Low-cement graded micro-expansion anti-interface void bridging fly ash backfill material and construction method thereof

Abstract

The application discloses a low-cement graded micro-expansion anti-interface void bridge abutment fly ash backfill material and belongs to the technical field of road engineering and bridge abutment backfill material. In view of the problems of interface void, bridgehead bumping disease and high cement consumption commonly existing in traditional bridge abutment backfill, the application takes fly ash as a main base material, adopts low-dose cement as a cementing agent, and realizes comprehensive performance breakthrough through three core technologies of synergistic innovation. The prepared backfill material realizes high compactness, excellent anti-void and anti-cracking performance in the bridge abutment backfill area, is convenient to construct, greatly reduces cement consumption, and has remarkable environmental protection benefits and engineering economic value.

Description

Technical Field

[0001] This invention relates to the field of road engineering and bridge construction technology, and in particular to a low-cement-graded micro-expansion anti-interfacial void fly ash backfill material for bridge backfill and its construction method. Background Technology

[0002] Bridge approach slab slab is a long-standing and serious quality defect in highway and urban road engineering, significantly impacting driving safety, comfort, and pavement lifespan. It manifests directly as severe bumps caused by abrupt changes in the longitudinal profile of the road surface when vehicles pass over structures such as bridges and culverts where they meet the roadbed. This defect not only reduces the level of road service but also accelerates wear and tear on vehicle components, leading to premature damage to the bridge approach pavement and expansion joints, and significantly increasing subsequent maintenance and repair costs.

[0003] The root cause of this defect lies in the uncoordinated deformation and significant differential settlement between the rigid bridge abutment (or culvert wall) and the flexible roadbed fill. Bridge abutment structures are typically supported by deep foundations such as pile foundations and spread foundations, and their settlement after construction is minimal, essentially zero. However, the adjacent roadbed fill, mainly composed of granular materials, undergoes continuous compression, consolidation, and secondary consolidation settlement under the long-term effects of its own weight, traffic loads, and environmental factors (such as humidity changes). This discontinuous settlement at the "rigid-flexible" connection is the fundamental reason for the formation of bridge approach steps.

[0004] The backfill area behind the abutment serves as the sole mechanical transition zone connecting the abutment and the roadbed, and its material properties and construction quality are crucial for controlling differential settlement. However, the backfill materials and technologies commonly used in current engineering practice have many limitations in addressing this core issue:

[0005] 1. Inherent defects of conventional backfill materials: Traditionally, gravel, crushed stone, lime-soil, or plain soil are commonly used for backfilling. These materials are typical granular materials, and their compaction degree is highly dependent on construction machinery and processes. In the narrow and confined working space behind bridge abutments, heavy compaction equipment such as large road rollers cannot work effectively, often resulting in insufficient compaction of the backfill material in this area, with a density far lower than that of general roadbed sections, thus becoming a "weak zone" for post-construction settlement.

[0006] 2. Shrinkage and Voiding Risks of Semi-rigid Materials: To improve the strength of backfill, semi-rigid materials such as cement-stabilized crushed stone and lime-fly ash stabilized soil are often used. Although these materials have high strength, they undergo significant drying and temperature shrinkage during hardening. When this shrinkage is constrained by the rigid abutment in front, it generates enormous tensile stress within the backfill and at the backfill-abutment interface, easily leading to material cracking or detachment from the abutment back, forming "interface voids." The appearance of voids not only weakens the overall structural integrity but also provides a channel for moisture accumulation and erosion, accelerating the development of defects.

[0007] 3. Poor stiffness matching leads to stress concentration: Whether it is loose fill or homogeneous semi-rigid material, its stiffness (elastic modulus) is often uniform in space. This artificially inserts a "subbase" with a fixed stiffness value between the high-stiffness bridge abutment concrete and the low-stiffness subgrade soil. This sudden change in stiffness distribution will cause stress concentration at the two interfaces (bridge abutment-backfill, backfill-subgrade) under load, like a "mechanical step," further inducing uneven settlement and pavement damage.

[0008] 4. Environmental and economic pressures: The extensive use of cement, lime and other cementing materials not only increases project costs, but their production process is also one of the main sources of energy consumption and carbon dioxide emissions, which contradicts the current advocacy of green and low-carbon infrastructure construction.

[0009] In summary, existing technologies have improved upon existing solutions by using single micro-expansion materials or fly ash backfilling, but significant shortcomings remain: single micro-expansion materials cannot match the differences in shrinkage deformation across different areas of the abutment, making it difficult to simultaneously address interface voids and stiffness transition issues; fly ash backfilling solutions often rely on chemical activators to enhance strength, resulting in high costs and potential environmental hazards, while cement usage remains high, failing to achieve synergistic optimization of performance and environmental protection. Therefore, the development of a novel bridge abutment backfill material is required to: ① actively compensate for shrinkage and prevent interface voids; ② achieve a smooth stiffness transition and eliminate stress concentration; ③ maximize the utilization of industrial solid waste and reduce cement usage while ensuring high performance; ④ be adaptable to construction in confined spaces and easy to compact. This has significant engineering application value and practical implications. Summary of the Invention

[0010] The purpose of this invention is to overcome the defects of existing bridge backfill materials and provide a low-cement-graded, micro-expansion, anti-interfacial void fly ash bridge backfill material and its construction method. This invention solves the technical problems of traditional bridge backfill materials, such as interface voids, bridge approach slab settlement, high cement consumption, and poor environmental performance. It achieves dense filling of the bridge backfill area, resistance to interface voids, and smooth transition of stiffness, while significantly improving the utilization rate of fly ash resources and reducing engineering costs and carbon emissions.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] This invention first provides a low-cement-graded, micro-expansion, anti-interfacial void bridge backfill material made of fly ash, specifically comprising:

[0013] 1. Core components and low-cement binder system

[0014] This invention uses fly ash, a solid waste from coal-fired power plants, as the main base material, accounting for 92% to 94% of the total dry mass of the backfill material, achieving high-value utilization of bulk industrial solid waste. Ordinary silicate cement is used as the binder, with a dosage of only 6% to 8% of the total dry mass of the backfill material, far lower than the 10% to 15% cement content in traditional cement-stabilized crushed stone, significantly reducing cement consumption and carbon emissions. This low-cement system does not rely on any chemical activators; it meets the strength and stability requirements of bridge backfill solely through the synergistic effect of fly ash particle size distribution optimization and cement hydration reaction, while avoiding the environmental hazards and increased costs associated with chemical activators.

[0015] 2. Graded micro-expansion precision anti-void design

[0016] To address the differences in constraints and shrinkage deformation in different areas of bridge backfill, this invention innovatively employs a zoned micro-expansion design to precisely match the shrinkage compensation needs of different areas, thereby fundamentally suppressing interface voids.

[0017] High expansion zone near the abutment: This area is strongly constrained by the rigidity of the abutment, and the drying shrinkage deformation of the backfill material is restricted. Tensile stress is easily generated at the interface. Therefore, it is set as a high expansion zone, and the material expansion rate is controlled at 0.08%~0.1%. The moderate micro-expansion effect compensates for the volume loss caused by cement hydration and drying shrinkage, offsets the tensile stress caused by the rigidity of the abutment, and ensures that the backfill material and the abutment interface are tightly bonded without any gaps.

[0018] Low-expansion zone away from the abutment: This area connects with the flexible subgrade and has weak constraints. The shrinkage and deformation of the backfill material are not restricted. If the expansion rate is too high, it will easily lead to material cracking or subgrade heave. Therefore, it is set as a low-expansion zone, with the material expansion rate controlled at 0.03%~0.05%. It only needs to compensate for its own drying shrinkage deformation to avoid structural damage caused by excessive expansion, while ensuring the deformation coordination with the subgrade.

[0019] The expansion rate is controlled by synergistic optimization of fly ash gradation, cement admixture and moisture content, without the need for additional expansion agents. In the high expansion zone, the volume stability during cement hydration is increased by adjusting the ratio of coarse fly ash to fine fly ash, thus achieving a precise micro-expansion effect. In the low expansion zone, the expansion rate is controlled within a reasonable range by reducing the volume change of the cement hydration reaction.

[0020] 3. Enhanced performance of fly ash through grading and blending

[0021] This invention employs a graded distribution design of "coarse fly ash + fine fly ash," which significantly improves the density, strength, and volume stability of the backfill through the particle size distribution effect, achieving performance enhancement without relying on chemical activators.

[0022] Coarse fly ash: with a particle size range of 45~75μm and a mass ratio of 60%~70%, it serves as a gradation skeleton, forming a stable particle support structure and providing early strength and overall skeleton stability for the backfill.

[0023] Fine fly ash: with a particle size ≤45μm and a mass ratio of 30%~40%, fills the gaps between coarse fly ash particles, optimizes the particle size distribution curve, and significantly improves the density of the backfill. At the same time, the pozzolanic activity of fine fly ash can undergo a secondary hydration reaction with cement hydration products, further improving the later strength and impermeability of the backfill.

[0024] This graded and compatible design increases the density of backfill material by 15% to 20% compared to single-size fly ash material, and increases the 28-day compressive strength by more than 30%. It effectively solves the problems of low early strength and large performance dispersion of pure fly ash material, while providing reliable strength guarantee for low cement system.

[0025] 4. Stiffness Gradual Cooperative Anti-Bouncing Design

[0026] To address the abrupt change in stiffness between bridge abutments (high stiffness) and roadbeds (low stiffness), this invention achieves a smooth transition in backfill material stiffness from the bridge abutment side to the roadbed side through material proportioning and performance gradient design, thereby eliminating the mechanical causes of bridge approach slab settlement at the root.

[0027] The compressive strength of the material on the abutment side is controlled at 1.2~1.5MPa after 28 days. It has high stiffness, which matches the stiffness of the rigid abutment, reduces stress concentration at the interface, and ensures the bond strength with the abutment.

[0028] The compressive strength of the material at 28 days is controlled at 0.6~0.9MPa, with low stiffness, which is coordinated with the stiffness of the flexible subgrade to avoid stress concentration and post-construction settlement caused by sudden changes in stiffness.

[0029] Gradual transition zone: A gradual transition section with a width of 1-2m is set between the high expansion zone and the low expansion zone. The material strength and stiffness decrease linearly from the abutment side to the roadbed side, realizing a continuous stiffness transition from "abutment-backfill zone-roadbed". This avoids the "hard-soft" abrupt change caused by the single stiffness of traditional backfill materials, effectively reduces stress concentration under vehicle load, reduces uneven settlement after construction, and alleviates bridge approach slab settlement.

[0030] This invention also provides a construction method for a low-cement-graded, micro-expansion, anti-interfacial void bridge backfill material made of fly ash, the steps of which are as follows:

[0031] S1: Material preparation and zoned formulation: Prepare backfill materials for high expansion zone and low expansion zone according to the design ratio: Mix coarse fly ash, fine fly ash and cement evenly in proportion. For high expansion zone material, control the expansion rate to 0.08%~0.1% by adjusting the moisture content and gradation parameters; for low expansion zone material, prepare according to conventional ratio, control the expansion rate to 0.03%~0.05%, and store them separately for later use.

[0032] S2: Layered backfilling and zoned construction: Backfilling is carried out in layers from the back of the bridge abutment towards the roadbed, with each layer controlled to be 15-20cm thick.

[0033] First, backfill the high-expansion zone material immediately adjacent to the back of the abutment. The backfilling range is within 1.5 to 2 meters of the back of the abutment to ensure the micro-expansion compensation effect of the abutment side interface.

[0034] Then backfill the adjacent gradient transition zone material to achieve a smooth connection between the high expansion zone and the low expansion zone;

[0035] Finally, backfill the low-expansion zone material away from the abutment until it is flush with the top surface of the roadbed.

[0036] S3: Compaction and Vibration and Quality Control: After each layer of backfill material is laid, a plate vibrator or small compaction equipment is used for compaction and vibration to control the compaction degree to ≥93%, of which the compaction degree of high-grade highway projects is ≥95%; during the vibration process, avoid excessive vibration to prevent material segregation, and at the same time ensure that the interface of the bridge abutment is compacted to eliminate interface voids.

[0037] S4: Moisturizing and subsequent construction: After backfilling is completed, cover with geotextile or plastic film for moisturizing and curing for 7-10 days. During this period, water should be sprayed regularly to keep the backfill material moist and ensure the normal progress of cement hydration and fly ash pozzolanic reaction. Subsequent pavement structure construction can only be carried out after the material strength reaches more than 80% of the design value to avoid early load damage to the backfill.

[0038] Compared with existing technologies, the low-cement-graded micro-expansion anti-interfacial void bridge backfill material and its construction method provided by this invention have the following significant technical, engineering, environmental, and economic benefits:

[0039] 1. Addressing the root cause of interface voids and enhancing structural integrity and durability: This invention innovatively employs a graded micro-expansion design. Addressing the deformation differences between the high-constraint zone on the abutment side and the low-constraint zone on the roadbed side, it utilizes differentiated expansion rates of 0.08%~0.1% and 0.03%~0.05% respectively, upgrading the traditional "passive crack prevention" approach to an "active shrinkage resistance" material design. Through precise micro-expansion effects, it compensates for volume losses caused by cement hydration and drying shrinkage, offsetting the interfacial tensile stress resulting from the rigid constraints of the abutment. This eliminates the core cause of interface voids at the material level, ensuring a tight fit between the backfill and the abutment interface. This significantly improves the integrity and long-term durability of the abutment-backfill-roadbed structure, avoiding the risks of rainwater erosion and scouring.

[0040] 2. Achieving a smooth transition in stiffness and effectively suppressing bridge approach slab settlement: This invention employs a gradual stiffness design, causing the 28-day compressive strength of the backfill material to decrease gradually from 1.2~1.5MPa to 0.6~0.9MPa from the abutment side to the roadbed side, creating a continuous "flexible transition zone" between the rigid abutment and the flexible roadbed. This design transforms the concentrated stress at the traditional "hard-soft" abrupt interface into distributed stress, significantly reducing the magnitude of uneven settlement and the risk of slab settlement. It alleviates bridge approach slab settlement and pavement cracking from a mechanical perspective, significantly improving driving comfort and road operational safety.

[0041] 3. Achieving a balance between high performance and low consumption, resolving the contradiction between strength and shrinkage: This invention employs a fly ash grading and blending technology. Through optimized gradation of coarse fly ash (45~75μm, accounting for 60%~70%) and fine fly ash (≤45μm, accounting for 30%~40%), the physical compaction effect of particles is fully utilized. Even with only 6%~8% cement content (far lower than the 10%~15% of traditional cement-stabilized materials), the required density and strength for engineering projects can still be achieved. This solution does not rely on chemical activators. It utilizes the pozzolanic activity of fly ash to enhance later-stage strength while significantly reducing the risk of drying shrinkage through low cement content, perfectly resolving the inherent contradiction between "strength requirements and shrinkage cracking" in bridge backfill materials.

[0042] 4. Strong construction adaptability, effectively ensuring construction quality in narrow spaces: The fly ash mixture of the present invention has good workability, excellent fluidity and compactability, and is easy to spread, vibrate or operate with small compaction equipment in the narrow working space behind the bridge abutment. It solves the problems of insufficient compaction and uneven density caused by the limited working space of traditional materials, effectively ensuring the uniformity and stability of construction quality, reducing construction difficulty and post-construction settlement risks.

[0043] 5. Outstanding environmental and economic benefits, aligning with green engineering development principles: This invention uses fly ash as the main base material, facilitating the large-scale disposal of industrial solid waste from coal-fired power plants, achieving high-value resource utilization of solid waste; simultaneously, cement usage is reduced by more than 60% compared to traditional methods, significantly reducing the high energy consumption and carbon emissions associated with cement production, thus conforming to the concepts of circular economy and green sustainable development. In terms of economics, the low-cost substitution of fly ash and the substantial reduction in cement usage directly lower material procurement and construction costs, resulting in significant social and economic benefits.

[0044] 6. Synergistic Performance Optimization for Excellent Long-Term Service Performance: The synergistic effect of three core technologies—graded micro-expansion, optimized fly ash gradation, and gradual stiffness variation—enables the backfill material to possess comprehensive properties including resistance to voids, cracking, settlement, low shrinkage, and high strength, avoiding the limitations of single-technology improvements. During long-term operation, the backfill exhibits excellent volume stability and interfacial bonding performance, with bridge abutment settlement consistently controlled within 3mm, and no significant cracking, voids, or vehicle bounce. This significantly reduces subsequent maintenance costs and extends the service life of the road structure. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the longitudinal cross-sectional structure of the graded micro-expansion backfill of fly ash at the bridge back. Detailed Implementation

[0046] The present invention will be further described in detail below with reference to specific embodiments, in order to more clearly illustrate the technical solution, implementation process and beneficial effects of the present invention. This is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0047] like Figure 1 As shown, this invention provides a low-cement-graded, micro-expansion, anti-interfacial void bridge backfill material made of fly ash and its construction method, specifically providing the following three embodiments:

[0048] Example 1: Backfilling behind bridges in standard sections of conventional highways

[0049] This embodiment describes the backfill material and construction method for bridges on secondary highways and conventional municipal roads.

[0050] 1.1 Material Composition and Parameters

[0051] Raw material ratio: Class II fly ash from coal-fired power plants is used as the main base material, and the amount of ordinary silicate cement is 7% of the total dry mass of the backfill material; the fly ash is graded and matched, with coarse fly ash having a particle size of 45~75μm and accounting for 65% by mass; fine fly ash having a particle size ≤45μm and accounting for 35% by mass, and no chemical activators or external expansion agents are added.

[0052] Partition performance parameters:

[0053] Material A (high expansion zone, adjacent to the abutment): expansion rate 0.09%, 28-day compressive strength 1.3MPa, backfill width 1.8m;

[0054] Material B (gradual transition zone): expansion rate 0.05%, 28-day compressive strength 1.0 MPa, backfill width 1.2 m;

[0055] Material C (low expansion zone, near the roadbed): expansion rate 0.04%, 28-day compressive strength 0.7 MPa.

[0056] 1.2 Construction Steps

[0057] S1: Construction preparation: Clean up debris on the back of the bridge abutment and the roadbed base, level the base, and divide the boundary lines of the high expansion zone, the gradual transition zone and the low expansion zone according to the design width;

[0058] S2: Material preparation: Prepare three mixtures of materials A, B and C according to the proportions, and control the moisture content of the mixtures to 16%~18% to ensure good workability;

[0059] S3: Layered backfilling: The material is laid in layers from the abutment to the roadbed, with each layer being 18cm thick. First, material A is laid, followed by material B and then material C.

[0060] S4: Compaction and Vibration: Material A on the abutment side is compacted using an immersion vibrator, while the transition zone and low expansion zone are compacted using a small static roller, controlling the overall compaction degree to be ≥94%;

[0061] S5: Maintenance: After backfilling is completed, cover with geotextile and sprinkle with water to maintain moisture for 7 days, during which time keep the surface of the backfill moist.

[0062] 1.3 Application Effects

[0063] The interface between the bridge abutment and the backfill has no voids or shrinkage cracks, and the interface bonding strength is 35% higher than that of traditional cement-soil. The stiffness transition is smooth, and after 3 years of operation, the settlement difference of the bridge approach section is ≤2mm, with no obvious vehicle bouncing. The fly ash utilization rate reaches 93%, and the cement consumption is reduced by more than 50% compared with traditional cement-stabilized crushed stone, meeting the long-term use requirements of conventional highways.

[0064] Example 2: Backfilling behind bridges on low-grade rural roads

[0065] This embodiment describes the backfill material and construction method for rural roads and bridges with low traffic loads, emphasizing economy and ease of construction.

[0066] 2.1 Material Composition and Parameters

[0067] Raw material proportions: The cement content is 6% of the total dry mass of the backfill material; the fly ash gradation is a combination of coarse fly ash (45~75μm, accounting for 60%) and fine fly ash (≤45μm, accounting for 40%).

[0068] Partition performance parameters:

[0069] Material A (high expansion zone): expansion rate 0.08%, 28-day compressive strength 1.2 MPa, backfill width 1.5 m;

[0070] Material B (gradual transition zone): expansion rate 0.03%, 28-day compressive strength 0.9 MPa, backfill width 1.0 m;

[0071] Material C (low expansion zone): expansion rate 0.03%, 28-day compressive strength 0.6 MPa.

[0072] 2.2 Construction Steps

[0073] S1: Construction preparation: Clean the foundation behind the bridge abutment and delineate the boundaries of the backfill zones;

[0074] S2: Material preparation: Mix fly ash and cement according to the proportion, and control the moisture content of the mixture to 17%~19%;

[0075] S3: Layered backfilling: The backfill is laid in 20cm thick layers and compacted manually with a small tamping machine, with a compaction degree ≥93%;

[0076] S4: Maintenance: Cover with plastic film to maintain moisture for 10 days, and spray water regularly during this period.

[0077] 2.3 Application Effect

[0078] The material has good workability, is suitable for the narrow working space behind the bridge abutment, and is easy to construct; the interface void rate is 0, the differential settlement of the bridgehead during the operation period is stable within 2mm, and there is no obvious vehicle bouncing phenomenon; the material cost is 40% lower than that of traditional backfill materials, which is both economical and environmentally friendly, and meets the use needs of low-grade rural roads.

[0079] Example 3: Backfilling behind high-grade heavy-load highway bridges

[0080] This embodiment describes the backfill material and construction method for high-grade heavy-load traffic bridges such as expressways and first-class highways, emphasizing high strength and deformation resistance.

[0081] 3.1 Material Composition and Parameters

[0082] Raw material proportions: The cement content is 8% of the total dry mass of the backfill material; the fly ash gradation is a combination of coarse fly ash (45~75μm, accounting for 70%) and fine fly ash (≤45μm, accounting for 30%).

[0083] Partition performance parameters:

[0084] Material A (high expansion zone): expansion rate 0.10%, 28-day compressive strength 1.5MPa, backfill width 2.0m;

[0085] Material B (gradual transition zone): expansion rate 0.08%, 28-day compressive strength 1.2 MPa, backfill width 1.5 m;

[0086] Material C (low expansion zone): expansion rate 0.05%, 28-day compressive strength 0.9 MPa.

[0087] 3.2 Construction Steps

[0088] S1: Construction preparation: The foundation behind the bridge abutment is compacted, and the boundaries of the zones are accurately divided according to the design width.

[0089] S2: Material preparation: Prepare three mixtures according to the formula, and strictly control the moisture content error within ±1%;

[0090] S3: Layered backfilling: The layered paving is 15cm thick and compacted using heavy-duty small compaction equipment with a compaction degree of ≥96%, ensuring that there are no hard boundaries between each zone.

[0091] S4: Maintenance: Moisturize and maintain for 7 days. After the material strength reaches more than 80% of the design value, proceed with the subsequent pavement structure construction.

[0092] 3.3 Application Effects

[0093] The backfill material has high strength, strong resistance to deformation and erosion, and the differential settlement at the bridgehead is ≤2mm during long-term operation. There are no interface voids, road surface cracking, or vehicle bouncing. The fly ash resource utilization rate reaches 95%, and the cement consumption is reduced by more than 60% compared with the traditional solution, meeting the durability requirements of high-grade heavy-load highways.

[0094] Example 4: Backfilling with traditional cement-stabilized crushed stone (comparative case)

[0095] This comparative case uses the currently common homogeneous cement-stabilized crushed stone backfilling process in engineering. The construction site, bridge specifications, geological conditions, construction environment, and maintenance cycle are completely consistent with the above three sets of examples, and are used to intuitively compare the comprehensive advantages of the present invention.

[0096] 4.1 Material Composition and Parameters

[0097] Raw material proportions: 5~31.5mm continuously graded crushed stone is used as the main material, accounting for 95% of the total dry mass; P・O 42.5 ordinary Portland cement is added at 5%; a single homogeneous proportion is adopted throughout the process, without fly ash admixture, particle grading, zoning design, gradient expansion and stiffness control.

[0098] Overall performance parameters: uniform expansion rate across the entire region 0.01%~0.02%, 28-day compressive strength 1.8~2.0MPa, design compaction degree ≥95%.

[0099] 4.2 Construction Steps

[0100] S1: Construction preparation: Clean up debris on the back of the bridge abutment and the roadbed base and level it. The entire site is not divided into functional zones and the construction is carried out in a unified manner.

[0101] S2: Material preparation: Cement-stabilized crushed stone mixture is mixed centrally on site, and the moisture content of the mixture is controlled at 14%~16%;

[0102] S3: Layered backfilling: The entire site is laid in uniform layers, with a single layer thickness of 15~20cm. Due to the narrow space behind the bridge abutment, only small compaction equipment is used for the operation.

[0103] S4: Compaction and Vibration: Uniform compaction throughout the entire area, with a design compaction degree of ≥93%~95%. It is difficult to compact the corners and edges of bridge abutments.

[0104] S5: Maintenance: After backfilling, cover with geotextile and sprinkle with water to keep it moist for 7-10 days. After maintenance, carry out subsequent road construction.

[0105] 4.3 Application Effects

[0106] After the material hardens, drying shrinkage is significant, and multiple micro-cracks appear at the interface between the abutment and the backfill, with local interface voids, the void rate being approximately 8% to 12%. The stiffness of the backfill is uniform throughout, with a significant abrupt change in stiffness between the rigid abutment, homogeneous backfill, and flexible subgrade, resulting in prominent stress concentration issues. Three years after commissioning, the differential settlement at the bridgehead reaches 6 to 8 mm, causing a strong sense of bumpiness during driving and significant bridgehead slab ...

[0107] The above three embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. In actual engineering applications, the cement content and fly ash gradation of each layer can be appropriately adjusted according to the actual conditions such as bridge abutment depth, soil conditions, and types of defects, within the scope defined by the claims of the present invention, and all such adjustments fall within the protection scope of the present invention.

Claims

1. A low-cement-graded, micro-expansion, anti-interfacial void bridge backfill material made of fly ash, characterized in that, Using fly ash as the main base material and low-dose cement as the binder, the design achieves dense filling of the bridge abutment backfill area, interface anti-void and smooth stiffness transition through the synergistic effect of graded micro-expansion design, graded fly ash compatibility and stiffness gradient design.

2. The low-cement-graded, micro-expansion, anti-interfacial void bridge backfill material for fly ash as described in claim 1, characterized in that, The graded micro-expansion design is as follows: a high expansion zone is formed in the backfill area near the abutment side, with an expansion rate of 0.08%~0.1%; and a low expansion zone is formed in the backfill area away from the abutment side, with an expansion rate of 0.03%~0.05%.

3. The low-cement-graded, micro-expansion, anti-interfacial void bridge backfill material for fly ash as described in claim 2, characterized in that, The fly ash grading and blending method is as follows: coarse fly ash and fine fly ash are used for grading, wherein the particle size of the coarse fly ash is 45~75μm and the mass ratio is 60%~70%; the particle size of the fine fly ash is ≤45μm and the mass ratio is 30%~40%.

4. The low-cement-graded, micro-expansion, anti-interfacial void bridge backfill material for fly ash as described in claim 3, characterized in that, The amount of low-dose cement used accounts for 6% to 8% of the total dry mass of the backfill material.

5. The low-cement-graded, micro-expansion, anti-interfacial void bridge backfill material for fly ash as described in claim 4, characterized in that, The stiffness gradient design is as follows: the compressive strength of the backfill material after curing decreases in a gradient from the abutment side to the roadbed side, wherein the 28-day compressive strength of the abutment side area is 1.2~1.5MPa, and the 28-day compressive strength of the roadbed side area is 0.6~0.9MPa.

6. The low-cement-graded, micro-expansion, anti-interfacial void bridge backfill material for fly ash as described in claim 5, characterized in that, The gradation of coarse and fine fly ash, together with the low dosage of 6% to 8% cement, produces a particle gradation effect, thereby improving the overall density and early strength of the backfill material.

7. A construction method for a low-cement-graded, micro-expansion, anti-interfacial delamination bridge backfill material with fly ash as described in any one of claims 1-6, characterized in that, Includes the following steps: S1: Based on the graded micro-expansion design, materials suitable for the high expansion region and low expansion region are formulated separately; S2: Backfill in layers from the back of the bridge abutment towards the roadbed, first backfilling the high expansion zone material, and then backfilling the adjacent low expansion zone material; S3: Compact or vibrate each layer of backfill material; S4: After backfilling is completed, perform moisturizing and maintenance.

8. The construction method of a low-cement graded micro-expansion anti-interfacial void bridge backfill material according to claim 7, characterized in that, In step S2, the backfilling range of the high expansion zone material is the area immediately adjacent to the back of the bridge abutment, and the backfilling interface between the high expansion zone material and the low expansion zone material is a gradual transition interface.

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