High-slump-retaining polycarboxylic water reducing agent for low-carbon high-bleeding-resistant concrete and preparation method thereof

Abstract

This invention relates to the field of concrete technology, specifically to a high-slump-retention polycarboxylate superplasticizer for low-carbon, high-permeability concrete and its preparation method. This superplasticizer is produced through aqueous free-radical copolymerization, introducing 2-hydroxyethyl methacrylate phosphate in stages, and using sodium salts of di[2-(methacryloyloxy)ethyl]phosphate and triethanolamine salt precursors in stepwise addition. Combined with a specific redox initiation system, the distribution and adsorption kinetics of the phosphate groups on the polymer chain are optimized. The resulting product significantly delays slump loss and improves concrete workability in low-carbon cementitious systems, while simultaneously enhancing water reduction rate and impermeability, making it suitable for concrete projects with high durability requirements.

Description

Technical Field

[0001] This invention relates to the field of concrete technology, and in particular to a high-slump-retention polycarboxylate superplasticizer for low-carbon, high-permeability concrete and its preparation method. Background Technology

[0002] As concrete technology moves towards low-carbon development, the application of high-mineral admixtures (such as slag powder, fly ash, and silica fume) is becoming increasingly widespread to reduce cement usage and carbon emissions. However, this low-carbon cementitious system typically employs a low water-cement ratio design, leading to a significant increase in the ionic strength of the pore solution in fresh concrete and aggravated fluctuations in calcium ion concentration, placing higher demands on the adsorption and dispersion behavior of water-reducing agents. While polycarboxylate superplasticizers, as high-performance admixtures, exhibit excellent slump retention in ordinary concrete, their molecular structure is easily affected by ionic strength under the aforementioned harsh conditions. The adsorption balance between carboxylic acid groups and phosphate ester groups is disrupted, leading to the problem of early over-adsorption followed by later dispersion attenuation.

[0003] Specifically, high-mineral admixtures exhibit high surface activity, competing with water-reducing agent molecules for adsorption, leading to unstable anchoring of the water-reducing agent on the particle surface. Especially under long-distance transportation or high-temperature construction conditions, slump loss accelerates, manifesting as a sharp drop in slump within 30 to 120 minutes after initial flowability meets standards. To compensate for this loss, additional water is often added or the amount of cementitious materials is increased on-site. This not only contradicts the low-carbon principle but also increases water consumption, raises the water-cement ratio, weakens concrete density, and consequently reduces impermeability and durability. Existing technologies attempt to improve slump retention by adjusting the molecular weight of the water-reducing agent or introducing functional monomers, but these often focus on optimizing a single parameter, such as increasing phosphate ester content to enhance anchoring, neglecting the compatibility between adsorption kinetics and the solution ionic environment.

[0004] Furthermore, if phosphate groups are added all at once or introduced in a concentrated manner, the water-reducing agent is prone to excessively rapid adsorption in the early stage and lacks sustained dispersion ability in the later stage. Improper introduction of bifunctional monomers such as di[2-(methacryloyloxy)ethyl]phosphate may lead to excessive crosslinking or uneven dispersion. Existing preparation methods mostly employ homogeneous feeding or simple time-sequence control, making it difficult to optimize the distribution of phosphate groups in the polymer chain segments and resist the synergistic impact of calcium ion fluctuations and competitive adsorption. In addition, the selection of counterionic forms (such as sodium salts or amine salts) does not consider temporal differences. While sodium salts have strong anchoring, they easily induce retardation, while amine salts have mild dispersion but insufficient early-stage effect. The lack of synergy between the two makes it difficult to achieve both slump retention and impermeability in low-carbon systems.

[0005] These issues collectively hinder the widespread application of low-carbon, high-permeability concrete, especially in applications requiring high durability such as tunnels and bridge deck paving, where slump loss and insufficient permeability resistance have become technical bottlenecks. Therefore, there is an urgent need for a water-reducing agent design that can achieve adsorption kinetic balance through molecular structure regulation, ensuring dispersion stability and long-term durability under high compaction systems. Summary of the Invention

[0006] In view of this, the purpose of this invention is to propose a high slump retention polycarboxylate superplasticizer for low-carbon, high-permeability concrete and its preparation method, so as to solve the problem that existing high slump retention polycarboxylate superplasticizers in low-carbon cementitious systems (high mineral admixtures, low water-cement ratio) suffer from rapid slump loss due to high solution ionic strength, fluctuations in calcium ions, and competition for adsorption on the surface of mineral admixtures, making it difficult to simultaneously maintain fluidity and meet permeability requirements.

[0007] To achieve the above objectives, the present invention provides a method for preparing a high-slump-retention polycarboxylate superplasticizer for low-carbon, high-permeability concrete, comprising the following steps:

[0008] (1) Di[2-(methacryloyloxy)ethyl] phosphate was prepared into a sodium salt precursor solution and a triethanolamine salt precursor solution, respectively. The sodium salt precursor solution was obtained by neutralizing di[2-(methacryloyloxy)ethyl] phosphate in the presence of sodium hydroxide aqueous solution and mixing it with mercaptoacetic acid. The triethanolamine salt precursor solution was obtained by neutralizing di[2-(methacryloyloxy)ethyl] phosphate in the presence of triethanolamine.

[0009] (2) Preparation of the first monomer solution A: After hydrolyzing maleic anhydride in deionized water, add acrylic acid, 2-hydroxyethyl methacrylate phosphate and mercaptoacetic acid and mix well; Preparation of the second monomer solution B: Mix acrylic acid, 2-hydroxyethyl methacrylate phosphate, mercaptoacetic acid and the triethanolamine salt precursor solution obtained in step (1) well.

[0010] (3) Add deionized water and isopentenyl alcohol polyoxyethylene ether to the reaction vessel and stir at 45°C under nitrogen protection to form a homogeneous solution;

[0011] (4) At 48-55℃, the first monomer solution A is added dropwise to the reactor, and ammonium persulfate solution and L(+)-ascorbic acid solution are added simultaneously as redox initiation system to initiate aqueous free radical copolymerization;

[0012] (5) The sodium salt precursor solution obtained in step (1) is added to the reactor in one go within 1 minute through the bottom feeder below the stirrer, and the redox initiation system is added simultaneously to continue the reaction;

[0013] (6) The second monomer solution B is added dropwise to the reaction vessel, and the redox initiation system is added dropwise simultaneously to continue the reaction, so as to obtain the polymer reaction solution;

[0014] (7) After cooling the polymer reaction solution, adjust the pH to 6.5-7.2 with sodium hydroxide aqueous solution, add water to adjust the solid content to 42%-48%, filter, and obtain high slump-retaining polycarboxylate superplasticizer for low carbon high impermeability concrete.

[0015] Preferably, in step (1), the amount of di[2-(methacryloyloxy)ethyl] phosphate in the sodium salt precursor solution is 2-3.5g, the amount of 30% sodium hydroxide aqueous solution is 0.76-1.33g, and the amount of mercaptoacetic acid is 0.6-1.0g.

[0016] Preferably, in step (1), the amount of di[2-(methacryloyloxy)ethyl]phosphate in the triethanolamine salt precursor solution is 1-2g, and the amount of triethanolamine is 0.43-0.86g.

[0017] Preferably, in step (2), the amount of 2-hydroxyethyl methacrylate phosphate in the first monomer solution A is 3-8g and the amount of mercaptoacetic acid is 0.8-1.2g, and the amount of 2-hydroxyethyl methacrylate phosphate in the second monomer solution B is 18-32g, the amount of acrylic acid is 80g, the amount of mercaptoacetic acid is 0.6-0.9g, and the amount of triethanolamine salt precursor solution is 1.43-2.86g.

[0018] Preferably, the ammonium persulfate solution and the L(+)-ascorbic acid solution each comprise: dissolving 1g of ammonium persulfate in 15g of deionized water to obtain ammonium persulfate solution I1; dissolving 0.3g of L(+)-ascorbic acid in 15g of deionized water to obtain L(+)-ascorbic acid solution R1; dissolving 0.5g of ammonium persulfate in 5g of deionized water to obtain ammonium persulfate solution I2; dissolving 0.1g of L(+)-ascorbic acid in 5g of deionized water to obtain L(+)-ascorbic acid solution R2; dissolving 0.5g of ammonium persulfate in 10g of deionized water to obtain ammonium persulfate solution I3; and dissolving 0.2g of L(+)-ascorbic acid in 10g of deionized water to obtain L(+)-ascorbic acid solution R3.

[0019] Preferably, in step (3), the amount of isopentenyl alcohol polyoxyethylene ether used is 240g.

[0020] Preferably, in step (4), the first monomer solution A is placed in a dropping funnel and its discharge pipe is inserted 20 mm below the liquid surface and 30 mm above the stirring paddle. The first monomer solution A is added dropwise within 15-30 min, and at the same time, ammonium persulfate solution I1 and L(+)-ascorbic acid solution R1 are added dropwise within 30-60 min. During the dropwise addition, the temperature of the reactor is controlled at 48-55℃. After the dropwise addition is completed, the reaction is kept warm for 30 min.

[0021] Preferably, in step (5), the stirring speed of the reactor is increased to 350 rpm and the end of the feed pipe at the bottom of the reactor is fixed 20 mm below the stirring paddle. The sodium salt precursor solution is added in one go within 1 min. Then, ammonium persulfate solution I2 and L(+)-ascorbic acid solution R2 are added dropwise simultaneously within 10-20 min, and the reaction continues at 48-55℃ for 15-30 min.

[0022] Preferably, in step (6), the stirring speed of the reactor is reduced to 250 rpm and the end of the top dropper is fixed 10 mm below the liquid surface. The second monomer solution B is added at a uniform rate within 60-100 min, and the ammonium persulfate solution I3 and L(+)-ascorbic acid solution R3 are added simultaneously within 70-110 min. The reactor temperature is maintained at 48-55℃ during the addition. After the addition is completed, the reaction is kept warm for 50-70 min.

[0023] Furthermore, the present invention also provides a high slump-retention polycarboxylate superplasticizer for low-carbon, high-permeability concrete, which is obtained by the above-mentioned preparation method of the high slump-retention polycarboxylate superplasticizer for low-carbon, high-permeability concrete.

[0024] The beneficial effects of this invention are:

[0025] This invention introduces 2-hydroxyethyl methacrylate phosphate into the polycarboxylic acid backbone in segments via aqueous solution free radical copolymerization, resulting in a phosphate group distribution with a sparser initial phase and a denser later phase within the polymer chain. This segmented feeding method optimizes the adsorption and release kinetics of the phosphate group. In a high-ionic-strength porous solution environment, the water-reducing agent molecules avoid excessive adsorption in the early stages, and in the later stages, the enrichment of phosphate groups provides a continuous anchoring effect, effectively delaying the slump decay over time. Simultaneously, the electrostatic repulsion of the acrylate carboxylic acid groups synergistically with the complexation of the phosphate group enhances the uniformity of particle dispersion, reduces the risk of bleeding, and lays the foundation for dense concrete formation.

[0026] During polymerization, the sodium di[2-(methacryloyloxy)ethyl]phosphate precursor is instantaneously added near the agitator at the bottom of the reactor, forming controllable micro-crosslinking points in the presence of the chain transfer agent mercaptoacetic acid. This localized high-concentration reaction promotes the formation of a micro-crosslinking network, enhancing the water-reducing agent's resistance to desorption on the cement particle surface and resisting dispersion attenuation caused by fluctuations in shear and ionic strength. The micro-crosslinking structure also improves the stability of the adsorption layer, inhibits flocculation caused by competitive adsorption of mineral admixtures, and ensures consistent flowability of concrete during pumping or transportation, thus improving construction reliability.

[0027] Furthermore, bis[2-(methacryloyloxy)ethyl]phosphate is produced in two counterionic forms: sodium salt and triethanolamine salt. The complementary functions are achieved through the timing and spatial differences in the feeding sequence—the sodium salt is added instantaneously first, followed by the triethanolamine salt dropwise. The sodium salt dissociates rapidly, forming a strong complex with calcium ions in the early stages to resist ion impact; the triethanolamine salt exhibits strong solvation and slow diffusion, providing mild and lasting steric hindrance in the later stages. The synergistic effect of both forms avoids the coagulation or retarding problems caused by strong anchoring alone, achieving a balance between the water-reducing agent's dispersibility, slump retention, and workability.

[0028] Overall, this water-reducing agent significantly improves the impermeability of concrete through multifunctional group synergy and process regulation. The optimized distribution of phosphate groups and the micro-crosslinked structure reduce porosity and enhance the density of the interfacial transition zone, enabling the concrete to exhibit high impermeability and low chloride ion flux at 28 days of age. This not only meets the strength development requirements of low-carbon concrete but also extends structural durability, making it suitable for high impermeability projects in harsh environments. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0030] Figure 1 The infrared spectrum of the polycarboxylate superplasticizer provided in Example 1 of this invention;

[0031] Figure 2 Thermogravimetric curves of the polycarboxylate superplasticizers provided in Example 1 and Comparative Examples 1, 2, 7, and 8 of this invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0033] Raw material source and specifications:

[0034] The isopentenyl alcohol polyoxyethylene ether used in the specific implementation method is the slump-retaining monomer TPEG2400 produced by Jiahe Chemical (Shanghai) Co., Ltd., with a relative molecular weight of 2400, moisture content ≤1%, hydroxyl value of 21-26 mgKOH / g, and double bond retention rate ≥90%.

[0035] Example 1:

[0036] Step S1: Take two beakers, A and B, and add 10g of deionized water and 5g of deionized water respectively. Stir in a 30℃ water bath. Add 2500mg of di[2-(methacryloyloxy)ethyl]phosphate to beaker A and stir until homogeneous emulsification. Then, add 950mg of 30% sodium hydroxide aqueous solution and 0.8g of mercaptoacetic acid and stir at 25℃ for 10min to obtain a sodium salt precursor solution of di[2-(methacryloyloxy)ethyl]phosphate. Add 1500mg of di[2-(methacryloyloxy)ethyl]phosphate to beaker B (same as above) and stir until homogeneous emulsification. Then, add 650mg of triethanolamine to obtain a triethanolamine salt precursor solution of di[2-(methacryloyloxy)ethyl]phosphate.

[0037] Step S2: Add 20g of deionized water to a beaker and heat to 50℃. While stirring at 300rpm, add 8g of maleic anhydride and maintain the temperature for 20min until complete hydrolysis and dissolution. Then cool to 30℃ and add 40g of acrylic acid and 5g of 2-hydroxyethyl methacrylate phosphate, followed by 1g of mercaptoacetic acid. Mix well to obtain the first monomer solution A. Add 30g of deionized water to another beaker. While stirring at 300rpm, add 80g of acrylic acid and 23g of 2-hydroxyethyl methacrylate phosphate. Mix well and add 0.7g of mercaptoacetic acid. Then add the di[2-(methacryloyloxy)ethyl]phosphate triethanolamine salt precursor solution obtained in Step S1 and stir for 15min to obtain the second monomer solution B. Take two other beakers and add 15g of deionized water and 1g of ammonium persulfate to dissolve, obtaining ammonium persulfate solution I1. Also, add 15g of deionized water and 0.3g of... L(+)-ascorbic acid was dissolved to obtain L(+)-ascorbic acid solution R1; then, 5g of deionized water and 0.5g of ammonium persulfate were added to two beakers respectively to obtain ammonium persulfate solution I2, and 5g of deionized water and 0.1g of L(+)-ascorbic acid were added to obtain L(+)-ascorbic acid solution R2; then, 10g of deionized water and 0.5g of ammonium persulfate were added to two beakers respectively to obtain ammonium persulfate solution I3, and 10g of deionized water and 0.2g of L(+)-ascorbic acid were added to obtain L(+)-ascorbic acid solution R3;

[0038] Step S3: Select a four-necked glass reactor (equipped with a mechanical stirrer, condenser, thermometer, nitrogen inlet pipe, and two drop pipes), add 150g of deionized water to the reactor and heat to 45℃ at 200rpm, then add 240g of isopentenyl alcohol polyoxyethylene ether and continue stirring for 30min until a homogeneous and transparent solution is formed; maintain stirring at 45℃ and purge with nitrogen for 30min, and maintain a slight positive pressure nitrogen protection at the top of the reaction system;

[0039] Step S4: Place the first monomer solution A obtained in step S2 into dropping funnel 1, place the ammonium persulfate solution I1 obtained in step S2 into dropping funnel 2, and place the L(+)-ascorbic acid solution R1 obtained in step S2 into dropping funnel 3; maintain the reaction vessel temperature of step S3 at 45℃ and stir at 200 rpm, insert the discharge tube of dropping funnel 1 20 mm below the liquid surface and 30 mm above the stirring paddle, drop the first monomer solution A within 20 min, and simultaneously drop the ammonium persulfate solution I1 and L(+)-ascorbic acid solution R1 obtained in step S2 within 40 min, control the vessel temperature at 50℃ during the dropping process, and continue to keep the reaction at the temperature for 30 min after the dropping is completed;

[0040] Step S5: Increase the stirring speed of the reactor after the reaction in step S4 to 350 rpm, and fix the end of the bottom feed pipe 20 mm below the stirring paddle. Add the sodium di[2-(methacryloyloxy)ethyl]phosphate precursor solution obtained in step S1 in one go within 1 min. Then, immediately add the ammonium peroxide disulfate solution I2 and L(+)-ascorbic acid solution R2 obtained in step S2 dropwise within 15 min, and continue the reaction at 50℃ for 20 min.

[0041] Step S6: Reduce the stirring speed of the reactor after the reaction in step S5 to 250 rpm, and fix the end of the top dropper tube 10 mm below the liquid surface. Add the second monomer solution B obtained in step S2 at a uniform rate over 80 min. At the same time, add the ammonium persulfate solution I3 and L(+)-ascorbic acid solution R3 obtained in step S2 simultaneously over 90 min. Maintain the reactor temperature at 50°C during the addition. After the addition is completed, continue to keep the reactor at the temperature for 60 min.

[0042] Step S7: After the heat preservation in step S6 is completed, the reactor is cooled to 35°C and nitrogen flow is stopped. Under stirring at 200 rpm, a 30% sodium hydroxide aqueous solution is added within 30 minutes to adjust the pH to 6.8. Then, deionized water is added to adjust the solid content to 45%. After stirring for another 20 minutes, the mixture is filtered through a 100-mesh filter cloth to obtain a high slump-retaining polycarboxylate superplasticizer for low-carbon, high-permeability concrete.

[0043] Example 2:

[0044] Compared with Example 1, this example optimizes the proportion of phosphorus-containing monomers in stages, the amount of two counterion forms of phosphorus-containing bifunctional monomers, the dropping time, and the endpoint pH and solid content, as follows, while the other conditions are the same as in Example 1.

[0045] In step S1: the amount of di[2-(methacryloyloxy)ethyl]phosphate in beaker A is adjusted to 3000 mg, the amount of 30% sodium hydroxide aqueous solution is adjusted to 1140 mg, and the amount of mercaptoacetic acid remains at 0.8 g; the amount of di[2-(methacryloyloxy)ethyl]phosphate in beaker B is adjusted to 1000 mg, and the amount of triethanolamine is adjusted to 430 mg.

[0046] In step S2: the amount of 2-hydroxyethyl methacrylate phosphate in the first monomer solution A is adjusted to 4g; the amount of 2-hydroxyethyl methacrylate phosphate in the second monomer solution B is adjusted to 30g.

[0047] In step S4: the dropping time of the first monomer solution A is adjusted to 18 min, and the synchronous dropping time of ammonium persulfate solution I1 and L(+)-ascorbic acid solution R1 is adjusted to 36 min.

[0048] In step S6: the uniform dripping time of the second monomer solution B is adjusted to 90 min, and the synchronous dripping time of ammonium persulfate solution I3 and L(+)-ascorbic acid solution R3 is adjusted to 100 min.

[0049] In step S7: Adjust the pH to 6.6 and the solid content to 44%.

[0050] Example 3:

[0051] Compared with Example 1, this example optimizes the proportion of phosphorus-containing monomers in stages, the amount of two counterionic forms of phosphorus-containing bifunctional monomers, the amount of mercaptoacetic acid, the polymerization temperature, the dropping time, and the endpoint pH and solid content, as follows, while the other conditions are the same as in Example 1.

[0052] In step S1: the amount of di[2-(methacryloyloxy)ethyl]phosphate in beaker A is adjusted to 2200 mg, the amount of 30% sodium hydroxide aqueous solution is adjusted to 836 mg, and the amount of mercaptoacetic acid is adjusted to 0.7 g; the amount of di[2-(methacryloyloxy)ethyl]phosphate in beaker B is adjusted to 1800 mg, and the amount of triethanolamine is adjusted to 780 mg.

[0053] In step S2: the amount of 2-hydroxyethyl methacrylate phosphate in the first monomer solution A is adjusted to 6g, and the amount of mercaptoacetic acid is adjusted to 0.9g; the amount of 2-hydroxyethyl methacrylate phosphate in the second monomer solution B is adjusted to 22g, and the amount of mercaptoacetic acid is adjusted to 0.6g.

[0054] In step S4: the dropping time of the first monomer solution A is adjusted to 25 min, the synchronous dropping time of ammonium persulfate solution I1 and L(+)-ascorbic acid solution R1 is adjusted to 50 min, and the temperature of the kettle is controlled at 48℃ during the dropping process.

[0055] In step S5: continue the reaction at 48°C for 20 minutes.

[0056] In step S6: the uniform dripping time of the second monomer solution B is adjusted to 70 min, and the synchronous dripping time of ammonium persulfate solution I3 and L(+)-ascorbic acid solution R3 is adjusted to 80 min. During the dripping, the kettle temperature is maintained at 48℃.

[0057] In step S7: Adjust the pH to 7.0 and the solid content to 46%.

[0058] Example 4:

[0059] Compared with Example 1, this example optimizes the proportion of phosphorus-containing monomers in stages, the amount of two counterionic forms of phosphorus-containing bifunctional monomers, the amount of mercaptoacetic acid, the polymerization temperature, the dropping time, and the endpoint pH and solid content, as follows, while the other conditions are the same as in Example 1.

[0060] In step S1: the amount of di[2-(methacryloyloxy)ethyl]phosphate in beaker A is adjusted to 2000 mg, the amount of 30% sodium hydroxide aqueous solution is adjusted to 760 mg, and the amount of mercaptoacetic acid is adjusted to 1.0 g; the amount of di[2-(methacryloyloxy)ethyl]phosphate in beaker B is adjusted to 2000 mg, and the amount of triethanolamine is adjusted to 860 mg.

[0061] In step S2: the amount of 2-hydroxyethyl methacrylate phosphate in the first monomer solution A is adjusted to 3g, and the amount of mercaptoacetic acid is adjusted to 1.1g; the amount of 2-hydroxyethyl methacrylate phosphate in the second monomer solution B is adjusted to 18g, and the amount of mercaptoacetic acid is adjusted to 0.8g.

[0062] In step S4: the dropping time of the first monomer solution A is adjusted to 15 min, the synchronous dropping time of ammonium persulfate solution I1 and L(+)-ascorbic acid solution R1 is adjusted to 30 min, and the temperature of the kettle is controlled at 52℃ during the dropping process.

[0063] In step S5: immediately afterward, ammonium persulfate solution I2 and L(+)-ascorbic acid solution R2 are added dropwise simultaneously within 12 minutes, and the reaction continues at 52°C for 15 minutes.

[0064] In step S6: the uniform drop time of the second monomer solution B is adjusted to 60 min, the synchronous drop time of ammonium persulfate solution I3 and L(+)-ascorbic acid solution R3 is adjusted to 70 min, the reactor temperature is maintained at 52℃ during the drop, and the reaction is continued for 50 min after the drop is completed.

[0065] In step S7: Adjust the pH to 6.5 and the solid content to 42%.

[0066] Example 5:

[0067] Compared with Example 1, this example optimizes the proportion of phosphorus-containing monomers in stages, the amount of two counterion forms of phosphorus-containing bifunctional monomers, the amount of mercaptoacetic acid, the dropping time, and the endpoint pH and solid content, as follows, while the other conditions are the same as in Example 1.

[0068] In step S1: the amount of di[2-(methacryloyloxy)ethyl]phosphate in beaker A is adjusted to 3500 mg, the amount of 30% sodium hydroxide aqueous solution is adjusted to 1330 mg, and the amount of mercaptoacetic acid is adjusted to 1.0 g; the amount of di[2-(methacryloyloxy)ethyl]phosphate in beaker B is adjusted to 1200 mg, and the amount of triethanolamine is adjusted to 520 mg.

[0069] In step S2: the amount of 2-hydroxyethyl methacrylate phosphate in the first monomer solution A is adjusted to 7g, and the amount of mercaptoacetic acid is adjusted to 1.2g; the amount of 2-hydroxyethyl methacrylate phosphate in the second monomer solution B is adjusted to 28g, and the amount of mercaptoacetic acid is adjusted to 0.9g.

[0070] In step S4: the dropping time of the first monomer solution A is adjusted to 22 min, and the synchronous dropping time of ammonium persulfate solution I1 and L(+)-ascorbic acid solution R1 is adjusted to 44 min.

[0071] In step S5: immediately afterward, ammonium persulfate solution I2 and L(+)-ascorbic acid solution R2 are added dropwise simultaneously within 20 min, and the reaction continues at 50℃ for 30 min.

[0072] In step S6: the uniform drop time of the second monomer solution B is adjusted to 100 min, and the synchronous drop time of ammonium persulfate solution I3 and L(+)-ascorbic acid solution R3 is adjusted to 110 min. After the drop is completed, the reaction is kept warm for another 70 min.

[0073] In step S7: Adjust the pH to 7.2 and the solid content to 48%.

[0074] Example 6:

[0075] Compared with Example 1, this example optimizes the proportion of phosphorus-containing monomers in stages, the amount of two counterionic forms of phosphorus-containing bifunctional monomers, the amount of mercaptoacetic acid, the polymerization temperature, the dropping time, and the endpoint pH and solid content, as follows, while the other conditions are the same as in Example 1.

[0076] In step S1: the amount of di[2-(methacryloyloxy)ethyl]phosphate in beaker A is adjusted to 2800 mg, the amount of 30% sodium hydroxide aqueous solution is adjusted to 1064 mg, and the amount of mercaptoacetic acid is adjusted to 0.6 g; the amount of di[2-(methacryloyloxy)ethyl]phosphate in beaker B is adjusted to 1600 mg, and the amount of triethanolamine is adjusted to 693 mg.

[0077] In step S2: the amount of 2-hydroxyethyl methacrylate phosphate in the first monomer solution A is adjusted to 8g, and the amount of mercaptoacetic acid is adjusted to 0.8g; the amount of 2-hydroxyethyl methacrylate phosphate in the second monomer solution B is adjusted to 32g, and the amount of mercaptoacetic acid is adjusted to 0.6g.

[0078] In step S4: the dropping time of the first monomer solution A is adjusted to 30 min, the synchronous dropping time of ammonium persulfate solution I1 and L(+)-ascorbic acid solution R1 is adjusted to 60 min, and the temperature of the kettle is controlled at 55℃ during the dropping process.

[0079] In step S5: immediately afterward, ammonium persulfate solution I2 and L(+)-ascorbic acid solution R2 are added dropwise simultaneously within 10 min, and the reaction continues at 55℃ for 25 min.

[0080] In step S6: Maintain the vessel temperature at 55°C during the dripping process.

[0081] In step S7: Adjust the pH to 6.8 and the solid content to 45%.

[0082] Comparative Example 1:

[0083] The difference from Example 1 is that in step S2, the amount of 2-hydroxyethyl methacrylate phosphate added to the first monomer solution A is adjusted from 5g to 28g, and 2-hydroxyethyl methacrylate phosphate is not added to the second monomer solution B; the other conditions are the same as in Example 1.

[0084] Comparative Example 2:

[0085] The difference from Example 1 is that in step S2, 2-hydroxyethyl methacrylate phosphate is not added to the first monomer solution A, and the amount of 2-hydroxyethyl methacrylate phosphate added to the second monomer solution B is adjusted from 23g to 28g; the other conditions are the same as in Example 1.

[0086] Comparative Example 3:

[0087] The difference from Example 1 is that in step S5, the sodium di[2-(methacryloyloxy)ethyl]phosphate precursor solution is added within 1 minute through the top dropper, and the end of the top dropper is fixed 10 mm below the liquid surface, instead of being added through the bottom feed pipe fixed 20 mm below the stirrer; the other conditions are the same as in Example 1.

[0088] Comparative Example 4:

[0089] The difference from Example 1 is that in step S5, the sodium di[2-(methacryloyloxy)ethyl]phosphate precursor solution, which was originally added all at once within 1 minute, is now added at a uniform rate within 30 minutes. After the addition of the precursor solution, ammonium persulfate solution I2 and L(+)-ascorbic acid solution R2 are added simultaneously within 15 minutes. The other conditions are the same as in Example 1.

[0090] Comparative Example 5:

[0091] The difference from Example 1 is that in step S1, the triethanolamine added to beaker B is replaced with 570 mg of 30% sodium hydroxide aqueous solution to obtain a sodium bis[2-(methacryloyloxy)ethyl]phosphate precursor solution; the other conditions are the same as in Example 1.

[0092] Comparative Example 6:

[0093] The difference from Example 1 is that in step S1, the 30% sodium hydroxide aqueous solution added to beaker A is replaced with 1083 mg of triethanolamine instead of 950 mg to obtain a di[2-(methacryloyloxy)ethyl]phosphate triethanolamine salt precursor solution; the other conditions are the same as in Example 1.

[0094] Comparative Example 7:

[0095] The difference from Example 1 is that in step S1, the amount of mercaptoacetic acid in beaker A is adjusted from 0.8g to 0g; the other conditions are the same as in Example 1.

[0096] Comparative Example 8:

[0097] The difference from Example 1 is that the sodium bis[2-(methacryloyloxy)ethyl]phosphate precursor solution obtained in step S1 is not added in step S5; the other conditions are the same as in Example 1.

[0098] Performance testing:

[0099] Sample preparation: The water-reducing agent products obtained in Examples 1-6 and Comparative Examples 1-8 were taken, and their solid content was adjusted to prepare water-reducing agent solutions with a solid content of 45% for use in mixture testing. The concrete used was a low-carbon cementitious system: 225 kg / m³ of general-purpose Portland cement. 3 Granulated blast furnace slag powder 135kg / m 3 67.5 kg / m³ of fly ash 3 Silica fume 22.5kg / m 3 Fine aggregate 720kg / m³ 3 Coarse aggregate 1050kg / m³ 3 Total water consumption: 135 kg / m³ 3 The solid content of the water-reducing agent is fixed at 0.2% of the total cementitious material. When the solid content of the water-reducing agent is 45%, the calculated dosage of the water-reducing agent solution is 2.0 kg / m³. 3 The water content in the water-reducing agent solution is 1.1 kg / m³. 3 Including the mixing water, the amount of deionized water added is 133.9 kg / m³. Each batch of concrete has a mixing volume of 30 L. A forced mixer is used. First, the cementitious materials and aggregates are dry-mixed for 30 seconds. Then, all the mixing water (including the water-reducing agent solution) is added and wet-mixed for 120 seconds. After standing for 60 seconds, it is remixed for 60 seconds to obtain the concrete mixture. The specimens used for molding are compacted on a vibrating table for 20 seconds and smoothed. They are then placed in a standard curing room at 20℃ and 95% relative humidity for 24 hours before demolding. Standard curing continues until the specified age before testing.

[0100] Infrared spectroscopy characterization: The water-reducing agent solution from Example 1 was sampled and vacuum-dried to constant weight at 40°C, then ground and passed through a 200-mesh sieve. A potassium bromide tableting method was used to prepare the sample; 1.0 mg of the dried sample was weighed and mixed with 100.0 mg of spectroscopically pure potassium bromide, then tableted. Fourier transform infrared spectroscopy was used in the wavenumber range of 4000 cm⁻¹. -1 -400cm -1 Scan, resolution 4cm -1 The result is as follows Figure 1 As shown.

[0101] Thermogravimetric analysis (TGA): Performed according to GB / T 27761-2011 "Test Method for Weight Loss and Residual Amount of Thermogravimetric Analyzer". Water-reducing agent samples from Example 1 and Comparative Examples 1, 2, 7, and 8 were sampled, vacuum dried to constant weight at 40℃, and 8.0 mg were weighed and placed in an alumina crucible. Nitrogen was used as the protective gas at a flow rate of 60 mL / min. The heating program started at 50℃, increased to 800℃ at a rate of 10℃ / min, and held for 10 min. The thermogravimetric curves were recorded, and the results are as follows: Figure 2 As shown.

[0102] Slump and slump loss over time: The test was conducted according to GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". The initial slump was measured immediately after mixing, and the mixture was placed in a covered container and left to stand at the same temperature of 25℃. The mixture was taken out at 30 min, 60 min and 120 min respectively, and remixed at low speed for 30 s. The slump was then measured according to the standard method, and the slump loss over time ΔS120=S0-S120 was calculated.

[0103] Water reduction rate and bleeding rate: The performance evaluation of water-reducing agents was conducted according to the methodology in GB 8076-2008 "Concrete Admixtures," using the slump test specified in GB / T 50080-2016 as the control index. Using a reference concrete without water-reducing agent, the initial slump of the reference concrete was adjusted to 220 mm, and the reference water volume W0 was recorded. With the water-reducing agent solid content at 0.20% of the cementitious material mass, the initial slump of the concrete with the water-reducing agent was also adjusted to 220 mm, and the water volume W1 was recorded. The water reduction rate R was calculated as R = (W0 - W1) / W0 × 100%. The bleeding rate was calculated according to GB / T 50080-2016. The mixture was placed in a bleeding container and allowed to stand for 120 minutes. Bleeding water was collected at specified time points, and the bleeding rate was calculated.

[0104] Compressive strength: Tested according to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". Prepare 150mm×150mm×150mm cube specimens, 3 specimens per group; after demolding, cure under standard conditions for 3d, 7d and 28d, and use a pressure testing machine to test the compressive strength at a loading rate of 0.5MPa / s; record the compressive strength / MPa at each age and take the arithmetic mean of the 3 specimens.

[0105] Impermeability test: The test was conducted according to GB / T 50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Concrete". Impermeable truncated cone specimens were prepared with an upper diameter of 175 mm, a lower diameter of 185 mm, and a height of 150 mm. There were 6 specimens in each group. After standard curing for 28 days, the impermeability test was carried out. The water pressure was increased by 0.1 MPa every 8 hours until seepage occurred. The water pressure value at the time of seepage was recorded and the impermeability pressure / MPa was calculated according to the standard method.

[0106] Chloride ion penetration resistance: The electrical flux method was used according to GB / T 50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Concrete". After preparation and curing for 28 days, a 100mm diameter, 50mm thick specimen disc was cut from a concrete cylinder. The specimen was vacuum-saturated with water according to standard methods and then installed in the electrical flux testing device. A 60V DC voltage was applied for 6 hours, and the current change over time was recorded. The total electrical flux / C was obtained by integration according to standard methods. The test results are shown in Table 1.

[0107] Table 1 Performance Test Results

[0108]

[0109] Data Analysis:

[0110] As can be seen from the data in Table 1, the polycarboxylate superplasticizer prepared by this invention exhibits high initial fluidity and a slow slump decay over time under the same dosage conditions, while maintaining a low bleeding rate. With increasing curing age, the compressive strength increases steadily, the impermeability pressure remains high, and the chloride ion flux resistance remains low. This may be because: the segmented introduction of 2-hydroxyethyl methacrylate phosphate makes the adsorption and release of phosphate groups more balanced, which is beneficial for both early dispersion and subsequent continuous lubrication; the carboxylic acid groups provided by acrylic acid enhance electrostatic repulsion and promote uniform particle dispersion; the introduction of sodium bis[2-(methacryloyloxy)ethyl]phosphate and triethanolamine bis[2-(methacryloyloxy)ethyl]phosphate precursors at different stages helps to form more uniform micro-crosslinking points and ionic environments, thus balancing slump retention and compact molding, ultimately leading to a simultaneous improvement in durability indicators.

[0111] As can be seen from the data in Table 1 for Example 1 and Comparative Examples 1 and 2, when 2-hydroxyethyl methacrylate phosphate is added only in the first or second stage, it is difficult to simultaneously maintain the fluidity and stability of the mixture. This manifests as accelerated slump decay or insufficient initial dispersion, which in turn induces bleeding and structural inhomogeneity. The main reason for this may be that the adsorption of phosphate groups has a characteristic of initial occupancy followed by sustained adsorption: adding too early will lead to rapid consumption of effective groups in the early stage and local over-adsorption, resulting in a lack of sustained lubrication in the later stage; adding too late will result in insufficient early dispersion driving force, leading to particle agglomeration and the formation of initial defects. In contrast, Example 1 uses segmented feeding, which makes the adsorption kinetics more balanced and forms an unpredictable synergistic gain.

[0112] As can be seen from the data in Table 1 for Example 1 and Comparative Examples 3 and 8, when the addition position of the sodium di[2-(methacryloyloxy)ethyl]phosphate precursor is changed or the precursor is omitted, the slump retention, impermeability, and chloride ion resistance all show a simultaneous downward trend. The reason for this is presumably that introducing the precursor rapidly below the agitator facilitates instantaneous dispersion and uniform reaction, enabling the formation of more uniformly distributed micro-crosslinking points and regulating the ionic environment during polymerization. If added near the liquid surface or not added at all, the local concentration gradient increases, easily leading to structural inhomogeneity and reduced utilization of effective groups, resulting in insufficient densification of the pore structure, thus making it difficult to achieve a synergistic improvement in slump retention, impermeability, and chloride ion resistance.

[0113] As can be seen from the data in Example 1 and Comparative Example 4 in Table 1, when the dropping time of the sodium di[2-(methacryloyloxy)ethyl]phosphate precursor was significantly prolonged and the initiator addition interval was shortened, the fluidity decay and durability of the mixture exhibited unfavorable fluctuations. The possible reasons are: prolonged dropping of the precursor kept the system in a longer low-concentration reaction window, resulting in more dispersed but insufficiently strong micro-crosslinking points; simultaneously, early initiator intervention weakened the structural locking effect of the precursor in the critical stage, causing the distribution of polymeric segments and functional groups to deviate from the optimal range, ultimately making it difficult to achieve a stable equilibrium between slump retention and densification. This phenomenon indicates a synergistic relationship between the precursor addition acceleration rate and the initiation sequence.

[0114] As can be seen from the data in Table 1 for Example 1 and Comparative Examples 5 and 6, when the formation modes of the sodium bis[2-(methacryloyloxy)ethyl]phosphate precursor and the triethanolamine bis[2-(methacryloyloxy)ethyl]phosphate precursor are altered, the matching relationship between fluidity, strength development, and durability indices is weakened, and the overall synergy is reduced. It is speculated that this is because different neutralization systems alter the ionic form of the functional groups and the ionic strength of the solution, affecting their adsorption configuration and reactivity on the particle surface; when the ionic form deviates from the combination of initial anchoring followed by regulation, the interfacial interaction is difficult to optimize simultaneously, and the overall performance cannot achieve the synergistic gain presented in Example 1.

[0115] As can be seen from the data in Table 1 for Example 1 and Comparative Example 7, when mercaptoacetic acid was not introduced to regulate polymer chain growth, the initial dispersion and later stability of the mixture were affected, exhibiting lower fluidity and faster decay, further impacting strength and durability. The main reason for this is likely that the absence of mercaptoacetic acid restricts chain transfer, causing the polymer molecular weight distribution to shift towards higher molecular weights, leading to increased solution viscosity, insufficient utilization of steric hindrance, and easy formation of bridging flocculation, thus reducing effective dispersion. Simultaneously, the accessibility of functional groups on the chain segments decreases, making it difficult to form a uniform adsorption layer, ultimately weakening the synergistic effect of multiple functional groups (1+1>2) in Example 1.

[0116] from Figure 1 It can be seen that in the infrared spectrum of the polycarboxylate superplasticizer obtained in Example 1, at 1725 cm⁻¹... -1 The presence of distinct strong absorption peaks on both sides corresponds to the C=O stretching vibrations of the ester and carboxyl groups, indicating the presence of acrylic acid, maleic anhydride, and methacrylic acid. 2 Hydroxyethyl phosphate esters all participated in the polymerization; 1600-1400cm -1 Carboxylate COO appears in the interval - The asymmetric and symmetric stretching peaks indicate that the carboxyl groups in the polymer backbone are well ionized, which is beneficial for the subsequent electrostatic dispersion of cement particles; 1100-1000 cm⁻¹ -1 The strong absorption bands within this range are attributed to the POC stretching vibration, proving the successful grafting of phosphorus-containing functional monomers; simultaneously, at 3400 cm⁻¹ -1 The broad peaks nearby are due to the -OH stretching vibration, indicating the presence of hydroxyl groups and a small amount of adsorbed water in the polymer.

[0117] from Figure 2 It can be seen that, under the same thermogravimetric testing conditions, the overall mass of the polycarboxylate superplasticizer prepared in Example 1 exhibits a three-stage slow weight loss characteristic as the temperature increases: in the low-temperature stage, only a small amount of adsorbed water and residual small molecules volatilize, the main decomposition peak shifts significantly to the later stage and the decomposition process is relatively slow, while in the high-temperature stage, a high degree of carbonization residue is still retained; in contrast, the low-temperature weight loss of Comparative Examples 1, 2, 7, and 8 is generally slightly larger, the main decomposition initiation temperature and the peak temperature of the maximum weight loss rate both shift to the earlier stage to varying degrees, and the high-temperature residual mass is significantly reduced, indicating that its molecular structure has poor thermal stability. Combining the slump loss over time, water reduction rate, bleeding rate, and performance test results such as water pressure resistance and chloride ion flux in Table 1, it can be inferred that Example 1, through the segmented introduction of methacrylic acid... 2 Hydroxyethyl ester phosphate and optimized di[2] The addition of sodium (methacryloyloxy)ethyl]phosphate / triethanolamine salt precursors resulted in a polycarboxylic acid backbone with better thermal stability and a more uniform micro-crosslinked structure.

[0118] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing a high-slump-retention polycarboxylate superplasticizer for low-carbon, high-permeability concrete, characterized in that, (1) Di[2-(methacryloyloxy)ethyl] phosphate was prepared into a sodium salt precursor solution and a triethanolamine salt precursor solution, respectively. The sodium salt precursor solution was obtained by neutralizing di[2-(methacryloyloxy)ethyl] phosphate in the presence of sodium hydroxide aqueous solution and mixing it with mercaptoacetic acid. The triethanolamine salt precursor solution was obtained by neutralizing di[2-(methacryloyloxy)ethyl] phosphate in the presence of triethanolamine. (2) Preparation of the first monomer solution A: After hydrolyzing maleic anhydride in deionized water, add acrylic acid, 2-hydroxyethyl methacrylate phosphate and mercaptoacetic acid and mix well; Preparation of the second monomer solution B: Mix acrylic acid, 2-hydroxyethyl methacrylate phosphate, mercaptoacetic acid and the triethanolamine salt precursor solution obtained in step (1) well. (3) Add deionized water and isopentenyl alcohol polyoxyethylene ether to the reaction vessel and stir at 45°C under nitrogen protection to form a homogeneous solution; (4) At 48-55℃, the first monomer solution A is added dropwise to the reactor, and ammonium persulfate solution and L(+)-ascorbic acid solution are added simultaneously as redox initiation system to initiate aqueous free radical copolymerization; (5) The sodium salt precursor solution obtained in step (1) is added to the reactor in one go within 1 minute through the bottom feeder below the stirrer, and the redox initiation system is added simultaneously to continue the reaction; (6) The second monomer solution B is added dropwise to the reaction vessel, and the redox initiation system is added dropwise simultaneously to continue the reaction, so as to obtain the polymer reaction solution; (7) After cooling the polymer reaction solution, adjust the pH to 6.5-7.2 with sodium hydroxide aqueous solution, add water to adjust the solid content to 42%-48%, filter, and obtain high slump-retaining polycarboxylate superplasticizer for low-carbon high impermeability concrete; The ammonium persulfate solution and the L(+)-ascorbic acid solution respectively comprise: dissolving 1g of ammonium persulfate in 15g of deionized water to obtain ammonium persulfate solution I1; dissolving 0.3g of L(+)-ascorbic acid in 15g of deionized water to obtain L(+)-ascorbic acid solution R1; dissolving 0.5g of ammonium persulfate in 5g of deionized water to obtain ammonium persulfate solution I2; dissolving 0.1g of L(+)-ascorbic acid in 5g of deionized water to obtain L(+)-ascorbic acid solution R2; dissolving 0.5g of ammonium persulfate in 10g of deionized water to obtain ammonium persulfate solution I3; and dissolving 0.2g of L(+)-ascorbic acid in 10g of deionized water to obtain L(+)-ascorbic acid solution R3. In step (5), the stirring speed of the reactor is increased to 350 rpm and the end of the feed pipe at the bottom of the reactor is fixed 20 mm below the stirring paddle. The sodium salt precursor solution is added in one go within 1 min. Then, ammonium persulfate solution I2 and L(+)-ascorbic acid solution R2 are added dropwise simultaneously within 10-20 min. The reaction is continued at 48-55℃ for 15-30 min.

2. The preparation method of the high-slump-retention polycarboxylate superplasticizer for low-carbon, high-permeability concrete according to claim 1, characterized in that, In step (1), the amount of di[2-(methacryloyloxy)ethyl] phosphate in the sodium salt precursor solution is 2-3.5g, the amount of 30% sodium hydroxide aqueous solution is 0.76-1.33g, and the amount of mercaptoacetic acid is 0.6-1.0g.

3. The preparation method of the high-slump-retention polycarboxylate superplasticizer for low-carbon, high-permeability concrete according to claim 1, characterized in that, In step (1), the amount of di[2-(methacryloyloxy)ethyl] phosphate in the triethanolamine salt precursor solution is 1-2g, and the amount of triethanolamine is 0.43-0.86g.

4. The preparation method of the high-slump-retention polycarboxylate superplasticizer for low-carbon, high-permeability concrete according to claim 1, characterized in that, In step (2), the amount of 2-hydroxyethyl methacrylate phosphate in the first monomer solution A is 3-8g and the amount of mercaptoacetic acid is 0.8-1.2g. In the second monomer solution B, the amount of 2-hydroxyethyl methacrylate phosphate is 18-32g, the amount of acrylic acid is 80g, the amount of mercaptoacetic acid is 0.6-0.9g, and the amount of triethanolamine salt precursor solution is 1.43-2.86g.

5. The preparation method of the high-slump-retention polycarboxylate superplasticizer for low-carbon, high-permeability concrete according to claim 1, characterized in that, In step (3), the amount of isopentenyl alcohol polyoxyethylene ether used is 240g.

6. The method for preparing high slump retaining polycarboxylate superplasticizer for low carbon high impermeability concrete according to claim 1, characterized in that, In step (4), the first monomer solution A is placed in the dropping funnel and its discharge pipe is inserted 20 mm below the liquid surface and 30 mm above the stirring paddle. The first monomer solution A is added dropwise within 15-30 min. At the same time, ammonium persulfate solution I1 and L(+)-ascorbic acid solution R1 are added dropwise within 30-60 min. During the dropwise addition, the temperature of the reactor is controlled at 48-55℃. After the dropwise addition is completed, the reaction is kept warm for 30 min.

7. The method for preparing high slump retaining polycarboxylate superplasticizer for low carbon high impermeability concrete according to claim 1, characterized in that, In step (6), the stirring speed of the reactor is reduced to 250 rpm and the end of the top drop tube is fixed 10 mm below the liquid surface. The second monomer solution B is added dropwise at a uniform rate within 60-100 min. At the same time, ammonium peroxydisulfate solution I3 and L(+)-ascorbic acid solution R3 are added dropwise simultaneously within 70-110 min. During the dropwise addition, the reactor temperature is maintained at 48-55℃. After the dropwise addition is completed, the reaction is kept warm for 50-70 min.

8. A high slump retention polycarboxylate superplasticizer for low carbon high impermeability concrete, characterized by, It is obtained by the preparation method of the high slump-retaining polycarboxylate superplasticizer for low-carbon, high-permeability concrete according to any one of claims 1-7.

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