30g of expansion agent B, 200g of fly ash, 450g of water and 12g of water-reducing agent, set the speed to 120r / min and mix for 4min. Discharge to obtain concrete.

[0061] Comparative Example 2

[0062] This comparative example provides a method for preparing concrete, including the following steps:

[0063] S1: Weigh 500g of calcium sulfate expanding agent using an electronic balance (accuracy 0.01g). Pour 2500g of 5% citric acid solution into a 5L beaker. Slowly add calcium sulfate to the citric acid solution and stir until homogeneous. Then, place the beaker in a CNC ultrasonic cleaner for ultrasonic treatment. Set the power to 300W, the frequency to 30kHz, and the time to 20min. After ultrasonic treatment, use a Buchner funnel and a 0.2μm microporous membrane, along with a circulating water multi-purpose vacuum pump, to perform vacuum filtration to separate the solid and liquid. Transfer the filter residue to an electric heating drying oven and dry it at 70℃ for 6h. Weigh 5g of basalt nanofibers and place them together with the dried calcium sulfate in a planetary ball mill. Set the speed to 400r / min and grind for 8min to obtain expanding agent A.

[0064] S2: Using a single-shaft forced concrete mixer, first add 1000g of cement and 2000g of sand and gravel, set the speed to 80r / min and dry mix for 1.5min. Then add 50g of expansion agent A, adjust the speed to 100r / min and mix for 2.5min. Finally, add 30g of calcium oxide expansion agent, 200g of fly ash, 450g of water and 12g of water-reducing agent, set the speed to 120r / min and mix for 4min. Discharge to obtain concrete.

[0065] Comparative Example 3

[0066] This comparative example provides a method for preparing concrete, including the following steps:

[0067] Using a single-shaft forced concrete mixer, first add 1000g of cement and 2000g of sand and gravel, set the speed to 80r / min and dry mix for 1.5min. Then add 50g of calcium sulfate expansion agent, adjust the speed to 100r / min and mix for 2.5min. Finally, add 30g of calcium oxide expansion agent, 200g of fly ash, 450g of water and 12g of water-reducing agent, set the speed to 120r / min and mix for 4min. The concrete is then discharged.

[0068] Comparative Example 4

[0069] This comparative example provides a method for preparing concrete, including the following steps:

[0070] S1: Weigh 500g of calcium sulfate expanding agent using an electronic balance (accuracy 0.01g). Measure 2500g of 5% citric acid solution and pour it into a 5L beaker. Slowly add calcium sulfate to the citric acid solution and stir evenly. Use a Buchner funnel and a 0.2μm microporous membrane, along with a circulating water multi-purpose vacuum pump, to filter and separate the solid and liquid. Transfer the filter residue to an electric heating drying oven, set the temperature to 70℃, and dry for 6 hours. Weigh 5g of basalt nanofibers and put them together with the dried calcium sulfate into a planetary ball mill. Set the speed to 400r / min and grind for 8 minutes to obtain expanding agent A.

[0071] S2: Weigh 1000g of calcium oxide expanding agent, 10g of polycarboxylate plasticizer, and 100g of silica fume using an electronic balance, pour them into a 5L plastic bucket, and manually stir to initially mix. Measure 200g of water and add it to the bucket. After stirring evenly, pour the mixture into a disc granulator, set the speed to 150r / min, and the granulation time to 20min to form particles with an average particle size of 3mm. Transfer the granulated particles to an electric thermostatic drying oven, set the temperature to 90℃, and dry for 8h to obtain expanding agent B.

[0072] S3: Using a single-shaft forced concrete mixer, first add 1000g of cement and 2000g of sand and gravel, set the speed to 80r / min and dry mix for 1.5min. Then add 50g of expansion agent A, adjust the speed to 100r / min and mix for 2.5min. Finally, add 30g of expansion agent B, 200g of fly ash, 450g of water and 12g of water-reducing agent, set the speed to 120r / min and mix for 4min. Discharge to obtain concrete.

[0073] Comparative Example 5

[0074] This comparative example provides a method for preparing concrete, including the following steps:

[0075] S1: Weigh 500g of calcium sulfate expanding agent using an electronic balance (accuracy 0.01g). Measure 2500g of water and pour it into a 5L beaker. Slowly add calcium sulfate to the water and stir until homogeneous. Then, place the beaker in a CNC ultrasonic cleaner for ultrasonic treatment. Set the power to 300W, the frequency to 30kHz, and the time to 20min. After ultrasonic treatment, use a Buchner funnel and a 0.2μm microporous membrane, along with a circulating water multi-purpose vacuum pump, to perform vacuum filtration to separate the solid and liquid. Transfer the filter residue to an electric heating drying oven and dry it at 70℃ for 6h. Weigh 5g of basalt nanofibers and place them together with the dried calcium sulfate in a planetary ball mill. Set the speed to 400r / min and grind for 8min to obtain expanding agent A.

[0076] S2: Weigh 1000g of calcium oxide expanding agent, 10g of polycarboxylate plasticizer, and 100g of silica fume using an electronic balance, pour them into a 5L plastic bucket, and manually stir to initially mix. Measure 200g of water and add it to the bucket. After stirring evenly, pour the mixture into a disc granulator, set the speed to 150r / min, and the granulation time to 20min to form particles with an average particle size of 3mm. Transfer the granulated particles to an electric thermostatic drying oven, set the temperature to 90℃, and dry for 8h to obtain expanding agent B.

[0077] S3: Using a single-shaft forced concrete mixer, first add 1000g of cement and 2000g of sand and gravel, set the speed to 80r / min and dry mix for 1.5min. Then add 50g of expansion agent A, adjust the speed to 100r / min and mix for 2.5min. Finally, add 30g of expansion agent B, 200g of fly ash, 450g of water and 12g of water-reducing agent, set the speed to 120r / min and mix for 4min. Discharge to obtain concrete.

[0078] Comparative Example 6

[0079] This comparative example provides a method for preparing concrete, including the following steps:

[0080] S1: Weigh 500g of calcium sulfate expanding agent using an electronic balance (accuracy 0.01g). Pour 2500g of 5% citric acid solution into a 5L beaker. Slowly add calcium sulfate to the citric acid solution and stir until homogeneous. Then, place the beaker in a CNC ultrasonic cleaner for ultrasonic treatment. Set the power to 300W, the frequency to 30kHz, and the time to 20min. After ultrasonic treatment, use a Buchner funnel and a 0.2μm microporous membrane, along with a circulating water multi-purpose vacuum pump, to perform vacuum filtration to separate the solid and liquid. Transfer the filter residue to an electric heating drying oven and dry it at 70℃ for 6h. Weigh 5g of basalt nanofibers and place them together with the dried calcium sulfate in a planetary ball mill. Set the speed to 400r / min and grind for 8min to obtain expanding agent A.

[0081] S2: Weigh 1000g of calcium oxide expanding agent and 100g of silica fume using an electronic balance, pour them into a 5L plastic bucket, stir manually to initially mix, add 200g of water to the bucket, stir evenly, pour the mixture into a disc granulator, set the speed to 150r / min, granulation time to 20min, forming particles with an average particle size of 3mm, transfer the granulated particles to an electric heating constant temperature forced air drying oven, set the temperature to 90℃, dry for 8h, to obtain expanding agent B.

[0082] S3: Using a single-shaft forced concrete mixer, first add 1000g of cement and 2000g of sand and gravel, set the speed to 80r / min and dry mix for 1.5min. Then add 50g of expansion agent A, adjust the speed to 100r / min and mix for 2.5min. Finally, add 30g of expansion agent B, 200g of fly ash, 450g of water and 12g of water-reducing agent, set the speed to 120r / min and mix for 4min. Discharge to obtain concrete.

[0083] Experimental Example

[0084] According to GB / T 50082-2009, the shrinkage rate of concrete prepared in Examples 1-6 and Comparative Examples 1-6 was tested. Shrinkage rate = (L0 - L) / ( ... t ) / (L0-L)×100%, where L0 is the initial length, L t L represents the test length, and L represents the support length.

[0085] According to GB / T 50164-2011, the crack incidence rate and impermeability grade of the concrete prepared in Examples 1-6 and Comparative Examples 1-6 were tested. Crack incidence rate = total crack length / specimen surface area × 100%.

[0086] According to GB / T 50080-2016, the porosity and setting time of the concrete prepared in Examples 1-6 and Comparative Examples 1-6 were tested. Porosity = (1-ρ / ρ0)×100%, where ρ is the apparent density and ρ0 is the theoretical density, taken as 2.4 g / cm³. 3 The initial setting is indicated when the test needle sinks 4±1mm from the bottom plate, and the final setting is indicated when it sinks 0.5mm.

[0087] According to GB / T 50081-2019, the compressive strength and tensile strength of the concrete prepared in Examples 1-6 and Comparative Examples 1-6 were tested.

[0088] The test results are shown in Table 1:

[0089] Table 1. Concrete performance test results of Examples 1-6 and Comparative Examples 1-6

[0090]

[0091]

[0092] Conclusions: Comparative Example 1 omitted the calcium sulfate expansion agent modification process and used only calcium oxide expansion agent. Due to the rapid hydration of calcium oxide, local stress concentration occurred, resulting in a 60.7% increase in shrinkage rate and a 191.7% increase in crack incidence compared to Example 1, with a porosity reaching 16.5% (12.5% ​​in Example 1). Comparative Example 2 only incorporated calcium oxide alone, lacking a granulation process, leading to rapid hydration of calcium oxide, local expansion stress concentration, and a shrinkage rate of 0.040% (42.9% higher than Example 1), with a crack incidence rate of 2.8% (1.2% in Example 1). Comparative Example 3 did not use any expansion agent modification or nanofiber reinforcement. The direct incorporation of calcium sulfate and calcium oxide resulted in asynchronous hydration, leading to a decrease in the concrete's impermeability grade. Comparative Example 4 omitted the ultrasonic treatment step, resulting in severe agglomeration of calcium sulfate particles and uneven dispersion with basalt fibers. The nanofibers could not form a three-dimensional crack-resistant network, resulting in a 35.7% increase in shrinkage rate and a 13.5% decrease in flexural strength compared to Example 1. In Comparative Example 5, where citric acid solution was replaced with water, no complex-modified layer formed on the calcium sulfate surface, the interfacial transition zone was weak, and the porosity increased by 8.0% (compared to Example 1), demonstrating the key role of citric acid solution in improving the dispersibility of the expansive agent. In Comparative Example 6, the polycarboxylate plasticizer was omitted. Although the setting time was similar to Example 1, the decreased slurry fluidity led to insufficient concrete density, and the crack incidence rate increased by 41.7% compared to Example 1.

[0093] Although the principles of the present invention have been described in detail above with reference to preferred embodiments, those skilled in the art should understand that the above embodiments are merely illustrative explanations of the implementation of the present invention and are not intended to limit the scope of the present invention. The details in the embodiments do not constitute a limitation on the scope of the present invention. Any obvious changes, such as equivalent transformations or simple substitutions, based on the technical solutions of the present invention without departing from the spirit and scope of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing multi-admixed concrete with adjusted setting state, characterized in that, Includes the following steps: S1: Add calcium sulfate expansion agent to acid solution, sonicate, filter and dry, then mix and grind with basalt nanofibers to obtain expansion agent A; S2: Calcium oxide expander, polycarboxylate plasticizer and silica fume are wet granulated and then dried to obtain expander B; S3: After dry mixing cement and sand, add the expansion agent A and stir. Finally, add expansion agent B, fly ash, water and water-reducing agent and stir again to obtain concrete.

2. The method for preparing multi-doped concrete with adjusted setting state according to claim 1, characterized in that, In step S1, the acid solution is selected from citric acid or dilute hydrochloric acid, or a mixture of both, wherein the concentration of citric acid is 5-10% and the concentration of dilute hydrochloric acid is 3-5%; and / or, The mass ratio of the calcium sulfate expanding agent to the acid solution is 1:4-6.

3. The method for preparing multi-doped concrete with adjusted concrete setting state according to claim 1, wherein in step S1, the ultrasonic treatment time is 10-30 min, the power is 200-500 W, and the frequency is 20-40 kHz; and / or, The drying temperature is 60-80℃, and the time is 4-8 hours.

4. The method for preparing multi-doped concrete with adjusted concrete setting state according to claim 1, wherein in step S1, the mass ratio of basalt nanofibers to calcium sulfate expanding agent is 0.005-0.02:1; and / or, The grinding speed is 300-500 r / min, and the grinding time is 5-10 min.

5. The method for preparing multi-doped concrete to adjust the setting state of concrete according to claim 1, wherein in step S2, the mass ratio of the calcium oxide expanding agent to the polycarboxylate plasticizer is 100:(0.5-2); and / or, The amount of silica fume added is 5-15% of the mass of the calcium oxide expanding agent.

6. The method for preparing multi-doped concrete with adjusted setting state according to claim 1, wherein in step S2, during wet granulation, the mass ratio of water to calcium oxide expanding agent is 1:0.15-0.25; and / or, The rotation speed during wet granulation is 100-200 r / min.

7. The method for preparing multi-doped concrete with adjusted concrete setting state according to claim 1, wherein in step S2, the drying temperature is 80-100℃; and / or, The drying time is 6-12 hours.

8. The method for preparing multi-admixed concrete with adjusted setting state according to claim 1, wherein in step S3, the mass ratio of cement, sand, expansive agent A, expansive agent B, fly ash, water, and water-reducing agent is 100:(150-220):(3-8):(1-5):(10-30):(33-65):(0.55-2.6); and / or, The dry mixing time is 1-2 minutes, and the rotation speed is 60-100 r / min; and / or, The stirring time is 2-3 minutes, and the rotation speed is 80-120 r / min; and / or, The secondary stirring time is 3-5 minutes, and the rotation speed is 100-150 r / min.

9. A multi-admixed concrete for adjusting the setting state of concrete, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. The application of the multi-doped concrete as described in claim 9, which adjusts the concrete setting state, in bridge engineering.

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