FRP-concrete interface agent and preparation method thereof

Abstract

The application relates to the technical field of building material interface agent preparation, in particular to an FRP-concrete interface agent and a preparation method thereof. The interface agent is prepared from the following raw materials: cement, which accounts for 29-31% of the total mass of the interface agent material; nano silicon oxide, which accounts for 2.0-2.1% of the mass of the cement; a water reducing agent, which accounts for 1.5% of the total mass of the cement and the nano silicon oxide; sand, which accounts for 1.375 times the total mass of the cement and the nano silicon oxide; fly ash, which accounts for 25% of the total mass of the cement and the nano silicon oxide; silica ash, which accounts for 31.3% of the total mass of the cement and the nano silicon oxide; and water, which accounts for 37.5% of the total mass of the cement and the nano silicon oxide. The interface agent can effectively improve the interface performance of the FRP bar-concrete by adding nano silicon oxide with a specific proportion.

Description

Technical Field

[0001] This invention relates to the field of interface agent preparation technology for building materials, and more particularly to an FRP-concrete interface agent and its preparation method. Background Technology

[0002] Fiber-reinforced plastics (FRP) bars are composite materials formed by pultrusion molding and surface treatment, using synthetic resin as the matrix phase and fibers (such as glass fiber, aramid fiber, carbon fiber, etc.) as the reinforcing phase. Engineering practice has proven that FRP bars can fundamentally eliminate engineering failures caused by steel corrosion, thereby significantly extending the service life of civil engineering structures.

[0003] However, the bond strength between FRP bars and concrete is relatively low, only 10%-20% of the bond strength between plain round steel bars and concrete. Therefore, improving the bond strength between FRP bars and concrete is the key to applying FRP bars to concrete structures.

[0004] Currently, common techniques for improving the bond performance of FRP (Fiberglass Reinforced Plastic) bars to concrete include physical roughening of the FRP bar surface, rib making, sand coating, chemical coating with coupling agents, alkali washing, plasma modification, and adding cement-based, epoxy resin-based, polyurethane-based, and modified composite interface agents between the FRP bar and concrete to strengthen the bond. However, these techniques all have certain limitations. For example, physical modification techniques offer limited improvement and are prone to damaging the FRP bar itself; in chemical modification, the compatibility of coupling agents with FRP bars and concrete is a significant issue; and existing interface agents generally suffer from low interfacial bond strength, poor residual bond performance, and are prone to debonding failure. Summary of the Invention

[0005] The purpose of this invention is to solve the problem of low bond strength between FRP bars and concrete materials, and to provide an FRP-concrete interface agent with high bond strength and its preparation method.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] This invention provides an FRP-concrete interface agent, the raw materials of which include: Cement: 29%-31% of the total mass of the interface agent material; Nano-silica: 1.0%-3.0% of the cement mass, preferably 2.0%-2.1%; Water-reducing agent: 1.5% of the total mass of cement and nano-silica; Sand: 1.375 times the total mass of cement and nano-silica; Fly ash: 25% of the total mass of cement and nano-silica; Silica fume: 31.3% of the total mass of cement and nano-silica; Water: 37.5% of the total mass of cement and nano-silica.

[0008] In the above technical solution, the cement is further described as grade 42.5 early-strength silicate cement.

[0009] In the above technical solution, the purity of the nano-silica is ≥99%, the particle size is 19-21 nm, and the specific surface area is ≥600 m². 2 / g.

[0010] In the above technical solution, the water-reducing agent is a polycarboxylate water-reducing agent with a solid content of 45% and a water-reducing efficiency of about 28%-30%.

[0011] In the above technical solution, the sand is further refined quartz sand with a particle size of 0.12-0.83 mm.

[0012] In the above technical solution, the silica fume contains 90%-92.5% silica, has a particle size of 0.05-0.15 μm, and a specific surface area of ​​17500-18500 m². 2 / kg.

[0013] Another aspect of the present invention provides a method for preparing the above-mentioned FRP-concrete interface agent, comprising the following steps: (1) Put water, water-reducing agent and nano-silica into a mixer and stir at a stirring speed of 135-145r / min for 15-20 seconds; (2) Add silica fume to the mixture obtained in step (1) and stir at a low speed of 135-145 r / min for 50-60 seconds; (3) Add cement and fly ash to the mixture obtained in step (2), first stir at a stirring speed of 135-145 r / min for 120-130 seconds, and then stir at a high speed of 275-295 r / min for 120-130 seconds. (4) Add sand to the mixture obtained in step (3), stir at a stirring speed of 135-145 r / min for 50-60 seconds, and then stir at a stirring speed of 275-295 r / min for 230-240 seconds to obtain FRP-concrete interface agent.

[0014] The mechanism by which nano-silica improves the interface between FRP reinforcement and concrete in this invention is as follows: Figure 3As shown, the improvement mechanism of nano-silica on the FRP reinforcement-concrete interface mainly includes the nano-enrichment effect and the nano-center effect. First, under the combined effect of the sidewall effect and the gravity effect, nano-silica is enriched at the FRP reinforcement-concrete interface. The enriched nano-silica acts as a nucleation site, adsorbing hydration products to form nano-center-shell units, thereby improving the microstructure of the interface region and restricting the growth of CH crystals. The dense microstructure is conducive to improving the physical bond between FRP reinforcement and concrete, and thus improving the crack-resistant bond strength of the FRP reinforcement-concrete interface.

[0015] The beneficial effects of this invention are as follows: The interface agent of this invention, by adding a specific proportion of nano-silica, can effectively improve the interfacial performance of FRP reinforcement-concrete. Specifically, the interface agent with a certain proportion of nano-silica can both increase the ultimate bond strength of FRP reinforcement-concrete, thereby enhancing bond reliability, and reduce the slip s corresponding to the ultimate bond strength. u This is beneficial for improving the stiffness of FRP-reinforced concrete structures; at the same time, it can reduce the slip corresponding to the residual bond strength, allowing the interfacial microstructure to reach a stable state more quickly. The microstructure in this stable state is more complete and can withstand greater bond stress. The improvement of residual bond strength can not only enhance the ductility of the structure and avoid brittle failure, but also buy time for structural monitoring, safety early warning and subsequent repair. Attached Figure Description

[0016] Figure 1 There are two types of surface rib morphologies for FRP ribs; Figure 2 These are the geometric dimensions of the specimen; Figure 3 This study explores the mechanism by which nano-silica improves the FRP bar-concrete interface. Detailed Implementation

[0017] 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.

[0018] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained commercially or prepared according to conventional methods known to those skilled in the art.

[0019] This invention provides an FRP-concrete interface agent, the raw materials of which include: Cement: 29%-31% of the total mass of the interface agent material; the cement is 42.5 grade early-strength Portland cement produced by Dalian Onoda Cement Co., Ltd. Nano-silica: 1.0%-3.0% of cement mass, with a purity ≥99%, particle size 20nm, and specific surface area ≥600m². 2 / g; Water-reducing agent: 1.5% of the total mass of cement and nano-silica. The water-reducing agent is a polycarboxylate high-efficiency water-reducing agent produced by Sika Company, with a solid content of 45% and a water reduction efficiency of about 30%. It is used to adjust the workability of fresh cement paste and disperse nano-fillers. Sand: 1.375 times the total mass of cement and nano-silica; the sand is refined quartz sand with a particle size range of 0.12-0.83 mm. Fly ash: 25% of the total mass of cement and nano-silica; the fly ash is secondary ash produced by Dalian Huaneng Power Plant. Silica fume: comprising 31.3% of the total mass of cement and nano-silica. The silica fume is No. 920 produced by Shanghai Tiankai Company, with a silica content of 90%-92.5%, a particle size of 0.05-0.15 μm, and a specific surface area of ​​18000 m². 2 / kg; Water: 37.5% of the total mass of cement and nano-silica.

[0020] The above-mentioned method for preparing FRP-concrete interface agent includes the following steps: (1) Put water, water-reducing agent and nano-silica into a mixer and stir at a stirring speed of 135-145r / min for 15-20 seconds; (2) Add silica fume to the mixture obtained in step (1) and stir at a low speed of 135-145 r / min for 50-60 seconds; (3) Add cement and fly ash to the mixture obtained in step (2), first stir at a stirring speed of 135-145 r / min for 120-130 seconds, and then stir at a high speed of 275-295 r / min for 120-130 seconds. (4) Add sand to the mixture obtained in step (3), stir at a stirring speed of 135-145 r / min for 50-60 seconds, and then stir at a stirring speed of 275-295 r / min for 230-240 seconds to obtain FRP-concrete interface agent.

[0021] Example 1 The FRP-concrete interface agent of this embodiment comprises the following raw materials: The mixture consists of cement, 2.0% nano-silica by weight of cement, 25% fly ash by weight of cement and nano-silica, 31.3% silica fume by weight of cement and nano-silica, 1.375 times the weight of sand by weight of cement and nano-silica, 37.5% water by weight of cement and nano-silica, and 1.5% water-reducing agent by weight of cement and nano-silica.

[0022] Its preparation method includes the following steps: (1) Put water, water-reducing agent and nano-silica into a mixer and stir for 20 seconds at a stirring speed of 140r / min; (2) Add silica fume to the mixture obtained in step (1) and stir at a low speed of 140 r / min for 60 seconds; (3) Add cement and fly ash to the mixture obtained in step (2), first stir at a stirring speed of 140 r / min for 120 seconds, and then stir at a high speed of 285 r / min for 120 seconds. (4) Add sand to the mixture obtained in step (3), stir at a stirring speed of 140 r / min for 60 seconds, and then stir at a stirring speed of 285 r / min for 240 seconds to obtain FRP-concrete interface agent.

[0023] Example 2 Unlike Example 1, the nano-silica is 1.0% of the cement mass, and the rest is the same as in Example 1.

[0024] Example 3 Unlike Example 1, the nano-silica is 3.0% of the cement mass, and the rest is the same as in Example 1.

[0025] Comparative Example 1 The FRP-concrete interface agent in this comparative example comprises the following raw materials: The ingredients are cement, 25% fly ash by weight of cement, 31.3% silica fume by weight of cement, 1.375 times the weight of sand by weight of cement, 37.5% water by weight of cement, and 1.5% water-reducing agent by weight of cement.

[0026] Its preparation method includes the following steps: (1) Put water and water-reducing agent into a mixer and stir for 20 seconds at a stirring speed of 140 r / min; (2) Add silica fume to the mixture obtained in step (1) and stir at a low speed of 140 r / min for 60 seconds; (3) Add cement and fly ash to the mixture obtained in step (2), first stir at a stirring speed of 140 r / min for 120 seconds, and then stir at a high speed of 285 r / min for 120 seconds. (4) Add sand to the mixture obtained in step (3), stir at a stirring speed of 140 r / min for 60 seconds, and then stir at a stirring speed of 285 r / min for 240 seconds to obtain FRP-concrete interface agent.

[0027] Test Example 1 1. FRP ribs: The selected FRP bars include GFRP bars with a tensile strength of 1000 MPa and CFRP bars with a tensile strength of 1800 MPa. The surface rib morphology of the two types of FRP bars is as follows: Figure 1 As shown.

[0028] 2. Test methods: (1) Place the FRP bar in the center of the mold and fix it with brackets at both ends to ensure that the FRP bar coincides with the axis of the specimen (deviation ≤ 1 mm). (2) Pour the prepared FRP-concrete interface agent into an oiled mold and vibrate for 60 seconds. The geometric dimensions of the specimen are as follows: Figure 2 As shown; (3) After curing the molded specimen in a curing chamber (temperature: 20±1℃, humidity>95%) for 24 hours, demold the specimen and cure it with plastic film for 28 days. (4) After curing for 28 days, take out the specimen, wipe the surface moisture dry, fix the specimen on the universal testing machine for pull-out test, and record the data for calculation.

[0029] The test results are shown in Table 1.

[0030] Table 1 Characteristic parameters of FRP bar-concrete interface bond-slip curve

[0031] As can be seen from Table 1, the ultimate bond strength (τ) of the FRP reinforcement-concrete composite samples in Examples 1-3 is... b,u Compared with Comparative Example 1, both showed an improvement, with the ultimate bond strength of FRP reinforcement-concrete corresponding to the slip (s). u Both decreased; meanwhile, the residual bond strength (τ) of FRP reinforcement-concrete also decreased. b,rThe performance of the GFRP reinforcement-concrete composite material was also improved. Specifically, the ultimate bond strength of the GFRP reinforcement-concrete composite material in Example 1 increased by 3.11 MPa (16.4%) compared to that in Comparative Example 1, and the ultimate bond strength of the CFRP reinforcement-concrete composite material increased by 12.37 MPa (37.8%) compared to that without nanofillers. The absolute (relative) decrease in slip corresponding to the ultimate bond strength of the GFRP reinforcement-concrete composite material in Example 1 was 0.365 mm (28.7%), and the absolute (relative) decrease in slip corresponding to the ultimate bond strength of the CFRP reinforcement-concrete composite material was 2.012 mm (35.4%). The maximum absolute (relative) increase in residual bond strength of the GFRP reinforcement-concrete composite material in Example 1 was 3.47 MPa (27.8%), and the maximum absolute (relative) increase in residual bond strength of the CFRP reinforcement-concrete composite material was 1.53 MPa (6.9%). The test results also show that the interface agent in Example 1 significantly improved the ultimate bond strength and residual bond strength of the FRP reinforcement-concrete composite material.

[0032] These phenomena indicate that the microstructure of the interface agent with added nano-silica reaches a new stable state within a shorter slip range. Simultaneously, the high residual bond strength also suggests that the microstructure of the FRP-reinforced concrete interface with added nano-silica is more complete when it reaches a stable state, and can withstand greater bond stress. The improved residual bond strength can provide a certain bond strength after failure, thereby improving the ductility of the FRP-reinforced concrete structure, avoiding brittle failure, and buying time for structural monitoring, safety warnings, and subsequent repairs.

[0033] 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. An FRP-concrete interface agent, characterized in that, The raw materials of the interface agent include: Cement: 29%-31% of the total mass of the interface agent material; Nano-silica: 1.0%-3.0% of the cement mass; Water-reducing agent: 1.5% of the total mass of cement and nano-silica; Sand: 1.375 times the total mass of cement and nano-silica; Fly ash: 25% of the total mass of cement and nano-silica; Silica fume: 31.3% of the total mass of cement and nano-silica; Water: 37.5% of the total mass of cement and nano-silica.

2. The FRP-concrete interface agent according to claim 1, characterized in that, The cement is grade 42.5 early-strength silicate cement.

3. The FRP-concrete interface agent according to claim 1, characterized in that, The nano-silica has a purity of ≥99%, a particle size of 19-21 nm, and a specific surface area of ​​≥600 m². 2 / g.

4. The FRP-concrete interface agent according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate water-reducing agent with a solid content of 45% and a water-reducing efficiency of 28%-30%.

5. The FRP-concrete interface agent according to claim 1, characterized in that, The sand is refined quartz sand with a particle size of 0.12-0.83 mm.

6. The FRP-concrete interface agent according to claim 1, characterized in that, The silica fume contains 90%-92.5% silica, has a particle size of 0.05-0.15 μm, and a specific surface area of ​​17500-18500 m². 2 / kg.

7. A method for preparing an FRP-concrete interface agent according to any one of claims 1-6, comprising the following steps: (1) Put water, water-reducing agent and nano-silica into a mixer and stir at a stirring speed of 135-145r / min for 15-20 seconds; (2) Add silica fume to the mixture obtained in step (1) and stir at a low speed of 135-145 r / min for 50-60 seconds; (3) Add cement and fly ash to the mixture obtained in step (2), first stir at a stirring speed of 135-145 r / min for 120-130 seconds, and then stir at a high speed of 275-295 r / min for 120-130 seconds. (4) Add sand to the mixture obtained in step (3), stir at a stirring speed of 135-145 r / min for 50-60 seconds, and then stir at a stirring speed of 275-295 r / min for 230-240 seconds to obtain FRP-concrete interface agent.

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