Composite concrete for bridge expansion joints and preparation method thereof

Abstract

The invention relates to composite concrete for a bridge expansion joint and a preparation method of the composite concrete, and relates to the technical field of bridge concrete. Comprising the following components in parts by weight: 18-20 parts of cement, 25-30 parts of river sand, 45-50 parts of stones and 5-7 parts of water, and further comprises rubber particles, basalt fibers and additives, the additives comprise a water reducing agent and a water repellent agent, when the concrete prepared by adopting a specific concrete formula and a specific preparation method provided by the invention is used for bridge expansion joints, synergistic unification of toughening and reinforcing is realized, and the service life of the bridge expansion joints is prolonged. The performance of toughness, impact resistance, fatigue resistance, strength, rigidity and the like of concrete is improved, the service life of a traditional bridge expansion joint can be greatly prolonged on the premise that the requirement for the strength of the bridge expansion joint concrete is met, and meanwhile bridge safety and driving comfort are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of bridge concrete technology, and in particular to a composite concrete for bridge expansion joints and its preparation method. Background Technology

[0002] Bridge expansion joints are critical structures designed to release and absorb various forces and displacements generated by factors such as temperature changes, loads and impacts, concrete shrinkage and creep, and construction and installation errors. They directly bear the repeated impacts of vehicle loads and are exposed to harsh natural environments such as rain, snow, and de-icing salt for extended periods, making them one of the weakest and most vulnerable parts of the bridge structure. Common problems with expansion joints include concrete damage, steel section fracture, waterstop damage, blockage, and steel section jamming or failure. Among these, concrete damage in the transition zone of the expansion joint is the most direct cause and the first sign of damage. Damage to the concrete in the transition zone will lead to the destruction of the entire bridge expansion joint anchorage system, ultimately resulting in the failure of the entire expansion joint device. Therefore, improving its quality, ensuring its function and performance, and extending its lifespan are crucial for maintaining the overall integrity of the expansion joint structure.

[0003] Currently, the most commonly used bridge expansion joint filling materials are ordinary concrete, steel fiber concrete, polypropylene fiber concrete, and epoxy resin concrete. These materials generally have disadvantages such as insufficient toughness and deformation capacity, low cost performance, and poor durability during use.

[0004] Also refer to Chinese invention patent CN113929376B, which discloses a rubber concrete, its preparation method, and a bridge. The rubber concrete comprises: 40-50 parts cement, 3-8 parts rubber particles, 40-80 parts fine aggregate, 70-160 parts coarse aggregate, 10-18 parts water, and 0.4-0.8 parts admixtures; the rubber particles have a particle size of 0.63-5 mm, and the particle size distribution includes: rubber particles with a particle size of 2.5-5 mm accounting for a certain percentage by weight. With a ratio of 0-2%, 1.25-2.5mm rubber particles account for 20-60% of the weight, and 0.63-1.25mm rubber particles account for 30-70% of the weight, the noise reduction performance of the concrete is improved. However, adding rubber particles to concrete is a typical practice of "trading strength for toughness". It will form several energy-dissipating clusters inside the concrete, which will greatly improve the toughness, impact resistance and fatigue resistance of the concrete, but will inevitably cause a significant decrease in the strength and stiffness of the concrete. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned problems by providing a composite concrete for bridge expansion joints and its preparation method.

[0006] The first aspect of this invention provides a composite concrete for bridge expansion joints, employing the following technical solution:

[0007] A composite concrete for bridge expansion joints comprises the following components by weight: 18-20 parts cement, 25-30 parts river sand, 45-50 parts gravel, and 5-7 parts water. It also includes rubber particles, basalt fibers, and admixtures. The amount of rubber particles is 0.1%-0.2% of the river sand (volume substitution rate), and the amount of basalt fibers is 0.2%-0.4% of the total mass of cement, river sand, rubber particles, and water.

[0008] By adopting the above technical solution, rubber particles and basalt fibers are simultaneously incorporated into concrete. The basalt fibers play a bridging and stitching role in the transition zone between the rubber particles and the cement paste. When microcracks initiate at the rubber particle interface and attempt to expand, the fibers act like "sewing thread" to cross the cracks and bridge them, thereby inhibiting the further expansion and extension of the cracks. This also appropriately compensates for the strength loss caused by the incorporation of rubber particles, thus achieving a synergistic unity of toughening and reinforcement. This increases the toughness, impact resistance, fatigue resistance, strength, and stiffness of the concrete.

[0009] Preferably, the additives include a water-reducing agent and a hydrophobic agent, wherein the water-reducing agent is a polycarboxylate-based water-reducing agent and the hydrophobic agent is an organosilicon-based hydrophobic agent.

[0010] By adopting the above technical solutions, the water-reducing agent improves the flowability and mechanical properties of the concrete mixture, while the hydrophobic agent improves the waterproofing performance of the concrete. When the hydrophobic agent is added to the concrete, the capillary walls inside the concrete change from hydrophilic to hydrophobic, and the water absorption rate of the concrete decreases significantly. At the same time, the hydrophobic agent improves the compatibility of the interface between rubber particles and basalt fibers and cement paste at the molecular level. One end of the hydrophobic agent combines with the hydroxyl groups on the surface of the rubber particles through chemical action, while the other end forms a strong covalent bond with the cement hydration products. The hydrophobic agent builds a "molecular bridge" between the cement hydration products and the rubber surface, thereby improving the dispersibility of basalt fibers in the concrete. In addition, one end of the hydrophobic agent forms a strong covalent bond with the surface of the basalt fibers, and the other end bonds with the cement matrix, thereby improving the bond strength between the basalt fibers and the cement matrix. Under the premise of meeting the concrete strength requirements of bridge expansion joints (strength grade not lower than C50), the service life of traditional bridge expansion joints can be greatly extended, while greatly improving bridge safety and driving comfort.

[0011] Preferably, the water-reducing agent is added at a dosage of 0.8% to 1.3% of the cement, the chloride ion content in the hydrophobic agent is not greater than 0.1%, and the dosage of the hydrophobic agent is 0.1 to 0.2 kg / m3.

[0012] Preferably, the composition includes the following components by weight: 19 parts cement, 28 parts river sand, 47 parts gravel, and 6 parts water. It also includes rubber granules, basalt fiber, water-reducing agent, and hydrophobic agent. The amount of rubber granules is 0.15% of the river sand (volume substitution rate), the amount of basalt fiber is 0.3% of the total mass of cement, river sand, rubber granules, and water, the amount of water-reducing agent is 1.1% of the cement mass, and the amount of hydrophobic agent is 0.15 kg / m3.

[0013] Preferably, the river sand is natural river sand with a particle size between 0.15 mm and 4.75 mm, a fineness modulus of 2.6 to 3.2, and a mud content of no more than 2%.

[0014] Preferably, the stones are natural crushed stone with a nominal particle size range of 5 mm to 25 mm and a crushing index of no more than 20%.

[0015] Preferably, the rubber granules are obtained by crushing waste tires, with a particle size range of 1 mm to 3 mm and an apparent density of 1200 to 1300 kg / m3.

[0016] Preferably, the basalt fiber has a diameter of 14μm to 16μm, a length of 18mm to 24mm, an elongation of 2.4% to 3.2%, a tensile strength of 3000MPa to 4000MPa, and an elastic modulus of 100GPa to 110GPa.

[0017] By adopting the above technical solution, optimizing the parameters and specifications of each component, the performance of concrete is improved. The gravel and river sand are obtained from natural processing, and the rubber particles are obtained from crushed waste tires, which reduces energy consumption and improves environmental performance.

[0018] A second aspect of the present invention provides a method for preparing composite concrete for bridge expansion joints, employing the following technical solution:

[0019] A method for preparing composite concrete for bridge expansion joints includes the following steps:

[0020] S1. Pretreatment: Weigh each raw material component according to the proportion, soak and clean the rubber particles in alkaline solution and then dry them, dissolve the additives in water to prepare mixture A, soak the basalt fiber in mixture A, and then take it out and dry it.

[0021] S2. Pre-mixing: Pour the weighed river sand and 10% of the weight of the mixed liquid A into the mixer for mixing. Then add the soaked basalt fiber into the mixer for mixing to obtain the mixture.

[0022] S3. Mixing: Pour cement, gravel and pretreated rubber granules into the mixture prepared in S2 and stir. Then pour in the remaining mixture A and stir together. After mixing, a concrete mixture is obtained.

[0023] S4. Pouring and curing: Pour the concrete mixture prepared in S3 into the reserved groove of the bridge expansion joint, and use a vibrator to fully vibrate it until the surface is covered with slurry and no air bubbles emerge. After pouring, immediately smooth the surface and cover it with plastic film for moisture retention and curing.

[0024] By adopting the above technical solution, the dispersibility of basalt fibers in concrete is greatly improved after soaking in a mixed solution prepared by mixing high-efficiency water-reducing agent and hydrophobic agent in water. The high-efficiency water-reducing agent and hydrophobic agent play a synergistic role. The hydrophobic agent modifies the surface of basalt fibers through chemical bonding, changing them from hydrophilic to hydrophobic, fundamentally weakening the hydrogen bonding force between fibers and eliminating the internal cause of agglomeration. The polycarboxylate water-reducing agent, by adsorbing onto cement particles, provides steric hindrance and electrostatic pressure, reducing the viscosity and flow resistance of cement paste, creating a superior external rheological environment for fiber dispersion and movement, and eliminating the external cause of agglomeration. The combined effect of these two agents enables basalt fibers to be stably and uniformly dispersed in concrete in the form of monofilaments or extremely fine bundles. When the treated basalt fibers are mixed with pre-wetted river sand, the combination of chemical and physical dispersion ensures that the basalt fibers are stably and uniformly dispersed in concrete in the form of monofilaments or extremely fine bundles, further improving the dispersibility of basalt fibers in concrete.

[0025] Preferably, the preparation method includes the following steps:

[0026] S1. Pretreatment: Weigh each raw material component according to the proportion, soak the rubber particles in a 3% sodium hydroxide solution for 4 hours and then dry them for later use, dissolve the additive in water to prepare mixture A, soak the basalt fiber in mixture A for 5 minutes, and then take it out and dry it.

[0027] S2. Pre-mixing: Pour the weighed river sand and 10% of the weight of the mixed liquid A into the mixer and mix for 2 minutes. Then add the soaked basalt fiber into the mixer and mix for 30-60 seconds to obtain the mixture.

[0028] S3. Mixing: Pour cement, gravel and pretreated rubber granules into the mixture prepared in S2 and stir for 1-2 minutes. Then pour in the remaining mixture A and stir for 1-2 minutes. After mixing, a concrete mixture is obtained.

[0029] S4. Pouring and curing: Pour the concrete mixture prepared in S3 into the reserved groove of the bridge expansion joint, and use a vibrator to fully vibrate it until the surface is covered with slurry and no air bubbles emerge. After pouring, immediately smooth the surface and cover it with plastic film for moisturizing and curing. The curing time shall not be less than 7 days.

[0030] In summary, this application includes at least one of the following beneficial technical effects:

[0031] 1. Traditional rubber concrete generally suffers from the problem of "trading strength for toughness". This application addresses this issue by simultaneously incorporating rubber particles and basalt fibers into the concrete. The basalt fibers play a bridging and stitching role in the transition zone between the rubber particles and the cement paste. When microcracks initiate at the rubber particle interface and attempt to propagate, the fibers act like "sewing thread" to cross the cracks and bridge them, thereby inhibiting further expansion and extension of the cracks. This also appropriately compensates for the strength loss caused by the incorporation of rubber particles, thus achieving a synergistic unity of toughening and reinforcement. This increases the toughness, impact resistance, fatigue resistance, strength, and stiffness of the concrete.

[0032] 2. Hydrophobic agents and water-reducing agents also have multiple effects such as "interface modification" and "dispersant". Hydrophobic agents modify the surface of basalt fibers through chemical bonding, making them change from hydrophilic to hydrophobic, thereby weakening the hydrogen bonding force between fibers from the root and eliminating the internal cause of agglomeration. Polycarboxylate water-reducing agents adsorb onto cement particles, providing steric hindrance and electrostatic pressure, reducing the viscosity and flow resistance of cement paste, creating a superior external rheological environment for fiber dispersion and movement, eliminating the external cause of agglomeration, thereby improving the dispersibility of basalt fibers and thus improving the performance of concrete.

[0033] 3. By first soaking basalt fibers in a mixed solution of hydrophobic and water-reducing agents, and then stirring them together with pre-wetted river sand, chemical dispersion and physical dispersion are combined. The operation is simple and effective, ensuring that basalt fibers are stably and uniformly dispersed in concrete in the form of monofilaments or extremely fine bundles. This further improves the dispersibility of basalt fibers in concrete. Under the premise of meeting the concrete strength requirements of bridge expansion joints, the service life of traditional bridge expansion joints can be greatly extended, while greatly improving bridge safety and driving comfort. Attached Figure Description

[0034] Figure 1 These are physical images of the concrete prepared in Embodiment 3 and Comparative Example 2 of this application, wherein... Figure 1 A is a distribution diagram of basalt fibers in the concrete prepared in Comparative Example 2. Figure 1 B is a distribution diagram of basalt fibers in the concrete prepared in Example 3;

[0035] Figure 2These are scanning electron microscope (SEM) images of the concrete prepared in Example 3 and Comparative Example 2 of this application, wherein... Figure 2 A shows the distribution of basalt fibers in the concrete prepared in Comparative Example 2 under an electron microscope. Figure 2 B is a diagram showing the distribution of basalt fibers in the concrete prepared in Example 3 under an electron microscope;

[0036] Figure 3 This is a scanned image of the concrete prepared in Example 3 of this application. Figure 3 A and Figure 3 B shows the distribution of basalt fibers at different locations;

[0037] Figure 4 This is a scanned image of concrete prepared in Example 3 of this application, wherein, Figure 4 A is a distribution diagram of rubber particles in concrete. Figure 4 B is a diagram of the interface between rubber particles and concrete. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0039] The sources of reagents and raw materials used in the following examples are as follows. Other specific conditions not specified shall be carried out in accordance with conventional conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0040] Component source:

[0041] Cement: Purchased from the market, type PO 52.5;

[0042] River sand: Purchase natural river sand from the market, with a particle size between 0.15 and 4.75 mm, a fineness modulus of 2.6 to 3.2, and a mud content not exceeding 2%;

[0043] Gravel: Purchase natural crushed stone from the market, with a crushing index of no more than 20% and a nominal particle size of 5-25mm;

[0044] Rubber granules: Purchase crushed waste tires from the market; particle size 1-3mm, apparent density 1200-1300 kg / m³ 3 ;

[0045] Basalt fiber: available on the market, diameter 14-16μm, length 18-24mm, elongation 2.4-3.2%, tensile strength 3000-4000MPa, elastic modulus 100-110GPa;

[0046] Water-reducing agent: Purchased from the market, polycarboxylate high-efficiency water-reducing agent, with a water reduction rate of over 30%;

[0047] Hydrophobic agent: purchased from the market, organosilicon (silane, isobutyltriethoxysilane emulsion selected), chloride ion content not exceeding 0.1%.

[0048] I. Implementation Examples

[0049] Example 1

[0050] A composite concrete for bridge expansion joints comprises 18 parts cement, 25 parts river sand, 50 parts gravel, 5 parts water, and rubber granules replacing 0.1% of the river sand by volume. The basalt fiber content is 0.2% of the total mass of cement, river sand, rubber granules, and water. The water-reducing agent content is 0.8% of the cement mass, and the hydrophobic agent content is 0.1 kg / m³. 3 .

[0051] A method for preparing composite concrete for bridge expansion joints includes the following steps:

[0052] S1. Pretreatment: Weigh each raw material component according to the proportion, soak the rubber particles in a 3% sodium hydroxide solution for 4 hours and then dry them for later use. Dissolve the water-reducing agent and the hydrophobic agent in the measured water to prepare the mixture A. Soak the basalt fiber in the mixture A for 5 minutes, and then take it out and dry it.

[0053] S2. Pre-mixing: Pour the weighed river sand and 10% of the weight of the mixed liquid A into the mixer and mix for 2 minutes. Then add the soaked basalt fiber into the mixer and mix for 30 seconds to obtain the mixture.

[0054] S3. Mixing: Pour cement, gravel and pretreated rubber granules into the mixture prepared in S2 and stir for 1 minute. Then pour in the remaining mixture A and stir for 2 minutes. After mixing, a concrete mixture is obtained.

[0055] S4. Pouring and curing: The concrete mixture prepared in S3 is poured into the reserved groove of the bridge expansion joint and fully vibrated with a vibrator until the surface is covered with slurry and no air bubbles emerge. After pouring, the surface is immediately smoothed and covered with plastic film for moisturizing and curing. The curing time is not less than 7 days, and 28 days is used in this embodiment.

[0056] Example 2

[0057] A composite concrete for bridge expansion joints comprises 20 parts cement, 30 parts river sand, 45 parts gravel, 7 parts water, 0.2% rubber granules replacing the river sand by volume, 0.4% basalt fiber by mass of cement, river sand, rubber granules, and water, 1.3% water-reducing agent by mass of cement, and 0.2 kg / m³ of hydrophobic agent. 3 .

[0058] A method for preparing composite concrete for bridge expansion joints includes the following steps:

[0059] S1. Pretreatment: Weigh each raw material component according to the proportion, soak the rubber particles in a 3% sodium hydroxide solution for 4 hours and then dry them for later use. Dissolve the water-reducing agent and the hydrophobic agent in the measured water to prepare the mixture A. Soak the basalt fiber in the mixture A for 5 minutes, and then take it out and dry it.

[0060] S2. Pre-mixing: Pour the weighed river sand and 10% of the weight of the mixed liquid A into the mixer and mix for 2 minutes. Then add the soaked basalt fiber into the mixer and mix for 60 seconds to obtain the mixture.

[0061] S3. Mixing: Pour cement, gravel and pretreated rubber granules into the mixture prepared in S2 and stir for 2 minutes. Then pour in the remaining mixture A and stir for 1 minute. After mixing, a concrete mixture is obtained.

[0062] S4. Pouring and curing: The concrete mixture prepared in S3 is poured into the reserved groove of the bridge expansion joint and fully vibrated with a vibrator until the surface is covered with slurry and no air bubbles emerge. After pouring, the surface is immediately smoothed and covered with plastic film for moisturizing and curing. The curing time is not less than 7 days, and 28 days is used in this embodiment.

[0063] Example 3

[0064] A composite concrete for bridge expansion joints comprises 19 parts cement, 28 parts river sand, 47 parts gravel, 6 parts water, and rubber granules replacing 0.15% of the river sand by volume. The basalt fiber content is 0.3% of the total mass of cement, river sand, rubber granules, and water. The water-reducing agent content is 1.1% of the cement mass, and the hydrophobic agent content is 0.15 kg / m³. 3 .

[0065] A method for preparing composite concrete for bridge expansion joints includes the following steps:

[0066] S1. Pretreatment: Weigh each raw material component according to the proportion, soak the rubber particles in a 3% sodium hydroxide solution for 4 hours and then dry them for later use. Dissolve the water-reducing agent and the hydrophobic agent in the measured water to prepare the mixture A. Soak the basalt fiber in the mixture A for 5 minutes, and then take it out and dry it.

[0067] S2. Pre-mixing: Pour the weighed river sand and 10% of the weight of the mixed liquid A into the mixer and mix for 2 minutes. Then add the soaked basalt fiber into the mixer and mix for 60 seconds to obtain the mixture.

[0068] S3. Mixing: Pour cement, gravel and pretreated rubber granules into the mixture prepared in S2 and stir for 2 minutes. Then pour in the remaining mixture A and stir for 2 minutes. After mixing, a concrete mixture is obtained.

[0069] S4. Pouring and curing: The concrete mixture prepared in S3 is poured into the reserved groove of the bridge expansion joint and fully vibrated with a vibrator until the surface is covered with slurry and no air bubbles emerge. After pouring, the surface is immediately smoothed and covered with plastic film for moisturizing and curing. The curing time is not less than 7 days, and 28 days is used in this embodiment.

[0070] Example 4

[0071] A composite concrete for bridge expansion joints differs from Example 3 in that it comprises 18 parts cement, 26 parts river sand, 48 parts gravel, 6 parts water, with rubber granules replacing 0.2% of the river sand by volume, basalt fiber at 0.3% of the total mass of cement, river sand, rubber granules, and water, water-reducing agent at 1.2% of the cement mass, and hydrophobic agent at 0.2 kg / m³. 3 .

[0072] The preparation method is the same as in Example 3, and will not be repeated here.

[0073] Example 5

[0074] A composite concrete for bridge expansion joints differs from Example 3 in that it comprises 20 parts cement, 27 parts river sand, 49 parts gravel, 6 parts water, with rubber granules replacing 0.15% of the river sand by volume, basalt fiber at 0.3% of the total mass of cement, river sand, rubber granules, and water, water-reducing agent at 1.1% of the cement mass, and hydrophobic agent at 0.15 kg / m³. 3 .

[0075] The preparation method is the same as in Example 3, and will not be repeated here.

[0076] Example 6

[0077] A composite concrete for bridge expansion joints differs from Example 3 in that it comprises 16 parts cement, 29 parts river sand, 48 parts gravel, 6 parts water, with rubber granules replacing 0.05% of the river sand by volume, basalt fiber at 0.1% of the total mass of cement, river sand, rubber granules, and water, water-reducing agent at 0.7% of the cement mass, and hydrophobic agent at 0.1 kg / m³. 3 .

[0078] The preparation method is the same as in Example 3, and will not be repeated here.

[0079] Example 7

[0080] A composite concrete for bridge expansion joints differs from Example 3 in that it comprises 19 parts cement, 32 parts river sand, 53 parts gravel, 6 parts water, with rubber granules replacing 0.3% of the river sand by volume, basalt fiber at 0.3% of the total mass of cement, river sand, rubber granules, and water, water-reducing agent at 1.2% of the cement mass, and hydrophobic agent at 0.15 kg / m³. 3 .

[0081] The preparation method is the same as in Example 3, and will not be repeated here.

[0082] Example 8

[0083] A composite concrete for bridge expansion joints differs from Example 3 in that it comprises 19 parts cement, 26 parts river sand, 48 parts gravel, 6 parts water, with rubber granules replacing 0.05% of the river sand by volume, basalt fiber at 0.5% of the total mass of cement, river sand, rubber granules, and water, water-reducing agent at 1.2% of the cement mass, and hydrophobic agent at 0.2 kg / m³. 3 .

[0084] The preparation method is the same as in Example 3, and will not be repeated here.

[0085] II. Comparative Example

[0086] Comparative Example 1

[0087] A composite concrete has the same composition as Example 1, but differs from Example 1 in that the preparation method is different. In this concrete preparation method, the rubber particles are not pretreated, while the remaining steps are the same as in Example 1.

[0088] Comparative Example 2

[0089] A composite concrete, with the same components as Example 2, differs from Example 2 in its preparation method. This concrete preparation method does not pretreat the basalt fibers and includes the following steps:

[0090] S1. Pretreatment: Weigh each raw material component according to the proportion, soak the rubber particles in a 3% sodium hydroxide solution for 4 hours and then dry them for later use. Dissolve the water-reducing agent and the hydrophobic agent in the measured water to prepare the mixture B.

[0091] S2. Mixing: Pour cement, gravel, basalt fiber, pretreated rubber particles and mixture B into a mixer and mix for 2 minutes to obtain concrete mixture.

[0092] S3. Pouring and curing: The concrete mixture prepared in S2 is poured into the reserved groove of the bridge expansion joint and fully vibrated with a vibrator until the surface is covered with slurry and no air bubbles emerge. After pouring, the surface is immediately smoothed and covered with plastic film for moisture retention and curing. The curing time is not less than 7 days, and 28 days is used in this comparative example.

[0093] Comparative Example 3

[0094] A composite concrete, differing from Example 3 in that it does not contain rubber particles, comprises 19 parts cement, 28 parts river sand, 47 parts gravel, 6 parts water, with basalt fiber added at 0.3% of the total mass of cement, river sand, and water, a water-reducing agent added at 1.1% of the cement mass, and a hydrophobic agent added at 0.15 kg / m³. 3 .

[0095] The preparation method includes the following steps:

[0096] S1. Pretreatment: Weigh each raw material component according to the proportion, dissolve the water-reducing agent and the hydrophobic agent in the measured water to prepare the mixture A, soak the basalt fiber in the mixture A for 5 minutes, and then take it out and dry it.

[0097] S2. Pre-mixing: Pour the weighed river sand and 10% of the weight of the mixed liquid A into the mixer and mix for 2 minutes. Then add the soaked basalt fiber into the mixer and mix for 60 seconds to obtain the mixture.

[0098] S3. Mixing: Pour the cement and gravel into the mixture prepared in S2 and stir for 2 minutes. Then pour in the remaining mixture A and stir for 2 minutes. After mixing, a concrete mixture is obtained.

[0099] S4. Pouring and curing: The concrete mixture prepared in S3 is poured into the reserved groove of the bridge expansion joint and fully vibrated with a vibrator until the surface is covered with slurry and no air bubbles emerge. After pouring, the surface is immediately smoothed and covered with plastic film for moisture retention and curing. The curing time is not less than 7 days, and 28 days is used in this comparative example.

[0100] Comparative Example 4

[0101] A composite concrete, differing from Example 3 in that it does not contain basalt fiber, and comprises 19 parts cement, 28 parts river sand, 47 parts gravel, 6 parts water, with rubber granules replacing 0.15% of the river sand by volume, a water-reducing agent at 1.1% of the cement mass, and a hydrophobic agent at 0.15 kg / m³. 3 .

[0102] A method for preparing composite concrete includes the following steps:

[0103] S1. Pretreatment: Weigh each raw material component according to the proportion, soak the rubber particles in a 3% sodium hydroxide solution for 4 hours and then dry them for later use. Dissolve the water-reducing agent and the hydrophobic agent in the measured water to prepare the mixture A.

[0104] S2. Mixing: Pour cement, river sand, gravel and pretreated rubber granules into a mixer and mix for 2 minutes. Then pour in mixture A and mix for 2 minutes. After mixing, a concrete mixture is obtained.

[0105] S3. Pouring and curing: The concrete mixture prepared in S2 is poured into the reserved groove of the bridge expansion joint and fully vibrated with a vibrator until the surface is covered with slurry and no air bubbles emerge. After pouring, the surface is immediately smoothed and covered with plastic film for moisture retention and curing. The curing time is not less than 7 days, and 28 days is used in this comparative example.

[0106] Comparative Example 5

[0107] A composite concrete, which differs from Example 3 in that it does not contain a hydrophobic agent, comprises 19 parts cement, 28 parts river sand, 47 parts gravel, 6 parts water, and rubber particles with a volume substitution rate of 0.15% to replace the river sand. The amount of basalt fiber is 0.3% of the total mass of cement, river sand, rubber particles and water, and the amount of water-reducing agent is 1.1% of the cement mass.

[0108] A method for preparing composite concrete includes the following steps:

[0109] S1. Pretreatment: Weigh each raw material component according to the proportion, soak the rubber particles in a 3% sodium hydroxide solution for 4 hours and then dry them for later use, dissolve the water-reducing agent in the measured water to prepare the mixture C, soak the basalt fiber in the mixture C for 5 minutes, and then take it out and dry it.

[0110] S2. Pre-mixing: Pour the weighed river sand and 10% of the weight of the mixed liquid C into the mixer and mix for 2 minutes. Then add the soaked basalt fiber into the mixer and mix for 60 seconds to obtain the mixture.

[0111] S3. Mixing: Pour cement, gravel and pretreated rubber granules into the mixture prepared in S2 and stir for 2 minutes. Then pour in the remaining mixture C and stir for 2 minutes. After mixing, a concrete mixture is obtained.

[0112] S4. Pouring and curing: The concrete mixture prepared in S3 is poured into the reserved groove of the bridge expansion joint and fully vibrated with a vibrator until the surface is covered with slurry and no air bubbles emerge. After pouring, the surface is immediately smoothed and covered with plastic film for moisture retention and curing. The curing time is not less than 7 days, and 28 days is used in this comparative example.

[0113] Comparative Example 6

[0114] A composite concrete, differing from Example 3 in that it does not contain rubber particles and basalt fibers, and comprises 19 parts cement, 28 parts river sand, 47 parts gravel, 6 parts water, with a water-reducing agent dosage of 1.1% of the cement mass and a water-repellent agent dosage of 0.15 kg / m³. 3 .

[0115] A method for preparing composite concrete includes the following steps:

[0116] S1. Dissolve the water-reducing agent and the hydrophobic agent in a measured amount of water to prepare a mixed solution D;

[0117] S2. Pour cement, river sand, and gravel into a mixer and mix for 2 minutes. Then pour in mixture D and mix for 2 minutes. After mixing, you will get a concrete mixture.

[0118] S3. Pour the concrete mixture prepared in S2 into the reserved groove of the bridge expansion joint, and use a vibrator to fully vibrate it until the surface is covered with slurry and no air bubbles emerge. After pouring, immediately smooth the surface and cover it with plastic film for moisture retention and curing. The curing time shall not be less than 7 days, and 28 days shall be used in this comparative example.

[0119] Comparative Example 7 (Blank Comparative Example)

[0120] A type of concrete, using conventional concrete formulation and preparation methods, includes 19 parts cement, 28 parts river sand, 47 parts gravel, 6 parts water, and a high-efficiency water-reducing agent at a dosage of 0.8% of the cement mass.

[0121] The preparation method is as follows:

[0122] S1. Dissolve the water-reducing agent in a measured amount of water to prepare a mixture E;

[0123] S2. Pour cement, river sand, and gravel into a mixer and mix for 2 minutes. Then pour in mixture E and mix for 2 minutes. After mixing, you will get a concrete mixture.

[0124] S3. Pouring and curing: The concrete mixture prepared in S2 is poured into the reserved groove of the bridge expansion joint and fully vibrated with a vibrator until the surface is covered with slurry and no air bubbles emerge. After pouring, the surface is immediately smoothed and covered with plastic film for moisture retention and curing. The curing time is not less than 7 days, and 28 days is used in this comparative example.

[0125] III. Performance Test Experiments and Results

[0126] The concrete prepared in Examples 1-8 and Comparative Examples 1-7 were subjected to performance tests under the same environmental conditions. The compressive strength, flexural strength, frost resistance, salt frost resistance, and shrinkage were tested in accordance with the relevant provisions of JTG3420-2020 "Test Procedures for Cement and Cement Concrete in Highway Engineering". The water absorption rate was tested in accordance with the relevant provisions of GB / T11970-1997 "Test Methods for Bulk Density, Moisture Content and Water Absorption of Aerated Concrete". The impact resistance was tested and analyzed in accordance with the relevant provisions of CECS13: 2009 "Standard for Test Methods of Fiber Reinforced Concrete".

[0127] The test results are shown in the table below:

[0128] Table 1 Comparison of Concrete Performance Test Results

[0129]

[0130] As shown in Table 1, regarding mechanical properties (compressive strength and flexural strength), the composite concrete prepared in Examples 1-8 exhibits compressive strengths ranging from 60.7 to 66.8 MPa and flexural strengths ranging from 6.51 to 6.78 MPa, demonstrating excellent overall mechanical properties and effectively bearing vehicle loads and temperature stresses at bridge expansion joints. The concrete prepared in Comparative Examples 1-6 exhibits compressive strengths ranging from 53.7 to 72.6 MPa and flexural strengths ranging from 5.92 to 7.14 MPa, showing fluctuations in mechanical properties. Some groups (such as Comparative Example 3) show lower compressive strengths, resulting in weaker mechanical bearing capacity compared to the examples. The concrete prepared in Comparative Example 7 (blank comparative example) has a compressive strength of 71.5 MPa and a flexural strength of 6.13 MPa. While its mechanical properties are high, its durability (e.g., 1.84% mass loss after 300 freeze-thaw cycles) and impact resistance (35 destructive impacts) are significantly lower than those of the examples, indicating suboptimal overall performance.

[0131] In terms of durability, firstly, in 300 freeze-thaw cycles, the mass loss rate of the embodiment was 0.65%–0.98%, and the dynamic elastic modulus loss rate was 7.47%–9.81%, both lower than the control group (mass loss rate 0.74%–1.62%, dynamic elastic modulus loss rate 8.86%–13.71%), indicating superior freeze-thaw resistance. The blank control group, however, had the worst freeze-thaw resistance with a mass loss rate of 1.84% and a dynamic elastic modulus loss rate of 15.76%. Secondly, in terms of salt-freezing resistance, the peeling amount per unit area of ​​the embodiment was 0.21–0.31 g / m², and the mass gain was 0.31%–0.36%, both lower than the control group (peeling amount 0.26–0.37 g / m², mass gain 0.36%–0.49%), indicating superior salt-freezing resistance. The blank control group, on the other hand, had the worst salt-freezing resistance with a peeling amount of 0.43 g / m² and a mass gain of 0.61%.

[0132] Regarding shrinkage and deformation performance, firstly, looking at the 28-day shrinkage rate, the sample shrinkage was concentrated in the range of 273–313 μm, which was lower than that of the control group (271–342 μm), indicating better shrinkage and deformation control. Secondly, looking at the water absorption rate, the sample shrinkage was 0.59%–0.98%, which was lower than that of the control group (0.90%–2.49%), indicating better impermeability. In contrast, the blank control sample had a shrinkage rate of 326 μm and a water absorption rate of 2.53%, showing the worst shrinkage and deformation and impermeability performance.

[0133] In terms of impact resistance, the examples exhibited excellent impact resistance with 146–327 impact cycles and 3219.3–7210.4 J of impact energy. The comparative examples, on the other hand, had 34–276 impact cycles and 749.7–6805.8 J of impact energy, indicating weaker impact resistance than the examples. The blank comparative examples, however, had the worst impact resistance with 35 impact cycles and 771.8 J of impact energy.

[0134] Comparative Example 2, which did not treat the basalt fibers, exhibited slightly inferior mechanical properties, durability, and overall performance compared to the Example group. The concrete prepared in Comparative Example 2 was compared with the concrete prepared in Example 3, and the results are as follows: Figure 1 As shown, where, Figure 1 A is a photograph of the concrete prepared according to Example 2. Figure 1 B is a photograph of the concrete prepared in Example 3. As shown in the figure, without treatment, basalt fibers easily aggregate, resulting in uneven dispersion. After treatment, the basalt fibers are stably and uniformly dispersed in the concrete as monofilaments or extremely fine bundles. Further electron microscopy scans of these two concrete samples yielded the following results: Figure 2 As shown, where, Figure 2 A shows the distribution of basalt fibers in the concrete prepared in Comparative Example 2 under an electron microscope. Figure 2B shows the distribution of basalt fibers in the concrete prepared in Example 3 under an electron microscope. As can be seen from the figure, the untreated basalt fibers formed "fiber bundles" with poor surface dispersion; the treated basalt fibers were well dispersed, and the interface transition zone with the cement matrix was denser. Further magnification scans of different locations in the concrete prepared in Example 3 yielded the following results: Figure 3 A and Figure 3 As shown in Figure B, the treated basalt fibers are more evenly distributed in the concrete matrix, forming a dense, randomized mesh support structure, which improves the workability and volume stability of the concrete. This further proves that treating basalt fibers with a mixture of hydrophobic and water-reducing agents can increase the dispersibility of basalt fibers, thereby improving the performance of concrete.

[0135] Comparative Example 3, lacking rubber particles, showed a significant decrease in the toughness, impact resistance, and fatigue resistance of the concrete, but an increase in strength and stiffness. Comparative Example 4, with the addition of rubber particles but lacking basalt fiber, exhibited a significant improvement in the toughness, impact resistance, and fatigue resistance of the concrete, but a substantial decrease in strength and stiffness compared to Comparative Example 3, consistent with the performance change trend of adding the corresponding component alone. The concretes of Examples 1-3 achieved a synergistic unity of toughening and reinforcement, increasing the toughness, impact resistance, fatigue resistance, strength, and stiffness of the concrete. Further scanning of the concrete prepared in Example 3 yielded the following results: Figure 4 As shown, where, Figure 4 A is a distribution diagram of rubber particles. Figure 4 B is a diagram of the interface between rubber particles and concrete. Figure 4 As shown in A, the rubber particles are uniformly dispersed in the concrete matrix, thereby reducing stress concentration, improving compressive and tensile strength, and forming a "barrier network" to reduce the penetration of moisture and harmful ions, thus improving impermeability. Simultaneously, the flexible buffering effect of the particles can reduce the damage to the matrix caused by ice crystals during freeze-thaw cycles, enhancing frost resistance. Figure 4 As shown in B, the rubber particles are tightly bonded to the concrete interface, and the "synergistic effect" between the rubber particles and the matrix is ​​enhanced, which further improves the mechanical properties. In addition, the tight interface can reduce the weakness of the interface transition zone and reduce the risk of interface deterioration during long-term service, thereby improving durability.

[0136] Comparative Example 5, which does not contain hydrophobic agents, has lower durability and shrinkage deformation properties than the Example group. Comparative Example 6, which does not contain basalt fiber and rubber particles, has properties that are only slightly better than the blank comparative example.

[0137] Therefore, when the above-mentioned concrete is used for bridge expansion joints, the example group exhibits excellent mechanical properties, effectively bearing vehicle loads and temperature stresses at the expansion joint. Furthermore, it demonstrates outstanding durability (300 freeze-thaw cycles, salt-freezing resistance) and impact resistance, providing long-term resistance to environmental erosion and vehicle impacts. Its excellent shrinkage deformation and impermeability reduce the risk of cracks and water seepage at the expansion joint. In contrast, due to differences in composition and preparation methods, the comparative group generally exhibits weaker durability (300 freeze-thaw cycles, salt-freezing resistance) and impact resistance compared to the example group, making it prone to cracking with long-term use. Problems such as cracks and spalling are present, and the shrinkage deformation and impermeability fluctuate greatly, with a high risk of cracks and water seepage at the expansion joints. The blank control is conventional concrete. When used for bridge expansion joints, its durability (mass loss rate of 1.84% after 300 freeze-thaw cycles and dynamic elastic modulus loss rate of 15.76%) and impact resistance (number of destructive impacts of 35 and destructive impact energy of 771.8J) are extremely poor. It is prone to failure after long-term use, and its shrinkage deformation (326μm) and impermeability (water absorption rate of 2.53%) are the worst, with an extremely high risk of cracks and water seepage at the expansion joints.

[0138] In summary, the concrete in the embodiments is superior to the control group and the blank control group in terms of core indicators such as mechanical properties, durability, shrinkage deformation, and impact resistance. It is the preferred solution for bridge expansion joint concrete. Among them, the indicators of Embodiment 3 are the best, which is the optimal embodiment of this application. When the concrete prepared by the specific concrete formula and specific preparation method provided by this method is used for bridge expansion joints, it achieves the synergistic unity of toughening and reinforcement, and increases the toughness, impact resistance, fatigue resistance, strength and stiffness of the concrete. Under the premise of meeting the strength requirements of bridge expansion joint concrete, it can greatly extend the service life of traditional bridge expansion joints, and at the same time greatly improve the safety of bridges and driving comfort.

Claims

1. A composite concrete for bridge expansion joints, characterized in that, It comprises the following components by weight: 18-20 parts cement, 25-30 parts river sand, 45-50 parts gravel, and 5-7 parts water. It also includes rubber granules, basalt fiber, and additives. The amount of rubber granules is 0.1%-0.2% of the river sand (volume substitution rate), and the amount of basalt fiber is 0.2%-0.4% of the total mass of cement, river sand, rubber granules, and water.

2. The composite concrete according to claim 1, characterized in that, The additives include water-reducing agents and hydrophobic agents, wherein the water-reducing agent is a polycarboxylate-based water-reducing agent and the hydrophobic agent is an organosilicon-based hydrophobic agent.

3. The composite concrete according to claim 2, characterized in that, The water-reducing agent is added at a dosage of 0.8% to 1.3% of the cement, the chloride ion content in the hydrophobic agent is not greater than 0.1%, and the dosage of the hydrophobic agent is 0.1 to 0.2 kg / m3.

4. The composite concrete according to claim 3, characterized in that, The product comprises the following components by weight: 19 parts cement, 28 parts river sand, 47 parts gravel, and 6 parts water. It also includes rubber granules, basalt fiber, water-reducing agent, and hydrophobic agent. The amount of rubber granules is 0.15% of the river sand (volume substitution rate), the amount of basalt fiber is 0.3% of the total mass of cement, river sand, rubber granules, and water, the amount of water-reducing agent is 1.1% of the cement mass, and the amount of hydrophobic agent is 0.15 kg / m3.

5. The composite concrete according to claim 1, characterized in that, The river sand used is natural river sand with a particle size between 0.15mm and 4.75mm, a fineness modulus of 2.6 to 3.2, and a mud content of no more than 2%.

6. The composite concrete according to claim 1, characterized in that, The stones used are natural crushed stone with a nominal particle size range of 5 mm to 25 mm and a crushing index of no more than 20%.

7. The composite concrete according to claim 1, characterized in that, The rubber granules are obtained by crushing waste tires, with a particle size range of 1 mm to 3 mm and an apparent density of 1200 to 1300 kg / m3.

8. The composite concrete according to claim 1, characterized in that, The basalt fibers have a diameter of 14μm to 16μm, a length of 18mm to 24mm, an elongation of 2.4% to 3.2%, a tensile strength of 3000MPa to 4000MPa, and an elastic modulus of 100GPa to 110GPa.

9. A method for preparing composite concrete for bridge expansion joints according to any one of claims 1-8, characterized in that, Includes the following steps: S1. Pretreatment: Weigh each raw material component according to the proportion, soak and clean the rubber particles in alkaline solution and then dry them, dissolve the additives in water to prepare mixture A, soak the basalt fiber in mixture A, and then take it out and dry it. S2. Pre-mixing: Pour the weighed river sand and 10% of the weight of the mixed liquid A into the mixer for mixing. Then add the soaked basalt fiber into the mixer for mixing to obtain the mixture. S3. Mixing: Pour cement, gravel and pretreated rubber granules into the mixture prepared in S2 and stir. Then pour in the remaining mixture A and stir together. After mixing, a concrete mixture is obtained. S4. Pouring and curing: Pour the concrete mixture prepared in S3 into the reserved groove of the bridge expansion joint, and use a vibrator to fully vibrate it until the surface is covered with slurry and no air bubbles emerge. After pouring, immediately smooth the surface and cover it with plastic film for moisture retention and curing.

10. The preparation method according to claim 9, characterized in that, Includes the following steps: S1. Pretreatment: Weigh each raw material component according to the proportion, soak the rubber particles in a 3% sodium hydroxide solution for 4 hours and then dry them for later use, dissolve the additive in water to prepare mixture A, soak the basalt fiber in mixture A for 5 minutes, and then take it out and dry it. S2. Pre-mixing: Pour the weighed river sand and 10% of the weight of the mixed liquid A into the mixer and mix for 2 minutes. Then add the soaked basalt fiber into the mixer and mix for 30-60 seconds to obtain the mixture. S3. Mixing: Pour cement, gravel and pretreated rubber granules into the mixture prepared in S2 and stir for 1-2 minutes. Then pour in the remaining mixture A and stir for 1-2 minutes. After mixing, a concrete mixture is obtained. S4. Pouring and curing: Pour the concrete mixture prepared in S3 into the reserved groove of the bridge expansion joint, and use a vibrator to fully vibrate it until the surface is covered with slurry and no air bubbles emerge. After pouring, immediately smooth the surface and cover it with plastic film for moisturizing and curing. The curing time shall not be less than 7 days.

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