To analyse the differences in the high-temperature performance of twin-screw desulphurised rubber powder/undesulphurised rubber powder composite SBS-modified asphalt and its mixes. This paper analyses the performance differences between desulphurised rubber powder composite SBS-modified asphalt (ACR/SBS), rubber powder composite SBS-modified asphalt (CR/SBS) and SBS-modified asphalt and their mixtures by multi-stress repeated creep recovery (MSCR) and submerged Hamburg rutting tests. In addition, fluorescence microscopy was used to reveal the micro-mechanisms underlying the differences in the high-temperature performance of the three asphalts. The results show that the twin-screw desulphurisation of rubber powder can significantly improve the high-temperature performance and water damage resistance of its composite-modified asphalt and mixture. The rutting depth of ACR/SBS-MA mixes was one-third and one-thirteenth of CR/SBS-MA mixes and SBS-MA mixes, respectively, under the hydrothermal coupling condition at 80 °C. The cross-linking bonds were opened during the twin-screw desulphurisation process to form a stable cross-linking network structure with SBS. The research of this thesis can lay theoretical and technical support for the promotion and application of desulphurised rubber-modified asphalt.

To investigate the rheological properties and influence mechanisms of twin-screw activated rubber composite-modified asphalt, we used SBS-modified asphalt (SBS) as the reference. Raw rubber powder composite-modified asphalt (RA/SBS) and activated rubber composite-modified asphalt (ARA/SBS) were prepared. A dynamic shear rheometer (DSR) and bending beam rheometer (BBR) were employed to comparatively analyze the rheological characteristics of the three modified asphalts, while Fourier transform infrared spectroscopy (FTIR) and fluorescence microscopy were used to reveal the micro-mechanisms in ARA/SBS. The results showed that ARA/SBS exhibited better storage stability and low-temperature flexibility compared to SBS and RA/SBS, and ARA/SBS demonstrated lower viscosity than RA/SBS. Among the three, ARA/SBS showed significantly improved high-temperature performance. The comparison of creep stiffness S and creep rate m indicated optimal performance in ARA/SBS, confirming that twin-screw activated rubber powder could significantly enhance the low-temperature properties of modified asphalt. Microscopically, chemical reactions occurred between oxygen-containing functional groups in activated rubber and polar groups in asphalt, while a cross-linked network structure formed between activated rubber molecules and asphalt molecular chains, improving compatibility and enhancing the rheological properties of composite modified asphalt.

The increase in the viscosity of high-rubber-content asphalt modified with rubber powder at high temperatures leads to processing difficulties and drastic changes in physical properties, which have long been a challenge in the asphalt industry. Although viscosity reducers have shown great potential in addressing these issues, their mechanisms of action in high-rubber-content asphalt modified with rubber powder remain unclear. This study employs diphenyl disulfide (DD) as a viscosity reducer and elucidates its mechanism of action in high-rubber-content asphalt, which includes three stages: (1) dissolution and dispersion in the asphalt matrix; (2) impregnation into the crosslinked network of the rubber powder; and (3) de-crosslinking via active free radicals. By optimizing the pre-impregnation time (12 h), temperature (110 °C), and rubber powder particle size (160–180 µm), the dispersion of DD can be enhanced, thereby improving the processability of high-rubber-content asphalt modified with rubber powder. Compared to untreated asphalt, the optimized conditions result in a significant reduction in the crosslinking density of 50% and a substantial decrease in viscosity at 180 °C. This study provides new insights into the viscosity reduction of high-rubber-content asphalt modified with rubber powder and contributes to a deeper understanding of the mechanisms of viscosity reducers.

In this study, four types of anti-ultraviolet aging agents—layered double hydroxides (LDHs), organic montmorillonite (OMMT), titanium dioxide (TiO₂), and ultraviolet absorber (UV326)—were employed to modify asphalt. The modified asphalt samples underwent Rolling Thin Film Oven Test (RTFOT) and xenon-lamp aging treatments, and we examined the evolution of their physical properties, rheological performance, and chemical composition. A principal component analysis (PCA) model built on representativeness, discriminative power, and non-redundancy reduced the multidimensional data to two principal components, which together captured 87.540% of the total variance. The dynamic principal component trajectories, plotted from the reduced-dimension data for the unaged–short-term-aged–xenon-lamp-aged process, revealed that anti-aging agents sharing the same protection mechanism led to comparable rates of high- and low-temperature performance deterioration during xenon-lamp aging, whereas agents with different mechanisms resulted in distinctly different patterns of performance deterioration. In the critical xenon-lamp aging stage, the neat asphalt exhibited a trajectory vector change of ΔPC1 = 0.92 and ΔPC2 = 1.25, corresponding to an angle of 54°, reflecting a low-temperature degradation. By contrast, the physical shielding agents LDHs and OMMT produced much steeper trajectories with angles of approximately −80°, where ΔPC2 values rose to as high as 3.67 and 2.19 respectively despite modest reductions in overall aging. The reflective agent TiO₂ showed a more moderate angle of 84°, with ΔPC1 and ΔPC2 values of 0.16 and 1.45, indicating a slight retardation of high-temperature performance loss. Notably, the UV absorber UV326 maintained the same trajectory angle of 56° as the neat asphalt but with reduced magnitudes of ΔPC1 = 0.63 and ΔPC2 = 0.94, suggesting a balanced delay in aging without altering its relative progression. This study proposes a novel analytical framework for mechanism-based clustering analysis and the precise selection of anti-aging agents for asphalt.

High soil sulfate levels can inhibit crop growth and accelerate concrete infrastructure degradation, highlighting the critical importance of rapid and accurate sulfate content determination. Nevertheless, conventional analytical techniques are laborious and intricate, and delays in processing may result in alterations to the material, owing to oxidation. We recognized the accuracy, reproducibility, and non-invasiveness of mid-infrared (MIR) spectroscopy as a rapid and straightforward technique for soil analysis. In this study, soil samples were collected from two depths (0–20 cm and 20–40 cm) across three regions in China: the arid northwestern region, the cold-temperate northeastern zone, and the subtropical southwestern region. One group was mixed with Na₂SO₄ (a readily soluble salt) at mass fractions ranging from 0.1% to 7%, while the other group was mixed with FeS₂ (a sulfide) at mass fractions ranging from 1% to 70%. This study aimed to develop a mid-infrared spectroscopy-based method for analyzing soluble sulfate and sulfide in soil. Three chemometric methods were evaluated: partial least squares regression (PLSR), principal component regression (PCR), and multivariate linear regression (MLR). Results showed that the MLR model provided superior predictive performance. For the 20–40 cm sodium sulfate-mixed soil from the arid northwestern region, the MLR model exhibited the best performance with an Rp² of 0.9535, an RMSEP of 0.0030, an RPD of 4.96, and an RPIQ of 6.26. For the 20–40 cm iron disulfide-mixed soil from the cold-temperate northeastern region, the MLR model demonstrated superior results with Rp², RMSEP, RPD, and RPIQ values of 0.9590, 0.042, 5.97, and 10.94, respectively. For the 0–20 cm iron disulfide-mixed soil from the subtropical southwestern region, the MLR model achieved the best performance with an Rp² of 0.9848, an RMSEP of 0.0025, an RPD of 14.20, and an RPIQ of 25.48. Despite regional variations in soil properties, this study successfully predicted sulfate and sulfide contents in soils from diverse areas using mid-infrared spectroscopy combined with appropriate chemometric methods. This approach provides reliable technical support for soil sulfate detection and offers significant practical value for soil assessment in both agricultural production and engineering construction.

To improve the efficiency of waste tire rubber powder modification in asphalt and its high-temperature performance, desulfurized rubber powder with different solubilities was prepared using a twin-screw extrusion process. Desulfurized rubber powder-modified asphalt was then produced using three types of base asphalt, Shell 90#, Zhenhai 90#, and GS 90#, as the base asphalt matrix. Dynamic shear rheometry (DSR), multi-stress creep recovery (MSCR), frequency scanning, Black curves, and complex modulus master curves were used to investigate the effects of rubber powder solubility. We focused on the complex shear modulus (G*), phase angle (δ), rut factor (|G*|/sin δ), creep recovery rate (R), and irreversible creep modulus (J_nr). The results indicate that desulfurization via twin-screw extrusion effectively breaks the sulfur cross-links in the rubber powder, as inferred from the significant increase in solubility, significantly improving rubber powder-asphalt compatibility. Of the three modified asphalts, Shell 90# desulfurized rubber powder-modified asphalt exhibited the slowest decay in high-temperature complex shear modulus, the smallest increase in phase angle, and the best high-temperature rutting factor stability. MSCR tests further confirmed that Shell 90# desulfurized rubber powder-modified asphalt exhibited the highest creep recovery rate, the lowest irreversible creep modulus, and the greatest resistance to permanent deformation. The black curve and the complex modulus master curve confirm that Shell 90# modified asphalt has the best viscoelastic balance and the most stable microstructure. These findings provide a theoretical basis for designing rubber-modified asphalt pavement materials for use in regions with high temperatures and heavy rainfall.