The Asphalt Mixture Accelerated Polishing Machine is a specialized testing instrument designed to evaluate the polishing resistance and skid durability of asphalt mixtures under simulated long-term traffic loading. Based on the accelerated polishing method, it measures changes in surface friction at different polishing stages, providing reliable data for pavement performance assessment, road material design, and quality control in highway engineering.

I. Product Purpose and Scope of Application

The TD760-1 Asphalt Mixture Accelerated Polishing Machine is designed and manufactured in accordance with T0760—2025 Test Method for Polishing Resistance of Asphalt Mixtures, and with reference to BS EN 1097-8 and EN 1097-8. It is a professional testing instrument.The device is used to simulate the surface polishing process of asphalt mixtures under long-term traffic loading. By measuring the friction coefficient of specimens at different polishing stages, it evaluates the anti-polishing performance and skid resistance durability of asphalt mixtures, providing reliable data for pavement material design and road performance assessment.

Scope of Application:

Suitable for indoor-formed asphalt mixture specimens (such as 300mm×300mm×50mm slabs formed by roller milling), and also suitable for field-cut slab specimens (cylinders or slabs with a diameter ≤225mm and a thickness ≤50mm).

It can complete the entire process of specimen surface sandblasting pretreatment, accelerated polishing, and friction coefficient determination, and supports the analysis of friction coefficient decay patterns under different polishing cycles (such as 4500, 7500, 90000, etc.).

II.Technical Parameters

1.Polishing System

The system is equipped with three conical polishing rollers evenly distributed along the circumference. The core is made of metal, and the outer layer is a rubber sleeve (Shore hardness 65A±3A). The surface is divided into 8 equal grooves, with an initial groove size of 4.5mm±0.5mm (depth) × 3.5mm±0.5mm (width).

Total vertical load of polishing rollers: 392N±3N;

Polishing rotation speed: 500 r/min±5 r/min.

2.Sand Blasting System

Nozzle diameter: 6.3 mm ± 0.2 mm;

Angle to specimen surface: 75° ± 5°;

Blasting distance: 70 mm ± 5 mm;

Specimen rotation speed: 24 r/s ± 2 r/s;

Blasting air pressure: 600 kPa ± 30 kPa;

The blasting area is an annular zone with a width of 40 mm on the specimen surface.

3.Polishing Fluid Supply Unit

A quartz powder–water mixture is used (quartz powder 62 g ± 2 g + water 1 L);

Water temperature: 20°C ± 5°C during polishing;

The mixture is continuously sprayed onto the specimen surface through a central nozzle;

Water pump flow rate: 5.0 L/min ± 0.5 L/min;

Nozzle diameter: 8.5 mm ± 0.5 mm.

4.Friction Coefficient Measurement System

Friction head rotation speed: 50 r/s ± 1 r/s (water supply starts when accelerated to 45 r/s ± 1 r/s);

Vertical load: 253 N ± 3 N;

Water supply temperature: 14°C ± 2°C;

Flow rate: 20 L/min ± 2 L/min;

Torque sensor range: 0–50 N·m, accuracy ±0.2%, sampling frequency ≥100 Hz;

Rotation speed measurement accuracy: ±2 r/s;

Vertical load sensor range: ≥4 kN, accuracy ±0.2%.

5.Clamping Device

Supports plate specimens of 300 mm × 300 mm × 50 mm or cylindrical specimens with a diameter ≤225 mm × 50 mm;

Includes a specimen holder and a friction coefficient standard plate holder;

Standard plate size: 300 mm × 300 mm × 7 mm;

Nominal friction coefficient range: 8–20;

Accuracy: ±3%.

6. Control System

Digital display control panel, allowing setting of polishing cycles, real-time counting, and monitoring of speed, load, and torque;

Supports automatic control, manual pause, and emergency stop functions.

7. Power Requirements:

AC 380V±10% (three-phase five-wire system), 50Hz;

Total Power: ≤3kW.

8. Equipment Dimensions (L×W×H): 1500mm × 1000mm × 1800mm (including control cabinet and guide rail system).

9. Total Weight: ≈500kg.

III. Equipment Structural Composition

The equipment is mainly composed of the following core systems:

1. Sand Blasting System

Includes a nozzle (adjustable angle up to 75° ± 5°), air pressure regulating valve, and specimen rotation drive device (24 r/s ± 2 r/s). It is used to remove the asphalt film on the specimen surface and expose the coarse aggregates.

2. Clamping Device

Includes a specimen holder (for fixing 300 mm × 300 mm plate specimens or cylindrical specimens) and a friction coefficient standard plate holder (for fixing standard plates with nominal values of 8–20).

3. Accelerated Polishing System

Polishing disc equipped with three conical polishing rollers, applying a vertical load of 392 N ± 3 N through a lifting mechanism;

Torque sensor (monitors torque during polishing, range 0–50 N·m, accuracy ±0.2%);

Polishing fluid supply unit (quartz powder–water mixing, temperature control, and spraying system);

Closed-loop load control unit to precisely maintain a 392 N ± 3 N load on the polishing rollers.

4. Washing System
High-pressure water flow (5 L/min ± 1 L/min) is used to remove abrasive residues from the specimen surface after polishing.

5. Friction Coefficient Measurement System

Friction head (three sliders with 120° ± 5° spacing; rubber sliders with Shore hardness 65A ± 3A, curvature radius 7.5 mm ± 0.5 mm, thickness 5 mm ± 1 mm, and average contact length 30 mm ± 1 mm);

Torque, speed, and vertical load sensors for real-time friction resistance data acquisition;

Water supply system (water temperature 14°C ± 2°C, flow rate 20 L/min ± 2 L/min).

6. Control Cabinet

Integrated operation panel (setting polishing cycles, start/pause/emergency stop), digital display screen (real-time monitoring of speed, load, torque, and cycle count), and safety protection circuit.

IV.Test Preparation

(1) Environmental and Equipment Requirements

Environmental conditions:

The entire test shall be conducted at a temperature of 20°C ± 5°C and a relative humidity of 50% ± 15%. The equipment shall be pre-conditioned in the same environment for at least 120 minutes. The polishing rollers and sliders shall be conditioned for at least 12 hours.

Equipment inspection:

·Polishing rollers:

Check that the rubber sleeves are not damaged or sticky, and that the surface shows no uneven wear or dark marks. (Shore hardness 65A ± 3A; dimensions: 36 mm ± 1 mm (top diameter) / 80 mm ± 1 mm (bottom diameter) / 57.5 mm ± 0.5 mm (height)).

Unused rollers shall be sealed and stored in a dark environment at 4–10°C.

·Friction head sliders:

Check that the rubber pads have a thickness ≥2 mm, with no damage or deformation. (Shore hardness 65A ± 3A; rebound value 67%–74%).

Unused sliders shall be sealed and stored in a dark environment at 4–10°C.

·Polishing disc and clamping device:

Remove any adhered debris and ensure the polishing disc bearings rotate freely. Confirm that the polishing fluid supply system (water pump flow rate 5.0 L/min ± 0.5 L/min) operates normally.

Preheating:

Start preheating 30 minutes in advance. Control the quartz powder–water mixture temperature at 25°C ± 5°C (which stabilizes at 20°C ± 5°C during polishing). Ensure the water supply temperature is stabilized at 14°C ± 2°C during friction coefficient testing.

(2) Specimen Preparation and Pre-treatment

1. Specimen types:

·Laboratory molded specimens:

Prepared by the roller compaction method according to T0703, forming 300 mm × 300 mm × 50 mm slab specimens. The deviation between measured and designed air voids shall be ≤1% (each group contains at least 2 valid specimens).

·Field specimens:

Cut 300 mm × 300 mm slab specimens or drill cores with a diameter of 225 mm. The thickness shall be processed to 50 mm. The cutting surface must be parallel to the top surface, and uneven bottoms shall be leveled using gypsum.

2. Sand blasting pre-treatment (only for specimens without traffic loading exposure):

·Dry the specimen surface using an electric fan. Place it horizontally and maintain at 5°C ± 3°C for at least 120 minutes for conditioning.

·With the surface facing upward, use a nozzle (6.3 mm ± 0.2 mm, air pressure 600 kPa ± 30 kPa) to sand blast a 40 mm-wide annular area for 120 s ± 5 s. Replace with fresh corundum powder for each operation.

·After sand blasting, use compressed air to remove residual particles. Then condition the specimen horizontally at 23°C ± 5°C for at least 120 minutes. Maintain this temperature throughout the entire test process.

V.Operating Procedure

(1) Specimen Polishing Process

Specimen installation:

Fix the pre-treated specimen onto the polishing unit clamping device and ensure the surface is level.

Load application:

Lower the polishing disc onto the specimen surface and apply a vertical load of 392 N ± 3 N through the closed-loop load control system.

Start polishing:

Activate the polishing fluid supply (quartz powder–water mixture spraying). The polishing disc rotates at 500 r/min ± 5 r/min, and the accelerated polishing process begins.

Polishing control:

·Select the polishing cycles according to test requirements (e.g., 90,000 cycles for standard polishing, or 4,500 / 7,500 / 15,000 cycles for degradation tests).

·Monitor torque fluctuation during the process. Within 10%–90% of polishing cycles, torque variation shall not exceed ±10% of the average value; otherwise, the specimen shall be discarded.

Post-polishing treatment:

After reaching the specified number of cycles, stop polishing. Rinse the specimen surface with water flow of 5 L/min ± 1 L/min for 180 s ± 5 s to remove residual abrasive material.

(2) Friction Coefficient Measurement Procedure

1.System calibration:

Before each test, verify the system using a friction coefficient standard plate (nominal value 8–20, accuracy ±3%). The difference between the two calibration results before and after testing shall not exceed 10%; otherwise, the data shall be considered invalid.

2.Specimen positioning:

Move the polished specimen via the sliding rail to directly beneath the friction head and secure it in place.

3.Measurement start:

·Accelerate the friction head to 50 r/s ± 1 r/s (water supply is activated at 45 r/s ± 1 r/s; water temperature 14°C ± 2°C, flow rate 20 L/min ± 2 L/min).

·The friction head automatically descends and applies a vertical load of 253 N ± 3 N onto the specimen surface.

·Record torque variation until the friction head stops rotating.

4.Data recording:

Sampling frequency shall be ≥100 Hz. Measure the friction coefficient of the standard plate twice before and after testing. The difference between results shall not exceed 10% for the data to be considered valid.

(3) Parallel Testing of Multiple Specimens

Each test group shall test at least two specimens in parallel; if the difference in friction coefficient between two specimens at 60km/h is greater than 3.5, a third specimen shall be added, and the two data with the smallest difference shall be used to calculate the final result.

VI. Data Processing

1. Calculation of Friction Coefficient for Individual Specimens: Calculate the friction coefficient μv at different speeds using formula (T0760-1) (accurate to 0.01), plot the μv-velocity V curve, and calculate the friction coefficient μ60 at 60 km/h using a 6th-order polynomial fitting.

2. Standard Plate Calibration: Calculate the average friction coefficient μk60 of the standard plate from the first and last measurements (accurate to 0.01).

3. Final Result: Friction coefficient μ60 of asphalt mixture at 60 km/h = μ60 (spectrum) - μk60 (spectrum) + μ (nominal value of standard plate) (accurate to 0.1).

4. Attenuation Law Analysis: Measure μ60 at different polishing cycles (e.g., 4500/7500…270000 times), and plot the μ60-polishing cycle curve (to evaluate the attenuation of anti-skid performance).

VII. Precautions

1.Safety operation:

During equipment operation, it is strictly prohibited to touch rotating parts (polishing disc and friction head). The protective door must remain closed. The emergency stop button shall only be used in abnormal situations.

2.Maintenance of key components:

·Polishing rollers:

Replace when used or stored for more than 2 years, or when uneven wear or damage occurs (all three rollers must be replaced simultaneously). Pre-polishing shall reach torque stability (≥300,000 cycles) or pass standard specimen validation (friction coefficient deviation ≤ ±3% after 90,000 cycles).

·Sliders:

Replace when used or stored for more than 1 year, or when rubber thickness is less than 2 mm (all three sliders must be replaced simultaneously). Pre-polishing requires testing of the standard plate five times (error ≤ ±3%).

·Standard plates and abrasives:

Regularly verify the validity of nominal values (standard plate stability ≥ 2 years; quartz powder purity ≥ 90%).

3.Environmental control:

The polishing fluid (quartz powder–water mixture) and water supply for friction testing must be strictly temperature-controlled (20°C ± 5°C and 14°C ± 2°C) to avoid test result deviation caused by temperature fluctuations.

4.Cleaning requirements:

After each test, clean residual abrasive material from the polishing disc and clamping device. Deposits from the polishing fluid shall not be reused.