As two kinds of solid wastes, waste tires and steel slag have caused serious threats to the environment. Both waste tire rubber (WTR) and steel slag powder (SSP) can improve the performance of asphalt, while the performance indexes and modification mechanism of modified asphalt are not clear. In this paper, asphalt modified with SSP and WTR was prepared, and its performance was evaluated. The physical properties of asphalt modified with SSP and WTR, including penetration, the softening point, and viscosity, were investigated. Furthermore, high-temperature performance, fatigue resistance, low-temperature performance, and blending mechanism of asphalt modified with SSP and WTR were tested with a dynamic shear rheometer (DSR), bending beam rheometer (BBR), and Fourier transform infrared spectrometer (FTIR). The results showed that with the same content of WTR and SSP, WTR reveals a more significant modification effect on physical properties, fatigue, and low-temperature performance of base asphalt than SSP. The anti-rutting performance of SSP-modified asphalt is better than that of WTR-modified asphalt at 30~42 °C, and the anti-rutting performance of WTR-modified asphalt is better than that of SSP-modified asphalt at 42~80 °C. When the total content of WTR and SSP is the same, the physical properties, high-temperature resistance, fatigue resistance, and low-temperature performance of the asphalt modified with WTR and SSP decrease with the decrease in the ratio of WTR and SSP, and their performance is between WTR-modified asphalt and SSP-modified asphalt. Infrared spectrum results verified that the preparation of WTR- and SSP-modified asphalt is mainly a physical blending process. Overall, this research is conducive to promoting the application of modified asphalt with WTR and SSP in the construction of high-standard pavement.

Foamed concrete (FC) is a lightweight building material widely used in thermal insulation walls, backfill, and other fields. Generally, foamed concrete is prepared using cement, which consumes a lot energy and resources. In this study, three kinds of special soil (SS) and slag powder (SP) were used to prepare foamed concrete. The content of SS was 25%, and the content of SP was 35%, 45%, and 55%. The mechanical properties, durability properties, and microstructure of special soil-slag foamed concrete (SSFC) were studied. With the increase in SP content, the water absorption and drying shrinkage of SSFC increased and the compressive strength of SSFC decreased. The water stability coefficients of SSFC were all higher than 0.7, which met the requirements of engineering applications. The porosity and the average diameter of pores of SSFC increased with the increase in SP content. The porosity of SSFC was less than 46% when the replacement percentage of SP was less than 35%. The successful application of SS and SP in foamed concrete provides an effective approach to waste utilization.

The use of steel slag powder instead of filler to prepare asphalt mortar was beneficial to realize the effective utilization of steel slag and improve the performance of asphalt concrete. Nevertheless, the anti-aging properties of steel-slag powder–asphalt mortar need to be further enhanced. This study used antioxidants and UV absorbers in steel-slag powder–asphalt mortar to simultaneously improve its thermal-oxidation and UV-aging properties. The dosage of modifier was optimized by second-generation non-inferior sorting genetic algorithm. Fourier-Transform Infrared Spectroscopy, a dynamic shear rheometer and the heavy-metal-ion-leaching test were used to evaluate the characteristic functional groups, rheological properties and heavy-metal-toxicity characteristics of the steel-slag-powder-modified asphalt mortar, respectively. The results showed that there was a significant correlation between the amount of modifier and G*, δ, and the softening point. When the first peak appeared for G*, δ, and the softening point, the corresponding dosages of x1 were 2.15%, 1.0%, and 1.1%, respectively, while the corresponding dosage of x2 were 0.25%, 0.76%, and 0.38%, respectively. The optimal value of the modifier dosage x1 was 1.2% and x2 was 0.5% after weighing by the NSGA-II algorithm. The asphalt had a certain physical solid-sealing effect on the release of heavy-metal ions in the steel-slag powder. In addition, the asphalt structure was changed under the synergistic effect of oxygen and ultraviolet rays. Therefore, the risk of leaching heavy-metal ions was increased with the inferior asphalt-coating performance on the steel-slag powder.

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The objective of this study is to develop a modified asphalt with excellent rheology and workability. Buton rock asphalt (BRA) composite modified warm mix asphalt (BCMWMA) was prepared, and its rheological properties and micromechanisms were investigated. Initially, warm mix asphalt (WMA) was prepared using 3 wt% Sasobit, and then four BCMWMA samples were prepared by blending 5 wt% to 20 wt% of BRA (with 5 wt% intervals). Subsequently, the microscopic morphology and modification mechanism of BCMWMA were analysed by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) tests. Finally, the rheological properties of BCMWMA were examined through conventional properties tests, rotational viscosity tests (RV), dynamic shear rheological tests (DSR) and bending beam rheometer tests (BBR). The results indicate that the BRA and Sasobit composite modifications primarily involve physical modification. BRA improves the high-temperature performance of the modified asphalt but reduces its low-temperature performance. Overall, the BCMWMA exhibits excellent high-temperature performance and workability, contributing to the green and sustainable development of asphalt pavement engineering.