A nano-modified cement-based repair material and a preparation method thereof

Abstract

The application relates to the technical field of building structures and traffic infrastructure repair, in particular to a nano-modified cement-based repair material and a preparation method thereof. The raw materials of the repair material composition include cement, fly ash, silica ash, a water reducing agent, sand, water and multilayer graphene; the mass of the multilayer graphene is 0.1%-1.0% of the total mass of the cement and the multilayer graphene; and the mass ratio of the sum of the mass of the cement and the mass of the multilayer graphene to the mass of the fly ash, the silica ash, the sand, the water, the water reducing agent and the multilayer graphene is 1:0.25:0.313:1.375:0.35:0.023. The multilayer graphene can greatly improve the interfacial bonding strength of new and old cement-based materials, fills the capillary holes on the surface of the old cement-based materials through the nano enrichment effect and nucleation effect, and significantly enhances the interfacial physical bonding force and mechanical engagement force.

Description

Technical Field

[0001] This invention relates to the field of building structure and transportation infrastructure repair technology, and more particularly to a nano-modified cement-based repair material and its preparation method. Background Technology

[0002] The interface between old and new cement-based materials is a core structural form widely used in civil engineering, primarily appearing in three areas: repair of cement-based structures, prefabricated structures, and recycled aggregate concrete. These structures combine the foundational load-bearing capacity of the old cement-based material with the repair and connection functions of the new cement-based material, making them crucial for ensuring the structural integrity of engineering projects. However, under the long-term influence of mechanical and environmental factors, existing cement-based materials and structures will exhibit deterioration phenomena such as cracks, voids, and honeycombing on their surfaces. Furthermore, the on-site connection of prefabricated components in prefabricated structures and the reuse of waste cement-based materials in recycled concrete both rely on the effective bonding between the old and new cement-based materials. Traditional interfaces between old and new cement-based materials have significant defects. The hydration products within the interface are loose and porous, containing a large number of CH crystals. The hydration products on the surface of the old cement-based material contain numerous unfilled capillaries, resulting in low bond strength between the old and new cement-based materials. Under stress, they struggle to work together effectively, leading to interface failure and consequently affecting the overall structural safety and durability.

[0003] Therefore, it is necessary to develop a high-viscosity and high-strength nano-modified cement-based repair material to improve the bonding performance between the old and new cement-based materials. Summary of the Invention

[0004] To address the problem of compromised safety, mechanical properties, and durability of repaired structures due to insufficient bonding strength and relative slippage at the interface between new and old cement-based materials, this invention provides a high-viscosity, high-strength nano-modified cement-based repair material and its preparation method.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] This invention provides a nano-modified cement-based repair material, the raw materials of which include: cement, fly ash, silica fume, water-reducing agent, sand, water, and multilayer graphene; The mass of the multilayer graphene is 0.1%-1.0% of the total mass of cement and multilayer graphene; The ratio of the sum of the mass of cement and multilayer graphene to the mass of fly ash, silica fume, sand, water, and water-reducing agent is 1:0.25:0.313:1.375:0.35:0.023.

[0007] The basic properties of the multilayer graphene are shown in Table 1.

[0008] Table 1

[0009] In the above technical solution, the mass of the multilayer graphene is further 0.3%-0.8% of the total mass of cement and multilayer graphene.

[0010] In the above technical solution, the cement is further described as grade 42.5 early-strength silicate cement.

[0011] In the above technical solution, the water-reducing agent is further described as a polycarboxylate water-reducing agent.

[0012] In the above technical solution, the sand is further refined quartz sand with a particle size of 0.12-0.83 mm.

[0013] Another aspect of the present invention provides a method for preparing the above-mentioned nano-modified cement-based repair material, comprising the following steps: (1) Mix water, water-reducing agent and multilayer graphene, and then place the mixture in an ultrasonic instrument to sonicate the solution for 4-6 min; (2) Pour the mixed solution obtained in step (1) into a mixing pot, add silica fume and stir at a stirring speed of 180-240 r / min for 40-80 s; (3) Add cement and fly ash to the mixture obtained in step (2), first stir at a stirring speed of 180-240 r / min for 100-140 s, and then stir at a stirring speed of 450-550 r / min for 100-140 s; (4) Put the sand into the mixture obtained in step (3), stir at a stirring speed of 180-240 r / min for 40-80s, and then stir at a stirring speed of 450-550 r / min for 200-300s.

[0014] The beneficial effects of this invention are as follows: 1. The multilayer graphene selected in this invention has excellent compatibility with cement-based materials, is suitable for resource recycling scenarios such as recycled aggregate concrete, and conforms to the concepts of energy conservation, environmental protection and sustainable development.

[0015] 2. The multilayer graphene of the present invention can significantly improve the interfacial bonding strength of new and old cement-based materials. Through the nano-enrichment effect and nucleation, it fills the capillary pores on the surface of the old cement-based material, significantly enhancing the physical bonding force and mechanical interlocking force of the interface.

[0016] 3. After the interface is repaired using the repair material of the present invention, interface defects are reduced and the structural density is improved, which significantly enhances the synergistic stress-bearing capacity of the new and old cement-based materials. It effectively avoids interface bonding failure in the repair structure, prefabricated component connection and recycled concrete, reduces the risk of brittle failure and improves the mechanical stability of the overall structure.

[0017] 4. The relative dosage of multilayer graphene in this invention is extremely low, requiring no changes to the traditional preparation and construction processes of cement-based materials. It is convenient to operate and cost-controllable, demonstrating significant economic advantages in engineering applications. Attached Figure Description

[0018] Figure 1 This is a schematic diagram showing the dimensions of the test specimens for the bond strength test of new and old cement-based materials. Figure 2 This is a schematic diagram of the splitting tensile test. a) is the interfacial bond strength test of new and old cement-based materials, and b) is the splitting tensile test of new / old cement-based materials. Figure 3 The microstructure of the fracture surface of the new cement-based material after using the repair materials of Comparative Example 1 and Example 3 (magnified 1000 times) is shown in a. a) using the repair material of Comparative Example 1 and b) using the repair material of Example 3. Figure 4 The microstructure of the fracture surface of the new cement-based material after repairing the interface with the repair materials of Comparative Example 1 and Example 3 (magnified 20,000 times) is shown in Figure a, where the repair material of Comparative Example 1 is used, and Figure b is where the repair material of Example 3 is used. Figure 5 Microscopic morphology of the fracture surface of the old cement-based material after repairing the interface using the repair material of Example 3 (magnified 20,000 times). Detailed Implementation

[0019] The following examples are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0020] In the following embodiments: The cement is grade 42.5 early-strength silicate cement produced by Dalian Onoda Cement Co., Ltd.

[0021] The fly ash is secondary ash produced by Dalian Huaneng Power Plant.

[0022] The silica fume is No. 920 silica fume produced by Shanghai Tiankai Company.

[0023] The water-reducing agent is a polycarboxylate high-efficiency water-reducing agent manufactured by Sika Corporation.

[0024] The sand is refined quartz sand with a particle size range of 0.12-0.83 mm.

[0025] Examples 1-5 This embodiment provides a nano-modified cement-reinforced steel grout, the raw materials of which include: cement, fly ash, silica fume, water-reducing agent, sand, water, and multilayer graphene, as shown in Table 2.

[0026] Table 2

[0027] Comparative Example 1 Unlike Example 1, no multilayer graphene was added, and the mass ratio of cement, fly ash, silica fume, sand, water, and water-reducing agent was 1:0.25:0.313:1.375:0.35:0.023.

[0028] Test Example 1 This invention characterizes the bond performance between the old and new cementitious surfaces after repair using a splitting tensile test (according to GB / T 50081-2019 Standard for Test Methods of Physical and Mechanical Properties of Concrete). The test is conducted 28 days after repair. First, splitting tensile tests are performed on six specimens in each group, and the average value of the results is taken as the bond strength between the old and new cementitious materials. The splitting tensile test loads the specimens to failure at a constant rate of 0.02 mm / min. Figure 2 As shown in figure a. Splitting tensile strength f t It can be calculated using the following formula.

[0029]

[0030] In the formula, P is the ultimate load at which the specimen fails; A is the area of ​​the splitting surface of the specimen, A = 1600 mm². 2 .

[0031] The bonding properties of Examples 1-5 and Comparative Example 1 are shown in Tables 3 and 4.

[0032] Table 3

[0033] Table 4

[0034] As shown in Tables 3 and 4, compared to the repair material sample of Comparative Example 1, the interfacial bond strength enhancement effect of the sample in Example 1 increased by 0.33 MPa (16.1%) in absolute (relative) terms; the interfacial bond strength enhancement effect of the sample in Example 2 increased by 0.54 MPa (26.3%) in absolute (relative) terms; the cracking bond strength of the cement-based material-reinforcing steel in the sample in Example 3 increased by 0.71 MPa (34.6%) in absolute (relative) terms; the interfacial bond strength enhancement effect of the sample in Example 4 increased by 0.59 MPa (28.8%) in absolute (relative) terms; and the interfacial bond strength enhancement effect of the sample in Example 5 increased by 0.28 MPa (13.7%) in absolute (relative) terms. This indicates that the interfacial bond strength between the old and new cement-based materials was enhanced by incorporating multilayer graphene.

[0035] After characterizing the bond strength between the new and old cement-based materials, splitting tensile tests were performed on both materials. Figure 2 As shown in b.

[0036] After specimen failure, the microstructure of the damaged surface of the new cementitious material was characterized using SEM. Figure 3 a, Figure 4 As can be seen, a large number of CH crystals appeared on the damaged surface of the new cementitious material using Comparative Example 1, and the CSH gel within the damaged surface was loose and porous. In contrast, the content of CH crystals on the damaged surface of the new cementitious material using Example 3 was significantly reduced, and the CSH gel on the damaged surface of the new cementitious material was more uniform and denser. Figure 3 b and Figure 4 As shown in b.

[0037] Figure 5 The microstructure of hydration products on the fracture surface of old cement-based materials. Figure 5 As can be seen, the hydration products in the damaged surface of the old cementitious material using the sample of Comparative Example 1 exhibit a large number of micropores. In contrast, the microstructure of the hydration products in the damaged surface of the old cementitious material using the sample of Example 3 is more compact, and no obvious micropores were observed.

[0038] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A nano-modified cement-based repair material, characterized in that, The repair material is composed of the following raw materials: cement, fly ash, silica fume, water-reducing agent, sand, water, and multilayer graphene. The mass of the multilayer graphene is 0.1%-1.0% of the total mass of cement and multilayer graphene; The ratio of the sum of the mass of cement and multilayer graphene to the mass of fly ash, silica fume, sand, water, and water-reducing agent is 1:0.25:0.313:1.375:0.35:0.

023.

2. The nano-modified cement-based repair material according to claim 1, characterized in that, The mass of the multilayer graphene is 0.3%-0.8% of the total mass of cement and multilayer graphene.

3. The nano-modified cement-based repair material according to claim 1, characterized in that, The cement is grade 42.5 early-strength silicate cement.

4. The nano-modified cement-based repair material according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate water-reducing agent.

5. The nano-modified cement-based repair material according to claim 1, characterized in that, The sand is refined quartz sand with a particle size of 0.12-0.83 mm.

6. A method for preparing a nano-modified cement-based repair material according to any one of claims 1-5, characterized in that, Includes the following steps: (1) Mix water, water-reducing agent and multilayer graphene, and then place the mixture in an ultrasonic instrument to sonicate the solution for 4-6 minutes; (2) Pour the mixed solution obtained in step (1) into a mixing pot, add silica fume and stir at a stirring speed of 180-240 r / min for 40-80 s; (3) Add cement and fly ash to the mixture obtained in step (2), first stir at a stirring speed of 180-240 r / min for 100-140 s, and then stir at a stirring speed of 450-550 r / min for 100-140 s; (4) Put the sand into the mixture obtained in step (3), stir at a stirring speed of 180-240 r / min for 40-80 s, and then stir at a stirring speed of 450-550 r / min for 200-300 s.

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