Improved boiling test method for asphalt adhesion to aggregate

Abstract

This invention belongs to the technical field of road engineering material performance testing, and specifically relates to an improved water-boiling test method for the adhesion of asphalt to aggregates. The method includes: S1: Randomly selecting a number of aggregates and preheating them to the mixing temperature ±5°C; S2: Preparing asphalt binder and heating it to a fluid state not exceeding the mixing temperature; S3: Immersing the aggregates in the preheated to a molten state of the asphalt binder for 45 seconds, ensuring the aggregates are completely coated, then suspending the aggregates in an environment of 145±5°C for a preset time, removing them and cooling them to room temperature; S4: Immersing the aggregates from S3 in boiling water for at least 3 minutes; S5: Transferring the boiled aggregate samples to clean water, observing the degree of asphalt film peeling off the surface, evaluating the asphalt film coating rate, and determining the adhesion grade based on the average coating rate. This method makes the laboratory test conditions closer to actual engineering conditions, improving the reliability and guiding value of the results.

Description

Technical Field

[0001] This invention belongs to the field of road engineering material performance testing technology, and specifically relates to an improved water boiling test method for the adhesion of asphalt to aggregates. Background Technology

[0002] The adhesion between asphalt and aggregate is a core indicator determining the water stability of asphalt mixtures, directly affecting the durability and service life of pavements under moisture erosion conditions. Currently, the widely followed standard test method in the industry is T0616-2025 "Adhesion Test between Asphalt and Aggregate" in the Ministry of Transport industry standard JTG 3410-2025 "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering". This method evaluates the anti-stripping ability by simulating the effect of hydrothermal conditions on the asphalt-aggregate interface, and is an important basis for material selection and quality control in engineering projects.

[0003] However, this method has inherent limitations in key steps, affecting the accuracy, repeatability, and practical guidance value of the test results. Specifically, in the asphalt coating stage, the standard requires that the aggregate be immersed in hot asphalt and allowed to drip freely under gravity and then cooled at room temperature. This process makes it difficult to control the uniform thickness of the asphalt film, resulting in large dispersion of results for the same group of samples. Furthermore, the preheating temperature of the aggregate is usually significantly lower than the actual mixing temperature, leading to insufficient fluidity and an excessively thick asphalt film after adhesion. This fails to accurately simulate the film coating state during construction, causing a disconnect between the test conditions and actual service conditions. In the boiling water immersion evaluation stage, the fixed 3-minute immersion time only reflects the initial adhesion performance of the material under short-term humid heat. It cannot effectively distinguish the performance differences of different types of asphalt (such as modified asphalt) or different rock aggregates (such as acid aggregates) under long-term or more severe hydrothermal environments, making the standard method insufficient in terms of applicability and differentiation for modern complex engineering materials.

[0004] Therefore, developing an improved testing method that can accurately control test variables, better simulate real service environments, and has broad material adaptability is of great significance for improving the scientific rigor and engineering applicability of evaluation technology. Summary of the Invention

[0005] The purpose of this invention is to provide an improved water boiling test method for the adhesion of asphalt to aggregates, so as to at least partially solve the above-mentioned problems.

[0006] This invention provides a method for testing the adhesion between asphalt and aggregates, comprising the following steps: S1: Randomly select several aggregate samples and preheat the aggregate samples to the mixing temperature ±5°C; S2: Prepare the asphalt binder and heat it to a temperature not exceeding the mixing temperature until it is in a fluid state; S3: Tie each aggregate sample with a thin thread and immerse it in preheated to a molten state of asphalt binder for 45 seconds to completely coat the aggregate sample with asphalt binder. Then remove the aggregate sample and hang it in an environment of 145±5°C to allow the free asphalt to flow off. After the preset time, remove it and let it cool naturally to room temperature. S4: Immerse the aggregate sample obtained in S3 in boiling water that is kept at a slight boiling state for at least 3 minutes; S5: Transfer the aggregate sample after boiling in water to clean water, observe the degree of peeling of the asphalt film on its surface, evaluate the asphalt film coating rate, and determine the adhesion level based on the average coating rate.

[0007] The adhesion test method between asphalt and aggregate provided by this invention may also have the following additional technical features: In some specific embodiments of the present invention, in step S1, the particle size of the aggregate sample is selected from 13.2-19 mm, 9.5-13.2 mm or 4.75-9.5 mm.

[0008] In some specific embodiments of the present invention, when the aggregate particle size is 13.2-19 mm, 9.5-13.2 mm, or 13.2-19 mm, 5 aggregate samples are taken for testing; when the aggregate particle size is 4.75-9.5 mm, 10 aggregate samples are taken for testing.

[0009] In some specific embodiments of the present invention, in S2, when the asphalt binder is base asphalt, the heating temperature is 160℃±5℃; when the asphalt binder is modified asphalt, the heating temperature is 170℃±5℃.

[0010] In some specific embodiments of the present invention, the slightly boiling state refers to a state in which the water temperature reaches the boiling point under local atmospheric pressure and continues to boil slowly.

[0011] In some specific embodiments of the present invention, in S3, the aggregate sample is suspended in an environment of 145±5°C for no less than 15 minutes.

[0012] In some specific embodiments of the present invention, in S3, the time for the aggregate sample to naturally cool to room temperature is not less than 2 hours.

[0013] In some specific embodiments of the present invention, in step S4, the soaking time is 3 min to 30 min.

[0014] In some specific embodiments of the present invention, when the asphalt binder contains an anti-stripping agent, a control group is set up, and soaking times of 3 min, 10 min, and 30 min are used respectively to compare and evaluate the effects of different anti-stripping agents.

[0015] In some specific embodiments of the present invention, in S5, the asphalt film coating rate is evaluated by comparing the surface condition of the aggregate sample with a standard chart of asphalt film peeling degree.

[0016] The asphalt-aggregate adhesion test method provided in this application achieves dual optimization by simulating real-world processes to optimize the asphalt film state and constructing graded, stringent boiling conditions. This not only makes laboratory test conditions closer to actual engineering conditions, improving the reliability and guiding value of the results, but more importantly, it provides a refined and graded evaluation method, particularly suitable for in-depth comparison, screening, and evaluation of the adhesion performance of high-performance asphalt binders, special aggregates, and various anti-stripping agents. This method significantly enhances the technical advancement and practical application value of asphalt-aggregate adhesion testing. Detailed Implementation

[0017] Exemplary embodiments of the present invention will now be described in more detail. It should be understood that the present invention may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0018] It should be understood that the terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “described” as used herein may also include the plural forms. The terms “comprising,” “including,” “containing,” and “having” are inclusive and therefore indicate the presence of the stated features, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein are not construed as requiring them to be performed in a particular order described or illustrated unless the order of performance is explicitly indicated. It should also be understood that additional or alternative steps may be used.

[0019] Although terms such as first, second, third, etc., may be used in this document to describe multiple elements, components, regions, layers, and / or segments, these elements, components, regions, layers, and / or segments should not be limited by these terms. These terms may be used only to distinguish one element, component, region, layer, or segment from another. Unless the context clearly indicates otherwise, terms such as "first," "second," and other numerical terms used herein do not imply order or sequence. Therefore, the first element, component, region, layer, or segment discussed below may be referred to as the second element, component, region, layer, or segment without departing from the teachings of the exemplary embodiments.

[0020] For ease of description, spatial relative terms may be used in the text to describe the relationship of one element or feature relative to another element or feature. These relative terms include, for example, "inside," "outside," "middle," "outer," "below," "below," "above," "over," etc. Such spatial relative terms are intended to include different orientations of the device in use or operation, in addition to those described in the text. For example, if the device in the text is flipped, an element described as "below other elements or features" or "below other elements or features" would subsequently be oriented as "above other elements or features" or "above other elements or features." Therefore, the example term "below" can include both upper and lower orientations. The device may be otherwise oriented (rotated 90 degrees or in other directions), and the spatial relative descriptors used in the text will be interpreted accordingly.

[0021] The adhesion test method between asphalt and aggregate provided in this invention aims to simulate the adhesion and retention capacity between the asphalt film and the aggregate surface during actual use, especially under water erosion conditions. This method is simple to operate, provides intuitive and reliable results, and is particularly suitable for comparing the effects of different types of asphalt, aggregates from different sources, or different anti-stripping agents.

[0022] The embodiments of the present invention will now be described in detail with reference to specific steps.

[0023] Experimental preparation: First, representative aggregates are selected based on the actual engineering conditions or research objectives. Preferably, the aggregate samples are those actually used in the engineering project, with particle sizes ranging from 13.2-19 mm, 9.5-13.2 mm, or 4.75-9.5 mm as needed. To obtain statistically reliable results, when the aggregate particle size is 13.2-19 mm or 9.5-13.2 mm, typically 5 aggregate samples are taken for testing; when the aggregate particle size is smaller, at 4.75-9.5 mm, 10 aggregate samples are taken for testing to ensure sufficient observation surface area. The selected aggregates should be clean and have a near-cubic shape.

[0024] Prepare the asphalt binder to be tested, including but not limited to base asphalt and various modified asphalts (such as SBS modified asphalt, rubber asphalt, etc.).

[0025] Prepare the anti-stripping agent.

[0026] Experimental steps: Step S1: Aggregate Preheating. Place a randomly selected number of aggregate samples (5 or 10) into an oven and preheat to a temperature range of ±5°C from the mixing temperature. The purpose of this step is to remove the moisture adsorbed on the aggregate surface and to bring the aggregate temperature close to the temperature during subsequent asphalt coating, ensuring good fluidity of the asphalt when in contact with the aggregate, and promoting full coating and adhesion.

[0027] Step S2: Heating the asphalt binder. Heat the asphalt binder to a temperature not exceeding the mixing temperature until the asphalt melts and becomes fluid. The heating temperature needs to be precisely controlled according to the type of asphalt: for base asphalt, the heating temperature is usually 160±5℃; for modified asphalt with higher viscosity, the heating temperature is usually 170±5℃. Ensure that the asphalt is heated evenly, without localized overheating and aging.

[0028] Step S3: Asphalt Coating and Shaping. Secure each preheated aggregate sample to the designated size using a thin thread (such as cotton or nylon thread). Immerse the tied aggregate completely in preheated asphalt binder at the specified temperature for 45 seconds, ensuring the aggregate surface is completely and evenly coated with the asphalt binder. Then, remove the asphalt-coated aggregate and suspend it in a constant temperature environment (such as an oven) maintained at 145±5°C for at least 15 minutes. This process simulates ensuring the fluidity of asphalt on the aggregate, allowing excess asphalt to drip off and separate, thus significantly reducing the thickness of the asphalt on the aggregate. Afterward, remove the sample and allow it to cool naturally at room temperature for at least 2 hours to ensure the asphalt film fully cures.

[0029] Step S4: Boiling Water Immersion Test. Heat a beaker of tap water and maintain a gentle boil. A gentle boil typically refers to a water temperature that is maintained at a low boil, generally around 90°C. However, the temperature may vary depending on atmospheric pressure in different regions; adjust the temperature before the test to meet the requirements. Immerse the asphalt-coated aggregate sample, cooled to room temperature in Step S3, into this gently boiling water. The basic test condition is immersion for at least 3 minutes. This step is the core of the test; the boiling water accelerates the erosion of the asphalt-aggregate interface, simulating the water damage process under humid and hot conditions.

[0030] Step S5: Observation and Rating. Quickly transfer the aggregate samples after boiling water treatment to room temperature clean water. Observe the peeling of the asphalt film on the aggregate surface visually or with the aid of tools. Evaluate the asphalt film coverage rate (i.e., the percentage of intact asphalt film area to the total surface area) of each aggregate. The specific evaluation method is as follows: compare the aggregate surface condition with the standard diagram attached to T0616 "Adhesion Test of Asphalt and Aggregate" in the industry standard "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG 3410-2025) to determine its peeling grade and corresponding coverage rate. Calculate the average coverage rate of all parallel test samples, and based on this average value, compare it with the grading standards specified in the procedure (e.g., ≥95% coverage rate is grade 5, 70%-95% is grade 4, etc.) to finally determine the adhesion grade of the asphalt and aggregate. The higher the grade, the better the water stripping resistance.

[0031] 1. Comparison of base asphalt

[0032] Note: 55444 / 4(-1)△ indicates that 55444 is the measured value, / 4 is the average measured value, and (-1) is the decrease in adhesion level between the improved method and the standard method under the same conditions.

[0033] The comparison shows that the improved method of this application can more accurately determine the adhesion grade between asphalt and aggregate.

[0034] 2. Extended applications of anti-stripping agents: When it is necessary to evaluate the effect of adding anti-stripping agents to asphalt, comparative tests can be conducted to effectively distinguish the performance differences of different types or dosages of anti-stripping agents.

[0035] The specific implementation method is as follows: a control group (without anti-stripping agent) and an experimental group (with different anti-stripping agents) are set up, and the boiling water immersion conditions are strengthened.

[0036] Anti-stripping agent is added to asphalt. The optimal dosage for the project is generally 0.5% to 1% of the asphalt mass. After adding the anti-stripping agent to the asphalt and stirring evenly, the asphalt binder is heated and aged until it reaches a melted and fluid state and kept at that temperature for 1 hour.

[0037] Subsequently, multiple soaking time gradients can be set for testing, such as soaking for 3 minutes (basic evaluation), 10 minutes (medium strength evaluation), and 30 minutes (severe condition evaluation). By comparing the degree of asphalt film peeling of different sample groups under the same soaking time, or comparing the coating rate decay of the same anti-stripping agent sample after different soaking times, the effectiveness and durability of different anti-stripping agents under short-term and long-term hydrothermal effects can be clearly and quantitatively distinguished. This is more scientific and comprehensive than evaluation based on a single soaking time.

[0038] This application also provides a set of embodiments and a set of comparative examples. The embodiments include nine control tests. The aggregate specifications are the same in the control tests, and the differences lie in whether an anti-stripping agent is used, the composition of the anti-stripping agent, and the boiling time. The comparative examples are set up in the same way, except that only a conventional boiling test is used, and the aggregate is not preheated to 180±10°C, and the asphalt-coated aggregate is not subsequently suspended in a constant temperature environment maintained at 145±5°C.

[0039] The results are as follows:

[0040] Note: 44333 / 3(-0)△ indicates that 44333 is the measured value, / 3 is the average measured value, and (-0) is the decrease in adhesion level between the improved method and the standard method under the same conditions.

[0041] 1) Comparison of boiling time: The adhesion grade decreases as the boiling time increases, and the grade decreases significantly after boiling for 10 minutes compared to boiling for 3 minutes, indicating that the 10-minute boiling time condition is more stringent.

[0042] 2) Comparison of anti-stripping agents: After boiling in water for 3 minutes, the difference in effect between the two anti-stripping agents was not significant; after boiling in water for 10 minutes and 30 minutes, the effect of the anti-stripping agents was Y1 > Y2 ≈ no measures were taken. Therefore, from the perspective of identifying anti-stripping agents, the boiling time should not be less than 10 minutes.

[0043] 3) Method comparison: Under the same anti-stripping measures and the same boiling time, the adhesion grades of the improved method and the standard method are similar after boiling for 3 minutes; the adhesion grades of the improved methods after boiling for 10 minutes and 30 minutes are slightly lower than those of the standard method (0.5 to 1 grade), and the improved methods are slightly more stringent than the standard method.

[0044] 4) Improved limestone method without anti-stripping measures: after boiling in water for 10 minutes, the adhesion grade is 3. The effect of the anti-stripping agent is judged based on this adhesion grade.

[0045] Based on the above results, it can be seen that the thickness of the asphalt film obtained by the improved boiling method is closer to the actual engineering situation. After boiling for 10 minutes, the adhesion grade differentiation is better. Considering the test efficiency, it is recommended to use the improved boiling method with a boiling time of 10 minutes. When evaluating the effect of the anti-stripping agent, compared with the results of the improved method for limestone without anti-stripping measures, it is recommended that the adhesion grade be no less than 3, i.e., BM10 ≥ 3.

[0046] Compared to traditional standard methods, the asphalt-aggregate adhesion test method provided in this application first preheats the aggregate to 180°C ± 10°C during the preparation stage to approximate the heating temperature of aggregate in a drying drum in actual engineering. Secondly, after impregnating the aggregate with hot asphalt, it is suspended in an environment of 145°C ± 5°C for a period of time and then allowed to cool naturally. These two processes simulate the state of the mixture during the hot storage stage after the hot aggregate comes into contact with asphalt in actual production. Under these conditions, excess asphalt will drip and separate from the aggregate surface due to gravity. Therefore, this method can significantly reduce and standardize the asphalt film thickness obtained in the test, making it closer to the true thickness of the asphalt film in asphalt mixtures in actual engineering. This effectively avoids the "artificially high" evaluation of adhesion performance caused by an excessively thick asphalt film under laboratory conditions, making the test results more representative of engineering applications and more accurate in prediction.

[0047] This application also innovatively introduces a graded, extended boiling time test mode (e.g., set to 3 min, 10 min, and 30 min). Short-duration boiling can be used for rapid assessment of basic adhesion levels; while extended boiling times create a more stringent, progressive water damage environment. This setup allows the test to not only effectively expose the performance degradation differences of different anti-stripping agents under continuous hydrothermal stress, but also simulate the impact of water damage under longer service conditions, providing a predictive basis for the long-term effectiveness and durability of anti-stripping agents. Furthermore, it significantly enhances the sensitivity and discriminative power of the test method for identifying high-level adhesion performance.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A test method for the adhesion between asphalt and aggregate, characterized in that, Includes the following steps: S1: Randomly select several aggregate samples and preheat the aggregate samples to the mixing temperature ±5°C; S2: Prepare asphalt binder and heat it to a flowable state not exceeding the mixing temperature; S3: Tie each aggregate sample with a thin thread and immerse it in preheated to a molten state of asphalt binder for 45 seconds to completely coat the aggregate sample with asphalt binder. Then remove the aggregate sample coated with asphalt and hang it in an environment of 145±5°C to allow the free asphalt to flow off. After a preset time, remove the aggregate sample and allow it to cool naturally to room temperature. S4: Immerse the aggregate sample obtained in S3 in boiling water that is kept at a slight boiling state for at least 3 minutes; S5: Transfer the aggregate sample after boiling in water to clean water, observe the degree of peeling of the asphalt film on its surface, evaluate the asphalt film coating rate, and determine the adhesion level based on the average coating rate.

2. The method for testing the adhesion between asphalt and aggregate according to claim 1, characterized in that, In step S1, the particle size of the aggregate sample is selected from 13.2-19 mm, 9.5-13.2 mm, or 4.75-9.5 mm.

3. The test method according to claim 2, characterized in that, When the aggregate particle size is 13.2-19mm, 9.5-13.2mm, or 13.2-19mm, take 5 aggregate samples for testing; when the aggregate particle size is 4.75-9.5mm, take 10 aggregate samples for testing.

4. The test method according to claim 1, characterized in that, In S2, when the asphalt binder is base asphalt, the heating temperature is 160℃±5℃; when the asphalt binder is modified asphalt, the heating temperature is 170℃±5℃.

5. The test method according to claim 1, characterized in that, In S4, the slightly boiling state refers to the state in which the water temperature reaches the boiling point under local atmospheric pressure and continues to boil slowly.

6. The test method according to claim 1, characterized in that, In S3, the aggregate sample is suspended in an environment of 145±5°C for no less than 15 minutes.

7. The test method according to claim 1, characterized in that, In S3, the aggregate sample is allowed to cool naturally to room temperature for no less than 2 hours.

8. The test method according to claim 1, characterized in that, In S4, the soaking time is 3-30 minutes.

9. The test method according to claim 8, characterized in that, When the asphalt binder contains an anti-stripping agent, a control group is set up, and the effects of different anti-stripping agents are compared and evaluated by using soaking times of 3 min, 10 min, and 30 min, respectively.

10. The test method according to claim 1, characterized in that, In S5, the asphalt film coating rate is evaluated by comparing the surface condition of the aggregate sample with a standard chart of asphalt film peeling degree.

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