Polycarboxylate superplasticizer as well as preparation method and application thereof

Abstract

The invention provides a polycarboxylate superplasticizer as well as a preparation method and application thereof, and belongs to the technical field of concrete admixtures. The polycarboxylate superplasticizer is prepared from the following raw materials: 100 parts of unsaturated polyether, 11 to 22 parts of diphosphonic acid ester, 17 to 65 parts of unsaturated phosphonated calix [n] arene, 6 to 12 parts of monounsaturated carboxylic acid, 2.5 to 8 parts of initiator and 1.5 to 6 parts of chain transfer agent, the molecular weight of the polycarboxylic acid water reducing agent is 8000 to 15000; the diphosphonic acid ester is an ester compound containing two phosphonate radicals; the unsaturated phosphonic calix [n] arene is a derivative of the phosphonic calix [n] arene. The obtained water reducing agent is good in viscosity reduction effect, the viscosity of the ultra-high performance concrete can be efficiently reduced when the water-binder ratio is 0.12-0.14, the fluidity is improved, the working effect of the ultra-high performance concrete is improved, and shrinkage of the ultra-high performance concrete is reduced to a certain extent.

Description

Technical Field

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

[0002] With the high-rise, lightweight, large-span and environmental complexity of modern buildings and engineering facilities, ultra-high performance concrete (UHPC) has been widely used due to its high overall strength, light self-weight and good durability. In order to achieve ultra-high strength, the water-binder ratio of UHPC is usually lower than 0.25, and sub-micron mineral admixtures need to be added to achieve the effect of close packing. For frontier projects such as cross-sea bridges, undersea tunnels, and military facility foundations, due to their extreme and complex application scenarios, higher requirements are put forward for cement-based materials. This requires further reduction of the water-binder ratio and optimization of the mixture ratio of cement-based materials.

[0003] Polycarboxylate water reducers have high water reduction rate and good plasticizing property, and have many advantages such as good adjustability of structure and performance, green and pollution-free, etc., so they are widely used in UHPC. Currently, the water-binder ratio of UHPC used is basically above 0.16. If the water-binder ratio needs to be further reduced, the viscosity of the system will increase significantly and the fluidity will become poor. The current water reducers cannot meet the workability requirements of ultra-low water-binder ratio UHPC. In addition, further reducing the water-binder ratio also means more serious shrinkage problems. Therefore, it is very important to design and synthesize high-performance polycarboxylate water reducers according to the characteristics of ultra-low water-binder ratio UHPC. Summary of the Invention

[0004] In view of the technical problems existing in the background art, the present invention provides a polycarboxylate water reducer and its preparation method and application, aiming to solve the technical problems that the existing water reducers cannot meet the workability requirements of ultra-low water-binder ratio UHPC, and the improvement effects on the fluidity, mechanical properties and shrinkage of ultra-low water-binder ratio UHPC are not good.

[0005] In the first aspect, the present invention provides a polycarboxylate water reducer. The preparation raw materials of the polycarboxylate water reducer include: 100 parts of unsaturated polyether, 11-22 parts of bisphosphonic acid ester, 17-65 parts of unsaturated phosphonated calix[n]arene, 6-12 parts of monounsaturated carboxylic acid, 2.5-8 parts of initiator, and 1.5-6 parts of chain transfer agent; the molecular weight of the polycarboxylate water reducer is 8000-15000; The bisphosphonic acid ester is an ester compound containing two phosphonic acid groups; The unsaturated phosphonated calix[n]arene is a derivative of phosphonated calix[n]arene, and the structural formula of phosphonated calix[n]arene is: ; where n≥4.

[0006] In the present invention, the unsaturated phosphonated calix[n]arene is an unsaturated calixarene containing n phosphonate groups.

[0007] Preferably, the polydispersity index PDI of the polycarboxylate superplasticizer is 1.2 - 1.6; the solid content of the polycarboxylate superplasticizer is 30% - 40%.

[0008] Preferably, the unsaturated polyether includes isopentenol polyoxyethylene ether; the monounsaturated carboxylic acid includes at least one of acrylic acid and methacrylic acid; the initiator includes at least one of ammonium persulfate, potassium persulfate, and sodium persulfate; the chain transfer agent includes at least one of mercaptoacetic acid, mercaptoethanol, mercaptopropionic acid, and sodium hypophosphite.

[0009] Preferably, the unsaturated phosphonated calix[n]arene is vinyl phosphonated calix[n]arene, where n ≥ 4.

[0010] Preferably, n is one of 4, 5, 6, and 8.

[0011] Preferably, the functional monomer includes hydroxyethylidene diphosphonic acid; the unsaturated acid includes acrylic acid.

[0012] In a second aspect, the present invention provides a method for preparing a polycarboxylate superplasticizer, comprising the following steps: S1. Preparation of bisphosphonate ester: Mix the unsaturated acid and the functional monomer, add a catalyst and an inhibitor, heat to 60 - 80°C, and react for 4 - 6 h to obtain the bisphosphonate ester; S2. Provide the unsaturated phosphonated calix[n]arene, mix the unsaturated polyether, bisphosphonate ester, unsaturated phosphonated calix[n]arene, monounsaturated carboxylic acid, initiator, chain transfer agent, and water, and react at 60 - 85°C for 3 - 4 h to obtain the polycarboxylate superplasticizer.

[0013] Preferably, in step S1, the catalyst includes at least one of concentrated sulfuric acid and p-toluenesulfonic acid; the inhibitor includes at least one of hydroquinone and p-tert-butylcatechol.

[0014] Preferably, the molar ratio of the functional monomer to the unsaturated acid is 1:(1.5 - 2); the dosage of the catalyst is 1% - 3% of the total mass of the unsaturated acid and the functional monomer; the dosage of the inhibitor is 0.5% - 2% of the total mass of the unsaturated acid and the functional monomer.

[0015] Preferably, in step S2, the unsaturated polyether, bisphosphonic acid ester, unsaturated phosphonated calix[n]arene, monounsaturated carboxylic acid, initiator, chain transfer agent and water are mixed, specifically as follows: The unsaturated polyether, bisphosphonic acid ester and unsaturated phosphonated calix[n]arene are mixed with water to prepare a base material, which is heated to 60-85°C and stirred until dissolved, and part of the initiator is added and stirred evenly; The monounsaturated carboxylic acid and the chain transfer agent are prepared into an aqueous solution A, and the remaining initiator is prepared into an aqueous solution B; The aqueous solution A and the aqueous solution B are added dropwise to the base material for reaction. The dropping time of the aqueous solution A is 3-3.5 h, and the dropping time of the aqueous solution B is 3.5-4 h. After the reaction is completed, it is kept warm for 1-2 h to obtain a polycarboxylate superplasticizer.

[0016] Preferably, the mass concentration of the base material is 50%-60%; the mass concentration of the aqueous solution A is 40%-50%; the mass concentration of the aqueous solution B is 5%-6%.

[0017] Preferably, in step S2, the unsaturated phosphonated calix[n]arene is vinylphosphonated calix[n]arene; The preparation method of vinylphosphonated calix[n]arene includes the following steps: Under the condition of 0-5°C, methacryloyl chloride is dropped into the N,N-dimethylformamide solution of phosphonated calix[n]arene, the temperature is adjusted to 20-25°C, and the reaction is carried out for 20-24 h. After cooling to room temperature, a polar solvent is added to the system to precipitate, and after solid-liquid separation, the solid is vinylphosphonated calix[n]arene.

[0018] Preferably, the molar ratio of phosphonated calix[n]arene to methacryloyl chloride is 1:(1.1-1.5); the mass ratio of phosphonated calix[n]arene to N,N-dimethylformamide is 1:(5-10).

[0019] Preferably, the polar solvent includes at least one of methanol and ethyl acetate.

[0020] Preferably, the mass ratio of the polar solvent to phosphonated calix[n]arene is (10-20):1.

[0021] In the third aspect, the present invention provides an application of a polycarboxylate superplasticizer in the preparation of UHPC.

[0022] Preferably, the UHPC is ultra-low water-binder ratio UHPC, and the water-binder ratio of the ultra-low water-binder ratio UHPC is 0.12-0.14.

[0023] The working principle of the present invention is: (1) The present invention prepares bisphosphonate esters by the esterification reaction of hydroxyethylidene diphosphonic acid and unsaturated acids. The bisphosphonate esters and unsaturated phosphonated calix[n]arenes participate in copolymerization reactions. Among them, the bisphosphonate esters contain two phosphonic acid groups, and the unsaturated phosphonated calix[n]arenes contain 4-8 phosphonic acid groups. Therefore, the polycarboxylate superplasticizer of the present invention contains multiple phosphonic acid groups, and the number of negatively charged phosphonic acid groups is greater than the number of negatively charged carboxyl groups of conventional polycarboxylate superplasticizers, with a higher anionic charge density. Its adsorption capacity on the surface of cementitious material particles is much greater than that of carboxyl groups. In addition, the phosphonic acid groups are not evenly distributed on the main chain of the entire superplasticizer molecule, but are "cluster-distributed". Where the phosphine-containing monomers appear, the phosphonic acid groups are concentrated to provide "anchor points", with a faster adsorption rate on the surface of cementitious material particles, better dispersion effect between cementitious material particles, and more free water can be released. The unsaturated phosphonated calix[n]arenes contain 4-8 benzene rings, and the benzene rings are hydrophobic rigid groups. Therefore, the rotation of the polycarboxylate superplasticizer molecules is hindered, increasing the rigidity of the polycarboxylate molecules, making the main chain of the superplasticizer not easily bent and entangled, and its main chain is more extended in the pore solution, exposing more -COO - 、-PO3 2- adsorbed on the surface of cementitious material particles, so the adsorption amount is larger and the adsorption layer is thicker.

[0024] (2) At an ultra-low water-cement ratio, the spacing between cementitious material particles is small and they are prone to agglomeration. The dispersion effect of electrostatic repulsion is particularly important. The superplasticizer molecules of the present invention can not only be dispersed by steric hindrance, but the high charge density of its main chain will make the electrostatic repulsion between cementitious material particles stronger and more stable, dispersing the agglomerated cementitious material particles, and then releasing more free water and reducing the viscosity of the slurry.

[0025] (3) The phosphonic acid groups on the main chain of the polycarboxylate superplasticizer of the present invention can undergo complexation reactions with calcium ions in the system to form stable complexes, covering the surface of cement particles and hindering the contact between cement particles and water, thereby delaying the hydration process of cement. At an ultra-low water-cement ratio, delaying hydration can reduce the rapid generation and accumulation of hydration products, avoiding a sharp increase in the viscosity of the slurry caused by excessive hydration products, and keeping the slurry at a relatively low viscosity and good fluidity for a certain period of time.

[0026] (4) The polycarboxylate superplasticizer PCEs of the present invention has a short main chain, long side chains, a small molecular weight, and multiple phosphonic acid groups and carboxylic acid groups on the main chain, with high surface activity. The low surface tension of the polycarboxylate superplasticizer can reduce the solid-liquid interfacial energy between cementitious material particles and the liquid phase. There is less bound water on the surface of cementitious material particles, and there is more free water in the system. In addition, the low surface tension of the liquid phase can enhance the activity of the gas-liquid interface, introduce appropriate bubbles, reduce the free energy of the system, and play a lubricating role between cementitious particles.

[0027] (5) The polycarboxylate water reducer of the present invention has a small molecular weight, a high density of phosphonic acid groups and carboxyl groups on the main chain, and contains multiple benzene rings. It has good surface activity, can significantly reduce the surface tension of the liquid phase of the cementitious material system, and its good dispersibility makes the hardened UHPC dense. The number of connected pores in the system is extremely small, which will slow down the evaporation rate of water in the pores, thus reducing the autogenous shrinkage and drying shrinkage of UHPC.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Starting from the molecular structure design of the polycarboxylate water reducer, the present invention grafts multiple carboxyl groups, "cluster-distributed" phosphonic acid groups and benzene rings on the main chain. The synergistic effect of each group makes the product have strong adsorption ability, fast adsorption speed, large adsorption capacity and thick adsorption layer on the surface of cementitious material particles. On the one hand, it disperses cement, silica fume and other cementitious material particles well through steric hindrance and electrostatic repulsion, releasing more free water; on the other hand, its low surface tension results in less bound water on the surface of cementitious material particles, delaying hydration and reducing the consumption of free water. Therefore, there is more free water in the system, and when the water-binder ratio of UHPC is as low as 0.12 - 0.14, the system viscosity is reduced and good workability is maintained.

[0029] (2) The polycarboxylate water reducer of the present invention can disperse cementitious material particles evenly and stably in an ultra-low water-binder ratio environment, enabling the cementitious material particles to be fully hydrated. After hardening, the structure is more dense, ensuring the integrity and uniformity of the UHPC structure and improving the mechanical properties of UHPC.

[0030] (3) The polycarboxylate water reducer of the present invention can reduce the autogenous shrinkage and drying shrinkage of UHPC.

[0031] (4) The polycarboxylate water reducer of the present invention can effectively inhibit the early hydration reaction rate of cement, so as to ensure that the slump loss of UHPC is controlled within a very small range within 2 - 4 hours after mixing. Even under adverse working conditions such as high temperature in summer and long-distance transportation, UHPC using this water reducer can still be successfully poured, greatly expanding the construction application scenarios of UHPC. Specific embodiments

[0032] The embodiments of the technical solution of the present invention will be described in detail below. The following embodiments are only used to illustrate the technical solution of the present invention more clearly, so they are only examples and cannot be used to limit the protection scope of the present invention.

[0033] For those not specifying specific techniques or conditions in the embodiments, they shall be carried out according to the techniques or conditions described in the literature in this field or according to the product specifications. For reagents or instruments not indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase or commonly used in this field.

[0034] In the following embodiments of the present invention, the synthesis process of phosphonated calix[n]arene refers to "Self-organised nano-arrays of p-phosphonic acid functionalised higher order calixarenes" published by Thomas E. Clark et al. in 《New Journal of Chemistry》 in 2008 (DOI: 10.1039 / B801256C); the specific steps of the synthesis process are as follows (where n takes 4, 5, 6, and 8 respectively in Examples 1 to 4): (1) The N,N-dimethylformamide solution of bromine is added dropwise to the N,N-dimethylformamide solution of calix[n]arene under stirring. After the mixture is stirred for 4 hours, the volatiles are removed under reduced pressure. Then, methanol is added to precipitate a solid. After filtration, the filter cake is washed several times with methanol to obtain intermediate a. Among them, the mass ratio of bromine to N,N-dimethylformamide is 1:5, the mass ratio of N,N-dimethylformamide to calix[n]arene is 40:1, and the molar ratio of bromine to calix[n]arene is 1.5n:1.

[0035] (2) Intermediate a and sodium acetate are added to acetic anhydride, and the mixture is slowly heated to reflux. After refluxing for 4 hours, it is naturally cooled to room temperature. Then, water is slowly added to quench the reaction. The precipitate is collected by filtration, and the filter cake is washed several times with methanol to obtain intermediate b. Among them, the molar ratio of sodium acetate to intermediate a is 1.5n:1, and the mass ratio of acetic anhydride to intermediate a is 10:1.

[0036] (3) Under nitrogen protection, intermediate b and nickel chloride are dissolved in benzonitrile, and the mixture is heated to 190 °C. Then, triethyl phosphite is slowly added dropwise. After stirring for 30 minutes, the volatiles are removed under reduced pressure. The residue is further purified by flash column chromatography and then recrystallized with toluene-n-hexane to obtain intermediate c. Among them, the molar ratio of nickel chloride to intermediate b is 0.25n:1, the mass ratio of benzonitrile to intermediate b is 5:1, and the molar ratio of triethyl phosphite to intermediate b is 2.5n:1.

[0037] (4) Methanol, tetrahydrofuran, and water are mixed in equal volumes at a ratio of 1:1:1. Intermediate c and potassium hydroxide are dissolved in the mixed solution and stirred for 4 hours. The solvent is removed under reduced pressure. Equal volumes of dichloromethane and 2 mol / L HCl are added to the residue. After sufficient stirring, the mixture is allowed to stand for phase separation. The lower organic phase is collected and washed once with 2 mol / L hydrochloric acid, then washed twice with water. Then, anhydrous magnesium sulfate is added for drying. After concentration under reduced pressure, intermediate d is obtained. Among them, the molar ratio of potassium hydroxide to intermediate c is 2.5n:1, the mass ratio of methanol to intermediate c is 20:1, and the mass ratio of dichloromethane to intermediate c is 30:1.

[0038] (5) Dissolve the intermediate d in dry acetonitrile, then add trimethylsilyl bromide, slowly heat to reflux, after refluxing for 16 hours, remove the volatiles under reduced pressure, grind the residue with a mixed solution of acetonitrile and water (the volume ratio of acetonitrile to water is 20:1), filter, collect the precipitate, and wash it with acetonitrile multiple times to obtain phosphonated calix[n]arene. Among them, the mass ratio of dry acetonitrile to intermediate d is 25:1, the molar ratio of trimethylsilyl bromide to intermediate d is 4n:1, and the mass ratio of acetonitrile to intermediate d during grinding is 20:1.

[0039] I. Preparation method Example 1 A polycarboxylate water reducer is prepared as follows: (1) Preparation of bisphosphonic acid ester: Place 14.4 parts of acrylic acid in a dry four-necked flask, then add 0.7 part of p-toluenesulfonic acid and 0.35 part of hydroquinone and stir evenly. Heat the temperature to 65 °C through a water bath, slowly add 20.6 parts of hydroxyethylidene diphosphonic acid, continuously stir during the reaction, and react for 4 h to obtain bisphosphonic acid ester.

[0040] (2) Preparation of vinyl phosphonated calix[4]arene: Refer to the method of Thomas E. Clark et al. in the article "Self-organised nano-arrays of p-phosphonic acidfunctionalised higher order calixarenes" published in 《New Journal of Chemistry》 in 2008 (DOI: 10.1039 / B801256C) to prepare phosphonated calix[4]arene (molecular weight is 744); Under stirring, add 7.4 parts of phosphonated calix[4]arene and 50 parts of N,N-dimethylformamide to a three-necked flask, adjust the temperature to 0 °C with an ice-water bath, slowly dropwise add 1.3 parts of methacryloyl chloride, after the addition is completed, raise the temperature to 25 °C, and react for 24 h; cool to room temperature, add 100 parts of methanol to the flask, and the solid obtained after solid-liquid separation is vinyl phosphonated calix[4]arene.

[0041] (3)Polymerization reaction: 100 parts of isopentenol polyoxyethylene ether TPEG-2400, 11 parts of bisphosphonate ester, 17 parts of vinylphosphonated calix[4]arene, and 1.25 parts of potassium persulfate were added to a four-necked flask, and water was added to prepare a bottom material with a mass concentration of 50 wt%. The bottom material was heated to 60 °C and stirred for 30 min to dissolve; 6 parts of acrylic acid and 1.5 parts of mercaptoacetic acid were prepared into a solution A with a mass concentration of 40 wt%, and 1.25 parts of potassium persulfate was prepared into a 5 wt% mixed solution B. Solution A and solution B were gradually added dropwise into the flask using a peristaltic pump for reaction. The dropping time of solution A was 3 h, and the dropping time of solution B was 3.5 h; after the dropping of solution B was completed, it was kept warm for 1 h, and then an appropriate amount of water was added to the four-necked flask to prepare a polycarboxylate superplasticizer with a solid content of 40%.

[0042] After testing, the molecular weight of the superplasticizer prepared in this example was 13,430, and the polydispersity index PDI was 1.39.

[0043] Example 2 A polycarboxylate superplasticizer is prepared as follows: (1)The preparation method of bisphosphonate ester is the same as that in step (1) of Example 1; (2)Preparation of vinylphosphonated calix[8]arene: Referring to the method of Thomas E. Clark et al. published in 《New Journal of Chemistry》 in 2008, 《Self-organised nano-arrays of p-phosphonic acidfunctionalised higher order calixarenes》 (DOI: 10.1039 / B801256C), phosphonated calix[8]arene (molecular weight 1488) was prepared.

[0044] Under stirring, 7.4 parts of phosphonated calix[8]arene and 50 parts of N,N-dimethylformamide were added to a three-necked flask, and the temperature was adjusted to 0 °C in an ice-water bath. 0.65 part of methacryloyl chloride was slowly added dropwise. After the addition was completed, the temperature was raised to 25 °C and reacted for 24 h; cooled to room temperature, 100 parts of methanol was added to the flask, and the solid obtained after solid-liquid separation was vinylphosphonated calix[8]arene.

[0045] (3)Polymerization reaction: 100 parts of isopentenol polyoxyethylene ether TPEG-2400, 22 parts of bisphosphonic acid ester, 65 parts of vinylphosphonated calix[8]arene, and 3.25 parts of sodium persulfate were added to a four-necked flask, and water was added to prepare a bottom material with a mass concentration of 60 wt%. The bottom material was heated to 85 °C and stirred for 30 min to dissolve; 12 parts of acrylic acid and 5 parts of mercaptopropionic acid were prepared into solution A with a concentration of 50 wt%, and 3.25 parts of sodium persulfate was prepared into a 5 wt% mixed solution B. Solution A and solution B were gradually added dropwise into the flask using a peristaltic pump for reaction. The dropping time of solution A was 3 h, and the dropping time of solution B was 3.5 h; after the dropping of solution B was completed, the temperature was kept for 1 h, and then an appropriate amount of water was added to the four-necked flask to prepare a polycarboxylate superplasticizer with a solid content of 40%.

[0046] After testing, the molecular weight of the superplasticizer prepared in this example was 11,950, and the polydispersity index PDI was 1.45.

[0047] Example 3 A polycarboxylate superplasticizer is prepared as follows: (1)The preparation method of bisphosphonic acid ester is the same as that in step (1) of Example 1; (2)Preparation of vinylphosphonated calix[5]arene: Referring to the method of Thomas E. Clark et al. published in 《New Journal of Chemistry》 in 2008, 《Self-organised nano-arrays of p-phosphonic acidfunctionalised higher order calixarenes》 (DOI: 10.1039 / B801256C), phosphonated calix[5]arene (molecular weight 930) was prepared.

[0048] Under stirring, 9.3 parts of phosphonated calix[5]arene and 60 parts of N,N-dimethylformamide were added to a three-necked flask, the temperature was adjusted to 0 °C in an ice-water bath, 1.3 parts of methacryloyl chloride was slowly added dropwise, and after the addition was completed, the temperature was raised to 25 °C and reacted for 24 h; cooled to room temperature, 120 parts of methanol was added to the flask, and the solid obtained after solid-liquid separation was vinylphosphonated calix[5]arene.

[0049] (3)Polymerization reaction: 100 parts of isopentenyl alcohol polyoxyethylene ether TPEG-2400, 16 parts of bisphosphonic acid ester, 30 parts of vinylphosphonated calix[5]arene, and 2.25 parts of ammonium persulfate were added to a four-necked flask, and water was added to prepare a bottom material with a concentration of 55 wt%. The bottom material was heated to 70 °C and stirred for dissolution for 30 min; 9 parts of acrylic acid and 3.5 parts of mercaptoethanol were formulated into solution A with a concentration of 50 wt%, and 2.25 parts of ammonium persulfate was formulated into a 5 wt% mixed solution B. Solution A and solution B were gradually added dropwise into the flask using a peristaltic pump for reaction. The dropping time of solution A was 3 h, and the dropping time of solution B was 3.5 h; after the dropping of solution B was completed, the temperature was kept for 1 h, and then an appropriate amount of water was added to the four-necked flask to prepare a polycarboxylate superplasticizer with a solid content of 40%.

[0050] Test showed that the molecular weight of the superplasticizer prepared in this example was 10755, and the polydispersity index PDI was 1.4.

[0051] Example 4 A polycarboxylate superplasticizer was prepared as follows: (1)The preparation method of bisphosphonic acid ester was the same as that in step (1) of Example 1; (2)Preparation of vinylphosphonated calix[6]arene: Referring to the method of Thomas E. Clark et al. published in "New Journal of Chemistry" in 2008, "Self-organised nano-arrays of p-phosphonic acidfunctionalised higher order calixarenes" (DOI: 10.1039 / B801256C), phosphonated calix[6]arene (molecular weight 1116) was prepared.

[0052] Under stirring, add 11.2 parts of phosphonated calix[6]arene and 70 parts of N,N-dimethylformamide to a three-necked flask, adjust the temperature to 0 °C in an ice-water bath, slowly add 1.3 parts of methacryloyl chloride dropwise, and after the dropping is completed, raise the temperature to 25 °C and react for 24 h; cool to room temperature, add 140 parts of methanol to the flask, and the solid obtained after solid-liquid separation is vinylphosphonated calix[6]arene.

[0053] (3) Polymerization reaction: 100 parts of isopentanol polyoxyethylene ether TPEG-2400, 18 parts of bisphosphonic acid ester, 36 parts of vinylphosphonated cup[6]arene, and 2 parts of ammonium persulfate were added to a four-necked flask, and water was added to prepare a base material with a concentration of 60 wt%. The base material was heated to 70 °C and stirred to dissolve for 30 min; 12 parts of acrylic acid and 5 parts of mercaptoethanol were prepared into a solution A with a concentration of 50 wt%, and 2 parts of ammonium persulfate were prepared into a mixed solution B with a concentration of 5 wt%. Liquid A and liquid B were gradually added dropwise to the flask using a peristaltic pump for reaction. The dropwise addition time of liquid A was 3 h, and the dropwise addition time of liquid B was 3.5 h. After the dropwise addition of liquid B was completed, the temperature was kept constant for 1 h. Then, an appropriate amount of water was added to the four-necked flask to prepare a polycarboxylic acid water reducer with a solid content of 40%.

[0054] After testing, the water reducer prepared in this embodiment has a molecular weight of 9810 and a polydispersity index (PDI) of 1.45.

[0055] Comparative Example 1 This comparative example is a powdered polycarboxylate water reducer PC-1021 produced by Suzhou Chemical Building Materials Co., Ltd.

[0056] Comparative Example 2 The difference between this comparative example and Example 4 is that no bisphosphonate is added in step (3).

[0057] Comparative Example 3 The difference between this comparative example and Example 4 is that vinylphosphonated calix[6]arene is not added in step (3).

[0058] Comparative Example 4 The difference between this comparative example and Example 4 is that no bisphosphonate and vinylphosphonated calix[6]arene are added in step (3).

[0059] 2. Test Method Ultra-low water-binder ratio UHPC was prepared using the water-reducing agents from Examples 1-4 and Comparative Examples 1-4. The cementitious material and aggregate mix ratios were as shown in Table 1, with water-binder ratios of 0.14 and 0.12, respectively. The water-binder dosage was 1% for a water-binder ratio of 0.14 and 1.2% for a water-binder ratio of 0.12.

[0060] Table 1 Ultra-high performance concrete mix ratio / g

[0061] 1. Fluidity test The test method for the fluidity of ultra-low water-binder ratio UHPC refers to the test method for the fluidity of neat cement paste in GB / T 8077-2012 "Test Methods for the Homogeneity of Concrete Admixtures". The difference is that the amount of water added is according to the water required by the designed water-binder ratio. The upper diameter of the frustum cone mold used is 70 mm, the lower diameter is 100 mm, and the height is 60 mm. The initial fluidity and 2-hour fluidity of the paste are tested respectively. The test results are shown in Table 2.

[0062] 2. Compressive Strength Test The mechanical property test is carried out according to GB / T 17671-2021 "Test Methods for the Strength of Cement Mortar". The 3-day and 28-day compressive strengths are tested respectively. The test results are shown in Table 2.

[0063] 3. Drying Shrinkage The drying shrinkage is tested with reference to JC / T603-2004 "Test Method for Drying Shrinkage of Cement Mortar". After standard curing for 72 hours, the length of the specimen is measured by a length comparator, which is defined as the initial length. Then the specimen is transferred to a drying shrinkage curing room with a temperature of 20°C and a humidity of 50% for continuous curing. The length comparator is used to measure the length of the specimen at 7 days, 14 days, and 28 days after hydration, and the length change rate is calculated. The test results are shown in Table 3.

[0064] 4. Autogenous Shrinkage The UHPC shrinkage test uses the YC-TBWS II series bellows autogenous shrinkage measuring instrument developed by Beijing Yichuang Times Technology Co., Ltd. according to ASTM C1698-09. During the test, the specimen is cast into a bellows with a length of (425±5) mm and a diameter of (78±2) mm to prevent the UHPC mixture from exchanging moisture with the outside. The test environment is a constant temperature laboratory with a temperature of (20±2)°C. The autogenous shrinkage change value of the paste is recorded 72 hours after initial setting. The test results are shown in Table 3.

[0065] III. Analysis of Test Results of Each Example and Comparative Example Table 2 Test Results of Fluidity and Compressive Strength of Ultra-Low Water-Binder Ratio UHPC

[0066] Table 3 Test Results of Drying Shrinkage and Autogenous Shrinkage of Ultra-Low Water-Binder Ratio UHPC (Water-Binder Ratio 0.14)

[0067] According to the test results in Table 2, at a water-binder ratio of 0.12 and 0.14, when the dosage of the water reducer is the same, the initial fluidity and 2-hour fluidity of the UHPC prepared in Examples 1-4 are significantly higher than those in Comparative Examples 1-4. And when the water-binder ratio is 0.12, this advantage is more obvious. Comparative Example 1 is a commercially available polycarboxylate water reducer. The main chain of the water reducer in Comparative Example 2 does not contain bisphosphonate esters. The main chain of the water reducer in Comparative Example 3 does not contain vinyl phosphonated calix[n]arenes. The main chain of the water reducer in Comparative Example 4 does not contain bisphosphonate esters and vinyl phosphonated calix[n]arenes. Compared with the comparative examples, multiple carboxyl groups, "cluster-distributed" phosphonic acid groups and benzene rings are grafted on the main chain of the water reducer in Examples 1-4. The synergistic effect of each group makes the product have strong adsorption ability, fast adsorption speed, large adsorption capacity and thick adsorption layer on the surface of the cementitious material particles. On the one hand, through steric hindrance and electrostatic repulsion, it can disperse cement, silica fume and other cementitious material particles well, releasing more free water; on the other hand, its low surface tension results in less bound water on the surface of the cementitious material particles, delaying hydration and reducing the consumption of free water. Therefore, there is more free water in the system, enabling the system to maintain good fluidity when the water-binder ratio of UHPC is as low as 0.12-0.14. Due to the uniform dispersion of the cementitious material particles, the cementitious material particles can be fully hydrated, and the structure is denser after hardening. Therefore, its 3-day and 28-day strengths are higher. The fluidity of each example basically has no loss or very little loss at 2 hours, and it can be applied to adverse working conditions such as high temperature in summer and long-distance transportation.

[0068] As can be seen from Table 3, the 28-day autogenous shrinkage of the UHPC prepared in Examples 1-4 is less than 300×10 -6 , and the 72-hour drying shrinkage is less than 400×10 -6 , which is significantly lower than the autogenous shrinkage and drying shrinkage of the UHPC prepared in Comparative Examples 1-4. This is because the water reducers in Examples 1-4 have small molecular weights, high densities of phosphonic acid groups and carboxyl groups on the main chain and contain multiple benzene rings, with good surface activity, which can significantly reduce the surface tension of the liquid phase in the cementitious material system. And their good dispersibility makes the hardened UHPC dense, with very few connected pores in the system, which will slow down the evaporation rate of water in the pores. Therefore, the autogenous shrinkage and drying shrinkage of UHPC are reduced.

[0069] In summary, the water reducer of the present invention can efficiently improve the fluidity of ultra-high performance concrete at a water-binder ratio of 0.12-0.14, improve its working effect, and reduce the shrinkage of ultra-high performance concrete to a certain extent, which can further broaden the application range of UHPC and promote the further development of UHPC.

[0070] It should be noted that the present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having the same constitution and achieving the same effects within the technical scope of the present invention are included in the technical scope of the present invention. In addition, within the scope not departing from the gist of the present invention, various modifications that can be conceived by those skilled in the art to the embodiments and other modes constructed by combining some constituent elements of the embodiments are also included in the scope of the present invention.

Claims

1. A polycarboxylate water reducer, characterized in that The raw materials for preparing the polycarboxylate water reducer include: 100 parts of unsaturated polyether, 11-22 parts of bisphosphonic acid ester, 17-65 parts of unsaturated phosphonated calix[n]arene, 6-12 parts of monounsaturated carboxylic acid, 2.5-8 parts of initiator, and 1.5-6 parts of chain transfer agent; The molecular weight of the polycarboxylate water reducer is 8000-15000; The bisphosphonic acid ester is an ester compound containing two phosphonic acid groups; The unsaturated phosphonated calix[n]arene is a derivative of phosphonated calix[n]arene; the structural formula of the phosphonated calix[n]arene is: ; where n ≥ 4.

2. The polycarboxylate water reducer according to claim 1, characterized in that, The polydispersity index PDI of the polycarboxylate water reducer is 1.2-1.6; the solid content of the polycarboxylate water reducer is 30%-40%.

3. A polycarboxylate water reducer according to claim 1, characterized in that, The unsaturated polyether includes isopentenol polyoxyethylene ether; the monounsaturated carboxylic acid includes at least one of acrylic acid and methacrylic acid; the initiator includes at least one of ammonium persulfate, potassium persulfate, and sodium persulfate; the chain transfer agent includes at least one of mercaptoacetic acid, mercaptoethanol, mercaptopropionic acid, and sodium hypophosphite.

4. A polycarboxylate water reducing agent according to claim 1, characterized in that, The unsaturated phosphonated calix[n]arene is vinyl phosphonated calix[n]arene, where n is one of 4, 5, 6, and 8.

5. A preparation method of a polycarboxylate water reducing agent according to any one of claims 1 to 4, characterized in that, It includes the following steps: S1. Preparation of bisphosphonic acid ester: Mix unsaturated acid with functional monomer, add catalyst and inhibitor, heat up to 60-80°C, and react for 4-6 h to obtain bisphosphonic acid ester; S2. Provide unsaturated phosphonated calix[n]arene, mix unsaturated polyether, bisphosphonic acid ester, unsaturated phosphonated calix[n]arene, monounsaturated carboxylic acid, initiator, chain transfer agent, and water, and react at 60-85°C for 3-4 h to obtain polycarboxylate water reducer.

6. The preparation method of a polycarboxylate water reducer according to claim 5, characterized in that, In the step S1, the catalyst includes at least one of concentrated sulfuric acid and p-toluenesulfonic acid; the inhibitor includes at least one of hydroquinone and p-tert-butylcatechol; the molar ratio of the functional monomer to the unsaturated acid is 1:(1.5-2); the dosage of the catalyst is 1%-3% of the total mass of the unsaturated acid and the functional monomer; the dosage of the inhibitor is 0.5%-2% of the total mass of the unsaturated acid and the functional monomer.

7. The preparation method of a polycarboxylate water reducer according to claim 5, characterized in that, The unsaturated phosphonated calix[n]arene is vinyl phosphonated calix[n]arene; the preparation method of the vinyl phosphonated calix[n]arene includes the following steps: Under the condition of 0-5°C, drop methacryloyl chloride into the N,N-dimethylformamide solution of phosphonated calix[n]arene, adjust the temperature to 20-25°C, react for 20-24 h, cool to room temperature, add polar solvent to the system, precipitate, and after solid-liquid separation, the solid is vinyl phosphonated calix[n]arene.

8. The preparation method of a polycarboxylate water reducing agent according to claim 7, characterized in that, The molar ratio of the phosphonated calix[n]arene to methacryloyl chloride is 1:(1.1-1.5); the mass ratio of the phosphonated calix[n]arene to N,N-dimethylformamide is 1:(5-10); the polar solvent includes at least one of methanol and ethyl acetate; the mass ratio of the polar solvent to the phosphonated calix[n]arene is (10-20):

1.

9. Use of a polycarboxylate water reducer as described in any one of claims 1 to 4 in the preparation of UHPC.

10. The application according to claim 9, wherein The UHPC is ultra-low water-binder ratio UHPC, and the water-binder ratio of the ultra-low water-binder ratio UHPC is 0.12 to 0.14.

Images