Nanoindentation testing method for composite asphalt mixture

Abstract

The invention provides a nanoindentation testing method for a composite asphalt mixture, and relates to the technical field of asphalt material performance research. The method comprises the following steps: S1, preparing a double-solid waste epoxy resin composite asphalt mixture test piece; s2, grinding and polishing the test piece by adopting a step rotating speed and composite lubricating liquid synergistic process so as to obtain the surface smoothness meeting the nanoindentation test requirement; s3, acquiring a macroscopic elastic modulus of the test piece, and automatically generating nanoindentation test parameters according to the macroscopic elastic modulus through a pre-established Sigmoid mapping model; and S4, carrying out nanoindentation test according to the test parameters so as to evaluate the micro-mechanical properties of the asphalt mortar, the aggregate and the interface transition area. By reasonably designing the mix proportion and the production process, efficient utilization of the waste asphalt pavement material and the steel slag is achieved, the resource utilization rate is increased, sustainable development is promoted, and a high-performance, economical and environment-friendly solution is provided for road maintenance and repair engineering under complex climate conditions.

Description

Technical Field

[0001] This invention relates to the field of asphalt material performance research technology, and in particular to a nanoindentation test method for composite asphalt mixtures. Background Technology

[0002] With increasing traffic axle loads and frequent extreme weather events, traditional single-use recycled asphalt mixtures face severe challenges in practical engineering applications, struggling to simultaneously meet the multi-objective synergistic requirements of high waste material content, excellent low-temperature crack resistance, and long-term durability. Especially under the coupled effects of light, water, and heat, the adhesion between asphalt and aggregates is prone to decline, and aging-induced microcracks continue to expand, ultimately leading to early road defects such as cracking and spalling, severely impacting road service life.

[0003] To overcome the aforementioned technical bottlenecks, a dual-solid-waste epoxy resin composite asphalt mixture has been developed in recent years. This material, based on the traditional aggregate-asphalt system, introduces high-performance modifiers such as epoxy resin and synergistically utilizes recycled asphalt pavement material (RAP) and industrial solid waste such as steel slag to construct a novel multiphase composite system. The aim is to achieve high-volume resource utilization while significantly improving the material's high-temperature rutting resistance, low-temperature crack resistance, fatigue durability, and noise reduction performance, representing the development direction of a new generation of functional and sustainable pavement materials.

[0004] In the multiphase structure of asphalt mixtures, the interface transition zone (ITZ) between the asphalt mastic and aggregates plays a crucial role. Due to factors such as asphalt component migration, enrichment, and localized aging, this region often becomes a mechanically weak point in the overall structure. Studies have shown that the micromechanical properties of the ITZ, particularly its strength and crack resistance, have a decisive influence on the macroscopic mechanical response and durability of asphalt mixtures. Under the long-term coupled influence of external loads and natural environmental factors (such as temperature cycling, moisture erosion, and ultraviolet radiation), stress concentration easily occurs in the ITZ region, becoming a preferred path for crack initiation and propagation, ultimately inducing overall structural failure.

[0005] Nanoindentation, as an advanced micro / nanoscale mechanical characterization technique, has been widely applied in recent years to the study of the microscopic properties of composite materials. Its basic principle involves using a high-precision diamond indenter to load the sample surface, recording the load-displacement curve in real time, and calculating key mechanical parameters such as hardness and elastic modulus of local material regions based on the Oliver-Pharr theoretical model. This technique is particularly suitable for the quantitative analysis of the mechanical properties of microphases such as asphalt mastics, aggregates, and ITZ, providing microscopic evidence for revealing the material reinforcement mechanism.

[0006] However, applying nanoindentation technology to composite asphalt mixtures still faces significant technical obstacles. Firstly, this technology has extremely stringent requirements for sample surface quality, demanding that the microscopic height difference in the test area (especially the asphalt-aggregate ITZ) be controlled within 100 μm. However, asphalt mixtures are typical multiphase heterogeneous materials, with the asphalt phase being highly thermally sensitive. During grinding and polishing, frictional heat can easily cause softening, adhesion, or even flow deformation, making it difficult to achieve the required surface smoothness and severely impacting test accuracy and repeatability.

[0007] Secondly, the design of composite asphalt mixtures emphasizes adaptation to local conditions, requiring comprehensive consideration of regional climatic conditions (such as temperature difference, solar radiation intensity, and rainfall), local resource characteristics (such as RAP content and steel slag properties), and traffic load levels (such as axle load and traffic volume). This leads to significant regional differences in their microstructure and macroscopic properties. These differences are not only reflected in the mechanical modulus and rheological behavior of each phase material but also in the interfacial bonding state and aging degree. Therefore, when conducting nanoindentation tests, using uniform or empirical test parameters (such as loading rate, maximum load, and holding time) is difficult to adapt to the characteristics of different material systems. This can easily result in shallow indentations or excessive creep, violating the basic assumptions of the data analysis model, introducing systematic errors, and reducing the accuracy and interphase comparability of test results.

[0008] Therefore, there is an urgent need to develop a systematic testing method that can take into account both high-quality surface treatment and intelligent parameter configuration, so as to ensure the reliable application of nanoindentation technology in this type of complex multiphase material. Summary of the Invention

[0009] In view of this, the present invention proposes a nanoindentation test method for composite asphalt mixtures, which prepares composite asphalt mixtures by combining epoxy resin with two solid wastes (RAP and steel slag), and proposes a test method for studying the interfacial zone polishing of the composite asphalt mixture.

[0010] The technical solution of this invention is implemented as follows: This invention provides a method for nanoindentation testing of composite asphalt mixtures, comprising the following steps: S1. Preparation of specimens of dual-solid-waste epoxy resin composite asphalt mixture; S2. The specimen is polished using a stepped rotation speed and composite lubricant process to obtain a surface finish that meets the requirements of nano-indentation testing. S3. Obtain the macroscopic elastic modulus of the specimen, and based on the macroscopic elastic modulus, automatically generate nanoindentation test parameters through a pre-built Sigmoid mapping model. S4. Perform nanoindentation tests according to the test parameters to evaluate the micromechanical properties of asphalt mortar, aggregates and interfacial transition zones.

[0011] Further, in step S1, the preparation method of the dual solid waste epoxy resin composite asphalt mixture is as follows: at a certain temperature, epoxy resin and curing agent are first mixed and stirred to obtain epoxy binder, then preheated SBS modified asphalt is added and stirred to form epoxy asphalt; subsequently, mineral powder, preheated basalt aggregate, RAP and steel slag are added, and the mixture is stirred to obtain composite asphalt mixture.

[0012] Furthermore, the preparation method of the specimen is as follows: the composite asphalt mixture is formed and cured by Marshall compaction, then cut into small specimens, and encapsulated and fixed with epoxy resin to obtain the test surface.

[0013] Further, in step S2, the grinding and polishing includes: performing dry grinding roughening, lubrication cooling, lubrication fine finishing and lubrication polishing processes on the surface to be tested in sequence; The lubrication cooling, lubrication finishing, and lubrication polishing are all performed using the composite lubricant.

[0014] Furthermore, the composite lubricant is atomized and sprayed using a pneumatic spraying device; wherein the spray orifice diameter is 0.2-0.3 mm and the pressure is 0.2-0.3 MPa.

[0015] Furthermore, the preparation method of the composite lubricant is as follows: polyether-modified silicone oil is stirred and dispersed with a portion of deionized water, then polyethylene glycol is added and stirred to dissolve, followed by the addition of the remaining deionized water, and the composite lubricant is obtained by stirring.

[0016] Furthermore, the surface tension of the composite lubricant is 22-26 mN / m.

[0017] Further, in step S3, the function of the Sigmoid mapping model is: In the formula, E is the macroscopic elastic modulus, y is the output test parameter, yMin and yMax are the minimum and maximum values ​​of the parameter, respectively, E50 is the inflection point modulus, and k is the curve steepness factor.

[0018] Furthermore, the automatically generated nanoindentation test parameters include: indenter type, control mode, loading rate, maximum load, holding time, and unloading rate.

[0019] Furthermore, when E ≤ 0.1 GPa, a spherical indenter is used; when E > 0.1 GPa, a Berkovich sharp indenter is used.

[0020] The nanoindentation testing method for composite asphalt mixtures of the present invention has the following advantages over the prior art: (1) By adopting the “stepped speed-composite lubrication” synergistic polishing process, this invention effectively solves the technical contradiction of “high speed is easy to soften and low speed is difficult to flatten” in traditional grinding, significantly suppresses friction temperature rise, avoids the softening and adhesion of asphalt phase, achieves high precision flatness of less than 100μm micro height difference on the surface of the specimen, and obtains a non-damaging, high-gloss surface that meets the requirements of nano-indentation test, providing a high-quality sample basis for micro-mechanical test.

[0021] (2) By establishing an intelligent parameter optimization method, the present invention automatically outputs nano-indentation test parameters (including indenter type, loading rate, maximum load, etc.) applicable to different phase regions, overcoming the problem of empirical parameter setting and large error caused by the multiphase nature and modulus dispersion of asphalt mixtures, and significantly improving the accuracy, repeatability and comparability of test data and interphase data.

[0022] (3) The composite asphalt mixture provided by the present invention can accurately obtain the elastic modulus, hardness and other mechanical parameters of micro-regions such as asphalt mastic, aggregate and interfacial transition zone (ITZ), effectively reveal the interaction mechanism between multiphase materials, and especially can quantitatively characterize the enhancing effect of modifiers such as epoxy resin on interfacial performance, providing reliable micromechanical basis and data support for the performance optimization and intelligent design of composite asphalt mixtures. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a process flow diagram for the specimen molding of the composite asphalt mixture of the present invention; Figure 2 These are microscope images of the test surface under different detection scales in Embodiment 7 of the present invention; Figure 3 This is an example diagram illustrating the program code description information for Embodiment 10 of the present invention; Figure 4 The image shows the MATLAB program execution result of Embodiment 10 of the present invention; Figure 5 This is a distribution diagram of the test points for indentation testing in Embodiment 10 of the present invention; Figure 6 The image shows the MATLAB program execution result of Comparative Example 7 of this invention. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] This invention proposes a nanoindentation testing method for composite asphalt mixtures. In the research process, firstly, the inventors selected epoxy resin, which possesses excellent mechanical properties and durability, as a modifier and determined the appropriate type and proportion of curing agent. Through experimental research on the influence of different solid waste addition ratios on the mixture performance, the optimal dosage range of RAP and steel slag was optimized to ensure that the recycled asphalt mixture exhibits good high-temperature stability, rutting resistance, and low-temperature crack resistance. Secondly, during the grinding and polishing process, the inventors presented a "stepped speed-composite lubrication" process: by using multi-stage variable speed grinding and the application of composite lubricant, the frictional temperature rise was effectively controlled, avoiding softening and adhesion of the asphalt phase, and achieving a high-precision flatness of less than 100 μm on the surface micro-height difference of the specimen, providing a high-quality sample basis for nanoindentation testing. Furthermore, addressing the issue of strong reliance on experience in setting nanoindentation test parameters, the inventors proposed a "macromodulus-microparameter" mapping strategy: a Sigmoid continuous mapping model was constructed based on the specimen's modulus. A one-click program was developed using MATLAB to automatically output the complete parameter range for nanoindentation testing, including indenter type, loading rate, and maximum load, ensuring comparable and reliable mechanical characterization of different hardness regions within a unified experimental framework. Finally, the performance changes of composite asphalt mixtures before and after the addition of epoxy resin to the dual solid waste were studied through systematic experiments, particularly the strength characteristics of the interfacial transition zone. The results showed that the introduction of epoxy resin significantly improved the hardness and crack resistance of the ITZ, resulting in a significant improvement in the overall fatigue performance and durability of the mixture.

[0027] The following are specific embodiments of the present invention.

[0028] Example 1 This embodiment provides a composite asphalt mixture, comprising: Raw materials: basalt aggregate, limestone mineral powder, SBS modified asphalt, RAP (sieved through a 5mm screen), steel slag (sieved through a 5mm screen), epoxy resin and curing agent; Material dosage: In the composite aggregate system that meets the technical requirements of "Technical Specification for Recycling Asphalt Pavement of Highway" (JTG / T 5521-2019) and "Steel Slag Powder for Cement and Concrete" (GB / T 20491-2017), the volume ratio of each functional component is precisely controlled as follows: stabilized steel slag accounts for 15% (allowable deviation ±1%), recycled asphalt pavement material (RAP) accounts for 25% (allowable deviation ±1%), epoxy resin and curing agent accounts for 20%, limestone mineral powder accounts for 5%, and basalt aggregate accounts for 35% (allowable deviation ±1%). Preparation steps: Preheat basalt aggregate to 180℃, RAP to 150℃, steel slag to 180℃, and SBS modified asphalt to 160℃; then at 60℃, mix epoxy resin (model: such as E-51, solid content ≥99%) and curing agent (model: polyamide 650, mass ratio of epoxy resin to epoxy resin 1:4) at a mass ratio of 50:50, stir for 2 minutes, add SBS modified asphalt, and continue stirring for 3 minutes; then add limestone mineral powder, preheated basalt aggregate, RAP, and steel slag, and stir evenly to obtain composite asphalt mixture.

[0029] Comparative Example 1 The difference from Example 1 is that no epoxy resin and curing agent were added, while the remaining materials and steps remained unchanged.

[0030] The composite asphalt mixtures prepared in Example 1 and Comparative Example 1 were subjected to compressive strength tests (《Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering》(JTG E20-2011)》), chemical resistance and aging resistance tests (《Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering》(JTG E20-2011)》), and fatigue performance tests (《Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering》(JTG E20-2011)》). The test results are as follows.

[0031] Test data shows that, in terms of mechanical properties, the compressive strength of the composite asphalt mixture without epoxy resin is 0.85 MPa; after adding epoxy resin, the compressive strength significantly increases to 1.47 MPa, an increase of 72.94%. This indicates that the addition of epoxy resin significantly enhances the mechanical properties of the mixture, enabling it to better withstand traffic loads.

[0032] In terms of chemical resistance and aging resistance, the mass loss rate of composite asphalt mixtures without epoxy resin after thermo-oxidative aging and UV aging was 15%. However, after adding epoxy resin, the mass loss rate was significantly reduced to 5%. This indicates that the addition of epoxy resin significantly improves the aging resistance of the mixture and extends its service life. Specifically, the three-dimensional network structure formed by epoxy resin can effectively protect asphalt from the effects of photo-oxidation and thermo-oxidation, thereby mitigating the negative impact of aging on the performance of the mixture.

[0033] In terms of fatigue resistance, the composite asphalt mixture without epoxy resin exhibited fatigue lives of 215,000, 68,000, and 12,000 cycles at strain control levels of 450 με, 650 με, and 850 με, respectively. In contrast, the composite asphalt mixture with epoxy resin, under the same strain control levels, showed fatigue lives of 6,532,000, 1,854,000, and 267,000 cycles, respectively. This demonstrates that at different stress levels, the fatigue life of the composite asphalt mixture with epoxy resin is significantly higher than that without. This indicates that the addition of epoxy resin significantly improves the fatigue resistance of the mixture, making it less prone to fatigue failure during long-term use. At a strain level of 450 με, the fatigue life with epoxy resin is approximately 30.4 times that without epoxy resin; at a strain level of 650 με, the fatigue life is approximately 27.3 times that without epoxy resin. This demonstrates that epoxy resin can effectively improve the fatigue performance of the mixture and extend its service life.

[0034] Example 2 The difference from Example 1 is that recycled asphalt pavement material (RAP) accounts for 25% (with an allowable deviation of ±1%), while the rest remains unchanged.

[0035] Comparative Example 2 The difference from Example 2 is that no epoxy resin and curing agent were added, while the remaining materials and steps remained unchanged.

[0036] Example 3 The difference from Example 1 is that the stabilized steel slag accounts for 15%, while the rest remains unchanged.

[0037] Comparative Example 3 The difference from Example 3 is that no epoxy resin and curing agent were added, while the remaining materials and steps remained unchanged.

[0038] The composite asphalt mixtures prepared in Examples 2-3 and Comparative Examples 2-3 were subjected to compressive strength tests, chemical resistance tests, aging resistance tests, and fatigue resistance tests. The test results are as follows.

[0039] Based on Examples 1-2 and Comparative Examples 1-2, it can be seen that when the RAP addition ratio increases from 20% to 25%, the compressive strength of the composite asphalt mixture without epoxy resin decreases from 0.85 MPa to 0.78 MPa. However, when epoxy resin is added to the mixture, even with the RAP addition ratio increasing to 25%, the compressive strength of the mixture remains at 1.40 MPa. This indicates that the addition of epoxy resin significantly improves the sensitivity of the mixture to the RAP addition ratio, allowing the mixture to maintain high compressive strength even at higher RAP addition ratios. Epoxy resin, through its three-dimensional network structure, enhances the adhesion between asphalt and aggregates, thereby mitigating the negative impact of increased RAP on the mixture strength.

[0040] Based on Examples 1 and 3, and Comparative Examples 1 and 3, it can be seen that when the steel slag addition ratio increases from 10% to 15%, the compressive strength of the composite asphalt mixture without epoxy resin increases from 0.90 MPa to 0.95 MPa. However, after adding epoxy resin, when the steel slag addition ratio increases from 10% to 15%, the compressive strength of the mixture increases from 1.50 MPa to 1.55 MPa. This indicates that the addition of epoxy resin further enhances the positive effect of steel slag in the mixture, allowing the steel slag addition ratio to be increased within a certain range without reducing the overall mechanical properties of the mixture. The addition of epoxy resin improves the interfacial adhesion between steel slag and asphalt, thereby increasing the strength of the mixture.

[0041] Taking the composite asphalt mixtures prepared in Example 1 and Comparative Example 1 as examples, specimen molding was carried out, such as... Figure 1 As shown, the following steps are taken: the mixed material is poured into a standard mold, and the specimen is formed using the Marshall compaction method to ensure the density and uniformity of the specimen; The Marshall compaction parameters include: 75 compaction passes per side and a compaction temperature of 150°C. The molded specimens must be cured in a 60°C oven for 4 days to ensure the strength of the mixture is achieved.

[0042] The composite asphalt mixture test blocks were precisely cut into cubes with sides of 15mm×15mm×15mm using IPG's LaserCube laser cube cutter. During the cutting process, ethanol was used for effective heat control to precisely avoid adverse conditions such as asphalt mixture sticking to the cutting tool due to abnormal temperature rise.

[0043] In a vacuum environment, epoxy resin AB glue is mixed and stirred until clear. It is then poured into a cylindrical mold with a diameter of 20mm along with the test block. The test block is required to be completely covered by the resin glue, with only the test surface exposed. The mixture is left to stand at room temperature for 24 hours to form a uniform sealing layer.

[0044] Example 4 This embodiment provides a composite lubricant, prepared by the following steps: Add 0.5 g of polyether-modified silicone oil and 10 g of deionized water to a clean beaker, and stir with a magnetic stirrer at 300 rpm for 5 min to fully disperse the polyether-modified silicone oil in the water and form a uniform premix. Add 2 g of polyethylene glycol to the premix and continue stirring at the same speed for 5 min until the polyethylene glycol is completely dissolved. Then add the remaining 87.5 g of deionized water and stir for 10 min to mix the system evenly, to obtain a composite lubricant with a surface tension of 22 mN / m.

[0045] Example 5 This embodiment provides a composite lubricant, prepared by the following steps: Add 0.5 g of polyether-modified silicone oil and 10 g of deionized water to a clean beaker, and stir with a magnetic stirrer at 400 rpm for 5 min to fully disperse the polyether-modified silicone oil in the water and form a uniform premix. Add 2 g of polyethylene glycol to the premix and continue stirring at the same speed for 5 min until the polyethylene glycol is completely dissolved. Then add the remaining 87.5 g of deionized water and stir for 10 min to mix the system evenly, to obtain a composite lubricant with a surface tension of 24 mN / m.

[0046] Example 6 This embodiment provides a composite lubricant, prepared by the following steps: Add 0.5 g of polyether-modified silicone oil and 10 g of deionized water to a clean beaker, and stir with a magnetic stirrer at 500 rpm for 5 min to fully disperse the polyether-modified silicone oil in the water and form a uniform premix. Add 2 g of polyethylene glycol to the premix and continue stirring at the same speed for 5 min until the polyethylene glycol is completely dissolved. Then add the remaining 87.5 g of deionized water and stir for 10 min to mix the system evenly, to obtain a composite lubricant with a surface tension of 26 mN / m.

[0047] Example 7 Based on the test surface prepared in Example 1, this example provides a method for grinding and polishing using stepped rotation speed and composite lubricant, including the following steps: (1) Dry grinding roughening stage: P800 sandpaper was used to dry grind the sample surface at a speed of 300 r / min for 15 minutes.

[0048] In this invention, this stage utilizes the mechanical cutting action of the abrasive to rapidly remove defects such as loose aggregates, burrs, and macroscopic protrusions from the sample surface. Furthermore, the use of dry grinding avoids the softening of the loose surface structure by the lubricant, ensuring cutting efficiency and material removal capacity during the roughening stage.

[0049] (2) Lubrication and cooling stage: P1500 sandpaper was used to wet grind the composite lubricant prepared in Example 4 at a speed of 150 r / min for 15 minutes. The composite lubricant was supplied in the form of mist using a pneumatic spray bottle with a diameter of 0.3 mm and a pressure of 0.2 MPa. The supply method was as follows: 0.5 ml was sprayed 3 times initially to ensure that a uniform water film was formed on the surface of the specimen; 0.5 ml was sprayed every 3 minutes during the process to maintain the continuity of the lubricating film and enhance heat dissipation. In this invention, this stage utilizes the synergistic effect of low rotational speed and the cooling and lubricating film formed by the lubricating fluid to effectively remove the heat accumulated during the dry grinding stage, rapidly reducing the sample surface temperature from 35-40℃ to below 30℃, providing a low-temperature stable base for subsequent finishing. Simultaneously, the lubricating fluid penetrates to the surface, softening the microscopic protrusions of the asphalt phase, which is beneficial for subsequent cutting with fine-grained abrasives.

[0050] (3) Lubrication and finishing stage: P1500 sandpaper is used to wet grind the composite lubricant prepared in Example 4 at a speed of 250 r / min for 20 minutes. The composite lubricant is supplied by spraying 0.5 ml every 2 minutes to keep the surface moist but without water accumulation, so as to avoid temperature rebound caused by the increase of friction coefficient.

[0051] In this invention, on a cooled substrate, the relative motion between the abrasive and the sample surface is enhanced by a moderate rotational speed, precisely removing scratches generated during the roughening stage and significantly improving surface smoothness. The friction-reducing properties of the composite lubricant effectively suppress the temperature rebound that may be caused by increased rotational speed, ensuring that the asphalt phase does not soften or stick. (4) Lubrication and polishing stage: P2500 sandpaper is used to wet grind the composite lubricant prepared in Example 4 at a speed of 100 r / min for 20 minutes. The composite lubricant is supplied by spraying 0.3 ml every 5 minutes to avoid scratches caused by insufficient lubrication of fine abrasive particles.

[0052] In this invention, under ultra-low rotational speed conditions, the fine-grained abrasive undergoes a "micro-slip friction" action with the sample surface, gently removing submicron-level scratches remaining from the finishing stage. This stage minimizes frictional heat generation, and combined with the flow and spreading effect of the composite lubricant, a test surface with micro-undulations of less than 100 μm, no thermal damage, and high smoothness is ultimately obtained, meeting the stringent requirements of nanoindentation for sample surface quality.

[0053] In this invention, it should be noted that the spraying process of the composite lubricant is a continuous process in the lubrication cooling stage, the lubrication finishing stage, and the lubrication polishing stage, with the only difference being the spraying frequency and dosage.

[0054] The smoothness of the test surface obtained in Example 7 was tested using an electron microscope at scales of 200 μm, 100 μm, 50 μm, and 20 μm. The results are as follows. Figure 2 As shown.

[0055] Depend on Figure 2 It can be seen that the smoothness of the surface to be tested after being treated by the grinding and polishing method of the present invention meets the high-precision test standard.

[0056] Example 8 Based on the test surface prepared in Example 1, this example provides a method for grinding and polishing using stepped rotation speed and composite lubricant, including the following steps: (1) Dry grinding roughening stage: P800 sandpaper was used to dry grind the sample surface at a speed of 300 r / min for 15 minutes.

[0057] (2) Lubrication and cooling stage: P1500 sandpaper was used to wet grind the composite lubricant prepared in Example 5 at a speed of 150 r / min for 15 minutes. The composite lubricant was supplied in the form of mist using a pneumatic spray bottle with a diameter of 0.3 mm and a pressure of 0.3 MPa. The supply method was as follows: 1 ml was sprayed 4 times initially to ensure that a uniform water film was formed on the surface of the specimen; 0.5 ml was sprayed every 4 minutes during the process to maintain the continuity of the lubricating film and enhance heat dissipation.

[0058] (3) Lubrication and finishing stage: P1500 sandpaper is used to wet grind the composite lubricant prepared in Example 5 at a speed of 250 r / min for 20 minutes. The composite lubricant is supplied by spraying 0.3 ml every 3 minutes to keep the surface moist but without water accumulation, so as to avoid temperature rebound caused by the increase of friction coefficient.

[0059] (4) Lubrication and polishing stage: P2500 sandpaper is used, and the composite lubricant prepared in Example 5 is sprayed at a speed of 100 r / min for wet grinding for 20 minutes. The composite lubricant is supplied by spraying 0.2 ml every 6 minutes to avoid scratches caused by insufficient lubrication of fine abrasive particles.

[0060] Example 9 Based on the test surface prepared in Example 1, this example provides a method for grinding and polishing using stepped rotation speed and composite lubricant, including the following steps: (1) Dry grinding roughening stage: P800 sandpaper was used to dry grind the sample surface at a speed of 300 r / min for 15 minutes.

[0061] (2) Lubrication and cooling stage: P1500 sandpaper was used to wet grind the composite lubricant prepared in Example 6 at a speed of 150 r / min for 15 minutes. The composite lubricant was supplied in the form of mist using a pneumatic spray bottle with a diameter of 0.2 mm and a pressure of 0.2 MPa. The supply method was as follows: 0.8 ml was sprayed 3 times initially to ensure that a uniform water film was formed on the surface of the specimen; 0.5 ml was sprayed every 3 minutes during the process to maintain the continuity of the lubricating film and enhance heat dissipation.

[0062] (3) Lubrication and finishing stage: P1500 sandpaper is used to wet grind the composite lubricant prepared in Example 6 at a speed of 250 r / min for 20 minutes. The composite lubricant is supplied by spraying 0.3 ml every 3 minutes to keep the surface moist but without water accumulation, so as to avoid temperature rebound caused by the increase of friction coefficient.

[0063] (4) Lubrication and polishing stage: P2500 sandpaper is used to wet polish the composite lubricant prepared in Example 6 at a speed of 100 r / min for 20 minutes. The composite lubricant is supplied by spraying 0.2 ml every 6 minutes to avoid scratches caused by insufficient lubrication of fine abrasive particles.

[0064] Comparative Example 4 The difference from Example 7 is that a composite lubricant was not used, the steps were adapted, and the rest remained unchanged.

[0065] Comparative Example 5 The difference from Example 7 is that stages (2) and (3) are omitted, while the rest remain unchanged.

[0066] Comparative examples 7 and 4-5 show that, due to the lack of stepped speed control and composite lubrication cooling mechanism, frictional heat is difficult to dissipate effectively during grinding, causing the sample surface temperature to easily exceed the asphalt softening point (45–60℃). This leads to asphalt phase softening, adhesion, and dragging phenomena, resulting in problems such as "blade sticking," dense surface scratches, and excessive micro-undulations (generally exceeding 100 μm). In contrast, this invention employs a "stepped speed-composite lubrication" synergistic polishing process. By rationally controlling the synergistic effect of the speed at each stage and the composite lubricant, the surface quality and preparation efficiency of the asphalt mixture sample are significantly improved. After rapid removal of macroscopic defects through dry grinding at 300 r / min, cooling is achieved through wet grinding at 150 r / min, followed by fine finishing at 250 r / min to eliminate scratches. Finally, high-gloss polishing is completed at 100 r / min with fine-grained sandpaper, controlling the micro-height difference on the sample surface within 100 μm, meeting the requirements for nano-indentation testing. This process effectively suppresses frictional temperature rise, avoids asphalt softening and performance degradation, reduces repeated grinding, significantly improves sample preparation efficiency, lowers costs, and ensures the authenticity of the mechanical properties of the samples. It provides a high-quality, high-efficiency, and low-damage sample preparation solution for the micromechanical characterization of composite asphalt mixtures.

[0067] Comparative Example 6 The difference from Example 7 is that the test surface prepared based on Comparative Example 1 is polished, while the other conditions remain unchanged.

[0068] Taking the test surfaces obtained in Example 7 and Comparative Example 6 as examples, the parameters of the Nano Indenter G200 nanoindenter were set, including: (I) Selection of pressure head type: Based on the hardness differences of different phase zones (aggregates, interfacial transition zone (ITZ), and asphalt mastic) in asphalt mixtures, the appropriate indenter geometry should be selected. For the harder aggregate and matrix phases, a sharp-tipped Berkovich indenter should be used to generate sufficient stress concentration and indentation depth, thereby improving the signal-to-noise ratio. For soft asphalt mastic or weak interfacial zones, a spherical indenter can be used to reduce local stress concentration, suppress excessive indentation and material extrusion, and ensure the stability of the testing process.

[0069] (II) Control Mode Setting Force Control Mode was used for indentation testing. This mode sets the maximum loading force rather than the indentation depth, allowing the indentation depth to be determined by the intrinsic mechanical properties of the material. This effectively avoids excessive indentation depth caused by displacement control in soft phases and its interference with the stress field of adjacent measuring points. At the same time, it ensures sufficient indentation response in hard phases, improving the consistency and comparability of test data for multiphase materials.

[0070] (III) Loading Rate Setting Taking into account the viscoelastic properties of asphalt binders, a reasonable loading rate should be set. The loading rate needs to balance the elastic response and creep behavior of the material: too high a rate can lead to instantaneous elastic deformation dominating, resulting in inflated measured values; too slow a rate can easily induce significant creep, affecting the analytical accuracy of the unloading curve. Therefore, a moderate loading rate should be selected to balance testing efficiency and the material's true mechanical response, ensuring that the loading process conforms to the deformation mechanism of viscoelastic materials.

[0071] (iv) Maximum load setting The maximum load is set based on the mechanical properties of the phase region to be tested, in order to control the indentation depth within a reasonable range. For soft phases (such as asphalt mortar), the load should not be too large to prevent excessive indentation depth from causing indenter adhesion or interference from the base effect; for hard phases (such as aggregate or modified interface regions), sufficient load needs to be applied to obtain an analytical indentation signal. The setting of the maximum load should ensure that effective and reliable load-displacement curves can be obtained in different phase regions.

[0072] (v) Setting the load retention time A holding period is set after the maximum load is reached to eliminate the creep effect of asphalt materials under continuous load. The holding time should be sufficient to allow the viscoplastic deformation inside the material to stabilize, ensuring that the deformation during the unloading phase is mainly elastic recovery, satisfying the basic assumption of "elastic unloading" in the Oliver-Pharr method, and improving the accuracy of modulus and hardness calculations.

[0073] (vi) Unloading rate setting The unloading process employs a slow unloading mode that matches the loading rate to avoid uneven stress release or dynamic effect interference caused by excessively rapid unloading. Appropriately setting the unloading rate helps obtain a smooth and stable unloading curve, improves data fitting accuracy, and ensures the reliable extraction of microscopic mechanical parameters (such as elastic modulus and hardness).

[0074] Furthermore, considering that the measured range of elastic modulus of asphalt mixtures spans 2.47 logarithmic periods (0.05–15 GPa, data from Li Peilong et al., "Dynamic Response Master Curve Analysis of Carbon Black Modified Asphalt Mixtures"), the inventors considered that when k=2.5, the 10%–90% transition band width ΔE≈1.76 GPa of the standard logistic function precisely covers the medium-to-high gradient segment of this range, avoiding both overshoot in the hard phase due to excessive steepness and distortion in the soft phase due to excessively gentle gradient. Taking k as an integer or half-integer can effectively suppress floating-point truncation error; 2.5 ensures no gradient overflow in MATLAB double-precision downprecision and facilitates cross-platform code reproduction. Therefore, this invention further solidifies k to 2.5, achieving a synergistic optimality among statistical optimality, engineering robustness, and computational simplicity.

[0075] Example 10 Based on the test surface obtained in Example 7, this embodiment provides a method for setting and testing nanoindentation parameters, including the following steps; According to the test method for uniaxial compression dynamic modulus in T0735 of the "Test Procedure for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20), a vertical axial load was applied to the specimen at a specified temperature and loading frequency, and its macroscopic elastic modulus E was calculated to be 1.2 GPa through the stress-strain response curve. Input the macroscopic elastic modulus E into the MATLAB program: When E>0.1 GPa, the material exhibits aggregate-dominated hard phase behavior. A Berkovich sharp indenter is selected to generate a sufficient stress gradient, thereby satisfying the mechanical assumptions of the Oliver-Pharr model. When E ≤ 0.1 GPa, the material is in a soft phase state dominated by asphalt mortar or the interface transition zone. A spherical indenter is used to reduce stress concentration and suppress excessive indentation. In this invention, a hard switching threshold of 0.1 GPa is used to ensure the distinction between soft and hard phases. Moreover, this threshold is highly consistent with the statistical results of the experimental database (false positive rate <2%). While ensuring accurate distinction between soft and hard phases, the decision-making logic is significantly simplified and the robustness of the algorithm is improved.

[0076] In this embodiment, the code description information table is exemplified as follows: Figure 3 As shown.

[0077] After confirming the pressure head type based on the above information, the following parameters are automatically calculated and output using the Sigmoid mapping model (k=2.5), including but not limited to control mode, loading rate, maximum load, holding time, and unloading rate.

[0078] In this embodiment, the MATLAB program execution result is as follows: Figure 4 As shown.

[0079] In this embodiment, a Berkovich indenter is selected based on the macroscopic elastic modulus of the specimen to ensure sufficient stress gradient in the aggregate-interface transition zone (ITZ) and improve the signal-to-noise ratio and accuracy of the indentation data.

[0080] In this embodiment, a force control mode is adopted to avoid excessively deep indentations of the soft phase (asphalt mortar) under displacement control, which could cause stress interference to adjacent areas and ensure the independence and comparability of test data in multiphase regions.

[0081] In this embodiment, the loading / unloading rate is set to 0.09 mN / s to ensure testing efficiency while effectively balancing the elastic and viscous responses of the asphalt material, preventing excessively high modulus due to excessively fast loading or significant creep due to excessively slow loading.

[0082] In this embodiment, the maximum load is 0.6 mN, which ensures that the indentation depth is sufficient to obtain reliable data, while avoiding the problem of indenter adhesion caused by excessively deep indentations.

[0083] In this embodiment, the holding time is set to 100 seconds to stabilize the creep inside the material and ensure that the unloading phase is mainly characterized by elastic recovery, which meets the requirements of the Oliver-Pharr method for "elastic unloading".

[0084] In this embodiment, the polished specimen is fixed on a Nano Indenter G200 nanoindenter, and the above parameter set is directly input into the instrument control system. Array indentation tests are performed on the asphalt mortar, aggregate, and interface transition zone (ITZ) on the specimen surface, as shown in the test points. Figure 5 As shown.

[0085] Comparative Example 7 The difference from Example 10 is that the nanoindentation parameters were set and tested based on the test surface obtained in Comparative Example 6. The macroscopic elastic modulus E of the test surface is 0.03 GPa. Figure 6 As shown.

[0086] The test results show that in the nanoindentation test, the average hardness of the interfacial transition zone (ITZ) without epoxy resin was 35.1 MPa, while the average hardness after adding epoxy resin significantly increased to 61.4 MPa, an increase of approximately 74.9%. This significant improvement indicates that the addition of epoxy resin effectively enhances the mechanical properties of the ITZ, thereby improving the overall micromechanical properties of the asphalt mixture. Specifically, epoxy resin, through its three-dimensional network structure, enhances the adhesion between asphalt and aggregates, improves the mechanical properties of the interfacial transition zone, and allows the ITZ to better disperse stress under external forces, reducing stress concentration and thus improving the overall stability and durability of the asphalt mixture. This result not only verifies the effectiveness of epoxy resin in improving the performance of the interfacial transition zone but also provides strong theoretical support for the application of composite asphalt mixtures under complex working conditions.

[0087] Comprehensive experimental analysis shows that the hardness of asphalt mixtures is ranked as follows: aggregate > interfacial transition zone (ITZ) > asphalt mastic.

[0088] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for testing nanoindentation in composite asphalt mixtures, characterized in that, Includes the following steps: S1. Preparation of specimens of dual-solid-waste epoxy resin composite asphalt mixture; S2. The specimen is polished using a stepped rotation speed and composite lubricant process to obtain a surface finish that meets the requirements of nano-indentation testing. S3. Obtain the macroscopic elastic modulus of the specimen, and based on the macroscopic elastic modulus, automatically generate nanoindentation test parameters through a pre-built Sigmoid mapping model. S4. Perform nanoindentation tests according to the test parameters to evaluate the micromechanical properties of asphalt mortar, aggregates and interfacial transition zones.

2. The nanoindentation test method for composite asphalt mixtures as described in claim 1, characterized in that, In step S1, the preparation method of the dual solid waste epoxy resin composite asphalt mixture is as follows: at a certain temperature, epoxy resin and curing agent are first mixed and stirred to obtain epoxy binder, then preheated SBS modified asphalt is added and stirred to form epoxy asphalt; subsequently, mineral powder, preheated basalt aggregate, RAP and steel slag are added, and the mixture is stirred to obtain composite asphalt mixture.

3. The nanoindentation test method for composite asphalt mixtures as described in claim 2, characterized in that, The specimen is prepared by molding and curing the composite asphalt mixture using the Marshall compaction method, then cutting it into small specimens, and encapsulating and fixing them with epoxy resin to obtain the test surface.

4. The nanoindentation test method for composite asphalt mixtures as described in claim 3, characterized in that, In step S2, the grinding and polishing includes: performing dry grinding roughening, lubrication cooling, lubrication fine finishing and lubrication polishing processes on the surface to be tested in sequence; The lubrication cooling, lubrication finishing, and lubrication polishing are all performed using the composite lubricant.

5. The nanoindentation test method for composite asphalt mixtures as described in claim 4, characterized in that, The composite lubricant is atomized and sprayed using a pneumatic spraying device. The spray orifice diameter is 0.2-0.3 mm, and the pressure is 0.2-0.3 MPa.

6. The nanoindentation test method for composite asphalt mixtures as described in claim 5, characterized in that, The method for preparing the composite lubricant is as follows: polyether-modified silicone oil is stirred and dispersed with a portion of deionized water, then polyethylene glycol is added and stirred to dissolve, followed by the addition of the remaining deionized water, and the composite lubricant is obtained by stirring.

7. The nanoindentation test method for composite asphalt mixtures as described in claim 5, characterized in that, The surface tension of the composite lubricant is 22-26 mN / m.

8. The nanoindentation test method for composite asphalt mixtures as described in claim 1, characterized in that, In step S3, the function of the Sigmoid mapping model is: In the formula, E is the macroscopic elastic modulus, y is the output test parameter, yMin and yMax are the minimum and maximum values ​​of the parameter, respectively, E50 is the inflection point modulus, and k is the curve steepness factor.

9. The nanoindentation test method for composite asphalt mixtures as described in claim 8, characterized in that, The automatically generated nanoindentation test parameters include: indenter type, control mode, loading rate, maximum load, holding time, and unloading rate.

10. The nanoindentation test method for composite asphalt mixtures as described in claim 8, characterized in that, When E ≤ 0.1 GPa, a spherical indenter is used; when E > 0.1 GPa, a Berkovich sharp indenter is used.

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