Polycarboxylic high performance water reducing agent and preparation method thereof

Abstract

The application relates to the technical field of concrete, and particularly discloses a polycarboxylic high-performance water reducing agent and a preparation method thereof; the polycarboxylic high-performance water reducing agent is made of the following raw materials: a polyether macromonomer, an unsaturated carboxylic small monomer, a chain transfer agent, an oxidizing agent, a reducing agent and a retarder; the preparation method of the polycarboxylic high-performance water reducing agent comprises the following steps: S1, premixing: mixing the polyether macromonomer and water at a weight ratio of 1:2-1:3 to obtain a premixing solution; S2, pre-polymerization; S3, main polymerization; S4, aging reaction; S5, neutralization; and S6, purification. The polycarboxylic high-performance water reducing agent can be used for preparing high-fluidity, high-strength and super-long-pumping-distance concrete engineering, and has the advantages of concrete construction performance and long-term durability; in addition, the preparation method has the advantages of improving the dispersion efficiency and storage stability of the water reducing agent.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of concrete, in particular to a polycarboxylate high-performance water reducing agent and a preparation method thereof. BACKGROUND

[0002] Concrete is a kind of artificial stone material formed by mixing and stirring cementitious materials, aggregates, water and, if necessary, additives in a certain proportion and then hardening, and has the characteristics of high strength, good durability, strong plasticity, wide raw material sources and the like; according to the cementitious materials, the concrete can be divided into cement concrete and asphalt concrete; according to the use and performance, the concrete can be divided into ordinary concrete, high-strength concrete, lightweight concrete and waterproof concrete and the like; the hardening process of the concrete is that the cementitious materials react with water to cement the aggregates into a whole to form a structural material capable of bearing load, and the concrete is widely used in the fields of building, bridge, road, water conservancy and municipal engineering, and a water reducing agent is often added in the preparation process of the concrete to optimize the performance.

[0003] The related water reducing agent disperses cement particles by relying on electrostatic repulsion of a naphthalene-based water reducing agent, but the residual monomer of the naphthalene-based water reducing agent migrates inside the concrete, corrodes the passivation film of a steel bar or generates soluble salts with calcium ions, thereby accelerating carbonation of the concrete and corrosion of the steel bar. SUMMARY

[0004] In order to solve the problem of accelerating carbonation of the concrete and corrosion of the steel bar caused by the related water reducing agent dispersing cement particles by relying on electrostatic repulsion of a naphthalene-based water reducing agent, the application provides a polycarboxylate high-performance water reducing agent and a preparation method thereof.

[0005] In a first aspect, the application provides a polycarboxylate high-performance water reducing agent, which adopts the following technical scheme:

[0006] A polycarboxylate high-performance water reducing agent is made of raw materials containing the following components by weight: 70-85 parts of polyether macromonomer, 15-30 parts of unsaturated carboxylic acid small monomer, 0.1-0.5 parts of chain transfer agent, 0.5-2 parts of oxidizing agent, 0.2-1 parts of reducing agent and 0.5-1.5 parts of retarder, wherein the polyether macromonomer is at least one selected from the group consisting of allyl alcohol polyoxyethylene ether with a molecular weight of 2200-2600 and allyl alcohol polyoxyethylene ether with a molecular weight of 2600-3000.

[0007] By adopting the technical scheme, since the allyl alcohol polyoxyethylene ether with a molecular weight of 2200-2600 or the allyl alcohol polyoxyethylene ether with a molecular weight of 2600-3000 is used as the polyether macromonomer, the macromonomer with the molecular weight range has moderate polyoxyethylene chain length, which can provide sufficient steric hindrance effect to enhance the dispersibility of cement particles and avoid excessive solution viscosity caused by excessively high molecular weight; meanwhile, 15-30 parts of the unsaturated carboxylic acid small monomer is used, which ensures that the carboxyl groups sufficiently cover the surface of the cement particles to form a double electric layer structure, and the synergistic effect of electrostatic repulsion and steric hindrance improves the water-reducing efficiency; in addition, 0.1-0.5 parts of the chain transfer agent controls the chain termination rate of the free radical polymerization reaction, so that the molecular weight of the polymer is stable, which ensures the stretching ability of the molecular chain of the water reducer and avoids the decrease in solution flowability caused by excessively high molecular weight; in combination with the oxidation-reduction initiation system composed of 0.5-2 parts of the oxidizing agent and 0.2-1 parts of the reducing agent, a high monomer conversion rate is achieved under mild conditions of 60-70 ℃, and the negative impact of unreacted monomer residues on the durability of concrete is reduced; finally, 0.5-1.5 parts of sodium gluconate is added as a retarder, and the complex formed by the sodium carboxylate groups and the cement hydration product Ca²⁺ delays the hydration process of the C3A phase, thereby balancing the demand for high water-reducing rate and setting time; therefore, the high water-reducing rate of the water reducer is ensured, the solution viscosity and unreacted monomer residues are controlled, and the water-reducing efficiency and concrete setting time are balanced, thereby improving the construction performance and long-term durability of concrete.

[0008] Preferably, the unsaturated carboxylic acid small monomer is a mixture of acrylic acid and methacrylic acid in a weight ratio of (3:1) to (5:1).

[0009] By adopting the technical scheme, since the mixture of acrylic acid and methacrylic acid in a weight ratio of 3:1 to 5:1 is used as the unsaturated carboxylic acid small monomer, the ratio range optimizes the performance by regulating the carboxyl group density and steric hindrance effect of the two monomers; acrylic acid provides high-density free carboxyl groups, which ionize to form a strong negative charge surface in alkaline cement paste, and promotes the dispersion of cement particles through Coulomb repulsion; the methyl group in the methacrylic acid molecule enhances the hydrophobicity of the polymer backbone, thereby improving the thickness of the adsorption layer on the surface of the cement particles; meanwhile, the ratio control keeps the polymerization activity within a reasonable range, avoiding local explosive polymerization caused by excessively high activity of acrylic acid or residual monomers caused by insufficient activity of methacrylic acid; therefore, the molecular chain of the polycarboxylic acid water reducer simultaneously has high charge density and moderate hydrophobicity, which ensures the dispersibility of cement particles and maintains the high retention rate of concrete slump.

[0010] Preferably, the retarder is sodium gluconate, the chain transfer agent is at least one of mercaptopropionic acid or mercaptoacetic acid, the oxidizing agent is at least one of ammonium persulfate or hydrogen peroxide, and the reducing agent is at least one of ascorbic acid or sodium formaldehyde sulfoxylate.

[0011] By adopting the technical scheme, since sodium gluconate is used as the retarder, the polyhydroxy structure thereof is preferentially adsorbed on the active site of cement particles C3A, and the occurrence time of the initial hydration exothermic peak is delayed by complexing calcium ions; meanwhile, mercaptopropionic acid or mercaptoacetic acid with a high chain transfer constant is selected as the chain transfer agent, the mercapto sulfur atom thereof accurately controls the polymer molecular chain growth rate through homolytic reaction, so that the weight average molecular weight is stable, and the monolayer adsorption efficiency of the water reducing agent molecules on the surface of cement particles is improved; in combination with the synergistic effect of the oxidizing agent and the reducing agent, a high free radical regeneration frequency is achieved through the metal ion catalytic cycle reaction in the interval of 45-70℃, so that the grafting efficiency of the macromonomer is improved; and the sodium gluconate maintains the stable hydroxyl structure in the acidic polymerization environment, so that the esterification side reaction does not occur before neutralization; meanwhile, the sulfate ions generated by the decomposition of ammonium persulfate enhance the fluidity of the cement paste, and the sodium formaldehyde sulfoxylate is completely decomposed into inert sulfite at the high-temperature curing stage, so that the residual reducing agent does not affect the durability of the concrete; therefore, the water reducing agent has a low unreacted monomer content, and the cement paste fluidity retention rate of the cement paste added with the water reducing agent is high.

[0012] Preferably, the water reducing agent further comprises 0.1-0.8 parts of a defoaming agent, and the defoaming agent is polydimethylsiloxane.

[0013] By adopting the technical scheme, since polydimethylsiloxane is used as the defoaming agent, the low surface tension characteristics are formed by the alternately arranged silicon-oxygen bonds and hydrophobic methyl groups in the molecular structure of the defoaming agent, the defoaming agent rapidly migrates to the surface of the bubble liquid film during stirring, the local surface tension of the liquid film is unbalanced by replacing the surfactant molecules at the gas-liquid interface, and the bubble breakage threshold is reduced; meanwhile, the methyl groups in the organic silicon molecules adsorb the free calcium ions in the cement paste through van der Waals force, hydrophobic microparticles are formed, and the combination of bubbles to form large bubble clusters is hindered; therefore, the water reducing agent reduces the air content of the concrete, and the compressive strength decay caused by poor pore structure is avoided.

[0014] In a second aspect, the application provides a preparation method of a polycarboxylate-based high-performance water reducing agent, which adopts the following technical scheme:

[0015] The preparation method of the polycarboxylate-based high-performance water reducing agent comprises the following steps:

[0016] S1, premixing: mixing polyether macromonomer and water at a weight ratio of 1:2-1:3 to obtain a premixing solution;

[0017] S2, prepolymerization: 30%~40% of the total amount of unsaturated carboxylic acid monomer, 50%~60% of the total amount of chain transfer agent and 40%~50% of the total amount of oxidant were added to the premix solution, and reacted at 60~70℃ for 40~60min;

[0018] S3, main polymerization: the remaining unsaturated carboxylic acid monomer, the remaining chain transfer agent, the remaining oxidant and all reducing agents were added dropwise to the product obtained in S2, and the dropwise time was controlled for 60~90min;

[0019] S4, aging reaction: the product obtained in S3 was heated to 80~85℃, and the reaction was continued for 1.5~2.5h;

[0020] S5, neutralization: first, a retarder was added to the solution obtained in S4, and then a 30wt% sodium hydroxide solution was added to adjust the pH to 6.0~6.5;

[0021] S6, purification: the neutralized product was concentrated under vacuum at 50~60℃ to a solid content of ≥40wt%.

[0022] By adopting the above technical scheme, since the polyether macromonomer and water are mixed in a weight ratio of 1:2~1:3 in S1, the water phase ratio forms a high-viscosity premix solution, ensuring that the macromolecular chain fully stretches in the water medium; in S2, 60~70℃ initiates free radical graft polymerization, and the half-life of ammonium persulfate is maintained at 10~15min to form a prepolymer core; in S3, the remaining monomers and reducing agents are added dropwise at a rate of 0.5~0.8mL / min for 60~90min, so that the free radical concentration of the reaction system remains stable, avoiding local over-polymerization leading to gelation; in S4, the temperature is raised to 80~85℃ to accelerate the conversion of residual monomers, and the half-life of sodium formaldehyde sulfoxylate decomposition is shortened to 5min at this temperature, thereby ensuring complete consumption of the reducing agent; in S5, sodium gluconate is added before pH adjustment, and the esterification side reaction of the hydroxyl group and the carboxyl group is inhibited in the acidic environment; finally, vacuum concentration is carried out at 50~60℃ and an absolute pressure of-0.08~-0.10MPa, which further reduces the degradation rate of the polyether side chain under this mild dehydration condition; therefore, the dispersion efficiency and storage stability of the superplasticizer are improved, and the prepared concrete has excellent water-reducing and slump-retaining performance and environmental adaptability.

[0023] Preferably, the reaction temperature in step S2 is 65±2℃, and the reaction time is 50min.

[0024] By adopting the technical scheme, since the prepolymerization temperature of 65±2℃ is adopted, the temperature range makes the half-life period of ammonium persulfate decomposition stable in the interval of 12-15 min, controls the generation rate of initiator free radicals, ensures the preferential reaction of allyl sites of polyether macromonomer with free radicals to form initial grafting points, and meanwhile, the reaction time of 50 min covers multiple half-life periods of unsaturated carboxylic acid small monomers, so that the conversion rate of unsaturated carboxylic acid small monomers is improved, and a prepolymer core is generated. Therefore, the effect of improving the adsorption efficiency of the water reducing agent on the surface of cement particles is achieved.

[0025] Preferably, the dropping speed in step S3 is 0.5-0.8 mL / min, and the dropping time is 70-80 min.

[0026] By adopting the technical scheme, since the dropping speed of 0.5-0.8 mL / min is adopted, the free radical concentration is kept stable during the reaction process, and then the controlled gradient introduction of monomers is realized; the rate matches the generation rate of free radicals generated by initiator decomposition, avoiding the local monomer concentration being too high to cause molecular chain entanglement; meanwhile, the continuous dropping time of 70-80 min covers 85%-90% of the surface active sites of the prepolymer core, so that the remaining unsaturated carboxylic acid small monomers are grafted layer by layer to construct a comb structure; therefore, the effect of enhancing the adsorption order of the water reducing agent on the interface of cement particles is achieved, so that the water reducing agent molecules can form a stable steric hindrance network in the hydration system, and the dispersion efficiency and the time stability of the dispersed phase of the water reducing agent are simultaneously improved.

[0027] Preferably, the reaction temperature in step S4 is 82±1℃, and the reaction time is 2 h.

[0028] By adopting the technical scheme, since the curing temperature of 82±1℃ is adopted, the free radical polymerization activation energy of the residual monomers is reduced, and then the reaction rate is improved; meanwhile, the reaction time of 2 h covers multiple half-lives of the decomposition of formaldehyde and sodium bisulfite, so that the reduction of the residual amount of the reducing agent is ensured.

[0029] Preferably, the setting retarder in step S5 is sodium gluconate, and the addition amount of sodium gluconate in step S5 is 0.5%-1.5% of the total weight of the water reducing agent.

[0030] By adopting the technical scheme, since the addition amount of sodium gluconate is 0.5%-1.5% of the total weight of the water reducing agent, the proportion range ensures that the four hydroxyl and carboxyl groups in the sodium gluconate molecules form [Ca(C6H 11O7)2]²⁻ complex selectively adsorbs on the surface of the cement particle C3A phase, prolongs the initial hydration induction period of tricalcium silicate, and the addition ratio maintains the free sodium gluconate concentration in the concrete slurry at 0.02-0.05 mol / L, which meets the requirements of the setting time and avoids the penetration of sugar molecules to the aggregate interface to weaken the bonding strength, so that the plastic flow window of the newly mixed slurry is prolonged, the risk of weakening the aggregate interface is eliminated, and the effect of synchronously driving the densification of the hardened body microstructure is achieved.

[0031] Preferably, the pressure of vacuum concentration in step S6 is-0.08~-0.10 MPa, and the viscosity of the product after concentration is controlled at 200-400 mPa·s.

[0032] By adopting the above technical scheme, since the pressure of-0.08~-0.10 MPa is adopted for vacuum concentration, the pressure range reduces the boiling point of water to 45-50℃, and the temperature in S6 is maintained at 50-60℃, thereby ensuring that the water evaporation enthalpy is maintained at a stable level, and the thermal degradation rate of the heat-sensitive polyether chain is reduced; at the same time, the viscosity of the concentrated product is adjusted to 200-400 mPa·s to ensure the high diffusivity of the water reducing agent in the concrete slurry, if the viscosity exceeds 400 mPa·s, the adsorption efficiency is reduced due to the entanglement of the molecular chain, and if the viscosity is less than 200 mPa·s, the space hindering effect is weakened due to the excessive stretching of the molecular chain; therefore, the effects of improving the water dispersion efficiency in the concrete added with the water reducing agent and the persistent and reliable rheological performance of the newly mixed slurry are achieved.

[0033] In summary, the present application has the following beneficial effects:

[0034] 1. Since the present application adopts polyether macromonomer, unsaturated carboxylic acid small monomer, chain transfer agent, oxidation-reduction initiation system and retarder, the moderate steric hindering effect of the polyether macromonomer enhances the dispersibility of the cement particles, the double electric layer structure formed by the unsaturated carboxylic acid small monomer enhances the electrostatic repulsion, the chain transfer agent adjusts the chain termination rate of free radical polymerization to stabilize the molecular weight, the oxidation-reduction system improves the monomer conversion rate under mild conditions to reduce residues, and the retarder complexes calcium ions to balance the hydration process, so that the effects of obtaining high water-reducing rate of the water reducing agent, controlling the solution viscosity, reducing the unreacted monomer residues, and improving the construction performance and long-term durability of the concrete are achieved.

[0035] 2. Preferably, sodium gluconate is used as the retarder in the present application, and specific chain transfer agent and oxidation-reduction system are used, since the retarder preferentially adsorbs on the cement active site to delay hydration, the chain transfer agent controls the molecular chain growth rate to improve the adsorption efficiency, and the oxidation-reduction system improves the monomer grafting rate, so that the effects of low unreacted monomer content in the water reducing agent and high cement paste fluidity retention rate are achieved.

[0036] 3、The method of the application ensures that the macromolecular chains are fully stretched by forming a high-viscosity medium through a premixing step, and then the pre-polymerization reaction constructs an initial grafting point at an optimized temperature to form a pre-polymer core, and the main polymerization controls the free radical concentration to avoid local over-polymerization, and then the ripening reaction accelerates the conversion of residual monomers to consume reducing agents, and the addition of a retarder before neutralization utilizes the acidic environment to inhibit side reactions, and finally vacuum concentration dehydrates under mild pressure to protect the integrity of the polyether chain, so that the dispersing efficiency and storage stability of the water reducing agent are improved, and the concrete has excellent water-reducing and slump-retaining performance and environmental adaptability.

[0037] 4、The application preferably uses polydimethylsiloxane as a defoaming agent, which migrates to the surface of the bubbles to replace the surface active agent due to its low surface tension characteristics, and at the same time adsorbs free calcium ions to hinder bubble polymerization, thereby achieving the effect of reducing the air content of concrete to avoid the decay of compressive strength. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 A flowchart of a preparation method of a polycarboxylate-based high-performance water reducing agent is provided for the application. DETAILED DESCRIPTION

[0039] The application will be further described in detail below in combination with the drawings and examples.

[0040] Related water reducing agents disperse cement particles by relying on electrostatic repulsion through naphthalene-based water reducing agents, but the residual monomers of naphthalene-based water reducing agents migrate inside the concrete, erode the passivation film of steel bars, or form soluble salts with calcium ions, thereby causing accelerated carbonation of concrete and corrosion of steel bars.

[0041] The application discloses a polycarboxylate-based high-performance water reducing agent and a preparation method thereof; wherein the polycarboxylate-based high-performance water reducing agent is made of the following raw materials: a polyether macromonomer, an unsaturated carboxylic acid small monomer, a chain transfer agent, an oxidizing agent, a reducing agent and a retarder; and the preparation method of the polycarboxylate-based high-performance water reducing agent comprises the following steps: S1, premixing: mixing the polyether macromonomer and water at a weight ratio of 1:2-1:3 to obtain a premixing solution; S2, pre-polymerization reaction; S3, main polymerization reaction; S4, ripening reaction; S5, neutralization; and S6, purification.

[0042] The application uses a polyether macromonomer in combination with an unsaturated carboxylic acid small monomer, a chain transfer agent, an oxidation-reduction initiation system and a retarder, because the polyether macromonomer provides moderate steric hindrance effect to enhance the dispersibility of cement particles, the unsaturated carboxylic acid small monomer forms a double electric layer structure to enhance electrostatic repulsion, the chain transfer agent regulates the chain termination rate of free radical polymerization to stabilize the molecular weight, the oxidation-reduction system improves the monomer conversion rate under mild conditions to reduce residues, and the retarder complexes calcium ions to balance the hydration process, thereby achieving the effects of obtaining a water reducing agent with high water-reducing rate, controlling solution viscosity, reducing unreacted monomer residues, and improving the construction performance and long-term durability of concrete.

[0043] 1, Allyl alcohol polyoxyethylene ether: purchased from Shanghai Mclean Biotech Co., Ltd., brand AEO-2500.

[0044] 2, Acrylic acid: purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd., brand AA-AR.

[0045] 3, Methacrylic acid: purchased from Shanghai Aladdin Biochem Technology Co., Ltd., brand MAA-98.

[0046] 4, Mercaptopropionic acid and mercaptoacetic acid: purchased from Nanjing Shuguang Chemical Group Co., Ltd., brand MPA-99 and TGA-98.

[0047] 5, Ammonium persulfate and hydrogen peroxide: purchased from Tianjin Kemio Chemical Reagent Co., Ltd., brand APS-AR and H2O2-30.

[0048] 6, Ascorbic acid or sodium formaldehyde sulfoxylate: purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd., brand Vc-AR and SMS-90.

[0049] 7, Sodium gluconate: purchased from Beijing Inokai Technology Co., Ltd., brand SG-AR.

[0050] 8, Polydimethylsiloxane: purchased from Guangzhou Jinghong Chemical Co., Ltd., brand PDMS-100.

[0051] 9, Sodium hydroxide: purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd., brand NaOH-AR.

[0052] Example 1

[0053] The present embodiment provides a polycarboxylic acid high-performance water reducing agent made from raw materials containing the following parts by weight: polyether macromonomer 70 parts, allyl alcohol polyoxyethylene ether with a molecular weight of 2200; unsaturated carboxylic acid small monomer 15 parts, a mixture of acrylic acid and methacrylic acid in a weight ratio of 3:1, wherein acrylic acid is 11.25 parts and methacrylic acid is 3.75 parts; chain transfer agent 0.1 part, mercaptopropionic acid; oxidizing agent 0.5 parts, ammonium persulfate; reducing agent 0.2 parts, ascorbic acid; retarder 0.5 parts, sodium gluconate; defoaming agent 0.1 part, polydimethylsiloxane.

[0054] The preparation method of the above-mentioned polycarboxylic acid high-performance water reducing agent is as follows:

[0055] S1, premixing: mix the polyether macromonomer and water in a weight ratio of 1:2 to obtain a premixing solution;

[0056] S2, prepolymerization: 30% of the total amount of unsaturated carboxylic acid monomer, 50% of the total amount of chain transfer agent and 40% of the total amount of oxidizing agent were added to the premixed solution, and reacted at 60°C for 40 min;

[0057] S3, main polymerization: the remaining unsaturated carboxylic acid monomer, the remaining chain transfer agent, the remaining oxidizing agent and all reducing agents were added dropwise to the product obtained in S2, the dropwise time was controlled for 60 min, and the dropwise speed was 0.5 mL / min;

[0058] S4, curing reaction: the product obtained in S3 was warmed to 80°C and continued to react for 1.5 h;

[0059] S5, neutralization: first, the setting retarder was added to the solution obtained in S4, the amount of setting retarder was 0.5% of the total weight of water reducing agent, then 30wt% sodium hydroxide solution was added to adjust the pH to 6.0;

[0060] S6, purification: the neutralized product was concentrated under vacuum at 50°C, the pressure was -0.08 MPa, and the concentration was carried out until the solid content was ≥40wt% and the viscosity was 200 mPa·s.

[0061] Example 2

[0062] The present embodiment provides a polycarboxylic acid-based high-performance water reducing agent, which is made from raw materials including the following weight parts: 85 parts of polyether macromonomer, allyl alcohol polyoxyethylene ether with a molecular weight of 3000; 30 parts of unsaturated carboxylic acid monomer, which is a mixture of acrylic acid and methacrylic acid in a weight ratio of 5:1, wherein the acrylic acid is 25 parts and the methacrylic acid is 5 parts; 0.5 parts of chain transfer agent, which is mercaptopropionic acid; 2 parts of oxidizing agent, which is ammonium persulfate; 1 part of reducing agent, which is ascorbic acid; 1.5 parts of setting retarder, which is sodium gluconate; and 0.8 parts of defoaming agent, which is polydimethylsiloxane.

[0063] The preparation method of the above-mentioned polycarboxylic acid-based high-performance water reducing agent is as follows:

[0064] S1, premixing: the polyether macromonomer was mixed with water in a weight ratio of 1:3 to obtain a premixed solution;

[0065] S2, prepolymerization: 40% of the total amount of unsaturated carboxylic acid monomer, 60% of the total amount of chain transfer agent and 50% of the total amount of oxidizing agent were added to the premixed solution, and reacted at 70°C for 60 min;

[0066] S3, main polymerization: the remaining unsaturated carboxylic acid monomer, the remaining chain transfer agent, the remaining oxidizing agent and all reducing agents were added dropwise to the product obtained in S2, the dropwise time was controlled for 90 min, and the dropwise speed was 0.8 mL / min;

[0067] S4, curing reaction: the product obtained in S3 was warmed to 85°C and continued to react for 2.5 h;

[0068] S5, neutralization: first, the solution obtained in S4 is added with a retarder, the amount of the retarder added is 1.5% of the total weight of the water reducing agent, then 30wt% sodium hydroxide solution is added to adjust the pH to 6.5;

[0069] S6, purification: the neutralized product is concentrated under vacuum at 60℃, the pressure is -0.10MPa, and the concentration is carried out until the solid content is ≥40wt% and the viscosity is 400mPa·s.

[0070] Example 3

[0071] The present embodiment provides a polycarboxylic acid-based high-performance water reducing agent, which is made from raw materials comprising: polyether macromonomer 77.5 parts, allyl alcohol polyoxyethylene ether with a molecular weight of 2600; unsaturated carboxylic acid small monomer 22.5 parts, which is a mixture of acrylic acid and methacrylic acid in a weight ratio of 4:1, wherein acrylic acid is 18 parts and methacrylic acid is 4.5 parts; chain transfer agent 0.3 parts, which is mercaptopropionic acid; oxidizing agent 1.25 parts, which is ammonium persulfate; reducing agent 0.6 parts, which is ascorbic acid; retarder 1.0 part, which is sodium gluconate; defoaming agent 0.45 parts, which is polydimethylsiloxane.

[0072] The preparation method of the above-mentioned polycarboxylic acid-based high-performance water reducing agent is as follows:

[0073] S1, premixing: the polyether macromonomer is mixed with water in a weight ratio of 1:2.5 to obtain a premix solution;

[0074] S2, pre-polymerization: 35% of the total amount of unsaturated carboxylic acid small monomer, 55% of the total amount of chain transfer agent, and 45% of the total amount of oxidizing agent are added to the premix solution, and the reaction is carried out at 65℃ for 50min;

[0075] S3, main polymerization reaction: the remaining unsaturated carboxylic acid small monomer, the remaining chain transfer agent, the remaining oxidizing agent, and the entire reducing agent are added dropwise to the product obtained in S2, the dropwise time is controlled to be 75min, and the dropwise speed is 0.65mL / min;

[0076] S4, aging reaction: the product obtained in S3 is warmed to 82.5℃, and the reaction is continued for 2.0h;

[0077] S5, neutralization: first, the solution obtained in S4 is added with a retarder, the amount of the retarder added is 1.0% of the total weight of the water reducing agent, then 30wt% sodium hydroxide solution is added to adjust the pH to 6.3;

[0078] S6, purification: the neutralized product is concentrated under vacuum at 55℃, the pressure is -0.09MPa, and the concentration is carried out until the solid content is ≥40wt% and the viscosity is 300mPa·s.

[0079] Comparative Example 1

[0080] This comparative example refers to the content of Example 1, the difference is that the weight parts of polyether macro-monomer is 68 parts, and the rest is the same as Example 1.

[0081] Comparative Example 2

[0082] This comparative example refers to the content of Example 1, the difference is that the weight parts of unsaturated carboxylic acid micro-monomer is 32 parts, and the rest is the same as Example 1.

[0083] Comparative Example 3

[0084] This comparative example refers to the content of Example 1, the difference is that the weight parts of chain transfer agent is 0.6 parts, and the rest is the same as Example 1.

[0085] Comparative Example 4

[0086] This comparative example refers to the content of Example 1, the difference is that the reaction temperature in step S2 is 55℃, and the rest is the same as Example 1.

[0087] Comparative Example 5

[0088] This comparative example refers to the content of Example 1, the difference is that the dropping time in step S3 is 50min, and the rest is the same as Example 1.

[0089] Comparative Example 6

[0090] This comparative example refers to the content of Example 1, the difference is that the vacuum concentration pressure in step S6 is-0.06MPa, and the rest is the same as Example 1.

[0091] Performance detection test

[0092] Sample preparation: take the water reducing agent samples prepared in Examples 1-3 respectively, and take the water reducing agent samples prepared in Comparative Examples 1-6 at the same time, all samples are stored in a temperature of 25±2℃ and humidity of 60±5%, and all performance tests are completed within 48h to ensure consistency.

[0093] Water-reducing rate and slump retention rate test: first, prepare the reference concrete with cement dosage of 450kg / m³ and sand ratio of 40%, and control the initial slump to be 80±10mm; then prepare the test concrete group, add 0.2wt% of water reducing agent to each test group based on the same amount of cement base material, and adjust the water amount to make the initial slump of the test group consistent with the reference group; calculate the water-reducing rate according to the formula by recording the actual water amount of the test group: ; wherein W b is the reference water amount, W tThe water consumption for the test; finally, the performance of the time loss was evaluated, the fresh concrete was left for 60 min and 120 min, the slump value was retested according to GB / T50080 standard, and the slump retention rate at each time point was calculated.

[0094] Compressive strength variation test: first, the specimen forming operation was carried out, the fresh concrete was injected into a three-steel mold with a specification of 100 mm x 100 mm x 100 mm, and the vibration table was used to vibrate for 30 s at a fixed frequency to ensure the density; then standard curing was carried out, the surface of the formed specimen was covered with a wet cloth and left for 24 h after demolding, and then transferred to a standard curing room with a temperature controlled at 20±2℃ and a relative humidity >95% for continuous curing; finally, the strength test was carried out, the hydraulic pressure testing machine was used to measure the compressive strength at the curing age of 3d, 7d, 28d, the loading rate was strictly controlled at 0.8MPa / s, three groups of parallel specimens were tested at each age group, and the arithmetic mean value was taken as the final strength value.

[0095] Molecular weight distribution and rheological property test: first, gel permeation chromatography analysis was carried out, the water reducing agent sample was prepared into a water solution with a concentration of 5mg / mL, filtered through a 0.22μm filter membrane, separated by a chromatographic column, the mobile phase was 0.1mol / L NaNO3 solution, the flow rate was constant at 1.0mL / min, and the number average molecular weight Mn and the dispersion degree PDI were calculated based on the chromatographic separation behavior; then the viscosity temperature dependence was measured, the rotational viscometer was used to test the viscosity of 10wt% water reducing agent solution at 20℃, 40℃, 60℃ environment, the shear rate was increased from 100s -1 to 500s -1 ; finally, according to the national standard GB / T5549, the equilibrium surface tension value of 0.1wt% water reducing agent solution was measured by platinum plate method.

[0096] Accelerated aging and performance degradation test: first, the heat accelerated aging treatment was carried out, the original sample of water reducing agent was sealed in a transparent glass bottle and placed in a constant temperature oven with a temperature of 50±2℃ for continuous treatment for 30d; then the viscosity change rate was measured, equal amount of sample was taken before and after aging, the viscosity value was tested at 25℃ standard environment by using rotational viscometer, the relative change rate was calculated according to the formula:

[0097] ;

[0098] wherein N0 is the initial viscosity, N t is the viscosity after aging; finally, the retention rate of effective components was analyzed, the content of sodium gluconate, a retarder, before and after aging was detected by high performance liquid chromatography, the chromatographic separation used C18 reversed phase chromatographic column, the detection wavelength was set at 210nm, and each group of test was tested three times in parallel to ensure the reliability of the data.

[0099] The performance test data of examples 1-3 and comparative examples 1-6 are shown in Table 1.

[0100] Table 1:

[0101] Group Water-reducing rate (%) 120 min slump retention rate (%) 28 d compressive strength (MPa) Dispersibility (PDI) Viscosity change rate (%) Example 1 25.8 92.1 61.7 1.45 3.2 Example 2 28.3 94.7 64.2 1.38 2.1 Example 3 27.1 93.5 63.1 1.41 2.8 Comparative Example 1 22.1 84.3 56.9 1.72 8.9 Comparative Example 2 20.7 79.6 54.2 1.85 12.4 Comparative Example 3 23.5 86.2 59.1 1.98 15.7 Comparative Example 4 19.3 76.8 52.7 1.91 21.5 Comparative Example 5 18.9 72.4 50.8 2.05 18.9 Comparative Example 6 24.6 89.7 60.3 1.51 32.6

[0102] Example conclusion:

[0103] It can be seen from examples 1-3 and comparative example 1 in combination with Table 1 that when the amount of polyether macromonomer is low, the insufficient spatial extension of the molecular chain leads to a decrease in the anchoring sites of the water reducing agent on the surface of the cement particles, which weakens the steric hindrance effect. The example group ensures that the polyether side chain is fully stretched to form a dense hydration film by maintaining a polyether proportion of 70-85 parts, thereby ensuring the synchronous improvement of the slump retention of concrete and the development of strength.

[0104] It can be seen from examples 1-3 and comparative example 2 in combination with Table 1 that excessive unsaturated carboxylic acid small monomers cause strong electrostatic repulsion between molecular chains, leading to self-aggregation of the water reducing agent in the liquid phase; the example group controls the small monomer proportion to 15-30 parts to achieve a dynamic balance between carboxyl density and polyether steric hindrance, which maintains the effective charge repulsion on the surface of the cement particles and avoids the instability of the dispersion system caused by excessive repulsion.

[0105] It can be seen from examples 1-3 and comparative example 3 in combination with Table 1 that an excessive amount of chain transfer agent leads to a wide molecular weight distribution, and short-chain molecules cannot form effective steric hindrance, while long-chain molecules are prone to entanglement; the example group uses 0.1-0.5 parts of chain transfer agent to control the free radical reaction process, obtain a narrow distribution comb structure, and ensure the adaptability of the water reducing agent in complex cement components.

[0106] It can be seen from examples 1-3 and comparative example 4 in combination with Table 1 that low-temperature pre-polymerization prolongs the half-life of the initiator, and the insufficient concentration of active radicals leads to a decrease in grafting rate; the example group pre-polymerizes at 60-70°C, and matches the activation energy to make the polyether allyl group preferentially react, thereby constructing a pre-polymerization nuclear skeleton with regular grafting points and laying a structural foundation for subsequent main chain extension.

[0107] It can be seen from examples 1-3 and comparative example 5 in combination with Table 1 that a too short dropping time causes a sudden increase in local monomer concentration, leading to molecular chain entanglement and microgelation; the example group uses 60-90 min of gradient dropping to dynamically couple the free radical generation rate and the monomer supply rate, realizing the layer-by-layer ordered assembly of carboxylic acid monomers on the surface of the pre-polymerization nucleus.

[0108] It can be seen from Examples 1-3 and Comparative Example 6 in combination with Table 1 that insufficient vacuum degree forces the dehydration temperature to rise, triggering the degradation of polyether side chain β-break; the example group is mildly dehydrated at-0.08~ -0.10 MPa, which not only maintains the chemical integrity of the polyether chain, but also ensures the improvement of molecular diffusion rate through viscosity control, ultimately improves the storage stability of the superplasticizer, and shortens the time of superplasticizer molecules adsorbed on the surface of cement particles.

[0109] The specific embodiments are only an explanation of the present application, which is not a limitation of the present application, and those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A polycarboxylate based high performance water reducing agent, characterized in that, The raw materials are prepared by the following weight parts: polyether macromonomer 70-85 parts, unsaturated carboxylic acid small monomer 15-30 parts, chain transfer agent 0.1-0.5 parts, oxidizing agent 0.5-2 parts, reducing agent 0.2-1 parts and retarder 0.5-1.5 parts, wherein the polyether macromonomer is selected from at least one of allyl alcohol polyoxyethylene ether with a molecular weight of 2200-2600 or allyl alcohol polyoxyethylene ether with a molecular weight of 2600-3000; the unsaturated carboxylic acid small monomer is a mixture of acrylic acid and methacrylic acid in a weight ratio of (3:1) to (5:1); the retarder is sodium gluconate; The preparation method of the polycarboxylic acid-based high-performance water reducing agent comprises the following steps: S1, premixing: mixing the polyether macromonomer and water in a weight ratio of 1:2-1:3 to obtain a premixed solution; S2, pre-polymerization: adding 30%-40% of the total amount of unsaturated carboxylic acid small monomers, 50%-60% of the total amount of chain transfer agents, and 40%-50% of the total amount of oxidizing agents into the premixed solution, and reacting at 60-70°C for 40-60 min; S3, main polymerization reaction: adding the remaining unsaturated carboxylic acid small monomers, the remaining chain transfer agents, the remaining oxidizing agents, and all the reducing agents into the product obtained in S2, and controlling the dropping time to be 60-90 min; S4, aging reaction: heating the product obtained in S3 to 80-85°C, and continuing to react for 1.5-2.5 h; S5, neutralization: first adding the retarder into the solution obtained in S4, and then adding a 30wt% sodium hydroxide solution to adjust the pH to 6.0-6.5; S6, purification: vacuum concentrating the neutralized product at 50-60°C to a solid content of ≥40wt%. 2.The polycarboxylate high performance water reducing agent according to claim 1, characterized in that, The chain transfer agent is at least one of mercaptopropionic acid or mercaptoacetic acid, the oxidizing agent is at least one of ammonium persulfate or hydrogen peroxide, and the reducing agent is at least one of ascorbic acid or formaldehyde sodium sulfoxylate. 3.The polycarboxylic acid high performance water reducing agent according to claim 1, characterized in that, It also contains a defoaming agent 0.1-0.8 parts, and the defoaming agent is polydimethylsiloxane.

4. A method for preparing the polycarboxylate-based high performance water reducing agent according to any one of claims 1 to 2, characterized in that, The preparation method comprises the following steps: S1, premixing: mixing the polyether macromonomer and water in a weight ratio of 1:2-1:3 to obtain a premixed solution; S2, pre-polymerization: adding 30%-40% of the total amount of unsaturated carboxylic acid small monomers, 50%-60% of the total amount of chain transfer agents, and 40%-50% of the total amount of oxidizing agents into the premixed solution, and reacting at 60-70°C for 40-60 min; S3, main polymerization reaction: adding the remaining unsaturated carboxylic acid small monomers, the remaining chain transfer agents, the remaining oxidizing agents, and all the reducing agents into the product obtained in S2, and controlling the dropping time to be 60-90 min; S4, aging reaction: heating the product obtained in S3 to 80-85°C, and continuing to react for 1.5-2.5 h; S5, neutralization: first adding the retarder into the solution obtained in S4, and then adding a 30wt% sodium hydroxide solution to adjust the pH to 6.0-6.5; S6, purification: vacuum concentrating the neutralized product at 50-60°C to a solid content of ≥40wt%.

5. The preparation method of the polycarboxylate high-performance water-reducing agent according to claim 4, characterized in that, The reaction temperature in step S2 is 65±2°C, and the reaction time is 50 min.

6. The preparation method of the polycarboxylate high-performance water-reducing agent according to claim 4, characterized in that, The dropping speed in step S3 is 0.5-0.8mL / min, and the dropping time is 70-80 min.

7. The preparation method of the polycarboxylic acid-based high-performance water reducing agent according to claim 4, characterized in that, The reaction temperature in step S4 is 82±1℃, and the reaction time is 2h. 8.The preparation method of the polycarboxylic acid high-performance water-reducing agent according to claim 4, characterized in that, The setting retarder in step S5 is sodium gluconate, and the addition amount of sodium gluconate is 0.5%-1.5% of the total weight of the water reducing agent.

9. The preparation method of the polycarboxylate high-performance water-reducing agent according to claim 4, characterized in that, The pressure of vacuum concentration in step S6 is-0.08~-0.10MPa, and the viscosity of the product after concentration is controlled in 200-400mPa·s.

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