Concrete polycarboxylate superplasticizer with high slump loss resistance and flocculation resistance and preparation method thereof

Abstract

The invention discloses a concrete polycarboxylic acid water reducing agent with high slump loss resistance and flocculation resistance and a preparation method of the concrete polycarboxylic acid water reducing agent, and belongs to the technical field of concrete admixtures. The water reducing agent is prepared from the following raw materials in parts by weight: 45 to 55 parts of isopentenyl polyoxyethylene ether, 3 to 8 parts of methacrylic acid phosphate, 8 to 12 parts of hydroxyethyl acrylate, 4 to 7 parts of N-isopropylacrylamide, 10 to 15 parts of auxiliary monomer, 8 to 12 parts of initiator and 0.3 to 0.6 part of chain transfer agent. And the technical problems that the fluidity of the concrete is reduced and the slump retaining effect is poor due to the fact that the temperature of the concrete is increased in the stirring process are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete admixtures, and particularly relates to a concrete polycarboxylate water reducer and a preparation method thereof. Background Art

[0002] Water reducer is a concrete admixture that can reduce the amount of mixing water while maintaining the slump of concrete. After being added to the concrete mixture, the water reducer has a dispersing effect on cement particles, which can improve its workability and reduce the unit water consumption. As the concrete mixing time goes by, the slump will decrease. In order to reduce the degree of slump decrease, adding water reducer can effectively improve the fluidity of the concrete mixture, that is, as time goes by, the degree of slump decreases. The existing water reducer is used in the process of concrete, and the slump range is 30mm-240mm. 。

[0003] For the machine-made sand in concrete, a large amount of soil and stone powder will be generated during the ore mining and crushing process, which is often treated by water washing. In order to reduce the production water consumption and meet environmental protection requirements, water-washed machine-made sand production companies often use flocculants to quickly settle, purify and clarify the sand washing water to accelerate recycling, resulting in residual flocculants on the surface of some machine-made sand, which will affect the fluidity and even strength of concrete. The specific mechanism of action is: during the production process of machine-made sand, it is inevitable that layered silicate clay minerals (such as montmorillonite and kaolin) are mixed, and their crystal structure exposes a large amount of unsaturated silicon (Si 4+ ), aluminum (Al 3+ ) and other metal ions, which react rapidly with water in an aqueous environment to form surface hydroxyl groups (-Si-OH, -Al-OH). The surface hydroxyl groups combine with residual flocculants (such as polyacrylamide used for machine-made sand cleaning) through hydrogen bonds or electrostatic effects to form a "clay-flocculant-cement particle" bridge structure, which causes a sudden drop in concrete fluidity. The strong polarity of the hydroxyl groups absorbs a large amount of free water, exacerbating the slump loss of the concrete. At the same time, since the concrete will be heated during the mixing process, this seriously affects the slump-preserving effect of the concrete.

[0004] Chinese patent CN114478939B discloses a slow-release polycarboxylate water reducer and a preparation method thereof. The water reducer uses isopentenyl polyoxyethylene ether, acrylic acid, acrylate monomers, sodium lignin sulfonate, polyethylene glycol monomethyl ether methacrylate, initiator and chain transfer agent as raw materials, and has the advantages of good slow-release performance, high dispersibility, strong adaptability, and effective inhibition of concrete slump loss. However, the water reducer cannot be used to treat machine-made sand containing residual flocculants, resulting in reduced concrete fluidity and rapid slump loss. At the same time, it is also impossible to avoid the problem of poor concrete fluidity caused by temperature rise during the mixing process of concrete. For ultra-long pumping concrete, the concrete slump retention effect is poor, and the effective use quality of concrete cannot be effectively guaranteed. For this reason, a high slump retention, anti-flocculation concrete polycarboxylate water reducer and a preparation method thereof are specially proposed to reduce the interference of residual flocculants while ensuring the slump index of ultra-long pumping concrete, providing reliable guarantee for the high-quality use of concrete. Summary of the invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a high slump retention, anti-flocculation concrete polycarboxylic acid water reducer and a preparation method thereof, so as to solve the technical problems that the existing water reducer cannot be used to treat machine-made sand containing residual flocculant, and the concrete fluidity is reduced due to the increase in temperature during the mixing process of concrete, resulting in poor slump retention effect.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A high-slump-retaining and anti-flocculation concrete polycarboxylate water-reducing agent, the raw materials of which include, by weight, 45-55 parts of isopentyl polyoxyethylene ether, 3-8 parts of methacrylate phosphate, 8-12 parts of hydroxyethyl acrylate, 4-7 parts of N-isopropylacrylamide, 10-15 parts of auxiliary monomers, 8-12 parts of initiators and 0.3-0.6 parts of chain transfer agents.

[0008] In the above technical solution, the temperature-sensitive group of NIPAM (N-isopropylacrylamide), i.e., the isopropylamide group (-CONH-C(CH 3 ) 2 ), this group gives the water reducer a unique temperature responsiveness. When the temperature rises during concrete mixing, the temperature-sensitive segments of NIPAM undergo a phase change, releasing adsorbed water, compensating for the water consumed by cement hydration, and maintaining the fluidity of the slurry. Compared with traditional water reducers (which rely only on electrostatic repulsion), the dynamic volume change of NIPAM can adapt to temperature fluctuations and achieve self-repairing collapse protection; at low temperatures, the hydrophilic segments enhance the coating of cement particles and block the adsorption sites of residual flocculants (such as anionic PAM). When hydrophobic shrinkage occurs at high temperatures, the released free water reducer molecules can continue to compete for adsorption of flocculants, forming a double anti-flocculation barrier. This improves the collapse protection and anti-flocculation effects of the water reducer.

[0009] Preferably, the auxiliary monomer is a mixture of nano-silicon dioxide, carbon nanotubes and zwitterionic monomers, and the mass ratio of the nano-silicon dioxide, carbon nanotubes and zwitterionic monomers is 1:1:8.

[0010] The zwitterionic monomer includes methacryloyloxyethyltrimethylammonium chloride or sulfobetaine.

[0011] In the above scheme, the quaternary ammonium group -N + (CH 3 ) 3 and sulfonic acid group -SO 3 H, through the alternating arrangement of positive and negative charges, forms a strong electrostatic barrier, inhibits the adsorption of clay particles on water reducer and maintains the fluidity of concrete.

[0012] In the above technical scheme, for concrete in high-salt environment, sulfobetaine is more suitable, which has salt resistance; in addition, sulfobetaine is less toxic and can avoid hazardous waste risks in the production process. Methacryloyloxyethyl trimethyl ammonium chloride is suitable for most ordinary environments without high-salt conditions, and the cost is relatively low. Generally, methacryloyloxyethyl trimethyl ammonium chloride is directly selected.

[0013] Preferably, the initiator comprises a mixed solution of an aqueous ammonium persulfate solution and an aqueous ascorbic acid solution, and the molar ratio of the aqueous ammonium persulfate solution to the aqueous ascorbic acid solution is 1:1.

[0014] Preferably, the mass fraction of the ammonium persulfate aqueous solution is 4%-6%, and the mass fraction of the ascorbic acid aqueous solution is 1%-3%. Preferably, the chain transfer agent includes mercaptopropionic acid or 3-mercaptopropionic acid isooctyl ester.

[0015] Preferably, the chain transfer agent comprises mercaptopropionic acid.

[0016] In the above technical scheme, mercaptopropionic acid is more suitable for aqueous room temperature systems, but it is volatile and the material loss during the reaction is large. 3-Mercaptopropionic acid isooctyl ester is suitable for non-aqueous phase high temperature systems, is not easy to volatilize, and the material loss during the reaction is small. This method belongs to an aqueous phase room temperature system, and mercaptopropionic acid is more suitable. The performance of the two is comparable at room temperature, but mercaptopropionic acid is cheaper.

[0017] The present invention also discloses a method for preparing a high-slump-retaining and anti-flocculation concrete polycarboxylate water-reducing agent, which specifically comprises the following steps:

[0018] Weigh the raw materials according to the mass fractions, mix the isopentenyl polyoxyethylene ether with deionized water to ensure that the solid content is 40%, add nano-silicon dioxide, and perform ultrasonic treatment;

[0019] After the isopentyl polyoxyethylene ether is heated to 35°C, a 5% ammonium persulfate aqueous solution is added dropwise at 1 mL / min for 0-0.5 h, and after the temperature is raised to 50°C-55°C, methacrylic acid phosphate and hydroxyethyl acrylate are simultaneously added dropwise at 2 mL / min for 0.5 h-1.5 h. After the addition of methacrylic acid phosphate and hydroxyethyl acrylate is completed, the temperature is raised to 60°C-65°C to obtain a solution to be polymerized;

[0020] Add carbon nanotubes to deionized water, and obtain a carbon nanotube suspension after ultrasonic treatment. Add the carbon nanotube suspension, zwitterionic monomer and N-isopropylacrylamide to the solution to be polymerized, add a chain transfer agent, stir for 3-4 hours in an environment of 60°C-65°C, and then add a 2% ascorbic acid aqueous solution;

[0021] 30% sodium hydroxide was added to adjust the pH to 6.9-7.2, and after cooling, a water reducing agent was obtained.

[0022] Preferably, the ultrasonic frequency is 35-45 Hz, and the ultrasonic time is 25-30 min.

[0023] In the above technical solution, isopentenyl polyoxyethylene ether (TPEG) is mixed with deionized water because TPEG is a hydrophilic macromolecular monomer, and its polyoxyethylene ether segment (-CH 2 -CH 2 -O-) needs to be fully dissolved in deionized water to form a uniform premix (solid content 40%) to provide a homogeneous reaction environment for subsequent polymerization reactions. The solid content is ensured to be 40% because 40% solid content can balance solubility and reaction activity. Too high a concentration (>50%) will lead to excessive viscosity and hinder monomer diffusion; too low a concentration (<30%) will reduce polymerization efficiency. Nano-silica is added to the isopentenyl polyoxyethylene ether aqueous solution and ultrasonically treated. The steric hindrance effect of TPEG and the polarity of deionized water are used to break the soft agglomeration of nanoparticles and prevent local uneven reactions caused by nano-agglomeration in subsequent polymerization.

[0024] The purpose of mixing carbon nanotubes with deionized water is as follows: 1) Breaking hydrophobic agglomeration: carbon nanotubes (CNTs) are prone to form hard agglomerations due to strong hydrophobicity and van der Waals forces. After being mixed with deionized water alone, they can be dispersed into single roots or small bundles through high-intensity ultrasound to form a stable suspension. The dispersion mechanism is: the high shear force generated by ultrasonic cavitation breaks the π-π stacking and van der Waals forces between carbon tubes, and the polarity of deionized water weakens the hydrophobic effect of carbon tubes. 2) Avoid competing with TPEG for the dispersion medium: if carbon nanotubes are directly added to the TPEG premix, their hydrophobic surface will preferentially adsorb TPEG molecules, resulting in a decrease in the effective concentration of TPEG and an incomplete polymerization reaction; the carbon tubes are coated with TPEG and lose their conductive network function. Step-by-step treatment ensures that TPEG and carbon nanotubes can perform their respective functions independently.

[0025] Chain transfer agents are added to control the molecular weight and chain structure of the polymerization reaction. Ascorbic acid is used to regulate the rate of polymerization or as a chain terminator.

[0026] In the above technical scheme, the hydrophilicity of the polymer is improved by introducing phosphate groups and hydroxyethyl acrylate groups through the polymerization reaction of methacrylate phosphate and hydroxyethyl acrylate, thereby enhancing the interaction between the polymer and water. The flexibility of the polymer molecular chain is improved by the polyoxyethylene chain segment of isopentyl polyoxyethylene ether and poly N-isopropylacrylamide (PNIPAM), thereby further improving the flexibility and ductility of the molecular chain.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention uses isopentenyl polyoxyethylene ether as the main chain monomer, and its polyoxyethylene chain segment (-CH 2 -CH 2 -O-) has good flexibility and ductility, which can enhance the flexibility of the molecular chain. With the cooperation of initiator, methacrylate phosphate and hydroxyethyl acrylate, a polymer chain containing phosphate group and hydroxyethyl ester group is formed through polymerization reaction. The phosphate group is introduced to form competitive adsorption with the hydroxyl group on the clay surface in the machine-made sand, which means that the phosphate group will occupy the adsorption site on the surface of the clay mineral, thereby blocking the flocculation channel between the clay particles. This competitive adsorption mechanism helps to reduce the interaction between clay particles, prevent them from aggregating into larger particles or floccules, and then block the flocculation channel to achieve an anti-flocculation effect. At the same time, the phosphate group in methacrylate phosphate has strong hydrophilicity, which can enhance the interaction between the polymer chain and water and improve the hydrophilicity. The hydroxyethyl ester group (-OH) in hydroxyethyl acrylate combines with water molecules through hydrogen bonds, further enhancing the hydrophilicity, thereby weakening the adsorption of free water by clay. Under the setting of auxiliary monomers, the water solubility and salt precipitation resistance of the water reducer are improved, and the poly N-isopropylacrylamide hydrogel (PNIPAM) formed by the polymerization of N-isopropylacrylamide is temperature sensitive, which can adjust the conformation of the molecular chain when the temperature changes, further adjust the flexibility, dynamically compensate for the loss of fluidity caused by the hydration reaction, and achieve self-adjustment and collapse protection. At the same time, the poly N-isopropylacrylamide hydrogel forms a temperature-sensitive functional film in the concrete, further improving the fluidity of the concrete after the temperature rises, making the concrete have high collapse protection, and ensuring the quality of concrete in the ultra-long pumping concrete scene.

[0029] Furthermore, nano-silica (filling and compacting effect) and carbon nanotubes (conductive dispersion effect) improve the dispersion stability of concrete particles; zwitterionic monomers (8:1:1 ratio) neutralize the anionic groups of residual flocculants on the surface of machine-made sand through positive and negative charges. The three synergistically reduce the probability of flocculant adsorption and enhance anti-flocculation ability. In addition, the positive and negative charges in zwitterionic monomers can combine with water molecules through electrostatic action, further improving water solubility.

[0030] Furthermore, methacryloyloxyethyltrimethylammonium chloride (cation) directly neutralizes the anionic flocculant, and sulfobetaine (zwitterion) prevents the flocculant from combining with cement particles through the charge shielding effect. The dual mechanism improves the adaptability to artificial sand containing flocculants.

[0031] Furthermore, the ammonium persulfate-ascorbic acid redox initiation system (5%+2% concentration, 1:1 molar ratio) achieves low-temperature controllable polymerization, avoids molecular chain breakage caused by high-temperature initiation, ensures the integrity of the temperature-sensitive group (NIPAM) in the molecular structure of the water reducer, and maintains the stability of the slump-retaining performance at high temperatures. In addition, when the ammonium persulfate concentration is <4%, the initiation rate is insufficient and the polymerization reaction is incomplete. When the concentration is >6%, the excess free radicals cause the chain to terminate too quickly and the molecular weight distribution becomes broad. When the ascorbic acid concentration is <1%, the reduction reaction rate is low and the initiation efficiency decreases; when it is >3%, the residual ascorbic acid interferes with the slump performance of the water reducer.

[0032] Furthermore, in the chain transfer agent, the carboxylic acid group (-COOH) of mercaptopropionic acid can partially neutralize the positive charge of the residual flocculant in the machine-made sand, weakening its electrostatic adsorption with cement particles; the hydrophobic side chain (isooctyl) of 3-mercaptopropionate can be embedded in the interlayer of clay particles, blocking the hydrogen bonding between the flocculant molecules and the clay hydroxyl groups through hydrophobic action.

[0033] Furthermore, an ultrasonic frequency of 35kHz can break soft agglomerates (nano-silica), and 45kHz is suitable for hard agglomerates (carbon nanotubes). The ultrasonic frequency within this range can cover the dispersion requirements of different nanomaterials; when the ultrasonic time is <25min, the nanomaterials are dispersed unevenly, and when it is >35min, the ultrasonic cavitation effect causes the polymer chains to break.

[0034] The present application also provides a method for preparing the above-mentioned concrete polycarboxylate water-reducing agent. First, a main chain adsorption group (phosphate) is first constructed by staged temperature-controlled polymerization (50°C→65°C), and then a temperature-sensitive monomer (NIPAM) is introduced to ensure that the functional groups are arranged in an orderly manner; secondly, ultrasonic treatment is performed to break the particle agglomeration of nano-silica and carbon nanotubes, improve their dispersion in the polymer, and enhance the physical barrier effect on the residual flocculant; thirdly, ascorbic acid is added later to ensure that the residual monomers are completely polymerized to avoid abnormal coagulation caused by unreacted monomers in concrete; finally, the pH is precisely controlled (6.9-7.2) to match the cement hydration environment and prevent acid-base fluctuations from destroying the molecular conformation of the water-reducing agent. In summary, the triple effects of phosphate groups (competitive adsorption), zwitterions (charge neutralization) and nanomaterials (physical barrier) enable the water reducer to maintain a good dispersion efficiency in the machine-made sand with residual flocculants; the temperature-sensitive group of N-isopropylacrylamide dynamically adjusts the fluid viscosity, so that the slump loss rate of concrete at a stirring temperature of 35-45°C is less than 10% in 2 hours, far exceeding the traditional water reducer (usually >30%). In addition, it is very necessary to use deionized water to dissolve isopentenyl polyoxyethylene ether and carbon nanotubes. Deionized water is still an irreplaceable optimal medium due to its purity, low cost and reaction compatibility. Its purity (conductivity <1μS / cm) can ensure that the TPEG molecular chain is fully extended and the nano-silica is stably dispersed. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0036] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0037] Herein, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0038] In this document, unless otherwise specified, “includes,” “including,” “contains,” “has,” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0039] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0040] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0041] The following examples use conventional instruments and equipment in the art. The experimental methods in the following examples where specific conditions are not specified are usually carried out under conventional conditions or under conditions recommended by the manufacturer. The various raw materials used in the following examples are conventional commercial products unless otherwise specified, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" means weight percentage, "part" means weight part, and ratio means weight ratio.

[0042] Example 1

[0043] A high-slump-retaining, anti-flocculation concrete polycarboxylate water-reducing agent, the raw materials of which include, by weight: 45 parts of isopentenyl polyoxyethylene ether TPEG 2400, 3 parts of methacrylate phosphate MAP, 8 parts of hydroxyethyl acrylate HEA, 4 parts of N-isopropylacrylamide NIPAM, 10 parts of auxiliary monomers, 8 parts of initiators and 0.3 parts of chain transfer agents, wherein the auxiliary monomers are nano-silicon dioxide, carbon nanotubes and zwitterionic monomers AMPS, and the weight ratio of nano-silicon dioxide, carbon nanotubes and zwitterionic monomers AMPS is 1:1:8;

[0044] The zwitterionic monomer AMPS is methacryloyloxyethyl trimethyl ammonium chloride, wherein the structural formula of methacryloyloxyethyl trimethyl ammonium chloride DMC is:

[0045] CH 2 =C(CH 3 )COOCH 2 CH 2 N+(CH 3 ) 3 Cl;

[0046] The initiator is a 5% by mass ammonium persulfate APS aqueous solution and a 2% by mass ascorbic acid Vc aqueous solution;

[0047] The molar ratio of the 5% ammonium persulfate APS aqueous solution to the 2% ascorbic acid Vc aqueous solution is 1:1.

[0048] The chain transfer agent is mercaptopropionic acid.

[0049] The raw materials are weighed according to the above mass fractions. The preparation method of concrete polycarboxylate water reducer specifically comprises the following steps:

[0050] Step 1: Mix isopentenyl polyoxyethylene ether with deionized water to ensure that the solid content is 40%, add nano-silicon dioxide, and perform 35kHz ultrasonic treatment for 27 minutes;

[0051] Step 2: After the isopentyl polyoxyethylene ether is heated to 35° C., a 5% ammonium persulfate aqueous solution is added dropwise at 1 mL / min for 0.1 h. After the temperature is raised to 50° C., methacrylic acid phosphate and hydroxyethyl acrylate are simultaneously added dropwise at 2 mL / min for 0.5 h. After the addition of methacrylic acid phosphate and hydroxyethyl acrylate is completed, the temperature is raised to 60° C. to obtain a solution to be polymerized;

[0052] Step 3: Add carbon nanotubes into deionized water, and obtain a carbon nanotube suspension after ultrasonic treatment at 45kHz for 27min. Add the carbon nanotube suspension, methacryloyloxyethyl trimethylammonium chloride and N-isopropylacrylamide into the solution to be polymerized, add mercaptopropionic acid, stir at 60°C for 3 hours, and then add 2% ascorbic acid aqueous solution;

[0053] Step 4: Add 30% sodium hydroxide to adjust the pH to 6.9, and after cooling, obtain the water reducing agent finished product 1.

[0054] Example 2

[0055] A high-slump-retaining, anti-flocculation concrete polycarboxylate water-reducing agent, the raw materials of which include, by weight: 240047 parts of isopentenyl polyoxyethylene ether TPEG, 4 parts of methacrylate phosphate MAP, 10 parts of hydroxyethyl acrylate HEA, 5 parts of N-isopropylacrylamide NIPAM, 11 parts of auxiliary monomers, 10 parts of initiators and 0.4 parts of chain transfer agents, wherein the auxiliary monomers are nano-silicon dioxide, carbon nanotubes and zwitterionic monomers AMPS, and the weight ratio of nano-silicon dioxide, carbon nanotubes and zwitterionic monomers AMPS is 1:1:8;

[0056] The zwitterionic monomer AMPS is sulfobetaine, wherein the structural formula of sulfobetaine SBMA is:

[0057] CH 3 (CH 2 )nN+(CH 3 ) 2 (CH 2 )mSO 3

[0058] Wherein, n is the length of the alkyl chain, which is between 7 and 17, and m is the number of methylene groups connecting the N atom and the S atom, and m≥2.

[0059] The initiator is a 5% by mass ammonium persulfate APS aqueous solution and a 2% by mass ascorbic acid Vc aqueous solution;

[0060] The molar ratio of the 5% ammonium persulfate APS aqueous solution to the 2% ascorbic acid Vc aqueous solution is 1:1.

[0061] The chain transfer agent is isooctyl 3-mercaptopropionate.

[0062] The raw materials are weighed according to the above mass fractions. The preparation method of concrete polycarboxylate water reducer specifically comprises the following steps:

[0063] Step 1: Mix isopentenyl polyoxyethylene ether with deionized water to ensure that the solid content is 40%, add nano-silicon dioxide, and perform 35kHz ultrasonic treatment for 30 minutes;

[0064] Step 2: After the isopentyl polyoxyethylene ether is heated to 35° C., a 4% ammonium persulfate aqueous solution is added dropwise at 1 mL / min for 0.3 h. After the temperature is raised to 52° C., methacrylic acid phosphate and hydroxyethyl acrylate are simultaneously added dropwise at 2 mL / min for 1 h. After the addition of methacrylic acid phosphate and hydroxyethyl acrylate is completed, the temperature is raised to 62° C. to obtain a solution to be polymerized;

[0065] Step 3: Add carbon nanotubes to deionized water, and perform ultrasonic treatment at 45kHz for 30 minutes to obtain a carbon nanotube suspension. Add the carbon nanotube suspension, sulfobetaine and N-isopropylacrylamide to the solution to be polymerized, add isooctyl 3-mercaptopropionate, stir at 62°C for 3.5 hours, and then add 1% ascorbic acid aqueous solution;

[0066] Step 4: Add 30% sodium hydroxide to adjust the pH to 7.0, and after cooling, obtain the water reducing agent finished product 2.

[0067] Example 3

[0068] A high-slump-retaining, anti-flocculation concrete polycarboxylate water-reducing agent, the raw materials of which include, by weight: 51 parts of isopentenyl polyoxyethylene ether TPEG2400, 5 parts of methacrylate phosphate MAP, 9 parts of hydroxyethyl acrylate HEA, 6 parts of N-isopropylacrylamide NIPAM, 12 parts of auxiliary monomers, 9 parts of initiators and 0.5 parts of chain transfer agents, wherein the auxiliary monomers are nano-silicon dioxide, carbon nanotubes and zwitterionic monomers AMPS, and the weight ratio of nano-silicon dioxide, carbon nanotubes and zwitterionic monomers AMPS is 1:1:8;

[0069] The zwitterionic monomer AMPS is methacryloyloxyethyl trimethyl ammonium chloride, and the structural formula of methacryloyloxyethyl trimethyl ammonium chloride DMC is:

[0070] CH 2 =C(CH 3 )COOCH 2 CH 2 N+(CH 3 ) 3 Cl;

[0071] The initiator is a 5% by mass ammonium persulfate APS aqueous solution and a 2% by mass ascorbic acid Vc aqueous solution;

[0072] The molar ratio of the 5% ammonium persulfate APS aqueous solution to the 2% ascorbic acid Vc aqueous solution is 1:1.

[0073] The chain transfer agent is mercaptopropionic acid.

[0074] The raw materials are weighed according to the above mass fractions. The preparation method of concrete polycarboxylate water reducer specifically comprises the following steps:

[0075] Step 1: Mix isopentenyl polyoxyethylene ether with deionized water to ensure that the solid content is 40%, add nano-silicon dioxide, and perform 35kHz ultrasonic treatment for 25 minutes;

[0076] Step 2: After the isopentyl polyoxyethylene ether is heated to 35° C., a 6% ammonium persulfate aqueous solution is added dropwise at 1 mL / min for 0.5 h. After the temperature is raised to 55° C., methacrylate phosphate and hydroxyethyl acrylate are simultaneously added dropwise at 2 mL / min for 1.5 h. After the addition of methacrylate phosphate and hydroxyethyl acrylate is completed, the temperature is raised to 65° C. to obtain a solution to be polymerized;

[0077] Step 3: Add carbon nanotubes to deionized water, and obtain a carbon nanotube suspension after ultrasonic treatment at 45kHz for 25 minutes. Add the carbon nanotube suspension, methacryloyloxyethyl trimethylammonium chloride and N-isopropylacrylamide to the solution to be polymerized, add mercaptopropionic acid, stir at 65°C for 4 hours, and then add 3% ascorbic acid aqueous solution;

[0078] Step 4: Add 30% sodium hydroxide to adjust the pH to 7.2, and after cooling, obtain the water reducing agent finished product 3.

[0079] Example 4

[0080] A high-slump-retaining, anti-flocculation concrete polycarboxylate water-reducing agent, the raw materials of which include, by weight: 53 parts of isopentenyl polyoxyethylene ether TPEG 2400, 6 parts of methacrylate phosphate MAP, 11 parts of hydroxyethyl acrylate HEA, 6 parts of N-isopropylacrylamide NIPAM, 14 parts of auxiliary monomers, 11 parts of initiators and 0.5 parts of chain transfer agents, wherein the auxiliary monomers are nano-silicon dioxide, carbon nanotubes and zwitterionic monomers AMPS, and the weight ratio of nano-silicon dioxide, carbon nanotubes and zwitterionic monomers AMPS is 1:1:8;

[0081] The zwitterionic monomer AMPS is methacryloyloxyethyl trimethyl ammonium chloride, wherein the structural formula of methacryloyloxyethyl trimethyl ammonium chloride DMC is:

[0082] CH 2 =C(CH 3 )COOCH 2 CH 2 N+(CH 3 ) 3 Cl;

[0083] The initiator is a 5% by mass ammonium persulfate APS aqueous solution and a 2% by mass ascorbic acid Vc aqueous solution;

[0084] The molar ratio of the 5% ammonium persulfate APS aqueous solution to the 2% ascorbic acid Vc aqueous solution is 1:1.

[0085] The chain transfer agent is mercaptopropionic acid.

[0086] The raw materials are weighed according to the above mass fractions. The preparation method of concrete polycarboxylate water reducer specifically comprises the following steps:

[0087] Step 1, mixing isopentenyl polyoxyethylene ether with deionized water to ensure a solid content of 40%, adding nano-silicon dioxide, and performing 40kHz ultrasonic treatment for 30 minutes;

[0088] Step 2: After the isopentyl polyoxyethylene ether is heated to 35° C., a 5% aqueous solution of ammonium persulfate is added dropwise at 1 mL / min for 0.1 h. After the temperature is raised to 50° C., methacrylic acid phosphate and hydroxyethyl acrylate are simultaneously added dropwise at 2 mL / min for 0.5 h. After the addition of methacrylic acid phosphate and hydroxyethyl acrylate is completed, the temperature is raised to 60° C. to obtain a solution to be polymerized;

[0089] Step 3: Add carbon nanotubes into deionized water, and obtain a carbon nanotube suspension after ultrasonic treatment at 45kHz for 30min. Add the carbon nanotube suspension, methacryloyloxyethyl trimethylammonium chloride and N-isopropylacrylamide into the solution to be polymerized, add mercaptopropionic acid, stir for 3h at 60°C, and then add 2% ascorbic acid aqueous solution;

[0090] Step 4: Add 30% sodium hydroxide to adjust the pH to 6.9, and after cooling, obtain the water reducing agent finished product 4.

[0091] Example 5

[0092] A high-slump-retaining, anti-flocculation concrete polycarboxylate water-reducing agent, the raw materials of which include, by weight: 55 parts of isopentyl polyoxyethylene ether TPEG 2400, 8 parts of methacrylate phosphate MAP, 12 parts of hydroxyethyl acrylate HEA, 7 parts of N-isopropylacrylamide NIPAM, 15 parts of auxiliary monomers, 12 parts of initiators and 0.6 parts of chain transfer agents, wherein the auxiliary monomers are nano-silicon dioxide, carbon nanotubes and zwitterionic monomers AMPS, and the weight ratio of nano-silicon dioxide, carbon nanotubes and zwitterionic monomers AMPS is 1:1:8;

[0093] The zwitterionic monomer AMPS is methacryloyloxyethyl trimethyl ammonium chloride, wherein the structural formula of methacryloyloxyethyl trimethyl ammonium chloride DMC is:

[0094] CH 2 =C(CH 3 )COOCH 2 CH 2 N+(CH 3 ) 3 Cl;

[0095] The initiator is a 5% by mass ammonium persulfate APS aqueous solution and a 2% by mass ascorbic acid Vc aqueous solution;

[0096] The molar ratio of the 5% ammonium persulfate APS aqueous solution to the 2% ascorbic acid Vc aqueous solution is 1:1.

[0097] The chain transfer agent is mercaptopropionic acid.

[0098] The raw materials are weighed according to the above mass fractions. The preparation method of concrete polycarboxylate water reducer specifically comprises the following steps:

[0099] Step 1, mixing isopentenyl polyoxyethylene ether with deionized water to ensure a solid content of 40%, adding nano-silicon dioxide, and performing 40kHz ultrasonic treatment for 30 minutes;

[0100] Step 2: After the isopentyl polyoxyethylene ether is heated to 35° C., a 5% aqueous solution of ammonium persulfate is added dropwise at 1 mL / min for 0.1 h. After the temperature is raised to 50° C., methacrylic acid phosphate and hydroxyethyl acrylate are simultaneously added dropwise at 2 mL / min for 0.5 h. After the addition of methacrylic acid phosphate and hydroxyethyl acrylate is completed, the temperature is raised to 60° C. to obtain a solution to be polymerized;

[0101] Step 3: Add carbon nanotubes into deionized water, and obtain a carbon nanotube suspension after ultrasonic treatment at 45kHz for 30min. Add the carbon nanotube suspension, methacryloyloxyethyl trimethylammonium chloride and N-isopropylacrylamide into the solution to be polymerized, add mercaptopropionic acid, stir for 3h at 60°C, and then add 2% ascorbic acid aqueous solution;

[0102] Step 4: Add 30% sodium hydroxide to adjust the pH to 6.9, and after cooling, obtain the finished water reducing agent 5.

[0103] Comparative Example 1

[0104] The anti-flocculating water-reducing agent is prepared by the preparation method of Example 2 of the Chinese patent application document "A preparation method of an anti-flocculating amphoteric polycarboxylic acid water-reducing agent (publication number: CN115594804 A)".

[0105] Comparative Example 2

[0106] The super-long slump-retaining water-reducing agent is prepared by the preparation method of Example 5 of the Chinese patent application document "A super-long slump-retaining polycarboxylic acid water-reducing agent and its preparation method (publication number: CN118307231 A)".

[0107] According to the component ratios of the concrete polycarboxylate water reducer proposed in the above-mentioned Examples 1 to 5, the concrete polycarboxylate water reducer was prepared, and the finished concrete polycarboxylate water reducer products corresponding to Examples 1 to 5 were obtained, which were respectively recorded as Finished Product 1, Finished Product 2, Finished Product 3, Finished Product 4 and Finished Product 5.

[0108] As a detailed description, N-isopropylacrylamide NIPAM is polymerized to obtain poly-N-isopropylacrylamide hydrogel PNIPAM, whose lower critical solution temperature LCST is 32°C.

[0109] Under low temperature conditions, that is, below the lower critical solution temperature LCST, the PNIPAM chain is hydrophilic, the molecular chain stretches, combines with water molecules through hydrogen bonds, and then adsorbs on the surface of cement particles, enhancing dispersibility and increasing the steric hindrance effect of the water reducer, thereby improving the fluidity of concrete.

[0110] Under high temperature conditions, that is, greater than the lower critical solution temperature LCST, hydrogen bonds are destroyed, hydrophobic isopropyl groups are exposed, PNIPAM segments dehydrate and shrink, and turn into a hydrophobic state, releasing the encapsulated water. At the same time, the conformation of the polymer is triggered to change, dynamically adjusting the adsorption behavior of the water reducer molecules on the surface of cement particles, offsetting the slump loss caused by the temperature increase.

[0111] The dynamic slump adjustment mechanism of PNIPAM includes:

[0112] When the temperature rises: the PNIPAM chain shrinks, accelerating the hydrolysis of the ester bond of the polycarboxylic acid main chain, releasing more carboxylic acid groups -COOH, enhancing the dispersibility of cement particles, and compensating for the slump loss caused by high temperature;

[0113] When the temperature drops: the PNIPAM chains re-extend and adsorb free water through hydrogen bonds, reducing the risk of water bleeding, while delaying the dispersion effect of the water reducer and avoiding excessive flow.

[0114] When the mud content of sand and gravel is greater than 2%, the dosage of finished product 1, finished product 2, finished product 3, finished product 4 and finished product 5 is 1.2%;

[0115] On the contrary, when the mud content of sand and gravel is less than 2%, the usage of finished product 1, finished product 2, finished product 3, finished product 4 and finished product 5 is 0.8%.

[0116] After adding finished product 1, finished product 2, finished product 3, finished product 4 and finished product 5 to concrete according to the above method, samples 1, sample 2, sample 3, sample 4 and sample 5 are obtained, and according to the water reducing agent provided in comparative example 1 and comparative example 2, comparative sample 1 and comparative sample 2 are obtained. According to the provisions of the "Standard for Test Methods for Performance of Ordinary Concrete Mixtures" GB / T 50080-2016, the slump tests of sample 1, sample 2, sample 3, sample 4, sample 5, comparative sample 1 and comparative sample 2 are carried out. The test results are as follows:

[0117] As shown in Table 1:

[0118] Initial slump 1h slump 2h slump Workability Sample 1 240mm 238mm 235mm good Sample 2 247mm 246mm 239mm good Sample 3 251mm 248mm 241mm better Sample 4 253mm 249mm 248mm better Sample 5 261mm 258mm 252mm better Comparison sample 1 247mm 237mm 198mm good Comparison sample 2 230mm 217mm 205mm good

[0119] Table 1

[0120] According to Table 1, it can be seen that the finished products obtained by using Examples 1 to 5 provided by the present invention, when put into use, the initial slump of the corresponding samples 1 to 5 is better than that of the comparative sample 1 and the comparative sample 2, and the slump in 1h and 2h are better than that of the comparative sample 1 and the comparative sample 2. At the same time, the slump change over time is relatively small, that is, the concrete polycarboxylate water-reducing agent prepared according to the present invention can maintain a good slump for a long time. Combined with the workability analysis, it can be seen that the concrete polycarboxylate water-reducing agent prepared by the present invention can provide concrete with more excellent high slump retention.

[0121] In order to determine the effect of ambient temperature on the slump of concrete with polycarboxylate water-reducing agent added, three equal portions of concrete were taken from sample 1 and the slump was tested at different ambient temperatures. The results are shown in Table 2:

[0122] Ambient temperature Initial slump 2h slump Loss Rate 25℃ 240mm 235mm 2.1％ 35℃ 245mm 230mm 6.1％ 45℃ 238mm 225mm 5.5％

[0123] Table 2

[0124] It can be seen from Table 2 that when the ambient temperature is 35°C, PNIPAM breaks through the LCST, and its initial slump is higher than the initial slump corresponding to 25°C, and at 45°C, the initial slump and the 2h slump are both close to the slump at an ambient temperature of 25°C, indicating that under a higher temperature environment, the concrete polycarboxylate water-reducing agent provided by the present invention can still provide a high slump-retaining effect for concrete. According to this characteristic, the concrete to which the concrete polycarboxylate water-reducing agent provided by the present invention is added can effectively adapt to an ultra-long pumping environment, that is, concrete with a conveying distance greater than 500m, and can provide good fluidity and anti-flocculation for this purpose, thereby ensuring the use quality of the concrete.

[0125] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A high slump retention and anti-flocculation concrete polycarboxylate water reducer, characterized in that: The raw materials include by weight: 45-55 parts of isopentyl polyoxyethylene ether, 3-8 parts of methacrylate phosphate, 8-12 parts of hydroxyethyl acrylate, 4-7 parts of N-isopropylacrylamide, 10-15 parts of auxiliary monomers, 8-12 parts of initiators and 0.3-0.6 parts of chain transfer agents.

2. A high slump retention, anti-flocculation concrete polycarboxylate water reducer according to claim 1, characterized in that: The auxiliary monomer comprises a mixture of nano-silicon dioxide, carbon nanotubes and zwitterionic monomers, and the mass ratio of the nano-silicon dioxide, carbon nanotubes and zwitterionic monomers is 1:1:

8.

3. A high slump retention, anti-flocculation concrete polycarboxylate water reducer according to claim 2, characterized in that: The zwitterionic monomer includes methacryloyloxyethyltrimethylammonium chloride or sulfobetaine.

4. A high slump retention, anti-flocculation concrete polycarboxylate water reducer according to claim 1, characterized in that: The initiator comprises a mixed solution of an ammonium persulfate aqueous solution and an ascorbic acid aqueous solution, wherein the molar ratio of the ammonium persulfate aqueous solution to the ascorbic acid aqueous solution is 1:

1.

5. A high slump retention, anti-flocculation concrete polycarboxylate water reducer according to claim 4, characterized in that: The mass fraction of the ammonium persulfate aqueous solution is 4%-6%, and the mass fraction of the ascorbic acid aqueous solution is 1%-3%.

6. A high slump retention, anti-flocculation concrete polycarboxylate water reducer according to claim 1, characterized in that: The chain transfer agent includes mercaptopropionic acid or isooctyl 3-mercaptopropionate.

7. The high slump retention and anti-flocculation concrete polycarboxylate water reducer according to claim 1, characterized in that: The chain transfer agent is mercaptopropionic acid.

8. The method for preparing the high slump retention and anti-flocculation concrete polycarboxylate water-reducing agent according to any one of claims 1 to 7, characterized in that: The following steps are involved: Weigh the raw materials according to the mass fractions, mix the isopentenyl polyoxyethylene ether with deionized water, then add nano-silicon dioxide, and perform ultrasonic treatment; After heating the isopentenyl polyoxyethylene ether, an aqueous solution of ammonium persulfate is added for reaction, and after the temperature is raised to 50°C-55°C, methacrylic acid phosphate and hydroxyethyl acrylate are added simultaneously, and then the temperature is raised to 60°C-65°C to obtain a solution to be polymerized; Add carbon nanotubes to deionized water, perform ultrasonic treatment to obtain a carbon nanotube suspension, add the carbon nanotube suspension, zwitterionic monomer and N-isopropylacrylamide to the solution to be polymerized, add a chain transfer agent, stir for 3-4 hours in an environment of 60° C.-65° C., and then add an ascorbic acid aqueous solution; Adjust the pH value to 6.9-7.2, and after cooling, obtain the water reducing agent.

9. The method for preparing a concrete polycarboxylate water-reducing agent according to claim 8, characterized in that: The ultrasonic frequency is 35-45 Hz, and the ultrasonic time is 25-30 min.

10. The method for preparing a concrete polycarboxylate water-reducing agent according to claim 8, characterized in that: The pH was adjusted with sodium hydroxide.