Introduction:

In modern highway engineering construction, the durability and safety of asphalt pavements are receiving increasing attention. Among these factors, the adhesion performance between asphalt and coarse aggregate directly affects the pavement's resistance to water damage, its resistance to spalling, and its overall service life. Therefore, conducting standardized adhesion tests is of great significance for ensuring project quality.

I. Background and Significance of the Test

The adhesion between asphalt and aggregate refers to the ability of asphalt to adhere to the surface of the aggregate. When adhesion is insufficient, "stripping" easily occurs under the combined effects of moisture and vehicle loads, leading to potholes, loosening, and other defects. Therefore, evaluating its performance through scientific testing is an important basis for material selection and construction control.

Currently, commonly used methods in engineering mainly include:

Boiling Method

Immersion Method

II. Detailed Explanation of the Boiling Method Test Procedure

1. Preparation

First, select five regular aggregates with a particle size of 13.2–19 mm and a near-cubic shape. After washing, dry them in an oven at 105°C ± 5°C and place them in a desiccator for later use. Simultaneously, add water to a large beaker and heat it to a boiling point.

2. Experimental Procedure

During the test, tie the aggregates with thin thread and heat them. Then, immerse each aggregate individually in hot asphalt at 130–150°C for approximately 45 seconds, ensuring the surface is completely coated with an asphalt film. Afterward, hang them to cool and drip off excess asphalt.

The cooled aggregates are then lifted again and immersed in slightly boiling water for 3 minutes. After removal and cooling, place them in room temperature water. The adhesion grade is evaluated by observing the peeling of the asphalt film.

3. Result Evaluation

Each test requires five parallel samples, and each sample is evaluated by at least two experienced testers. The final result is the average grade.

III. Detailed Explanation of the Water Immersion Test Procedure

1. Preparation

Select 200g of aggregate with a particle size of 9.5–13.2 mm, wash and dry it for later use. Simultaneously, heat the asphalt to the specified mixing temperature and prepare a constant temperature water bath at 80°C ± 1°C.

2. Experimental Procedure

Mix the aggregate according to the specified ratio (5.5g ± 0.2g asphalt per 100g of aggregate) and stir under high temperature to ensure the aggregate is completely coated with asphalt. Then, take 20 particles and spread them on a glass plate, allowing them to cool at room temperature for 1 hour.

After cooling, immerse the glass plate in 80°C constant temperature water for 30 minutes, then transfer it to cold water. Observe the area of asphalt film peeling off to evaluate the adhesion performance.

3. Result Evaluation

Estimate the percentage of asphalt peeling area using visual inspection. The average value should be taken after independent evaluation by at least two testers to improve the reliability of the results.

It is worth noting that the regulations specifically recommend that, to improve the accuracy of visual inspection, several standard samples with different stripping rates be prepared in advance for comparison. These samples can be obtained by mixing modified asphalt with acidic aggregates and then soaking them in water, or by mixing the same type of asphalt with different aggregates and then soaking them in water, and then carefully calculating the stripping area ratio, thereby providing testers with a reliable basis for comparison.

IV. Industry Applications and Development Trends

With the continuous development of transportation infrastructure, the requirements for material performance are also increasing. In recent years, more and more laboratories have introduced automated testing equipment and digital image analysis technology to improve the objectivity and efficiency of adhesion assessment.

Furthermore, the application of environmentally friendly materials and high-performance modified asphalt has also provided new solutions for improving adhesion performance.

V. Conclusion

Industry experts point out that both the boiling and immersion methods essentially aim to objectively evaluate the compatibility of asphalt and aggregate by simulating water damage, the most common cause of road surface defects. With the increasing severity of traffic loads and the complex and variable climate in my country, higher demands are being placed on the water resistance of pavement materials. These two tests not only act as gatekeepers for the selection of engineering materials but also provide crucial technical support for optimizing asphalt mixture design and rationally selecting anti-stripping agents.

Currently, these standardized testing methods are widely used in highway engineering for material quality monitoring, construction process optimization, and scientific research and teaching. By strictly controlling the adhesion between asphalt and aggregate, the durability and service life of pavement structures are improved from the source, providing a safer, more comfortable, and smoother traffic environment for the public.