To comprehensively evaluate the antiageing performance of recycled engine oil bottom (REOB) used in asphalt rejuvenation, ageing performance studies were carried out on REOB, REOB-rejuvenated asphalt, and REOB-rejuvenated asphalt mixture. The thin film oven test (TFOT) results of REOB and a professional regenerant, RA5, were compared to verify the ageing resistance of REOB as an asphalt regenerant. The quality and viscosity of REOB-rejuvenated asphalt, RA5-rejuvenated asphalt, and base asphalt were measured after extended TFOT (ageing times for 5 h, 10 h, 15 h, 20 h, and 25 h), and the low-temperature performance of three aged asphalts was evaluated by bending beam rheological tests. The corresponding three kinds of asphalt mixtures were used to design and pave surface layers of a full-scale indoor test road. The long-term fatigue performance of indoor asphalt pavement was investigated by a self-developed rotary accelerated loading test (RALT) system. The results show that when used as an asphalt regenerant, REOB meets the antiageing requirements listed in the technical specification. The short-term (TFOT ageing time less than or equal to 10 h) ageing resistance of REOB-rejuvenated asphalt is better than that of RA5-rejuvenated asphalt but worse than that of base asphalt, whereas the long-term (TFOT ageing time greater than or equal to 15 h) ageing resistance of REOB-rejuvenated asphalt is the worst among the three tested asphalts. After long-term ageing, REOB-rejuvenated asphalt is prone to cracking at low temperatures because of its rapid increase in stiffness and sharp decrease in stress relaxation performance. Increasing temperatures increases the deflection value of asphalt pavement as the number of loading cycles increase. High-temperature ageing significantly aggravates the increase of the deflection value of REOB-rejuvenated asphalt pavement under RALT long-term loading, which makes it most prone to fatigue failure among the three pavements. Therefore, the above test results show that REOB used in asphalt pavement rejuvenation is prone to premature and excessive damage.

Numerous environmental pollution and resource waste problems are associated with recycled engine oil bottom (REOB), which cannot be effectively recycled. Based on the similarity compatibility theory and component adjustment theory, comparing the physical and rheological properties of laboratory-aged asphalt under three types of REOB (defined as REOB-1, REOB-2, and REOB-3) with different dosages, the optimum type and dosage of REOB as asphalt regenerant were explored. The rejuvenation mechanism of REOB on aged asphalt was revealed by combined performance, four-component, and infrared spectroscopy analyses. The relationship between the four components and physical rheological indexes in the process of asphalt rejuvenated by REOB was quantitatively obtained by the grey relationship analysis. The results show that only REOB-3 with a dosage of 7% on the aged asphalt has the best comprehensive rejuvenation effect. Also, the high-temperature rutting resistance of rejuvenated asphalt with 7% REOB-3 is better than that of the original asphalt, but the low-temperature flexibility and the crack resistance performance have yet to be improved. The mechanism through which REOB rejuvenates aged asphalt is an incomplete component adjustment; some of the components undergo physical or chemical reactions and transformations. Accordingly, the asphaltene content and the intensity of sulfoxide functional groups in aged asphalt decrease, thereby achieving rejuvenation gradually with the addition of REOB. A grey relationship analysis demonstrates that asphaltenes have the greatest influence on high-temperature performance and that low-temperature performance requires a reasonable combination of four components. Moreover, a comprehensive advantage analysis reveals that REOB is the most sensitive to the softening point and that the asphaltene content has the greatest influence on the physical and rheological properties of REOB-rejuvenated asphalt. Therefore, the asphaltene content should be strictly controlled during the addition of REOB to rejuvenate aged asphalt.

REOB (Recycled Engine Oil Bottom) rejuvenated asphalt can solve the problems of environmental pollution and resource waste. In order to improve the performance of REOB rejuvenated asphalt, an SBS modifier was applied. An orthogonal test was carried out to optimize the preparation scheme of SBS/REOB-modified rejuvenated asphalt, and the physical rheological properties and microscopic mechanisms of modified rejuvenated asphalt with different SBS and REOB dosages were studied. The test results show that the optimal mixture of the SBS/REOB-modified and rejuvenated asphalt is 9% REOB + 4.5% SBS, the optimal shear time is 40 min, and the shear rate is 5000 r/min. SBS modification of the REOB rejuvenated asphalt can obtain the same excellent high temperature performance as ordinary SBS-modified asphalt, and the modification process can greatly improve the high-temperature deformation resistance of rejuvenated asphalt. After SBS modification of the REOB rejuvenated asphalt, its S value is significantly lower than the base asphalt and the REOB rejuvenated asphalt, and its m value is also greatly improved compared with the base asphalt and the REOB rejuvenated asphalt, indicating that the low-temperature performance of the modified rejuvenated asphalt is greatly improved compared with the rejuvenated asphalt and is better than the base asphalt. The fluorescence microscopic test revealed that both the modified rejuvenated asphalt and the SBS-modified new asphalt prepared in the laboratory showed a continuous asphalt phase, and the SBS phase of the modified rejuvenated asphalt could basically reach the level of finished modified asphalt.

To solve the problem that waste oil residues cannot be utilized and to reuse the aged asphalt, suitable modifiers were selected to compound the aged asphalt with waste oil residues to study its performance. SBS/REOB modified-rejuvenated asphalt was prepared by a high-speed shearing mechanism with aged asphalt, Recycled Engine Oil Bottom (REOB), Styrenic Block Copolymers (SBS) modifier, and stabilizer. The effects of SBS content, REOB content, shear time, and shear rate on the conventional physical properties of asphalt were studied by orthogonal grey correlation analysis, and the optimum preparation scheme of SBS/REOB modified-rejuvenated asphalt was determined. The high and low temperature rheological properties of SBS/REOB modified-rejuvenated asphalt were studied using the Multiple Stress Creep Recover (MSCR) test and bending beam rheological (BBR) test. The mechanism of SBS/REOB on the modification and regeneration of aged asphalt was explored through four component tests and Fourier transforms infrared spectroscopy. The results show that the optimum preparation scheme is 4.5% SBS dosage, 9% REOB dosage, 50 min~60 min shear time, and 4500 r/min shear rate. The addition of SBS improves the elastic recovery performance and high temperature deformation resistance of REOB rejuvenated asphalt. At the same time, the S-value decreases and the m-value increases, which significantly improves the low temperature cracking resistance of REOB rejuvenated asphalt. The addition of REOB achieves component blending and regeneration of aged asphalt by supplementing the light components. After the addition of SBS absorbs the light component and swelling reaction occurs, the whole modification-regeneration process is mainly physical co-mixing and co-compatibility.

The Bayan Nur Section of the Jing-Xin Expressway is located in the Hetao irrigation area. In this area, open river flooding is employed to irrigate the farmland, which causes seasonal subgrade immersion. With the fluctuation in the water levels, the water content of the subgrade soil increases, and the soil strength decreases due to water infiltration and capillary action. Thus, a field test section is built for long-term monitoring of the earth pressure, pore pressure, and settlement, and gravel cushion and reinforcement materials are utilized to reinforce the foundation in the test section. The test results show that the tidal variation in the groundwater level is obvious during the irrigation season, with the maximum increase in the pore pressure being 147.7 %, and the highest water level being 0.9 m above the ground. The change of subgrade soil moisture content and subgrade buoyancy results in the change of subgrade base pressure direction. The pressure distribution of the subgrade base after the reinforcement of the sand-gravel cushion and geotechnical materials presents an inverted bell type, which is similar to the pressure distribution of the rigid foundation base. The restraint and tension film effect of the cushion and reinforcement materials helps in improving the rigidity of the subgrade base.