Preparation method of special admixture for reservoir rockfill self-compacting concrete

Abstract

This invention relates to the field of concrete admixture technology, and more particularly to a method for preparing a special admixture for self-compacting concrete in reservoir riprap, comprising the following steps: S1, using N-vinylformamide, itaconic acid, and octadecyl methacrylate as reactive monomers, adding an initiator, and preparing a terpolymer through a copolymerization reaction; S2, compounding and mixing the terpolymer with a slump retainer, a shrinkage reducer, an air-entraining agent, an antifoaming agent, and water to obtain the special admixture. The special admixture prepared by this invention enables the concrete mixture to have good initial fluidity, a fast diffusion rate, maintain good flowability over a long period of time, possess good gap passage and water retention, and effectively control the drying shrinkage of concrete.

Description

Technical Field

[0001] This invention relates to the field of concrete admixture technology, and in particular to a method for preparing a special admixture for self-compacting concrete of reservoir rockfill. Background Technology

[0002] Rockfill concrete is a large-volume concrete construction technology used in water conservancy projects such as reservoirs and dams. Its basic principle is to pre-pile large-diameter boulders into a mass, and then pour special self-compacting concrete into the gaps in the pile of boulders. It can flow and fill all the complex pores by its own weight, and can solidify with the boulders into a dense whole structure without manual vibration. It can effectively reduce the temperature control risks common in traditional large-volume concrete, while improving construction efficiency.

[0003] Patent publication number CN108640610A discloses an underwater self-compacting concrete and its construction method. The concrete, by weight, comprises: 400-610 parts aggregate, 124-211 parts sand, 200-220 parts cement, 46-70 parts fly ash, 110-180 parts water, and 2-3.1 parts admixtures. During construction, a retaining wall framework is first built around the pouring area using riprap, and formwork is erected on the pouring surface. Then, the underwater self-compacting concrete is poured directly. Relying on its own weight, the concrete completely fills the gaps between the riprap and is not easily washed away by water, ultimately forming a riprap concrete with a complete structure, high density, good bonding, and meeting the requirements for strength and impermeability.

[0004] In existing technologies, conventional polycarboxylate superplasticizers, when applied to self-compacting concrete for reservoir riprap, often fail to provide sufficient plastic viscosity and cohesion while simultaneously imparting extremely low yield stress to ensure ultra-high fluidity. This leads to aggregate segregation and slurry bleeding when the concrete passes through complex and narrow riprap pores, affecting structural homogeneity. Furthermore, these admixtures have limited wetting and bonding capabilities on rough riprap surfaces, and their dispersibility and slump retention deteriorate rapidly under harsh conditions common in field construction, such as temperature fluctuations and long-distance transportation, making it difficult to maintain stable workability. Moreover, most existing solutions focus on optimizing the rheological properties of fresh concrete, neglecting the long-term crack resistance of large-volume concrete structures like reservoir dams, particularly regarding the reduction of autogenous and drying shrinkage, thus posing a potential safety hazard for the long-term project. Summary of the Invention

[0005] To address the problems mentioned in the background section, this invention provides a method for preparing a special admixture for self-compacting riprap concrete in reservoirs.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a special admixture for self-compacting riprap concrete in reservoirs includes the following steps: S1. Using N-vinylformamide, itaconic acid and octadecyl methacrylate as monomers, and adding an initiator, a terpolymer was prepared by copolymerization. S2. The terpolymer is compounded and mixed with slump retainer, shrinkage reducer, air-entraining agent, defoamer and water to obtain a special admixture for self-compacting riprap concrete in reservoirs.

[0007] Further, in step S1, the mass ratio of N-vinylformamide, itaconic acid, and octadecyl methacrylate is (2.5-4.5):(1-3):(0.5-2), preferably (3.0-4.0):(1.5-2.5):(0.8-1.5), the initiator is selected from at least one of azobisisobutyronitrile, ammonium persulfate, or potassium persulfate, and the amount of initiator added is 0.3-0.8% of the total mass of the three reaction monomers, preferably 0.4-0.6%.

[0008] Furthermore, step S1 specifically includes the following steps: Octadecyl methacrylate and emulsifier were added to deionized water for pre-emulsification to obtain a pre-emulsion. Itaconic acid and N-vinylformamide were added to the pre-emulsion to adjust the pH of the system. The reaction system was heated, an initiator was added, and the reaction was stirred for 2-6 hours. After the reaction was completed, the mixture was filtered and purified to obtain a terpolymer.

[0009] The emulsifier is selected from at least one of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, or sulfosuccinate salt, and its amount is 1-5% of the mass of octadecyl methacrylate. The amount of deionized water is 2-4 times the total mass of the three reactive monomers.

[0010] Furthermore, the pre-emulsification treatment is shear emulsification, with a temperature of 30-40℃, a shearing speed of 300-6000 rpm, preferably 1000-3000 rpm, and a pre-emulsification time of 10-30 min.

[0011] Furthermore, the pH of the system is adjusted to 4.0-5.0, the target temperature for heating is 65-75℃, the stirring speed is 100-200 rpm, the pH is adjusted using a 10-20% sodium hydroxide solution or concentrated hydrochloric acid, the heating rate is 1-3℃ / min, and the reaction time is preferably 3-5 h.

[0012] Furthermore, in step S2, based on the total mass of the special additives, the mass percentage of each compound component is as follows: terpolymer 40-60%, slump retainer 15-25%, shrinkage reducer 2.0-5.0%, air-entraining agent 0.3-1.0%, defoamer 0.05-0.15%, and the balance is water.

[0013] The preferred mass percentages of each compound component are: 45-55% terpolymer, 18-22% slump retainer, 3.0-4.5% shrinkage reducer, 0.5-0.8% air-entraining agent, 0.08-0.12% defoamer, and the balance being water.

[0014] Further, in step S2, the slump retainer is selected from polycarboxylic acid slump retainers, which are obtained by copolymerization of allyl polyoxyethylene ether and unsaturated carboxylic acid monomers, and the shrinkage reducing agent is selected from at least one of polyoxyethylene alkyl ether, polyoxyethylene aryl ether, or polyethylene glycol.

[0015] Further, in step S2, the air-entraining agent is selected from at least one of rosin thermal polymer, sodium dodecylbenzene sulfonate, or sodium α-olefin sulfonate, and the defoamer is selected from polyether-modified silicone defoamer or mineral oil-based defoamer. The saponification value of the rosin thermal polymer is 120-180 mg KOH / g; the number of carbon atoms of the olefin in the sodium α-olefin sulfonate is 14-18; and the carrier oil in the mineral oil-based defoamer is white oil or liquid paraffin.

[0016] According to another aspect of the present invention, a special admixture for self-compacting riprap concrete for reservoirs prepared by the above preparation method is provided, with a pH value of 6.0-7.5, preferably 6.5-7.2; the recommended dosage of the special admixture is 0.4-0.8% of the total mass of the cementitious materials.

[0017] The beneficial effects of this invention are: 1. In the technical solution of this invention, the copolymer backbone is composed of N-vinylformamide (which partially forms an ethyleneamine structure after hydrolysis) and itaconic acid units. The dicarboxyl group of itaconic acid acts as a strongly polar anchoring group, while the ethyleneamine structure provides hydrophilic and cationic properties, forming zwitterionic characteristics and enhancing its adaptability to adsorption on complex cement mineral surfaces. Octadecyl methacrylate provides ultra-long hydrophobic alkyl side chains. Driven by molecular thermal motion, the long-chain alkyl groups aggregate with each other through hydrophobic association, forming a weakly connected, three-dimensional dynamic network micelle structure. Under high shear rates such as stirring and pumping, the hydrophobic physical cross-linking network between copolymer molecules is destroyed by shear force, and the dynamic network temporarily dissociates. At this time, the copolymer mainly exerts the electrostatic repulsion and steric hindrance effect of traditional polycarboxylate superplasticizers, releasing a large amount of free water. The slurry exhibits extremely low shear viscosity, achieving ultra-high fluidity, and can freely flow and fill the gaps in the riprap. Once shearing stops, hydrophobic association rapidly recovers under molecular thermal motion, dynamic network reconstruction increases the yield stress and plastic viscosity of the slurry, effectively locking in cement particles, mineral admixtures, and free water, preventing them from settling and bleeding through the riprap skeleton under gravity, thus solving the problem of segregation in ultra-large gap concrete.

[0018] 2. In the technical solution of the present invention, the polymer copolymerizes a strongly adsorbent monomer with a hydrophobic monomer containing a long-chain alkyl group to form an amphiphilic structure that has both strong adsorption anchoring ability and hydrophobic association properties. This allows it to form a dynamic and reversible weak cross-linked network in the cement paste, which helps to improve the cohesion and stability of the paste while ensuring that the concrete obtains excellent fluidity. This improves the tendency of aggregate segregation and paste bleeding that easily occur when concrete fills the complex voids of riprap, and promotes the formation of a more uniform and dense overall structure.

[0019] 3. In the technical solution of the present invention, the slow-release characteristics of the slump-preserving component can continuously supplement the dispersion effect of cement particles within a certain period of time, forming a synergy with the initial dispersion effect of the main polymer, thereby mitigating the loss of workability caused by factors such as time and temperature, broadening the operable window of construction, and enhancing the adaptability to fluctuations in the external environment.

[0020] 4. The shrinkage-reducing components introduced into the formulation help to weaken the driving force causing shrinkage at the physicochemical level by reducing the surface tension of the capillary solution, thereby potentially reducing the risk of early shrinkage cracking in large-volume concrete. Furthermore, the high-quality microbubble system formed through the synergistic regulation of air-entraining and defoaming components not only improves workability during the fresh mixing stage but also is expected to enhance the concrete's impermeability and freeze-thaw resistance after hardening. Attached Figure Description

[0021] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] In the following preparation examples and embodiments, itaconic acid (CAS No.: 97-65-4) and octadecyl methacrylate (CAS No.: 32360-05-7) were purchased from Jiangsu Bosite Chemical Technology Co., Ltd., and N-vinylformamide (CAS No.: 13162-05-5) was purchased from Shanghai Jizhi Biochemical Technology Co., Ltd.; the emulsifiers fatty alcohol polyoxyethylene ether (AEO-9), alkylphenol polyoxyethylene ether (OP-10), and sulfosuccinate salt (Aerosol-OT) were purchased from Liaoning Aoke Chemical Co., Ltd. The following products were purchased from Sinopharm Chemical Reagent Co., Ltd.: ammonium persulfate (CAS No.: 7727-54-0), potassium persulfate (CAS No.: 7727-21-1), and azobisisobutyronitrile (CAS No.: 78-67-1); polycarboxylate slump retainer solution (SPS-100) was purchased from Liaoning Kelong Fine Chemical Co., Ltd.; shrinkage reducer polyoxyethylene lauryl ether and polyethylene glycol-600 were purchased from Shanghai Kanglang Biotechnology Co., Ltd.; and air-entraining agent and defoamer were purchased from Nanjing Xinyi Synthetic Technology Co., Ltd. Example 1

[0024] This embodiment provides a method for preparing a special admixture for self-compacting riprap concrete in reservoirs: S1. Add 200g of deionized water to a flask. Mix 5.0g of fatty alcohol polyoxyethylene ether (AEO-9) emulsifier with 20.0g of octadecyl methacrylate evenly, and add the mixture to the flask while stirring. Pre-emulsify the mixture at 35℃ and 1500rpm for 20 minutes to obtain a milky white pre-emulsion. Add 40.0g of itaconic acid and 100.0g of... to the pre-emulsion sequentially. N-vinylformamide was prepared by adjusting the pH of the system to 4.5 with a 15% sodium hydroxide solution. The reaction system was heated to 70°C at a rate of 2°C / min and the temperature was kept stable. 0.96g of ammonium persulfate (APS) initiator was weighed, dissolved in 10mL of deionized water, and slowly added dropwise to the reaction system over 30min through a constant pressure dropping funnel. After the addition was completed, the stirring speed was controlled at 150rpm and the reaction was carried out at 70°C for 4h. After the reaction was completed, the product was cooled to room temperature and filtered to obtain a light yellow terpolymer. S2. Based on the preparation of 1000g of special additive product, the following compounding is carried out: Terpolymer: 500g; Slump retainer: 200g of a polycarboxylic acid slump retainer solution obtained by copolymerizing allyl polyoxyethylene ether with a number average molecular weight of 2000 and acrylic acid; Shrinkage reducer: 30g of polyoxyethylene lauryl ether (alkyl C12, EO=10); Air entrainer: 5g of sodium α-olefin sulfonate (AOS, C14-16) powder; Defoamer: 1.0g of polyether modified organosilicon defoamer, and water is added to make up to a total mass of 1000g. The above components are added to the mixing vessel in sequence and stirred at 300rpm for 30min until the system is uniform, thus obtaining the light yellow special additive. Example 2

[0025] This embodiment provides a method for preparing a special additive with another formulation, which is basically the same as the preparation method in Example 1, with the main difference being: S1. Add 150g of deionized water to a flask. Mix 1.8g of alkylphenol polyoxyethylene ether emulsifier with 18.0g of octadecyl methacrylate and add the mixture to the flask. Pre-emulsify at 38℃ and 2500rpm for 15min. Add 45.0g of itaconic acid and 112.5g of N-vinylformamide to the pre-emulsion in sequence. Adjust the pH of the system to 4.2 with concentrated hydrochloric acid. Heat to 68℃ at a rate of 1.5℃ / min. Separately weigh 0.88g of potassium persulfate, dissolve it in water, and add it dropwise. React at 68℃ and 120rpm for 4.5h with stirring. Cool and filter to obtain the terpolymer. S2. Based on the preparation of 1000g of product, the following are the components: terpolymer: 550g; slump retainer: 150g of polycarboxylate slump retainer solution; shrinkage reducer: 40g of polyethylene glycol-600 (PEG-600); air entrainer: 8g of rosin thermal polymer (saponification value 150 mgKOH / g); defoamer: 1.2g of mineral oil-based defoamer, and water to make up to 1000g. Example 3

[0026] This embodiment provides a method for preparing a special additive with another formulation, which is basically the same as the preparation method in Example 1, with the main difference being: S1. Add 250g of deionized water to a flask. Mix 3.0g of sulfosuccinate emulsifier with 15.0g of octadecyl methacrylate and add the mixture to the flask. Pre-emulsify at 32℃ and 800rpm for 25min. Add 30.0g of itaconic acid and 75.0g of N-vinylformamide to the pre-emulsion in sequence. Adjust the pH to 4.8 with 10% NaOH solution. Heat to 72℃ at a rate of 3℃ / min. Weigh 0.60g of azobisisobutyronitrile and dissolve it in a small amount of ethanol. Add the solution dropwise. React at 72℃ and 180rpm for 3.5h with stirring. Cool and filter to obtain the terpolymer.

[0027] S2. Based on the preparation of 1000g of product: terpolymer: 550g; slump retainer: 250g of polycarboxylate slump retainer solution; shrinkage reducer: 25g of polyoxyethylene octylphenyl ether; air entrainer: 3.5g of sodium dodecylbenzenesulfonate; defoamer: 0.8g of polyether modified silicone defoamer, and water to make up to 1000g. Example 4

[0028] This embodiment provides a method for preparing a special additive with another formulation, which is basically the same as the preparation method in Example 1, with the main difference being: S1. Add 220g of deionized water to a flask. Mix 2.5g of fatty alcohol polyoxyethylene ether emulsifier with 16.0g of octadecyl methacrylate and add the mixture to the flask. Pre-emulsify at 36℃ and 2000rpm for 18min. Add 38.0g of itaconic acid and 95.0g of N-vinylformamide to the pre-emulsion in sequence. Adjust the pH to 4.6 with 12% sodium hydroxide solution. Heat to 72℃ at a rate of 2.5℃ / min. Separately weigh 0.75g of a mixture of ammonium persulfate and potassium persulfate (mass ratio 1:1) and dissolve it in water. Add the mixture slowly dropwise. React at 72℃ and 160rpm for 3.5h with stirring. Cool and filter to obtain the terpolymer. S2. Based on the preparation of 1000g of product, the following are the components: terpolymer: 480g; slump retainer: 210g of polycarboxylic acid slump retainer solution obtained by copolymerizing allyl polyoxyethylene ether and methacrylic acid; shrinkage reducer: 35g of polyoxyethylene oil-based ether; air entrainer: 4.0g of sodium dodecylbenzenesulfonate; defoamer: 1.1g of mineral oil-based defoamer (carrier is white oil), and water to make up to 1000g. Example 5

[0029] This embodiment provides a method for preparing a special additive with another formulation, which is basically the same as the preparation method in Example 1, with the main difference being: S1. Add 180g of deionized water to a flask. Mix 1.2g of alkylphenol polyoxyethylene ether and sulfosuccinate salt emulsifier (mass ratio 1:1) with 12.0g of octadecyl methacrylate and add to the flask. Pre-emulsify at 33℃ and 1200rpm for 22min. Add 25.0g of itaconic acid and 62.5g of N-vinylformamide to the pre-emulsion in sequence. Adjust the pH of the system to 4.3 with concentrated hydrochloric acid. Heat to 67℃ at a heating rate of 1.8℃ / min. Weigh 0.50g of azobisisobutyronitrile initiator and dissolve it in an appropriate amount of isopropanol. Add the solution dropwise and react at 67℃ and 130rpm for 5h. Cool and filter to obtain the terpolymer. S2. Based on the preparation of 1000g of product, the following are the components: terpolymer: 420g; slump retainer: 230g of polycarboxylic acid slump retainer solution; shrinkage reducer: 28g of a mixture of polyethylene glycol-400 (PEG-400) and polyoxyethylene nonylphenyl ether (mass ratio 2:1); air entrainer: 6.5g of sodium α-olefin sulfonate; defoamer: 0.9g of polyether modified silicone defoamer, and water to make up to 1000g. Example 6

[0030] This embodiment provides a method for preparing a special additive with another formulation, which is basically the same as the preparation method in Example 1, with the main difference being: S1. Add 240g of deionized water to a flask. Mix 4.0g of fatty alcohol polyoxyethylene ether emulsifier with 24.0g of octadecyl methacrylate and add the mixture to the flask. Pre-emulsify at 39℃ and 2800rpm for 12min. Add 50.0g of itaconic acid and 108.0g of N-vinylformamide to the pre-emulsion in sequence. Adjust the pH to 4.9 with 18% sodium hydroxide solution. Heat to 74℃ at a rate of 2.2℃ / min. Separately weigh 1.09g of potassium persulfate initiator, dissolve it in water, and add it dropwise. React at 74℃ and 190rpm for 3h. Cool and filter to obtain the terpolymer. S2. Based on the preparation of 1000g of product, the following are the components: terpolymer: 520g; slump retainer: 190g of polycarboxylic acid slump retainer solution; shrinkage reducer: 42g of polyoxyethylene tridecyl ether; air entrainer: 7.2g of rosin thermal polymer (saponification value 160 mg KOH / g); defoamer: 1.0g of a mixture of polyether modified silicone defoamer and mineral oil-based defoamer (mass ratio 1:1), and water to make up to 1000g.

[0031] Comparative Example 1 The main difference between this comparative example and Example 1 is that a terpolymer is not prepared; the remaining steps are the same as in Example 1.

[0032] Comparative Example 2 The difference between this comparative example and Example 2 is that octadecyl methacrylate is not added; the remaining steps are the same as in Example 2.

[0033] Comparative Example 3 The difference between this comparative example and Example 3 is that itaconic acid is not added, while the remaining steps are the same as in Example 3.

[0034] Comparative Example 4 The difference between this comparative example and Example 4 is that N-vinylformamide is not added; the remaining steps are the same as in Example 4.

[0035] Comparative Example 5 The difference between this comparative example and Example 5 is that no slump retainer is added; the remaining steps are the same as in Example 5.

[0036] Comparative Example 6 The difference between this comparative example and Example 6 is that no shrinkage agent is added, while the remaining steps are the same as in Example 6.

[0037] Comparative Example 7 The difference between this comparative example and Example 1 is that no air-entraining agent is added; the remaining steps are the same as in Example 1.

[0038] Prepare the special admixtures prepared in Examples 1-6, and the comparative samples prepared in Comparative Examples 1-7. Also prepare the following cementitious materials: P·O 42.5 grade ordinary Portland cement, Grade II fly ash, and S95 grade mineral powder. Wash and dry medium sand (fineness modulus 2.6-2.8) and 5-20mm continuously graded crushed stone, preparing the materials according to a 48% sand ratio requirement. Prepare clean crushed stone of 40-80mm as a simulated rockfill material, and determine its bulk porosity. The total amount of cementitious materials is 420 kg / m³, with a cement, fly ash, and mineral powder mass ratio of 280:70:70 and a water-cement ratio of 0.42. The admixture dosage for all samples is 0.6% of the total mass of cementitious materials (based on effective solid content).

[0039] After wetting the mixer, add the dry materials in the following order: coarse aggregate, fine aggregate, and cementitious materials (cement, fly ash, mineral powder). Premix for 60 seconds to ensure uniform mixing. Premix the admixture sample with the total mixing water. Pour the admixture-containing aqueous solution into the mixer at a uniform rate within 1 minute and continue mixing for 180 seconds. After discharging, manually and quickly agitate the mixture 3-5 times to ensure uniformity. Immediately begin the various fresh mix performance tests. Thoroughly clean the mixer and equipment before changing each admixture sample. Refer to SL / T 352-2020 "Test Procedures for Hydraulic Concrete" and GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures" for the following tests: (I) Test of workability of freshly mixed concrete 1. Slump Flow (SF) and T500 Time (completed within 5 minutes of discharge): Place the slump cone on the centrally moistened slump measuring plate, add the concrete mixture in three layers and compact it. Vertically lift the slump cone and use a stopwatch to record the time it takes for the concrete spread edge to reach the 500mm diameter mark; this is T500. 500 Time (s). After the concrete stops flowing, measure the expansion diameter in two perpendicular directions and take the average value as the slump spread SF (mm).

[0040] 2. V-funnel outflow time (Tv): Place the moistened V-funnel stably and seal the lower outlet with a baffle. Fill the funnel with concrete mixture and smooth the surface. Quickly open the baffle and start timing simultaneously. Record the time it takes for all the concrete to flow out of the funnel, which is Tv (s).

[0041] 3. Performance Loss Over Time: After testing the initial performance, the remaining concrete mixture was covered with a damp cloth and allowed to stand at room temperature (20±2℃). At 60 min and 120 min of standing time, the concrete was poured back into the mixer and quickly mixed for 30 seconds to restore homogeneity. Then, the slump flow (SF) and T... 500 Time-based testing. Calculate the collapse spread retention rate (%) at each time point = (expired SF / initial SF) × 100%.

[0042] 4. Gap Passability Test: Using a J-ring device, place it over the slump cylinder and repeat the slump spread test. Measure the spread diameter (SF) of the concrete after passing through the J-ring. J Calculate the difference ΔSF (mm), ΔSF = SF - SF J The results are shown in Tables 1 and 2:

[0043] Table 1. Test results of the fluidity index of freshly mixed concrete

[0044]

[0045] Table 2. Results of Stability and Gap Passability Tests for Freshly Mixed Concrete

[0046]

[0047] (II) Simulation test of rockfill filling Prepare a box with dimensions of 150cm x 30cm x 60cm (length x width x height). A circular pouring port with a diameter of approximately 10cm is opened at the bottom of one side, and a detachable guide funnel is connected to it. Clean, unweathered crushed stone with a particle size of 40-80mm is selected as the simulated material, and its porosity should be controlled between 38-42% to simulate the accumulation state of a rockfill. The above-mentioned fresh concrete mixture is poured into the pouring port at one end of the device at a uniform and continuous rate, controlled at 10L / min. Pouring is stopped when the concrete flow front approaches the end of the device. Allow the concrete to stand for 30 minutes to stabilize, and then conduct the following tests: 1. Pressure bleeding rate test: The pressure bleeding test method shall be carried out in accordance with the national standard GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures" and the pressure bleeding rate (%) shall be calculated.

[0048] 2. Hardened Concrete Performance Testing: Two sets of specimens were molded for each sample. Six 100mm×100mm×100mm cube specimens were used for compressive strength testing; three 100mm×100mm×515mm prism specimens were used for drying shrinkage testing. All specimens were compacted and smoothed on a vibrating table, and covered with plastic film to prevent moisture evaporation. After 24 hours of molding, the specimens were demolded and immediately placed in a standard curing room (temperature 20±2℃, relative humidity above 95%) for curing. At 7 days of standard curing, the corresponding cube specimens were removed, surface water was wiped dry, and their compressive strength was tested on a pressure testing machine; the average value was recorded. The prism specimens were removed after 3 days of curing in the standard curing room and transferred to a constant temperature and humidity chamber (temperature 20±2℃, relative humidity 60±5%). On the day of transfer (recorded as day 0 as the baseline length), the initial length of the specimen was measured using a non-contact shrinkage meter or a dial indicator. The length change was then measured on days 1, 7, 14, and 28, and the drying shrinkage value (με) after 28 days was calculated.

[0049] 3. Permeability Testing: Frustum-shaped permeability test specimens were used, with a top diameter of 175mm, a bottom diameter of 185mm, and a height of 150mm. Six permeability test specimens were formed for each concrete sample (formed simultaneously with the compressive strength test specimens). After compaction and surface finishing on a vibrating table, the specimens were covered with plastic film to prevent moisture evaporation. After 24 hours of molding, the specimens were demolded and immediately placed in a standard curing room (temperature 20±2℃, relative humidity above 95%) for 28 days of curing. The curing conditions were the same as for the compressive strength test specimens. After 28 days of curing, the specimens were removed and their surface moisture was wiped dry. The specimens were mounted on the permeability tester, and the perimeter was sealed with sealant to ensure that water pressure was applied only from the bottom surface. Starting with a water pressure of 0.1MPa, the water pressure was increased by 0.1MPa every 8 hours, and the permeability was observed. When three out of six specimens showed permeability, the test was stopped, and the water pressure value at that time (in MPa) was recorded. Calculate the impermeability grade, which is represented by "W", and the number is 10 times the maximum water pressure (MPa). If there is still no leakage when the water pressure is increased to 1.2 MPa, the test is stopped and the grade is W12.

[0050] The results are shown in Table 3-4:

[0051] Table 3. Test results of concrete stability, strength and drying shrinkage properties

[0052]

[0053] Table 4. Test results of concrete impermeability (28 days)

[0054]

[0055] As shown in Table 1, the initial slump expansion of Examples 1-6 was between 675-695 mm, indicating that the concrete mixtures prepared with the special admixtures in these examples had good initial fluidity. The initial slump expansion of Comparative Examples 1-4 was lower than that of the Examples, possibly because Comparative Example 1 did not prepare a terpolymer, and Comparative Examples 2-4 lacked one of the following components: octadecyl methacrylate, itaconic acid, and N-vinylformamide, respectively. The terpolymer and its components play a role in dispersing and lubricating in concrete; the lack of these components will affect the dispersion of cement particles and the fluidity of the mixture.

[0056] Initial T in Examples 1-6 500 A time between 3.0 and 3.9 seconds indicates a relatively fast diffusion rate of the concrete mixture. The initial T values ​​for Comparative Examples 1-4... 500 The times were all longer than in the examples, consistent with the initial slump expansion results, further illustrating that the absence of terpolymers or their key components reduces the fluidity of concrete mixtures and slows down the diffusion rate.

[0057] The outflow times from the V-funnel in Examples 1-6 ranged from 8.0 to 10.8 seconds, indicating that the concrete mixture flowed smoothly out of the V-funnel. The outflow times from the V-funnel in Comparative Examples 1-4 were all longer than those in the Examples, reflecting that the concrete mixtures in these comparative samples had higher viscosity and poorer fluidity, leading to longer outflow times.

[0058] As shown in Table 2, although the slump expansion of Examples 1-6 decreased to varying degrees at 60 min and 120 min, it still remained at a relatively high level, indicating that these special admixtures can enable the concrete mixture to maintain good fluidity over a longer period of time. Comparative Examples 1-4 showed a greater decrease in slump expansion at 60 min and 120 min, especially Comparative Example 1, indicating that the lack of terpolymers or their key components significantly reduces the concrete mixture's ability to maintain fluidity over time.

[0059] The 120-minute SF retention rates of Examples 1-6 were between 93.3% and 95.7%, indicating that these specialized admixtures effectively maintained the long-term fluidity of the concrete mixture. The 120-minute SF retention rates of Comparative Examples 1-4 were all lower than those of the Examples, further demonstrating the importance of the terpolymer and its key components in maintaining the long-term fluidity of the concrete mixture.

[0060] The difference between the J-ring spread and the slump spread (ΔSF) in Examples 1-6 was between 35-40 mm, indicating that the concrete mixture had good gap-passing properties and could fill the voids in the riprap well. The ΔSF in Comparative Examples 1-4 was greater than that in the Examples, indicating that the concrete mixtures in these comparative samples had poor gap-passing properties. This may be due to the lack of terpolymers or their key components, leading to poorer cohesiveness and flowability coordination in the concrete mixture, making it difficult to pass through narrow gaps smoothly.

[0061] Table 3 shows that the pressure bleeding rates of Examples 1-6 ranged from 4.8% to 6.3%, indicating that the concrete mixtures prepared with these special admixtures have good water retention properties and can effectively reduce the bleeding phenomenon of concrete under pressure. The pressure bleeding rates of Comparative Examples 1, 3, and 4 were significantly higher than those of the Examples, possibly because they lacked terpolymers or their key components, affecting the internal structure and water retention performance of the concrete mixtures. Comparative Example 5, which did not contain a slump retainer, also had a high pressure bleeding rate, indicating that the slump retainer also has a certain impact on the water retention of concrete.

[0062] The 7-day compressive strengths of Examples 1-6 ranged from 29.5 to 33.5 MPa, indicating that these specialized admixtures promoted the early strength development of concrete. The 7-day compressive strengths of Comparative Examples 1-4 were all lower than those of the Examples, possibly due to the lack of terpolymers or their key components, which affected the cement hydration process and the compactness of the concrete. Comparative Example 7, without the addition of an air-entraining agent, had a relatively high compressive strength; however, while air-entraining agents improve the workability of concrete, they may also reduce the concrete strength to some extent.

[0063] The 28-day drying shrinkage value of Examples 1-6 was 453 × 10⁻⁶. -6 -492×10 -6 The results indicate that these specialized admixtures have a certain controlling effect on the drying shrinkage of concrete. The 28-day drying shrinkage values ​​of Comparative Examples 1-4 are all lower than those of the Example, possibly because the concrete in these comparative samples has poorer density and more internal pores, resulting in relatively faster moisture loss during drying and thus lower shrinkage values. However, this does not necessarily mean better concrete performance; it may even affect the durability of the concrete. Comparative Example 6, which did not contain a shrinkage-reducing agent, had a drying shrinkage value similar to that of the Example, indicating that the shrinkage-reducing agent plays an important role in controlling the drying shrinkage of concrete.

[0064] As shown in Table 4, the impermeability grades of Examples 1-6 are between W8 and W11 (maximum water pressure 0.80-1.10 MPa), indicating that the special admixture prepared in this invention can significantly improve the impermeability of concrete and form a dense microstructure. The impermeability grades of Comparative Examples 1, 3, and 4 are only W4 or W5, significantly lower than the examples. This is because the lack of terpolymers or their key monomers leads to increased porosity and poorer pore connectivity within the cement paste, weakening its resistance to pressurized water penetration. Comparative Example 2 has an impermeability grade of W6, indicating that the absence of hydrophobic components affects the paste density and pore structure stability. Comparative Example 5 has an impermeability grade of W7, and its rapid loss of workability may lead to decreased molding uniformity, indirectly affecting impermeability. Comparative Examples 6 and 7 both achieved a permeability rating of W8, which meets the basic design requirements. This indicates that the shrinkage reducer and air-entraining agent do not have a decisive influence on permeability performance under certain conditions. However, the high-quality microbubble system introduced by the air-entraining agent actually helps to block capillary channels. In the examples, the microbubble system formed by the synergistic regulation of air-entraining and defoaming components further optimizes the pore structure, thereby achieving better permeability performance.

[0065] In each embodiment, the terpolymer is polymerized from fatty alcohol polyoxyethylene ether, octadecyl methacrylate, itaconic acid, and N-vinylformamide, etc., and plays a role in dispersion, lubrication, and water retention in concrete. The hydrophilic and hydrophobic groups in its molecular structure may adsorb onto the surface of cement particles, forming a hydration film that prevents cement particle aggregation, thereby improving the fluidity of concrete. Simultaneously, the terpolymer can also adjust the viscosity of concrete and improve its porosity. Slump retainers can slow down the hydration process of cement, reduce slump loss during mixing and transportation, and maintain the long-term fluidity of concrete. The presence of slump retainers helps maintain good workability of concrete for a longer period. Shrinkage reducers can reduce the surface tension of pore water inside concrete, reducing shrinkage stress during drying and effectively controlling drying shrinkage. Air-entraining agents can introduce a large number of tiny, uniformly distributed air bubbles into concrete, improving its workability, such as increasing fluidity and reducing bleeding and segregation. However, the introduction of air-entraining agents can also reduce the strength of concrete to some extent, therefore, the dosage of air-entraining agents needs to be reasonably controlled.

[0066] In summary, the technical solution provided by this invention prepares a terpolymer containing fatty alcohol polyoxyethylene ether, octadecyl methacrylate, itaconic acid, and N-vinylformamide, and combines it with slump retainers, shrinkage reducers, and air-entraining agents to prepare a special admixture. This special admixture enables the concrete mixture to have good initial fluidity, fast diffusion speed, smooth V-funnel outflow, maintain good time-dependent fluidity for a long time, and has good gap passage and water retention. It promotes the early strength development of concrete and effectively controls the drying shrinkage of concrete, making it suitable for self-compacting concrete for reservoir rockfill.

[0067] In the description of this specification, the reference to terms such as "embodiment," "various embodiments," etc., indicates that a specific feature, structure, material, or characteristic described in connection with that embodiment or preparation example is included in at least one embodiment of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments.

[0068] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a special admixture for self-compacting riprap concrete in reservoirs, characterized in that, Includes the following steps: S1. Using N-vinylformamide, itaconic acid and octadecyl methacrylate as monomers, and adding an initiator, a terpolymer was prepared by copolymerization. S2. The terpolymer is compounded and mixed with slump retainer, shrinkage reducer, air entrainer, defoamer and water to obtain a special admixture for self-compacting riprap concrete in reservoirs. In step S1, the mass ratio of N-vinylformamide, itaconic acid, and octadecyl methacrylate is (2.5-4.5):(1-3):(0.5-2). The initiator is selected from at least one of azobisisobutyronitrile, ammonium persulfate, or potassium persulfate, and the amount of initiator added is 0.3-0.8% of the total mass of the three reactive monomers. In step S2, based on the total mass of the special additives, the mass percentage of each compound component is as follows: terpolymer 40-60%, slump retainer 15-25%, shrinkage reducer 2.0-5.0%, air-entraining agent 0.3-1.0%, defoamer 0.05-0.15%, and the balance is water.

2. The preparation method according to claim 1, characterized in that, Step S1 specifically includes the following steps: Octadecyl methacrylate and emulsifier were added to deionized water for pre-emulsification to obtain a pre-emulsion. Itaconic acid and N-vinylformamide were added to the pre-emulsion to adjust the pH of the system. The reaction system was heated, an initiator was added, and the reaction was stirred for 2-6 hours. After the reaction was completed, the mixture was filtered and purified to obtain a terpolymer.

3. The preparation method according to claim 2, characterized in that, The pre-emulsification process is shear emulsification, with a temperature of 30-40℃ and a shearing speed of 300-6000 rpm.

4. The preparation method according to claim 2, characterized in that, Adjust the pH of the system to 4.0-5.0, the target temperature for heating is 65-75℃, and the stirring speed is 100-200 rpm.

5. The preparation method according to claim 1, characterized in that, In step S2, the slump retainer is selected from polycarboxylic acid slump retainers, which are obtained by copolymerization of allyl polyoxyethylene ether and unsaturated carboxylic acid monomers, and the shrinkage reducing agent is selected from at least one of polyoxyethylene alkyl ether, polyoxyethylene aryl ether, or polyethylene glycol.

6. The preparation method according to claim 1, characterized in that, In step S2, the air-entraining agent is selected from at least one of rosin thermal polymer, sodium dodecylbenzene sulfonate, or sodium α-olefin sulfonate, and the defoamer is selected from polyether modified silicone defoamer or mineral oil-based defoamer.

7. A special admixture for self-compacting riprap concrete in reservoirs, prepared by the method described in any one of claims 1-6, characterized in that, The pH value is 6.0-7.5.

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