A magnesium phosphate cement material with micro-crack self-healing function and a preparation method thereof

Abstract

The application provides a magnesium phosphate cement material with a micro-crack self-healing function and a preparation method thereof, and belongs to the technical field of inorganic cementing materials.The magnesium phosphate cement material comprises the following components in mass fractions: 100-120 parts of dead-burned magnesia; 40-60 parts of potassium dihydrogen phosphate; 5-15 parts of borax; 2-4 parts of nano silicon dioxide; 5-10 parts of microencapsulated silica sol; 3-8 parts of self-repairing microbial strain embedding capsules; 0.5-1 part of fiber; and 20-30 parts of water.The application firstly proposes to embed microencapsulated inorganic gel, microbial induced mineralization and multi-scale reinforcing factors (nano SiO2 and basalt fiber) into the MPC cement system in a cooperative mode to form a four-element cooperative self-healing system of "microcapsule-microorganism-nano-fiber".

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inorganic cementitious materials, and particularly relates to a magnesium phosphate cement material with micro-crack self-healing function and a preparation method thereof. BACKGROUND

[0002] Magnesium phosphate cement (MPC) is an inorganic cementitious material with fast hardening, high strength, low shrinkage and good bonding performance, which is generated by the reaction of magnesium oxide (MgO) and phosphate, and has been widely used in road repair, military emergency and engineering construction under extreme conditions in recent years. However, the problems of brittleness and poor crack self-healing ability still limit its application in high stress and complex environment. At present, the ordinary self-healing cement-based materials mostly use microcapsules, superabsorbent polymers (SAP) or calcium carbonate precipitation reaction as the healing mechanism, and still have problems such as slow response, poor compatibility and high cost. For the MPC system, due to its special acid-base environment and hydration mechanism, there is no mature self-healing scheme.

[0003] Therefore, researchers try to explore the performance of self-healing MPC through research, but most of them are limited to the observation of macroscopic crack closure effect, and lack of in-depth revelation of the healing reaction path, product composition and formation kinetics at the microscale. Moreover, the design of self-healing materials mostly depends on trial-and-error method and empirical formula, and lacks precise control model and design theory for the unique hardening characteristics and acid-base environment of MPC materials. At the same time, the commonly used organic microcapsule wall materials (such as PU and PMMA) are easily degraded in the strong acid environment of MPC, which leads to premature rupture or failure of microcapsules, poor encapsulation stability and release controllability. Moreover, the self-healing reaction liquid (such as phosphate, water glass and carbonate system) has complex reaction coupling with MPC system, which is prone to problems such as abnormal setting and interface weakening.

[0004] Therefore, how to obtain a self-healing magnesium phosphate cement-based repair material and a preparation method thereof is a technical problem to be solved at present. SUMMARY

[0005] The present application aims to provide a magnesium phosphate cement material with micro-crack self-healing function and a preparation method thereof, which is used to solve the technical problems of brittleness, easy cracking, lack of crack closure and repair ability of magnesium phosphate cement (MPC) material in practical application.

[0006] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0007] The present application provides a magnesium phosphate cement material with micro-crack self-healing function, which comprises the following components in mass fraction:

[0008] 100-120 parts of dead-burned magnesium oxide;

[0009] Potassium dihydrogen phosphate 40~60 parts;

[0010] Borax 5~15 parts;

[0011] Nano-silica 2~4 parts;

[0012] Microencapsulated silica sol 5~10 parts;

[0013] Self-repairing microbial strain embedding capsule 3~8 parts;

[0014] Fiber 0.5~1 part;

[0015] Water 20~30 parts.

[0016] Further, the microencapsulated silica sol is an inorganic composite microcapsule having an inorganic siliceous material shell layer and being suitable for encapsulating a healing-promoting solution.

[0017] Further, the self-repairing microbial strain embedding capsule is a microcapsule system in which alkaliphilic carbonate depositing bacteria Bacillus pasteurii and nutrients required for inducing mineralization thereof are jointly embedded in a carrier shell layer.

[0018] Further, the dead-burned magnesium oxide is obtained by grinding magnesite calcined at a high temperature of 1500~1800℃, and the purity of the dead-burned magnesium oxide is ≥90%;

[0019] The potassium dihydrogen phosphate is an industrial-grade potassium dihydrogen phosphate with a purity of ≥99.9%;

[0020] The nano-silica has a median particle size of 5~10nm and a purity of ≥99.9%.

[0021] Further, the fiber comprises basalt fiber, and the fiber has a length of 10~15mm and a diameter of 15~20μm.

[0022] The borax is chemical analysis pure sodium tetraborate Na2B4O7·5H2O.

[0023] The application further provides a preparation method of the magnesium phosphate cement material with the micro-crack self-healing function.

[0024] 1) mixing the dead-burned magnesium oxide, the potassium dihydrogen phosphate, the borax, the nano-silica and the fiber in a proportion to form a mixture A;

[0025] 2) mixing the microencapsulated silica sol, the self-repairing microbial strain embedding capsule and the mixture A to obtain a mixture B;

[0026] 3) mixing the mixture B with water to obtain a mixture C, i.e. the magnesium phosphate cement material with the micro-crack self-healing function.

[0027] Further, in the step 1), the rotating speed of mixing is 100-150 r / min, and the mixing time is 1-5 min.

[0028] Further, in the step 2), the rotating speed of mixing is 100-150 r / min, and the mixing time is 1-2 min.

[0029] The beneficial effects of the present application are as follows:

[0030] The present application is directed to the fact that the traditional MPC does not have crack healing ability, and the present application realizes efficient and repeatable healing by embedding a microcapsule + microorganism double system, fills the technical gap, and first constructs a self-healing function system of MPC material. The microcapsulated silica sol / microorganism is used to solve the degradation and failure problem of capsules in the acidic environment of MPC, and realize the interface high responsiveness and delayed release function. The present application not only meets the actual needs of the traditional road and bridge repair field, but also responds to the technical direction of "green and efficient upgrading of materials under the background of double carbon", and provides a new idea and technical path for the functionalization, intelligentization and multi-field coupling adaptation of MPC materials. Compared with the prior art, the present application has the following significant innovation points and beneficial technical effects:

[0031] The function realization of the present application depends on the "structure regulation + functional capsule + interface reaction" three-in-one design principle. Firstly, the nano SiO2 particles play a role of "nano skeleton" in the slurry, fill the MPC slurry pores, promote the efficient combination of Mg 2+ and PO4 3- , and establish a filling and densification mechanism; at the same time, a magnesium silicate complex is formed to improve the interface density and the uniformity of hydration products.

[0032] The present application first uses a double self-healing mechanism in the MPC material system. The microcapsule I releases the coagulable and highly reactive Si(OH)4 or Si-OH substances at the crack tip, fills the fine cracks, and forms a dense gel product for rapid physical plugging. The microorganism capsule II releases the alkaliphilic bacteria that can induce calcium carbonate precipitation after the crack is formed and water penetrates, generates crystals in the crack for repair, and forms a gel + mineral double repair network structure, which significantly improves the crack closure rate and regeneration ability. This method realizes the complete crack closure process from early rapid physical filling to late continuous crystal generation, which is significantly better than single self-healing means. The present application innovatively introduces the self-repairing mechanism induced by Bacillus pasteurii into the MPC-based material system, which is a very rare research direction in current literature. This innovation successfully realizes the compatibility breakthrough of the phosphate gel system and the microbial repair mechanism, and solves the technical bottleneck that the traditional microbial self-repairing system cannot survive in an acidic or high ionic strength environment.

[0033] The nano-SiO2 participates in the reaction at the initial hydration stage, fills the pores and improves the compactness of the cement paste; the basalt fiber improves the fracture toughness and prevents crack propagation through the “bridging-deflection-crack resistance” mechanism; and the material as a whole forms a “dense-flexible-toughened-healing” multi-scale self-regulating microstructure. After the structure is damaged, the material can self-sense crack generation, activate the capsule and initiate the self-repairing reaction, realize the self-repairing function without external intervention, greatly reduce the maintenance frequency, and has a broad application prospect in engineering intelligentization.

[0034] The application provides a self-healing magnesium phosphate cement-based repair material and a preparation method thereof.

[0035] Table 1 Performance comparison

[0036] BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The application provides a preparation flowchart of the self-healing magnesium phosphate cement-based repair material. DETAILED DESCRIPTION

[0038] The application provides a magnesium phosphate cement material with a micro-crack self-healing function, which comprises the following components in mass fractions:

[0039] 100-120 parts of dead burned magnesium oxide;

[0040] 40-60 parts of potassium dihydrogen phosphate;

[0041] 5-15 parts of borax;

[0042] 2-4 parts of nano-silicon dioxide;

[0043] 5-10 parts of microencapsulated silica sol;

[0044] 3-8 parts of self-repairing microbial strain embedding capsules;

[0045] 0.5-1 part of fiber;

[0046] 20-30 parts of water.

[0047] In the present application, the content of the heavy-burned magnesium oxide is preferably 105-115 parts by mass, and further preferably 110 parts by mass.

[0048] In the present application, the content of the potassium dihydrogen phosphate is preferably 45-55 parts by mass, and further preferably 50-52 parts by mass.

[0049] In the present application, the content of the borax is preferably 8-12 parts by mass, and further preferably 9-11 parts by mass.

[0050] In the present application, the content of the nano-silicon dioxide is preferably 2.5-3.5 parts by mass, and further preferably 4 parts by mass. In the present application, the nano-silicon dioxide can regulate the micro-nano pore structure of the MPC, plays a role of "nano skeleton" in the MPC slurry, fills the pores of the MPC slurry, promotes the efficient combination of Mg 2+ and PO4 3- ; and forms a magnesium silicate complex, improves the interface density and the uniformity of the hydration product.

[0051] In the present application, the content of the microencapsulated silicon sol is preferably 6-9 parts by mass, and further preferably 7-8 parts by mass.

[0052] In the present application, the content of the self-repairing microbial strain embedding capsule is preferably 4-7 parts by mass, and preferably 5-6 parts by mass.

[0053] In the present application, the content of the fiber is preferably 0.6-0.9 parts by mass, and further preferably 0.7-0.8 parts by mass.

[0054] In the present application, the content of the water is preferably 22-28 parts by mass, and further preferably 24-26 parts by mass.

[0055] In the present application, the microencapsulated silicon sol is an inorganic composite microcapsule with an inorganic siliceous material shell layer and suitable for packaging a healing-promoting solution (phosphate), for releasing active substances after the occurrence of cracks and promoting the generation of self-healing products.

[0056] In the present application, by packaging a siliceous sol type densifying agent in a controllable release type shell material and applying it to a cementing material system such as MPC, the material can automatically release the densifying agent after cracking, repair micro-cracks, and improve the interface density and durability.

[0057] In the present application, the self-repairing microbial strain embedding capsule is a microcapsule system formed by embedding alkaliphilic carbonate depositing bacteria Bacillus pasteurii and nutrients required for inducing mineralization of the same in a carrier shell layer. The self-repairing microbial strain embedding capsule (Bacillus pasteurii) mainly encapsulates calcium carbonate depositing strains, and after cracks occur, the microorganisms induce calcium carbonate deposition to fill the cracks under suitable moisture conditions, thereby realizing self-healing.

[0058] In the present application, the dead-burned magnesium oxide is obtained by grinding magnesite calcined at a high temperature of 1500-1800 DEG C, and the purity of the dead-burned magnesium oxide is greater than or equal to 90%, preferably the dead-burned magnesite calcined at a high temperature of 1700 DEG C and ground to have a purity of 92%;

[0059] The potassium dihydrogen phosphate is an industrial grade potassium dihydrogen phosphate with a purity greater than or equal to 99.9%;

[0060] The median particle size of the nano-silicon dioxide is 5-10 nm, and the purity is greater than or equal to 99.9%.

[0061] In the present application, the fiber comprises basalt fiber, the length of the fiber is 10-15 mm, preferably 12 mm, and the diameter is 15-20 microns, preferably 17.4 microns; the basalt fiber is distributed in the MPC system to form a "three-dimensional interlaced network structure", spanning the nano-micron-millimeter scale, providing crack pinning resistance and energy dissipation mechanism, and improving the transition of the failure mode from brittleness to toughness;

[0062] The borax is chemical analysis pure sodium tetraborate Na2B4O7·5H2O.

[0063] The present application also provides a preparation method of the magnesium phosphate cement material with the micro-crack self-healing function.

[0064] 1) mixing the dead-burned magnesium oxide, the potassium dihydrogen phosphate, the borax, the nano-silicon dioxide and the fiber in proportion to form a mixture A;

[0065] 2) mixing the microencapsulated silica sol, the self-repairing microbial strain embedding capsule and the mixture A to obtain a mixture B;

[0066] 3) mixing the mixture B with water to obtain a mixture C, which is the magnesium phosphate cement material with the micro-crack self-healing function.

[0067] In the present application, in step 1), the rotation speed of mixing is 100-150 r / min, preferably 120 r / min; and the mixing time is 1-5 min, preferably 2-3 min.

[0068] In the present application, the rotating speed of mixing in step 2) is 100-150 r / min, preferably 120 r / min; the mixing time is 1-2 min, preferably 1-1.5 min.

[0069] In the present application, after the mixture C is stirred uniformly, it is cast and shaped, and then left to stand at room temperature for 12 h to form initial strength; when microcracks are formed in the material, the healing reaction is started through the self-healing system.

[0070] The technical solutions provided by the present application are described in detail below in conjunction with examples, but they should not be understood as limiting the scope of protection of the present application.

[0071] The potassium dihydrogen phosphate used in the following examples is an industrial-grade potassium dihydrogen phosphate with a purity of ≥99.9%; the nano-SiO2 has a median particle size of 7 nm and a purity of ≥99.9%; the borax is a chemical analysis pure sodium tetraborate Na2B4O7·5H2O; and the basalt fiber is a 12 mm chopped fiber with a diameter of 17.4 μm.

[0072] Example 1

[0073] For self-healing of road cracks, the components and amounts used in the present example are as follows:

[0074] Take 100 parts of dead-burned magnesite, 40 parts of potassium dihydrogen phosphate, 10 parts of borax, 3 parts of nano-silicon dioxide, and 0.8 parts of basalt fiber, and stir them uniformly to obtain mixture A; add 5 parts of microencapsulated silica sol and 3 parts of self-repairing microbial strain embedding capsules, and mix them at low speed to obtain mixture B; then add 30 parts of water, and mix them quickly to obtain mixture C.

[0075] After the mixture is stirred uniformly, it is poured into the cracks within 3 minutes, an interface of 10 mm deep groove is set, and then the test piece is placed on the test piece rack for air curing, wherein the air curing temperature is 20±2 ℃, and the air humidity is 70±5%.

[0076] Example 2

[0077] For the development of MPC reinforcing and repairing materials for self-healing of bridge expansion joint parts, the components and amounts used in the present example are as follows:

[0078] Take 120 parts of dead-burned magnesite, 60 parts of potassium dihydrogen phosphate, 12 parts of borax, 4 parts of nano-silicon dioxide, and 1 part of basalt fiber, and stir them uniformly to obtain mixture A; add 5 parts of microencapsulated silica sol and 4 parts of self-repairing microbial strain embedding capsules, and mix them at low speed to obtain mixture B; then add 30 parts of water, and mix them quickly to obtain mixture C.

[0079] After the mixture is stirred evenly, it is poured into the interface within 3 minutes of pouring, the interface is set to a 10 mm deep groove, and it is placed on a test piece rack for air curing, wherein the air curing temperature is 20±2 ℃, and the air humidity is 70±5%.

[0080] Example 3

[0081] For active crack repair of concrete wall surfaces of underground garages, the components and amounts used in the present embodiment are as follows:

[0082] Take 120 parts of heavy burned magnesite, 50 parts of potassium dihydrogen phosphate, 10 parts of borax, 4 parts of nano silicon dioxide, and 0.6 parts of basalt fiber, stir evenly to obtain mixture A; add 8 parts of microencapsulated silica sol and 8 parts of self-repairing microbial strain embedding capsules, mix at low speed to obtain mixture B; then add 30 parts of water, stir quickly, and mix evenly to obtain mixture C.

[0083] After the mixture is stirred evenly, it is poured into the interface within 3 minutes of pouring, the interface is set to a 10 mm deep groove, and it is placed on a test piece rack for air curing, wherein the air curing temperature is 20±2 ℃, and the air humidity is 70±5%.

[0084] Example 4

[0085] For crack repair of anti-cracking self-healing system components in urban underground space structures (such as subway segments and tunnel lining), the components and amounts used in the present embodiment are as follows:

[0086] Take 105 parts of heavy burned magnesite, 55 parts of potassium dihydrogen phosphate, 8 parts of borax, 3 parts of nano silicon dioxide, and 0.5 parts of basalt fiber, stir evenly to obtain mixture A; add 8 parts of microencapsulated silica sol and 5 parts of self-repairing microbial strain embedding capsules, mix at low speed to obtain mixture B; then add 30 parts of water, stir quickly, and mix evenly to obtain mixture C.

[0087] After the mixture is stirred evenly, it is poured into the interface within 3 minutes of pouring, the interface is set to a 10 mm deep groove, and it is placed on a test piece rack for air curing, wherein the air curing temperature is 20±2 ℃, and the air humidity is 70±5%.

[0088] Example 5

[0089] For anti-chloride salt corrosion and crack self-repairing in marine engineering components (pier, pile foundation, concrete pavement, etc.), the components and amounts used in the present embodiment are as follows:

[0090] Take 118 parts of calcined magnesia, 60 parts of potassium dihydrogen phosphate, 5 parts of borax, 4 parts of nano silicon dioxide, 0.7 parts of basalt fiber, stir evenly to get mixture A; add 10 parts of microencapsulated silica sol and 5 parts of self-repairing microbial strain embedding capsules, mix at low speed to get mixture B; then add 30 parts of water, stir quickly, mix evenly to get mixture C.

[0091] After stirring the mixture evenly, cast and form within 3 minutes and pour into the interface, set the interface to 10 mm deep groove and place on the test specimen rack for air curing, wherein the air curing temperature is 20±2 ℃ and the air humidity is 70±5%.

[0092] Comparative Example 1

[0093] The same as Example 1, except that no microencapsulated silica sol is added.

[0094] Comparative Example 2

[0095] The same as Example 2, except that no self-repairing microbial strain embedding capsules are added.

[0096] Comparative Example 3

[0097] The same as Example 3, except that no nano silicon dioxide is added.

[0098] Performance Test

[0099] The test sample of the magnesium phosphate cement-based repair material with self-healing performance after pouring is measured for the flexural strength at 7 d, the crack regeneration observation after dynamic fatigue loading (1 Hz, 30 million cycles), and the water permeation amount test to evaluate the 28 d self-healing efficiency. The test results are shown in Table 2.

[0100] Table 2 Self-healing measurement results of the magnesium phosphate cement-based repair material with self-healing performance

[0101]

[0102] As shown in Table 2, the microencapsulated silica sol, self-repairing microbial strain embedding capsule and multi-scale reinforcing factor (nano-SiO2 and basalt fiber) are embedded in the MPC cement system to form a four-element synergistic self-healing system of "microcapsule-bacteria-nano-fiber", and the flexural strength recovery rate of the present application is more than 87% within 7 days, the cracks are not expanded after 300,000 dynamic fatigue cycle load, and the self-healing efficiency is reduced to less than 8% of the initial value in the 28 d water permeability test. Compared with the weakness of the traditional MPC self-healing material, the toughness and crack resistance are poor, the present application is complementary to the self-healing mechanism by the composite of microencapsulated silica sol and self-repairing microbial strain embedding capsule, a new mode of "double-track healing" is formed, the complete crack closure process from early rapid physical filling to late continuous crystal generation is realized, which is significantly better than single self-healing means, and the durability life is greatly improved. The present application effectively shows that the MPC system realizes the comprehensive advantages of mechanical enhancement, self-healing and environmental adaptability through the synergistic effect of multiple functional components, the overall performance is at the international advanced level, has engineering application conditions, realizes "quick opening + long-lasting durability", not only widens the application scene of MPC, but also improves the engineering value of MPC in the field of high durability requirements such as transportation, municipal administration and underground engineering, and has obvious industrialization popularization prospect.

[0103] As shown in the above examples, the present application provides a magnesium phosphate cement material with microcrack self-healing function and a preparation method thereof, and the microencapsulated inorganic gel, microbial induced mineralization and multi-scale reinforcing factor (nano-SiO2 and basalt fiber) are embedded in the MPC cement system to form a four-element synergistic self-healing system of "microcapsule-bacteria-nano-fiber". The material has high toughness, rapid repair, automatic healing, crack closure and high durability, which is a major technical breakthrough in the field of municipal repair materials. The present application adopts complementary self-healing mechanism, forms a new mode of "double-track healing", uses the microencapsulated inorganic gel which can swell and release high-reactivity substances to fill fine cracks, forms dense gel products and self-repairing microbial strain embedding capsules to generate calcium carbonate crystals in situ, and continuously chemically heals microcracks for a long time, realizes the complete crack closure process from early rapid physical filling to late continuous crystal generation, and is significantly better than single self-healing means. With the aid of nano-SiO2 and fiber, the material forms a multi-scale self-regulating microstructure of "dense-flexible-toughening-healing". After the structure is damaged, the material can self-perceive crack generation, activate the capsule and realize the self-repairing function without external intervention, greatly reduces the maintenance frequency, and has broad engineering intelligent application prospect.

[0104] The above merely describes the preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the protection scope of the present application.

Claims

1. A magnesium phosphate cement material having a microcrack self-healing function, characterized by, Components comprising the following mass fractions: 100~120 parts of dead-burned magnesium oxide; 40~60 parts of potassium dihydrogen phosphate; 5~15 parts of borax; 2~4 parts of nano-silicon dioxide; 5~10 parts of microencapsulated silica sol; 3~8 parts of self-repairing microbial strain embedding capsules; 0.5~1 part of fiber; 20~30 parts of water; The microencapsulated silica sol is an inorganic composite microcapsule having an inorganic siliceous material shell layer and being suitable for encapsulating a pro-healing solution. The self-repairing microbial strain embedding capsules are a microcapsule system formed by embedding alkaliphilic carbonate depositing bacteria Bacillus pasteurii and nutrients required for inducing mineralization thereof in a carrier shell layer.

2. The magnesium phosphate cement material having a microcrack self-healing function according to claim 1, characterized by, The dead-burned magnesium oxide is obtained by grinding magnesite calcined at a high temperature of 1500~1800℃, and the purity of the dead-burned magnesium oxide is ≥90%; The potassium dihydrogen phosphate is an industrial-grade potassium dihydrogen phosphate with a purity of ≥99.9%; The nano-silicon dioxide has a median particle size of 5~10nm and a purity of ≥99.9%.

3. The magnesium oxyphosphate cement material having a microcrack self-healing function according to claim 2, characterized by, The fiber comprises basalt fiber, and the length of the fiber is 10~15mm and the diameter is 15~20μm. The borax is chemical analysis pure sodium tetraborate Na2B4O7·5H2O.

4. The method for producing a magnesium phosphate cement material having a microcrack self-healing function according to any one of claims 1 to 3, characterized by, The method comprises the following steps: 1) mixing the dead-burned magnesium oxide, potassium dihydrogen phosphate, borax, nano-silicon dioxide and fiber in a proportion to form a mixture A; 2) mixing the microencapsulated silica sol, self-repairing microbial strain embedding capsules and mixture A to obtain a mixture B; 3) mixing the mixture B with water to obtain a mixture C, which is a magnesium phosphate cement material having a micro-crack self-healing function.

5. The method of producing a magnesium phosphate cement material having a microcrack self-healing function according to claim 4, characterized by, In the step 1), the rotation speed of mixing is 100~150r / min, and the mixing time is 1~5min.

6. The method for producing a magnesium phosphate cement material having a microcrack self-healing function according to claim 4 or 5, characterized in that, In the step 2), the rotation speed of mixing is 100~150r / min, and the mixing time is 1~2min.

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