Concrete high-concentration self-healing anti-crack waterproof agent and preparation method thereof

Abstract

The invention belongs to the technical field of building materials, and particularly relates to a concrete high-concentration self-healing anti-crack waterproof agent and a preparation method thereof. The concrete high-concentration self-healing anti-cracking waterproof agent is prepared from the following raw materials in percentage by weight: 16 to 20 percent of silicate, 8 to 12 percent of modified nano silicon dioxide, 3 to 4 percent of sodium hydroxide, 2 to 3 percent of triethanolamine, 4 to 5 percent of retarder, 0.3 to 0.5 percent of defoaming agent, 1.5 to 2.5 percent of shrinkage reducing agent, 3 to 4 percent of anti-freezing agent and the balance of deionized water. The high-concentration self-healing anti-cracking waterproof agent for the concrete is a low-carbon and environment-friendly water-based waterproof agent, and the compactness, the impermeability, the durability, the cracking resistance and the self-repairing performance of the concrete can be improved.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a high-concentration self-healing crack-resistant and waterproof concrete agent and its preparation method. Background Technology

[0002] Concrete waterproofing agents are chemical additives used to improve the impermeability of concrete. Currently, commonly used waterproofing agents in China include sodium methylsilicate, potassium silicate, higher fatty acids, triethanolamine, and ferric chloride, among others. Sodium methylsilicate and potassium silicate waterproofing agents have the advantages of strong alkalinity and low price. However, their disadvantage is that when applied to the surface for waterproofing, they require the absorption of oxygen and water from the air to react and achieve a waterproofing effect, but this produces reactants. Higher fatty acid waterproofing agents can significantly reduce capillary water absorption in concrete, but excessive dosage or poor compatibility with cement / admixtures can lead to uneven concrete density, weakening later-stage strength, and reducing waterproofing performance under long-term immersion. Triethanolamine and ferric chloride are also commonly used as waterproofing agents, effectively improving the impermeability of concrete, but they cannot solve the problem of concrete cracking. Improper use of triethanolamine can seriously damage the later-stage hardening performance of concrete, while ferric chloride corrodes internal steel reinforcement, accelerating steel corrosion, and its use has been restricted. Oil-based waterproofing agents, also known as solvent-based waterproofing agents, use oil as a carrier, making it easier to penetrate deep into the object and generally providing better waterproofing. However, because they are not environmentally friendly materials and cannot be mixed with concrete, they are rarely used in construction.

[0003] Some waterproofing agents on the market contain a high amount of oxides in their ingredients, and chloride ions are harmful to concrete. After use, they can easily corrode steel bars and have poor waterproofing effects in the later stages. Alternatively, the waterproofing agent may increase shrinkage after use, causing concrete to crack. Or, the waterproofing agent may be a powder product, requiring a large amount to be added during use. Therefore, due to various objective factors, waterproofing agents on the market often produce many adverse reactions in actual engineering applications and fail to achieve the ideal waterproofing effect. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a high-concentration self-healing crack-resistant and waterproofing agent for concrete and its preparation method. When this high-concentration self-healing crack-resistant and waterproofing agent is incorporated into concrete, it reacts chemically with cement mineral components and hydration precipitates to generate gels and crystals. This effectively controls early-stage cracking in concrete, reduces the temperature rise of concrete, and automatically repairs micro-cracks in concrete, significantly improving the compactness, impermeability, crack resistance, and durability of concrete.

[0005] The present invention discloses a high-concentration self-healing crack-resistant and waterproof concrete agent, which, by weight percentage, comprises: 16-20% silicate, 8%-12% modified nano silica, 3%-4% sodium hydroxide, 2%-3% triethanolamine, 4%-5% retarder, 0.3%-0.5% defoamer, 1.5%-2.5% shrinkage reducer, 3%-4% antifreeze agent, and deionized water to make up to 100%, with a pH of 12-14.

[0006] The silicate is a composite of lithium silicate and sodium silicate, with a mass ratio of lithium silicate:sodium silicate = 1:2. When the high-concentration self-healing crack-resistant and waterproofing agent is added to concrete, the lithium silicate and sodium silicate solutions penetrate into the concrete and react with the hydration products Ca(OH)₂ in the concrete to form calcium silicate gel and lithium hydroxide and sodium hydroxide. Sodium silicate provides a strongly alkaline environment, rapidly reacting with Ca(OH)₂ in the concrete to form CSH gel, quickly improving surface strength and density. Lithium silicate contains Li... + Ions can effectively inhibit the alkali-aggregate reaction, and the reaction product, Li-Si-H gel, is more stable, can penetrate deep into pores, and provide a more durable dense and hydrophobic effect; the two complement each other, taking into account both immediate and long-term performance. LiOH and NaOH can further react with CO2 to continuously produce a gel to repair concrete cracks, thereby achieving excellent waterproofing effect.

[0007] This invention utilizes a silane coupling agent (KH-570) and a vinyl monomer (such as acrylic acid) for surface graft polymerization modification of nano-silica. This solves the dispersion and interface problems encountered when using the material in concrete, transforming it from a passive filler into an active functional repair unit. When added to concrete, it primarily plays a core role in dispersion, reinforcement, toughening, shrinkage reduction, and repair promotion. The core of this invention's product is "self-healing," "waterproofing," and "crack resistance," requiring the additive to not only fill pores but also strengthen and repair the matrix. The functional groups (such as -COOH) on the graft polymer shell can react with Ca in cement hydration products. 2+ Ion coordination or cross-linking occurs, chemically anchoring nanoparticles within the cementitious stone. The silicates and sodium hydroxide in the formulation create a highly alkaline environment, which is precisely where the carboxyl groups (-COOH) in the grafted polymer (such as polyacrylic acid) are converted into highly reactive carboxylates (-COO). - Ideal conditions are found for active silica to maximize its reactivity with calcium ions, accelerating the formation of beneficial products. Upon contact with water, active silica reacts with calcium hydroxide in concrete to form water-insoluble calcium aluminosilicate crystals. After repair, these crystals integrate with the concrete, effectively blocking capillaries and microcracks. Even if the cracks undergo minor changes later, the highly active crystal growth factors migrate to the cracks following moisture, and the secondary crystallization process continues upon re-contamination with water, demonstrating continuous repair capabilities.

[0008] In this invention, the role of triethanolamine is: (1) to inhibit precipitation: active ions in the waterproofing agent (such as Ca) 2+ SiO3 2- (2) Stabilize pH value: Although sodium hydroxide provides an initial highly alkaline environment, the pH value may fluctuate due to carbonation and other reasons during long-term storage or contact with concrete. Triethanolamine has a certain alkaline buffering capacity, which helps to maintain the pH stability of the system. (3) Triethanolamine has weak surface activity, which can reduce the surface tension of the solution, help the active ingredients to disperse more evenly in the solution, prevent particle agglomeration and sedimentation, and improve the physical stability of the preparation. (4) Promote setting and early strength: In concrete, low dosage of triethanolamine has the effect of promoting setting and early strength. (5) Promote crystallization: Triethanolamine can react with Ca in cement hydration products. 2+ The reaction generates complexes, which can then decompose and promote the formation of more insoluble crystals, accelerating and enhancing the self-healing process. (6) Improved microstructure: By regulating the hydration process, the pore structure of concrete can be made denser, creating a better base for waterproofing and self-healing.

[0009] The retarder is sodium gluconate or sodium citrate.

[0010] The defoamer is an organosilicone defoamer.

[0011] The shrinkage reducing agent is a polyether-based shrinkage reducing agent.

[0012] The antifreeze agent is propylene glycol.

[0013] The preparation method of the aforementioned high-concentration self-healing crack-resistant and waterproof concrete agent comprises the following specific steps: (1) Add sodium hydroxide to a portion of deionized water in batches and stir until completely dissolved; then add retarder, antifreeze, shrinkage reducer and triethanolamine in sequence and stir until completely dissolved to obtain solution I; the stirring speed in step (1) is 300-400 rpm.

[0014] In this invention, sodium hydroxide is added first for dissolution. Sodium hydroxide dissolution is a strongly exothermic process and requires complete dissolution to provide a highly alkaline environment. Dissolving it with partially deionized water first allows for control of heat and concentration, creating a stable and homogeneous alkaline reaction platform for subsequent components. Then, organic additives (retarders, antifreeze, shrinkage reducers, and triethanolamine) are added sequentially. The addition of triethanolamine here serves two main purposes: First, it is itself a good dispersant and stabilizer for the subsequent nano-silica dispersion; its early addition prepares the solution for the next step. Second, it can complex with ions in the solution, preventing unnecessary precipitation in later steps.

[0015] (2) Under stirring, add modified nano-silica to solution I. After the addition is complete, continue high-speed shearing until the system is uniformly translucent to obtain solution II.

[0016] In this invention, modified nano-silica must be added and subjected to high-speed shearing before adding silicate. Modified nano-silica has a huge specific surface area and is extremely prone to agglomeration. In an alkaline solution I containing triethanolamine, continuous high-speed shearing can provide sufficient energy and shear force to break up the nano-agglomerates, allowing them to be uniformly dispersed as native particles or extremely small agglomerates, forming solution II. If silicate is added first, the viscosity and reactivity of the entire system will increase sharply. At this point, adding modified nano-silica will almost make it impossible to achieve effective dispersion, and the nanoparticles will form irreversible hard agglomerates or react rapidly with silicate to form a gel, resulting in precipitation, thickening, or even solidification and spoilage of the product. The stirring speed in step (2) is 600-800 rpm.

[0017] (3) Add silicate to solution II and stir to mix evenly; then add defoamer and the remaining deionized water to obtain a high-concentration self-healing crack-resistant waterproofing agent for concrete.

[0018] Silicates are very reactive at high alkalinity. They are added last to avoid premature and uncontrollable reactions with the whole system, especially to avoid sudden changes in the viscosity of the system during the dispersion of nano-silica, and to ensure that the nano-dispersion step can be completed smoothly.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) The high-concentration self-healing crack-resistant waterproofing agent for concrete described in this invention is a liquid product. The effective components in the waterproofing agent have been uniformly dispersed and dissolved. In ready-mixed concrete, the liquid agent can be dispersed in the mixing water more quickly and evenly, so that it can be evenly distributed to every corner of the concrete, so that the waterproofing and self-healing functions are covered without dead corners.

[0020] (2) This invention stably combines different types of active substances, activators, regulators, etc., into a multifunctional integrated product, highly "concentrating" multiple functions into a single product. Using this invention, the use of other admixtures is eliminated or significantly reduced. Using this invention, a dosage of only 0.2% of the total mass of concrete cementitious materials is sufficient to achieve excellent results.

[0021] (3) The use of triethanolamine in this invention can effectively prevent the active ingredients from precipitating and failing during storage, thus ensuring long-term storage stability.

[0022] (4) The waterproofing agent of the present invention has a pH of 12-14, which avoids problems such as concrete corrosion, reduced concrete strength and damage to the internal waterproofing of concrete caused by admixtures with low pH value. Detailed Implementation

[0023] Example 1 A highly concentrated self-healing crack-resistant and waterproof concrete agent, by weight percentage, comprises: 5.5% lithium silicate, 11% sodium silicate, 11% modified nano silica, 3% sodium hydroxide, 2.5% triethanolamine, 4% sodium gluconate, 0.3% organosilicon defoamer, 2.0% polyether shrinkage reducer, 3.5% propylene glycol, and deionized water to bring the total to 100%, with a pH of 12.7.

[0024] The specific preparation steps are as follows: (1) Add sodium hydroxide to a portion of deionized water in batches and stir until completely dissolved; then add retarder, antifreeze, shrinkage reducer and triethanolamine in sequence and stir until completely dissolved to obtain solution I.

[0025] (2) Under stirring, add modified nano-silica to solution I. After the addition is complete, continue high-speed shearing until the system is uniformly translucent to obtain solution II.

[0026] (3) Add silicate to solution II and stir to mix evenly; then add defoamer and the remaining deionized water to obtain a high-concentration self-healing crack-resistant waterproofing agent for concrete.

[0027] In step (1), the stirring speed is 300 rpm.

[0028] In step (2), the stirring speed is 600 rpm.

[0029] Example 2 A highly concentrated self-healing crack-resistant and waterproof concrete agent, by weight percentage, comprises: 6.4% lithium silicate, 12.8% sodium silicate, 10% modified nano silica, 3.5% sodium hydroxide, 2% triethanolamine, 4.5% sodium citrate, 0.4% organosilicon defoamer, 2.5% polyether shrinkage reducer, 3.2% propylene glycol, and deionized water to bring the total to 100%, with a pH of 12.3.

[0030] The specific preparation steps are as follows: (1) Add sodium hydroxide to a portion of deionized water in batches and stir until completely dissolved; then add retarder, antifreeze, shrinkage reducer and triethanolamine in sequence and stir until completely dissolved to obtain solution I.

[0031] (2) Under stirring, add modified nano-silica to solution I. After the addition is complete, continue high-speed shearing until the system is uniformly translucent to obtain solution II.

[0032] (3) Add silicate to solution II and stir to mix evenly; then add defoamer and the remaining deionized water to obtain a high-concentration self-healing crack-resistant waterproofing agent for concrete.

[0033] In step (1), the stirring speed is 400 rpm.

[0034] In step (2), the stirring speed is 600 rpm.

[0035] Example 3 A highly concentrated self-healing crack-resistant and waterproof concrete agent, by weight percentage, comprises: 6% lithium silicate, 12% sodium silicate, 8% modified nano silica, 4% sodium hydroxide, 3% triethanolamine, 5% sodium gluconate, 0.5% organosilicon defoamer, 1.5% polyether shrinkage reducer, 4% propylene glycol, and deionized water to bring the total to 100%, with a pH of 12.5.

[0036] The specific preparation steps are as follows: (1) Add sodium hydroxide to a portion of deionized water in batches and stir until completely dissolved; then add retarder, antifreeze, shrinkage reducer and triethanolamine in sequence and stir until completely dissolved to obtain solution I.

[0037] (2) Under stirring, add modified nano-silica to solution I. After the addition is complete, continue high-speed shearing until the system is uniformly translucent to obtain solution II.

[0038] (3) Add silicate to solution II and stir to mix evenly; then add defoamer and the remaining deionized water to obtain a high-concentration self-healing crack-resistant waterproofing agent for concrete.

[0039] In step (1), the stirring speed is 300 rpm.

[0040] In step (2), the stirring speed is 800 rpm.

[0041] Example 4 A highly concentrated self-healing crack-resistant and waterproof concrete agent, by weight percentage, comprises: 5.7% lithium silicate, 11.4% sodium silicate, 12% modified nano silica, 3% sodium hydroxide, 2.6% triethanolamine, 4% sodium citrate, 0.35% organosilicon defoamer, 1.7% polyether shrinkage reducer, 3% propylene glycol, and deionized water to bring the total to 100%, with a pH of 12.8.

[0042] The specific preparation steps are as follows: (1) Add sodium hydroxide to a portion of deionized water in batches and stir until completely dissolved; then add retarder, antifreeze, shrinkage reducer and triethanolamine in sequence and stir until completely dissolved to obtain solution I.

[0043] (2) Under stirring, add modified nano-silica to solution I. After the addition is complete, continue high-speed shearing until the system is uniformly translucent to obtain solution II.

[0044] (3) Add silicate to solution II and stir to mix evenly; then add defoamer and the remaining deionized water to obtain a high-concentration self-healing crack-resistant waterproofing agent for concrete.

[0045] In step (1), the stirring speed is 400 rpm.

[0046] In step (2), the stirring speed is 800 rpm.

[0047] Comparative Example 1 A highly concentrated self-healing crack-resistant and waterproof concrete agent, by weight percentage, comprises: 6% lithium silicate, 12% sodium silicate, 8% modified nano silicate, 4% sodium hydroxide, 5% sodium gluconate, 0.5% organosilicon defoamer, 1.5% polyether shrinkage reducer, 4% propylene glycol, and deionized water to make up to 100%.

[0048] The specific preparation steps are as follows: (1) Add sodium hydroxide to a portion of deionized water in batches and stir until completely dissolved; then add retarder, antifreeze and shrinkage reducer in sequence and stir until completely dissolved to obtain solution I.

[0049] (2) Under stirring, add modified nano-silica to solution I. After the addition is complete, continue high-speed shearing until the system is uniformly translucent to obtain solution II.

[0050] (3) Add silicate to solution II and stir to mix evenly; then add defoamer and the remaining deionized water to obtain a high-concentration self-healing crack-resistant waterproofing agent for concrete.

[0051] In step (1), the stirring speed is 300 rpm.

[0052] In step (2), the stirring speed is 800 rpm.

[0053] Test case 1. Compressive strength ratio

[0054] The compressive strength ratio of the high-concentration self-healing crack-resistant and waterproof concrete agent was tested according to the current standards JC / T474 "Waterproofing Agents for Mortar and Concrete" and T / CECS 10461 "High-concentration Self-healing Crack-resistant and Waterproof Concrete Agent". The test results show that the compressive strength ratio is higher than 110% in both cases. The later-stage strength of the concrete does not decrease with age.

[0055] Table 1. Results of the compressive strength ratio test .

[0056] 2. Permeability height ratio The penetration height ratio of the high-concentration self-healing crack-resistant waterproofing agent for concrete was tested according to the current standards JC / T474 "Waterproofing Agents for Mortar and Concrete" and T / CECS 10461 "High-concentration Self-healing Crack-resistant Waterproofing Agent for Concrete". The test results show that the penetration height ratio is less than 30% in both cases.

[0057] Table 2. Results of the Permeability Height Ratio Test .

[0058] 3. Shrinkage ratio Concrete shrinkage refers to the reduction in volume that occurs during the initial setting or hardening process of concrete. It is a technical indicator for controlling long-term concrete shrinkage, and significant shrinkage can cause concrete cracking.

[0059] The shrinkage rate of the high-concentration self-healing crack-resistant waterproofing agent for concrete was tested according to the current standards JC / T474 "Waterproofing Agents for Mortar and Concrete" and T / CECS 10461 "High-concentration Self-healing Crack-resistant Waterproofing Agent for Concrete". The test results show that the shrinkage rate is less than 100% in both cases.

[0060] Table 3. Results of Shrinkage Ratio Test Verification .

[0061] 4. The self-healing ability of concrete cracks is higher than that of concrete cracks. By adding a high-concentration self-healing crack-resistant and waterproofing agent to concrete, it reacts with the hydration products in cement in a secondary hydration reaction to generate water-insoluble crystals, which fill the capillary pores and micro-cracks in cement concrete, thereby quantifying the self-healing repair ability of cement concrete crack parameters (width, depth, etc.) or performance indicators (strength, impermeability, etc.).

[0062] This test was conducted according to the current standard T / CECS 913 "Standard for Test Method of Self-Healing Performance of Cement Concrete". The current standard T / CECS 10461 "High-Concentration Self-Healing Crack-Resistant Waterproofing Agent for Concrete" stipulates that the self-healing capacity of concrete cracks should be no less than 150%. The test results show that the results are all far higher than the standard limit of 150%.

[0063] Table 4. Test results of the self-healing ability of concrete cracks .

[0064] 5. Crack reduction rate Adding a high-concentration self-healing crack-resistant and waterproofing agent to concrete to reduce cracking is an effective measure to improve the crack resistance of concrete. Crack reduction rate is a highly intuitive performance indicator for quantifying the effectiveness of concrete crack control, reflecting the improvement in concrete's crack resistance.

[0065] The crack reduction rate of the high-concentration self-healing crack-resistant and waterproofing agent for concrete was tested according to the current standard T / CECS 10461 "High-concentration self-healing crack-resistant and waterproofing agent for concrete". The test results show that the crack reduction rate is not less than the limit requirement of 35%.

[0066] Table 5. Test results of crack reduction rate .

[0067] 6. Crack repair efficiency Crack repair efficiency is the core indicator for measuring the effect of self-healing materials or technologies on concrete crack repair. The evaluation of repair effect cannot be based solely on whether the crack is "closed". Instead, it needs to be judged comprehensively from multiple dimensions such as crack repair rate, compressive strength recovery rate, and impermeability repair rate.

[0068] Table 6. Test results verifying crack repair efficiency .

[0069] Repair effect: Within the crack width range of less than 0.4 mm in concrete, the test results show that the concrete with high-concentration self-healing crack-resistant and waterproof agent achieved a crack repair rate of 95.25%, a compressive strength recovery rate of 94.1%, and a permeability repair rate of 95.55%. Electron microscopy revealed the formation of effective crystals and gels at the crack sites. This proves that adding high-concentration self-healing crack-resistant and waterproof agent to concrete can achieve a very ideal repair effect.

Claims

1. A highly concentrated self-healing crack-resistant and waterproof concrete agent, characterized in that, By weight percentage, its raw material composition is as follows: silicate 16-20%, modified nano silica 8%-12%, sodium hydroxide 3%-4%, triethanolamine 2%-3%, retarder 4%-5%, defoamer 0.3%-0.5%, shrinkage reducer 1.5%-2.5%, antifreeze 3%-4%, deionized water to make up to 100%, pH=12-14.

2. The high-concentration self-healing crack-resistant and waterproof concrete agent according to claim 1, characterized in that, The silicate is a mixture of lithium silicate and sodium silicate, with a mass ratio of lithium silicate:sodium silicate = 1:

2.

3. The high-concentration self-healing crack-resistant and waterproof concrete agent according to claim 1, characterized in that, The retarder is sodium gluconate or sodium citrate.

4. The preparation method of the high-concentration self-healing crack-resistant and waterproof concrete agent according to any one of claims 1-3, characterized in that, The specific steps are as follows: (1) Add sodium hydroxide to a portion of deionized water in batches and stir until completely dissolved; then add retarder, antifreeze, shrinkage reducer and triethanolamine in sequence and stir until completely dissolved to obtain solution I; (2) Under stirring, add modified nano-silica to solution I. After the addition is complete, continue high-speed shearing until the system is uniformly translucent to obtain solution II. (3) Add silicate to solution II and stir to mix evenly; then add defoamer and the remaining deionized water to obtain a high-concentration self-healing crack-resistant waterproofing agent for concrete.

5. The preparation method of the high-concentration self-healing crack-resistant and waterproof concrete agent according to claim 4, characterized in that, In step (1), the stirring speed is 300-400 rpm.

6. The preparation method of the high-concentration self-healing crack-resistant and waterproof concrete agent according to claim 4, characterized in that, In step (2), the stirring speed is 600-800 rpm.