Polycarboxylic acid admixture as well as preparation method and application thereof

Abstract

The invention relates to the technical field of additives for cement concrete, in particular to a polycarboxylic acid additive and a preparation method and application thereof.The polycarboxylic acid additive is prepared from a polymeric base material, a material A and a material B. The polymeric base material comprises a macromonomer, 2-acrylamide-2-methylpropanesulfonic acid, part of a first comonomer and water, the material A comprises an initiator, a molecular weight regulator and water, and the material B comprises residual first comonomer, second comonomer and water; the first comonomer comprises any one or two of acrylic acid and methacrylic acid; the second comonomer is a mixture of hydroxypropyl acrylate and hydroxyethyl acrylate. The polycarboxylic acid admixture integrates the functions of water reduction, delayed coagulation and air entraining, is very high in water-reducing rate, high in compressive strength ratio, proper in air content, good in workability maintaining effect of a roller compacted concrete mixture, good in delayed coagulation effect, reasonable in initial and final setting time distribution and convenient to construct, and solves the problems faced by roller compacted concrete at present.

Description

Technical Field

[0001] The invention relates to the technical field of cement concrete admixtures, in particular to a polycarboxylic acid admixture and a preparation method and application thereof. Background Art

[0002] Roller compacted concrete is a dry, cement-poor concrete with the advantages of simple structure, fast construction, high strength, few shrinkage joints, low cement consumption, low cost, and reduced construction environmental pollution. Roller compacted concrete usually refers to the use of silicate cement, pozzolanic admixtures, water, admixtures, sand and graded coarse aggregates to mix into a dry, hard concrete with no slump. Among them, the role of admixtures in roller compacted concrete is becoming more and more important.

[0003] Roller compacted concrete is often used in the construction of earth-rock dams. When used, the same transportation and paving equipment as earth-rock dam construction can be used, and the layers can be compacted with a vibrating roller. Roller compacted concrete dams have the characteristics of small concrete volume, high strength, good anti-seepage performance, good durability, and overflow of the dam body. They also have the advantages of simple, fast, economical construction procedures for earth-rock dams, and the use of large general-purpose machinery.

[0004] In addition, due to the characteristics of easy construction, high degree of mechanization, short construction period and low project cost, roller compacted concrete has been continuously used in water conservancy and hydropower projects in various countries around the world for many years, and then used in parking lots, freight yards and some low-speed highway surfaces. In recent years, with the improvement and improvement of roller compacted concrete construction technology, roller compacted concrete pavement can be used to pave higher-grade highway pavements.

[0005] A large number of studies have shown that in addition to having a good water-reducing effect, admixtures for roller compacted concrete also need to have good retarding and air-entraining effects. Among them, the water-reducing effect is to reduce the water consumption of roller compacted concrete, reduce the water-cement ratio, and improve the strength of concrete. At the same time, it can improve the workability of roller compacted concrete and solve the problem of high water demand of concrete; the retarding effect is to meet the technical requirements of the relatively long construction time of roller compacted concrete. Roller compacted concrete needs to have the characteristics of long retarding time and good plasticity; the air-entraining effect is to improve the impermeability, frost resistance, and compactability of roller compacted concrete. Therefore, admixtures for roller compacted concrete need to have multiple functions such as water reduction, retarding and air entraining.

[0006] At present, in order to meet the functions of water reduction, slow setting and air entrainment, the admixtures used in RCC are mostly compounded with admixtures of different functions. The compounding scheme is adopted mainly because there is no admixture that integrates the above-mentioned multiple functions so far, and the demand for multifunctional admixtures in the field of RCC is becoming more and more urgent. First, it integrates multiple functions into one, is easy to use, reduces the probability of construction errors, and improves construction efficiency; second, multifunctional admixtures bring great convenience to the production, storage and transportation of RCC admixtures; third, multifunctional admixtures can save comprehensive costs. Since the use areas of RCC (such as dams) are usually in remote areas with inconvenient transportation, the lack of one admixture will have a very large impact on the construction; and the multifunctional admixture greatly reduces the probability of such errors and can better ensure the stable construction of the project.

[0007] Polycarboxylate water reducer is the latest generation of high-performance water reducer, which has been widely used in cement concrete. Based on different cements and different construction requirements, a variety of polycarboxylate water reducers with different functions have been developed, such as high-efficiency water-reducing type, collapse-preserving type, and early-strength type.

[0008] However, there are few reports on polycarboxylic acid water-reducing agents specifically used for RCC that combine water reduction, retarding setting and air entraining. As we all know, there have been a lot of studies on the correlation between the molecular structure of polycarboxylic acid water-reducing agents and their performance, and there is a relatively mature design theory. However, for the special system of RCC, the existing design theory cannot be fully used to guide the molecular design of related polycarboxylic acid admixtures. For example, the water reduction effect is not the first priority for RCC, while the retarding setting and air entraining effects are often more important for RCC. Therefore, the design and synthesis of a multifunctional polycarboxylic acid admixture for RCC is still a technical challenge.

[0009] In view of this, the present invention is proposed. Summary of the invention

[0010] The object of the present invention is to provide a polycarboxylic acid admixture for roller compacted concrete and a preparation method thereof. The polycarboxylic acid admixture integrates water reduction, retarding setting and air entraining functions, has a high water reduction rate, a high compressive strength ratio, an appropriate air content, a good effect of maintaining the workability (VC value) of the roller compacted concrete mixture, a good retarding effect, and a reasonable distribution of initial and final setting time for easy construction, thereby specifically solving the problems currently faced by roller compacted concrete.

[0011] In a first aspect, the present invention provides a polycarboxylic acid admixture, which is prepared by free radical copolymerization of a polymer base material, an A material and a B material, wherein the polymer base material comprises a macromonomer, 2-acrylamide-2-methylpropanesulfonic acid, a portion of a first comonomer and water, the A material comprises an initiator, a molecular weight regulator and water, and the B material comprises the remaining first comonomer, a second comonomer and water; Wherein, the macromonomer is a polyether-type macromolecule containing a polyoxyethylene ether group; The first comonomer includes any one or both of acrylic acid and methacrylic acid; The second comonomer is a mixture of hydroxypropyl acrylate and hydroxyethyl acrylate.

[0012] The polycarboxylic acid admixture of the present invention is prepared by free radical copolymerization of a polymer base material, an A material and a B material, wherein the polymer base material comprises a polyether-type macromolecule containing a polyoxyethylene ether group, 2-acrylamide-2-methylpropane sulfonic acid and an acrylic monomer, the A material mainly comprises an initiator and a molecular weight regulator, and the B material mainly comprises an acrylic monomer and an acrylic hydroxy ester monomer.

[0013] The "comb-like" or "branch-like" structure formed after the polymerization of polyoxyethylene ether macromonomers can form a three-dimensional cross with the side chains on the surface of other particles, thereby hindering the approach of cement particles to each other and achieving the effect of dispersion (i.e. water reduction). Moreover, this steric hindrance will not weaken with the extension of time. Therefore, the dispersing effect of polycarboxylic acid water reducer is more lasting.

[0014] 2-Acrylamide-2-methylpropanesulfonic acid (AMPS) is a vinyl monomer with a sulfonic acid group. Firstly, the AMPS molecular structure contains strong anionic, water-soluble sulfur groups, shielded amide groups and unsaturated double bonds. Therefore, the addition of AMPS can enhance the dispersibility and dispersion retention of the water reducer and the adsorption capacity of cement particles, thereby improving the fluidity, strength and durability of the concrete; secondly, AMPS has good thermal stability and hydrolysis stability, which can ensure that the water reducer maintains stable performance during long-term storage and use; thirdly, AMPS as A functional monomer that can copolymerize with other monomers such as acrylic acid, methacrylic acid, hydroxypropyl acrylate and hydroxyethyl acrylate to form a polycarboxylic acid water reducer with a specific molecular structure; finally, the molecular structure of AMPS contains carboxylic acid groups with scale inhibition and dispersibility and highly polar sulfonic acid groups. These groups can improve calcium tolerance and have a significant scale inhibition effect on calcium phosphate, calcium carbonate, zinc scale, etc. in water, and have excellent dispersibility. Therefore, the addition of AMPS can further improve the scale inhibition performance of the water reducer and reduce cracks and defects caused by water evaporation and chemical reactions in the hardening process of concrete.

[0015] The first acrylic acid comonomer and the second acrylic acid hydroxy ester comonomer are copolymerized to obtain polycarboxylic acid. The carboxyl groups on the main chain of the polycarboxylic acid can interact strongly with cement particles (complexation and hydrogen bonding), thereby playing the role of a traditional water reducer. In addition, by replacing part of the acrylic acid with acrylic acid hydroxy ester, part of the carboxyl groups can be protected in the form of ester groups, and the terminal hydroxyl groups can enhance the hydrophilicity of the polycarboxylic acid admixture. Under the alkaline environment of the cement paste, the ester groups of the polycarboxylic acid admixture prepared in this way gradually hydrolyze and release carboxyl groups, which can play the role of continuously dispersing cement. Therefore, the hydrolysis effect of small molecular ester compounds can be used to adjust the retarding performance of the polycarboxylic acid water reducer. At the same time, the small molecular propylene glycol and / or ethylene glycol generated by hydrolysis can be adsorbed on the surface of cement, fly ash or sand and gravel particles, which can not only play a plasticizing role, but also play an air entraining, anti-seepage and anti-freezing role.

[0016] Therefore, the polycarboxylic acid admixture of the present invention integrates the functions of water reduction, retarding setting and air entraining, has a high water reduction rate, a high compressive strength ratio, and an appropriate air content. Under a certain water consumption, it has a smaller VC value, and the VC value retention effect is greatly improved compared with commercially available products; the retarding effect is good, the initial setting is significantly prolonged, the early cement hydration speed of concrete can be delayed, the time for the maximum temperature inside the concrete to appear is delayed, and the maximum temperature inside the concrete is reduced, the temperature control difficulty is reduced, and the initial and final setting time distributions are reasonable and convenient for construction; it has good construction adaptability, can meet the use requirements of roller compacted concrete and various low-slump concretes, and specifically solves the problems currently faced by roller compacted concrete.

[0017] As a preferred embodiment of the present technical solution, the macromonomer used in the present invention includes a mixture of any one or more of allyl polyoxyethylene ether, isopentanol polyoxyethylene ether and methyl allyl polyoxyethylene ether in any proportion; and the molecular weight of the above macromonomer is preferably 1500-3000.

[0018] As a preferred embodiment of the present technical solution, the molar ratio of the macromonomer to 2-acrylamide-2-methylpropane sulfonic acid of the present invention is 5:1-10:1. By adjusting the ratio of AMPS to the macromonomer, the molecular structure of the polycarboxylic acid water-reducing agent can be optimized to meet the demand for water-reducing performance.

[0019] The ratio of the sum of the molar amounts of the first comonomer and the second comonomer (i.e., the comonomer content) to the molar amount of the macromonomer is 1:3 to 3:1. When used, the ratio between the two can be adjusted according to the performance of the admixture. For example, if the admixture needs to have good water-reducing performance, the macromonomer content is increased; if the admixture needs to have good retarding performance, the comonomer concentration is increased.

[0020] The molar ratio of the first comonomer to the second comonomer is 1:1 to 1:3. Similarly, when used, the ratio of the two can be adjusted according to the performance of the polycarboxylic acid admixture. For example, if good initial fluidity is required, the content of the first comonomer is increased. If good fluidity needs to be maintained in the later stage, the content of the second comonomer is increased.

[0021] As a preferred embodiment of the present technical solution, the mass ratio of part of the first comonomer to the remaining first comonomer is 4:6~6:4.

[0022] Since the reaction activity of the macromonomer is relatively low, the macromonomer is first polymerized with part of the acrylic acid (or methacrylic acid) for a period of time, and then the remaining acrylic acid (or methacrylic acid) and hydroxy acrylate are added for copolymerization. This is not only beneficial to increase the polymerization degree of the macromonomer, but also the distribution of each monomer on the molecular chain is more uniform (mainly random copolymerization rather than block copolymerization), and the resulting polycarboxylic acid admixture has better performance.

[0023] As a preferred embodiment of the present technical solution, in the second comonomer, the molar ratio of hydroxypropyl acrylate to hydroxyethyl acrylate is 3:7-7:3.

[0024] As a preferred embodiment of the present technical solution, the initiator includes any one or more of potassium persulfate, ammonium persulfate, sodium persulfate and a mixture of hydrogen peroxide / vitamin E; the molecular weight regulator includes any one or more of thioglycolic acid and mercaptopropionic acid. The amount of the initiator and the molecular weight regulator is preferably such that the concentration of the initiator in the final reaction system is 0.1% to 1wt%, and the concentration of the molecular weight regulator is 0.5 to 5wt%.

[0025] In a second aspect, the present invention further discloses a method for preparing the above-mentioned polycarboxylic acid admixture, which should also fall within the protection scope of the present invention. Specifically, the preparation method comprises the following steps: First, add material A to the polymerization base continuously, and then start to add material B continuously after the reaction for 20 to 40 minutes. After the addition of material A and material B is completed, keep the temperature for 1 to 2 hours, stop the reaction and stir to cool down. After the reaction system cools to room temperature, adjust the pH value of the polymerization solution to 6 to 8.

[0026] As a preferred embodiment of the present technical solution, the time for continuous and stable addition of material A is 1 to 4 hours, and the time for continuous and stable addition of material B is 1.5 to 5 hours; the temperature of the entire polymerization reaction is 40 to 80°C, and the mass concentration of the polymer after the reaction is completed is preferably 20% to 60%.

[0027] The water used in the polymerization is deionized water or distilled water. The amount of water added to the polymerization base material, A material and B material is based on the complete and uniform dissolution of the macromonomer, the first comonomer, AMPS and the second comonomer.

[0028] As a preferred embodiment of the present technical solution, in the reaction system, the mass concentration of the initiator is 0.1% to 1%, and the mass concentration of the molecular weight regulator is 0.5% to 5%.

[0029] As a preferred embodiment of the present invention, the alkali used to adjust the pH is sodium hydroxide or sodium carbonate.

[0030] In a third aspect, the present invention also discloses the application of the above-mentioned polycarboxylic acid admixture in roller compacted concrete, which should also fall within the protection scope of the present invention.

[0031] The polycarboxylic acid admixture of the present invention has at least the following beneficial effects: 1. The polycarboxylic acid admixture of the present invention is prepared by free radical copolymerization of polyether-type macromolecules containing polyoxyethylene ether groups, acrylic acid and acrylic acid hydroxy esters. The prepared polycarboxylic acid admixture includes two main components: polyoxyethylene ether macromonomer polymer and polycarboxylic acid. The carboxylic acid groups on the main chain can interact strongly with cement particles (complexation and hydrogen bonding), thereby playing the role of a traditional water reducer; and the "comb-like" or "branch-like" structure formed after the polymerization of polyoxyethylene ether macromonomers forms a three-dimensional intersection with the side chains on the surface of other particles, thereby hindering the cement particles from approaching each other and achieving the effect of dispersion (i.e., water reduction). The above-mentioned steric hindrance will not weaken with the extension of time, so the dispersing effect of the polycarboxylic acid admixture is more durable; 2. The second comonomer in the polycarboxylic acid admixture of the present invention is hydroxyl acrylic acid ester, that is, part of the carboxyl groups are protected in the form of ester groups, and the terminal hydroxyl groups can enhance the hydrophilicity of the polycarboxylic acid admixture. Under the alkaline environment of cement paste, the ester groups of the polycarboxylic acid admixture gradually hydrolyze and release carboxyl groups, which can play a role in continuous dispersion of cement. Therefore, the hydrolysis effect of small molecular ester compounds can be used to adjust the retarding properties of the polycarboxylic acid water reducer. At the same time, the small molecular propylene glycol and / or ethylene glycol generated by hydrolysis can be adsorbed on the surface of cement, fly ash or sand and gravel particles, which can not only play a plasticizing role, but also play an air entraining, anti-seepage and anti-freezing role; 3. The polycarboxylic acid admixture of the present invention integrates the functions of water reduction, retarding setting and air entraining, has a high water reduction rate, a high compressive strength ratio, an appropriate air content, a good VC value retention effect, a good retarding effect, and a reasonable distribution of initial and final setting time, which is convenient for construction, and specifically solves the problems currently faced by roller compacted concrete; 4. The polycarboxylic acid admixture of the present invention can not only improve the performance of rolled concrete and reduce the cost of use, but also bring great convenience to the construction control of rolled concrete, reduce risks and hidden dangers, provide a broader operating space for the application of rolled concrete, and have good economic and social benefits. DETAILED DESCRIPTION

[0032] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0033] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form also includes the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this description, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0034] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Example 1 Preparation of base material: first prepare the polymerization base material in a stirred polymerization kettle, add 290 kg of isopentanol polyoxyethylene ether with an average molecular weight of 2000, 6.1 kg of 2-acrylamide-2-methylpropanesulfonic acid, 6.5 kg of acrylic acid and 400 kg of water, and stir until completely dissolved; Prepare material A: add 8.5 kg of initiator hydrogen peroxide / vitamin E mixture, 42.5 kg of molecular weight regulator mercaptopropionic acid and 60 kg of water into the material A tank, stir and mix evenly for later use; Prepare material B: add 9.5 kg of acrylic acid, 14.5 kg of hydroxypropyl acrylate, 12.9 kg of hydroxyethyl acrylate and 50 kg of water into the material B tank, stir and mix evenly for later use.

[0036] Turn on the heating, heat the solution in the polymerization kettle to 60°C, and then start to add material A, and use a metering pump to control the continuous and uniform addition of material A, and the addition time is controlled within 2 hours; 30 minutes after the addition of material A, start to add material B, and also use a metering pump to control the continuous and uniform addition of material B, and the addition time is controlled within 2.5 hours.

[0037] After the addition of material A and material B, the reaction was kept warm for 1.5 hours, and then the temperature was lowered. After the reaction system was cooled to room temperature, the polymerization solution was neutralized with 30% sodium hydroxide solution to pH = 6-7.

[0038] Example 2 Preparation of base material: first prepare the polymerization base material in a stirred polymerization kettle, add 300 kg of methyl allyl polyoxyethylene ether with an average molecular weight of 2500, 9 kg of 2-acrylamide-2-methylpropane sulfonic acid, 12 kg of acrylic acid and 400 kg of water, and stir until completely dissolved; Prepare material A: add 10 kg of initiator potassium persulfate, 50 kg of molecular weight regulator thioglycolic acid and 60 kg of water into the material A tank, stir and mix evenly for later use; Prepare material B: add 15 kg of acrylic acid, 18 kg of hydroxypropyl acrylate, 15 kg of hydroxyethyl acrylate and 50 kg of water into the material B tank, stir and mix evenly for later use.

[0039] Turn on the heating, heat the solution in the polymerization kettle to 70°C, and then start to add material A, and use a metering pump to control the continuous and uniform addition of material A, and the addition time is controlled to be 3 hours; 30 minutes after the addition of material A, start to add material B, and also use a metering pump to control the continuous and uniform addition of material B, and the addition time is controlled to be 4 hours.

[0040] After the addition of material A and material B, the reaction was kept warm for 2 hours, and then the temperature was lowered. After the reaction system was cooled to room temperature, the polymerization solution was neutralized with 30% sodium hydroxide solution to pH = 6-7.

[0041] Example 3 Preparation of base material: first prepare the polymerization base material in a stirred polymerization kettle, add 300 kg of allyl polyoxyethylene ether with an average molecular weight of 2200, 10 kg of 2-acrylamide-2-methylpropane sulfonic acid, 8.5 kg of acrylic acid and 400 kg of water, and stir until completely dissolved; Prepare material A: add 12 kg of initiator ammonium persulfate, 45 kg of molecular weight regulator thioglycolic acid and 60 kg of water into the material A tank, stir and mix evenly for later use; Prepare material B: add 10 kg of acrylic acid, 18 kg of hydroxypropyl acrylate, 15 kg of hydroxyethyl acrylate and 50 kg of water into the material B tank, stir and mix evenly for later use.

[0042] Turn on the heating, heat the solution in the polymerization kettle to 80°C, and then start to add material A, and use a metering pump to control the continuous and uniform addition of material A, and the adding time is controlled to be 3 hours; start to add material B 30 minutes after the addition of material A, and also use a metering pump to control the continuous and uniform addition of material B, and the adding time is controlled to be 4 hours.

[0043] After the addition of material A and material B, the reaction was kept warm for 2 hours, and then the temperature was lowered. After the reaction system was cooled to room temperature, the polymerization solution was neutralized with 30% sodium hydroxide solution to pH = 6-7.

[0044] Example 4 Preparation of base material: first prepare the polymerization base material in a stirred polymerization kettle, add 290 kg of isopentanol polyoxyethylene ether with an average molecular weight of 2000, 8.5 kg of 2-acrylamide-2-methylpropanesulfonic acid, 8.5 kg of methacrylic acid and 400 kg of water, and stir until completely dissolved; Prepare material A: add 10 kg of initiator hydrogen peroxide / vitamin E mixture, 45 kg of molecular weight regulator mercaptopropionic acid and 60 kg of water into the material A tank, stir and mix evenly for later use; Prepare material B: add 12kg methacrylic acid, 13kg hydroxypropyl acrylate, 18kg hydroxyethyl acrylate and 50kg water into the material B tank, stir and mix evenly for later use.

[0045] Turn on the heating, heat the solution in the polymerization kettle to 50°C, and then start to add material A, and use a metering pump to control the continuous and uniform addition of material A, and the addition time is controlled to be 3 hours; start to add material B 60 minutes after the addition of material A, and also use a metering pump to control the continuous and uniform addition of material B, and the addition time is controlled to be 4 hours.

[0046] After the addition of material A and material B, the reaction was kept warm for 2 hours, and then the temperature was lowered. After the reaction system was cooled to room temperature, the polymerization solution was neutralized with 30% sodium hydroxide solution to pH = 6-7.

[0047] Comparative Example 1 A commercially available slow-setting high-efficiency water-reducing agent commonly used in roller compacted concrete.

[0048] Comparative Example 2 The common commercially available slow-setting polycarboxylic acid high-performance water-reducing agent AN4000 produced by a certain company.

[0049] Comparative Example 3 The common commercially available slow-setting polycarboxylic acid high-performance water-reducing agent KDSP type produced by a certain company.

[0050] Comparative Example 4 This comparative example is substantially the same as Example 1, except that the mixture of hydroxypropyl acrylate and hydroxyethyl acrylate in Example 1 is completely replaced by acrylic acid.

[0051] Comparative Example 5 This comparative example is substantially the same as Example 1, except that the mixture of hydroxypropyl acrylate and hydroxyethyl acrylate in Example 1 is replaced by a mixture of hydroxypropyl methacrylate and hydroxyethyl methacrylate.

[0052] Test Example 1 The present invention refers to the technical requirements for slow-setting high-performance water reducers in the national standard GB 8076-2008 "Concrete Admixtures" and the industry standard DL / T 5100-2014 "Technical Specifications for Hydraulic Concrete Admixtures", and the homogeneity of the polycarboxylic acid admixtures prepared in the above embodiments and control examples is tested. The specific test results are shown in Table 1-2.

[0053] Table 1 Homogeneity test results

[0054] Table 2 Homogeneity test results

[0055] It can be seen from Table 1-2 that the polycarboxylic acid admixtures prepared in Examples 1-4 of the present invention fully meet the technical requirements for the homogeneity index of slow-setting high-performance water-reducing agents in the national standard GB8076-2008 "Concrete Admixtures" and the industry standard DL / T 5100-2014 "Technical Specifications for Hydraulic Concrete Admixtures".

[0056] Comparative Example 1 is a retarding high-efficiency water-reducing agent for roller compacted concrete admixtures currently used in the market, but there are problems such as high chloride ion content and high alkali content. The high chloride ion content has the risk of corroding steel bars, and the high alkali content has a certain negative impact on the later strength and durability of concrete, and there is also a risk of alkali-aggregate reaction; Comparative Examples 2-3 are ordinary commercially available retarding polycarboxylic acid high-performance water-reducing agents, and Comparative Examples 4-5 are self-produced polycarboxylic acid admixtures analogous to Example 1. The chloride ion content and alkali content of Comparative Examples 2-5 are very low, and both meet the technical requirements for the homogeneity index of retarding high-performance water-reducing agents in GB 8076-2008 "Concrete Admixtures" and DL / T5100-2014 "Technical Specifications for Hydraulic Concrete Admixtures".

[0057] Test Example 2 The present invention further adopts the roller compacted concrete mix ratio used in the current project, and uses the polycarboxylic acid admixtures in the embodiments and the control examples in the following mix ratios to carry out concrete tests (Table 3), and tests the properties of the resulting mixtures (Table 4), and the test method is as follows: (1) Water reduction rate The water reduction ratio was determined by using a mix ratio of 360 kg / m 3 The cement dosage, 45% sand ratio, and repeated adjustment of water consumption to make the concrete slump 200mm~220mm, the recorded water consumption is the baseline water consumption of the control group (W B Add appropriate amount of admixtures and adjust the water consumption repeatedly to make the slump of concrete 210mm±10mm. The water consumption is recorded as the water consumption of the experimental group (W A ).

[0058] Water reduction rate according to W R =(W B -W A ) / W B* 100% calculation.

[0059] (2) Water seepage rate The water seepage rate is tested in accordance with the provisions of DL / T 5150-2017 "Test Procedures for Hydraulic Concrete", and the test materials and mix ratio are the same as the mix ratio determined by water reduction rate. The water seepage rate of the reference group is recorded as (B B ), the water seepage rate of the experimental group with appropriate amount of admixture is (B A ).

[0060] The water bleeding rate ratio should be based on B R =B A / B B *100% calculation.

[0061] (3) Compressive strength ratio The compressive strength ratio test is carried out in accordance with the determination method of DL / T 5150-2017 "Test Procedure for Hydraulic Concrete".

[0062] (4) Coagulation time The setting time is determined by using the same concrete mix ratio as that used to determine the VC value. The resulting mixture is sieved through a 4.75 mm sieve to obtain mortar. According to the method for determining the setting time specified in DL / T 5433-2009 "Test Procedure for Hydraulic Roller Compacted Concrete", the initial setting time and final setting time of the reference group without admixtures, the initial setting time and final setting time of the group with appropriate admixtures are measured, and the corresponding differences are the initial setting extension time and the final setting extension time.

[0063] In this experiment, the sand is medium sand with a fineness modulus of 2.7 and a mud content of 0.7%; the crushed stone is obtained by crushing granite with a continuous gradation of 5~37.5mm; the fly ash is Huadian Grade 1 fly ash, and the cement is low-alkali cement.

[0064] Table 3 RCC mix ratio (unit: kg)

[0065] Table 4 Performance of RCC mixture

[0066] Test Example 3 The present invention tests the VC value at each stage of the construction process. In this test example, the VC value is determined by using the C20 secondary grade roller compacted concrete mix ratio actually used in the project, and the test mixing is carried out according to the method required by DL / T 5433-2009 "Test Procedure for Hydraulic Roller Compacted Concrete", and the obtained mixture is screened out of aggregates above 40mm. The total weight of the slide bar and the counterweight block is 17.75kg, and the initial VC value is measured. The mixture is covered with a wet sack, and the VC value is re-measured after 1 hour, and the loss of VC value within 1 hour can be obtained. The test is repeated every 1 hour, and the VC value can be continuously recorded until it is approximately equal to 25s (the test results are shown in Table 5).

[0067] Table 5 Test results of VC value of RCC with different polycarboxylic acid admixtures

[0068] Dynamic control of VC value is the key to ensure the rollability and interlayer bonding of RCC. The VC value of RCC is one of the important indicators for quality control at the construction site. The VC value specified in my country's RCC construction specifications is within 2~12s. A large amount of construction experience shows that the VC value within 3~6.5s is most conducive to construction and interlayer bonding.

[0069] Combined with Tables 3-5 in the above-mentioned Test Examples 2 and 3, it can be seen that the polycarboxylic acid admixtures prepared in Examples 1-4 of the present invention have a high water reduction rate, a high compressive strength ratio, and an appropriate air content. Under a certain water consumption, they have a small VC value and a good VC value retention effect, and are more suitable for roller compacted concrete. Under the condition of meeting the good VC value of roller compacted concrete, the obtained concrete is soft, not easy to harden, easy to roll, has a better air entrainment effect, and has the characteristics of reasonable initial and final setting time distribution and convenient construction, which is more conducive to ensuring good engineering quality and specifically solves the problems currently faced by roller compacted concrete.

[0070] Comparative Example 1 is a retarding high-efficiency water-reducing agent commonly used in the market for roller compacted concrete admixtures. It has a very low water reduction rate, so a very high dosage is required. It has a very low air content, a relatively low compressive strength ratio, a suitable initial setting time, but a long final setting time, which prolongs the construction time of roller compacted concrete, reduces construction efficiency, and increases construction costs. Comparative Example 2-3 is a common commercially available slow-setting polycarboxylic acid high-performance water-reducing agent. When used in roller compacted concrete, it generally has the following problems: high water reduction rate but poor adaptability, very low air content, large fluctuation of VC value, extreme sensitivity, hard and dry concrete slab is difficult to roll, uneven slurry discharge, excessive loss of VC value during operation, unreasonable setting time and difficulty in construction; In Comparative Example 4, the mixture of hydroxypropyl acrylate and hydroxyethyl acrylate in Example 1 was completely replaced with acrylic acid. Since the selection of raw materials was not the most preferred combination, the water reduction rate was very high when used in rolled concrete, but the adaptability was poor, the air content was low, the VC value fluctuated greatly, was extremely sensitive, the dry and hard concrete was hardened and difficult to roll, the slurry was uneven, the VC value lost too much during the operation, and the setting time was unreasonable and difficult to construct. In Control Example 5, the mixture of hydroxypropyl acrylate and hydroxyethyl acrylate in Example 1 was replaced with a mixture of hydroxypropyl methacrylate and hydroxyethyl methacrylate. Since the selection of raw materials was not the most preferred combination, the water reduction rate was high but the adaptability was general when used in rolled concrete, the air content was low, the VC value fluctuated greatly and was relatively sensitive, the dry hard concrete slurry was uneven, and the unreasonable setting time affected the construction.

[0071] Engineering application cases The Julius Nyerere Hydropower Station is located on the Rufuji River in southeastern Tanzania, about 350 kilometers from Dar es Salaam, the largest city in Tanzania. The main tasks of the project are power generation and irrigation. The power station has 9 units with a total installed capacity of 2,115MW and an annual power generation of 6,307GW•h.

[0072] The project is the largest hydropower project in Africa so far. Once completed, it will surpass Egypt's Aswan High Dam (2,100 MW), Mozambique's Cahora Bassa Dam (2,075 MW) and Angola's Laúca Dam (2,069 MW) to become the dam with the largest installed capacity in Africa.

[0073] The maximum dam height of the project is about 131m, and the total water storage capacity exceeds 30 billion cubic meters. After the project is completed, the installed capacity of the power station will account for more than 60% of the total installed capacity of power stations in Tanzania, and it will become its main power energy production base.

[0074] The main construction content of the project includes a main dam and ancillary structures, of which the main project involves open excavation of about 5 million cubic meters of earth and stone, 592,400 cubic meters of stone tunnel excavation, 2.372 million cubic meters of concrete, 57,000 tons of steel bars, and 295,000 cubic meters of curtain consolidation grouting.

[0075] The project is located in Tanzania National Park, which has a tropical marine climate and a high annual average temperature. The environmental protection requirements near the dam area are high, and the terrain and geological conditions are complex; the temperature in the dry season is very high, and the temperature changes greatly in each season; the local construction material production capacity is low, and the transportation conditions are limited; the industrial foundation is weak, and materials are relatively scarce.

[0076] Table 6 shows the mix proportion of RCC for this project (C20), and Table 7 shows the performance index of RCC.

[0077] Table 6 Project Roller Compacted Concrete Mix Ratio (Unit: kg)

[0078] Table 7 Performance index of RCC

[0079] From Tables 6-7, it can be seen that the air content of the project is appropriate after using the polycarboxylic acid admixture of the present invention, and the resulting rolled concrete mixture is soft and easy to roll; the VC value is small and the VC value retention effect is good; the retarding effect is good, and the on-site setting time detection shows that the initial and final setting times are reasonably distributed, which is very convenient for project construction.

[0080] In summary, the polycarboxylic acid admixture of the present invention integrates water reduction, retarding setting and air entraining functions, has a high water reduction rate, a high compressive strength ratio, and an appropriate air content. Under a certain water consumption, it has a smaller VC value, and the VC value retention effect is greatly improved compared with commercially available products; the retarding effect is good, the initial setting is significantly prolonged, the early cement hydration speed of concrete can be delayed, the time for the maximum temperature inside the concrete to appear is delayed, and the maximum temperature inside the concrete is reduced, the temperature control difficulty is reduced, and the initial and final setting time distributions are reasonable and convenient for construction; it has good construction adaptability, can meet the use requirements of roller compacted concrete and various low-slump concretes, and solves the problems currently faced by roller compacted concrete in a targeted manner.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A polycarboxylic acid admixture, characterized in that: The method is prepared by free radical copolymerization of a polymer base material, an A material and a B material, wherein the polymer base material comprises a macromonomer, 2-acrylamide-2-methylpropanesulfonic acid, a part of a first comonomer and water, the A material comprises an initiator, a molecular weight regulator and water, and the B material comprises the remaining first comonomer, a second comonomer and water; Wherein, the macromonomer is a polyether-type macromolecule containing a polyoxyethylene ether group; The first comonomer includes any one or both of acrylic acid and methacrylic acid; The second comonomer is a mixture of hydroxypropyl acrylate and hydroxyethyl acrylate.

2. The polycarboxylic acid admixture according to claim 1, characterized in that The macromonomer includes any one or more of allyl polyoxyethylene ether, isopentanol polyoxyethylene ether and methyl allyl polyoxyethylene ether; The molecular weight of the macromonomer is 1500-3000.

3. The polycarboxylic acid admixture according to claim 1, characterized in that: The molar ratio of the macromonomer to 2-acrylamide-2-methylpropanesulfonic acid is 5:1 to 10:1; The ratio of the sum of the molar amounts of the first comonomer and the second comonomer to the molar amount of the macromonomer is 1:3 to 3:1; The molar ratio of the first comonomer to the second comonomer is 1:1 to 1:

3.

4. The polycarboxylic acid admixture according to claim 1, characterized in that: The mass ratio of part of the first comonomer to the remaining first comonomer is 4:6~6:

4.

5. The polycarboxylic acid admixture according to claim 1, characterized in that: In the second comonomer, the molar ratio of hydroxypropyl acrylate to hydroxyethyl acrylate is 3:7 to 7:

3.

6. The polycarboxylic acid admixture according to claim 1, characterized in that: The initiator includes any one or more of potassium persulfate, ammonium persulfate, sodium persulfate and a hydrogen peroxide / vitamin E mixture; The molecular weight regulator includes any one or more of thioglycolic acid and mercaptopropionic acid.

7. The method for preparing the polycarboxylic acid admixture according to any one of claims 1 to 6, characterized in that: The following steps are involved: First, add material A to the polymerization base continuously, and then start to add material B continuously after the reaction for 20 to 40 minutes. After the addition of material A and material B is completed, keep the temperature for reaction for 1 to 2 hours. After the reaction system cools to room temperature, adjust the pH value of the polymerization solution to 6 to 8.

8. The preparation method according to claim 7, characterized in that: The continuous and stable addition time of material A is 1~4h, and the continuous and stable addition time of material B is 1.5~5h; The temperature of the entire polymerization reaction is 40~80℃.

9. The preparation method according to claim 7, characterized in that: In the reaction system, the mass concentration of the initiator is 0.1%~1%, and the mass concentration of the molecular weight regulator is 0.5%~5%.

10. Use of the polycarboxylic acid admixture according to any one of claims 1 to 6 in roller compacted concrete.

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