A self-healing cementitious composite material and a method of making the same

Abstract

The present application belongs to the technical field of engineering cement-based composite materials, and particularly relates to a self-healing cement-based composite material and a preparation method thereof. Raw material composition of the self-healing cement-based composite material comprises Portland cement, fly ash, slag powder, water reducing agent, fiber, SAP and capsule type additive. The capsule type additive comprises an inner core and a silica coating shell layer, and the inner core comprises a silane modified ethylene-acrylic ester-GMA terpolymer and a sodium carbonate activator. The self-healing cement-based composite material of the present application can effectively limit cracking through fiber reinforcement ductility, and further realizes good synergistic self-healing performance through SAP and the capsule type additive. The self-healing cement-based composite material has the advantages of low cost, stable performance and easy industrialization.

Description

Technical Field

[0001] This invention belongs to the field of engineering cement-based composite materials technology, specifically relating to a self-healing cement-based composite material and its preparation method. Background Technology

[0002] Engineering cement-based composites (ECC), also known as bendable cement or engineering viscous cement, are suitable for applications such as seismic-resistant structures, impact-resistant structures, hydraulic dams, bridge connecting plates, bridge deck paving, and building reinforcement and repair. This material exhibits high ductility and toughness, displays multi-crack characteristics under tension, and possesses self-healing crack capabilities.

[0003] The self-healing behavior of ECC mainly stems from the following aspects:

[0004] Swelling effect: When the crack comes into contact with moisture in the external environment, the hydrated calcium silicate gel layer on both sides of the crack absorbs water and swells, thereby reducing the crack width.

[0005] Secondary hydration: Incompletely hydrated cementitious materials react with calcium hydroxide to produce hydrated calcium aluminate and hydrated calcium silicate crystals, which fill the cracks.

[0006] Carbonation: When free calcium ions inside the matrix or calcium salts in the external solution meet carbonate or bicarbonate ions, calcium carbonate precipitate is formed and fills the cracks.

[0007] Impurity accumulation: Particles that fall off the surface of the crack and impurities in the water accumulate in the crack, healing the crack.

[0008] Furthermore, the study also showed that the products of swelling and secondary hydration are twice the volume of cement and can effectively heal cracks with a width of 100 μm and below.

[0009] Studies have shown that the self-healing effect of ECC decreases significantly with increasing crack width. For cracks with larger widths (>150 μm), traditional self-healing methods are often ineffective.

[0010] To improve self-healing performance, various modifiers need to be introduced, including microbial mineralization (such as the patent with publication number CN114804788A), shape memory alloys (such as the patents with publication numbers CN109836102A and CN121800490A), superabsorbent polymers (SAP, such as the patent with publication number CN112939550A), and self-repair technologies such as polymer capsules (such as the patents with publication numbers CN115536329A and CN111908860A), allowing materials to sense damage and automatically initiate a repair process under specific conditions. However, microbial mineralization has poor stability and durability, shape memory alloys are costly, and superabsorbent polymers and polymer capsules do not significantly improve self-healing performance when used alone. Furthermore, the design of the polymer capsule core composition is crucial for improving self-healing performance. Summary of the Invention

[0011] In view of the shortcomings and deficiencies of the existing technology, the primary objective of this invention is to provide a self-healing cement-based composite material.

[0012] Another object of the present invention is to provide a method for preparing the above-mentioned self-healing cement-based composite material.

[0013] The objective of this invention is achieved through the following technical solution:

[0014] A self-healing cement-based composite material, the raw material composition of which includes silicate cement, fly ash, slag powder, water-reducing agent, fiber, superabsorbent polymer (SAP) and capsule-type additive; the capsule-type additive includes an inner core and a silica-coated shell layer, the inner core including a silane-modified ethylene-acrylate-glycidyl methacrylate (GMA) terpolymer and a sodium carbonate activator.

[0015] Preferably, the silicate cement is PO 52.5 cement.

[0016] Preferably, the water-reducing agent is a polycarboxylate water-reducing agent.

[0017] Preferably, the fiber is made of polyvinyl alcohol fiber, polyethylene fiber, polypropylene fiber or basalt fiber.

[0018] Preferably, the SAP is a sodium polyacrylate superabsorbent polymer.

[0019] Preferably, the silane-modified ethylene-acrylate-GMA terpolymer is obtained by ring-opening grafting reaction of ethylene-acrylate-GMA terpolymer and aminosilane coupling agent under anhydrous solvent conditions.

[0020] Preferably, the weight ratio of the raw materials is as follows: 500-1000 parts silicate cement, 100-400 parts fly ash, 50-300 parts slag powder, 5-30 parts water-reducing agent, 3-20 parts fiber, 3-20 parts superabsorbent polymer (SAP), and 5-50 parts capsule-type additive.

[0021] Preferably, the mass ratio of silane-modified ethylene-acrylate-GMA terpolymer to sodium carbonate activator in the inner core is 100:10-40.

[0022] The preparation method of the above-mentioned self-healing cement-based composite material includes the following steps:

[0023] S1. Add the ethylene-acrylate-GMA terpolymer and aminosilane coupling agent to an anhydrous solvent and stir to dissolve. Heat to 50-90℃ and react for 1-5 hours. Then add sodium carbonate powder and stir to disperse. Dry the mixture by vacuum spray to obtain the core particles.

[0024] S2. Dissolve tetraethyl orthosilicate in ethanol, then add the core particles of S1 and stir to disperse. Then add ammonia water dropwise and stir for 1-3 hours. Dry the mixture by vacuum spray to obtain a capsule-type additive with a silica-coated shell.

[0025] S3. Silicate cement, fly ash and slag powder are mixed together, and then water-reducing agent aqueous solution is added and mixed evenly to obtain a slurry. Then fiber, SAP and capsule-type additives are added and mixed evenly. After degassing the mixed slurry, it is cured to obtain a self-healing cement-based composite material.

[0026] Preferably, the GMA content in the ethylene-acrylate-GMA terpolymer is 6-10 wt%.

[0027] Preferably, the aminosilane coupling agent is silane coupling agent KH-550, and the mass of the aminosilane coupling agent added is 1-2 times the mass of GMA in the ethylene-acrylate-GMA terpolymer.

[0028] Preferably, the anhydrous solvent is one or a mixture of several of benzene, toluene, xylene, and ethyl acetate.

[0029] Preferably, the amount of tetraethyl orthosilicate added is 1-2 times the mass of the core particles.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] The self-healing cement-based composite material of this invention effectively limits cracking through fiber reinforcement, and exhibits multi-crack characteristics after cracking, achieving harmless crack dispersion and possessing advantages such as high ductility and surface protection. Furthermore, it combines SAP and encapsulated additives to achieve excellent self-healing performance. The synergistic self-healing mechanism of SAP and encapsulated additives is as follows:

[0032] When the ECC exhibits multi-crack development under tension, the SAP at the cracks absorbs water and expands, generating a volume expansion effect that initially fills and seals the cracks. The capsule-type additive at the cracks fractures due to the high brittleness of its silica coating layer. The inner core, consisting of silane-modified ethylene-acrylate-GMA terpolymer and sodium carbonate activator, is then exposed and comes into contact with the water-swelled SAP. The SAP undergoes a dissolution and infiltration process with the highly compatible silane-modified ethylene-acrylate-GMA terpolymer, releasing water directionally. This process also activates the sodium carbonate activator, promoting the absorption of calcium... 2+ Dissolved and reacted with CO3 2- The reaction generates calcium carbonate precipitate, which is deposited in the crack to achieve chemical repair. On the other hand, the directionally released water hydrolyzes the coupling groups of the silane-modified ethylene-acrylate-GMA terpolymer to generate highly active silanol groups, which further undergo coupling reactions with the deposited calcium carbonate precipitate, the cement matrix at the crack, the broken shell silica, and the particles that have fallen off the crack surface, forming an overall high-strength coupling composite repair layer, thereby significantly improving the self-healing repair effect. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0034] Example 1

[0035] A method for preparing a self-healing cement-based composite material includes the following steps:

[0036] S1. An ethylene-acrylate-GMA terpolymer with a GMA content of approximately 8 wt% was added to a mixed solvent of toluene and ethyl acetate (v:v=1:1) and stirred until dissolved. The amount of KH-550 added was 12% of the mass of the ethylene-acrylate-GMA terpolymer. The mixture was heated to 70°C and reacted for 3 hours. Then, sodium carbonate powder was added and stirred to disperse the mixture. The amount of sodium carbonate powder added was 25% of the mass of the ethylene-acrylate-GMA terpolymer. The mixture was then vacuum spray-dried to obtain the core particles.

[0037] S2. Dissolve tetraethyl orthosilicate in ethanol, then add the core particles from S1 and stir to disperse. The mass ratio of tetraethyl orthosilicate to core particles is 1.5:1. Then, add ammonia water dropwise to control the pH value to 9-10 and stir for 2 hours. The mixture is then vacuum spray-dried to obtain a capsule-type additive with a silica-coated shell.

[0038] S3. Prepare raw materials according to the weight ratio. Mix 750 parts of PO 52.5 silicate cement, 250 parts of fly ash and 150 parts of slag powder. Then add 350 parts of 5wt% polycarboxylate superplasticizer aqueous solution and mix at high speed to obtain a slurry. After reducing the mixing speed, add 15 parts of polyvinyl alcohol fiber, 12 parts of sodium polyacrylate (SAP) and 30 parts of capsule-type additive and mix well. After degassing the mixed slurry, cure it to obtain a self-healing cement-based composite material.

[0039] Example 2

[0040] A method for preparing a self-healing cement-based composite material includes the following steps:

[0041] S1. An ethylene-acrylate-GMA terpolymer with a GMA content of approximately 8 wt% was added to a mixed solvent of toluene and ethyl acetate (v:v=1:1) and stirred until dissolved. The amount of KH-550 added was 8% of the mass of the ethylene-acrylate-GMA terpolymer. The mixture was heated to 60°C and reacted for 2 hours. Then, sodium carbonate powder was added and stirred until dispersed. The amount of sodium carbonate powder added was 40% of the mass of the ethylene-acrylate-GMA terpolymer. The mixture was then vacuum spray-dried to obtain core particles.

[0042] S2. Dissolve tetraethyl orthosilicate in ethanol, then add the core particles from S1 and stir to disperse. The mass ratio of tetraethyl orthosilicate to core particles is 1:1. Then, add ammonia water dropwise to control the pH value to 9-10 and stir for 2 hours. The mixture is then vacuum spray-dried to obtain a capsule-type additive with a silica-coated shell.

[0043] S3. Prepare raw materials according to the weight ratio. Mix 1000 parts of PO 52.5 silicate cement, 400 parts of fly ash and 100 parts of slag powder. Then add 400 parts of 6wt% polycarboxylate superplasticizer aqueous solution and mix at high speed to obtain a slurry. After reducing the mixing speed, add 20 parts of polyvinyl alcohol fiber, 5 parts of sodium polyacrylate (SAP) and 50 parts of capsule-type additive and mix well. After degassing the mixed slurry, cure it to obtain a self-healing cement-based composite material.

[0044] Example 3

[0045] A method for preparing a self-healing cement-based composite material includes the following steps:

[0046] S1. An ethylene-acrylate-GMA terpolymer with a GMA content of approximately 8 wt% was added to a mixed solvent of toluene and ethyl acetate (v:v=1:1) and stirred until dissolved. The amount of KH-550 added was 16% of the mass of the ethylene-acrylate-GMA terpolymer. The mixture was heated to 80°C and reacted for 4 hours. Then, sodium carbonate powder was added and stirred until dispersed. The amount of sodium carbonate powder added was 15% of the mass of the ethylene-acrylate-GMA terpolymer. The mixture was then vacuum spray-dried to obtain core particles.

[0047] S2. Dissolve tetraethyl orthosilicate in ethanol, then add the core particles from S1 and stir to disperse. The mass ratio of tetraethyl orthosilicate to core particles is 2:1. Then, add ammonia water dropwise to control the pH value to 9-10 and stir for 2 hours. The mixture is then spray-dried under vacuum to obtain a capsule-type additive with a silica-coated shell.

[0048] S3. Prepare raw materials according to the weight ratio. Mix 600 parts of PO 52.5 silicate cement, 100 parts of fly ash and 300 parts of slag powder. Then add 300 parts of 2wt% polycarboxylate superplasticizer aqueous solution and stir at high speed to obtain a slurry. After reducing the stirring speed, add 5 parts of polyvinyl alcohol fiber, 10 parts of sodium polyacrylate (SAP) and 10 parts of capsule-type additive and stir to mix evenly. After degassing the mixed slurry, cure it to obtain a self-healing cement-based composite material.

[0049] Comparative Example 1

[0050] A method for preparing a self-healing cement-based composite material differs from Example 1 in that the core particles are prepared using an unmodified ethylene-acrylate-GMA terpolymer instead of an aminosilane coupling agent-modified ethylene-acrylate-GMA terpolymer; the remaining preparation steps are the same. The preparation steps of the core particles are as follows:

[0051] An ethylene-acrylate-GMA terpolymer with a GMA content of approximately 8 wt% was added to a mixed solvent of toluene and ethyl acetate (v:v=1:1) and stirred to dissolve. Then, sodium carbonate powder was added and stirred to disperse the terpolymer. The amount of sodium carbonate powder added was 25% of the mass of the ethylene-acrylate-GMA terpolymer. The mixture was then vacuum spray-dried to obtain the core particles.

[0052] Comparative Example 2

[0053] A method for preparing a self-healing cement-based composite material differs from Example 1 in that epoxy resin is used instead of the ethylene-acrylate-GMA terpolymer in the preparation of the core particles; the remaining preparation steps are the same. The preparation steps of the core particles are as follows:

[0054] Bisphenol A type epoxy resin and aminosilane coupling agent KH-550 were added to a mixed solvent of toluene and ethyl acetate (v:v=1:1) and stirred to dissolve. The amount of KH-550 added was 12% of the mass of the epoxy resin. The mixture was heated to 70℃ and reacted for 3 hours. Then, sodium carbonate powder was added and stirred to disperse the mixture. The amount of sodium carbonate powder added was 25% of the mass of the ethylene-acrylate-GMA terpolymer. The mixture was then vacuum spray-dried to obtain the core particles.

[0055] Self-healing performance test:

[0056] The cement-based composite materials obtained in the above examples and comparative examples were cured for 28 days in a standard curing room at 20°C and 95% relative humidity. Microcracks were then induced using a three-point bending loading method, with the crack width controlled between 0.4-0.6 mm. The samples were then cured under standard conditions for another 28 days to allow for self-healing repair. The changes in surface cracks over time were observed using a digital three-dimensional video microscope, and the crack area repair rate was calculated as (1 - surface crack area after self-healing repair / surface crack area before self-healing repair × 100%). The compressive strength of the samples before and after repair was tested, and the compressive strength recovery rate was calculated as (compressive strength after self-healing repair / compressive strength before self-healing repair × 100%). The results are shown in the table below:

[0057] Table 1 Comparison of self-healing properties of the examples and comparative samples

[0058]

[0059] The results of Examples 1-3 in Table 1 show that the cement-based composite material of the present invention exhibits good self-healing properties under different cement gel compositions. Comparative Example 1 shows that the self-healing repair filler layer obtained without silane coupling agent modification has weaker bonding strength, leading to a significant decrease in compressive strength recovery rate. Comparative Example 2 shows that the synergistic repair effect of epoxy resin and SAP modified with silane coupling agent is significantly reduced. This indicates that the dissolution and infiltration effect between SAP and modified epoxy resin after water absorption and swelling is weak, making it difficult to fully activate the hydrolytic coupling reaction of sodium carbonate activator and coupling groups.

[0060] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A self-healing cement-based composite material, characterized in that: The raw material composition includes silicate cement, fly ash, slag powder, water-reducing agent, fiber, SAP and capsule-type additive; the capsule-type additive includes an inner core and a silica-coated shell, the inner core includes silane-modified ethylene-acrylate-GMA terpolymer and sodium carbonate activator.

2. The self-healing cement-based composite material according to claim 1, characterized in that: The silicate cement used is PO 52.5 cement, and the water-reducing agent used is polycarboxylate water-reducing agent.

3. The self-healing cement-based composite material according to claim 1, characterized in that: The fibers are made of polyvinyl alcohol fiber, polyethylene fiber, polypropylene fiber or basalt fiber.

4. The self-healing cement-based composite material according to claim 1, characterized in that: The SAP uses sodium polyacrylate.

5. The self-healing cement-based composite material according to claim 1, characterized in that: The silane-modified ethylene-acrylate-GMA terpolymer was obtained by ring-opening grafting reaction of the ethylene-acrylate-GMA terpolymer and an aminosilane coupling agent under anhydrous solvent conditions.

6. The self-healing cement-based composite material according to claim 1, characterized in that: The weight proportions of the raw materials are as follows: 500-1000 parts silicate cement, 100-400 parts fly ash, 50-300 parts slag powder, 5-30 parts water-reducing agent, 3-20 parts fiber, 3-20 parts SAP, and 5-50 parts capsule-type additive.

7. The self-healing cement-based composite material according to claim 1, characterized in that: The mass ratio of silane-modified ethylene-acrylate-GMA terpolymer to sodium carbonate activator in the inner core is 100:10-40.

8. A method for preparing a self-healing cement-based composite material according to any one of claims 1-7, characterized in that: Includes the following steps: S1. Add the ethylene-acrylate-GMA terpolymer and aminosilane coupling agent to an anhydrous solvent and stir to dissolve. Heat to 50-90℃ and react for 1-5 hours. Then add sodium carbonate powder and stir to disperse. Dry the mixture by vacuum spray to obtain the core particles. S2. Dissolve tetraethyl orthosilicate in ethanol, then add the core particles of S1 and stir to disperse. Then add ammonia water dropwise and stir for 1-3 hours. Dry the mixture by vacuum spray to obtain a capsule-type additive with a silica-coated shell. S3. Silicate cement, fly ash and slag powder are mixed together, and then water-reducing agent aqueous solution is added and mixed evenly to obtain a slurry. Then fiber, SAP and capsule-type additives are added and mixed evenly. After degassing the mixed slurry, it is cured to obtain a self-healing cement-based composite material.

9. The method for preparing a self-healing cement-based composite material according to claim 8, characterized in that: The ethylene-acrylate-GMA terpolymer contains 6-10 wt% GMA, and the aminosilane coupling agent used is silane coupling agent KH-550. The mass of the aminosilane coupling agent added is 1-2 times the mass of GMA in the ethylene-acrylate-GMA terpolymer.

10. The method for preparing a self-healing cement-based composite material according to claim 8, characterized in that: The anhydrous solvent is one or a mixture of several of benzene, toluene, xylene, and ethyl acetate, and the amount of tetraethyl orthosilicate added is 1-2 times the mass of the core particles.

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