Study on the interaction state between polymer modifiers and asphalt based on precise grinding

2.1. Materials and preparation

This study utilized 70# grade A base asphalt with a softening point of 47 °C, penetration of 6.7 mm, and ductility (10 °C) of 60 cm as the base material, with polyester-based resin serving as the primary asphalt modifier to prepare modified asphalt. The modifier’s key technical specifications are shown in Table 1, with three particle sizes (0.075 mm, 0.15 mm, and 0.3 mm) investigated at a fixed dosage of 6 % by asphalt mass. The modified asphalt was prepared through high-speed shear mixing (3500 rpm, 160 ℃ and 20 min), with the resulting samples designated as SPMA-756 (0.075 mm modifier, 6 % dosage), SPMA-156 (0.15 mm modifier, 6 % dosage), and SPMA-306 (0.3 mm modifier, 6 % dosage).

2.2. Method

3.1. Pavement performance

Fig. 1 presents the road performance of resin-modified asphalt binders with different modifier particle sizes. SPMA samples exhibited lower penetration values than the base asphalt binder, indicating that the resin modifier increased the binder’s viscosity. The softening points of SPMA samples were consistently higher than those of the base binder, demonstrating that reducing modifier particle size enhances the high-temperature performance of asphalt binders. However, the addition of modifiers adversely affected low-temperature performance.

Fig. 1Road performance test results modified asphalt with modifiers of different particle sizes

a) Penetration

b) Softening point

c) Ductility

3.2. PG grading

Fig. 2 presents the rutting factor ($G$/$\mathrm{s}\mathrm{i}\mathrm{n}\delta$), phase angle ($\delta$), and high-temperature failure temperatures of the asphalt binders at different temperatures. As anticipated, the incorporation of modifiers enhanced the $G$/$\mathrm{s}\mathrm{i}\mathrm{n}\delta$ values of the asphalt binders, indicating improved rutting resistance. Compared to the base asphalt binder, SPMA-756, SPMA-156, and SPMA-306 demonstrated that failure temperature was increased by 9.1 %, 7.1 %, and 6.3 %, respectively. These results confirm that the resin modifiers enhance the high-temperature rutting resistance of asphalt binders effectively, with smaller modifier particles exhibiting more pronounced improvement effects.

Fig. 2PG grading test results of modified asphalt with modifiers of different particle sizes

a) Rutting factor

b) Failure temperature

c) Phase angle

3.3. Segregation test

Fig. 3 presents the segregation test results of modified asphalt with different modifier particle sizes. In penetration tests, SPMA-756 exhibited a minimal penetration difference of 0.45 mm, while SPMA-156 and SPMA-306 showed larger differences of 0.51 mm (+13.3%) and 0.63 mm (+40 %), respectively. Similarly, softening point tests revealed differences of 0.8 °C for SPMA-756, increasing to 1.1 °C and 1.4 °C for SPMA-156 and SPMA-306. These findings clearly indicate that the compatibility of resin-modified asphalt systems improves with decreasing modifier particle size, as finer particles promote more uniform dispersion within the asphalt matrix.

Fig. 3Segregation test results of modified asphalt with modifiers of different particle sizes

a) Penetration difference

b) Softening point difference

3.4. Han curve analysis

Fig. 4 presents the Han curves of modified asphalt binders with different modifier particle sizes. The results show that all modified asphalt binders maintain excellent linear relationships (slope < 2) in the temperature range of 10-40 °C, confirming their characteristics as multiphase polymer systems with good dispersion stability. Comparative analysis reveals that the slope of Han curves decreases with increasing modifier particle size in the 10-50 °C range, suggesting that larger particles adversely affect the compatibility of modified asphalt, which may be attributed to their surface microstructure and swelling behavior. Notably, the terminal portions of Han curves exhibit varying degrees of dispersion (as highlighted in red boxes). Specifically, SPMA-756 (0.075 mm) shows slight dispersion at 60-70 °C, while SPMA-156 (0.15 mm) begins to display observable dispersion at 50 °C. Most significantly, SPMA-306 (0.3 mm) demonstrates severe dispersion at 50 °C. This temperature-dependent phenomenon primarily results from the gradual weakening of interfacial bonding strength between the modifier and asphalt matrix at elevated temperatures, which facilitates relative displacement and eventual phase separation of the modifier particles.

Fig. 4Han plots of modified asphalt with modifiers of different particle sizes

a) Base asphalt

b) SPMA756

c) SPMA759

d) SPMA7512

Fig. 5SEM results of interactions between modifiers and base asphalt binders

3.5. Scanning electron microscopy test

Fig. 5 shows SEM results of the interface between modifiers and base asphalt. Analysis of Fig. 5 reveals that the 0.3 mm modifier has a rough and porous surface, with the base asphalt failing to adequately infiltrate the 0.3 mm modifier. A clear gap exists at the interface between the two materials, indicating relatively poor interaction between the 0.3 mm modifier and base asphalt.

Analysis of Fig. 5(e)-(g) shows that the 0.15 mm modifier surface also contains numerous shallow pores. During mixing, the base asphalt can better combine with the 0.15 mm modifier. Furthermore, the abundant pores on the surface of the 0.15 mm modifier increase its surface area, facilitating contact with the base asphalt binder. Analysis of Fig. 5(h)-(j) demonstrates that the interface between the 0.075 mm modifier and base asphalt is smooth and continuous. The asphalt achieves good infiltration of the 0.075 mm modifier, enhancing the bonding between them and reducing the likelihood of compatibility issues in the modified asphalt binder.