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Millimeter-scale magnesian refractory granules were found to be a unique magnesian-expansive component in steel slag. To systematically study the effects of these granular magnesian-expansive components on the volume stability of cement-based materials containing steel slag, an investigation of their existing forms and influence on the volume stability was conducted in this paper. The various-sizing waste–magnesium–chromate-based refractory brick (Mg-Cr brick) granules and different (FeO + MnO)/MgO ratios' synthetic MgO·xFeO·yMnO ternary solid solutions granules were adopted to simulate magnesian-expansive granules by partially replacing manufactured sand in mortar. The 100 °C–3 h boiling and 213 °C–2 MPa–3 h autoclaving treatments were adopted as volume stability testing methods. The results indicated that whether Mg-Cr brick or MgO·xFeO·yMnO solid solution, the concentration of expansive stress and the anisotropy expansion came with the granular size rising weakening the volume stability of cement-based materials which contained magnesian-expansive granules, significantly. Meanwhile, this phenomenon resulted in the ineffectiveness of the single linear expansion rate when assessing the qualification of volume stability. Furthermore, it also changed the mortars' failure mode from "muddy damage" to "break into blocks". Especially, there is no volume stability issue when the MgO·xFeO·yMnO satisfied (FeO + MnO)/MgO ≥ 1.00. Considering the significant effect of the granular magnesian-expansive components on the volume stability of cement-based materials containing steel slag, it is imperative to enhance the detection of both MgO content and mineral existing forms in steel slag in practical applications. For recommendation, the threshold value of conducting autoclaved volume stability testing on steel slag should be set at MgO ≥ 3%. Furthermore, the qualification cannot be judged by the single linear expansion rate; the specimens' appearance integrity and strength loss should also be noted. [ABSTRACT FROM AUTHOR]

• The relationship between GGBFS:FA ratio and geopolymer strength in the whole humid-heat-treating temperature range presents a mountain-shaped respond-surface containing "positive-side" and "negative-side". • Appropriate humid-heat-treating makes the strength of GFS geopolymer with 50% SS dosage reach to more than 70 MPa, which realizes the "win–win" of high SS utilization and high strength. • The micro-hydration process on "positive-side" and "negative-side" are distinct for the crystallization of massive matrix gels causing by distinct Ca/(Si + Al) value. In order to improve the comprehensive utilization of steel slag in China, the ternary geopolymer with ground granulated blast furnace slag (GGBFS), fly ash (FA), and steel slag (SS) was prepared under the fixed addition of 50% SS in this research. The GGBFS:FA ratio was optimized to improve the mechanical performance of ternary groups. Humid-heat-treating ranging from 60 °C to 195 °C was adopted as the accelerated method to try to further strengthen the geopolymers compared with the standard curing. The strength development and hydration mechanism with different GGBFS:FA ratios were studied. The result revealed that appropriate humid-heat-treating significantly improved the geopolymers' strength, which built a mountain-shaped response surface with the variations of the GGBFS:FA ratio and the corresponding treating parameters. The reasons for this phenomenon were the different activities of GGBFS, FA, and SS under different treating conditions, as well as the change of Ca/(Si + Al) ratio in hydration products that cause massive matrix gels with low Ca/(Si + Al) crystallized to crystal calcium silicate hydrated with high Ca/(Si + Al). The crystallization of massive matrix gels made the initial dense structure break up, resulting in a loss of strength in geopolymers. The suggested Ca/(Si + Al) ratio value in whole raw material mixtures of GFS should be lower than 1.0, which reflects the GGBFS:FA = 4:1 in the system with 50% SS. Hence, the treating parameters needed to be controlled and selected in practical application, respectively. [ABSTRACT FROM AUTHOR]

To overall investigate the mechanical performance of resilient wheels to suppress the vehicle–bridge (especially LSB) coupled vibration, the coupled dynamic characteristics of metro train–LSB considering nonlinear resilient wheels are studied. Firstly, the mechanical property test of rubber of resilient wheel is designed and conducted, the mechanical characteristics of the nonlinear resilient wheel (NLRW) and linear resilient wheel (LRW) are discussed, and the dynamic model of LRW and NLRW are established. Then, based on train–track–bridge dynamic interaction theory, the coupled dynamic models of metro train–LSB considering LRW and NLRW are established, respectively. Adopting the established model, the dynamic influences of NLRW and LRW on the metro train–LSB coupled system are investigated by long-short wave irregularity excitation. The effects of damping characteristics of LRW and NLRW on the metro train–LSB system are discussed from the time–frequency domain. Results show that the wheel–rail vertical force of NLRW is smaller than that of LRW. The acceleration of the web, axle box, bogie, and car body of the NLRW is smaller than that of the LRW. The main frequency of wheel–rail vertical force under the action of NLRW and LRW is about 4 and 22 Hz. The main frequencies of the rim and web of the NLRW are about 25 Hz, while those of the LRW are about 50 and 25 Hz, respectively. The acceleration of the web of the NLRW is significantly smaller than that of the LRW. The main frequency of acceleration of the LSB is about 10 Hz, and the acceleration of the LSB under the action of NLRW is significantly less than that of the LRW when the frequency is in the range of 22–62 Hz. Vibrations of the metro train and LSB increase with the increase of speed, and the dynamic response of the metro train–LSB system under the action of NLRW is smaller than that of LRW. [ABSTRACT FROM AUTHOR]