Self-repairing concrete complexing agent and preparation method thereof

Abstract

The invention relates to a self-repairing concrete complexing agent and a preparation method thereof, and belongs to the technical field of concrete.The self-repairing concrete complexing agent is prepared from 1-4 parts of microorganism induction repairing agent, 2-6 parts of nanometer wollastonite, 10-15 parts of slow-release repairing liquid and 0.02-0.12 part of magnesium oxide. Triple repair mechanisms of microbial mineralization, chemical gel and nano-filling are fused, crack initiation and expansion to a stable whole stage are covered, the repair system is far better than a single repair system, the slow release liquid realizes on-demand release of the repair agent, one-time consumption failure is avoided, durability is improved by 50% or above, nano wollastonite and magnesium oxide micro-expansion synergistically enhance compactness, and the repair effect is good. Meanwhile, the method is compatible with an existing concrete production line, complex equipment is not needed, energy consumption is reduced, the use amount of components is small, microbial metabolism and natural minerals are further utilized, pollution of chemical expanding agents is reduced, only water triggering is needed in the repairing process, no toxic by-product is generated, and the method meets the green building material standard.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite agent preparation, and particularly relates to a self-healing concrete composite agent and a preparation method thereof. Background Art

[0002] As the core material of construction engineering, concrete has long faced the problem of cracks caused by environmental erosion and load effects. Therefore, with the development of technology, self-healing concrete has emerged. It is a functional building material that can automatically generate repair substances such as calcium carbonate and silica gel at the cracks through internal active ingredients such as microorganisms and chemical repair agents, and can restore the structural integrity and durability. The self-healing concrete composite agent is the core functional material added to concrete, including components such as microbial inducer, nano-filler, and slow-release repair liquid, which work together to achieve crack closure, strength recovery, and impermeability improvement.

[0003] However, generally, traditional composite agents mostly rely on a single repair mechanism such as only microbial or chemical repair, and have disadvantages such as low repair efficiency, poor durability, and high cost. Traditional repair methods such as surface plastering of mortar and epoxy resin grouting require manual intervention and only target surface damage, and cannot repair internal microcracks. The repair effect is short-lived and the cost is high.

[0004] In addition, the construction waste generated by traditional methods exacerbates environmental pollution and is difficult to meet the requirements of modern engineering for sustainability. Summary of the Invention

[0005] The purpose of the present invention is to provide a self-healing concrete composite agent and a preparation method thereof to solve the above problems.

[0006] The present invention achieves the above purpose through the following technical solutions:

[0007] The present invention provides a self-healing concrete composite agent. By weight, the raw materials for preparing the self-healing concrete composite agent include:

[0008] 1-4 parts of microbial-induced repair agent, 2-6 parts of nano-wollastonite, 10-15 parts of slow-release repair liquid, and 0.02-0.12 parts of magnesium oxide.

[0009] Preferably, by weight, the microbial-induced repair agent includes: 0.5-2 parts of Bacillus pasteurii and 0.5-2 parts of calcium carbonate.

[0010] Preferably, by weight, the slow-release repair liquid includes: 5-7.5 parts of sodium silicate, 5-7.5 parts of polyacrylamide, and 2-4 parts of calcium nitrite.

[0011] Preferably, the specific production steps of the nano-wollastonite are: (i) dissolving a calcium source and a silicon source in deionized water, adding a polycarboxylate water-reducing agent and a surfactant into the deionized water and stirring evenly to obtain a calcium source solution and a silicon source solution; (ii) slowly dripping the calcium source solution into the silicon source solution and stirring to obtain a mixed solution, and adjusting the pH to 10-12 with dilute nitric acid; (iii) transferring the mixed solution to a hydrothermal reactor, the reaction temperature is 180-200°C, and the reaction time is 12-24h; (iv) cooling to room temperature, collecting the precipitate by centrifugation, and washing it alternately with deionized water and ethanol for 5 times to remove residual ions and surfactants; (v) drying the precipitate, and calcining the dried product at 500-700°C for 2 hours to obtain nano-wollastonite.

[0012] Preferably, the calcium source is any one of calcium nitrate or calcium chloride, the silicon source is any one of sodium silicate or ethyl orthosilicate, and the surfactant is any one of hexadecyltrimethylammonium bromide or polyvinylpyrrolidone.

[0013] Preferably, the molar ratio of the calcium source to the silicon source is Ca:Si=1:1, and the added amount of the surfactant is 0.1-0.5wt%.

[0014] Preferably, the specific production steps of the magnesium oxide are: (i) grinding the magnesium compound into fine powder; (ii) placing the powder in a muffle furnace, heating it to 800-1200° C., and keeping it warm for 2-4 hours; (iii) cooling it to room temperature to obtain a block or granular magnesium compound; (iv) crushing and refining the particles by ball milling to obtain nano-grade magnesium oxide.

[0015] Preferably, the magnesium compound includes any one of magnesium carbonate or magnesium hydroxide.

[0016] Based on the above self-repairing concrete composite, the present invention also proposes a preparation process of the self-repairing concrete composite, comprising the following steps:

[0017] S1. Inoculate Bacillus pasteurianus into LB liquid culture medium, shake culture at 20-40° C. for 12-24 hours to obtain a bacterial suspension, mix calcium carbonate powder with the bacterial suspension in proportion, add 10% trehalose and stir for 15-30 minutes, dry under vacuum at 30-50° C., crush and pass through a 200-mesh sieve to obtain a microbial induced repair agent;

[0018] S2. Add polyacrylamide into 80°C deionized water, slowly add calcium nitrite powder into the polyacrylamide solution, stir for 10-15 minutes until completely dissolved, add sodium silicate solution, stir and mix evenly, allow sodium silicate and calcium nitrite to react fully, and form a gel-like slow-release repair solution after cooling;

[0019] S3, adding nano-wollastonite into anhydrous ethanol, ultrasonically dispersing for 30 minutes, and collecting the powder by centrifugation for later use;

[0020] S4. Add the microbial induced repair agent, nano-wollastonite and magnesium oxide into a high-speed mixer in proportion, stir and mix, then add the sustained-release repair liquid, continue stirring until a viscous slurry is formed, spray dry the slurry to obtain a granular composite with a particle size of 0.5-1mm.

[0021] Preferably, the mass ratio of calcium carbonate powder to bacterial suspension in step S1 is 1:1, the mass ratio of polyacrylamide to ionized water in step S2 is 1:10, and the mass ratio of nano-wollastonite to anhydrous ethanol in step S3 is 1:10.

[0022] The beneficial effects of the present invention are: the present invention integrates the triple repair mechanisms of microbial mineralization, chemical gel and nano-filling, covering the entire stage from crack initiation to expansion to stability, with a 7-day healing rate of up to 92%, and a compressive strength recovery of 94%, far exceeding a single repair system. The sustained-release liquid realizes the on-demand release of the repair agent to avoid one-time consumption failure, and the permeability coefficient is reduced by 88%, and the durability is improved by more than 50%. Nano-wollastonite and magnesium oxide micro-expansion synergistically enhance the density and resist secondary cracking. At the same time, it is compatible with the existing concrete production line through microbial vacuum drying protection activity, nano-material hydrothermal low-temperature synthesis, and spray drying into particles. It does not require complex equipment, reduces energy consumption, and uses a small amount of components. It also uses microbial metabolism and natural minerals to reduce chemical expansion agent pollution. The repair process only requires water triggering, has no toxic by-products, and meets green building material standards. DETAILED DESCRIPTION

[0023] The present application is described in further detail below. It is necessary to point out that the following specific implementation methods are only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Technical personnel in this field can make some non-essential improvements and adjustments to the present application based on the above application content.

[0024] 1. Materials

[0025] Unless otherwise specified, the methods used in the present invention are conventional methods known to those skilled in the art, and the reagents and other materials used are commercially available products unless otherwise specified.

[0026] 2. Process

[0027] Example 1: In this example, the weight proportions of the self-repairing concrete composite are as follows:

[0028] Microbial induced repair agent: 2.5 parts, including 1.25 parts of Bacillus pasteurianus + 1.25 parts of calcium carbonate + 3 parts of calcium nitrite;

[0029] Nano wollastonite: 4.0 parts;

[0030] Slow-release liquid: 6.25 parts of sodium silicate + 6.25 parts of polyacrylamide;

[0031] Magnesium oxide: 0.07 part;

[0032] Among them, the preparation environment is: microbial culture temperature: 30 °C, hydrothermal time of nano-wollastonite: 18 hours, calcination temperature of magnesium oxide: 600 °C;

[0033] Specifically, a preparation method of a self-healing concrete admixture includes the following steps:

[0034] The microbial-induced repair agent is prepared according to the following process:

[0035] (1) Inoculate 1.25 parts of Bacillus pasteurii into LB liquid medium, shake and culture at 30 °C for 18 hours to obtain a bacterial suspension, and add 10% trehalose and stir for 20 minutes;

[0036] (2) Mix 1.25 parts of calcium carbonate powder and the bacterial suspension in a mass ratio of 1:1, stir for 20 minutes, vacuum dry at 40 °C and then crush through a 200-mesh sieve. After drying, trehalose forms an amorphous glassy matrix, which wraps the bacterial cells to isolate oxygen and external stress and maintain the activity of the bacterial cells;

[0037] The nano-wollastonite is prepared according to the following process: The calcium source (calcium nitrate) and the silicon source (sodium silicate) are mixed in a molar ratio of Ca:Si = 1:1, and 0.3 wt% CTAB surfactant is added; Dissolve the calcium source and the silicon source in deionized water, add 0.5 part of polycarboxylate superplasticizer and the surfactant to deionized water and stir evenly to obtain a calcium source solution and a silicon source solution. Through the electrostatic repulsion and steric hindrance effects of its molecular chains, the aggregation of nano-wollastonite particles is inhibited; Slowly drip the calcium source solution into the silicon source solution and stir and mix to obtain a mixed solution, and adjust the pH to 10 - 12 with dilute nitric acid; Transfer the mixed solution to a hydrothermal reaction kettle, with a reaction temperature of 180 - 200 °C and a time of 12 - 24 h; Cool to room temperature, centrifuge to collect the precipitate, wash it alternately with deionized water and ethanol 5 times to remove residual ions and surfactants, and perform ultrasonic dispersion treatment on the precipitate with a polycarboxylate superplasticizer solution, so that its long side chain structure forms a lubricating layer between the particles to improve the fluidity during subsequent concrete mixing; Dry the precipitate, calcine the dried product at 500 - 700 °C, mix the polycarboxylate superplasticizer solution with the dried product, make it form a coating layer through chemical adsorption, and then calcine to fix the dispersed structure to obtain nano-wollastonite.

[0038] Among them, the hydrothermal reaction conditions are 180 °C, 18 hours, calcination temperature 600 °C, 2 hours;

[0039] The sustained-release solution was prepared according to the following process: 6.25 parts of polyacrylamide were added to 80°C deionized water (mass ratio 1:10), calcium nitrite powder was slowly added to the polyacrylamide solution, stirred for ≥10 minutes until completely dissolved, and after dissolved, 6.25 parts of sodium silicate solution were added, stirred and cooled to form a gel;

[0040] The magnesium oxide is prepared according to the following process: a magnesium compound (magnesium carbonate or magnesium hydroxide) is ground into fine powder; the powder is placed in a muffle furnace, heated to 900°C, and kept warm for 3 hours; cooled to room temperature to obtain a block or granular magnesium compound; and ball milled to nanometer level.

[0041] (3) Compound agent mixing: dissolve 2% sodium alginate aqueous solution in deionized water, mix the microbial induced repair agent, nano-wollastonite, and magnesium oxide, add the sustained-release solution, and spray dry into 0.5-1 mm particles;

[0042] The microbial induced repair agent and sodium alginate solution were mixed in a mass ratio of 1:2-1:3, stirred to a uniform suspension, and the mixture was dropped into a 2% calcium chloride solution by spraying. The mixture was allowed to stand for 20-30 minutes to allow the sodium alginate to be fully cross-linked, and then washed with deionized water for 5 times to remove residual Ca 2 +, vacuum drying at low temperature (30℃) until the moisture content is ≤8%,

[0043] Add sodium alginate microcapsules, nano-wollastonite and magnesium oxide into a high-speed mixer at a mass ratio of 3:2:1. Add a slow-release repair liquid and control the liquid-solid ratio to 1:1.5-1:2. Rotate at 300-500rpm for 15-20 minutes to form a uniform viscous slurry. Adjust the atomizer (rotation speed 15,000-20,000rpm, air inlet temperature: 120-140℃, air outlet temperature: 50-60℃, atomization pressure: 0.2-0.4MPa) to control the particles to 0.5-1mm to obtain a composite agent.

[0044] Example 2, in this example, the weight parts of materials are as follows:

[0045] Microbial induced repair agent: 4.0 parts, including 2.0 parts of Bacillus pasteurianus and 2.0 parts of calcium carbonate, the ratio of bacterial suspension to calcium carbonate is 2.0 parts:2.0 parts, and the remaining steps are the same as in Example 1;

[0046] Example 3, in this example, the weight parts of materials are as follows:

[0047] Nano wollastonite: 6.0 parts, the amount of calcium source and silicon source is increased to 6.0 parts, and the remaining steps are the same as in Example 1;

[0048] Example 4, in this example, the materials are in the following composition by weight:

[0049] Slow-release liquid: 7.5 parts of sodium silicate + 5.0 parts of polyacrylamide. The amount of sodium silicate is increased to 7.5 parts, and the amount of polyacrylamide is reduced to 5.0 parts. The remaining steps are the same as in Example 1;

[0050] Example 5. In this example, the materials in parts by weight are composed of the following components:

[0051] Magnesium oxide: 0.12 part

[0052] Other components are the same as in Example 1;

[0053] Among them, the preparation environment is: microbial culture temperature: 40 °C, hydrothermal time of nano-wollastonite: 24 hours, calcination temperature of magnesium oxide: 700 °C

[0054] The microbial-induced repair agent is prepared according to the following process: the culture temperature of the bacterial suspension is increased to 40 °C, and the rest is the same as in Example 1;

[0055] The nano-wollastonite is prepared according to the following process: the hydrothermal reaction time is extended to 24 hours, and the rest is the same as in Example 1;

[0056] The magnesium oxide is prepared according to the following process: the calcination temperature is increased to 700 °C, and the calcination time is 4 hours;

[0057] The parameters of Examples 1 to 5 are shown in Table (1):

[0058] Table 1 Parameter table of Examples 1 to 5

[0059] Parameter Example 1 Example 2 Example 3 Example 4 Example 5 Microbially Induced Remediation Agent 2.5 parts 4.0 parts 2.5 parts 2.5 parts 2.5 parts Nanosilicate 4.0 parts 4.0 parts 6.0 parts 4.0 parts 4.0 parts Sustained Release Solution (Si:PVP) 6.25:6.25 6.25:6.25 6.25:6.25 7.5:5.0 6.25:6.25 Magnesium Oxide 0.07 parts 0.07 parts 0.07 parts 0.07 parts 0.12 parts Microbial Culture Temperature 30℃ 30℃ 30℃ 30℃ 40℃ Hydrothermal Time of Nanosilicate 18 hours 18 hours 18 hours 18 hours 24 hours Calcination Temperature of Magnesium Oxide 600℃ 600℃ 600℃ 600℃ 700℃

[0060] III. Performance test

[0061] Mix the raw materials according to the parameters of Examples 1 to 5 and the formula of the examples, pour standard concrete test blocks (100×100×100 mm 3 ), preset a 0.3 mm crack, and conduct a self-healing performance test on the prepared self-healing concrete composite agent sample. The test blocks are immersed in deionized water and cured at a constant temperature of 25 °C. Specifically, it includes the following test procedures:

[0062] a. After 7 days, measure the change in crack width with a microscope and record the crack healing rate;

[0063] b. Calculate the ratio of the compressive strength of the repaired test block to the original strength, and calculate the compressive strength recovery rate;

[0064] c. Calculate the change in chloride ion penetration coefficient after repair, and calculate the reduction rate of penetration coefficient;

[0065] d. Record the time required for the crack to completely close and compare the repair time;

[0066] e. Record the performance parameters, as shown in Table 2:

[0067] Table 2 Self-healing performance test results of Examples 1 to 5

[0068] Performance Index Example 1 Example 3 Example 4 Example 5 Fracture Healing Rate (%) 78 85 88 82 Compressive Strength Recovery Rate (%) 86 90 89 88 Permeability Coefficient Reduction Rate (%) 75 80 83 78 Remediation Time (days) 14 12 11 13

[0069] IV. Analysis conclusions

[0070] According to the above comparative experiments, when the microbial-induced repair agent is increased to 4 parts, the highest crack healing rate and compressive strength recovery rate are 92% and 94%, the microbial activity is enhanced, and the calcium carbonate deposition efficiency is improved. When the nano-wollastonite is increased to 6 parts, the compressive strength recovery rate is relatively high at 90%. The nano-wollastonite fills the micropores and improves the compactness, but the dispersibility requirement is high, and excessive amounts are prone to agglomeration. Furthermore, when the proportion of the slow-release sodium silicate solution is increased, although the reduction rate of the permeability coefficient is significant (83%), the sodium silicate quickly forms a gel to block the cracks, but the reduction of polyacrylamide may reduce the adhesiveness of the slow-release solution. Finally, when the magnesium oxide is increased to 0.12 parts, the calcination temperature increases, enhancing the activity of the magnesium oxide and shortening the repair time. However, the high-temperature process has high energy consumption and a low demand priority;

[0071] In summary, the sample in Example 2 has a high healing rate of 92%, a strength recovery of 94%, and a rapid repair in 10 days. The core advantages are high microbial load, synergistic effect, and economy. Among them, the activity of Bacillus pasteurii is sufficient, maximizing the calcium carbonate deposition efficiency. The nano-wollastonite (4 parts) and the slow-release solution (6.25:6.25) balance the filling and cementing properties, and the amount of magnesium oxide is moderate (0.07 parts), with controllable process costs. Therefore, Example 2 is the best example.

[0072] The above-described examples only represent several embodiments of the present invention. The description is relatively specific and detailed, but it should not be construed as limiting the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A self-repairing concrete composite, characterized in that: The raw materials for preparing the self-repairing concrete composite agent include, by weight: 1-4 parts of microbial induced repair agent, 2-6 parts of nano-wollastonite, 10-15 parts of sustained-release repair liquid, and 0.02-0.12 parts of magnesium oxide.

2. A self-repairing concrete composite according to claim 1, characterized in that: In parts by weight, the microbial induced repair agent includes: 0.5-2 parts of Bacillus pasteurianus and 0.5-2 parts of calcium carbonate.

3. A self-repairing concrete composite according to claim 1, characterized in that: In parts by weight, the sustained-release repairing liquid comprises: 5-7.5 parts of sodium silicate, 5-7.5 parts of polyacrylamide, and 2-4 parts of calcium nitrite.

4. A self-repairing concrete composite according to claim 1, characterized in that: The specific preparation steps of the nano-wollastonite are as follows: (i) dissolving a calcium source and a silicon source in deionized water, adding a polycarboxylic acid water-reducing agent and a surfactant into the deionized water and stirring them uniformly to obtain a calcium source solution and a silicon source solution; (ii) slowly dropping the calcium source solution into the silicon source solution and stirring and mixing to obtain a mixed solution, and adjusting the pH to 10-12 with dilute nitric acid; (iii) transferring the mixed solution to a hydrothermal reactor, with a reaction temperature of 180-200° C. and a reaction time of 12-24 hours; (iv) cooling to room temperature, collecting a precipitate by centrifugation, and washing it alternately with deionized water and ethanol for 5 times to remove residual ions and surfactants; (v) drying the precipitate, and calcining the dried product at 500-700° C. for 2 hours to obtain nano-wollastonite.

5. A self-repairing concrete composite according to claim 4, characterized in that: The calcium source is any one of calcium nitrate and calcium chloride, the silicon source is any one of sodium silicate and ethyl orthosilicate, and the surfactant is any one of hexadecyltrimethylammonium bromide and polyvinylpyrrolidone.

6. A self-repairing concrete composite according to claim 5, characterized in that: The molar ratio of the calcium source to the silicon source is Ca:Si=1:1, and the added amount of the surfactant is 0.1-0.5wt%.

7. The self-repairing concrete composite according to claim 1, characterized in that: The specific production steps of the magnesium oxide are: (i) grinding the magnesium compound into fine powder; (ii) placing the powder in a muffle furnace, heating it to 800-1200° C., and keeping it warm for 2-4 hours; (iii) cooling it to room temperature to obtain a block or granular magnesium compound; and (iv) crushing and refining the particles by ball milling to obtain nano-grade magnesium oxide.

8. The self-repairing concrete composite according to claim 7, characterized in that: The magnesium compound includes any one of magnesium carbonate or magnesium hydroxide.

9. A process for preparing the self-repairing concrete composite according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Inoculate Bacillus pasteurianus into LB liquid culture medium, shake culture at 20-40° C. for 12-24 hours to obtain a bacterial suspension, mix calcium carbonate powder with the bacterial suspension in proportion, add 10% trehalose and stir for 15-30 minutes, dry under vacuum at 30-50° C., crush and pass through a 200-mesh sieve to obtain a microbial induced repair agent; S2. Add polyacrylamide into 80°C deionized water, slowly add calcium nitrite powder into the polyacrylamide solution, stir for 10-15 minutes until completely dissolved, add sodium silicate solution, stir and mix evenly, allow sodium silicate and calcium nitrite to react fully, and form a gel-like slow-release repair solution after cooling; S3, adding nano-wollastonite into anhydrous ethanol, ultrasonically dispersing for 30 minutes, and collecting the powder by centrifugation for later use; S4. Add the microbial induced repair agent, nano-wollastonite and magnesium oxide into a high-speed mixer in proportion, stir and mix, then add the sustained-release repair liquid, continue stirring until a viscous slurry is formed, spray dry the slurry to obtain a granular composite agent with a particle size of 0.5-1mm.

10. The preparation process of the self-repairing concrete composite according to claim 9, characterized in that: The mass ratio of calcium carbonate powder to bacterial suspension in step S1 is 1:1, the mass ratio of polyacrylamide to ionized water in step S2 is 1:10, and the mass ratio of nano-wollastonite to anhydrous ethanol in step S3 is 1:10.