A permeability resistant concrete and a method of making the same

Abstract

The application belongs to the technical field of building materials, and particularly relates to a permeation-resistant concrete and a preparation method thereof. The permeation-resistant concrete comprises cementitious materials, aggregates, water and a self-repairing functional component; the self-repairing functional component comprises polyacrylic acid, polyaspartic acid, a calcium ion supplement and a reaction promoter. The application utilizes polyacrylic acid and polyaspartic acid as complex carriers of calcium ions. When micro-cracks appear in the concrete, directional migration is driven by a concentration gradient to the deep part of the cracks, a substitution reaction occurs between the calcium ions and silicate and carbonate in the pore solution, hydrated calcium silicate and calcium carbonate precipitates are generated to fill the cracks, and the polymers are re-released into the next cycle to realize multiple self-repairing. The permeation-resistant concrete prepared by the application has high permeation resistance, deep repair depth, can be effectively self-repaired multiple times, and is suitable for important engineering structures with high permeation resistance requirements such as underground engineering, tunnels, water conservancy dams, ocean platforms and the like.

Description

Technical Field

[0001] This application belongs to the field of building materials technology, and in particular relates to an impermeable concrete and its preparation method. Background Technology

[0002] As the most widely used building material in the world today, concrete's impermeability is of paramount importance. Due to its inherent composition and hardening characteristics, traditional concrete inevitably contains multi-scale pore structures (from nanoscale gel pores to micrometer-scale capillaries) and microcracks. These defects are interconnected, forming channels for the penetration of moisture and harmful media. How to maximally cut off these channels and improve the density and impermeability of concrete is a core research topic in the field of building materials science.

[0003] Currently, the main technical paths for achieving self-repair of concrete cracks include the following categories: (1) Microbial-induced calcium carbonate precipitation: Calcium carbonate is precipitated by the metabolism of bacteria to fill cracks. However, bacteria have a low survival rate in the strongly alkaline environment of concrete, consume nutrients quickly, have limited repair depth, and are costly; (2) Microcapsule self-repair: The repair agent is encapsulated in microcapsules. When the crack extends to the microcapsule, the capsule breaks and releases the repair agent to fill the crack. However, there are problems such as one-time release, poor compatibility between the capsule and the matrix, complex preparation process, high cost, and difficulty in effectively repairing deep cracks. (3) Modification of cementitious materials: By adding industrial waste such as fly ash, slag, and silica fume, the active SiO2 and Al2O3 are used to react with the cement hydration product calcium hydroxide to generate more CSH gel to fill pores and microcracks. However, this technology relies on continuous hydration reaction, and the repair efficiency decreases with the increase of hydration degree, making it difficult to meet the repair needs after multiple cracking. (4) Penetrating crystalline waterproofing materials: These materials utilize active chemical substances (such as sodium silicate, sodium carbonate, complexing agents, etc.) to react with cement hydration products, generating insoluble crystals to seal pores and cracks. For example, Chinese patent CN121494397A uses refined silica powder, quartz sand, silicates, and alkali metal salt composites. When in contact with water in the mixed concrete, these components dissolve and penetrate the concrete's capillaries and microcracks, improving the concrete's impermeability and density. CN117865551A uses sodium bentonite, sodium methylsilicate, penetrant, sulfoaluminate cement, zirconium silicate, and complexing agents (2-[3-(4-pentylphenyl)prop-2-enoylamino]benzoic acid and sodium ethylenediaminetetraacetate) to form a self-healing waterproofing material. CN119569397B discloses a self-healing crystalline impermeable high-durability cement-based material, using diethylenetriaminepentaacetic acid as a chelating agent in conjunction with a crystallizing precipitant. However, the active components of traditional permeation crystallization materials are mostly small molecule complexing agents (such as EDTA, citric acid, diethylenetriaminepentaacetic acid, etc.), which react with Ca... 2+It forms a simple 1:1 complex, and the active component is consumed in one step during the reaction, resulting in weak secondary repair ability; moreover, the reaction is too fast and a dense layer is easily formed on the surface of the crack, which hinders the active material from penetrating into the depth of the crack, thus limiting the repair depth. Summary of the Invention

[0004] To address the aforementioned issues, the purpose of this application is to overcome the problems of existing concrete repair agents, such as one-time consumption, limited repair depth, poor matrix compatibility, high cost, and complex processes. The application provides an impermeable concrete and its preparation method that can achieve deep, uniform, and repeatedly triggered water-resistant self-healing functions in concrete microcracks without depleting its self-healing active components, while ensuring good compatibility with the cement matrix, ease of processing, and economic feasibility.

[0005] To achieve the above objectives, this application adopts the following technical solution:

[0006] In one aspect, this application provides a waterproof concrete.

[0007] A type of impermeable concrete comprises cementitious materials (cement: P.O42.5 ordinary Portland cement, 2800-3200 parts; fly ash: Grade II fly ash, 700-800 parts), aggregates (fine aggregates: artificial sand or natural sand, fineness modulus 2.6-2.8, 7200-7800 parts; coarse aggregates: 5-25mm continuously graded crushed stone, 11000-11800 parts), admixtures (water-reducing agent: polycarboxylate-based high-efficiency water-reducing agent, 20-25 parts; air-entraining agent: AIR202 type air-entraining agent, 1.5-2.0 parts), and self-healing functional components; the dosage of the self-healing functional components is 2.0-3.5% of the total mass of the cementitious materials.

[0008] The self-repairing functional component consists of complex polymer A, complex polymer B, calcium ion supplement, and reaction promoter, and is formulated according to the following mass ratio: 80-120 parts of complex polymer A (polyacrylic acid (PAA), molecular weight 2000-5000), 15-25 parts of complex polymer B (polyaspartic acid (PAsp), molecular weight 3000-6000), 180-220 parts of calcium ion supplement (saturated calcium hydroxide solution), 4-6 parts of reaction promoter (triethanolamine), and 650-750 parts of solvent (deionized water).

[0009] In this technical solution, PAA in this molecular weight range has a suitable hydrodynamic radius (approximately 5-8 nm) in concrete pore fluid, enabling it to enter the capillary system (10-100 nm in diameter) for deep migration without being trapped by gel pores (<5 nm). Simultaneously, it possesses a sufficient carboxyl group density (approximately 20-50 carboxyl groups / molecular chain) to ensure multidentate complexation capability. PAsp molecular chains with a molecular weight of 3000-6000 contain both carboxyl and amide groups. The amide groups can form a hydrogen bond network with silicate ions, providing a template for CSH gel nucleation and inducing the formation of CSH with a higher degree of polymerization. The molecular weight selection balances complexation stability and migration ability. PAA provides the primary calcium ion complexation capability, while PAsp provides the inducing template for CSH gel formation. At this compound ratio, PAA and PAsp synergistically achieve a co-existing structure of calcium carbonate crystals and CSH gel. Triethanolamine, as a reaction promoter, can react with Ca... 2+ It forms a moderately stable complex, accelerates the transfer of calcium ions between the polymer and the precipitated anion, and improves the reaction kinetic efficiency.

[0010] Furthermore, the self-healing functional component is prepared according to the following steps:

[0011] (1) Preparation of mother liquor: Weigh PAA and mix it evenly with about one-third of deionized water. While stirring, slowly add saturated calcium hydroxide solution dropwise, monitoring the pH value of the solution in real time. When the pH reaches 8.5-9.0, stop adding the solution and continue stirring for 30 minutes to allow PAA and Ca to react. 2+ The pre-complex was fully formed, yielding the PAA-Ca complex mother liquor.

[0012] (2) Composite modification: PAsp is slowly added to the above PAA-Ca complex mother liquor, the reaction system is heated to 40±2℃, stirred until PAsp is completely dissolved, triethanolamine is added, stirring is continued for 15 min, and cooled to room temperature to obtain a concentrated solution of composite functional components.

[0013] (3) Concentration adjustment: Dilute the above-mentioned compound functional component concentrate with the remaining deionized water to the target concentration and set aside.

[0014] Furthermore, the polyacrylic acid mentioned in (1) is a 50% aqueous solution, the concentration of the calcium hydroxide saturated solution is 1.1-1.3 g / L, and the pH adjustment is monitored in real time using a pH meter.

[0015] Furthermore, the target concentration mentioned in (2) is 2.5-7.5% effective content of polyacrylic acid and 0.5-1.5% effective content of polyaspartic acid.

[0016] Secondly, this application provides a method for preparing impermeable concrete.

[0017] A method for preparing impermeable concrete includes the following steps:

[0018] Step 1: Raw material pretreatment

[0019] Accurately weigh the cement, fly ash, sand, and gravel according to the mix proportion and set aside; then dissolve the water-reducing agent in part of the mixing water (solubility is 1:10, water temperature 20-25℃); weigh the air-entraining agent separately and mix it evenly with the remaining mixing water; extract the self-healing functional components according to the designed dosage and set aside, and shake well before use.

[0020] Step 2: Stirring Process

[0021] Using a forced-action concrete mixer, mix according to the following procedure:

[0022] Dry mixing stage: Add sand, gravel, cement, and fly ash for 25-35 seconds, mixing speed: 30 rpm; Initial wetting stage: Add 70% mixing water (including water-reducing agent) for 50-70 seconds, mixing speed: 30 rpm; Functional component addition: Slowly and evenly add self-healing functional components for 25-35 seconds; Final mixing stage: Add the remaining 30% mixing water (including air-entraining agent) for 110-130 seconds, mixing speed: 35 rpm.

[0023] Step 3: Shaping and Curing

[0024] The mixed concrete mixture is poured into a test mold, vibrated and smoothed, covered and cured for 24 hours, then demolded and moved into a standard curing room for curing to the specified age.

[0025] This application utilizes polyacrylic acid and polyaspartic acid as complexing carriers for calcium ions. When microcracks appear in concrete, they migrate directionally to the depths of the cracks through a concentration gradient, react with silicate and carbonate ions in the pore fluid to generate hydrated calcium silicate and calcium carbonate precipitates that fill the cracks. At the same time, the polymer is released back into the next cycle, achieving multiple self-repair.

[0026] Compared with the prior art, this application has the following beneficial effects:

[0027] 1. Based on the “complexation-substitution” cyclic reaction mechanism of PAA / PAsp, the active component is released back into the pore solution after completing calcium ion transport and precipitation induction, realizing recycling and enabling multiple repairs of cracks, thus significantly extending the service life of concrete structures.

[0028] 2. The PAA / PAsp polymer used in this application has a moderate molecular weight (2000-6000). Its complex migrates directionally in concrete pores through a concentration gradient and achieves "leapfrog" advancement by utilizing dynamic adsorption-desorption equilibrium to deeply repair cracks.

[0029] 3. The repair product induced by this application is a symbiotic structure of calcium carbonate crystals and CSH gel, which has good chemical compatibility with the cement matrix. The repair layer forms an "interface-free transition" with the cement stone matrix, with an interfacial bonding strength of 2-3 MPa and a mechanical property recovery of over 90%, avoiding the problem of easy detachment of traditional repair materials.

[0030] 4. The concrete prepared in this application can achieve a permeability grade of P14 or higher, which is more than 75% higher than the benchmark group and more than 40% higher than traditional permeable crystalline materials. It exhibits stable long-term permeability resistance and maintains high permeability even after multiple cracking events.

[0031] 5. The raw materials for preparing impermeable concrete in this application are readily available, the process is simple, and the cost is controllable. Attached Figure Description

[0032] Figure 1 This is a SEM image of the self-healing cross-section of the impermeable concrete in Embodiment 1 of the present invention.

[0033] Figure 2 This is a diagram of the self-healing impermeable concrete in Embodiment 1 of the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the following embodiments are only for explaining the invention and not for limiting it. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0035] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0036] (a) Raw material preparation

[0037] Prepare the raw materials according to the following proportions (Table 1):

[0038] Table 1 Concrete Material Proportions

[0039]

[0040] Self-healing kit distribution (based on a preparation volume of 10 kg):

[0041] (1) Weigh 1.0 kg of polyacrylic acid (PAA, 50% aqueous solution, molecular weight 3000); add 2.0 kg of deionized water and stir magnetically for 10 min;

[0042] (2) Slowly add saturated calcium hydroxide solution (1.2 g / L) to adjust the pH to 8.5, using about 0.2 kg in total, and continue stirring for 30 min;

[0043] (3) Weigh 0.2 kg of polyaspartic acid (PAsp, molecular weight 4000), add it to the above solution, heat in a water bath at 40°C, and stir magnetically for 60 min until completely dissolved;

[0044] (4) Add 0.05 kg of triethanolamine, stir for 15 min, add 6.55 kg of deionized water to dilute to 10 kg, and stir evenly.

[0045] (II) Concrete Preparation

[0046] Prepare the concrete using a 60L forced concrete mixer according to the following steps:

[0047] 1. Add sand, gravel, cement, and fly ash, and dry mix for 30 seconds;

[0048] 2. Add 70% mixing water (containing water-reducing agent) and stir for 60 seconds;

[0049] 3. Slowly add 10 kg / m³ of the self-healing component and stir for 30 seconds;

[0050] 4. Add the remaining 30% of the mixing water (including the air-entraining agent) and stir for 120 seconds;

[0051] 5. Slump test result: 185mm, air content: 5.2%, meets requirements;

[0052] 6. Molding test specimens: The above mixture is placed into a mold that has been pre-coated with a release agent;

[0053] 7. Vibrate on the vibrating table for 10 seconds, then smooth the surface;

[0054] 8. Cover with plastic film and demold after 24 hours;

[0055] 9. Standard maintenance until 28 days.

[0056] A separate benchmark group is established:

[0057] (a) Raw material preparation

[0058] It is basically the same as Example 1, except that it does not contain self-healing components.

[0059] (II) Concrete Preparation

[0060] It does not contain self-healing components, and is otherwise the same as in Example 1.

[0061] Performance testing:

[0062] 1. Mechanical properties: Tested according to GB / T50081-2019, the results are shown in Table 2;

[0063] Table 2 Mechanical Performance Tests

[0064]

[0065] The results in Table 2 show that the introduction of the self-healing component has a slight impact on the early strength (reducing it by about 2.4%), but the 28-day strength is slightly higher than that of the baseline group, indicating that the repair products generated later filled the internal pores and compensated for the early strength loss.

[0066] 2. Impermeability: Tested according to the stepwise pressure method of GB / T50082-2009, the results are shown in Table 3:

[0067] Table 3. Water Resistance Test

[0068]

[0069] As can be seen from Table 3, the impermeability grade increased from P8 to P14, an improvement of 75%, indicating that the self-healing component significantly improved the impermeability of concrete.

[0070] 3. Self-healing performance

[0071] Crack prefabrication: Take prism specimens cured for 28 days and prefabricate cracks using the three-point bending method. Initial crack width: 0.3-0.4 mm (measured using a crack width observation instrument).

[0072] Repair and maintenance:

[0073] The precast crack test block was completely immersed in water (20±2℃), and observed at 3d, 7d, 14d, and 28d respectively (e.g., Figure 2 (As shown).

[0074] The repair results are shown in Table 4:

[0075] Table 4 Self-healing test results

[0076]

[0077] Microscopic examination of sections revealed that the repair depth was 10-20 mm.

[0078] Analysis of repaired products:

[0079] XRD analysis of the repair product scraped from the crack revealed the following main mineral phases: calcite-type calcium carbonate (CaCO3): approximately 60%; hydrated calcium silicate (CSH): approximately 35%; and calcium hydroxide: approximately 5%.

[0080] Secondary repair capability test:

[0081] The repaired test blocks were subjected to load again to cause them to crack again (crack width 0.3-0.4 mm), and then soaked in water for curing. Multiple repair capacity tests were conducted, as shown in Table 5.

[0082] Table 5 Results of Secondary Repair Capability Test

[0083]

[0084] The results show that this solution can achieve more than three effective repairs, enabling recycling and significantly extending the service life of concrete structures.

[0085] 4. Microscopic mechanism verification

[0086] Take a sample of the crack cross-section, sputter-coated it with gold, and then observe it using SEM. Figure 1 As shown:

[0087] from Figure 1 As can be seen, the repair products coexist in two forms: spherical calcium carbonate crystals (2-5 μm in diameter) and CSH gel. There are no obvious cracks in the interface transition zone, and the repair layer is well bonded to the cement stone body.

[0088] Example 2

[0089] (a) Raw material preparation

[0090] The method is basically the same as in Example 1, except that the concentration of the self-healing component is adjusted to a low concentration group (diluted by 1 time).

[0091] Self-repairing group allocation system:

[0092] Take the medium-concentration self-healing component prepared in Example 1, add an equal volume of deionized water to dilute it, and stir evenly.

[0093] (II) Concrete Preparation

[0094] Same as Example 1.

[0095] Example 3

[0096] (a) Raw material preparation

[0097] The method is basically the same as in Example 1, except that the concentration of the self-healing component is adjusted to a high concentration (concentrated to 2 / 3 of the original volume).

[0098] Preparation method of high-concentration self-healing components:

[0099] The medium-concentration self-healing component prepared in Example 1 was concentrated to 2 / 3 of its original volume by rotary evaporation in a 40°C water bath.

[0100] (II) Concrete Preparation

[0101] Same as Example 1.

[0102] Comparative Example 1

[0103] (a) Raw material preparation

[0104] Commercially available penetrating crystalline waterproofing agent (main components: sodium silicate, sodium carbonate, complexing agent, etc.) is used, and added according to the manufacturer's recommended dosage (2% of the adhesive material).

[0105] (II) Concrete Preparation

[0106] Same as Example 1, except that the self-healing component is replaced with a commercially available penetrating crystallizing waterproofing agent.

[0107] Comparative Example 2

[0108] (a) Raw material preparation

[0109] The self-healing component contains only PAA and no PAsp; otherwise, it is the same as in Example 1.

[0110] Self-repairing group allocation system:

[0111] (1) Weigh 1.0 kg of polyacrylic acid (PAA, 50% aqueous solution, molecular weight 3000), add 2.0 kg of deionized water, and stir magnetically for 10 min;

[0112] (2) Slowly add saturated calcium hydroxide solution (1.2 g / L), adjust the pH to 8.5, and continue stirring for 30 min;

[0113] (3) Add 0.05 kg of triethanolamine, stir for 15 min, add 6.95 kg of deionized water to dilute to 10 kg, and stir evenly.

[0114] (II) Concrete Preparation

[0115] Same as Example 1.

[0116] (III) The comprehensive performance test results are shown in Table 6:

[0117] Table 6. Overall Performance Test Results

[0118]

[0119] As shown in Table 6, the low-concentration group (Example 2) still significantly improved impermeability, but its repair efficiency was slightly lower than that of the medium-concentration group. The high-concentration group (Example 3) had impermeability and repair efficiency comparable to the medium-concentration group, but its 28-day strength was slightly lower (5% lower than that of Example 1), indicating that excessively high concentrations of polymer may have a certain delaying effect on cement hydration. The traditional penetrating crystallizing material (Comparative Example 1) had a certain effect in the first repair (closure rate of 60%), but its secondary repair ability was significantly reduced (closure rate of only 25%). The sample without PAsp (Comparative Example 2) had slightly lower impermeability and repair efficiency than Example 1.

[0120] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A permeability resistant concrete, characterized in that, The product comprises cementing materials, aggregates, water, and a self-healing functional component. The self-healing functional component includes complexing polymer A, complexing polymer B, a calcium ion supplement, and a reaction promoter. Complexing polymer A is polyacrylic acid with a molecular weight of 2000-5000; complexing polymer B is polyaspartic acid with a molecular weight of 3000-6000; the calcium ion supplement is a saturated calcium hydroxide solution; and the reaction promoter is triethanolamine. The mass percentages of each component in the self-healing functional component are: 80-120 parts polyacrylic acid, 15-25 parts polyaspartic acid, 180-220 parts saturated calcium hydroxide solution, 4-6 parts triethanolamine, and 650-750 parts deionized water.

2. The anti-infiltration concrete according to claim 1, characterized in that, The self-healing functional component is added at a rate of 2.0-3.5% of the total mass of the cementitious material.

3. The impermeable concrete according to claim 1, characterized in that, The cementitious material comprises cement and fly ash, with a cement to fly ash mass ratio of 3.5-4.5:

1.

4. The impermeable concrete according to claim 1, characterized in that, The aggregate includes fine aggregate and coarse aggregate, with the fineness modulus of the fine aggregate being 2.6-2.8 and the coarse aggregate having a continuous gradation of 5-25 mm particle size.

5. The impermeable concrete according to claim 1, characterized in that, It also includes additives; the additives are water-reducing agents and air-entraining agents.

6. A method for preparing impermeable concrete as described in any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Preparation of self-healing functional components: Dilute polyacrylic acid with deionized water and stir until homogeneous at 20-25℃; slowly add saturated calcium hydroxide solution, controlling the adding rate at 5-10 mL / min, adjust the pH to 8.5-9.0, and continue stirring for 20-40 min to obtain a polyacrylic acid-calcium complex mother liquor; add polyaspartic acid to the polyacrylic acid-calcium complex mother liquor, heat to 38-42℃, and stir at a constant temperature for 50-70 min until completely dissolved; add triethanolamine and continue stirring for 10-20 min; cool to room temperature, add deionized water to adjust to the target concentration, and obtain the self-healing functional components; Step 2: Weigh the raw materials: Weigh the cement, fly ash, aggregate, water, admixtures, and the self-healing functional components prepared in Step 1 according to the mixing ratio; Step 3: Mixing: Put cement, fly ash and aggregate into the mixer and dry mix for 25-35 seconds; add 70% of the mixing water containing water-reducing agent and mix for 50-70 seconds; add the self-healing functional component and mix for 25-35 seconds; add the remaining 30% of the mixing water containing air-entraining agent and continue mixing for 110-130 seconds. Step 4: Molding and Curing: Pour the mixed concrete mixture into the test mold, vibrate and smooth it, cover and cure for 24 hours, then remove it from the mold and move it to the standard curing room for curing until the specified age.

7. The preparation method according to claim 6, characterized in that, In step one, the polyacrylic acid is a 50% aqueous solution, the concentration of the calcium hydroxide saturated solution is 1.1-1.3 g / L, and the pH adjustment is monitored in real time using a pH meter.

8. The preparation method according to claim 6, characterized in that, The target concentration mentioned in step one is an effective content of 2.5-7.5% for polyacrylic acid and an effective content of 0.5-1.5% for polyaspartic acid.

9. The preparation method according to claim 6, characterized in that, The mixing described in step three uses a forced concrete mixer. The mixing speed is 28-32 rpm in the dry mixing stage and 33-37 rpm in the final mixing stage.

Images