Composite cement particle with core-shell structure as well as preparation method and application of composite cement particle

Abstract

The invention discloses a composite cement particle with a core-shell structure as well as a preparation method and application thereof, the composite cement particle comprises: an inner core comprising cement particles modified by a silane coupling agent; a housing comprising a superabsorbent polymer; the shell covers the inner core. According to the composite cement particle silane coupling agent, a chemical bonding interface is formed between cement particles and SAP, an inorganic-organic synergistic effect is created, the comprehensive performance of the material is enhanced, and the SAP with the core-shell structure tends to be better than early shrinkage control and strength retention of high-performance concrete of common SAP; the mechanism is different from a post-cracking and post-healing mechanism of a self-repairing material. The composite cement particle is simple in preparation process, the cost is reduced by 50% or above compared with a nano composite material, and the composite cement particle is suitable for high-strength concrete, repair engineering and 3D printing building materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building materials, in particular to a core-shell structure composite cement particle and a preparation method and application thereof. BACKGROUND

[0002] In high-performance cement-based materials, low water-binder ratio design can significantly improve strength and durability, but also accompanied by significant autogenous shrinkage. This autogenous shrinkage is mainly due to the self-drying effect in the hydration process, i.e. the capillary pressure caused by the gradual reduction of internal water, thereby causing volume shrinkage. If not timely controlled, autogenous shrinkage can easily cause microcracks or even through cracks in the early stages of hardening, ultimately reducing the integrity and durability of the structure. To alleviate autogenous shrinkage, various internal curing techniques such as lightweight aggregate (LWA), superabsorbent polymer (SAP) and expansive agent are used. These methods can supplement free water and resist capillary pressure to some extent, but each of the above methods has its own limitations in practical application. For example, lightweight aggregate needs to be pre-saturated and may form a weak interface transition zone (ITZ) at the interface, affecting the overall density and consistency of the material; expansive agents such as ettringite-based materials may induce delayed ettringite formation (DEF) during long-term service, causing expansion cracking or even spalling.

[0003] Among them, superabsorbent polymer (SAP) as an internal curing agent for concrete can effectively alleviate the autogenous shrinkage and cracking problem of high-strength concrete. However, traditional SAPs leave pores after releasing water, leading to an increase in the porosity of concrete and a significant decrease in strength (usually a loss of 6%~30%), which seriously restricts its engineering application. In the prior art, researchers have tried to improve the pore structure by combining nanomaterials (such as SiO2) or adjusting the particle size of SAPs, but there are problems such as high cost, complex process or limited effect.

[0004] In recent years, cement-based composite materials have attracted attention due to their low cost, high activity and self-repairing potential. If cement particles and SAPs can be combined, the pores can be filled by continuous hydration of cement, which can fundamentally solve the problem of strength loss of SAPs. However, the interface compatibility between cement particles and polymers is poor, and direct compounding can easily lead to loose structure and low water absorption efficiency. SUMMARY

[0005] The present application aims to at least solve one of the above technical problems in the prior art. To this end, the purpose of the present application is to provide a core-shell structure composite cement particle and a preparation method and application thereof.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows: The first aspect of the present application provides a composite cement particle, comprising: an inner core comprising silane coupling agent modified cement particles; A shell comprising a superabsorbent polymer; The shell coats the core.

[0007] Different from the common passivation starting mode of traditional technology, in the present application, the composite cement particles of core-shell structure form a structural stable responsive composite system, in which the silane coupling agent forms a chemical bonding interface between the cement particles and the SAP, creating inorganic-organic synergistic effect and enhancing the comprehensive performance of the material; the SAP carries the cement particles into the cement matrix, and after absorbing water, the SAP can continuously release water in the cement hydration process, ensuring the relative humidity in the cement matrix; at the same time, it promotes the hydration of the cement matrix around the SAP, avoiding the self-shrinkage behavior caused by the decrease of internal relative humidity. Through the self-humidification process, the strength retention and shrinkage risk synchronous control are realized in the early stage of concrete service, the structural durability is improved, and the later maintenance demand is reduced. Finally, the composite cement particles of core-shell structure realize the compression strength retention and shrinkage inhibition of the cement matrix through the double pore regulation mechanism: first, the SAP water absorption network can refine the macropores and reduce the pore connectivity; second, the water absorbed by the SAP polymer part also provides water for the cement core wrapped inside the SAP, promoting its hydration, and the silane coupling agent modified cement particles continuously hydrate to generate C-S-H gel, filling the micron-sized pores and enhancing the matrix density.

[0008] In some embodiments, the mass ratio of the silane coupling agent modified cement particles to the superabsorbent polymer is 30-65:70-35; such as 30:70, 40:60, 50:50, 65:35, etc. In the present application, the content of the silane coupling agent modified cement particles can be adjusted according to actual needs to balance the shrinkage inhibition and strength.

[0009] In some embodiments, the silane coupling agent is combined with the hydroxyl group on the surface of the cement particles through siloxane bond.

[0010] In some embodiments, the mass ratio of the silane coupling agent to the cement particles is 0.05-0.2:1, such as 0.08-0.15:1.

[0011] In some embodiments, the silane coupling agent comprises at least one of KH550, KH560, KH570 (γ-methacryloxypropyltrimethoxysilane), KH792, DL602, and DL171.

[0012] In some embodiments, the superabsorbent polymer comprises poly(4-sodium styrene sulfonate), poly(2-acrylamide-2-methylpropane sulfonic acid), poly[2-(methyl)acrylamide-2-methylpropane sulfonic acid], poly(2-acrylamido-2-phenylpropane sulfonic acid), poly[3-(acrylamido)cyclohexane sulfonic acid], poly(2-acrylamide-2-methylpropane sulfonic acid- co- sodium 4-styrenesulfonate), poly[2-acrylamido-2-methylpropanesulfonic acid- co - 3-(acrylamido)cyclohexanesulfonic acid].

[0013] In some embodiments, the superabsorbent polymer is formed by copolymerization of water-absorbing monomers.

[0014] In some embodiments, the superabsorbent polymer is coated on the surface of the silane coupling agent modified cement particles by copolymerization of water-absorbing monomers.

[0015] In some embodiments, the water-absorbing monomers include at least one of sodium 4-styrenesulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 2-(methyl)acrylamido-2-methylpropanesulfonic acid, 2-acrylamido-2-phenylpropanesulfonic acid, and cyclohexyl acrylamide sulfonic acid. Compared with carboxylic acid-containing monomers or acrylamide monomers, the above-mentioned monomers have greater steric hindrance and are not sensitive to high-valence metal ions, and can stably exist in a complex ion system of cement, and the superabsorbent polymer formed has excellent water absorption performance.

[0016] In some embodiments, the average particle size of the cement particles is 1-200 µm, such as 10-150 µm, 15-120 µm, etc. In the present application, the average particle size is obtained by laser diffraction analysis (Malvern Zetasizer Ultra).

[0017] In some embodiments, the average thickness of the shell is 1-10 µm, such as 3-8 µm, 4-6 µm, 5 µm.

[0018] In a second aspect of the present application, a preparation method of the composite cement particles is provided, which comprises the following steps: The silane coupling agent modified cement particles, a crosslinking agent, and a photoinitiator are added to a solution of water-absorbing monomers, and a polymerization reaction is carried out under light irradiation. After freeze-drying, the composite cement particles are obtained.

[0019] In the present application, the silane coupling agent modified cement particles can provide reaction sites, introduce a water-absorbing monomer system, and directly coat on the surface in situ, so as to realize uniform generation of the polymer shell on the particle surface. This strategy not only improves the uniformity of coating and the stability of structure, but also realizes the adjustability of shell thickness by controlling the monomer diffusion and reaction rate, and effectively improves the stability and consistency of the self-healing reaction.

[0020] In some embodiments, the light irradiation uses ultraviolet light; the wavelength of the light is 350-380 nm, such as 360-370 nm; and the time of the polymerization reaction is 30-60 min.

[0021] In some embodiments, the temperature of the freeze-drying is -80 to -50℃; and the time is 50~90h.

[0022] In some embodiments, the method for preparing the composite cement particle further comprises controlling the thickness of the reaction system solution to be below 5mm. In the present application, the thickness of the reaction system solution is controlled to be below 5mm, so that the UV light can initiate the solution reaction in a shorter time, and the sedimentation of the cement particles in the solution is avoided, thereby optimizing the coating effect of the composite cement particle.

[0023] In the present application, the silane coupling agent modified cement particle can be a commercially available product, or can be prepared according to the technology disclosed in the prior art; in some embodiments, the method for preparing the silane coupling agent modified cement particle comprises: dispersing the cement particle in anhydrous ethanol, adding a silane coupling agent, and stirring to obtain the silane coupling agent modified cement particle.

[0024] In some embodiments, the mass-volume ratio of the cement particle to anhydrous ethanol is 1: (3~6) g / mL.

[0025] In some embodiments, the stirring rate is 300~500rpm, such as 300~400rpm, 350rpm; and the stirring time is 12~48h, such as 20~30h.

[0026] In some embodiments, the crosslinking agent comprises at least one of N,N'-methylenebisacrylamide (MBA), ethylene glycol bisglycidyl ether, and N-methylol acrylamide.

[0027] In some embodiments, the amount of the crosslinking agent added is 0.5%~1.5% of the mass of the hydrophilic monomer.

[0028] In some embodiments, the photoinitiator comprises at least one of 2-hydroxy-2-methyl-1-phenyl-1-propanone (HMPP), 2,2-dimethoxy-phenylphenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, and 2,4,6-trimethylbenzoyldiphenyl phosphine oxide (TPO).

[0029] In some embodiments, the amount of the photoinitiator added is 0.05%~0.2% of the mass of the hydrophilic monomer, such as 0.08%~0.15%.

[0030] In a third aspect of the present application, a cement-based material is provided, comprising the composite cement particle.

[0031] In some embodiments, the content of the composite cement particles is 0.1-1.0 wt%, such as 0.1-0.5 wt%. In the present application, the composite cement particles can be used as an internal curing agent for cement-based materials such as high-strength concrete, thereby improving the compressive strength and reducing the autogenous shrinkage.

[0032] In a fourth aspect of the present application, the composite cement particles or the cement-based materials are used in concrete, repair engineering materials, and 3D printing building materials.

[0033] The present application has the following advantages: The silane coupling agent in the composite cement particles forms a chemical bonding interface between the cement particles and the SAP, creating an inorganic-organic synergistic effect, enhancing the overall performance of the material, and the core-shell structure SAP is more inclined to have higher performance concrete than ordinary SAP in early shrinkage control and strength retention, which is different from the later cracking and healing mechanism of self-healing materials.

[0034] Through the synergistic effect of the silane coupling agent modified cement particles and the SAP, the core-shell structure SAP achieves a 28-day compressive strength retention rate of 99.6%, which is significantly better than traditional SAP. The core-shell structure composite cement particles of the present application reduce the 14-day autogenous shrinkage of concrete by 61.4%, which is better than the prior art (usually ≤40%), and solves the problem of strength loss caused by pore residue in traditional SAP.

[0035] Compared with traditional cement-based materials, the composite cement particles of the present application are outstanding in reducing autogenous shrinkage, and can effectively reduce the autogenous shrinkage rate by ≥60%. This is very beneficial for high-strength concrete and extreme environment engineering applications.

[0036] The preparation process of the composite cement particles of the present application is simple, and the cost is reduced by more than 50% compared with nanocomposites, which is suitable for high-strength concrete, repair engineering, and 3D printing building materials. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 SEM images of cement particles (a) and composite cement particles (b) in Example 1 of the present application.

[0038] Figure 2 FT-IR spectra of cement particles, KH570 modified cement particles, and composite cement particles in Example 1 of the present application.

[0039] Figure 3 XRD spectra of cement particles, KH570 modified cement particles, and composite cement particles in Example 1 of the present application.

[0040] Figure 4 Porosity test results of the composite cement particles in Examples 1-4 of the present application.

[0041] Figure 5 The shrinkage rate and strength retention rate of the composite cement particles of Example 1 to Example 4 of the present application are shown in the following graphs. DETAILED DESCRIPTION

[0042] The content of the present application is further described in detail through specific examples. The raw materials, reagents or devices used in the examples and comparative examples can be obtained from conventional commercial channels or can be obtained by prior art methods, unless otherwise specified. Unless otherwise specified, the test or test method is a conventional method in the art.

[0043] In the following examples or comparative examples, the raw material information is as follows: Cement particles: P·I 42.5, China Building Material Research Institute; AMPS monomer: purity ≥ 99%, Shanghai Aladdin Reagent Co., Ltd.; Acrylic acid monomer (AA monomer): purity ≥ 99%, Shanghai Aladdin Reagent Co., Ltd.; Crosslinking agent MBA: chemical pure, National Pharmaceutical Group Chemical Reagent Co., Ltd.; Photoinitiator HMPP: light-cured grade, Sigma-Aldrich; Deionized water: resistivity ≥ 18 MΩ·cm; Anhydrous ethanol: analytical pure, Shanghai Maikeling Biochemical Technology Co., Ltd.; Silane coupling agent KH570: purity ≥ 97%, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0044] The preparation method of the cement particles modified by the silane coupling agent is as follows: 5 g of P·I 42.5 cement particles (laser diffraction analysis (Malvern Zetasizer Ultra) showed that the median particle size was 18.5 µm) were dispersed in 20 mL of anhydrous ethanol, 0.5 g of KH570 coupling agent and 0.5 g of deionized water were added, and the mixture was stirred at a speed of 350 rpm for 24 h, then vacuum filtered and dried at 60°C for 1 h to obtain modified cement particles.

[0045] Raw material composition of the composite cement particles of the examples and comparative examples: Table 1

[0046] The preparation method of the composite cement particles of the examples and comparative examples is as follows: The AMPS monomer or acrylic monomer is dissolved in deionized water, NaOH is added to adjust the pH to neutral, modified cement particles, MBA crosslinking agent and HMPP photoinitiator are sequentially added, and magnetic stirring is carried out at a speed of 500 rpm for 30 min until uniform; the mixed solution is poured into a culture dish (thickness ≤5 mm), and irradiated under a 365 nm ultraviolet lamp for 30 min to form a gel.

[0047] Post-processing: freeze-drying the gel at -70°C for 72 h, crushing through a 200 mesh sieve to obtain core-shell structure composite cement particles.

[0048] The composite cement particles prepared in Examples 1 to 4 are sequentially labeled as core-shell structure composite cement particles 30, core-shell structure composite cement particles 40, core-shell structure composite cement particles 50, and core-shell structure composite cement particles 65.

[0049] Test Example 1 In this test example, the cement particles, KH570 modified cement particles and the core-shell structure composite cement particles in Example 1 are characterized, and the specific process is as follows: The micro-morphology changes from cement particles to core-shell structure composite cement particles are observed using a scanning electron microscope, and the results are shown in Figure 1 , wherein a is the SEM image of the cement particles; b is the SEM image of the composite cement particles in Example 1.

[0050] It can be seen that the core-shell structure composite cement particles retain the irregular morphology and size of the cement particles, but a smooth polymer film is formed on the surface.

[0051] The cement particles, KH570 modified cement particles and the core-shell structure composite cement particles in Example 1 are tested using an infrared spectrum tester (FT-IR), and the results are shown in Figure 2 .

[0052] As can be seen, the composite cement particles exhibit functional groups specific to polymers, such as the stretching vibration peak of sulfonic acid group at 1045 cm -1 , indicating that the superabsorbent polymer is successfully coated on the composite cement particles.

[0053] The structure of the cement particles, KH570 modified cement particles and the core-shell structure composite cement particles in Example 1 are tested using an X-ray diffractometer (XRD), and the results are shown in Figure 3 .

[0054] As can be seen, the core-shell structure composite cement particles exhibit a broad peak of non-crystalline polymer at a position of 18° in 2θ.

[0055] Test Example 2 This experimental example performs porosity analysis on composite cement particles from different embodiments. The specific process is as follows: Preparation of cement paste samples: First, add the predetermined amounts of cement, water, 0.25 wt% high-efficiency water-reducing agent (PCE), and 0.2 wt% composite cement particles to a mixing bowl; no composite cement particles were added to the control group. Stir slowly for 120 seconds, let stand for 15 seconds, then stir rapidly for 120 seconds to achieve a uniform consistency. Control the water-cement ratio (w / c) of the cement paste samples to be 0.20, and maintain the fluidity at 210 ± 10 mm.

[0056] Sample preparation and curing: The prepared cement paste was poured into a prismatic mold with dimensions of 40 mm × 40 mm × 160 mm. The specimens were cured for 28 days in a standard curing chamber at 20 ± 2℃ and 95% relative humidity. Subsequently, 3-5 g sample blocks were extracted from the cement paste samples. Hydration was terminated with anhydrous ethanol, and the samples were dried in a vacuum chamber for 48 hours before being used to test porosity and average pore size.

[0057] The results are as follows Figure 4 As shown, the cement sample in the control group without the addition of the composite cement particles from Examples 1-4 is labeled R, and the cement paste samples with the addition of the composite cement particles from Examples 1-4 are labeled SI, S-II, S-III, and S-IV, respectively. The average pore sizes of the corresponding samples are: R: 32.78 μm; SI: 33.91 μm; S-II: 30.65 μm; S-III: 29.13 μm; S-IV: 26.47 μm.

[0058] It can be seen that as the content of modified cement particles in the core-shell composite cement particles increases, the core-shell composite cement particles can reduce the porosity of the cement paste sample.

[0059] Experimental Example 3 This experimental example tests the mechanical properties of composite cement particles from different embodiments. The specific process is as follows: The cement paste prepared according to the method in Test Example 2 above was poured into a prismatic mold with dimensions of 40 mm × 40 mm × 160 mm. The specimens were placed in a curing chamber at a temperature of 20 ± 2℃ and a relative humidity (RH) of 95%. The curing time was set at 28 days. The compressive strength of the specimens was tested according to the Chinese National Standard GB / T 17671-2021. Three specimens were taken from each group for testing, and the average value was taken as the final compressive strength.

[0060] The compressive strength test was conducted in accordance with GB / T 17671-2021.

[0061] The autogenous shrinkage rate of cement paste over 14 days was measured using the corrugated tube method according to ASTM C1698-19.

[0062] The results are shown in the table below. Figure 2 As shown.

[0063] Table 2

[0064] It can be seen that all embodiments exhibit early shrinkage reduction effects, while the compressive strength is slightly lower than that of the baseline group, but remains at a high level. In particular, the compressive strength of Example 4 (110.97 MPa) almost recovers to the level of the baseline group (111.02 MPa). This is because the outer shell of the composite cement particles is a water-absorbing polymer that can absorb additional water during slurry mixing. In the later stage of cement hydration, it provides moisture to the cement matrix, maintains the relative humidity inside the cement sample, and promotes the degree of hydration, thus exhibiting a better shrinkage effect. As the modified cement particle content in Example 1 is low, the outer shell of the composite cement particles exhibits better water absorption performance, thus exhibiting the best shrinkage reduction effect. Also, because the modified particle content is low, the effect of filling pores in the later stage is weaker, resulting in lower compressive strength in all embodiments. Compared with Comparative Example 1, although it also shows a certain shrinkage reduction effect, it leads to a significant decrease in compressive strength, only 87 MPa. This indicates that the composite material treated by the technology of the present invention exhibits significant strength performance due to the structural characteristics of the monomer. Overall, the core-shell structure in composite cement particles can reduce the early autogenous shrinkage of high-performance cement-based materials while maintaining a high level of compressive strength, which is superior to conventional SAP on the market.

[0065] 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 composite cement particle, characterized in that: include: The core consists of cement particles modified with silane coupling agents; The outer shell includes a superabsorbent polymer; The outer shell covers the core.

2. The composite cement particles according to claim 1, characterized in that: The mass ratio of the silane coupling agent-modified cement particles to the superabsorbent polymer is 30~65:70~35.

3. The composite cement particles according to claim 1, characterized in that: The silane coupling agent is bonded to the hydroxyl groups on the surface of cement particles via siloxane bonds; and / or, the superabsorbent polymer is copolymerized with water-absorbing monomers to coat the surface of the cement particles modified by the silane coupling agent.

4. The composite cement particles according to claim 1, characterized in that: The superabsorbent polymers include sodium poly(4-styrene sulfonate), poly(2-acrylamido-2-methylpropanesulfonic acid), poly[2-(meth)acrylamido-2-methylpropanesulfonic acid], poly(2-acrylamido-2-phenylpropanesulfonic acid), poly[3-(acrylamido-2-cyclohexanesulfonic acid], poly(2-acrylamido-2-methylpropanesulfonic acid- co Sodium 4-styrenesulfonate), poly[2-acrylamide-2-methylpropanesulfonic acid- co At least one of [-3-(acrylamido)cyclohexanesulfonic acid].

5. The composite cement particles according to claim 3, characterized in that: The absorbent monomer includes at least one of sodium 4-styrene sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, 2-acrylamido-2-phenylpropanesulfonic acid, and cyclohexylacrylamidosulfonic acid.

6. A method for preparing composite cement particles according to any one of claims 1 to 5, characterized in that: Includes the following steps: Silane coupling agent-modified cement particles, crosslinking agent, and photoinitiator are added to a solution of water-absorbing monomers. The mixture is then subjected to light irradiation to carry out a polymerization reaction, followed by freeze-drying to obtain composite cement particles.

7. The method for preparing composite cement particles according to claim 6, characterized in that: The method for preparing the silane coupling agent modified cement particles includes: dispersing cement particles in anhydrous ethanol, adding a silane coupling agent, and stirring to obtain the silane coupling agent modified cement particles.

8. The method for preparing composite cement particles according to claim 6, characterized in that: The method for preparing the composite cement particles also includes controlling the thickness of the reaction system solution of the polymerization reaction to be less than 5 mm.

9. A cement-based material, characterized in that: Includes the composite cement particles as described in any one of claims 1 to 5.

10. The application of the composite cement particles according to any one of claims 1 to 5 or the cement-based material according to claim 9 in concrete, repair engineering materials, and 3D printed building materials.

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