阅读说明：本技术 一种混凝土减水剂及其生产方法 (Concrete water reducing agent and production method thereof ) 是由 段平娥 张召伟 于 2021-11-01 设计创作，主要内容包括：本发明公开了一种混凝土减水剂及其生产方法,主要原料包括：甲基烯基聚氧乙烯醚、苯乙烯磺酸钠、氧化石墨烯、丙稀酰胺聚合物,丙烯酸、木质素磺酸钙、芦丁；将氧化石墨烯用作聚羧酸减水剂共聚物的单体,采用自由基共聚法制备得到氧化石墨烯聚羧酸减水剂层间配合物,再加入了一定配比的丙稀酰胺聚合物,能有效降低水泥浆体的黏度,达到阻泥的效果,还能改善混凝土的保坍性能,有助于混凝土抗压性能的提升。不仅如此,在减水剂中添加木质素磺酸钠和芦丁还能够有效提高混凝土的抗氯离子渗透性能。(The invention discloses a concrete water reducing agent and a production method thereof, and the concrete water reducing agent mainly comprises the following raw materials: methyl alkenyl polyoxyethylene ether, sodium styrene sulfonate, graphene oxide, acrylamide polymer, acrylic acid, calcium lignosulfonate and rutin; graphene oxide is used as a monomer of a polycarboxylate water reducer copolymer, a free radical copolymerization method is adopted to prepare an graphene oxide polycarboxylate water reducer interlayer complex, and an acrylamide polymer with a certain proportion is added, so that the viscosity of cement paste can be effectively reduced, the mud blocking effect is achieved, the slump retaining performance of concrete can be improved, and the improvement of the compression resistance of the concrete is facilitated. Moreover, sodium lignosulfonate and rutin are added into the water reducing agent, so that the chloride ion penetration resistance of the concrete can be effectively improved.)

1. The production method of the concrete water reducing agent is characterized by comprising the following steps:

s1, mixing 180-200 parts by weight of methyl alkenyl polyoxyethylene ether, 7-9 parts by weight of sodium styrene sulfonate and 100-120 parts by weight of water, heating to 40-55 ℃, and stirring for 30-40 min to dissolve to obtain a mixed solution;

s2, adding 60-90 parts by weight of graphene oxide solution and 8-13 parts by weight of acrylamide polymer into the mixed solution in the step S1, stirring and mixing for 20-30 min, adding 5-8 parts by weight of oxidant, adding 10-12 parts by weight of reducing agent after reacting for 30-35 min, reacting for 30-60 min, and then preserving heat of the mixed solution at 55-60 ℃ for 6-8 h;

s3, adding acrylic acid into the heat-preserved solution, mixing for 30-40 min, adding 28-30 wt% of NaOH aqueous solution, adjusting the pH value to 6-7, cooling to 20-25 ℃, adding 10-15 parts by weight of calcium lignosulphonate and 5-15 parts by weight of rutin, and uniformly mixing to obtain the concrete water reducer.

2. The production method of the concrete water reducer according to claim 1, wherein the graphene oxide solution is prepared by the following method: taking 2.4-3 g of graphite powder, adding 72-80 mL of mixed acid of 95-98 wt% of sulfuric acid and 80-85 wt% of phosphoric acid into an ice water bath, wherein the volume ratio of the sulfuric acid to the phosphoric acid is (9-10): 1, stirring for 20-30 min, and adding 3-5 g of NaNO₃Reacting for 15-20 min, slowly adding 9.6-10 g of potassium permanganate, stirring for 2-3H, stirring for 2-2.5H at 39-42 ℃, adding 123-131 mI of water, heating to 92-95 ℃, stirring for 1.5-2H, and slowly dropwise adding 25-30% by volume of H₂O₂And (3) reacting the aqueous solution for 1-2 hours, adding 300-500 mL of 1mol/L HC1, stirring for 1-1.5 hours, pouring out the product, adding 500-700 mL of water, and putting the product into an ultrasonic pot for ultrasonic treatment for 3-4 hours to obtain the graphene oxide solution.

3. The production method of the concrete water reducer according to claim 1, wherein the acrylamide polymer is prepared by the following method: dissolving acrylamide in water, and adding ammonium persulfate and sodium methyl acrylate sulfonate, acrylamide: ammonium persulfate: the mol ratio of the sodium methallyl sulfonate is 3: (0.8-1): (0.8-1), stirring for 1-1.5 h, heating to 55-60 ℃, preserving heat for 1-2 h, cooling to 20-25 ℃, and adjusting the pH to 7-8 by using 25-30 wt% of NaOH aqueous solution to obtain the acrylamide polymer.

4. The production method of the concrete water reducing agent according to claim 1, characterized in that: the oxidant in step S2 is a mixture of ammonium persulfate and hydrogen peroxide.

5. The production method of the concrete water reducing agent according to claim 1, characterized in that: the oxidant in the step S2 is prepared by mixing ammonium persulfate and 30 wt% aqueous hydrogen peroxide in a mass-to-volume ratio of 2: 5 g/mL.

6. The production method of the concrete water reducing agent according to claim 1, characterized in that: the reducing agent in step S2 is L-ascorbic acid.

7. The production method of the concrete water reducing agent according to claim 1, characterized in that: the molar ratio of the methyl alkenyl polyoxyethylene ether to the acrylic acid in the step S1 is 1: (1-2).

8. A concrete water reducing agent is characterized in that: the concrete water reducing agent is prepared by the production method of the concrete water reducing agent according to any one of claims 1 to 7.

Technical Field

The invention relates to the technical field of concrete admixtures, in particular to a concrete water reducing agent and a production method thereof.

Background

The polycarboxylate superplasticizer is a novel superplasticizer which is developed most rapidly in recent years, and as a third-generation superplasticizer, compared with the traditional lignin water reducers and naphthalene water reducers, the polycarboxylate superplasticizer has the characteristics of high water reducing rate, good environmental protection property, excellent comprehensive performance and the like. And the polycarboxylic acid water reducing agent is known as the development direction of concrete admixtures in future, but the development of China is still in the initial stage. The research of the polycarboxylic acid water reducing agent in China begins at the middle and later stages of the 90 s in the 20 th century, the industrial production and the application of the polycarboxylic acid water reducing agent in the early stage of the 21 st century are widely applied to the projects of railway passenger transport special lines, south-to-north water diversion, ports and docks, hydroelectric dams, municipal administration and the like. In recent years, natural high-quality sandstone resources are increasingly tense, low-grade aggregate is increasingly used, the influence of the content of sand and stone on the polycarboxylate superplasticizer is more and more prominent, the further application of the polycarboxylate superplasticizer in premixed concrete is limited, and more importantly, the clay can also reduce the later-stage compressive strength of the concrete and influence the durability of the concrete. How to inhibit the negative effect of the clay on the polycarboxylate superplasticizer becomes an urgent problem to be solved.

At present, modification treatment can be carried out on a polycarboxylate superplasticizer from the molecular structure of the polycarboxylate superplasticizer for improving the mud resistance of the superplasticizer, and the modification treatment generally comprises the following five forms: the water reducing agent with a micro-crosslinking side chain structure is developed, the steric hindrance is improved, the adsorption of soil to the water reducing agent is reduced, and the dispersibility and slump retaining property of the water reducing agent are improved; rigid groups are introduced into the side chains of the polycarboxylic acid water reducing agent, so that the rigidity of the side chains can be improved, the water reducing agent molecules keep enough steric hindrance, and simultaneously, large-volume side chains are difficult to extend into soil layers to form intercalation adsorption, thereby ensuring higher water reducing rate and slump retaining property; the tail end of a long side chain of the polycarboxylic acid water reducing agent is subjected to charge modification, the entanglement effect of the long side chain is reduced through charge repulsion, the long side chain with negative charges at the end part can also have the repulsion effect on the soil with electronegativity, and the adsorption consumption of the soil on the water reducing agent is reduced; the length of the side chain of the water reducing agent molecule is increased, so that the steric hindrance of the water reducing agent molecule is effectively increased, the water reducing agent molecule is structurally more difficult to form intercalation adsorption on a lamellar structure of soil, the adsorption consumption of the soil on the polycarboxylic acid water reducing agent is reduced, and the high dispersibility of cement particles is obtained; various charged functional group modified polycarboxylic acid water reducing agents with mud resistance are introduced, the synthesis method mainly comprises a free radical monomer polymerization method and a two-step synthesis method, and the water reducing agents achieve the mud and slump loss resistance effect by introducing functional groups with different functions and electric charge quantities. In addition, the water reducing agent can be compounded with an anti-mud sacrificial agent when in use, the sacrificial agent is preferentially adsorbed by the mud to occupy the adsorption sites of the mud, the adsorption quantity of the mud to the water reducing agent is reduced, a large amount of unadsorbed polycarboxylic acid water reducing agent in cement slurry fully plays a dispersing role, and the effectiveness of the water reducing agent is maintained.

Chinese patent CN 107129177A discloses an anti-mud polycarboxylic acid water reducing agent, a production method and application thereof in concrete, the water reducing agent is a compound consisting of 100 parts by mass of the polycarboxylic acid water reducing agent and 0.01-5 parts by mass of a quaternized lignosulfonate anti-mud sacrificial agent, the fluidity of mud-containing cement paste can be obviously improved, such as slump or expansion, the cement paste has obvious anti-mud property, and the dispersing performance is excellent; chinese patent CN 111592272A discloses a polycarboxylate superplasticizer for machine-made sand concrete prestressed members and a production method thereof, wherein the polycarboxylate superplasticizer is prepared from the following raw materials in parts by mass: 50-100 parts of polyether macromonomer, 20-40 parts of ester macromonomer, 5-15 parts of maleic acid-beta-cyclodextrin, 5-15 parts of styrene, 30-60 parts of acrylic monomer, 10-30 parts of unsaturated phosphate ester and 5-25 parts of ammonium cation unsaturated monomer are used for preparing a polymer with the molecular weight of 15000-80000 in a free radical polymerization mode, 0-4 parts of a compound organic silicon defoamer, 0-10 parts of an early strength agent and 5-15 parts of a sacrificial agent are compounded, and then an alkali solution is added for neutralization. However, in the anti-mud polycarboxylate superplasticizer in the prior art, a sacrificial agent with high affinity needs to be introduced to maintain the dispersing capacity of the polycarboxylate superplasticizer, and the sacrificial agent does not have negative charges like the polycarboxylate superplasticizer and can interfere with the intercalation process. However, the introduction of the sacrificial agent tends to produce severe foaming, thereby reducing the mechanical properties of the concrete, and in addition, the dosage of the sacrificial agent required may be high, which is not economical and environmentally friendly. Therefore, the preparation of the high-efficiency water reducing agent which can effectively resist mud, does not need to introduce a large amount of sacrificial agents and does not reduce the mechanical property of concrete is urgent.

Disclosure of Invention

In order to solve the technical problems, the invention provides a concrete water reducing agent and a production method thereof, and the technical scheme is as follows:

a production method of a concrete water reducing agent comprises the following steps:

s1, mixing 180-200 parts by weight of methyl alkenyl polyoxyethylene ether, 7-9 parts by weight of sodium styrene sulfonate and 100-120 parts by weight of water, heating to 40-55 ℃, and stirring for 30-40 min to dissolve to obtain a mixed solution;

s2, adding 60-90 parts by weight of graphene oxide solution and 8-13 parts by weight of acrylamide polymer into the mixed solution in the step S1, stirring and mixing for 20-30 min, adding 5-8 parts by weight of oxidant, adding 10-12 parts by weight of reducing agent after reacting for 30-35 min, reacting for 30-60 min, and then preserving heat of the mixed solution at 55-60 ℃ for 6-8 h;

s3, adding acrylic acid into the heat-preserved solution, mixing for 30-40 min, adding 28-30 wt% of NaOH aqueous solution, adjusting the pH value to 6-7, cooling to 20-25 ℃, adding 10-15 parts by weight of calcium lignosulphonate and 5-15 parts by weight of rutin, and uniformly mixing to obtain the concrete water reducer.

Further, the oxidant in step S2 is a mixture of ammonium persulfate and hydrogen peroxide.

Further, the oxidant ammonium persulfate in the step S2 is mixed with 30 wt% aqueous hydrogen peroxide in a mass volume ratio of 2: 5 g/mL.

Further, the reducing agent in step S2 is L-ascorbic acid.

Further, the molar ratio of the methyl alkenyl polyoxyethylene ether to the acrylic acid in the step S1 is 1: (1-2).

The graphene oxide solution is prepared by the following method: taking 2.4-3 g of graphite powder, adding 72-80 mL of mixed acid of 95-98 wt% of sulfuric acid and 80-85 wt% of phosphoric acid into an ice water bath, wherein the volume ratio of the sulfuric acid to the phosphoric acid is (9-10): 1, stirring for 20-30 min, and adding 3-5 g of NaNO₃Reacting for 15-20 min, slowly adding 9.6-10 g of potassium permanganate, stirring for 2-3H, stirring for 2-2.5H at 39-42 ℃, adding 123-131 mI of water, heating to 92-95 ℃, stirring for 1.5-2H, and slowly dropwise adding 25-30% by volume of H₂O₂And (3) reacting the aqueous solution for 1-2 hours, adding 300-500 mL of 1mol/L HC1, stirring for 1-1.5 hours, pouring out the product, adding 500-700 mL of water, and putting the product into an ultrasonic pot for ultrasonic treatment for 3-4 hours to obtain the graphene oxide solution.

Graphene oxide is a two-dimensional nanomaterial formed by oxidizing graphene, and has a large specific surface area and a small pore size. Chemical functional groups such as hydroxyl, carboxyl, epoxy and the like in the graphene oxide structure can generate various interactions with the cement-based material, and the performance of the cement-based material is greatly influenced. Generally, the addition of graphene oxide to a cement-based material improves the microstructure performance of concrete, forms a more compact and uniform network structure, improves the mechanical properties of concrete, and prolongs the service life.

Meanwhile, the inventor finds that graphene oxide can be used as a monomer of a polycarboxylate superplasticizer copolymer, after the graphene oxide polycarboxylate superplasticizer interlayer complex is prepared by adopting a free radical copolymerization method, the graphene oxide polycarboxylate superplasticizer is added into a cement-based composite material, so that graphene oxide nanosheets can be uniformly dispersed in a cement matrix, the graphene oxide surface and polycarboxylate superplasticizer macromolecule are covalently grafted, and due to the electrostatic repulsion and steric hindrance effects, the fluidity of cement slurry can be improved, and the mud blocking effect is achieved. In addition, the graphene oxide polycarboxylate superplasticizer can promote crystallization of calcium hydroxide in cement paste, refine particle size and improve mechanical properties of concrete.

The acrylamide polymer is prepared by adopting the following method: dissolving acrylamide in water, and adding ammonium persulfate and sodium methyl acrylate sulfonate, acrylamide: ammonium persulfate: the mol ratio of the sodium methallyl sulfonate is 3: (0.8-1): (0.8-1), stirring for 1-1.5 h, heating to 55-60 ℃, preserving heat for 1-2 h, cooling to 20-25 ℃, and adjusting the pH to 7-8 by using 25-30 wt% of NaOH aqueous solution to obtain the acrylamide polymer.

The inventors have found that the incorporation of a low molecular weight acrylamide polymer into a polycarboxylic acid water reducing agent results in a conformational change in the water reducing agent in the cement suspension, while imparting a lower surface tension to the water reducing agent. The change of the conformation and the surface tension of the water reducing agent is supposed to generate the effect of being beneficial to reducing the viscosity of cement paste, thereby improving the fluidity of concrete to a certain extent. In addition, the hydrophobic structure unit in the water reducing agent is more curled in conformation in an aqueous solution, and can shield part of carboxylic acid adsorption groups on the main chain of the water reducing agent, so that the adsorption quantity of the water reducing agent on cement particles is reduced, the residual water reducing agent in cement interstitial fluid is increased, and the slump retaining performance is improved.

The invention also provides a concrete water reducing agent prepared by the production method.

According to the invention, graphene oxide is used as a monomer of a polycarboxylate water reducer copolymer, a free radical copolymerization method is adopted to prepare the graphene oxide polycarboxylate water reducer interlayer complex, the graphene oxide surface is covalently grafted with polycarboxylate water reducer macromolecules, and due to the electrostatic repulsion and steric hindrance effects, the fluidity of cement paste can be improved, and the mud blocking effect is achieved. In addition, the acrylamide polymer with a certain proportion is added on the basis of introducing the graphene oxide, so that the surface tension of the water reducing agent can be further changed, the viscosity of cement paste is reduced, and the slump retaining performance of concrete can be improved. In addition, sodium lignosulfonate and rutin are added into the water reducing agent, so that the chloride ion penetration resistance of the concrete can be effectively improved.

Detailed Description

The technical solutions in the embodiments of the present invention are clearly and completely described below. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention. The operations referred to in the examples are, unless otherwise specified, all those of ordinary skill in the art.

Some raw material parameters in the comparative examples and examples of the invention are as follows:

methylenylpolyoxyethylene ether, model TPEG-2400, available from Wuhanxin Jiali Biotech Co., Ltd;

sodium styrene sulfonate, CAS No.: 2695-37-6, available from Kyobei Makesi technologies, Inc.;

acrylic acid, CAS No.: 79-10-7, available from Shanghai Michelin Biotechnology, Inc.;

graphite powder of 200 meshes, purchased from a processing plant of a tourmaline mineral product in Lingshan county;

cement, 325 huarun cement, was purchased from rungai building materials ltd, mountain of buddha.

Example 1

The preparation method of the concrete water reducing agent comprises the following steps:

s1, mixing 180 parts by weight of methyl alkenyl polyoxyethylene ether, 7 parts by weight of sodium styrene sulfonate and 100 parts by weight of distilled water, heating to 50 ℃, and stirring for 30min to dissolve to obtain a mixed solution;

s2, adding 80 parts by weight of graphene oxide solution into the mixed solution in the step S1, stirring and mixing for 30min, adding 2 parts by weight of sulfuric acid and 5 parts by weight of 30 wt% aqueous hydrogen peroxide solution, reacting for 30min, adding 10 parts by weight of L-ascorbic acid, reacting for 30min, and then preserving the temperature of the mixed solution at 60 ℃ for 6 h;

s3, adding 58 parts by weight of acrylic acid into the heat-preserved solution, mixing for 40min, and then adding 30 wt% of NaOH aqueous solution to adjust the pH value to 7; and cooling to 25 ℃ to obtain the concrete water reducing agent.

The graphene oxide solution is prepared by the following method: taking 2.4g of graphite powder, adding 72mL of mixed acid of 97 wt% sulfuric acid and 85 wt% sulfuric acid and phosphoric acid into an ice-water bath, wherein the volume ratio of the sulfuric acid to the phosphoric acid is 9:1, stirring for 30min, and then adding 3g of NaNO₃Reacting for 20min, slowly adding 9.6g of potassium permanganate, stirring for 2H, stirring for 2.5H at 40 ℃, adding 123mI deionized water, heating to 95 ℃, stirring for 1.5H, and slowly adding 30% volume fraction H₂O₂And after the reaction is carried out for 1h, 300mL of HC1 with the concentration of 1mol/L is added, the mixture is stirred for 1.5h, the product is poured out, 500mL of water is added, and the mixture is placed in an ultrasonic pot and is subjected to ultrasonic treatment for 3h, so that the graphene oxide solution is obtained.

Example 2

The preparation method of the concrete water reducing agent comprises the following steps:

s1, mixing 180 parts by weight of methyl alkenyl polyoxyethylene ether, 7 parts by weight of sodium styrene sulfonate and 100 parts by weight of distilled water, heating to 50 ℃, and stirring for 30min to dissolve to obtain a mixed solution;

s2, adding 80 parts by weight of graphene oxide solution and 8 parts by weight of acrylamide polymer into the mixed solution in the step S1, stirring and mixing for 30min, adding 2 parts by weight of sulfuric acid and 5 parts by weight of 30 wt% aqueous hydrogen peroxide solution, reacting for 30min, adding 10 parts by weight of L-ascorbic acid, reacting for 30min, and then preserving the temperature of the mixed solution at 60 ℃ for 6 h;

s3, adding 58 parts by weight of acrylic acid into the heat-preserved solution, mixing for 40min, and then adding 30 wt% of NaOH aqueous solution to adjust the pH value to 7; and cooling to 25 ℃ to obtain the concrete water reducing agent.

The graphene oxide solution is prepared by the following method: taking 2.4g of graphite powder, adding 72mL of mixed acid of 97 wt% sulfuric acid and 85 wt% sulfuric acid and phosphoric acid into an ice-water bath, wherein the volume ratio of the sulfuric acid to the phosphoric acid is 9:1, stirring for 30min, and then adding 3g of NaNO₃Reacting for 20min, slowly adding 9.6g of potassium permanganate, stirring for 2H, stirring for 2.5H at 40 ℃, adding 123mI deionized water, heating to 95 ℃, stirring for 1.5H, and slowly adding 30% volume fraction H₂O₂And after the reaction is carried out for 1h, 300mL of HC1 with the concentration of 1mol/L is added, the mixture is stirred for 1.5h, the product is poured out, 500mL of water is added, and the mixture is placed in an ultrasonic pot and is subjected to ultrasonic treatment for 3h, so that the graphene oxide solution is obtained.

The acrylamide polymer is prepared by adopting the following method: dissolving 0.3mol of acrylamide in 250mL of water, adding 0.08mol of ammonium persulfate and 0.08mol of sodium methallyl sulfonate, stirring for 1h, heating to 55 ℃, keeping the temperature for 2h, cooling to 25 ℃, and then adjusting the pH to 7 by using 30 wt% of NaOH aqueous solution to obtain the acrylamide polymer.

Example 3

The preparation method of the concrete water reducing agent comprises the following steps:

s1, mixing 180 parts by weight of methyl alkenyl polyoxyethylene ether, 7 parts by weight of sodium styrene sulfonate and 100 parts by weight of distilled water, heating to 50 ℃, and stirring for 30min to dissolve to obtain a mixed solution;

s2, adding 8 parts by weight of acrylamide polymer into the mixed solution in the step S1, stirring and mixing for 30min, adding 2 parts by weight of sulfuric acid and 5 parts by weight of 30 wt% aqueous hydrogen peroxide, reacting for 30min, adding 10 parts by weight of L-ascorbic acid, reacting for 30min, and then preserving the temperature of the mixed solution at 60 ℃ for 6 h;

s3, adding 58 parts by weight of acrylic acid into the heat-preserved solution, mixing for 40min, and then adding 30 wt% of NaOH aqueous solution to adjust the pH value to 7; and cooling to 25 ℃ to obtain the concrete water reducing agent.

The acrylamide polymer is prepared by adopting the following method: dissolving 0.3mol of acrylamide in 250mL of water, adding 0.08mol of ammonium persulfate and 0.08mol of sodium methallyl sulfonate, stirring for 1h, heating to 55 ℃, keeping the temperature for 2h, cooling to 25 ℃, and then adjusting the pH to 7 by using 30 wt% of NaOH aqueous solution to obtain the acrylamide polymer.

Comparative example 1

The preparation method of the concrete water reducing agent comprises the following steps:

s1, mixing 180 parts by weight of methyl alkenyl polyoxyethylene ether, 7 parts by weight of sodium styrene sulfonate and 100 parts by weight of distilled water, heating to 50 ℃, and stirring for 30min to dissolve to obtain a mixed solution;

s2, adding 2 parts by weight of sulfuric acid and 5 parts by weight of 30 wt% aqueous hydrogen peroxide into the mixed solution in the step S1, reacting for 30min, adding 10 parts by weight of L-ascorbic acid, reacting for 30min, and then preserving the temperature of the mixed solution at 60 ℃ for 6 h;

s3, adding 58 parts by weight of acrylic acid into the heat-preserved solution, mixing for 40min, and then adding 30 wt% of NaOH aqueous solution to adjust the pH value to 7; and cooling to 25 ℃ to obtain the concrete water reducing agent.

Comparative example 2

The preparation method of the concrete water reducing agent comprises the following steps:

s1, mixing 180 parts by weight of methyl alkenyl polyoxyethylene ether, 7 parts by weight of sodium styrene sulfonate and 100 parts by weight of distilled water, heating to 50 ℃, and stirring for 30min to dissolve to obtain a mixed solution;

s2, adding 80 parts by weight of graphene oxide solution and 8 parts by weight of acrylamide into the mixed solution in the step S1, stirring and mixing for 30min, adding 2 parts by weight of sulfuric acid and 5 parts by weight of 30 wt% aqueous hydrogen peroxide solution, reacting for 30min, adding 10 parts by weight of L-ascorbic acid, reacting for 30min, and then preserving the temperature of the mixed solution at 60 ℃ for 6 h;

s3, adding 58 parts by weight of acrylic acid into the heat-preserved solution, mixing for 40min, and then adding 30 wt% of NaOH aqueous solution to adjust the pH value to 7; and cooling to 25 ℃ to obtain the concrete water reducing agent.

The graphene oxide solution is prepared by the following method: taking 2.4g of graphite powder, adding 72mL of mixed acid of 97 wt% sulfuric acid and 85 wt% sulfuric acid and phosphoric acid into an ice-water bath, wherein the volume ratio of the sulfuric acid to the phosphoric acid is 9:1, stirring for 30min, and then adding 3g of NaNO₃Reacting for 20min, slowly adding 9.6g of potassium permanganate, stirring for 2H, stirring for 2.5H at 40 ℃, adding 123mI deionized water, heating to 95 ℃, stirring for 1.5H, and slowly adding 30% volume fraction H₂O₂And after the reaction is carried out for 1h, 300mL of HC1 with the concentration of 1mol/L is added, the mixture is stirred for 1.5h, the product is poured out, 500mL of water is added, and the mixture is placed in an ultrasonic pot and is subjected to ultrasonic treatment for 3h, so that the graphene oxide solution is obtained.

Example 4

The preparation method of the concrete water reducing agent comprises the following steps:

s1, mixing 180 parts by weight of methyl alkenyl polyoxyethylene ether, 7 parts by weight of sodium styrene sulfonate and 100 parts by weight of distilled water, heating to 50 ℃, and stirring for 30min to dissolve to obtain a mixed solution;

s2, adding 80 parts by weight of graphene oxide solution and 8 parts by weight of acrylamide polymer into the mixed solution in the step S1, stirring and mixing for 30min, adding 2 parts by weight of sulfuric acid and 5 parts by weight of 30 wt% aqueous hydrogen peroxide solution, reacting for 30min, adding 10 parts by weight of L-ascorbic acid, reacting for 30min, and then preserving the temperature of the mixed solution at 60 ℃ for 6 h;

s3, adding 58 parts by weight of acrylic acid into the heat-preserved solution, mixing for 40min, and then adding 30 wt% of NaOH aqueous solution to adjust the pH value to 7; and cooling to 25 ℃, adding 12 parts by weight of calcium lignosulphonate and 12 parts by weight of rutin, and uniformly mixing to obtain the concrete water reducer.

The preparation method of the graphene oxide solution is the same as that in example 2, and details are not repeated here.

The preparation method of the acrylamide polymer is the same as that of example 2, and the details are not repeated herein.

Test example 1

The water reducing agents of examples 1 to 3 and comparative examples 1 and 2 were subjected to a cement paste fluidity test, and the cement paste fluidity thereof was measured by using cement commercially available on a cigarette bench according to the test method for concrete admixture uniformity of GB/T8077-2012. 294g of cement and 6g of montmorillonite are poured into a stirred tank, and 6g of water reducing agent is added to 87g of water, and then the mixture is poured into the stirred tank. After the stirring kettle is fixed, slowly stirring for 60s and then quickly stirring for 60s, taking down the stirring kettle, pouring cement paste into the mold, and then slowly lifting the mold to enable the cement paste to dispersedly flow on the glass plate. The net pulp fluidity at 0min and 30min was measured, the two largest diameters in the flow range were measured with a measuring tape, and the average was taken as the net pulp fluidity, and the test results are shown in table 1.

TABLE 1 neat paste fluidity

As can be seen from Table 1, the graphene oxide polycarboxylate water reducer is added into the cement-based composite material, so that graphene oxide nanosheets can be uniformly dispersed in a cement matrix, the graphene oxide surface and polycarboxylate water reducer macromolecules are covalently grafted, the fluidity of cement paste can be improved due to electrostatic repulsion and steric hindrance, and the micromolecule acrylamide polymer is introduced on the basis, so that the viscosity of the cement paste can be further reduced, and the fluidity of the cement paste can be improved.

Test example 2

The water reducing agents of examples 1 to 3 and comparative examples 1 and 2 were subjected to a montmorillonite interlamellar spacing test, the specific test method being: pouring 1g of montmorillonite and 1g of water reducing agent into a beaker filled with 48g of water, uniformly stirring, oscillating and centrifuging, taking out the lower-layer precipitate, drying, grinding, and tabletting to obtain a sample to be detected. After the XRD test is finished, the 2A value of the characteristic absorption peak of the montmorillonite adsorbed concrete water reducer is obtained through mapping, the numerical value of the interlayer distance is calculated through a Bragg equation 2dsin theta-n lambda, and the test result is shown in a table 2.

TABLE 2 table of montmorillonite interlamellar spacing measurement results

Examples	2θ/°	d/nm
			Example 1	6.58	1.32
Example 2	6.64	1.28
			Example 3	6.54	1.31
Comparative example 1	6.08	1.42
			Comparative example 2	6.23	1.36

Montmorillonite is a hydrous phyllosilicate mineral and has high water absorption. The polycarboxylate water reducing agent is easy to be intercalated and adsorbed with montmorillonite, and long side chains of the water reducing agent are inserted into an interlayer structure of the montmorillonite, so that the interlayer distance of the montmorillonite is increased, and the dispersing performance of the water reducing agent on cement particles is reduced. Therefore, the strength of intercalation adsorption is determined by measuring the interlayer spacing of the montmorillonite, and the advantages and the disadvantages of the mud resistance of the water reducing agent are reflected. Table 2 shows that after the polycarboxylic acid water reducing agent is polymerized with graphene oxide and acrylamide polymer, the side groups of the polycarboxylic acid water reducing agent are changed, so that the hydrophobic structure units in the water reducing agent are more curled in the aqueous solution, and the carboxylic acid adsorption groups on the main chain of the water reducing agent are shielded, so that the interlayer spacing of montmorillonite is reduced, the adsorption capacity of the water reducing agent on cement particles is reduced, and the residual water reducing agent in the cement interstitial fluid is increased.

Test example 3

The water reducing agents of examples 1-3 and comparative examples 1 and 2 were prepared into cement paste according to the method of test example 1, and then poured into a mold to prepare a test piece of 100mm × 100mm × 100mm, and the test piece was cured at 20 ℃ and 95% relative humidity for 24 hours, and then demolded to test the compressive strength of cement, the concrete compressive strength was determined by reference to GB/T50081-2002, and the test results are shown in Table 3.

TABLE 3 compressive Strength of concrete

As can be seen from Table 3, the polycarboxylic acid water reducer, the graphene oxide and the acrylamide polymer are polymerized, so that the fluidity of cement mortar is increased, the mud blocking effect is achieved, and the compressive strength of cement is enhanced. After the graphene oxide is added, the crystallization of calcium hydroxide in cement paste can be promoted, the particle size can be refined, the mechanical property of concrete can be improved, and the addition of the acrylamide polymer increases a hydrophobic structure unit for the water reducing agent, so that the conformation in an aqueous solution is more curled, and the compressive strength of the concrete can be further enhanced.

Test example 4

The test of the chlorine ion penetration resistance of the concrete is carried out by referring to a method recorded in chapter three of research on the chlorine ion penetration resistance and carbonization resistance of graphene oxide recycled concrete (Miao boat, Shenyang building university, Master's academic paper), and the test is carried out by taking multiple measured values and averaging the measured values.

Raw materials: 350g of 32.5-grade portland cement, 5g of a water reducing agent, 900g of coarse aggregate, 560 g of fine aggregate and 150 g of water. The coarse aggregate is stone with an average particle size of 5.5mm, the fine aggregate is machine-made sand with an average particle size of 3mm, and the water reducing agent is the concrete water reducing agent of example 2 or 4.

TABLE 4 chloride ion permeability resistance of the concretes

	Diffusion coefficient of chloride ion (10)-9cm2/s)
		Example 2	18.5
Example 4	10.7

As can be seen from the above table, the concrete water reducing agent of example 4 has significantly better resistance to chloride ion penetration of concrete than the concrete water reducing agent of example 3. The reason for this may be: the calcium lignosulfonate can improve the pore structure between the aggregate and the cement mortar, reduce the porosity and reduce CO₂The penetration channel enables the interior of the structure to be combined more compactly, thereby improving the chlorine ion penetration resistance of the recycled concrete.