A high-slump concrete and a method for producing the same

Abstract

The application relates to the technical field of building materials, and discloses high-slump concrete and a preparation method thereof, the concrete being made of coarse aggregate, fine aggregate, Portland cement, fly ash, mineral powder, water and components A, B and C; the component A is a low-substitution-degree phosphate esterified starch solution, the component B is a mixed solution of sodium metaborate and sodium gluconate, and the component C is a mixed solution of polycarboxylic acid water reducing agent and polyvinyl alcohol. The preparation method comprises the following steps: first, surface modification is carried out on the aggregate, part of the water and the component A through low-speed stirring; then, cementitious materials are added and stirred to be activated; finally, the remaining water and the components B and C are added and stirred at high speed to discharge. The phosphate esterified starch and the borate are used to construct a shear-sensitive dynamic crosslinking network in an alkaline environment, the problem of slurry aggregate separation and large slump loss over time is effectively solved while the high fluidity of the concrete is ensured, and the anti-segregation performance is improved.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a high slump concrete and its preparation method. Background Technology

[0002] With the development of modern engineering construction towards large spans, super high-rise buildings, and complex structures, pumped concrete construction technology has been widely used. To meet the requirements of long-distance pumping and the pouring of densely reinforced structures, concrete typically needs to have high fluidity (i.e., high slump). In actual production, to achieve high slump, the amount of water used or the dosage of water-reducing agents is often increased. While this reduces the yield stress of the slurry, it also weakens the slurry's ability to suspend coarse aggregates. When the slurry viscosity is insufficient, coarse aggregates are prone to settling under gravity, leading to bleeding, segregation, and stratification in the concrete, severely affecting the homogeneity and mechanical properties of the hardened concrete.

[0003] To address the segregation problem, existing technologies often employ the addition of viscosity modifiers (such as cellulose ethers and polyacrylamide) to increase the viscosity of the slurry. However, these traditional thickening components typically increase the viscosity of concrete in both static and flowing states proportionally, lacking sufficient shear-thinning properties. This results in improved anti-segregation performance of the concrete, but also excessive frictional resistance during pumping, increasing construction difficulty and making it challenging to achieve a balance between static stability and pumpability.

[0004] Furthermore, high-slump concrete also faces the problem of slump loss over time during transportation and while awaiting pouring. Due to the continuous consumption of free water during cement hydration and the decline in the dispersing ability of water-reducing agents, the fluidity of concrete often decreases after a period of time from the mixer, failing to meet construction requirements. Although this can be adjusted by adding retarders, a single retarder component is unlikely to simultaneously maintain fluidity and develop early strength. Moreover, some organic thickening components are prone to degradation or conformational curling in the strongly alkaline environment of cement hydration, resulting in significant fluctuations in the rheological properties of the paste over time.

[0005] In terms of preparation technology, existing concrete mixing methods typically involve adding all raw materials at once or performing only simple dry-wet separation mixing. For concrete systems containing polymeric modifiers, this mixing method easily leads to the modifiers rapidly swelling and agglomerating upon contact with water due to excessively high local concentrations, making it difficult to disperse evenly throughout the paste. This not only reduces the effectiveness of the modifiers but also fails to form an effective bonding layer at the interface between aggregates and paste, causing the interfacial transition zone to become a weak point in the concrete structure and limiting the improvement of the overall anti-segregation performance of the concrete. Summary of the Invention

[0006] The technical problem solved by this invention is that existing high-slump concrete, while maintaining high fluidity, is difficult to balance anti-segregation performance and slump retention capacity, resulting in paste-aggregate separation, bleeding, and significant losses over time.

[0007] To address the above problems, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides a high slump concrete, which adopts the following technical solution:

[0009] A high-slump concrete is made from raw materials comprising the following parts by weight: 1030-1060 parts coarse aggregate; 710-740 parts fine aggregate; 220-235 parts silicate cement; 75-85 parts fly ash; 80-90 parts mineral powder; 175-185 parts water; 1.10-1.25 parts component A; 0.50-0.70 parts component B; and 3.90-4.30 parts component C.

[0010] By adopting the above technical solution, the components work synergistically to improve the rheological properties of concrete paste. The specific process is as follows: After the low-substituted phosphorylated starch in component A enters the mixing water system, it complexes with calcium ions in the liquid phase using its phosphate groups, adsorbing onto the surface of cement particles and aggregates. Simultaneously, its molecular chains maintain an extended conformation in the aqueous phase, increasing the base viscosity of the paste liquid phase and inhibiting free water migration. Based on this, sodium metaborate in component B hydrolyzes in the alkaline environment generated during cement hydration to generate tetrahydroxyborate ions [B(OH)4]. - This ion, acting as a crosslinking center, undergoes a condensation reaction with the cis-ortho-dihydroxyl groups on the phosphorylated starch molecular chain to form borate ester bonds. These chemical bonds possess dynamic reversibility, creating a three-dimensional spatial network structure within the slurry that is sensitive to shear rate: in a static state, the network structure remains intact and provides yield stress, supporting the suspension of coarse aggregate and preventing sedimentation and segregation; under shear stress during pumping or casting, the network structure dissociates, releasing the trapped flowing water and imparting high fluidity to the concrete. Simultaneously, sodium gluconate in component B regulates the coordination balance of borate esters and the cement hydration rate, while the polycarboxylate superplasticizer in component C disperses cement particles through steric hindrance, and polyvinyl alcohol utilizes hydroxyl groups to enhance the crosslinking network and strengthen interfacial adhesion. These mechanisms collectively achieve the concrete's resistance to segregation and its long-term stability under high slump conditions.

[0011] Preferably, component A, component B, and component C have the following characteristics: component A is an aqueous solution of low-substituted phosphorylated starch with a degree of substitution (DS) between 0.05 and 0.10, and the solid content of component A is 20%-30%; component B is a mixed aqueous solution of sodium metaborate and sodium gluconate, and the solid content of component B is 25%-35%; component C is a mixture of polycarboxylate superplasticizer and polyvinyl alcohol.

[0012] By adopting the above technical solution, the degree of substitution (DS) of component A is limited to between 0.05 and 0.10, balancing the water solubility and adsorption properties of starch molecules. This ensures that starch molecules can both fully expand in water to form a network framework and effectively anchor themselves on the particle surface. Adding components A, B, and C in a liquid form at specific concentrations leverages the rapid dispersion of the liquid phase, allowing the reactants to quickly and evenly distribute during stirring, avoiding uneven reaction or abnormal coagulation caused by excessively high local concentrations.

[0013] Preferably, in component B, the mass ratio of sodium metaborate to sodium gluconate is 1:(0.8-1.2); and in component C, the mass ratio of polycarboxylate superplasticizer to polyvinyl alcohol solids is (9-11):1.

[0014] By adopting the above technical solution, the mass ratio of sodium metaborate to sodium gluconate is adjusted to control the formation kinetics and strength of the cross-linking network, preventing false setting due to excessively rapid cross-linking or insufficient anti-segregation due to excessively slow cross-linking. The ratio of polycarboxylate superplasticizer to polyvinyl alcohol is set to ensure water reduction rate and slurry fluidity, while utilizing the long-chain hydroxyl structure of polyvinyl alcohol to improve pore characteristics and reduce internal defects in concrete.

[0015] Preferably, the coarse aggregate is 5-25mm continuously graded crushed stone; the fine aggregate is medium sand; and the strength grade of the silicate cement is 42.5 or 52.5. More preferably, the particle size distribution of the coarse aggregate is as follows: 25%-35% of particles with a diameter of 5-10mm, 45%-55% of particles with a diameter of 10-20mm, and 15%-25% of particles with a diameter of 20-25mm.

[0016] By employing the above technical solution, the aggregate packing state is optimized using a specific proportion of continuously graded crushed stone, reducing the porosity between aggregates and thus decreasing the volume of slurry required to fill the voids. With the total amount of cementitious material remaining constant, increasing the thickness of the slurry layer coating the aggregate surface reduces the plastic viscosity of the concrete, thereby improving pumpability. The skeletal structure formed by this particle size distribution matches the rheological network constructed by components A and B, further preventing the settling tendency of large aggregate particles under gravity and improving the homogeneity of the concrete.

[0017] Secondly, the present invention provides a method for preparing high-slump concrete, which adopts the following technical solution:

[0018] A method for preparing high-slump concrete includes the following steps: S1, coarse aggregate and fine aggregate are added to a mixer, along with 50%-60% of the total water volume and all of component A. The mixer speed is controlled at 30-50 rpm, and the mixture is stirred for 40-50 seconds to obtain a pretreated aggregate mixture; S2, silicate cement, fly ash, and mineral powder are added to the pretreated aggregate mixture, and the mixture is stirred evenly to obtain an activated paste mixture; S3, the remaining water is added to the activated paste mixture, along with all of component B and component C. The mixer speed is controlled at 90-120 rpm, and the mixture is stirred for another 90-120 seconds to obtain high-slump concrete.

[0019] By employing the above technical solution, the rheological structure of concrete is constructed by controlling the water addition sequence and stirring speed in conjunction with the chemical reaction process. In step S1, low-substituted phosphorylated starch (component A) is preferentially mixed with aggregates and part of the mixing water. Stirring at a low speed of 30-50 rpm avoids crushing of the coarse aggregates while allowing starch molecules to physically adsorb onto the aggregate surface using phosphate groups, thus modifying the aggregate surface. In step S2, after the addition of the cementitious material, a hydration reaction occurs, increasing the pH value of the liquid phase. The alkaline environment promotes the conformational extension of the starch molecular chains adsorbed on the aggregate surface, exposing more active hydroxyl sites and forming an activated paste layer encapsulating the aggregate. In step S3, the remaining water is added, and components B and C are introduced. At this time, the stirring speed is increased to 90-120 rpm, using high shear force to rapidly disperse small amounts of components B and C throughout the system. This process avoids premature agglomeration of components A and B at localized high concentrations, instead promoting cross-linking reactions between metaborate ions and starch molecular chains in a dispersed state. This cross-linked network structure, generated under shearing action, is more uniformly distributed and can effectively connect aggregates and paste, thereby improving the anti-segregation performance of concrete.

[0020] Preferably, in step S1, the low-substituted phosphate-esterified starch in component A is prepared by the following steps: (1) 100 parts by weight of starch is dispersed in 140-160 parts by weight of water, 6.0-12.0 parts by weight of phosphate mixed esterification agent and 3.0-6.0 parts by weight of urea are added, and the mixture is stirred evenly to obtain a starch suspension; the starch is selected from corn starch or cassava starch; (2) the pH value of the starch suspension is adjusted to 5.5-6.5 with dilute hydrochloric acid or sodium hydroxide solution, the liquid phase is removed, and the mixture is dried at 55-60℃ until the moisture content is less than 15% to obtain esterification reaction precursor powder; (3) the esterification reaction precursor powder is reacted at 120-130℃ for 60-90 minutes, and the crude product is obtained after natural cooling; (4) the crude product is washed with ethanol aqueous solution, dried and pulverized to obtain low-substituted phosphate-esterified starch.

[0021] By adopting the above technical solution, low-substituted phosphate-esterified starch is prepared by semi-dry solid-phase reaction, and the product performance is limited by controlling the reaction parameters. In step (1), urea is added to act as a penetrant and catalyst, which helps to destroy the crystalline structure of starch particles and promotes phosphate penetration. In step (2), the pH value is controlled in the weakly acidic range of 5.5-6.5, which can balance the esterification reaction efficiency and inhibit the hydrolytic degradation of starch at high temperature. In step (3), the phosphate is dehydrated and polymerized and grafted onto starch molecules through a constant temperature reaction of 120-130℃; the reaction time is controlled at 60-90 minutes, and the degree of substitution (DS) is controlled at a low level of 0.05-0.10 to ensure that the product has suitable water solubility and thickening properties, and to avoid the paste being too viscous due to excessive substitution. The alcohol washing process in step (4) removes unreacted free phosphate and prevents residual ions from interfering with the setting time and strength development of concrete.

[0022] In summary, the present invention has at least one of the following beneficial technical effects:

[0023] 1. This invention resolves the contradiction between the anti-segregation performance and high fluidity of high-slump concrete by constructing a shear-sensitive dynamic crosslinking network using low-substituted phosphated starch and sodium metaborate. The phosphated starch adsorbs onto the aggregate surface and extends into the paste, forming reversible chemical bonds with borate ions generated from the hydrolysis of sodium metaborate. This structure provides sufficient yield stress in a static state, effectively suspending coarse aggregate and preventing paste-aggregate separation and bleeding. Under shearing forces such as pumping or pouring, the network structure temporarily unwinds and releases the trapped flowing water, ensuring good workability of the concrete.

[0024] 2. This invention utilizes the regulatory effect between components to reduce slump loss over time. The degree of substitution of phosphated starch is strictly controlled between 0.05 and 0.10 to ensure that it maintains a suitable molecular conformation in an alkaline environment, which can maintain adsorption stability without excessively increasing the viscosity of the system. In conjunction with sodium gluconate to regulate the hydration rate of the cementitious material and the coordination balance of borate, the consumption rate of free water inside the paste is slowed down, so that the concrete can still maintain its initial rheological properties after long-term transportation.

[0025] 3. This invention optimizes the micro-interface structure of concrete through a step-by-step water addition and variable-speed mixing process. The preferential low-speed mixing promotes the formation of a uniform adsorption layer of modified starch on the aggregate surface, and the subsequent high-speed shearing promotes the formation of a cross-linked network at the solid-liquid interface, avoiding local agglomeration of thickening components. In addition, polyvinyl alcohol, with its abundant hydroxyl groups, participates in the network construction, enhances the adhesion of the transition zone between the paste and aggregate, reduces internal pore defects, and improves the homogeneity of the hardened concrete. Detailed Implementation

[0026] Preparation Examples 1-4:

[0027] Preparation Example 1:

[0028] This preparation example provides a low-substituted phosphorylated starch as component A, comprising the following steps:

[0029] Weigh 100 parts by weight of corn starch and disperse it in 140 parts by weight of deionized water. Add 6.0 parts by weight of phosphate mixed esterification agent and 3.0 parts by weight of urea. Stir at 300 rpm for 30 minutes at room temperature to form a uniformly dispersed starch suspension.

[0030] The pH of the starch suspension was adjusted to 5.5 using dilute hydrochloric acid or sodium hydroxide solution. After removing the liquid phase by vacuum filtration, the filter cake was dried in a 55°C oven until the moisture content was less than 15%. The powder was then ground and sieved to obtain the esterification reaction precursor powder.

[0031] The esterification precursor powder was placed in a reaction vessel equipped with a temperature control system, heated to 120°C, and reacted at a constant temperature for 60 minutes to graft phosphate groups onto the starch molecular chain. After natural cooling, the crude product was obtained.

[0032] The crude product was washed twice with a 50% ethanol aqueous solution to remove unreacted free phosphate. After drying and pulverizing at 80°C, the target low-substituted phosphated starch was obtained, and its degree of substitution (DS) was determined to be 0.052.

[0033] Preparation Example 2:

[0034] This preparation example provides a low-substituted phosphorylated starch as component A, comprising the following steps:

[0035] Weigh 100 parts by weight of tapioca starch and disperse it in 150 parts by weight of deionized water. Add 9.0 parts by weight of phosphate mixed esterification agent and 4.5 parts by weight of urea. Stir at 350 rpm for 30 minutes at room temperature to form a uniformly dispersed starch suspension.

[0036] The pH of the starch suspension was adjusted to 6.0 using dilute hydrochloric acid or sodium hydroxide solution. After removing the liquid phase by vacuum filtration, the filter cake was dried in a 55°C oven until the moisture content was less than 15%. The powder was then ground and sieved to obtain the esterification reaction precursor powder.

[0037] The esterification precursor powder was placed in a reaction vessel equipped with a temperature control system, heated to 125°C, and reacted at a constant temperature for 75 minutes to graft phosphate groups onto the starch molecular chain. After natural cooling, the crude product was obtained.

[0038] The crude product was washed twice with a 50% ethanol aqueous solution to remove unreacted free phosphate. After drying and pulverizing at 80°C, the target low-substituted phosphated starch was obtained, and its degree of substitution (DS) was determined to be 0.076.

[0039] Preparation Example 3:

[0040] This preparation example provides a low-substituted phosphorylated starch as component A, comprising the following steps:

[0041] Weigh 100 parts by weight of corn starch and disperse it in 160 parts by weight of deionized water. Add 12.0 parts by weight of phosphate mixed esterification agent and 6.0 parts by weight of urea. Stir at 400 rpm for 30 minutes at room temperature to form a uniformly dispersed starch suspension.

[0042] The pH of the starch suspension was adjusted to 6.5 using dilute hydrochloric acid or sodium hydroxide solution. After removing the liquid phase by vacuum filtration, the filter cake was dried in a 60°C oven until the moisture content was less than 15%. The powder was then ground and sieved to obtain the esterification reaction precursor powder.

[0043] The esterification precursor powder was placed in a reaction vessel equipped with a temperature control system, heated to 130°C, and reacted at a constant temperature for 90 minutes to graft phosphate groups onto the starch molecular chain. After natural cooling, the crude product was obtained.

[0044] The crude product was washed twice with a 50% ethanol aqueous solution to remove unreacted free phosphate. After drying and pulverizing at 80°C, the target low-substituted phosphated starch was obtained, and its degree of substitution (DS) was determined to be 0.098.

[0045] Preparation Example 4:

[0046] This comparative preparation example provides a phosphorylated starch with a high degree of substitution for subsequent comparative experiments to verify the critical significance of parameter limits, including the following steps:

[0047] Weigh 100 parts by weight of corn starch and disperse it in 150 parts by weight of deionized water. Add 20.0 parts by weight of phosphate mixed esterification agent and 10.0 parts by weight of urea. Stir at 400 rpm for 30 minutes at room temperature to form a uniformly dispersed starch suspension.

[0048] The pH of the starch suspension was adjusted to 6.0 using dilute hydrochloric acid or sodium hydroxide solution. After removing the liquid phase by vacuum filtration, the filter cake was dried in a 60°C oven until the moisture content was less than 15%. The powder was then ground and sieved to obtain the esterification reaction precursor powder.

[0049] The esterification precursor powder was placed in a reaction vessel equipped with a temperature control system, heated to 145°C, and reacted at a constant temperature for 120 minutes to promote a higher degree of esterification. After natural cooling, the crude product was obtained.

[0050] The crude product was washed twice with a 50% ethanol aqueous solution to remove unreacted free phosphate. After drying and pulverizing at 80°C, highly substituted phosphated starch was obtained, with a degree of substitution (DS) of 0.185.

[0051] Examples 1-3:

[0052] Example 1:

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

[0054] S1. 1030 parts by weight of coarse aggregate (5-25mm continuously graded crushed stone, of which 25% is 5-10mm, 50% is 10-20mm, and 25% is 20-25mm) and 710 parts by weight of fine aggregate (medium sand) are added to a twin-shaft forced mixer. 87.5 parts by weight of water (50% of the total water volume) and 1.10 parts by weight of component A are added. Component A is a 22% aqueous solution of low-substituted phosphorylated starch (DS=0.052) obtained in Preparation Example 1. The mixer is started and stirred at 30 rpm for 40 seconds to form discontinuous adsorption points on the surface of the aggregate by the phosphorylated starch molecules, thus obtaining a pretreated aggregate mixture.

[0055] S2. Keep the mixer running and add 220 parts by weight of silicate cement (P.O42.5), 75 parts by weight of fly ash and 80 parts by weight of mineral powder to the pretreated aggregate mixture; continue mixing for 60 seconds to induce the starch molecular chain conformation to unfold using the alkaline environment generated by the hydration of the cementitious material, and obtain an activated slurry mixture.

[0056] S3. Add the remaining 87.5 parts by weight of water to the activated slurry mixture, and simultaneously add 0.50 parts by weight of component B and 3.90 parts by weight of component C; component B is a 28% solids content aqueous solution of sodium metaborate and sodium gluconate in a mass ratio of 1:0.8; component C is a 40% solids content mixture of polycarboxylate superplasticizer (PCE) and polyvinyl alcohol (PVA) in a solids mass ratio of 9:1; adjust the mixer speed to 90 rpm and continue stirring for 90 seconds to construct a controlled dynamic crosslinking network, and discharge the material to obtain the target high slump concrete.

[0057] Example 2:

[0058] This embodiment provides a method for preparing high slump concrete, including the following steps:

[0059] S1. 1044 parts by weight of coarse aggregate (5-25mm continuously graded crushed stone, of which 30% is 5-10mm, 50% is 10-20mm, and 20% is 20% is 20-25mm) and 726 parts by weight of fine aggregate (medium sand) are added to a twin-shaft forced mixer. 99 parts by weight of water (55% of the total water volume) and 1.17 parts by weight of component A are added. Component A is a 25% aqueous solution of low-substituted phosphorylated starch (DS=0.076) obtained in Preparation Example 2. The mixer is started and stirred at 40 rpm for 45 seconds to form discontinuous adsorption points on the surface of the aggregate by the phosphorylated starch molecules, thus obtaining a pretreated aggregate mixture.

[0060] S2. Keep the mixer running and add 227 parts by weight of silicate cement (P.O42.5), 78 parts by weight of fly ash and 86 parts by weight of mineral powder to the pretreated aggregate mixture; continue mixing for 60 seconds to induce the starch molecular chain conformation to unfold using the alkaline environment generated by the hydration of the cementitious material, and obtain an activated slurry mixture.

[0061] S3. Add the remaining 81 parts by weight of water to the activated slurry mixture, and simultaneously add 0.59 parts by weight of component B and 4.11 parts by weight of component C; component B is a 30% solids content aqueous solution of sodium metaborate and sodium gluconate in a mass ratio of 1:1; component C is a 40% solids content mixture of polycarboxylate superplasticizer (PCE) and polyvinyl alcohol (PVA) in a solids mass ratio of 10:1; adjust the mixer speed to 105 rpm and continue stirring for 105 seconds to construct a controlled dynamic crosslinking network, and discharge the material to obtain the target high slump concrete.

[0062] Example 3:

[0063] This embodiment provides a method for preparing high slump concrete, including the following steps:

[0064] S1. 1060 parts by weight of coarse aggregate (5-25mm continuously graded crushed stone, of which 35% is 5-10mm, 50% is 10-20mm, and 15% is 20-25mm) and 740 parts by weight of fine aggregate (medium sand) are added to a twin-shaft forced mixer. 111 parts by weight of water (60% of the total water volume) and 1.25 parts by weight of component A are added. Component A is a 28% aqueous solution of low-substituted phosphated starch (DS=0.098) obtained in Preparation Example 3. The mixer is started and stirred at 50 rpm for 50 seconds to form discontinuous adsorption points on the surface of the aggregate by the phosphated starch molecules, thus obtaining a pretreated aggregate mixture.

[0065] S2. Keep the mixer running and add 235 parts by weight of silicate cement (P.O52.5), 85 parts by weight of fly ash and 90 parts by weight of mineral powder to the pretreated aggregate mixture; continue mixing for 60 seconds to induce the starch molecular chain conformation to unfold using the alkaline environment generated by the hydration of the cementitious material, and obtain an activated slurry mixture.

[0066] S3. Add the remaining 74 parts by weight of water to the activated slurry mixture, and simultaneously add 0.70 parts by weight of component B and 4.30 parts by weight of component C; component B is a 32% solids content aqueous solution of sodium metaborate and sodium gluconate in a mass ratio of 1:1.2; component C is a 40% solids content mixture of polycarboxylate superplasticizer (PCE) and polyvinyl alcohol (PVA) in a solids mass ratio of 11:1; adjust the mixer speed to 120 rpm and continue stirring for 120 seconds to construct a controlled dynamic crosslinking network, and discharge the material to obtain the target high slump concrete.

[0067] Comparative Examples 1-5:

[0068] Comparative Example 1:

[0069] This comparative example aims to verify the importance of the three-step process sequence of the present invention in constructing an ordered microstructure. Compared with Example 2, the difference lies in the change of the feeding sequence and process steps. Specifically, in step S1, water (100% of the total amount), coarse aggregate, fine aggregate, cement, fly ash, mineral powder, and all components A, B, and C are added to the mixer at once; the separate operations in steps S2 and S3 are eliminated, and the mixture is directly subjected to high-speed mixing for 120 seconds before being discharged; the specifications and proportions of the remaining raw materials are the same as in Example 2.

[0070] Comparative Example 2:

[0071] This comparative example aims to verify the role of component A in resisting mud and assisting in network construction. Compared with Example 2, the difference is that component A was not added. Specifically, in step S1, only water and aggregate were added and mixed, without adding component A (interfacial anchoring agent); the remaining raw material ratios, process steps, and parameters are the same as in Example 2.

[0072] Comparative Example 3:

[0073] This comparative example aims to verify the crucial significance of limiting the degree of substitution (DS 0.05-0.10) in avoiding concrete strength reduction. Compared with Example 2, the difference lies in the type of component A, specifically: the high-substitution degree phosphated starch (DS=0.185) obtained in Preparation Example 4 is used instead of the low-substitution degree phosphated starch obtained in Preparation Example 2; the remaining raw material ratios, process steps and parameters are the same as in Example 2.

[0074] Comparative Example 4:

[0075] This comparative example aims to verify the effect of introducing sodium gluconate as a competing ligand on preventing flash coagulation and achieving "controlled cross-linking". Compared with Example 2, the difference lies in the composition of component B. Specifically, component B does not contain sodium gluconate (competing ligand) and is prepared solely by dissolving sodium metaborate in water, while maintaining the same amount of sodium metaborate as in Example 2; the remaining raw material ratios, process steps, and parameters are the same as in Example 2.

[0076] Comparative Example 5:

[0077] This comparative example aims to verify the contribution of the "borate PVA" dynamic network to the segregation resistance of high-slump concrete. Compared to Example 2, the difference lies in the removal of the chemical components that construct the dynamic network. Specifically: component B (a buffered crosslinking initiator) is not added; component C does not contain polyvinyl alcohol (PVA), but is only a pure polycarboxylate superplasticizer (PCE) solution, and the amount of PCE used is consistent with the total solids content of component C in Example 2; the remaining raw material specifications, process steps, and parameters are the same as in Example 2.

[0078] Test Example 1-3:

[0079] Test Example 1: Workability Test of Freshly Mixed Concrete

[0080] Experimental method description:

[0081] This test was conducted according to GB / T50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures", with the ambient temperature controlled at 20±2℃ and the relative humidity at 60±5%. The experimental procedure is as follows:

[0082] First, an initial slump test is conducted. The concrete mixture is placed into a standard slump cone in three layers, each layer is tamped 25 times, and after smoothing, the cone is lifted vertically. The difference between the highest point of the mixture and the height of the cone is measured to characterize the yield flow capacity of the concrete under gravity. Next, the slump cone emptying time is measured. The slump cone is inverted and the bottom is sealed. After filling with concrete, the bottom seal is opened and timing begins. The time required for the concrete to completely empty from the cone is recorded. This indicator reflects the viscosity characteristics of the paste under shear conditions and the pumping resistance. Then, a static segregation rate test is performed using a sieve analysis method. The fresh concrete is allowed to stand for 30 minutes, and approximately 5 kg of the top 1 / 4 of the concrete is washed and sieved through a 4.75 mm square-hole sieve. The mass of the coarse aggregate remaining on the sieve is weighed, and the percentage deviation from the theoretical mix proportion is calculated. Finally, the macroscopic state of the mixture is directly observed upon discharge, and the encapsulation, bleeding, and presence of clumping are recorded.

[0083] Test results:

[0084] The test data for each embodiment and comparative example are recorded in Table 1.

[0085] Table 1. Rheological and stability test data of fresh concrete in each group

[0086] Group Initial slump (mm) Emptying time of the inverted drum (s) Static segregation rate (%) Aircraft status observation Example 1 185 7.4 1.8 The slurry is full, the aggregate is evenly distributed, and there is no bleeding. Example 2 215 6.8 0.9 The slurry has high fluidity, tightly encapsulates the crushed stone, and exhibits no segregation. Example 3 205 8.2 1.2 It has good cohesiveness, no settling, and moderate flow rate. Comparative Example 1 195 9.5 11.4 The gravel is unevenly distributed, with localized accumulations. Comparative Example 2 145 16.3 4.2 The slurry has low fluidity, is viscous, and exhibits high resistance during tamping. Comparative Example 3 220 6.5 1.5 It has high fluidity, the slurry is oily, and the appearance is uniform. Comparative Example 4 65 >45.0 -- False coagulation occurs, resulting in loose, fragmented pieces that cannot be unloaded. Comparative Example 5 230 5.1 32.6 Severe segregation, coarse aggregate settling to the bottom, surface bleeding.

[0087] Note: "--" indicates that the mixture has undergone false coagulation, lost its fluidity and become loose and fragmented, making it impossible to sieve and determine the segregation rate according to standard methods.

[0088] Results Analysis and Conclusions:

[0089] Based on the data in Table 1, the chemical action mechanism of each component is analyzed as follows:

[0090] Data from Examples 1 to 3 show that the concrete prepared by this invention maintains a high slump (185-215 mm) while controlling the static segregation rate at a low level (0.9%-1.8%). Compared with Comparative Example 5, which did not construct a borate ester-PVA dynamic network, although achieving a slump of 230 mm, exhibited a static segregation rate as high as 32.6%, demonstrating severe paste-aggregate separation. This comparison confirms that the dynamic borate ester bonds formed in the examples provide sufficient yield stress to suspend coarse aggregate in a static state; and in the inverted cylinder evacuation test, the evacuation time of the examples (6.8-8.2 s) was not prolonged due to the introduction of the cross-linked structure, indicating that the chemical bond is shear-sensitive and undergoes rapid dissociation under shear, exhibiting shear-thinning characteristics, which meets the requirements for pumping construction.

[0091] In Comparative Example 4, after removing sodium gluconate from component B, the initial slump dropped sharply to 65 mm, and the material could not be properly emptied, exiting the machine as loose, fragmented pieces. This was due to the lack of a competing ligand buffering effect; the borate ions rapidly cross-linked upon contact with the PVA molecular chains, leading to localized gelation. In Example 2, the introduction of a buffering mechanism effectively slowed down the reaction kinetics, ensuring uniform dispersion of the material during stirring.

[0092] The influence of process sequence on the orderliness of the microstructure is reflected in the difference between Example 2 and Comparative Example 1. Comparative Example 1, which uses a one-time feeding process, has a significantly higher static segregation rate (11.4%) than Example 2 (0.9%). This indicates that, in the absence of step-by-step control, the adsorption and reaction of phosphated starch, borates, and PVA are in a state of disordered competition, failing to effectively form a directional bridging structure on the aggregate surface, thus reducing the stabilizing ability of the slurry on the aggregate.

[0093] Furthermore, in Comparative Example 2, the absence of component A resulted in a slump reduction to 145 mm. This was because the lack of phosphated starch preferentially occupied high-energy sites on the aggregate surface, leading to partial adsorption of the subsequently added polycarboxylate superplasticizer (PCE) by the aggregate or mud-containing components, thus reducing the effective amount of PCE used to disperse cement particles. The addition of component A acted as a site-sealing agent, ensuring the dispersion efficiency of PCE.

[0094] It should be noted that Comparative Example 3 used phosphoric acid esterified starch with a high degree of substitution (DS=0.185), and its fresh mixing properties were similar to those of Example 2. This indicates that the difference in the degree of substitution of phosphoric acid esterified starch is not mainly reflected in the rheology during the fresh mixing stage, and its influence on the interfacial strength after hardening will be further verified in subsequent mechanical property tests.

[0095] Test Example 2: Slump Loss Over Time Test

[0096] Experimental method description:

[0097] This test was conducted according to GB / T50080-2016 standard, with the ambient temperature controlled at 20±2℃. The concrete mixture from Test Example 1, after the initial slump test, was re-placed into a non-absorbent iron container, and the surface was covered with an impermeable plastic film to simulate moisture control under closed transport conditions. After standing for 60 minutes, the covering was removed, and the mixture was poured into a mixer for 30 seconds of remixing to restore homogeneity. The slump value after 1 hour was then measured using the standard slump cone method, and the difference between the initial value and the 1-hour value was calculated as the time-dependent slump loss.

[0098] Test results:

[0099] The time-lapse test data for each embodiment and comparative example are recorded in Table 2.

[0100] Table 2. Concrete slump loss over time test data for each group

[0101] Group Initial slump (mm) Slump in 1 hour (mm) Loss over time (mm) Remark Example 1 185 178 7 Liquidity remained stable Example 2 215 208 7 Liquidity remained stable Example 3 205 192 13 Liquidity remained stable Comparative Example 1 195 165 30 Significant decrease in fluidity was observed. Comparative Example 2 145 85 60 Severe compaction, loss of pumping capacity Comparative Example 3 220 210 10 Liquidity remained stable Comparative Example 4 65 -- -- Initial false coagulation, no time-lapse test performed. Comparative Example 5 230 225 5 Although the values ​​are high, they are accompanied by severe segregation.

[0102] Note: "--" indicates that the mixture had already undergone pseudo-setting in the initial stage and lost its plasticity, so no subsequent time-lapse test was conducted.

[0103] Results Analysis and Conclusions:

[0104] Table 2 shows the impact of interface anchoring components and process sequence on the flow retention capacity of concrete:

[0105] The slump loss over time in Examples 1 to 3 was 7-13 mm. The mechanism is that the low-substituted phosphorylated starch added in step S1 preferentially adsorbs onto the active sites on the aggregate surface and onto the mud-containing components. This preferential adsorption mechanism reduces the adsorption consumption of the aggregate by the subsequently added polycarboxylate superplasticizer (PCE), allowing a higher proportion of PCE molecules to remain in the liquid phase to maintain the dispersion effect on the cementitious material, thereby suppressing the loss of flowability during the settling process.

[0106] In Comparative Example 2, without the addition of component A, the slump loss reached 60 mm in 1 hour, with a final value of only 85 mm. In the absence of competitive adsorption of starch molecules, PCE molecules were largely adsorbed by aggregates and mud, resulting in a decrease in the concentration of effective dispersant in the liquid phase over time, and flocculation of the slurry.

[0107] Comparative Example 1 used a one-time feeding process, and the time loss was 30 mm, which was higher than the 7 mm in Example 2. In the mixed feeding mode, phosphated starch and PCE competed for aggregate surface sites simultaneously. The lack of preferential adsorption conditions provided by the step-by-step process resulted in some PCE still being consumed by the aggregate, and the slump retention efficiency was lower than that of the step-by-step process.

[0108] The loss over time in Comparative Example 5 was only 5 mm, but combined with the segregation phenomenon in Test Example 1, its high slump value originated from the precipitation of slurry after slurry-bone separation, rather than the colloidal dispersion stability, and thus belonged to false flowability.

[0109] In summary, by preferential discontinuous anchoring of low-substituted phosphated starch, the ineffective consumption of PCE can be suppressed, and the time-related fluidity loss of high-slump concrete can be controlled.

[0110] Test Example 3: Mechanical Property Testing of Hardened Concrete

[0111] Experimental method description:

[0112] This test was conducted according to GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". The reconstituted concrete mixture from Test Example 1 was selected and placed into a standard cast iron cube mold (150mm × 150mm × 150mm). The mold was placed on a high-frequency vibration table and vibrated until the surface was covered with slurry and no air bubbles were released. The molded specimen was covered with a waterproof film and left to stand at 20±5℃ for 24 hours before demolding. Immediately after demolding, the specimen was transferred to a standard curing room at 20±2℃ and a relative humidity of over 95% for curing. When the curing period reached 28 days, the specimen was removed, the surface moisture was wiped dry, and the compressive strength was tested using an electro-hydraulic servo pressure testing machine at a loading rate of 0.5MPa / s. The failure load was recorded, and the compressive strength value was calculated. The result was the arithmetic mean of three specimens.

[0113] Test results:

[0114] The 28-day compressive strength test data for each embodiment and comparative example are recorded in Table 3.

[0115] Table 3. 28-day compressive strength test data of concrete in each group

[0116] Group 28-day compressive strength (MPa) Description of damage patterns Example 1 43.6 Shear failure, with fracture surfaces in the aggregate. Example 2 48.2 Conical failure, some coarse aggregate was broken. Example 3 51.5 Brittle fracture, high proportion of aggregate fracture Comparative Example 1 41.8 Interface peeling, microcracks visible at the plasmid-bone interface. Comparative Example 2 39.4 The interior has honeycomb-like gaps and insufficient density. Comparative Example 3 34.7 The failure occurs along the edge of the aggregate, with minimal fracture of the aggregate. Comparative Example 4 -- -- Comparative Example 5 38.1 The specimen showed low strength at the top and excessive aggregate buildup at the bottom.

[0117] Note: "--" indicates that due to false setting or severe segregation of the freshly mixed concrete, it was impossible to make standard molded specimens and strength testing was not conducted.

[0118] Results Analysis and Conclusions:

[0119] Table 3 shows the influence of the degree of substitution and microstructure of phosphorylated starch on the strength of the transition zone at the interface of hardened concrete.

[0120] The 28-day compressive strength of Examples 1 to 3 ranged from 43.6 MPa to 51.5 MPa, with the failure mode accompanied by aggregate fracture, indicating that the interfacial bond strength between cement paste and aggregate was higher than the strength of the aggregate itself. This confirms that low-substitution-degree (DS 0.05-0.10) phosphate-esterified starch is discontinuously distributed on the aggregate surface. This distribution pattern, while adsorbing component C, retains the exposed aggregate surface area, allowing cement hydration products to grow directly on the aggregate surface and form chemical bonds, without blocking the penetration of hydration products to the aggregate surface.

[0121] The compressive strength of Comparative Example 3 was 34.7 MPa, lower than that of Example 2 (48.2 MPa), and the failure surface mainly occurred along the aggregate interface. This is because a highly substituted (DS 0.185) phosphorylated starch was used, and the high grafting density resulted in starch molecules forming a dense, continuous film layer on the aggregate surface. This organic film layer blocked the contact between calcium ions and the active sites on the aggregate surface, inhibited the directional alignment of calcium hydroxide crystals and the formation of CSH gel at the interface, and caused the interfacial transition zone to become a mechanically weak point.

[0122] Comparative Example 1 used a one-time feeding process and achieved a strength of 41.8 MPa. In the mixed feeding system, the uniformity of the distribution of each component at the microscopic interface decreased, and the locally existing polymer-rich areas interfered with the cement hydration process, leading to fluctuations in macroscopic mechanical properties.

[0123] The strength reduction in Comparative Example 2 and Comparative Example 5 was mainly due to defects in the fresh mix performance. Comparative Example 2 suffered from insufficient compaction due to poor fluidity, resulting in internal pores; Comparative Example 5 suffered from uneven material distribution due to segregation, causing stress concentration in areas rich in slurry under stress, leading to failure.

[0124] In summary, controlling the low degree of substitution of phosphated starch and combining it with a stepwise adsorption process can improve the rheological properties of concrete while ensuring its mechanical strength after hardening.

Claims

1. A high-slump concrete, characterized in that, Made from the following ingredients in parts by weight: 1030-1060 parts coarse aggregate; 710-740 parts fine aggregate; 220-235 parts of silicate cement; 75-85 parts fly ash; 80-90 parts of mineral powder; 175-185 parts water; Component A: 1.10-1.25 parts; Component B: 0.50-0.70 parts; Component C: 3.90-4.30 parts.

2. The high slump concrete according to claim 1, characterized in that, Component A, component B, and component C have the following characteristics: Component A is an aqueous solution of low-substituted phosphorylated starch with a degree of substitution (DS) between 0.05 and 0.10, and the solid content of component A is 20%-30%. Component B is a mixed aqueous solution of sodium metaborate and sodium gluconate, and the solid content of component B is 25%-35%. Component C is a mixture of polycarboxylate superplasticizer and polyvinyl alcohol.

3. The high slump concrete according to claim 2, characterized in that, In component B, the mass ratio of sodium metaborate to sodium gluconate is 1:(0.8-1.2); In component C, the solid mass ratio of polycarboxylate superplasticizer to polyvinyl alcohol is (9-11):

1.

4. The high slump concrete according to claim 1, characterized in that, The coarse aggregate is 5-25mm continuously graded crushed stone; the fine aggregate is medium sand; and the strength grade of the silicate cement is 42.5 or 52.

5.

5. The high slump concrete according to claim 4, characterized in that, The particle size distribution of the coarse aggregate is as follows: particles with a diameter of 5-10 mm account for 25%-35%, particles with a diameter of 10-20 mm account for 45%-55%, and particles with a diameter of 20-25 mm account for 15%-25%.

6. A method for preparing high-slump concrete, characterized in that, The preparation of a high-slump concrete according to any one of claims 1-4 includes the following steps: S1. Put coarse aggregate and fine aggregate into a mixer, add 50%-60% of the total water volume and all of component A, and stir for 40-50 seconds to obtain a pretreated aggregate mixture. S2. Add silicate cement, fly ash and mineral powder to the pretreated aggregate mixture, stir evenly to obtain an activated slurry mixture; S3. Add the remaining water to the activated slurry mixture, and simultaneously add all of the components B and C, continue stirring for 90-120 seconds, and discharge to obtain the high slump concrete.

7. The method for preparing high-slump concrete according to claim 6, characterized in that, In step S1, the low-substituted phosphorylated starch in component A is prepared through the following steps: (1) Disperse 100 parts by weight of starch in 140-160 parts by weight of water, add 6.0-12.0 parts by weight of phosphate mixed esterification agent and 3.0-6.0 parts by weight of urea, stir evenly to obtain starch suspension; (2) Adjust the pH of the starch suspension to 5.5-6.5, remove the liquid phase, and dry it at 55-60℃ until the moisture content is less than 15% to obtain the esterification reaction precursor powder; (3) The esterification reaction precursor powder is reacted at 120-130℃ for 60-90 minutes, and then naturally cooled to obtain the crude product. (4) The crude product is washed with an aqueous ethanol solution, dried and pulverized to obtain the low-substituted phosphated starch.

8. The method for preparing high-slump concrete according to claim 7, characterized in that, In step (1), the starch is selected from corn starch or tapioca starch.

9. The method for preparing high-slump concrete according to claim 6, characterized in that, In step S1, the speed of the mixer is 30-50 rpm; in step S3, the speed of the mixer is 90-120 rpm.

10. The method for preparing high-slump concrete according to claim 7, characterized in that, In step (2), the pH of the starch suspension is adjusted to 5.5-6.5 using dilute hydrochloric acid or sodium hydroxide solution.