Construction method of ultra-high performance concrete for hogging moment area of continuous beam bridge

Abstract

The invention relates to the technical field of concrete construction, in particular to a construction method of ultra-high performance concrete for a negative moment area of a continuous beam bridge. The method comprises the following steps: S1, earlier-stage treatment and formwork erection: earlier-stage treatment is performed on a concrete bridge floor base layer of a negative moment area of a continuous beam bridge, and a bottom formwork and a side formwork of an ultra-high performance concrete pavement layer of the negative moment area are arranged on the base layer after earlier-stage treatment is completed to form a construction base layer after formwork erection; s2, reinforcing mesh binding, wherein the construction base layer after formwork erecting serves as a construction foundation, and binding construction of a reinforcing mesh is conducted on the construction base layer; s3, UHPC pouring is conducted, specifically, the bound steel reinforcement framework structure serves as a construction base, a UHPC mixture is prepared through a dry mixing method, after performance detection is qualified, pouring is conducted in the to-be-paved area, vibrating and leveling are conducted, and a UHPC structure layer is formed; and S4, UHPC maintenance is conducted. The use of prestressed materials is reduced, the labor and machine cost is reduced by combining the shortening of the construction period, meanwhile, steel consumption and construction energy consumption are reduced, and green construction is achieved. The method is mainly applied to construction of the ultra-high performance concrete for the hogging moment area.

Description

Technical Field

[0001] This invention relates to the field of concrete construction technology, and more specifically, to a method for constructing ultra-high performance concrete in the negative bending moment zone of continuous beam bridges. Background Technology

[0002] The highway system promotes the operational philosophy of "safety, speed, and comfort," which places higher demands on the quality of highway bridge structures. As a result, the simply-supported-to-continuous beam bridge, a type of bridge that combines the advantages of both simply supported beam bridges and continuous beam bridges, has emerged. For traditional simply supported beam bridges, the presence of expansion joints on the bridge deck severely affects driving comfort. Therefore, simply supported beam bridges with continuous deck structures effectively solve this engineering problem. The essence of a continuous deck structure is to replace part of the expansion joint structure, forming a reinforced concrete truss, thereby achieving a longer continuous bridge deck and improving the bridge's driving performance.

[0003] In terms of structural stress, under vertical forces, the structure is primarily considered as a simply supported system. A portion of the vertical and horizontal forces are transferred horizontally between the continuous steel reinforcement bars of the bridge deck, sharing the load and exhibiting characteristics of a partially continuous beam. Under load, the concrete slabs in the continuous sections of the bridge deck bear significant tensile stress, making them prone to cracking. Since the cracks are located directly above the bridge deck and open upwards, further rainwater infiltration will cause corrosion of the continuous steel reinforcement bars. Currently, insufficient durability due to concrete cracking in the continuous sections of the simply supported beam bridge deck has become a common structural problem in this type of bridge. To resist the tensile stress generated in the negative bending moment zone, measures such as adjusting the construction sequence of the bridge deck and applying prestress to the bridge deck in the negative bending moment zone are commonly used to improve the stress distribution in this zone. The system transformation process inevitably involves the generation of secondary internal forces and the adjustment and redistribution of structural internal forces. Different construction procedures will result in completely different stresses. The stress can be optimized by adjusting the construction sequence of the bridge deck, including adjusting the paving sequence of the precast bridge deck, the sequence and timing of the steel beams and precast bridge deck forming overall stiffness, and the construction sequence of the cast-in-place section of the wet joint. The application of prestress in the negative bending moment zone of the bridge deck usually adopts the tensioning prestressing tendon method, the preloading method, and the jacking method. The above-mentioned prestressing measures can prevent concrete cracking to varying degrees and achieve the purpose of increasing structural stiffness. However, due to the limitations of construction technology, the prestressing method has drawbacks such as complex process, inconvenient construction, blockage of prestressing ducts, large prestress loss, and uncontrollable preload. Summary of the Invention

[0004] To overcome the shortcomings of the existing technology, the present invention provides a construction method for ultra-high performance concrete in the negative bending moment zone of continuous beam bridges.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: The construction method for ultra-high performance concrete in the negative bending moment zone of a continuous beam bridge includes the following steps: S1. Pre-treatment and formwork erection: Pre-treatment is carried out on the concrete bridge deck base in the negative bending moment zone of the continuous beam bridge. After completion, the bottom form and side form of the ultra-high performance concrete pavement layer in the negative bending moment zone are set on the base to form the construction base after the formwork is erected. The ultra-high performance concrete is concrete with a tensile strength of 8MPa or more and a flexural strength of 22MPa or more, made by using cementitious materials, fine aggregates and steel fibers with different particle size distributions at an ultra-low water-cement ratio of about 0.18 to achieve a dense packing state. An expansion agent is added to compensate for cement hydration shrinkage. It is also known as UHPC. S2. Reinforcing mesh binding: Using the construction base after the formwork is erected as the construction foundation, the reinforcing mesh is bound on it. After position adjustment and cleaning, a binding reinforcing mesh skeleton structure is formed. S3, UHPC pouring: Using the completed steel reinforcement skeleton structure as the construction base, UHPC mixture is prepared by dry mixing method. After passing the performance test, it is poured and vibrated to level the area to be paved to form a UHPC structural layer. S4. UHPC Maintenance: Based on the temperature conditions of the construction environment, adopt the corresponding maintenance method to complete the UHPC construction in the negative bending moment zone of the continuous beam bridge.

[0006] Step S1 includes surface roughening treatment, rebar installation, cleaning treatment, and water saturation treatment. The concrete bridge deck base after surface roughening treatment, rebar installation, and cleaning treatment is the object of water saturation treatment, and the concrete bridge deck base after water saturation treatment is the base for formwork construction. The roughness depth of the base after surface roughening treatment is ≥3mm, and the duration of water saturation treatment is not less than 12 hours. During formwork construction, the formwork joints are tight, and when the joints are greater than 5mm, sealing measures are used to seal the joints.

[0007] During the rebar installation, the rebar density at the edge of the concrete bridge deck base is greater than the internal rebar density, and all rebars are bent into hooks; the rebars within a 3m range on both sides of the support in the continuous beam bridge are densified to form densified rebar sections.

[0008] In step S2, the rebar connection adopts the binding method, and the binding length is not less than 35d, where d is the diameter of the rebar. When the rebar is positioned, if the rebars collide, the principle is to move the secondary rebars to avoid the main rebars. If the rebar position conflicts with the ventilation hole, the rebar position is adjusted appropriately. After the binding is completed, the exposed part of the pre-embedded rebar is cleaned. The cleaned rebar skeleton structure serves as the construction base for UHPC casting.

[0009] In step S3, the process of preparing UHPC mixture by dry mixing is as follows: various solid raw materials and water-reducing agents are premixed into dry mixture in the factory and transported to the construction site. The dry mixture is then mixed with water on site to form UHPC mixture. Before mixing, the mixing equipment is checked for condition. During the mixing process, steel fiber anti-balling measures are taken. After the mixture is completed, the slump is tested and standard test specimens for performance testing are made. The qualified mixture is discharged within 15 minutes and used as raw material for UHPC casting. After casting, the mixture is leveled and smoothed using a vibrating device to form the UHPC structural layer.

[0010] The on-site mixing adopts a 1.5m³ forced mixer, and 1 cubic meter of UHPC mixture is mixed each time. The mixing process of dry mixture and water is to dry mix for 3 minutes, and then continue to wet mix for 1-2 minutes after the mixture has flowed. The batching error of dry mixture is controlled within 2%, and the metering error of water is controlled within 1%. The anti-balling measure of steel fiber is to put steel fiber and quartz sand into the loader for pre-dispersion in layers, and then dry mix them together with other dry materials.

[0011] In step S4, the process is divided into ambient temperature moisturizing curing and low temperature heat preservation curing based on temperature conditions. Ambient temperature curing is defined as a daily average temperature ≥ 5℃, and low temperature curing is defined as a daily average temperature < 5℃. Ambient temperature moisturizing curing involves immediately covering the UHPC structural layer with a curing film after leveling and smoothing. The film is continuously covered and moisturized by spraying water mist for 24 hours after pouring. After 24 hours, water mist is sprayed onto the surface of the structural layer and then geotextile is covered. The moisturizing curing time is no less than 7 days, and the number of water sprays per day is no less than 3 times. Low temperature heat preservation curing involves covering the surface of the UHPC structural layer with a curing film and adding a layer of heat-insulating cotton quilt or geotextile on the outside of the film. The overlap width of the curing film is greater than 20cm, and the overlap is covered with heavy objects.

[0012] During the UHPC curing process, ensure that the curing membrane is intact and that there are condensation droplets on the inner surface; conduct on-site inspection of the structural layer within 12 hours before the final setting of the UHPC, and immediately perform surface finishing or grouting treatment if obvious surface collapse or rebar protrusion is found. After the treatment is completed, continue to complete the curing operation according to the corresponding temperature conditions.

[0013] Compared with existing technologies, the beneficial effects of this invention are as follows: UHPC possesses ultra-high mechanical properties, and the addition of an expansion agent compensates for hydration shrinkage, effectively resisting tensile stress in the negative bending moment zone and preventing concrete cracking. Simultaneously, its excellent durability prevents the penetration of corrosive substances, avoids steel reinforcement corrosion, and significantly extends the service life of the bridge. Targeted quality control measures are implemented for each stage of base treatment, steel reinforcement binding, UHPC preparation and pouring, and curing, avoiding problems such as steel fiber balling and UHPC drying shrinkage micro-cracks, ensuring that the performance of UHPC materials is fully utilized and construction quality is stable. The use of prestressed materials is reduced, and combined with the shortened construction period, reduced labor and machinery costs, and reduced steel consumption and construction energy consumption, achieving green construction, improving bridge driving comfort, reducing later maintenance and traffic interruption issues, and possessing good promotional value. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the construction process of the present invention; Figure 2 This is a schematic diagram of the UHPC casting area in this invention. Detailed Implementation

[0015] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0016] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0017] like Figure 1 , Figure 2 As shown, the construction method of ultra-high performance concrete in the negative bending moment zone of a continuous beam bridge includes the following steps: S1. Pre-treatment and formwork erection: Pre-treatment is carried out on the concrete bridge deck base in the negative bending moment zone of the continuous beam bridge. After completion, the bottom form and side form of the ultra-high performance concrete pavement layer in the negative bending moment zone are set on the base to form the construction base after the formwork is erected. The ultra-high performance concrete is concrete with a tensile strength of 8MPa or more and a flexural strength of 22MPa or more, made by using cementitious materials, fine aggregates and steel fibers with different particle size distributions at an ultra-low water-cement ratio of about 0.18 to achieve a dense packing state. An expansion agent is added to compensate for cement hydration shrinkage. It is also known as UHPC. S2. Reinforcing mesh binding: Using the construction base after the formwork is erected as the construction foundation, the reinforcing mesh is bound on it. After position adjustment and cleaning, a binding reinforcing mesh skeleton structure is formed. S3, UHPC pouring: Using the completed steel reinforcement skeleton structure as the construction base, UHPC mixture is prepared by dry mixing method. After passing the performance test, it is poured and vibrated to level the area to be paved to form the UHPC structural layer. S4. UHPC Maintenance: Based on the temperature conditions of the construction environment, adopt the corresponding maintenance method to complete the UHPC construction in the negative bending moment zone of the continuous beam bridge.

[0018] Preferably, step S1 includes surface roughening treatment, rebar installation, cleaning treatment, and water saturation treatment. The concrete bridge deck base after surface roughening treatment, rebar installation, and cleaning treatment is the object of water saturation treatment. The concrete bridge deck base after water saturation treatment is the base for formwork construction. The roughness depth of the base after surface roughening treatment is ≥3mm, and the water saturation treatment time is not less than 12h. During formwork construction, the formwork joints are tight. When the joint is greater than 5mm, sealing measures are used to seal the joints.

[0019] Preferably, during the rebar installation, the rebar density at the edge of the concrete bridge deck base is greater than the internal rebar density, and all rebars are bent into hooks; the rebars within a 3m range on both sides of the support in the continuous beam bridge are densified to form densified rebar sections.

[0020] Preferably, in step S2, the rebar connection adopts the binding method, and the binding length is not less than 35d, where d is the diameter of the rebar; if the rebars collide during rebar positioning, the principle is to move the secondary rebars to avoid the main rebars; if the rebar position conflicts with the ventilation hole, the rebar position is adjusted appropriately; after binding, the exposed part of the pre-embedded rebar is cleaned, and the cleaned rebar skeleton structure serves as the construction base for UHPC casting.

[0021] Preferably, in step S3, the process of preparing UHPC mixture by dry mixing is as follows: various solid raw materials and water-reducing agents are premixed into dry mixture in the factory and transported to the construction site. The dry mixture is then mixed with water on site to form UHPC mixture. Before mixing, the mixing equipment is checked for condition. During the mixing process, steel fiber anti-balling measures are taken. After the mixture is completed, the slump is tested and standard test specimens for performance testing are made. The qualified mixture is discharged within 15 minutes and used as raw material for UHPC casting. After casting, the mixture is leveled and smoothed using a vibrating device to form the UHPC structural layer.

[0022] Preferably, a 1.5m³ forced mixer is used for on-site mixing, and 1 cubic meter of UHPC mixture is mixed each time. The mixing process of dry mix and water is to dry mix for 3 minutes, and then continue wet mixing for 1-2 minutes after the mixture has flowed. The batching error of dry mix is ​​controlled within 2%, and the metering error of water is controlled within 1%. The anti-balling measure for steel fiber is to put steel fiber and quartz sand into the loader for pre-dispersion in layers, and then dry mix them together with other dry materials.

[0023] Preferably, in step S4, the curing process is divided into normal temperature moisturizing curing and low temperature heat preservation curing based on temperature conditions. Normal temperature curing is defined as a daily average temperature ≥ 5℃, and low temperature curing is defined as a daily average temperature < 5℃. For normal temperature moisturizing curing, after the UHPC structural layer is vibrated and smoothed, a curing film is immediately covered. The film is continuously covered and moisturized by spraying water mist for 24 hours after pouring. After 24 hours, water mist is sprayed onto the surface of the structural layer and then geotextile is covered. The moisturizing curing time is not less than 7 days, and the number of water sprays per day is not less than 3 times. For low temperature heat preservation curing, a curing film is covered onto the surface of the UHPC structural layer, and an insulating cotton quilt or geotextile is added to the outside of the film. The overlap width of the curing film is greater than 20cm, and the overlap is covered with a heavy object.

[0024] Preferably, during the UHPC curing process, the curing membrane is kept intact and has condensation on its inner surface. A site inspection of the structural layer is conducted within 12 hours before the final setting of the UHPC. If surface collapse or obvious rebar protrusions are found, immediate surface finishing or grouting is performed. After treatment, curing is continued under the corresponding temperature conditions. The above description only details preferred embodiments of the present invention; however, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention, and all such changes should be included within the protection scope of the present invention.

Claims

1. A construction method for ultra-high performance concrete in the negative bending moment zone of a continuous beam bridge, characterized in that, Includes the following steps: S1. Pre-treatment and formwork erection: Pre-treatment is carried out on the concrete bridge deck base in the negative bending moment zone of the continuous beam bridge. After completion, the bottom form and side form of the ultra-high performance concrete pavement layer in the negative bending moment zone are set on the base to form the construction base after the formwork is erected. The ultra-high performance concrete is concrete with a tensile strength of 8MPa or more and a flexural strength of 22MPa or more, made by using cementitious materials, fine aggregates and steel fibers with different particle size distributions at an ultra-low water-cement ratio of about 0.18 to achieve a dense packing state. An expansion agent is added to compensate for cement hydration shrinkage. It is also known as UHPC. S2. Reinforcing mesh binding: Using the construction base after the formwork is erected as the construction foundation, the reinforcing mesh is bound on it. After position adjustment and cleaning, a binding reinforcing mesh skeleton structure is formed. S3, UHPC pouring: Using the completed steel reinforcement skeleton structure as the construction base, UHPC mixture is prepared by dry mixing method. After passing the performance test, it is poured and vibrated to level the area to be paved to form a UHPC structural layer. S4. UHPC Maintenance: Based on the temperature conditions of the construction environment, adopt the corresponding maintenance method to complete the UHPC construction in the negative bending moment zone of the continuous beam bridge.

2. The construction method for ultra-high performance concrete in the negative bending moment zone of a continuous beam bridge according to claim 1, characterized in that: Step S1 includes surface roughening treatment, rebar installation, cleaning treatment, and water saturation treatment. The concrete bridge deck base after surface roughening treatment, rebar installation, and cleaning treatment is the object of water saturation treatment, and the concrete bridge deck base after water saturation treatment is the base for formwork construction. The roughness depth of the base after surface roughening treatment is ≥3mm, and the duration of water saturation treatment is not less than 12 hours. During formwork construction, the formwork joints are tight, and when the joints are greater than 5mm, sealing measures are used to seal the joints.

3. The construction method for ultra-high performance concrete in the negative bending moment zone of a continuous beam bridge according to claim 2, characterized in that: During the rebar installation, the rebar density at the edge of the concrete bridge deck base is greater than the internal rebar density, and all rebars are bent into hooks; the rebars within a 3m range on both sides of the support in the continuous beam bridge are densified to form densified rebar sections.

4. The construction method for ultra-high performance concrete in the negative bending moment zone of a continuous beam bridge according to claim 1, characterized in that: In step S2, the rebar connection adopts the binding method, and the binding length is not less than 35d, where d is the diameter of the rebar. When the rebar is positioned, if the rebars collide, the principle is to move the secondary rebars to avoid the main rebars. If the rebar position conflicts with the ventilation hole, the rebar position is adjusted appropriately. After the binding is completed, the exposed part of the pre-embedded rebar is cleaned. The cleaned rebar skeleton structure serves as the construction base for UHPC casting.

5. The construction method for ultra-high performance concrete in the negative bending moment zone of a continuous beam bridge according to claim 1, characterized in that: In step S3, the process of preparing UHPC mixture by dry mixing is as follows: various solid raw materials and water-reducing agents are premixed into dry mixture in the factory and transported to the construction site. The dry mixture is then mixed with water on site to form UHPC mixture. Before mixing, the mixing equipment is checked for condition. During the mixing process, steel fiber anti-balling measures are taken. After the mixture is completed, the slump is tested and standard test specimens for performance testing are made. The qualified mixture is discharged within 15 minutes and used as raw material for UHPC casting. After casting, the mixture is leveled and smoothed using a vibrating device to form the UHPC structural layer.

6. The construction method for ultra-high performance concrete in the negative bending moment zone of a continuous beam bridge according to claim 5, characterized in that: The on-site mixing adopts a 1.5m³ forced mixer, and 1 cubic meter of UHPC mixture is mixed each time. The mixing process of dry mixture and water is to dry mix for 3 minutes, and then continue to wet mix for 1-2 minutes after the mixture has flowed. The batching error of dry mixture is controlled within 2%, and the metering error of water is controlled within 1%. The anti-balling measure of steel fiber is to put steel fiber and quartz sand into the loader for pre-dispersion in layers, and then dry mix them together with other dry materials.

7. The construction method for ultra-high performance concrete in the negative bending moment zone of a continuous beam bridge according to claim 1, characterized in that: In step S4, the curing is divided into normal temperature moisturizing curing and low temperature heat preservation curing according to temperature conditions. Normal temperature means the daily average temperature is ≥5℃, and low temperature means the daily average temperature is <5℃. Normal temperature moisturizing curing is as follows: after the UHPC structural layer is vibrated and smoothed, a curing film is immediately covered. After the pouring is completed, the film is continuously covered and moisturized by spraying water mist for 24 hours. After 24 hours, water mist is sprayed on the surface of the structural layer and then covered with geotextile. The moisturizing curing time is not less than 7 days, and the number of times water is sprayed is not less than 3 times a day. Low-temperature insulation and curing involves covering the surface of the UHPC structural layer with a curing film, and adding a layer of insulation cotton quilt or geotextile on the outside of the film; the overlap width of the curing film is greater than 20cm, and the overlap is covered with heavy objects.

8. The construction method for ultra-high performance concrete in the negative bending moment zone of a continuous beam bridge according to claim 7, characterized in that: During the UHPC curing process, ensure that the curing membrane is intact and that there are condensation droplets on the inner surface; conduct on-site inspection of the structural layer within 12 hours before the final setting of the UHPC, and immediately perform surface finishing or grouting treatment if obvious surface collapse or rebar protrusion is found. After the treatment is completed, continue to complete the curing operation according to the corresponding temperature conditions.

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