Polycarboxylic viscosity reducer, its preparation method and use

Abstract

The application belongs to the technical field of concrete admixtures, and discloses a polycarboxylic acid viscosity reducer, a preparation method and application thereof. First, an unsaturated phosphate ester mixture is synthesized by using an unsaturated alcohol or ester, an inhibitor and phosphorus pentoxide; second, a reducing agent, a chain transfer agent I, an unsaturated acid or ester, an organosilane monomer, a crosslinking agent and water are prepared into different dropping solutions according to a specific combination; then, the unsaturated phosphate ester mixture, an unsaturated polyoxyethylene ether, an unsaturated small monomer, a chain transfer agent II and water are mixed, an initiator is added after being dissolved by heating, the above solutions are added dropwise according to a specific procedure, and the polycarboxylic acid viscosity reducer is obtained by keeping warm, curing and adjusting the solid content. The polycarboxylic acid viscosity reducer containing phosphate groups and organosilane groups and synthesized by molecular structure design can effectively reduce the viscosity of super-high performance concrete under the condition of a small amount of addition, and can be applied to super-high performance concrete with a water-binder ratio of less than or equal to 0.14.

Description

Technical Field

[0001] This invention belongs to the field of concrete admixture technology, specifically relating to a polycarboxylate viscosity reducer, its preparation method, and its application. Background Technology

[0002] The main raw materials of ultra-high performance concrete (UHVPC) are cementitious materials, silica fume, polycarboxylate thickeners, fine aggregates, and steel fibers. Based on the theory of close-packed particles, UHVPC is formulated with components that fill each other, significantly reducing pore size and porosity under extremely low water-cement ratio conditions. Simultaneously, the incorporated silica fume and other mineral admixtures are active ingredients that can form hydrated calcium silicate with calcium hydroxide, resulting in extremely high internal density. This leads to ultra-high strength, high durability, excellent ductility, superior wear resistance, and excellent corrosion and chemical resistance. Therefore, UHVPC has enormous application potential in steel bridge deck paving, steel-concrete composite beams, prefabricated connections for assembled bridges, building curtain walls, prefabricated buildings, maintenance and reinforcement, and impact and abrasion resistance, offering socio-economic and environmental benefits that ordinary concrete cannot achieve.

[0003] Silica fume is the most difficult component to disperse in ultra-high performance concrete (UHVPC), and ordinary polycarboxylate viscosity reducers are ineffective at dispersing it. Furthermore, UHVPC has an extremely low water-cement ratio, leading to a significant increase in the amount of polycarboxylate viscosity reducer required. However, the actual adsorption rate is low, resulting in a reduced thickness of the water film layer between slurry particles and increased residual viscosity reducer in pore liquid. This results in high viscosity of the UHVPC slurry, which gradually increases with the amount of polycarboxylate viscosity reducer used. Higher slurry viscosity makes it easier for steel fibers to disperse unevenly during mixing, requiring large-scale specialized mixing equipment. These conditions are difficult to meet in on-site casting, therefore, UHVPC often needs to be prefabricated in a factory.

[0004] Currently, commercially available industrial-grade ultra-high performance concrete (UHVPC) precast components typically have a water-cement ratio ≥0.18. This water-cement ratio limitation restricts the strength and related durability of UHVPC to meet the requirements of certain specific projects. Developing a viscosity reducer suitable for even lower water-cement ratios would allow for the production of UHVPC with excellent workability without increasing the dosage. Further reducing the water-cement ratio would not only significantly improve the density and strength of UHVPC but also substantially enhance its corrosion resistance and abrasion resistance, greatly expanding its application areas and enabling it to play a more powerful role. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology by providing a polycarboxylic acid viscosity reducer, its preparation method and application. Through molecular structure design, a micro-crosslinked polycarboxylic acid viscosity reducer containing phosphate groups and organosilicon alkyl groups is synthesized, which can effectively reduce the viscosity of ultra-high performance concrete under low dosage conditions and is applicable to ultra-high performance concrete with a water-cement ratio ≤0.14.

[0006] To address the technical problem proposed in this invention, this invention provides a method for preparing a polycarboxylate viscosity reducer, comprising the following steps:

[0007] 1) Under stirring conditions, unsaturated alcohols or esters are first mixed with polymerization inhibitors, then phosphorus pentoxide is added, the temperature is raised and kept at the temperature for reaction, and after the reaction is completed, the mixture is cooled to room temperature to obtain a mixture of unsaturated phosphate esters.

[0008] 2) Mix the reducing agent, chain transfer agent I, and water to obtain solution A; mix the unsaturated acid or ester with the organosilane monomer and water to obtain solution B; mix the crosslinking agent with water to obtain solution C;

[0009] 3) Mix the unsaturated phosphate ester mixture, unsaturated polyoxyethylene ether, unsaturated monomer, chain transfer agent II and water, heat to a certain temperature, and stir until completely dissolved to obtain solution D;

[0010] 4) Maintain a certain temperature and stirring conditions, add initiator to solution D, stir, and then start adding solution A and solution B dropwise. After solution A is added, raise the temperature to the second stage temperature and start adding solution C dropwise. After solutions B and C are added, keep warm and mature.

[0011] 5) After the curing process is complete, water is added to adjust the solid content to obtain the polycarboxylic acid viscosity reducer.

[0012] In the above scheme, the unsaturated alcohol or ester is one or more of isopentenol, methyl allyl alcohol, hydroxypropyl methacrylate, hydroxyethyl acrylate, and hydroxypropyl acrylate; isopentenol is preferred.

[0013] In the above scheme, the polymerization inhibitor is one or more of hydroquinone, p-hydroxyanisole, and phenothiazine; hydroquinone is preferred.

[0014] In the above scheme, in step 1), the molar ratio of unsaturated alcohol or ester, polymerization inhibitor, and phosphorus pentoxide is (1.5-2.4):(0.0005-0.001):1.

[0015] In the above scheme, in step 1), the temperature is controlled below 25℃ before heating.

[0016] In the above scheme, in step 1), the heating temperature is 60-70℃ and the holding time is 2-3 hours.

[0017] In the above scheme, the unsaturated phosphate ester mixture obtained in step 1) is a mixture of unsaturated phosphate monoesters and diesters, with unsaturated phosphate monoesters as the main product.

[0018] Furthermore, the molecular structural formulas of the unsaturated phosphate monoester and diester are as follows:

[0019] Unsaturated phosphate monoesters: Unsaturated phosphate diester:

[0020] In the formula, R is selected from

[0021] One of them.

[0022] In the above scheme, the reducing agent is one or more of sodium formaldehyde sulfoxylate, modified sodium formaldehyde sulfoxylate, ascorbic acid, sodium bisulfite, and ferrous sulfate; sodium formaldehyde sulfoxylate is preferred.

[0023] In the above scheme, the chain transfer agent I is one or more of mercaptopropionic acid, mercaptoacetic acid, and mercaptoethanol; mercaptoacetic acid is preferred.

[0024] In the above scheme, the mass fractions of each raw material in solution A are as follows: reducing agent 1-3.5 parts, chain transfer agent I 15-22.2 parts, and water 60 parts.

[0025] In the above scheme, the unsaturated acid or ester is one or more of acrylic acid, methacrylic acid, butyl acrylate, and hydroxyethyl acrylate; preferably methacrylic acid.

[0026] In the above scheme, the organosilane monomer is one or more of γ-(methacryloyloxy)propyltrimethoxysilane and vinyltriethoxysilane; vinyltriethoxysilane is preferred.

[0027] In the above scheme, the mass fractions of each raw material in solution B are as follows: 50-60 parts of unsaturated acid or ester, 17.5-24 parts of organosilane monomer, and 80 parts of water.

[0028] In the above scheme, the crosslinking agent is one or more of ethylene glycol dimethacrylate and polyethylene glycol diacrylate; preferably polyethylene glycol diacrylate.

[0029] Furthermore, the molecular weight of polyethylene glycol diacrylate is 200–600.

[0030] In the above scheme, the mass fractions of each raw material in solution C are as follows: 8-16 parts of crosslinking agent and 24.3 parts of water.

[0031] In the above scheme, the unsaturated polyoxyethylene ether is one or more of methyl allyl alcohol polyoxyethylene ether (HPEG), isopentenyl alcohol polyoxyethylene ether (TPEG), 4-hydroxybutyl vinyl ether (VPEG), and ethylene glycol monovinyl polyethylene glycol ether (EPEG); preferably methyl allyl alcohol polyoxyethylene ether.

[0032] In the above scheme, the molecular weight of the unsaturated polyoxyethylene ether is 1000-2400.

[0033] In the above scheme, the unsaturated monomer is one or more of sodium p-styrene sulfonate, N,N-dimethylacrylamide, fumaric acid, acrylamide, acryloyloxyethyltrimethylammonium chloride, and dimethylamine methacrylate; preferably acrylamide.

[0034] In the above scheme, the chain transfer agent II is one or more of sodium methylpropenesulfonate, sodium allyl sulfonate, sodium 2-acrylamido-2-methylpropenesulfonate, and sodium hypophosphite; sodium hypophosphite is preferred.

[0035] In the above scheme, the temperature of the aforementioned section is 35-45℃.

[0036] In the above scheme, the initiator is one or more of hydrogen peroxide, ammonium persulfate, potassium persulfate, potassium hydrogen persulfate, and sodium persulfate; hydrogen peroxide is preferred.

[0037] In the above scheme, the mass fractions of each raw material in steps 3) to 4) are as follows: 10-23 parts of unsaturated phosphate ester mixture, 320-340 parts of unsaturated polyoxyethylene ether, 18-38 parts of unsaturated small monomer, 8-24 parts of chain transfer agent II, 13-23 parts of initiator, and 300 parts of water.

[0038] In the above scheme, after the initiator is added, the mixture is stirred for 5 to 10 minutes before the addition of solution A and solution B begins.

[0039] In the above scheme, solution A is added dropwise over 1.5 to 2 hours.

[0040] In the above scheme, when solution A is completely added, the number-average molecular weight Mn of the intermediate product is 10,000 to 14,000, and the polydispersity index PID is 1.35 to 1.5.

[0041] In the above scheme, the temperature of the two sections is 60-70℃.

[0042] In the above scheme, solution B is added dropwise over 2 to 2.5 hours.

[0043] In the above scheme, solution C is added dropwise over 0.5 to 1 hour.

[0044] In the above scheme, the ripening time is 0.5 to 1 hour.

[0045] In the above scheme, the solid content of the polycarboxylic acid viscosity reducer is 40-45%.

[0046] In the above scheme, the number-average molecular weight Mn of the polycarboxylic acid viscosity reducer is 16,000 to 20,000, and the polydispersity index (PID) is 1.2 to 1.3.

[0047] The present invention also provides a polycarboxylic acid viscosity reducer, which is prepared according to the above method.

[0048] The present invention also provides an application of polycarboxylate viscosity reducer in ultra-high performance concrete. The application method is as follows: during the mixing process of ultra-high performance concrete, the polycarboxylate viscosity reducer is added together with water and stirred.

[0049] In the above scheme, the dosage of the polycarboxylate viscosity reducer is 5-8‰ of the total mass of the ultra-high performance concrete cementitious material.

[0050] In the above scheme, the water-cement ratio of the ultra-high performance concrete is 0.13 to 0.14.

[0051] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0052] This invention synthesizes a micro-crosslinked polycarboxylic acid viscosity reducer containing phosphate groups and organosilicon alkyl groups through molecular structure design. This reducer can effectively lower the viscosity of ultra-high performance concrete under low dosage conditions and is applicable to ultra-high performance concrete with a water-cement ratio ≤0.14. Specifically:

[0053] 1) Grafting substances containing unsaturated double bonds and strongly electronegative phosphate groups onto the main chain improves the adsorption capacity of polycarboxylate viscosity reducer molecules for cement and silica fume, reduces the residual amount of polycarboxylate viscosity reducer in pore fluid, and lowers the viscosity of ultra-high performance concrete.

[0054] 2) When organosilanes containing unsaturated double bonds are grafted into the main chain, the siloxane groups on the side chain are prone to hydrolysis to produce silanol groups, which chemically bond with the silanol groups on the surface of silica fume. Since the strength of the chemical bond is much higher than the electrostatic adsorption of general polycarboxylate viscosity reducers, it can significantly increase the adsorption amount of polycarboxylate viscosity reducers on the surface of silica fume and significantly improve the dispersion effect on cement-silica fume slurry.

[0055] 3) Control the side chain length of polycarboxylate viscosity reducer and select unsaturated polyoxyethylene ether with a molecular weight of 1000-2400 to make its water film layer on the cement surface thinner, so as to release more free water for slurry flow.

[0056] 4) Controlling the molecular weight of the viscosity reducer to maintain a number average molecular weight below 20,000 ensures a smaller overall molecular weight, allowing for easier expansion in the slurry and increasing the degree of freedom of the polycarboxylate viscosity reducer within the slurry. Furthermore, introducing crosslinking monomers with double-bond symmetric structures bridges some small-molecule viscosity reducers that are insufficient to adsorb onto the cement surface due to their small molecular weight and limited number of electrostatic adsorption groups. This creates a small-molecule, micro-crosslinked polycarboxylate viscosity reducer, forming a new, effective small molecule that enhances its electrostatic adsorption capacity and increases its steric hindrance effect. Adding this to ultra-high performance concrete improves its workability and increases the utilization rate of ineffective small molecules. Detailed Implementation

[0057] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0058] Example 1

[0059] A method for preparing a polycarboxylic acid viscosity reducer includes the following steps:

[0060] 1) Take isopentenol and hydroquinone into a three-necked flask, start the stirrer, stir for 5 minutes, then add phosphorus pentoxide at room temperature (below 25℃). The molar ratio of isopentenol, hydroquinone and phosphorus pentoxide is 1.8:0.0006:1. After the addition is complete, quickly heat to 65℃, keep warm for 2 hours, stop stirring, and cool to room temperature to obtain a mixture of unsaturated phosphate esters.

[0061] 2) Mix 1.2 parts ascorbic acid, 15.2 parts mercaptoethanol and 60 parts water to obtain solution A; mix 45 parts acrylic acid, 7.1 parts hydroxyethyl acrylate, 19.6 parts vinyltriethoxysilane and 80 parts water to obtain solution B; mix 11.6 parts ethylene glycol dimethacrylate and 24.3 parts water to obtain solution C;

[0062] 3) Take 10 parts of unsaturated phosphate ester mixture, 320 parts of methyl allyl alcohol polyoxyethylene ether (molecular weight 1800), 19.5 parts of acryloyloxyethyl trimethylammonium chloride, 12 parts of sodium hypophosphite and 300 parts of water and put them into a four-necked flask. Start the stirrer and heat to 36°C. Stir until completely dissolved to obtain solution D.

[0063] 4) Maintain the temperature at 36℃ and stir continuously. Add 5.8 parts of hydrogen peroxide and 12.6 parts of sodium persulfate to solution D. After stirring for 5 minutes, start adding solutions A and B dropwise. Solution A is added dropwise after 1.5 hours. Immediately raise the temperature to 66℃ and start adding solution C dropwise. Solution C is added dropwise after 0.5 hours. Solution B is added dropwise after a total of 2 hours. Then keep warm and mature for 1 hour.

[0064] 5) After the curing process is complete, add water to adjust the solid content to 40.6% to obtain polycarboxylate viscosity reducer Q1.

[0065] The polycarboxylic acid viscosity reducer Q1 prepared in this invention is a mixture of R1 and R1-Y1-R1;

[0066] The structural formula for R1 is:

[0067]

[0068] In the formula, the ratio of a, b, c, d, e, and f is approximately 20:70:6:6:9:10, and n is 35 to 45.

[0069] The structural formula of Y1 is:

[0070]

[0071] In the formula, n is 1.

[0072] Example 2

[0073] A method for preparing a polycarboxylic acid viscosity reducer includes the following steps:

[0074] 1) Take hydroxypropyl methacrylate and hydroquinone and put them into a three-necked flask. Start the stirrer and stir for 5 minutes. Then add phosphorus pentoxide at room temperature (below 25°C). The molar ratio of hydroxypropyl methacrylate, hydroquinone and phosphorus pentoxide is 2.2:0.0008:1. After the addition is complete, quickly heat to 65°C and keep warm for 3 hours. Stop stirring and cool to room temperature to obtain a mixture of unsaturated phosphate esters.

[0075] 2) Mix 3.2 parts of sodium formaldehyde sulfoxylate, 17.2 parts of mercaptoacetic acid and 60 parts of water to obtain solution A; mix 57 parts of acrylic acid, 23.5 parts of vinyltriethoxysilane and 80 parts of water to obtain solution B; mix 16 parts of polyethylene glycol diacrylate (molecular weight 600) and 24.3 parts of water to obtain solution C;

[0076] 3) Take 16.2 parts of unsaturated phosphate ester mixture, 340 parts of methyl allyl alcohol polyoxyethylene ether (molecular weight 1800), 21 parts of N,N-dimethylacrylamide, 22 parts of sodium allyl sulfonate and 300 parts of water and put them into a four-necked flask. Start the stirrer and heat to 40°C. Stir until completely dissolved to obtain solution D.

[0077] 4) Maintain the temperature at 40℃ and stir continuously. Add 13.5 parts of hydrogen peroxide to solution D and stir for 8 minutes. Then start adding solution A and solution B dropwise. Solution A is added dropwise after 1.7 hours. Immediately raise the temperature to 70℃ and start adding solution C dropwise. Solution C is added dropwise after 0.5 hours. Solution B is added dropwise after a total of 2 hours. Then keep warm and mature for 1 hour.

[0078] 5) After the curing process is complete, add water to adjust the solid content to 45% to obtain polycarboxylate viscosity reducer Q2.

[0079] The polycarboxylic acid viscosity reducer Q2 prepared in this invention is a mixture of R2 and R2-Y2-R2;

[0080] The structural formula for R2 is:

[0081]

[0082] In the formula, the ratio of a, b, c, d, e, f is approximately 20:75:7:12:11:17, and n is 35 to 45.

[0083] The structural formula for Y2 is:

[0084]

[0085] In the formula, n is 6 to 10.

[0086] Example 3

[0087] A method for preparing a polycarboxylic acid viscosity reducer includes the following steps:

[0088] 1) Take methyl allyl alcohol and phenothiazine into a three-necked flask, start the stirrer, stir for 5 minutes, then add phosphorus pentoxide at room temperature (below 25℃). The molar ratio of methyl allyl alcohol, phenothiazine and phosphorus pentoxide is 2.4:0.0009:1. After the addition is complete, quickly heat to 70℃, keep warm for 2.5 hours, stop stirring, and cool to room temperature to obtain a mixture of unsaturated phosphate esters.

[0089] 2) Mix 3.5 parts of sodium formaldehyde sulfoxylate, 22.1 parts of mercaptopropionic acid, and 60 parts of water to obtain solution A; mix 59.9 parts of acrylic acid, 17.6 parts of γ-(methacryloyloxy)propyltrimethoxysilane, and 80 parts of water to obtain solution B; mix 13 parts of polyethylene glycol diacrylate (molecular weight 400) and 24.3 parts of water to obtain solution C;

[0090] 3) Take 12.5 parts of unsaturated phosphate ester mixture, 330 parts of isopentenyl alcohol polyoxyethylene ether (molecular weight 2400), 37 parts of acrylamide, 16 parts of sodium methacrylate sulfonate and 300 parts of water into a four-necked flask, start the stirrer and heat to 44°C, stir until completely dissolved to obtain solution D.

[0091] 4) Maintain the temperature at 44℃ and stir continuously. Add 15.5 parts of hydrogen peroxide to solution D and stir for 5 minutes. Then start adding solutions A and B dropwise. Solution A is added dropwise after 1.8 hours. Immediately raise the temperature to 70℃ and start adding solution C dropwise. Solution C is added dropwise after 1 hour. Solution B is added dropwise after a total of 2.5 hours. Then keep warm and mature for 0.5 hours.

[0092] 5) After the curing process is complete, water is added to adjust the solid content to 43.2% to obtain polycarboxylate viscosity reducer Q3.

[0093] The polycarboxylic acid viscosity reducer Q3 prepared in this invention is a mixture of R3 and R3-Y3-R3;

[0094] The structural formula for R3 is:

[0095]

[0096] In the formula, the ratio of a, b, c, d, e, f is approximately 20:103:8:11:9:49, and n is 45 to 55.

[0097] The structural formula for Y3 is:

[0098]

[0099] In the formula, n is 3 to 7.

[0100] Example 4

[0101] A method for preparing a polycarboxylic acid viscosity reducer includes the following steps:

[0102] 1) Add hydroxyethyl acrylate and hydroquinone to a three-necked flask, start the stirrer, stir for 5 minutes, then add phosphorus pentoxide at room temperature (below 25℃). The molar ratio of hydroxyethyl acrylate, hydroquinone and phosphorus pentoxide is 1.7:0.0006:1. After the addition is complete, quickly raise the temperature to 60℃, keep it at that temperature for 2.5 hours, stop stirring, and cool to room temperature to obtain an unsaturated phosphate ester mixture.

[0103] 2) Mix 2.7 parts of modified sodium formaldehyde sulfoxylate E51, 16.2 parts of mercaptoacetic acid, and 60 parts of water to obtain solution A; mix 55 parts of methacrylic acid, 23.4 parts of γ-(methacryloyloxy)propyltrimethoxysilane, and 80 parts of water to obtain solution B; mix 8.6 parts of polyethylene glycol diacrylate (molecular weight 200) and 24.3 parts of water to obtain solution C;

[0104] 3) Take 22 parts of unsaturated phosphate ester mixture, 325 parts of isopentenyl alcohol polyoxyethylene ether (molecular weight 1800), 16.5 parts of acrylamide, 13 parts of fumaric acid, 9 parts of sodium hypophosphite and 300 parts of water and put them into a four-necked flask. Start the stirrer and heat to 40°C. Stir until completely dissolved to obtain solution D.

[0105] 4) Maintain the temperature at 40℃ and stir continuously. Add 23 parts of ammonium persulfate to solution D. After stirring for 10 minutes, start adding solutions A and B dropwise. Solution A is added dropwise after 1.5 hours. Immediately raise the temperature to 70℃ and start adding solution C dropwise. Solution C is added dropwise after 0.5 hours. Solution B is added dropwise after a total of 2 hours. Then keep warm and mature for 1 hour.

[0106] 5) After the curing process is complete, add water to adjust the solid content to 42% to obtain polycarboxylate viscosity reducer Q4.

[0107] The polycarboxylic acid viscosity reducer Q4 prepared in this invention is a mixture of R4 and R4-Y4-R4;

[0108] The structural formula for R4 is:

[0109]

[0110] In the formula, the ratio of a, b, c, d, e, f is approximately 20:68:7:12:9:23, and n is 35 to 45.

[0111] The structural formula for Y4 is:

[0112]

[0113] In the formula, n is 1 to 4.

[0114] Comparative Example 1

[0115] Comparative Example 1 is the same as Example 1 in all other steps except that step 1) is not performed, so that the unsaturated phosphate ester mixture is not added in step 3).

[0116] Comparative Example 2

[0117] Comparative Example 2 is the same as Example 2 in all other steps, except that: solution C is not prepared in step 2), so solution C is not added in step 4).

[0118] Comparative Example 3

[0119] Comparative Example 3 is the same as Example 3 in all other steps, except that γ-(methacryloyloxy)propyltrimethoxysilane is not added when preparing solution B in step 2).

[0120] Comparative Example 4

[0121] Comparative Example 4 is the same as Example 4 in all other steps, except that the molecular weight of the isopentenyl alcohol polyoxyethylene ether added in step 3) is 3000.

[0122] Comparative Example 5

[0123] Comparative Example 5 is the same as Example 2 in all other steps, except that: in step 2), 10.5 parts of mercaptoacetic acid are added when preparing solution A; and solution C is not prepared in step 2), so solution C is not added in step 4).

[0124] Comparative Example 6

[0125] Comparative Example 6 is a commercially available polycarboxylate viscosity reducer.

[0126] Application examples

[0127] The polycarboxylate viscosity reducers in Examples 1-4 and Comparative Examples 1-6 were used to prepare ultra-high performance concrete.

[0128] The raw material composition of ultra-high performance concrete is: 668 kg / m³ of PO 52.5 cement. 3 Silica fume 170Kg / m 3 201 kg / m³ of fly ash 3 81 kg / m³ of ultrafine mineral powder 3 12.96 kg / m² of steel fiber 3 Quartz sand 1018Kg / m 3 Water 156.8Kg / m 3 Liquid defoamer 0.95Kg / m³ 3 The water-to-binder ratio is 0.14.

[0129] The specific preparation process is as follows: First, mix the polycarboxylate viscosity reducer, liquid defoamer, and water evenly to prepare a working solution for later use. Then, weigh out each powder of ultra-high performance concrete according to the set ratio and pour it into the mixing pot. Turn on the mortar mixer and slowly stir for 5 to 10 minutes. Then, slowly pour in the working solution while stirring, and pour it all in within 20 to 40 seconds. Keep stirring and wait until the powder in the pot has completely become a flowable slurry. Then, add steel fibers while stirring, and add them all in 0.5 to 1 minute. Continue stirring for 5 to 8 minutes and then remove the pot from the heat.

[0130] Performance testing

[0131] The intermediate and final products of the polymerization process in Examples 1-4 and Comparative Examples 1-5 of this invention were tested using gel permeation chromatography-differential refractive index detector-18-angle laser scattering instrument. The results were as follows: number average molecular weight Mn, weight average molecular weight Mw, polydispersity index (PID), percentage of the right shoulder area of ​​the right shoulder of the polycarboxylic acid viscosity reducer main peak with an elution time greater than 14.2 min (standard curve: when the retention time is 14.2 min, the corresponding PEG standard Mn 4100), i.e., the percentage of the right shoulder, and conversion rate of unsaturated polyoxyethylene ether. The test results are shown in Table 1.

[0132] Table 1. Detection results of intermediate and final products during polymerization.

[0133]

[0134] According to the test results in Table 1, in Examples 1-4 with added crosslinking agents, as well as Comparative Examples 1 and 3, the area of ​​the right shoulder of the main peak of the polycarboxylic acid viscosity reducer with an outflow time greater than 14.2 min was reduced by more than 5%. That is, the ineffective small molecule viscosity reducer with a number average molecular weight Mn of less than 4100 was transformed into an effective large molecule viscosity reducer through the bridging effect of the crosslinking agent.

[0135] The performance of the ultra-high performance concrete prepared for the corresponding use case was tested. The fluidity test was carried out in accordance with GB / T2419-2005 "Method for Determination of Flowability of Cement Mortar", the mechanical property test was carried out in accordance with GB / T 17671-2021 "Method for Testing the Strength of Cement Mortar (ISO Method)", and the Min-V funnel emptying time test was carried out in accordance with GB / T50080-2016 "Standard for Test Method of Performance of Ordinary Premixed Materials". The test results are shown in Tables 2 and 3.

[0136] Table 2 Initial flowability of ultra-high performance concrete with different dosages of polycarboxylate viscosity reducer

[0137]

[0138] Note: The dosage of polycarboxylate viscosity reducer is calculated based on the mass ratio of the folded solidified material to the cementitious material of ultra-high performance concrete.

[0139] Table 3 Performance test results of ultra-high performance concrete with a polycarboxylate viscosity reducer dosage of 7‰

[0140]

[0141] According to the test results in Table 2, at the same dosage level, the initial flowability of the ultra-high performance concrete prepared in Examples 1-4 was significantly higher than that of Comparative Examples 1-6. At a lower dosage level (5-7‰), the initial flowability of Examples 1-4 was 225-305 mm, while the initial flowability of the commercially available polycarboxylate viscosity reducer in Comparative Example 6, at a dosage of 1.1%, could only reach 200 mm. Because the viscosity reducer in Comparative Example 1 did not contain phosphate groups, the adsorption effect of the corresponding viscosity reducer molecules on cement and silica fume was relatively weak, and it could not effectively exert its dispersing effect. Because the viscosity reducer in Comparative Example 3 did not contain siloxane groups, its dispersing effect on silica fume was poor, affecting its flowability. Comparative Example 4 used isopentenyl alcohol polyoxyethylene ether with a molecular weight of 3000. Compared with other examples, the viscosity reducer molecule had a longer side chain, resulting in a thicker water film layer. In an extremely low water-cement ratio environment of 0.14, the amount of free water directly affected the flowability of the paste, thus resulting in poor flowability. Comparative Example 5 and commercially available viscosity reducers both have relatively large molecular weights. The viscosity reducer molecules coil within the slurry, failing to function effectively and simultaneously increasing the slurry viscosity. Based on the results in Tables 1 to 3, the smaller the molecular weight of the viscosity reducer, the stronger its dispersing effect, the shorter the corresponding Min-V funnel emptying time, and the lower the slurry viscosity.

[0142] In summary, the polycarboxylate viscosity reducer provided by this invention exhibits excellent dispersibility in ultra-high performance concrete with a water-cement ratio of 0.14. This viscosity reducer has a small molecular weight, allowing its side chains to extend more easily in the slurry, resulting in higher degrees of freedom. It also possesses carboxyl groups, phosphate groups, and silanol groups generated after hydrolysis, which effectively enhance the adsorption of the viscosity reducer on cement and silica fume. Therefore, only a small molecular weight viscosity reducer can provide sufficient electrostatic adsorption on the surfaces of cement and silica fume. Furthermore, the effective molecular content of the viscosity reducer is significantly increased after bridging with a crosslinking agent, effectively reducing its dosage in ultra-high performance concrete. This results in a substantial reduction in the viscosity of ultra-high performance concrete under ultra-low water-cement ratio conditions of 0.14, thereby improving its workability.

[0143] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a polycarboxylate viscosity reducer, characterized in that, Includes the following steps: 1) Under stirring conditions, unsaturated alcohols or esters are first mixed with polymerization inhibitors, then phosphorus pentoxide is added, the temperature is raised and the reaction is maintained at that temperature, and after the reaction is completed, the mixture is cooled to room temperature to obtain a mixture of unsaturated phosphate esters; the unsaturated alcohols or esters are one or more of isopentenol, methyl allyl alcohol, hydroxypropyl methacrylate, hydroxyethyl acrylate, and hydroxypropyl acrylate. 2) Mix 1-3.5 parts of reducing agent, 15-22.2 parts of chain transfer agent I, and 60 parts of water to obtain solution A; mix 50-60 parts of unsaturated acid or ester, 17.5-24 parts of organosilane monomer, and 80 parts of water to obtain solution B; mix 8-16 parts of crosslinking agent and 24.3 parts of water to obtain solution C; the organosilane monomer is one or more of γ-(methacryloyloxy)propyltrimethoxysilane and vinyltriethoxysilane; 3) Mix 10-23 parts of unsaturated phosphate ester mixture, 320-340 parts of unsaturated polyoxyethylene ether with a molecular weight of 1000-2400, 18-38 parts of unsaturated monomers, 8-24 parts of chain transfer agent II, and 300 parts of water, heat to 35-45 ℃, and stir until completely dissolved to obtain solution D; the unsaturated monomers are one or more of sodium p-styrene sulfonate, N,N-dimethylacrylamide, fumaric acid, acrylamide, acryloyloxyethyltrimethylammonium chloride, and dimethylamine methacrylate; 4) Maintaining a temperature of 35-45 °C and stirring conditions, add 13-23 parts of initiator to solution D. After stirring, start adding solutions A and B dropwise. After solution A is added dropwise in 1.5-2 h, raise the temperature to 60-70 °C and start adding solution C dropwise. After solution B is added dropwise in 2-2.5 h, and solution C is added dropwise in 0.5-1 h. Then keep warm and mature for 0.5-1 h. 5) After the curing is completed, water is added to adjust the solid content to obtain a polycarboxylic acid viscosity reducer; the number average molecular weight Mn of the polycarboxylic acid viscosity reducer is 16000~20000 and the polydispersity index is 1.2~1.

3.

2. The method for preparing the polycarboxylate viscosity reducer according to claim 1, characterized in that, The polymerization inhibitor is one or more of hydroquinone, p-hydroxyanisole, and phenothiazine; in step 1), the molar ratio of unsaturated alcohol or ester, polymerization inhibitor, and phosphorus pentoxide is (1.5~2.4):(0.0005~0.001):1, the heating temperature is 60~70 ℃, and the holding time is 2~3h.

3. The method for preparing the polycarboxylate viscosity reducer according to claim 1, characterized in that, The reducing agent is one or more of sodium formaldehyde sulfoxylate, modified sodium formaldehyde sulfoxylate, ascorbic acid, sodium bisulfite, and ferrous sulfate; the chain transfer agent I is one or more of mercaptopropionic acid, mercaptoacetic acid, and mercaptoethanol.

4. The method for preparing the polycarboxylate viscosity reducer according to claim 1, characterized in that, The unsaturated acid or ester is one or more of acrylic acid, methacrylic acid, butyl acrylate, and hydroxyethyl acrylate.

5. The method for preparing the polycarboxylate viscosity reducer according to claim 1, characterized in that, The crosslinking agent is one or more of ethylene glycol dimethacrylate and polyethylene glycol diacrylate.

6. The method for preparing the polycarboxylate viscosity reducer according to claim 1, characterized in that, The unsaturated polyoxyethylene ether is one or more of methyl allyl alcohol polyoxyethylene ether, isopentenyl alcohol polyoxyethylene ether, 4-hydroxybutyl vinyl ether, and ethylene glycol monovinyl polyethylene glycol ether.

7. The method for preparing the polycarboxylate viscosity reducer according to claim 1, characterized in that, The chain transfer agent II is one or more of sodium methpropylene sulfonate, sodium allyl sulfonate, sodium 2-acrylamido-2-methylpropene sulfonate, and sodium hypophosphite; the initiator is one or more of hydrogen peroxide, ammonium persulfate, potassium persulfate, potassium peroxymonosulfate, and sodium persulfate.

8. A polycarboxylate viscosity reducer prepared by the method according to any one of claims 1 to 7, characterized in that, The polycarboxylic acid viscosity reducer has a number-average molecular weight (Mn) of 16,000 to 20,000 and a polydispersity index of 1.2 to 1.

3.

9. The application of the polycarboxylate viscosity reducer as described in claim 8 in ultra-high performance concrete.

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