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.

Research on the retaining structures for high‐steep slopes is extremely significant because of its real‐world applications and far‐reaching implications. A flexible geocell‐reinforced ecological retaining wall as a high‐steep slope protection scheme was developed and applied to the slope protection project of the Ji‐Lai Expressway by analyzing the reinforcement mechanism of the geocell used. The lateral displacement and Earth pressure distribution on the flexible ecological retaining wall applied to the high‐steep slope were studied using finite element numerical simulations and verified using field experiments. Results reveal that the wall maximum horizontal displacement is 2/3 H away from the wall toe because of the replacement of the upper part of soil. There is an obvious bucking effect on the active Earth pressure around the stiffened site, and the flexible deformation of the retaining wall helped effectively release some of the Earth pressure. Consequently, the measured value is lower than the theoretical value. Through this case study, it is demonstrated that the flexible ecological retaining wall as a slope protection technology can be successfully applied to steep slopes with a height of more than 15 m. Moreover, it brings significant advantages for protecting the ecological environment and improving the highway landscape.

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.

The practical performance of recycled asphalt obtained from recycled engine oil bottom (REOB) was evaluated by paving a test road of base asphalt and REOB-recycled asphalt mixture in a laboratory, where accelerated loading tests with 700,000 cycles were conducted. During accelerated loading, pavement temperature, layer bottom strain, pavement skid resistance, and rutting were monitored. The performance of pavement core material was tested after loading to analyze the index change of binder and the compaction degree of the mixture. The results show that the long-term anti-rutting ability of REOB-recycled asphalt pavement is approximately 10% higher than that of the base asphalt pavement, although the long-term anti-sliding force and anti-fatigue performance are poor. A developed model of rut with loading time can better predict the development trends of these parameters with loading cycles. The performance test of the pavement material after loading shows that 700,000 cycles can only degrade the performance of the test pavement, not damage it. The recycled asphalt pavement with 7% REOB has basically the same performance as the base asphalt under 700,000 cycles, indicating that REOB-recycled asphalt pavement can ensure basic road performance, while providing economic and environmental advantages. These results provide a reference for the application and form optimization of REOB-recycled asphalt pavement.

In order to conserve non-renewable natural resources, waste cooking oil (WCO) in bitumen can help lower CO₂ emissions and advance the environmental economy. In this study, three different components of WCO were isolated and then, together with polyphosphoric acid (PPA), used separately as bitumen modifiers to determine the suitability of various substances in WCO with PPA. Conventional tests, including penetration, softening point temperature, and ductility, and the dynamic shear rheology (DSR) test, including temperature sweep and frequency sweep, were used to evaluate the influence of WCO/PPA on the traditional performance and rheological properties at high and low temperatures. The results indicate that WCO reduced the ductility and penetration value, when the use of PPA increased the softening point temperature and high-temperature performance. Compared to reference bitumen, the rutting factor and viscous activation energy (Ea) of bitumen modified with 4% WCO and 2% PPA has the most significant increase by 18.6% and 31.5, respectively. All components of WCO have a significant impact on improving the low-temperature performance of PPA-modified bitumen. The performance of the composite-modified bitumen at low temperatures is negatively affected by some waxy compounds in WCO, such as methyl palmitate, which tends to undergo a solid–liquid phase change as the temperature decreases. In conclusion, the inclusion of WCO/PPA in bitumen offers a fresh approach to developing sustainable pavement materials.

Polyurethane cement (PUC) is now commonly used in the reinforcement of old bridges, which exhibit various issues such as poor toughness, temperature-sensitive mechanical properties, and brittle failure. These problems can lead to the failure of the reinforcement effect of the PUC on old bridges in certain operating environments, leading to the collapse of such reinforced bridges. In order to alleviate these shortcomings, in this study, the toughness of PUC is improved by adding polyvinyl alcohol (PVA) fiber, carbon fiber, and steel fiber. In addition, we study the change law of the flexural strength of PUC between −40 °C and +40 °C. The control parameters evaluated are fiber type, fiber volume ratio, and temperature. A series of flexural tests and scanning electron microscope (SEM) test results show that the flexural strength first increases and then decreases with the increase in the volume-doping ratio of the three fibers. The optimum volume-mixing ratios of polyvinyl alcohol (PVA) fiber, carbon fiber, and steel fiber are 0.3%, 0.04% and 1%, respectively. Excessive addition of fiber will affect the operability and will adversely affect the mechanical properties. The flexural strength of both fiber-reinforced and control samples decreases with increasing temperature. Using the flexural test results, a two-factor (fiber content, temperature) BP neural network flexural strength prediction model is established. It is verified that the model is effective and accurate, and the experimental value and the predicted value are in good agreement.