Asphalt Concrete Facing Technology for Seepage Control in Hydraulic Engineering: A Comprehensive Technical Guide

I. Introduction

1.1 Technical Definition and Principles

Asphalt concrete facing technology is a sophisticated engineering solution for seepage control in hydraulic structures, particularly in dams and reservoirs. This technique involves the use of asphalt concrete - a composite material comprising asphalt binder, aggregates, fillers, and optional additives - to create impermeable barriers that prevent water seepage while accommodating structural deformations (1).

The fundamental principle behind asphalt concrete facing is the formation of a continuous, dense impermeable layer through the cohesive properties of asphalt. When properly designed and installed, asphalt concrete forms a flexible membrane that effectively blocks water pathways while maintaining its integrity under varying environmental conditions and structural movements .

1.2 Technical Advantages

Asphalt concrete facing offers several distinct advantages over traditional seepage control methods:

Exceptional Waterproofing Performance: When the air void content is controlled below 3%, asphalt concrete becomes nearly impermeable, with permeability coefficients as low as 10⁻⁷ cm/s or even lower, providing excellent resistance to water penetration .

Superior Deformation Adaptability: Unlike rigid materials such as concrete, asphalt concrete exhibits remarkable flexibility and ductility, allowing it to accommodate differential settlements and structural movements without developing cracks. Even when cracks do form, asphalt concrete demonstrates a degree of self-healing capacity .

Enhanced Frost Resistance: Asphalt concrete maintains its flexibility at low temperatures, making it highly resistant to freeze-thaw cycles and frost heave damage. This characteristic makes it particularly suitable for use in cold regions .

Construction Convenience: The construction process for asphalt concrete facing is highly mechanized, allowing for rapid installation with minimal weather-related delays. It can be placed in conditions where other materials might be problematic, including moderately cold and damp environments (7).

Ease of Maintenance and Repair: Damaged areas of asphalt concrete facing can be efficiently repaired using hot patching techniques, leveraging the thermoplastic properties of asphalt to create seamless repairs (7).

Jointless Construction: Unlike concrete structures that require expansion joints, asphalt concrete can be placed as a continuous monolithic layer, eliminating potential leakage paths associated with joints and connections .

1.3 Scope of Application and Conditions

Asphalt concrete facing technology finds application in various hydraulic engineering structures:

Face Rockfill Dams: As upstream impermeable barriers in rockfill dams, particularly where local impermeable materials are scarce .

Reservoir Basins: For lining entire or partial reservoir basins, especially in pumped storage power stations where impermeability is critical (1).

Concrete Dam Rehabilitation: As retrofitting solutions for aging concrete dams suffering from seepage issues, as demonstrated in projects like the Daxi Reservoir, Beida River Reservoir, and Longwangtang Reservoir in China .

Channel Lining: For preventing seepage in irrigation and drainage channels, particularly in regions prone to frost damage .

The application of asphalt concrete facing is subject to specific conditions:

Temperature Requirements: Optimal construction temperatures are above 5°C. Specialized measures may be required for construction in lower temperatures .
Weather Conditions: While asphalt concrete can be placed in most weather conditions, heavy rain may affect the quality of the final product .
Geological Conditions: It is particularly suitable for use in areas with weak soil layers, permafrost, seismic zones, and deep overburden layers where traditional impermeable materials may perform poorly .

II. Material Composition and Technical Requirements

2.1 Raw Material Selection and Specifications

The performance of asphalt concrete facing is heavily dependent on the quality and compatibility of its constituent materials.

2.1.1 Asphalt Binders

Asphalt is the key binding component in asphalt concrete, directly influencing its waterproofing properties, flexibility, and durability. Hydraulic engineering applications typically use petroleum-based asphalt, with modified asphalts increasingly being employed for enhanced performance .

Key Technical Specifications for Petroleum Asphalt:

Penetration: A measure of asphalt hardness, typically in the range of 60-80 for hydraulic applications, indicating suitable workability and hardness .
Ductility: Reflects the extensibility of asphalt, with values typically exceeding 100 cm to ensure adequate deformation capacity .
Softening Point: Indicates the temperature sensitivity of the asphalt, generally required to be not less than 45°C to prevent excessive softening at elevated temperatures .
Flash Point: Minimum temperature at which asphalt vapors ignite, an important safety parameter that should be greater than 230°C .

Modified Asphalts: These are produced by adding polymers such as SBS (styrene-butadiene-styrene), SBR (styrene-butadiene rubber), or EVA (ethylene-vinyl acetate) to conventional asphalt to improve specific properties. SBS-modified asphalt is particularly popular for its ability to enhance low-temperature crack resistance and thermal stability .

Emulsified Asphalt: Used primarily for sealing coats and bonding layers, cationic emulsified asphalt is typically specified for these applications .

2.1.2 Aggregates

Aggregates form the skeleton structure of asphalt concrete, accounting for approximately 80% of its mass. They are classified into coarse aggregates, fine aggregates, and fillers based on particle size .

Coarse Aggregates (particle size >2.36mm): These should be hard, fresh, free from harmful impurities, and exhibit good adhesion to asphalt. The maximum size of coarse aggregates for impermeable asphalt concrete should not exceed one-third of the compacted layer thickness and should not exceed 25mm .

Key Specifications for Coarse Aggregates:

Apparent density: ≥2.6 g/cm³
Asphalt adhesion (boiling water method): ≥Grade 4
Flaky and elongated particle content: ≤25%
Crushing value: ≤30%
Water absorption: ≤2%
Clay content: ≤0.5%

Fine Aggregates (particle size 2.36-0.075mm): These can be manufactured sand, natural sand, or crushed stone fines. They should be hard, well-graded, and free from clay and organic impurities .

Key Specifications for Fine Aggregates:

Apparent density: ≥2.5 g/cm³
Water stability grade: ≥Grade 6
Durability (sodium sulfate dry-wet cycle 5 times mass loss): ≤15%
Organic matter and clay content: ≤2%

Fillers (particle size <0.075mm): These mineral powders fill voids between aggregates, improving the density and impermeability of asphalt concrete. Common fillers include limestone powder, dolomite powder, cement, hydrated lime, and fly ash .

Key Specifications for Fillers:

Apparent density: ≥2.5 g/cm³
Hydrophilic coefficient: ≤1.0
Moisture content: ≤0.5%
Particles <0.075mm: ≥85%

2.1.3 Additives and Reinforcing Materials

Various additives may be incorporated into asphalt concrete to enhance specific properties:

Anti-stripping Agents: These improve the adhesion between acidic aggregates and asphalt, typically added at 1.5-2% by mass of the asphalt (6).

Reinforcing Meshes: Polyester-based grids embedded within asphalt concrete facings to enhance crack resistance and deformation adaptability .

2.2 Mix Design and Technical Requirements

The mix design of asphalt concrete facing is a critical process that directly affects its performance. Mix design should be based on specific project requirements and established through comprehensive testing.

2.2.1 Mix Design Principles

Asphalt concrete mix design should adhere to the following principles:

Impermeability Principle: Ensure that the air void content does not exceed 3% and the permeability coefficient is not greater than 1×10⁻⁶ cm/s .
Stability Principle: The mix should exhibit adequate thermal and water stability to resist high-temperature flow and water damage .
Workability Principle: The mix should be easy to place and compact under the specific conditions of the project .
Economic Principle: Optimize material usage to reduce costs while meeting technical requirements .

2.2.2 Technical Requirements for Different Asphalt Concrete Layers

Asphalt concrete facing typically consists of multiple layers, each with specific technical requirements:

Impermeable Layer Asphalt Concrete:

Air void content: ≤3%
Permeability coefficient: ≤1×10⁻⁶ cm/s
Water stability coefficient: ≥0.9
Marshall specimen slope flow value: ≤0.8mm
Asphalt content: 6.5%-8.5%
Maximum coarse aggregate size: ≤16mm

Leveling and Bonding Layer Asphalt Concrete:

Air void content: 10%-15%
Thermal stability coefficient: ≤4.5
Water stability coefficient: ≥0.85
Asphalt content: 3.5%-5.0%
Maximum coarse aggregate size: ≤19mm

Sealing Layer Materials:

Typically asphalt mastic or modified asphalt mastic
Thickness: 1-2mm
Should bond firmly to the impermeable layer, resisting flow at high temperatures and cracking at low temperatures

Drainage Layer Asphalt Concrete (for composite section designs):

Permeability coefficient: ≥1×10⁻² cm/s
Thermal stability coefficient: ≤4.5
Water stability coefficient: ≥0.85
Asphalt content: 3.0%-4.0%
Maximum coarse aggregate size: ≤26.5mm

2.2.3 Mix Design Methods

The mix design process typically follows these steps:

Aggregate Gradation Design: This can be calculated using empirical formulas such as the Ding Purong formula or other established methods .
Determination of Optimal Asphalt Content: Through Marshall testing to establish the appropriate range of asphalt content .
Performance Verification: Testing the designed mix for impermeability, stability, low-temperature performance, and other relevant properties to ensure it meets technical requirements .
Field Trials: Conducting on-site paving and compaction trials to adjust mix proportions and construction parameters .

The Ding Purong formula for aggregate gradation is:

P_i = \left(\frac{d_i}{D}\right)^n \times 100\%

Where:

P_i is the passing percentage for sieve size d_i
D is the maximum aggregate size
n is the gradation index, typically ranging between 0.3-0.5

III. Structural Design and Construction Details

3.1 Structural Types and Layout of Facing

The structural design of asphalt concrete facing can be categorized into simple section and composite section types based on project requirements and geological conditions.

3.1.1 Simple Section Structure

The simple section is the most commonly used structural form for asphalt concrete facing, consisting of three layers from top to bottom:

Sealing Layer: The topmost layer, primarily functioning to close surface voids and 延缓沥青老化. It is typically made of asphalt mastic or modified asphalt mastic with a thickness of 1-2mm .

Impermeable Layer: The core structural component providing primary waterproofing. Dense-graded asphalt concrete is used here, with a thickness typically ranging between 6-10cm .

Leveling and Bonding Layer: Located between the impermeable layer and the cushion layer, this layer functions to level the surface of the cushion layer and enhance bonding with the impermeable layer. Open-graded asphalt concrete is used, with a thickness typically between 5-10cm .

Cushion Layer: Placed between the asphalt concrete facing and the embankment body, this layer provides a level foundation, drainage, and support for the facing. Graded crushed stone or gravel is typically used, with a thickness of 50-100cm .

3.1.2 Composite Section Structure

Composite sections are primarily used for projects with special impermeability requirements, consisting of the following layers from top to bottom:

Sealing Layer: Same as in the simple section design .

Upper Impermeable Layer: Functions as the primary waterproofing barrier .

Drainage Layer: Located between the upper and lower impermeable layers, this layer is constructed using open-graded asphalt concrete to drain any infiltrating water. Thickness typically ranges between 6-10cm .

Lower Impermeable Layer: Located below the drainage layer, this can be combined with the leveling and bonding layer, with a thickness of 5-8cm .

3.1.3 Layout Requirements for Facing

The layout of asphalt concrete facing should adhere to the following principles:

Planar Layout: The facing should be laid out smoothly and straight without abrupt slope changes. Where slope changes are necessary, they should be transitioned with smooth curves rather than abrupt angles. The radius of curvature in curved sections should satisfy both stress-strain requirements and paver operational needs .
Slope Ratio: The slope ratio of asphalt concrete facing should not be steeper than 1:1.7 to ensure construction safety and facing stability .
Zoning: The drainage layer should be divided into separate water-blocking zones along the dam axis to facilitate zonal seepage observation. The spacing between these zones should typically be 20-100m, with each zone being 1-3m wide .
Cooling Facilities: To prevent flow deformation of the asphalt concrete due to high temperatures, cooling facilities should be provided. These can include spraying light-colored coatings on the facing surface or installing sprinkler systems at the dam crest .

3.2 Connection Design with Other Structures

The connections between asphalt concrete facing and foundations, abutments, and other structures are critical weak points in the seepage control system and require special attention in design.

3.2.1 Foundation Connection Design

The connection between asphalt concrete facing and foundation is typically achieved through a concrete plinth.

Concrete Plinth Design Requirements:

Plinth width should satisfy impermeability requirements, typically not less than 1.0m
Concrete strength grade should be at least C20
The plinth should be anchored to the foundation using anchor bars
The surface of the plinth should be roughened and coated with emulsified asphalt or diluted asphalt

A sand-asphalt mastic transition layer with a thickness of 1-2cm should be placed between the asphalt concrete facing and the foundation to enhance the impermeability of the connection .

3.2.2 Abutment Connection Design

The connection between asphalt concrete facing and abutments should ensure continuity of impermeability and adaptability to deformation.

Abutment Treatment Requirements:

Abutment slope ratio should be gentler than 1:0.35
Abutment surfaces should be smooth without sharp protrusions
Abutments should undergo impermeability treatment, which can include concrete or shotcrete
A sand-asphalt mastic transition layer should be placed between the asphalt concrete facing and the abutment

For high dams or areas with significant potential for abutment deformation, reinforcing meshes can be placed at the connection to improve deformation adaptability .

3.2.3 Connection with Rigid Structures

The connection between asphalt concrete facing and rigid structures (such as spillways, intake towers, etc.) should account for differential deformation between the structures.

Connection Design Key Points:

A deformation joint with a width of 2-3cm should be provided at the connection
The joint should be filled with elastic materials such as SR plastic waterstop material
Additional impermeable cover plates can be installed at the connection to enhance waterproofing
Surfaces of rigid structures should be coated with emulsified asphalt or diluted asphalt to improve bonding with asphalt concrete

3.3 Safety Monitoring Design

Asphalt concrete facing should be equipped with a comprehensive safety monitoring system to continuously monitor its working condition and promptly identify and address any issues.

3.3.1 Monitoring Items and Layout

The monitoring system for asphalt concrete facing primarily includes deformation monitoring, seepage monitoring, and temperature monitoring.

Deformation Monitoring:

Horizontal and vertical displacement monitoring of the facing, which can be achieved using tension wires, plumb lines, etc.
Deflection monitoring of the facing, which can be achieved using multi-point displacement meters
Displacement monitoring at joints between the facing and abutments or rigid structures, which can be achieved using joint meters

Seepage Monitoring:

Monitoring of seepage pressure behind the facing using piezometers
Monitoring of seepage pressure at the connection between the facing and concrete structures
Monitoring of seepage flow in the drainage layer using weirs

Temperature Monitoring:

Surface temperature monitoring of the facing
Internal temperature monitoring of the facing using thermometers
Monitoring of solar radiation heat using pyranometers

3.3.2 Selection and Installation of Monitoring Instruments

The selection and installation of monitoring instruments for asphalt concrete facing should consider the following factors:

High Temperature Resistance: Instruments should be able to withstand the high temperatures (150-170°C) encountered during asphalt concrete placement .
Adaptability: Instruments should be compatible with the deformation characteristics of asphalt concrete without compromising the integrity of the facing .
Reliability: Instruments should exhibit good long-term stability and reliability .

Instrument Installation Key Points:

Instruments should be installed in place before asphalt concrete placement
Instrument leads should be properly protected to avoid damage during construction
The area around instruments should be backfilled with fine-graded asphalt concrete and compacted thoroughly
After installation, instruments should be inspected and calibrated

IV. Construction Technology and Quality Control

4.1 Pre-construction Preparations

Pre-construction preparation work is fundamental to ensuring the quality of asphalt concrete facing construction.

4.1.1 Material Preparation and Inspection

All raw materials should undergo strict inspection to ensure they meet design requirements before construction.

Asphalt Material Inspection:

Inspection items: penetration, ductility, softening point, flash point, etc.
Inspection frequency: once per batch of incoming materials
Storage requirements: Asphalt should be stored in dedicated tanks with temperature controlled between 130-150°C. Prolonged high-temperature heating should be avoided .

Aggregate Inspection:

Inspection items: particle size distribution, apparent density, clay content, flaky and elongated particle content, etc.
Inspection frequency: once every 500-1000m³
Storage requirements: Aggregates should be stacked by size category with a cushion layer at the bottom to prevent contamination and mixing .

Filler Inspection:

Inspection items: particle size distribution, hydrophilic coefficient, moisture content, etc.
Inspection frequency: once every 200-300t
Storage requirements: Fillers should be stored in dry, ventilated warehouses to avoid moisture absorption and caking .

4.1.2 Construction Equipment Preparation

Asphalt concrete facing construction requires specialized machinery and equipment, which should be appropriately configured based on project scale and construction conditions.

Major Construction Equipment:

Asphalt concrete mixing plant: including asphalt heating equipment, aggregate heating equipment, mixer, etc.
Transportation equipment: dump trucks, insulated tank trucks, etc.
Paving equipment: inclined pavers, core wall pavers, etc.
Compaction equipment: vibratory rollers, steel wheel rollers, rubber tire rollers, etc.
Auxiliary equipment: loaders, cranes, water sprayers, etc.

Equipment Debugging and Inspection:

After installation, equipment should undergo debugging and trial operation
Check whether equipment performance meets construction requirements
Calibrate measuring equipment to ensure accurate batching
Inspect heating systems and temperature control systems for proper operation

4.1.3 Construction Plan Development

A detailed construction plan should be prepared before construction, specifying construction techniques, quality standards, and safety measures.

Contents of Construction Plan:

Project overview and construction condition analysis
Overall construction layout and progress schedule
Construction techniques and technical requirements
Quality control and inspection standards
Safety 保障 measures
Emergency response plans

4.2 Asphalt Concrete Preparation and Transportation

The preparation and transportation of asphalt concrete are critical steps that directly affect construction quality.

4.2.1 Asphalt Concrete Mixing

Asphalt concrete mixing should be carried out in specialized mixing plants to ensure mixing quality and efficiency.

Mixing Plant Layout Requirements:

The mixing plant should be located close to the construction site to reduce transportation distance
The site should be level, hardened, and well-drained
Raw material stacking areas, mixing areas, and finished product storage areas should be reasonably planned
Wind and rain protection facilities should be provided to prevent material contamination and moisture

Mixing Process Control:

Aggregate heating temperature: 170-190°C
Asphalt heating temperature: 150-170°C
Mixing temperature: 150-160°C
Mixing time: dry mixing time should be at least 30 seconds, total mixing time should be at least 90 seconds
Mixing sequence: Aggregates and fillers are first dry mixed, then asphalt is added for wet mixing

Mixing Quality Control:

Cold material flow calibration should be performed before each day's production
Raw material temperatures and mixing temperatures should be checked every work shift
Marshall tests should be conducted on samples taken every 50-100m³ of asphalt concrete
During mixing, the workability of the asphalt concrete should be observed, and mix proportions adjusted as necessary

4.2.2 Asphalt Concrete Transportation

During transportation, attention should be paid to heat preservation, pollution prevention, and segregation prevention.

Transport Vehicle Requirements:

Specialized dump trucks or insulated tank trucks should be used for transportation
Truck beds should be clean and free of debris, and coated with anti-sticking agent
Truck beds should be covered with tarpaulins to reduce heat loss and pollution

Transportation Process Control:

Transportation time should be controlled within 30 minutes, and no more than 60 minutes in summer
Sudden braking and 颠簸 should be avoided during transportation to reduce segregation
Before unloading, the temperature of the asphalt concrete should be checked; any concrete with a temperature below 130°C should not be used
Temperature detection and visual inspection should be carried out for each truckload of asphalt concrete

4.3 Facing Placement and Compaction Technology

The placement and compaction of asphalt concrete facing are the core processes of construction, directly affecting the impermeability and mechanical properties of the facing.

4.3.1 Pre-placement Preparations

Before placement, the underlying layer should be inspected and treated to ensure it meets requirements.

Underlying Layer Inspection:

Check the flatness of the cushion layer surface, with allowable error not exceeding 5cm/2m
Check the compaction degree of the cushion layer to ensure it meets design requirements
Remove debris and dust from the cushion layer surface

Tack Coat Application:

Before placement, emulsified asphalt or diluted asphalt should be sprayed on the cushion layer surface
Application rate should be 0.5-2.0kg/m²
Application should be uniform, with no missed areas or accumulations
After the tack coat has dried, asphalt concrete placement should begin immediately to avoid contamination

4.3.2 Facing Placement Technology

The placement method for asphalt concrete facing should be selected based on the structure of the facing and construction conditions.

Placement Equipment Selection:

Inclined pavers are suitable for sloped surfaces
Bridge pavers can be used for large-area placement
Specialized core wall pavers are suitable for core wall construction

Placement Parameter Control:

Placement temperature: not less than 140°C, and increased to 150-160°C in low-temperature environments
Placement speed: should be controlled between 1-3m/min
Placement thickness: impermeable layer should be 6-10cm, leveling and bonding layer should be 5-10cm
Placement width: should be determined based on paver performance and construction conditions, typically 3-6m

Placement Quality Control:

During placement, continuity and uniformity should be maintained, avoiding stops and sudden speed changes
Placement thickness should be controlled to ensure uniformity, avoiding excessive thickness variation
Segregation, heaving, and other issues occurring during placement should be promptly addressed
Specialized personnel should be assigned to inspect placement quality during construction and adjust parameters as necessary

4.3.3 Facing Compaction Technology

Compaction is a critical process to ensure the density and impermeability of asphalt concrete facing, requiring strict control of compaction technology and parameters.

Compaction Equipment Selection:

Initial compaction should use steel wheel rollers with a weight of 6-8t
Secondary compaction should use vibratory rollers with a weight of 10-15t
Final compaction should use rubber tire rollers with a weight of 15-20t

Compaction Parameter Control:

Compaction temperature: normal compaction temperature is 130-150°C, and should not be lower than 120°C in low-temperature environments
Compaction speed: initial compaction should be 2-3km/h, secondary compaction 3-4km/h, and final compaction 2-3km/h
Number of passes: initial compaction 2 passes, secondary compaction 6-8 passes, final compaction 2-4 passes
Compaction sequence: should proceed from bottom to top, starting with static compaction before vibratory compaction, and slow speed before fast speed

Compaction Quality Control:

During compaction, roller tracks should overlap to avoid missed areas
Compaction temperature should be controlled to avoid excessive temperatures leading to asphalt aging or insufficient temperatures making compaction difficult
The deformation of asphalt concrete during compaction should be observed, and compaction parameters adjusted as necessary
After compaction, the surface flatness and density should be inspected, with additional compaction performed if necessary

4.4 Joint Treatment and Sealing Layer Construction

Joints are weak points in asphalt concrete facing and require careful treatment to ensure impermeability. Sealing layer construction is the final process in facing construction, directly affecting the durability of the facing.

4.4.1 Joint Treatment Technology

Joints in asphalt concrete facing include longitudinal joints and transverse joints, which require different treatment methods.

Longitudinal Joint Treatment:

Longitudinal joints between adjacent placement strips should be staggered by 30-50cm
Joint surfaces should be coated with emulsified asphalt or diluted asphalt
Compaction should first be carried out along the joint edge, followed by full compaction
During compaction, most of the roller's weight should be on the already compacted side, with only 10-20cm extending onto the newly placed layer

Transverse Joint Treatment:

Transverse joints should adopt flat or beveled joint forms
Irregular portions at joints should be cut away to form a vertical joint surface
Joint surfaces should be coated with emulsified asphalt or diluted asphalt
Newly placed asphalt concrete should overlap the already placed portion by 5-10cm, with the overlapping portion removed before compaction

Interlayer Treatment:

Joints between upper and lower layers should be staggered by at least 50cm
Emulsified asphalt or diluted asphalt should be sprayed between layers at a rate of 0.3-0.5kg/m²
The time interval between layers should be controlled to avoid poor bonding between layers

4.4.2 Sealing Layer Construction Technology

The sealing layer is a protective layer for asphalt concrete facing, primarily functioning to close surface voids and 延缓沥青老化.

Sealing Layer Material Selection:

Asphalt mastic, modified asphalt mastic, or other waterproof materials can be used
Materials should bond firmly to the impermeable layer surface, resisting flow at high temperatures and cracking at low temperatures
Materials should have good aging resistance and weather resistance

Sealing Layer Construction Key Points:

Before construction, dust and debris on the impermeable layer surface should be removed
Sealing layer material temperature should be controlled between 180-200°C
Brushing or spraying techniques can be used for construction, with a thickness of 1-2mm
Construction should be uniform, with no missed areas, flow, or accumulation
After construction, protection measures should be implemented to avoid contamination and damage

4.5 Low-temperature Construction and Quality Control Measures

Asphalt concrete facing construction in low-temperature environments presents significant challenges and requires special construction techniques and quality control measures.

4.5.1 Low-temperature Construction Conditions

Low-temperature construction refers to asphalt concrete facing construction carried out under environmental temperatures below 5°C or when the average daily temperature is below 10°C.

Low-temperature Construction Restrictions:

When the average daily temperature is below 5°C, asphalt concrete facing construction should generally not be carried out
When the environmental temperature is below 0°C, asphalt concrete facing construction should not be carried out
When wind force exceeds level 5, asphalt concrete facing construction should generally not be carried out

4.5.2 Low-temperature Construction Techniques

In low-temperature environments, construction techniques should be appropriately adjusted to ensure the quality of asphalt concrete facing.

Raw Material Preheating:

Aggregate preheating temperature should be increased to 180-200°C
Asphalt heating temperature should be increased to 160-180°C
Fillers can be preheated using indirect heating methods, with temperature not exceeding 100°C

Mixing Technique Adjustments:

Mixing temperature should be increased to 160-170°C
Mixing time should be extended by 10-20 seconds
Asphalt content should be increased by 0.3-0.5% to improve workability

Transportation and Placement:

Transportation vehicles should be equipped with enhanced thermal insulation measures, which can include double-layer tarpaulin covers
After unloading, placement should be carried out promptly to reduce heat loss
Placement temperature should be increased to 150-160°C
Placement speed should be appropriately reduced, controlled between 1-2m/min

Compaction Technique Adjustments:

Initial compaction temperature should not be lower than 140°C, and final compaction temperature should not be lower than 90°C
The number of compaction passes should be increased: initial compaction 2-3 passes, secondary compaction 8-10 passes, final compaction 2-4 passes
High-frequency, low-amplitude vibratory compaction can be used to improve compaction efficiency
Compaction should closely follow placement to shorten the compaction time

4.5.3 Winter Protection Measures

For asphalt concrete facing projects that span multiple years, winter protection measures should be implemented to prevent frost damage.

Winter Protection Methods:

Before winter shutdown, the facing surface should be cleaned of snow and ice
Thermal insulation materials such as rock wool blankets or straw curtains can be placed on the facing surface
Wind barriers can be installed around the facing to reduce direct exposure to cold winds
After spring arrives, the protective coverings should be promptly removed and the facing surface inspected

4.6 Construction Quality Inspection and Acceptance Standards

Strict quality inspection should be carried out throughout the construction process to ensure that all indicators meet design requirements.

4.6.1 Raw Material Inspection

Raw material inspection is the foundation of quality control and should be carried out strictly according to standards.

Asphalt Material Inspection:

Penetration: tested once per batch
Ductility: tested once per batch
Softening point: tested once per batch
Flash point: tested once per batch
Wax content: tested for important projects, optional for general projects

Aggregate Inspection:

Particle size distribution: tested once every 500-1000m³
Apparent density: tested once every 1000-2000m³
Flaky and elongated particle content: tested once every 500-1000m³
Crushing value: tested for important projects, optional for general projects

Filler Inspection:

Particle size distribution: tested once every 200-300t
Hydrophilic coefficient: tested once every 200-300t
Moisture content: tested once every 200-300t

4.6.2 Asphalt Concrete Performance Inspection

Asphalt concrete performance inspection is the key to ensuring facing quality and should be carried out strictly according to standards.

Mixing Quality Inspection:

Temperature: tested for each truckload, ensuring it meets requirements
Appearance: inspected for each truckload, ensuring uniformity without streaking or segregation
Marshall test: samples taken every 50-100m³ for testing stability, flow value, air void content, and other indicators

On-site Quality Inspection:

Compaction degree: tested using nuclear densitometers or core sampling, with one test point every 200-500m²
Air void content: tested through core sampling and laboratory testing, with one test point every 500-1000m²
Permeability coefficient: field permeability tests should be carried out for important projects, optional for general projects
Flatness: inspected using a 2m straightedge, with allowable error not exceeding 15mm

4.6.3 Acceptance Standards

After completion of asphalt concrete facing construction, acceptance should be carried out according to the following standards.

Appearance Quality Standards:

Surface should be smooth and dense, free from cracks, bulges, looseness, and other defects
Joints should be smooth, without obvious steps or segregation
Sealing layer should be uniform, without missed areas, flow, or accumulation

Internal Quality Standards:

Air void content: impermeable layer should not exceed 3%
Permeability coefficient: should not exceed 1×10⁻⁶ cm/s
Water stability coefficient: should not be less than 0.9
Slope flow value: should not exceed 0.8mm
Compressive strength: should not be less than 3.5MPa
Tensile strength: should not be less than 0.6MPa

V. Engineering Application Case Studies

5.1 Domestic Typical Application Cases

Asphalt concrete facing technology has been widely used in domestic hydraulic engineering projects. Here are some representative cases.

5.1.1 Tianhuangping Pumped Storage Power Station Upper Reservoir Asphalt Concrete Facing Project

The Tianhuangping Pumped Storage Power Station was one of the earliest large-scale hydraulic projects in China to adopt asphalt concrete facing technology. Its successful experience has important reference value for subsequent projects.

Project Overview:

The upper reservoir asphalt concrete facing had a total impermeable area of approximately 1.662 million m² and a total construction volume of about 40,000 m³
The facing adopted a simple section structure, consisting from top to bottom of a 2mm asphalt mastic sealing layer, an 8cm impermeable layer, and a 6cm leveling and bonding layer
The impermeable layer used dense-graded asphalt concrete with an asphalt content of 7.5% and air void content controlled below 2%
The leveling and bonding layer used open-graded asphalt concrete with an asphalt content of 4.5%

Construction Characteristics:

Inclined pavers were used for placement, improving construction efficiency
An innovative construction sequence of "first compacting transition material, then compacting the core wall" was adopted
Construction temperatures were strictly controlled to ensure the workability and compactability of asphalt concrete
A comprehensive safety monitoring system was established to continuously monitor facing performance

Operation Effect:

Since its commissioning, the Tianhuangping Pumped Storage Power Station has demonstrated excellent impermeability performance of the asphalt concrete facing
Monitoring data shows that facing deformations are within design allowable limits, with no obvious cracks or seepage phenomena
The facing has withstood multiple extreme temperature and water level changes, proving the reliability of asphalt concrete facing technology

5.1.2 Three Gorges Project Maopingxi Embankment Dam Asphalt Concrete Core Wall Project

The Maopingxi Embankment Dam is an important component of the Three Gorges Project, using an asphalt concrete core wall as its impermeable structure. It is one of the highest asphalt concrete core wall dams in China.

Project Overview:

Maximum dam height is 104m, with the asphalt concrete core wall reaching a maximum height of 94m
The core wall has a top width of 0.5m and a bottom width of 1.2m, with a total asphalt concrete placement volume of approximately 50,000 m³
The core wall used rolled asphalt concrete with an asphalt content of 6.4%
Limestone was used for aggregates, limestone powder for fillers, and 60-80 penetration grade road petroleum asphalt

Construction Characteristics:

Specialized pavers and vibratory rollers were used for core wall construction
Construction temperatures and compaction parameters were strictly controlled
An innovative construction technique of "first compacting transition material, then compacting the core wall" was adopted
A comprehensive monitoring system was established to monitor deformation and seepage of the core wall

Operation Effect:

Since completion, the Maopingxi Embankment Dam has demonstrated excellent impermeability performance of the asphalt concrete core wall
Monitoring data shows that core wall deformations are within design allowable limits, with minimal seepage
The core wall has withstood multiple high water level and seismic load tests, proving the reliability of asphalt concrete core wall technology

5.1.3 Henan Guowang Baoquan Pumped Storage Power Station Upper Reservoir Asphalt Concrete Facing Project

The Baoquan Pumped Storage Power Station upper reservoir asphalt concrete facing project is one of the largest asphalt concrete facing impermeable projects in China.

Project Overview:

The upper reservoir asphalt concrete facing had a total impermeable area of approximately 1.662 million m² and a total construction volume of about 40,000 m³
The facing adopted a simple impermeable structure, consisting from top to bottom of a 2mm asphalt mastic sealing layer, an 8cm impermeable layer, and a 6cm leveling and bonding layer
The impermeable layer used dense-graded asphalt concrete with an asphalt content of 7.0%
The leveling and bonding layer used open-graded asphalt concrete with an asphalt content of 4.0%

Construction Characteristics:

Construction began on March 1, 2006, and was completed on May 5, 2008
Inclined pavers were used for placement, achieving a high degree of construction mechanization
Construction temperatures and compaction parameters were strictly controlled to ensure asphalt concrete density
An innovative construction technique of "layered placement and layered compaction" was adopted

Operation Effect:

Since its commissioning, the Baoquan Pumped Storage Power Station upper reservoir has demonstrated excellent impermeability performance of the asphalt concrete facing
Monitoring data shows that facing deformations are within design allowable limits, with no obvious seepage phenomena
The facing has withstood multiple extreme weather and water level changes, proving the reliability of asphalt concrete facing technology

5.1.4 Dalian Daxi Reservoir, Beida River Reservoir, Longwangtang Reservoir Asphalt Concrete Panel Seepage Control Projects

Three concrete gravity dams in Dalian City adopted asphalt concrete panels for seepage control treatment, representing successful applications of asphalt concrete facing technology in the reinforcement of concrete dams.

Project Overview:

The three reservoirs' dams were all built in the 1920s and 1930s, with aging concrete and seepage problems
Asphalt concrete panels were used for seepage control treatment, with precast concrete panels installed externally for protection
The asphalt concrete panels mainly consisted of an asphalt concrete impermeable layer and a precast concrete protective layer
The asphalt concrete impermeable layer had a thickness of 8-10cm, and the precast concrete protective layer had a thickness of 5-8cm

Construction Characteristics:

The construction process was simple, mainly including anchor bar installation, precast concrete panel installation, asphalt concrete mixing, and pouring
Asphalt concrete was mixed on-site and placed and compacted manually
An innovative construction sequence of "first installing precast concrete panels, then pouring asphalt concrete" was adopted
Special attention was paid to the bonding between asphalt concrete and concrete dam bodies during construction

Operation Effect:

After seepage control treatment with asphalt concrete panels, the seepage problems of the three reservoirs were completely resolved
After years of operation, the asphalt concrete panels have demonstrated excellent impermeability performance with no obvious seepage phenomena
The asphalt concrete panels have shown good resistance to shrinkage and adaptability to temperature changes, proving the effectiveness of this technology in concrete dam reinforcement

5.2 Foreign Typical Application Cases

Asphalt concrete facing technology has a history of nearly a century of application abroad, with mature technology and wide application.

5.2.1 Spain PozadeLosRamos Rockfill Dam Asphalt Concrete Diaphragm Wall Seepage Control Project

The PozadeLosRamos rockfill dam in Spain is the world's highest rockfill dam with an asphalt concrete diaphragm wall, with a dam height of 134m. Completed in 1984, it has been operating well to this day.

Project Overview:

Dam height is 134m, using an asphalt concrete diaphragm wall as the impermeable structure
The diaphragm wall thickness is 30-50cm, constructed in three layers
The asphalt concrete used a dense gradation design with an asphalt content of 6.5-7.5%
A protective layer was provided on the diaphragm wall surface to prevent ultraviolet aging and mechanical damage (1)

Technical Characteristics:

A special asphalt concrete mix design was adopted to improve low-temperature crack resistance and high-temperature stability
An innovative "stepped" construction method was developed to solve the technical challenges of high dam asphalt concrete construction
A comprehensive safety monitoring system was established to continuously monitor diaphragm wall performance
Advanced construction equipment and techniques were used to ensure construction quality (1)

Operation Effect:

Since its completion, the dam's asphalt concrete diaphragm wall has demonstrated excellent impermeability performance with no obvious seepage phenomena
The diaphragm wall has withstood multiple earthquake and flood tests, showing good seismic performance and deformation adaptability
Monitoring data shows that diaphragm wall deformations are within design allowable limits, with stable asphalt concrete performance and no obvious aging phenomena (1)

5.2.2 Switzerland Gepatsch Rockfill Dam Asphalt Concrete Facing Project

The Gepatsch rockfill dam in Switzerland is a famous asphalt concrete facing project in Europe, with a dam height of 150m, making it one of the world's highest asphalt concrete facing dams.

Project Overview:

Dam height is 150m, using an asphalt concrete facing as the impermeable structure
The facing adopted a composite section structure with a total thickness of 20-25cm
The impermeable layer used dense-graded asphalt concrete with an asphalt content of 7.0-7.5%
The drainage layer used open-graded asphalt concrete with an asphalt content of 3.5-4.0%

Technical Characteristics:

A special asphalt concrete mix design was adopted to improve impermeability and mechanical properties
An innovative construction technique of "phased construction and layer-by-layer compaction" was adopted
A comprehensive drainage system was established to promptly drain any infiltrating water
A protective coating was applied to the facing surface to prevent ultraviolet aging and temperature cracks

Operation Effect:

Since its completion, the dam's asphalt concrete facing has demonstrated excellent impermeability performance with minimal seepage
The facing has withstood multiple extreme weather and water level changes, showing good durability and deformation adaptability
Monitoring data shows that facing deformations are within design allowable limits, with stable asphalt concrete performance and no obvious aging phenomena

5.3 Case Experience Summary and Enlightenment

Through analysis of domestic and foreign typical cases, the following experiences and enlightenments can be summarized:

Material Selection is Fundamental: The successful application of asphalt concrete facing technology 离不开 high-quality raw materials and reasonable mix design. According to project characteristics and environmental conditions, suitable asphalt, aggregates, fillers, and additives should be selected, and the optimal mix proportion determined through testing.
Construction Technology is Key: The construction technology of asphalt concrete facing directly affects its impermeability and mechanical properties. According to project characteristics and site conditions, suitable construction equipment and process parameters should be selected, and construction quality strictly controlled.
Monitoring System is Guarantee: A comprehensive safety monitoring system is an important guarantee for the safe operation of asphalt concrete facing. According to project importance and characteristics, reasonable monitoring items and instruments should be set up, and a perfect monitoring data analysis and early warning mechanism established.
Adaptability is Advantage: Asphalt concrete facing has good deformation adaptability, especially suitable for use in areas with weak soil layers, permafrost, seismic zones, and deep overburden layers. In these areas, asphalt concrete facing technology often has more advantages than other impermeable technologies.
Innovation is Development Driver: The development of asphalt concrete facing technology 离不开 Continuous exploration of new materials, new technologies, and new equipment applications should be carried out to improve the performance and construction efficiency of asphalt concrete facing.
Experience Reference is Shortcut: There are already numerous asphalt concrete facing engineering cases at home and abroad, accumulating rich experience. In engineering practice, these experiences should be fully referenced to avoid repeating mistakes and improve engineering quality and efficiency.

VI. Comparative Analysis of Asphalt Concrete Facing Technology and Other Seepage Control Technologies

6.1 Comparison with Concrete Facing Seepage Control Technology

Concrete facing seepage control technology is another commonly used seepage control technology in hydraulic engineering. Compared with asphalt concrete facing technology, they each have their advantages and disadvantages.

6.1.1 Comparison of Impermeability Performance

Impermeability Performance Index Comparison:

Asphalt concrete facing: permeability coefficient ≤1×10⁻⁶ cm/s, air void content ≤3%
Ordinary concrete facing: permeability coefficient ≤1×10⁻⁷ cm/s, impermeability grade ≥W4
Reinforced concrete facing: permeability coefficient ≤1×10⁻⁸ cm/s, impermeability grade ≥W6

In terms of impermeability performance indicators, the permeability coefficient of concrete facing is slightly lower than that of asphalt concrete facing, but in practical engineering, both can meet the requirements of most hydraulic projects.

Impermeability Reliability Comparison:

Asphalt concrete facing: monolithic without joints, high impermeability reliability, cracks have certain self-healing capacity
Concrete facing: has expansion joints, joint leakage risk exists, cracks have poor self-healing capacity

Due to its monolithic construction without expansion joints, asphalt concrete facing reduces seepage paths and has relatively higher impermeability reliability. The expansion joints of concrete facing are weak points in impermeability that require special waterstop structures.

6.1.2 Comparison of Deformation Adaptability

Deformation Adaptability Index Comparison:

Asphalt concrete facing: elongation at break ≥10%, can adapt to large deformations
Ordinary concrete facing: elongation at break ≤0.1%, poor deformation adaptability
Reinforced concrete facing: elongation at break ≤0.2%, deformation adaptability slightly improved

The deformation adaptability of asphalt concrete facing is much better than that of concrete facing, making it particularly suitable for use in areas prone to large deformations.

Temperature Deformation Comparison:

Asphalt concrete facing: coefficient of linear expansion is approximately (6-10)×10⁻⁵/℃, temperature deformation is relatively large
Concrete facing: coefficient of linear expansion is approximately (1-2)×10⁻⁵/℃, temperature deformation is relatively small

Asphalt concrete has a larger coefficient of linear expansion and more obvious temperature deformation, but due to its good flexibility, temperature deformation will not lead to structural damage. Concrete facing has smaller temperature deformation, but due to its rigidity, temperature stress may cause facing cracking.

6.1.3 Comparison of Construction Performance

Construction Convenience Comparison:

Asphalt concrete facing: requires specialized equipment and technology, complex construction process
Concrete facing: construction is relatively simple, fast, and has low technical requirements for construction personnel

The construction of concrete facing is relatively simple and fast, with low technical requirements for construction personnel, making it suitable for use in areas with poor construction conditions. The construction of asphalt concrete facing requires specialized equipment and technology, with higher technical requirements.

Climate Adaptability Comparison:

Asphalt concrete facing: can be constructed in low temperature and humid environments, but too low temperature will affect construction quality
Concrete facing: construction is greatly affected by climate, generally requiring suspension of work in low temperature and rainy conditions

Asphalt concrete facing has better climate adaptability than concrete facing, especially in rainy and low temperature environments.

6.1.4 Comparison of Durability

Frost Resistance Comparison:

Asphalt concrete facing: good frost resistance, maintaining certain flexibility at low temperatures, not easily damaged by frost heave
Concrete facing: good frost resistance, but may be damaged by repeated freeze-thaw cycles

Asphalt concrete facing maintains certain flexibility at low temperatures and has better frost resistance durability than concrete facing, making it particularly suitable for use in cold regions.

Aging Resistance Comparison:

Asphalt concrete facing: surface is prone to aging, but internal aging is slow, service life is about 30-50 years
Concrete facing: good durability, service life is about 50-100 years

The durability of concrete facing is better than that of asphalt concrete facing, with a longer service life. The surface of asphalt concrete facing is susceptible to ultraviolet and oxygen aging and requires a sealing layer for protection.

6.1.5 Economic Comparison

Cost Comparison:

Asphalt concrete facing: comprehensive cost is about 200-250 yuan/m² (including base layer)
Ordinary concrete facing: comprehensive cost is about 150-200 yuan/m² (including base layer)
Reinforced concrete facing: comprehensive cost is about 250-300 yuan/m² (including base layer)

In terms of cost, ordinary concrete facing is the cheapest, followed by asphalt concrete facing, and reinforced concrete facing is the most expensive. However, asphalt concrete facing has fast construction speed, can shorten the construction period, and indirectly reduce costs.

Maintenance Cost Comparison:

Asphalt concrete facing: simple maintenance, local damage can be hot-patched, low maintenance cost
Concrete facing: complex maintenance, cracks are difficult to repair, high maintenance cost

The maintenance cost of asphalt concrete facing is lower than that of concrete facing, especially in the later service period, the advantage is more obvious.

6.2 Comparison with Geomembrane Seepage Control Technology

Geomembrane seepage control technology is another commonly used seepage control technology. Compared with asphalt concrete facing technology, they each have their advantages and disadvantages.

6.2.1 Comparison of Impermeability Performance

Impermeability Performance Index Comparison:

Asphalt concrete facing: permeability coefficient ≤1×10⁻⁶ cm/s, air void content ≤3%
Geomembrane: permeability coefficient ≤1×10⁻¹¹ cm/s, tensile strength ≥20kN/m
Composite geomembrane: permeability coefficient ≤1×10⁻¹⁰ cm/s, tensile strength ≥25kN/m

In terms of impermeability performance indicators, the permeability coefficient of geomembrane is much lower than that of asphalt concrete facing, with better impermeability performance. However, the integrity of geomembrane has a great impact on impermeability effect, once damaged, impermeability performance will be greatly reduced.

Impermeability Reliability Comparison:

Asphalt concrete facing: monolithic without joints, high impermeability reliability, local damage can be repaired
Geomembrane: has seams, joint leakage risk exists, difficult to repair after damage

Asphalt concrete facing is a monolithic structure without joints, with high impermeability reliability. Geomembrane needs to be spliced, and joints are weak points in impermeability, and once damaged, repair is more difficult.

6.2.2 Comparison of Deformation Adaptability

Deformation Adaptability Index Comparison:

Asphalt concrete facing: elongation at break ≥10%, can adapt to large deformations
Geomembrane: elongation at break ≥300%, extremely strong deformation adaptability
Composite geomembrane: elongation at break ≥200%, strong deformation adaptability

The deformation adaptability of geomembrane is much better than that of asphalt concrete facing, especially suitable for use in areas with large deformations.

Puncture Resistance Comparison:

Asphalt concrete facing: good puncture resistance, not easily punctured by sharp objects
Geomembrane: poor puncture resistance, easily punctured by sharp objects

Asphalt concrete facing has better puncture resistance than geomembrane and has more advantages in environments with sharp objects.

6.2.3 Comparison of Construction Performance

Construction Convenience Comparison:

Asphalt concrete facing: requires professional equipment and technology, complex construction process
Geomembrane: simple construction, fast speed, low technical requirements for construction personnel

The construction of geomembrane is simpler and faster than that of asphalt concrete facing, with lower technical requirements for construction personnel, suitable for use in areas with poor construction conditions.

Climate Adaptability Comparison:

Asphalt concrete facing: can be constructed in low temperature and humid environments, but too low temperature will affect construction quality
Geomembrane: construction is less affected by climate, can be constructed in harsh environments

The climate adaptability of geomembrane is better than that of asphalt concrete facing, especially in extreme weather conditions, the advantage is more obvious.

6.2.4 Comparison of Durability

Aging Resistance Comparison:

Asphalt concrete facing: surface is prone to aging, but internal aging is slow, service life is about 30-50 years
Geomembrane: poor aging resistance, especially when exposed to sunlight, aging speed is fast
Composite geomembrane: better aging resistance, but still not as good as asphalt concrete facing

The durability of asphalt concrete facing is better than that of geomembrane, especially in exposed environments, the advantage is more obvious. Geomembrane generally needs to set up protective layers to avoid direct exposure to sunlight.

Service Life Comparison:

Asphalt concrete facing: service life is about 30-50 years
Geomembrane: service life is about 15-30 years (exposed), 30-50 years (buried)
Composite geomembrane: service life is about 20-40 years (exposed), 40-60 years (buried)

Under buried conditions, the service life of geomembrane and composite geomembrane is comparable to or even longer than that of asphalt concrete facing. However, in exposed conditions, the service life of asphalt concrete facing is longer.

6.2.5 Economic Comparison

Cost Comparison:

Asphalt concrete facing: comprehensive cost is about 200-250 yuan/m² (including base layer)
Geomembrane: comprehensive cost is about 10-20 yuan/m² (material only), 30-50 yuan/m² (including construction)
Composite geomembrane: comprehensive cost is about 20-30 yuan/m² (material only), 50-70 yuan/m² (including construction)

In terms of cost, geomembrane and composite geomembrane are much cheaper than asphalt concrete facing, especially in large-area seepage control projects, the advantage is more obvious.

Maintenance Cost Comparison:

Asphalt concrete facing: simple maintenance, local damage can be hot-patched, low maintenance cost
Geomembrane: complex maintenance, difficult to repair after damage, high maintenance cost

The maintenance cost of asphalt concrete facing is lower than that of geomembrane, especially in the later service period, the advantage is more obvious.

6.3 Comparison with Clay Core Wall Seepage Control Technology

Clay core wall seepage control technology is the most traditional seepage control technology in earth-rock dams. Compared with asphalt concrete facing technology, they each have their advantages and disadvantages.

6.3.1 Comparison of Impermeability Performance

Impermeability Performance Index Comparison:

Asphalt concrete facing: permeability coefficient ≤1×10⁻⁶ cm/s, air void content ≤3%
Clay core wall: permeability coefficient ≤1×10⁻⁷ cm/s, dry density ≥1.6g/cm³
High-plasticity clay core wall: permeability coefficient ≤1×10⁻⁸ cm/s, dry density ≥1.7g/cm³

In terms of impermeability performance indicators, the permeability coefficient of clay core wall is slightly lower than that of asphalt concrete facing, but in practical engineering, both can meet the requirements of most hydraulic projects.

Impermeability Reliability Comparison:

Asphalt concrete facing: monolithic without joints, high impermeability reliability, local damage can be repaired
Clay core wall: has horizontal layered joints, joints may become seepage channels
High-plasticity clay core wall: good integrity, low risk of joint seepage

The impermeability reliability of asphalt concrete facing is higher than that of ordinary clay core wall, but the impermeability reliability of high-plasticity clay core wall is comparable to that of asphalt concrete facing.

6.3.2 Comparison of Deformation Adaptability

Deformation Adaptability Comparison:

Asphalt concrete facing: elongation at break ≥10%, can adapt to large deformations
Clay core wall: large dry shrinkage and wet expansion deformation, poor deformation adaptability
High-plasticity clay core wall: good plasticity, strong deformation adaptability

The deformation adaptability of asphalt concrete facing is better than that of ordinary clay core wall, but not as good as that of high-plasticity clay core wall.

Seismic Performance Comparison:

Asphalt concrete facing: good flexibility, strong seismic performance
Clay core wall: may produce cracks and liquefaction under seismic loading
High-plasticity clay core wall: good seismic performance

The seismic performance of asphalt concrete facing is better than that of clay core wall, especially suitable for use in earthquake-prone areas.

6.3.3 Comparison of Construction Performance

Construction Convenience Comparison:

Asphalt concrete facing: requires professional equipment and technology, complex construction process
Clay core wall: simple construction, low technical requirements, can use local materials
High-plasticity clay core wall: requires special clay materials, complex construction process

The construction of ordinary clay core wall is the simplest, with low technical requirements, can use local materials, and low cost. The construction processes of asphalt concrete facing and high-plasticity clay core wall are complex and require professional equipment and technology.

Climate Adaptability Comparison:

Asphalt concrete facing: can be constructed in low temperature and humid environments, but too low temperature will affect construction quality
Clay core wall: greatly affected by climate, cannot be constructed in rainy and low temperature weather
High-plasticity clay core wall: strict requirements on climate conditions, construction affected by climate

The climate adaptability of asphalt concrete facing is better than that of clay core wall, especially in rainy and low temperature environments, the advantage is more obvious.

6.3.4 Comparison of Durability

Frost Resistance Comparison:

Asphalt concrete facing: good frost resistance, maintaining certain flexibility at low temperatures, not easily damaged by frost heave
Clay core wall: poor frost resistance, easily damaged by frost heave
High-plasticity clay core wall: better frost resistance, but still not as good as asphalt concrete facing

The frost resistance durability of asphalt concrete facing is much better than that of clay core wall, especially suitable for use in cold regions.

Aging Performance Comparison:

Asphalt concrete facing: surface is prone to aging, but internal aging is slow, service life is about 30-50 years
Clay core wall: good durability, service life is about 50-100 years
High-plasticity clay core wall: good durability, service life is about 60-100 years

The durability of clay core wall is better than that of asphalt concrete facing, especially in the later service period, the advantage is more obvious.

6.3.5 Economic Comparison

Cost Comparison:

Asphalt concrete facing: comprehensive cost is about 200-250 yuan/m² (including base layer)
Clay core wall: comprehensive cost is about 80-120 yuan/m² (including foundation treatment)
High-plasticity clay core wall: comprehensive cost is about 150-200 yuan/m² (including foundation treatment)

In terms of cost, clay core wall is the cheapest, followed by high-plasticity clay core wall, and asphalt concrete facing is the most expensive. However, asphalt concrete facing has fast construction speed, can shorten the construction period, and indirectly reduce costs.

Maintenance Cost Comparison:

Asphalt concrete facing: simple maintenance, local damage can be hot-patched, low maintenance cost
Clay core wall: complex maintenance, cracks are difficult to repair, high maintenance cost
High-plasticity clay core wall: relatively simple maintenance, cracks have certain self-healing capacity

The maintenance cost of asphalt concrete facing is lower than that of clay core wall, especially in the later service period, the advantage is more obvious.

6.4 Comprehensive Evaluation and Selection Recommendations for Different Seepage Control Technologies

Based on the above comparative analysis, a comprehensive evaluation of the four seepage control technologies can be made, and selection recommendations provided.

6.4.1 Comprehensive Performance Evaluation

Comprehensive Performance Evaluation Table:

Evaluation Index	Asphalt Concrete Facing	Concrete Facing	Geomembrane	Clay Core Wall
Impermeability Performance	★★★★☆	★★★★★	★★★★★	★★★★☆
Deformation Adaptability	★★★★☆	★★★☆☆	★★★★★	★★★☆☆
Frost Resistance Durability	★★★★★	★★★☆☆	★★★☆☆	★★☆☆☆
Seismic Performance	★★★★☆	★★★☆☆	★★★★☆	★★☆☆☆
Construction Convenience	★★★★☆	★★★☆☆	★★★★★	★★★★☆
Climate Adaptability	★★★★☆	★★★☆☆	★★★★★	★★★☆☆
Durability	★★★★☆	★★★★☆	★★★☆☆	★★★★★
Economy	★★★☆☆	★★★★☆	★★★★★	★★★★★
Maintenance Cost	★★★★☆	★★★☆☆	★★★☆☆	★★★☆☆

Note: ★ indicates performance level, with more ★ indicating better performance, up to ★★★★★.

6.4.2 Applicability Conditions Analysis

Based on the characteristics of different seepage control technologies, their applicability conditions are as follows:

Applicability Conditions for Asphalt Concrete Facing Technology:

Cold and severe cold regions
Areas with weak soil layers, deep overburden layers
Earthquake-prone areas
Areas with large deformations
Areas lacking local impermeable materials
Projects with high requirements for seepage control reliability
Projects with tight construction schedules

Applicability Conditions for Concrete Facing Technology:

Mild climate regions
Areas with good foundation conditions
Areas with low deformation requirements
Areas with abundant sand and gravel resources
Projects with high requirements for durability
Projects with tight cost constraints

Applicability Conditions for Geomembrane Seepage Control Technology:

Areas with complex terrain
Areas with high deformation requirements
Areas with poor construction conditions
Areas with extreme climate conditions
Projects with extremely tight cost constraints
Temporary projects or repair projects

Applicability Conditions for Clay Core Wall Seepage Control Technology:

Mild climate regions
Areas with abundant clay resources
Areas with low deformation requirements
Projects with high durability requirements
Projects with extremely tight cost constraints
Permanent projects

6.4.3 Selection Recommendations

Based on specific project conditions and requirements, the following selection recommendations are provided for seepage control technologies:

Selection Based on Project Characteristics:

High dams and important projects should give priority to asphalt concrete facing or reinforced concrete facing
Low dams and small projects can consider ordinary concrete facing or clay core wall
Projects with large deformations should give priority to geomembrane or asphalt concrete facing
Cold region projects should give priority to asphalt concrete facing
Projects in areas with weak soil layers and deep overburden should give priority to asphalt concrete facing
Earthquake-prone area projects should give priority to asphalt concrete facing or geomembrane

Selection Based on Material Resources:

Areas with abundant clay resources can give priority to clay core wall
Areas with abundant sand and gravel resources can give priority to concrete facing
Areas lacking local impermeable materials should give priority to asphalt concrete facing or geomembrane

Selection Based on Construction Conditions:

Projects with tight construction schedules should give priority to asphalt concrete facing or geomembrane
Projects in areas with poor construction conditions should give priority to geomembrane
Rainy area projects should give priority to asphalt concrete facing
Low temperature area projects should give priority to asphalt concrete facing

Selection Based on Economic Conditions:

Projects with tight cost constraints should give priority to clay core wall or ordinary concrete facing
Projects with moderate cost requirements but high performance requirements should give priority to asphalt concrete facing
Temporary projects with extremely tight cost constraints can consider geomembrane

Selection Based on Environmental Conditions:

Cold region projects should give priority to asphalt concrete facing
Hot region projects can consider concrete facing or clay core wall
Humid region projects should give priority to asphalt concrete facing
Arid region projects can consider concrete facing or clay core wall

Selection Based on Project Lifespan:

Short-term projects can consider geomembrane or ordinary concrete facing
Long-term projects should give priority to asphalt concrete facing or reinforced concrete facing
Permanent projects should give priority to asphalt concrete facing or clay core wall

In practical engineering, a combination of multiple seepage control technologies can also be considered according to specific circumstances, such as the asphalt concrete facing + geomembrane combined seepage control technology, giving full play to their respective advantages and improving seepage control effectiveness and reliability.

VII. Conclusions and Outlook

7.1 Main Conclusions

Through systematic analysis of asphalt concrete facing seepage control technology, the following main conclusions can be drawn:

Obvious Technical Advantages: Asphalt concrete facing seepage control technology has excellent impermeability, good deformation adaptability, strong frost resistance durability, convenient construction, easy repair and maintenance, and other advantages, especially suitable for use in cold regions, weak soil layers, deep overburden layers, earthquake-prone areas and other special conditions.
Key Material Composition: The performance of asphalt concrete facing mainly depends on the selection of raw materials and mix design. According to project characteristics and environmental conditions, suitable asphalt, aggregates, fillers and additives should be selected, and the optimal mix proportion determined through testing.
Reasonable Structural Design: The structural design of asphalt concrete facing should be based on project requirements and geological conditions. Simple section is suitable for general projects, and composite section is suitable for projects with special impermeability requirements. The facing layout should be smooth and straight, avoiding sudden changes.
Mature Construction Technology: The construction technology of asphalt concrete facing has matured, including raw material preparation, asphalt concrete mixing and transportation, facing placement and compaction, joint treatment and sealing layer construction. During construction, key indicators such as temperature, thickness and compaction parameters should be strictly controlled.
Strict Quality Control: Strict quality control should be carried out during asphalt concrete facing construction, including raw material inspection, mixing quality inspection and on-site quality inspection. All indicators should meet design requirements to ensure the impermeability and mechanical properties of the facing.
Abundant Application Cases: There are numerous asphalt concrete facing seepage control engineering cases at home and abroad, accumulating rich experience. These cases prove that asphalt concrete facing seepage control technology is a reliable and efficient seepage control technology with broad application prospects.
Excellent Comprehensive Performance: Compared with concrete facing, geomembrane, clay core wall and other seepage control technologies, asphalt concrete facing technology has obvious advantages in impermeability, deformation adaptability, frost resistance durability and seismic performance, especially suitable for use in special conditions in hydraulic engineering.
Reasonable Economy: Although the cost of asphalt concrete facing is higher than that of ordinary concrete facing and clay core wall, considering its fast construction speed, low maintenance cost and long service life, the comprehensive economy is reasonable.

7.2 Development Trends and Outlook

With the continuous advancement of science and technology and the accumulation of engineering practice, asphalt concrete facing seepage control technology will show the following development trends:

Material Innovation:

Development of high-performance modified asphalt to improve the low-temperature crack resistance, high-temperature stability and durability of asphalt concrete
Research on new types of aggregates and fillers to improve the performance of asphalt concrete and reduce costs
Development of environmentally friendly asphalt concrete to reduce environmental pollution during construction
Research on self-healing asphalt concrete to improve the reliability and service life of facing (2)

Technological Innovation:

Development of automated and intelligent construction equipment to improve construction efficiency and quality
Research on low-temperature construction technology to expand the application range of asphalt concrete facing
Exploration of new construction technologies such as 3D printing technology in asphalt concrete facing construction
Research on rapid construction technology to further shorten the construction period (1)

Structural Innovation:

Development of new structural forms such as reinforced asphalt concrete facing and composite asphalt concrete facing
Research on ultra-thin asphalt concrete facing to reduce material usage and costs
Exploration of new connection structures to improve the reliability of connections between facing and foundations, abutments and other structures
Development of self-monitoring asphalt concrete facing to achieve real-time monitoring of facing performance (4)

Application Expansion:

Expansion of applications in marine engineering such as breakwaters and artificial islands
Expansion of applications in urban underground engineering such as metro tunnels and utility tunnels
Expansion of applications in environmental protection engineering such as landfills and hazardous waste treatment sites
Expansion of applications in military engineering such as underground fortifications and protective works (10)

Theoretical Deepening:

Deepening research on the rheology of asphalt concrete to establish more complete constitutive models
Research on the damage mechanism and failure criteria of asphalt concrete to improve the scientific nature of design
Development of numerical simulation technology for asphalt concrete facing to provide theoretical support for design and construction
Establishment of a life cycle assessment system for asphalt concrete facing to optimize project investment benefits (3)

Standard Perfection:

Improvement of design, construction and acceptance standards for asphalt concrete facing
Development of technical standards for new asphalt concrete materials
Establishment of safety monitoring and maintenance standards for asphalt concrete facing
Development of environmental protection standards for asphalt concrete facing to promote green construction (10)

7.3 Engineering Practice Recommendations

Based on the characteristics and development trends of asphalt concrete facing seepage control technology, the following engineering practice recommendations are proposed:

Technology Selection According to Local Conditions: According to project characteristics, geological conditions, climate environment, material resources and other factors, comprehensively consider the advantages and disadvantages of various seepage control technologies, and select the most suitable seepage control technology.
Emphasis on Material Selection and Mix Design: Material selection and mix design are the foundation for the successful application of asphalt concrete facing technology. The quality of raw materials should be strictly controlled, and the optimal mix proportion determined through testing.
Strengthening Construction Process Control: Construction process control is the key to ensuring the quality of asphalt concrete facing. Key indicators such as temperature, thickness and compaction parameters should be strictly controlled, and construction quality inspection and acceptance strengthened.
Improving Monitoring Systems: According to project importance and characteristics, reasonable monitoring items and instruments should be set up, and a perfect monitoring data analysis and early warning mechanism established to achieve real-time monitoring of facing performance.
Focusing on Innovative Applications: Actively explore the application of new materials, new technologies and new equipment, improve the performance and construction efficiency of asphalt concrete facing, and promote technological progress.
Strengthening Experience Summarization and Exchange: Timely summarize engineering experience, strengthen technical exchanges, and promote the popularization, application and development of asphalt concrete facing seepage control technology.
Cultivating Professional Talents: Asphalt concrete facing seepage control technology involves multiple fields such as materials, structures and construction, requiring high-quality professional talents. Relevant talent cultivation should be strengthened to improve technical level and innovation ability.
Promoting Green Construction: Pay attention to environmental protection issues during asphalt concrete facing construction, promote green construction technology, reduce environmental pollution, and achieve sustainable development.

In summary, asphalt concrete facing seepage control technology is an advanced and reliable seepage control technology with broad application prospects. With the continuous advancement of science and technology and the accumulation of engineering practice, asphalt concrete facing seepage control technology will continue to develop and improve, providing higher quality, more economical and more environmentally friendly solutions for seepage control projects in hydraulic engineering and other fields.

参考资料

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THE END

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