Water-based nano anti-crack waterproof agent for concrete and preparation method of water-based nano anti-crack waterproof agent

Abstract

The invention discloses a water-based nano anti-crack waterproof agent for concrete and a preparation method of the water-based nano anti-crack waterproof agent, and relates to the field of building materials. 10 to 25% of a silane emulsion; 20-40% of an acrylate copolymer emulsion; 0.5 to 5% of modified nano cellulose; 3-8% of a polycarboxylic acid water reducer; 0.1-1% of a defoaming agent; and the balance of water. Nano silica sol permeates concrete capillary pores and participates in a hydration reaction to improve the compactness of a matrix, a three-dimensional toughening network is constructed in cooperation with oriented crosslinking of carboxyl on the surface of TEMPO oxidized nano cellulose and gamma-aminopropyl silane, and micro cracks are covered with a flexible sealing layer formed by an acrylate copolymer. Active inhibition of cracks and long-acting blocking of water are synergistically realized, shearing force is regulated and controlled in a segmented manner through a stepped stirring process, the demulsification risk of an emulsion is avoided, and the storage stability of a system is remarkably improved.

Description

Technical Field

[0001] The present invention relates to building material technology, in particular to a water-based nano anti-cracking waterproofing agent for concrete and a preparation method thereof. Background Art

[0002] As the most widely used building material in construction projects, concrete's durability directly impacts the service life of engineering structures. Under complex environmental conditions, concrete is susceptible to microcracks due to factors such as water penetration, chemical attack, and shrinkage, resulting in a decrease in its impermeability. Traditional waterproofing technologies rely heavily on silicone hydrophobic agents or polymer emulsions, but these technologies face technical bottlenecks such as insufficient compatibility with cement-based materials and poor long-term durability. With the development of nanomaterial technology, the introduction of nanoparticles into concrete waterproofing agents has become an important approach to improving material performance. However, the dispersion stability and interfacial bonding efficiency of nanoparticles in composite systems remain key issues restricting their engineering applications. Summary of the Invention

[0003] The purpose of the present invention is to provide a water-based nano-anti-cracking waterproofing agent for concrete and a preparation method thereof, so as to solve the above-mentioned deficiencies in the prior art.

[0004] In order to achieve the above object, the present invention provides a water-based nano anti-cracking waterproofing agent for concrete, which comprises the following components by weight percentage:

[0005] Nano silica sol 15-30%;

[0006] Silane emulsion 10-25%;

[0007] Acrylate copolymer emulsion 20-40%;

[0008] Modified nanocellulose 0.5-5%;

[0009] Polycarboxylic acid water reducer 3-8%;

[0010] Defoaming agent 0.1-1%;

[0011] Water balance.

[0012] Furthermore, the nano-silica sol has a silica particle size of 5-30 nm, a solid content of 30±2 wt %, and a pH value of 9.0-10.5.

[0013] Furthermore, the silane emulsion is a mixture of methyltrimethoxysilane and γ-aminopropyltriethoxysilane, with a mass ratio of 1:2 to 1:4.

[0014] Furthermore, the modified nanocellulose is cellulose nanocrystals oxidized by 2,2,6,6-tetramethylpiperidin-1-oxyl free radical (TEMPO), with a carboxyl content of 0.8-1.2 mmol / g and a length of 100-500 nm.

[0015] Another aspect of the present invention provides a method for preparing the above-mentioned water-based nano anti-cracking waterproofing agent for concrete, comprising the following steps:

[0016] S1. Under nitrogen protection, nano-silica sol and silane emulsion were mixed and reacted at 40-50°C for 30 minutes;

[0017] S2. Add the acrylic copolymer emulsion to the product of step S1, and stir and mix at 25-35° C. for 40 minutes;

[0018] S3, adding the modified nanocellulose aqueous dispersion to the mixture obtained in step S2 at a rate of 1-2 mL / min, and stirring continuously for 1 hour after the addition is complete;

[0019] S4. Add polycarboxylic acid water reducer and defoamer, and stir and disperse at 600-800 rpm for 15 minutes;

[0020] S5. Add water to adjust the solid content of the system to 35-50 wt %, and filter to obtain the finished product.

[0021] Furthermore, in step S1, 0.1-0.5% of the mass of the silane emulsion is added as a dibutyltin dilaurate catalyst.

[0022] Furthermore, the modified nanocellulose aqueous dispersion in step S3 has a solid content of 3-5 wt %, and is subjected to 300-500 W ultrasonic treatment for 10-15 minutes before being added dropwise.

[0023] Furthermore, in step S5, 2-amino-2-methyl-1-propanol is used to adjust the pH of the system to 8.0-9.0.

[0024] Furthermore, the stirring process of step S2 is carried out in two stages:

[0025] Stage 1: stirring at 200-300 rpm for 20 minutes;

[0026] Second stage: stirring at 400-500 rpm for 20 minutes.

[0027] Furthermore, in step S4, the defoaming agent is a polyether-modified polysiloxane defoaming agent, and after addition, the system is homogenized at 0.1-0.3 MPa for 5 minutes.

[0028] Compared with the prior art, the water-based nano anti-cracking waterproof agent for concrete and the preparation method thereof provided by the application can penetrate the nano silicon sol into the capillary pores of concrete and participate in the hydration reaction to improve the compactness of the matrix, construct a three-dimensional toughening network through the directional crosslinking of the carboxyl groups on the surface of the TEMPO oxidized nano cellulose and the gamma-aminopropyl silane, and form a flexible sealing layer covering the micro cracks by the acrylic ester copolymer, so that the active inhibition of cracks and the long-term moisture barrier are achieved.

[0029] The step-by-step control of shear force through the step-by-step stirring process can avoid the risk of emulsion demulsification, and the uniform dispersion of the nano components can be ensured by the catalytic hydrolysis of silane and the ultrasonic pretreatment of cellulose, so that the storage stability of the system is significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can also be obtained by those skilled in the art according to these drawings.

[0031] Figure 1 The preparation method flow chart of the water-based nano anti-cracking waterproof agent for concrete provided by the embodiments of the present application. DETAILED DESCRIPTION

[0032] In order to make those skilled in the art better understand the technical solutions of the present application, the present application will be further described in detail with reference to the drawings.

[0033] The present application provides a water-based nano anti-cracking waterproof agent for concrete, which comprises the following components by weight percentage:

[0034] Nano silicon sol 15-30%, the silicon dioxide particle size of the nano silicon sol is 5-30 nm, the solid content is 30±2wt%, and the pH value is 9.0-10.5;

[0035] Silane emulsion 10-25%, the silane emulsion is a mixture of methyltrimethoxysilane and gamma-aminopropyl triethoxysilane, and the mass ratio of the two is 1:2 to 1:4;

[0036] Acrylate copolymer emulsion 20-40%;

[0037] Modified nano cellulose 0.5-5%, the modified nano cellulose is cellulose nanocrystal treated by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) oxidation, the carboxyl content is 0.8-1.2 mmol / g, and the length is 100-500 nm;

[0038] Polycarboxylic acid type water reducing agent 3-8%;

[0039] Defoaming agent 0.1-1%;

[0040] Water balance.

[0041] Nano-silica sol (15-30%) is based on 5-30nm silica particles. Its alkaline environment (pH 9.0-10.5) maintains colloidal stability and enhances concrete density by penetrating concrete pores and reacting with hydration products. Silane emulsion (10-25%) is a 1:2 to 1:4 mixture of methyltrimethoxysilane and γ-aminopropyltriethoxysilane. The former forms a hydrophobic barrier, while the aminopropyl group of the latter bonds with the carboxyl groups of cellulose to enhance toughness. Acrylate copolymer emulsion (20-40%) provides a flexible film to cover microcracks. TEMPO-oxidized nanocellulose (0.5-5%) bridges cracks and strengthens the network thanks to its carboxyl content (0.8-1.2 mmol / g) and nanoscale length (100-500 nm). Polycarboxylate superplasticizer (3-8%) simultaneously optimizes concrete workability and particle dispersion. Defoamer (0.1-1%) and the balance of water ensure system stability.

[0042] See also Figure 1 The present invention also provides a method for preparing a water-based nano anti-cracking waterproofing agent for concrete, comprising the following steps:

[0043] S1. Under nitrogen protection, nano-silica sol and silane emulsion were mixed and reacted at 40-50°C for 30 minutes;

[0044] S2. Add the acrylic copolymer emulsion to the product of step S1, and stir and mix at 25-35° C. for 40 minutes;

[0045] S3, adding the modified nanocellulose aqueous dispersion to the mixture obtained in step S2 at a rate of 1-2 mL / min, and stirring continuously for 1 hour after the addition is complete;

[0046] S4. Add polycarboxylic acid water reducer and defoamer, and stir and disperse at 600-800 rpm for 15 minutes;

[0047] S5. Add water to adjust the solid content of the system to 35-50 wt %, and filter to obtain the finished product.

[0048] In step S1, a dibutyltin dilaurate catalyst is added in an amount of 0.1-0.5% by mass of the silane emulsion. The hydrolysis and polycondensation of silane is catalyzed by the addition of dibutyltin dilaurate, and the reaction is protected by nitrogen to prevent air moisture from interfering with the reaction.

[0049] The modified nanocellulose aqueous dispersion in step S3 has a solid content of 3-5 wt %, and is ultrasonically treated at 300-500 W for 10-15 minutes before being added dropwise to ensure uniform dispersion of the fibers.

[0050] In step S5, 2-amino-2-methyl-1-propanol is used to adjust the pH of the system to 8.0-9.0 to stabilize the activity of the system.

[0051] The stirring process in step S2 is carried out in two stages: the first stage: stirring at 200-300 rpm for 20 minutes; the second stage: stirring at 400-500 rpm for 20 minutes. The gradient shear force is used to gradually merge the acrylic emulsion and the silane-modified sol to prevent demulsification caused by high rotation speed.

[0052] The defoaming agent in step S4 is a polyether-modified polysiloxane defoaming agent. After addition, the system is homogenized at 0.1-0.3 MPa for 5 minutes to eliminate bubbles.

[0053] The following examples are provided to further illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are by weight. Unless otherwise specified, all components used are commercially available.

[0054] Example 1

[0055] A water-based nano anti-cracking waterproofing agent for concrete, comprising the following components by weight percentage:

[0056] Nano silica sol 22%;

[0057] Methyltrimethoxysilane 10%;

[0058] γ-aminopropyltriethoxysilane 8%;

[0059] Acrylate copolymer emulsion 38%;

[0060] TEMPO nanocellulose 2.5%;

[0061] Polycarboxylate water reducer 6%;

[0062] Polyether modified defoamer 0.3%;

[0063] Deionized water balance.

[0064] A method for preparing the above-mentioned aqueous nano anti-cracking waterproofing agent for concrete comprises the following steps:

[0065] S1. Nitrogen was passed through the reactor for 10 min to replace the air. Nano-silica sol (particle size 20 nm, pH 10.2), methyltrimethoxysilane, γ-aminopropyltriethoxysilane, and dibutyltin dilaurate catalyst (0.4% by weight of the total silane mass) were added. The mixture was stirred at 45° C. for 30 min (rotation speed 400 rpm).

[0066] S2. Add acrylate copolymer emulsion (solid content 48%, Tg = 8°C) to the product of step S1, and stir and mix at 30°C for 40 minutes;

[0067] S3. Prepare a 4.0 wt% dispersion of TEMPO nanocellulose (length 200 nm, carboxyl content 1.1 mmol / g) in deionized water, ultrasonicate at 400 W for 12 min, and add the dispersion dropwise to the reactor at a rate of 1.2 mL / min using a constant flow pump. Stir at a constant speed (350 rpm) at 30°C for 60 min.

[0068] S4. Add polycarboxylic acid water reducer and defoamer, stir and disperse at 700 rpm for 15 minutes, and homogenize at 0.2 MPa pressure for 5 minutes;

[0069] S5. Add 2-amino-2-methyl-1-propanol dropwise to adjust the pH to 8.8, add water to adjust the solid content of the system to 35-50 wt %, and filter through a 400-mesh stainless steel sieve to obtain a finished product.

[0070] Example 2

[0071] A water-based nano anti-cracking waterproofing agent for concrete, comprising the following components by weight percentage:

[0072] Nano silica sol 22%;

[0073] Methyltrimethoxysilane 10%;

[0074] γ-aminopropyltriethoxysilane 8%;

[0075] Acrylate copolymer emulsion 38%;

[0076] TEMPO nanocellulose 2.5%;

[0077] Polycarboxylate water reducer 6%;

[0078] Polyether modified defoamer 0.3%;

[0079] Deionized water balance.

[0080] A method for preparing the above-mentioned aqueous nano anti-cracking waterproofing agent for concrete comprises the following steps:

[0081] S1. Nitrogen was passed through the reactor for 10 min to replace the air. Nano-silica sol (particle size 20 nm, pH 10.2), methyltrimethoxysilane, γ-aminopropyltriethoxysilane, and dibutyltin dilaurate catalyst (0.4% by weight of the total silane mass) were added. The mixture was stirred at 45° C. for 30 min (rotation speed 400 rpm).

[0082] S2, acrylic ester copolymer emulsion (solid content 48%, Tg = 8°C) was added to the product of step S1, and stirred at 30°C at 250 rpm for 20 min, then switched to 450 rpm for 20 min;

[0083] S3, TEMPO nanocellulose (length 200 nm, carboxyl content 1.1 mmol / g) was mixed with deionized water to form a 4.0 wt% dispersion, and treated with 400 W ultrasonic for 12 min, then added dropwise to the reaction kettle at a rate of 1.2 mL / min, and stirred at 30°C at a constant speed (350 rpm) for 60 min;

[0084] S4, polycarboxylic acid type water reducing agent and defoaming agent were added, and stirred at 700 rpm for 15 min, and treated with homogenization at a pressure of 0.2 MPa for 5 min;

[0085] S5, 2-amino-2-methyl-1-propanol was added dropwise to adjust the pH to 8.8, water was added to adjust the solid content of the system to 35-50 wt%, and the finished product was obtained after filtration through a 400 mesh stainless steel screen.

[0086] Comparative Example 1

[0087] Components: same as Example 1.

[0088] Preparation method:

[0089] a, nitrogen was passed into the reaction kettle for 10 min to replace air, and nanosilica sol (particle size 20 nm, pH 10.2), methyltrimethoxysilane, and γ-aminopropyltriethoxysilane were added, and stirred at 45°C for 30 min (rotation speed 400 rpm);

[0090] b, acrylic ester copolymer emulsion (solid content 48%, Tg = 8°C) was added to the product of step a, and stirred at 30°C for 40 min;

[0091] c, TEMPO nanocellulose (length 200 nm, carboxyl content 1.1 mmol / g) was mixed with deionized water to form a 4.0 wt% dispersion, and treated with 400 W ultrasonic for 12 min, then added dropwise to the reaction kettle at a rate of 1.2 mL / min, and stirred at 30°C at a constant speed (350 rpm) for 60 min;

[0092] d, polycarboxylic acid type water reducing agent and defoaming agent were added, and stirred at 700 rpm for 15 min, and treated with homogenization at a pressure of 0.2 MPa for 5 min;

[0093] e, 2-amino-2-methyl-1-propanol was added dropwise to adjust the pH to 8.8, water was added to adjust the solid content of the system to 35-50 wt%, and the finished product was obtained after filtration through a 400 mesh stainless steel screen.

[0094] Comparative Example 2

[0095] Components: Same as Example 1.

[0096] Preparation method:

[0097] a. Nitrogen was passed through the reactor for 10 minutes to replace the air. Nano-silica sol (particle size 20 nm, pH 10.2), methyltrimethoxysilane, γ-aminopropyltriethoxysilane, and dibutyltin dilaurate catalyst (0.4% by weight of the total silane mass) were added. The mixture was stirred at 45°C for 30 minutes (rotating speed 400 rpm).

[0098] b. Add acrylate copolymer emulsion (solid content 48%, Tg = 8°C) to the product of step a, and stir and mix at 30°C for 40 minutes;

[0099] c. Prepare a 4.0 wt% dispersion of TEMPO nanocellulose (length 200 nm, carboxyl content 1.1 mmol / g) and deionized water, add it dropwise to the reactor at a rate of 1.2 mL / min using a constant flow pump, and stir at a constant speed (350 rpm) at 30°C for 60 min;

[0100] d. Add polycarboxylic acid water reducer and defoamer, stir and disperse at 700 rpm for 15 minutes, and homogenize at 0.2 MPa pressure for 5 minutes;

[0101] e. Add 2-amino-2-methyl-1-propanol dropwise to adjust the pH to 8.8, add water to adjust the solid content of the system to 35-50 wt %, and filter through a 400-mesh stainless steel sieve to obtain the finished product.

[0102] Comparative Example 3

[0103] Components: Same as Example 1.

[0104] Preparation method:

[0105] a. Nitrogen was passed through the reactor for 10 minutes to replace the air. Nano-silica sol (particle size 20 nm, pH 10.2), methyltrimethoxysilane, γ-aminopropyltriethoxysilane, and dibutyltin dilaurate catalyst (0.4% by weight of the total silane mass) were added. The mixture was stirred at 45°C for 30 minutes (rotating speed 400 rpm).

[0106] b. Add acrylate copolymer emulsion (solid content 48%, Tg = 8°C) to the product of step S1, and stir at 350 rpm for 40 min at 30°C;

[0107] c. Prepare a 4.0 wt% dispersion of TEMPO nanocellulose (length 200 nm, carboxyl content 1.1 mmol / g) in deionized water, ultrasonicate at 400 W for 12 min, and add the resulting dispersion dropwise to the reactor at a rate of 1.2 mL / min using a constant flow pump. Stir at 350 rpm for 60 min at 30°C.

[0108] d. Add polycarboxylic acid water reducer and defoamer, stir and disperse at 700 rpm for 15 minutes, and homogenize at 0.2 MPa pressure for 5 minutes;

[0109] e. Add 2-amino-2-methyl-1-propanol dropwise to adjust the pH to 8.8, add water to adjust the solid content of the system to 35-50 wt %, and filter through a 400-mesh stainless steel sieve to obtain the finished product.

[0110] Comparative experimental example

[0111] The differences between Examples 1-2, Comparative Examples 1-3 and similar commercially available products in terms of concrete impermeability, mechanical properties, durability and construction performance are as follows:

[0112] Experimental Materials:

[0113] Examples 1-2 and Comparative Examples 1-3 (prepared according to the formula and process);

[0114] A commercially available brand of nano-anti-cracking waterproofing agent (solid content 40%, pH 8.5);

[0115] Benchmark cement (P·O 42.5), standard sand, tap water;

[0116] Concrete impermeability tester, universal testing machine, shrinkage and expansion tester, pH meter, solid content tester.

[0117] Experimental steps:

[0118] 1. Preparation of concrete test blocks:

[0119] Mixing ratio: cement: sand: stone: water = 1:2.2:3.5:0.5 (mass ratio), the amount of waterproofing agent is 2% of the cement mass;

[0120] Preparation method: weigh the raw materials in proportion, mix the waterproofing agent with water and add to the mixer; stir slowly for 30 seconds, add cement, sand and stone, and stir quickly for 120 seconds; pour into a 40mm×40mm×160mm triple mold and vibrate to form; remove the mold after 24 hours and perform standard curing (20±2℃, RH≥95%) until the age of 28 days.

[0121] 2. Performance testing:

[0122] 2.1. Anti-permeability test (refer to GB / T 50082-2009)

[0123] Apparatus: Concrete permeability instrument (HS-4S type)

[0124] Method:

[0125] After 28d curing, dry the test block at 60℃ for 48h;

[0126] Coat the side of the test block with sealing material and install it into the permeability instrument;

[0127] Start from 0.1MPa and increase the pressure step by step (0.1MPa per step, constant pressure for 8h), record the pressure value when water permeates;

[0128] Calculate the permeability pressure ratio: Permeability pressure ratio = (reference concrete permeability pressure / sample permeability pressure) x 100%.

[0129] 2.2, Mechanical property test (refer to GB / T 50081-2019)

[0130] Compressive strength:

[0131] Cure the test block to 3d, 7d, 28d age;

[0132] Use the universal testing machine to load to failure at a rate of 0.5MPa / s, and record the peak load.

[0133] 2.3, Shrinkage test (refer to GB / T 50082-2009)

[0134] Method: Demould the test block 1d after moulding, and measure the initial length;

[0135] Place it in a dry environment (20±2℃, RH 60±5%), and measure the length at 1d, 3d, 7d, 14d, 28d respectively;

[0136] Calculate the shrinkage: Shrinkage = (L0-Lt) / L0 x 100%, where L0 is the initial length, and Lt is the length at t days. t t

[0137] 2.4, Water absorption test

[0138] Method:

[0139] After 28d curing, dry the test block at 105℃ to constant weight (m1);

[0140] Soak it in water for 24h, and weigh it after wiping the surface dry (m2);

[0141] Calculate the water absorption: Water absorption = (m2-m1) x 100%.

[0142] 2.5, pH value and solid content determination ​​

[0143] pH value: Use a pH meter to directly measure the waterproofing agent solution;

[0144] Solid content: Take 1 g of sample, dry it at 105°C to constant weight, and calculate the mass loss rate.

[0145] The experimental results are as follows:

[0146]

[0147]

[0148] As can be seen from the above, the anti-seepage pressure of Examples 1-2 is significantly better than that of the comparative example and the commercially available product, indicating that the catalyst (dibutyltin dilaurate) and the ultrasonic dispersion process (missing in Comparative Example 2) are crucial to the dispersibility of the nanomaterial. After the segmented stirring is adopted in Example 2, the anti-seepage pressure is further increased to 1.9 MPa, which is better than 1.8 MPa (constant stirring) in Example 1. The segmented stirring can effectively promote the bonding of the nanomaterial to the matrix;

[0149] The 28d compressive strength of Examples 1-2 was higher than that of the comparative example. Due to the synergistic effect of TEMPO nanocellulose and acrylate emulsion, the segmented stirring process of Example 2 increased the compressive strength to 53.1 MPa, which was higher than the 52.3 MPa of Example 1. The segmented stirring optimized the dispersion of the materials and significantly improved the mechanical properties.

[0150] The shrinkage rate of the examples (0.032%-0.035%) is much lower than that of the comparative examples and commercially available products, proving that the nano-silica sol and silane coupling agent effectively inhibit concrete shrinkage. The water absorption rate data is consistent with the impermeability trend, reflecting the densification effect of the waterproofing agent.

[0151] The pH value (8.8) and solid content (42%-42.3%) of the embodiment meet the industry standards.

[0152] The present invention uses nano-silica sol (15-30%) to fill capillary pores and participate in the hydration reaction, TEMPO-oxidized nano-cellulose (0.5-5%) forms a tough network through directional cross-linking with γ-aminopropylsilane through carboxyl groups, and acrylic ester copolymer emulsion (20-40%) forms a flexible film to cover micro-cracks. The three work together to effectively reduce the number of cracks in concrete within 24 hours.

[0153] The risk of high shear demulsification is avoided through a step-by-step stirring process. Combined with silane-catalyzed hydrolysis (0.1-0.5% dibutyltin dilaurate) and ultrasonic pretreatment of nanocellulose, uniform and stable dispersion of nanocomponents in the emulsion is achieved, effectively extending the product storage period.

[0154] The above description is merely illustrative of certain exemplary embodiments of the present invention. It goes without saying that those skilled in the art will be able to modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and description are illustrative in nature and should not be construed as limiting the scope of protection of the claims.

Claims

1. A water-based nano anti-cracking waterproofing agent for concrete, characterized in that: The following components are included by weight percentage: Nano silica sol 15-30%; Silane emulsion 10-25%; Acrylate copolymer emulsion 20-40%; Modified nanocellulose 0.5-5%; Polycarboxylic acid water reducer 3-8%; Defoaming agent 0.1-1%; Water balance.

2. A water-based nano anti-cracking waterproofing agent for concrete according to claim 1, characterized in that: The silica particle size of the nano-silica sol is 5-30 nm, the solid content is 30±2 wt%, and the pH value is 9.0-10.

5.

3. A water-based nano anti-cracking waterproofing agent for concrete according to claim 1, characterized in that: The silane emulsion is a mixture of methyltrimethoxysilane and gamma-aminopropyltriethoxysilane, with a mass ratio of 1:2 to 1:

4.

4. The water-based nano anti-cracking waterproofing agent for concrete according to claim 1, characterized in that: The modified nanocellulose is cellulose nanocrystals oxidized by 2,2,6,6-tetramethylpiperidin-1-oxyl free radical (TEMPO), with a carboxyl content of 0.8-1.2 mmol / g and a length of 100-500 nm.

5. A method for preparing a water-based nano anti-cracking waterproofing agent for concrete according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Under nitrogen protection, nano-silica sol and silane emulsion were mixed and reacted at 40-50°C for 30 minutes; S2. Add the acrylic copolymer emulsion to the product of step S1, and stir and mix at 25-35° C. for 40 minutes; S3, adding the modified nanocellulose aqueous dispersion to the mixture obtained in step S2 at a rate of 1-2 mL / min, and stirring continuously for 1 hour after the addition is complete; S4. Add polycarboxylic acid water reducer and defoamer, and stir and disperse at 600-800 rpm for 15 minutes; S5. Add water to adjust the solid content of the system to 35-50 wt %, and filter to obtain the finished product.

6. The method for preparing a water-based nano anti-cracking waterproofing agent for concrete according to claim 5, characterized in that: In step S1, 0.1-0.5% of the mass of the silane emulsion is added as a dibutyltin dilaurate catalyst.

7. The method for preparing a water-based nano anti-cracking waterproofing agent for concrete according to claim 5, characterized in that: The modified nanocellulose aqueous dispersion in step S3 has a solid content of 3-5 wt %, and is ultrasonically treated at 300-500 W for 10-15 minutes before being added dropwise.

8. The method for preparing a water-based nano anti-cracking waterproofing agent for concrete according to claim 5, characterized in that: In step S5, 2-amino-2-methyl-1-propanol is used to adjust the pH of the system to 8.0-9.

0.

9. The method for preparing a water-based nano anti-cracking waterproofing agent for concrete according to claim 5, characterized in that: The stirring process of step S2 is carried out in two stages: Stage 1: stirring at 200-300 rpm for 20 minutes; Second stage: stirring at 400-500 rpm for 20 minutes.

10. The method for preparing a water-based nano anti-cracking waterproofing agent for concrete according to claim 5, characterized in that: The defoaming agent in step S4 is a polyether-modified polysiloxane defoaming agent. After addition, the system is homogenized at 0.1-0.3 MPa for 5 minutes.

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