The solidification property and mechanism of soft soil based on the industrial waste residue was studied systematically. First, the properties of soft soil solidified by single blast furnace slag, phosphogypsum and cement were carried out, and the solidification effect of Portland cement was better compared with blast furnace slag and phosphogypsum. Second, the composite solidification agent formula with excellent solidification performance was developed, and the mass ratio of Portland cement, blast furnace slag and phosphogypsum was 1:2.3:0.8. At this time, compressive strength was up to 8845.1 kPa. Finally, the composition and microstructure of the solidification soft soil was studied by X-ray diffractometer and scanning electron microscope. Calcium hydroxide formed by the hydration of Portland cement and calcium sulfate in phosphogypsum were used as activators for hydration reaction of blast furnace slag, and more hydration products under the synergistic action of Portland cement hydration and blast furnace slag hydration were formed. Hydrated calcium silicate colloid and Ettringite crystal played an important role in skeleton and filling, and the structure of soft soil solidified by composite solidification agent was the most compact.

The long-term properties of solidified soft soil, including an immersion test, the dry–wet cycle and the freeze–thaw cycle, were systematically studied. Firstly, the immersion stability of solidified soft soil was confirmed. The appearance of soft soil solidified by a solidified agent and raw fine aggregate did not change significantly, and it was still intact without damage when the soaking time increased up to 28 d. Secondly, the mass and compressive strength loss of solidified soft soil were determined. When the number of dry–wet cycles was one, three, five and seven, the accumulated-mass loss rate was 1.4%, 3.0%, 4.5% and 6.0%, respectively, and the compressive-strength loss rate was −10.3%, 13.9%, 41.2% and 53.6%, respectively. Compared with solidified soft soil under standard curing environments, solidified soft soil after seven dry–wet cycles showed small cracks, and the structural compactness began to decline. Finally, the influence of the freeze–thaw cycle on the mass, compressive strength and microstructure of solidified soft soil was confirmed. When the number of freeze–thaw cycles was 5, 10, 15 and 20, the accumulated-mass loss rate was 12.6%, 16.7%, 17.9% and 18.8%, respectively. The microstructure of the solidified soft soil was damaged, and the increase in porosity was the main reason for its strength reduction or even failure. Nevertheless, soft soil with a solidified agent and recycled fine aggregate had no obvious damage to the microstructure, and the freeze–thaw resistance was relatively superior.

The influence of recycled fine aggregate content on the properties of soft soil solidified by industrial waste residue was systematically studied. First, the addition of recycled fine aggregate may provide skeleton support, which was conducive to improving the solidification properties. Comparing the addition of recycled fine aggregate content and a composite solidification agent separately, the compressive strength increased 48.01 times and 1.32 times, respectively. Second, the composition and quantity of the hydration products were analyzed by X-ray diffraction (XRD) and thermal gravity analysis (TG/DTG). In addition to silicon dioxide and aluminum oxide, a number of new minerals, including hydrated calcium silicate, calcium hydroxide and ettringite, were produced under different recycled fine aggregate contents. The diffraction peak of hydrated calcium hydroxide was weak, which indicated that the crystallinity and relative content was low. The main reason for this was that it was consumed as the activator of the secondary hydration reaction of blast furnace slag. With the increase in recycled fine aggregate content, the total weight loss (hydration products, crystal water, impurities) increased significantly, at rates of 6.9%, 7.0%, 7.2%, 8.8% and 9.7%. The addition of recycled fine aggregate does not change the composition and quantity of the hydration products, and the increased weight loss in this part might be caused by the cement paste attached to the surface of the recycled fine aggregate. Finally, their microstructure was analyzed by scanning electron microscopy (SEM). Larger and more pores appeared in the solidification system with the increase in recycled fine aggregate, and a large amount of ettringite was prepared. An excess in recycled fine aggregate caused more pores, and the negative impact of too many pores exceeded the lifting effect of the aggregate, resulting in the decline of its mechanical properties. Therefore, there was a suitable range for the use of recycled fine aggregate, which was not more than 40%. In conclusion, recycled fine aggregate not only acts as a skeleton to improve solidification strength, but could also realize the comprehensive utilization of waste, which provided a new scheme for solid waste utilization and soft soil solidification.

Based on the cable-stayed beam model, this paper studies the nonlinear coupled vibration behavior of basalt fiber-reinforced polymer (BFRP) cables on long-span cable-stayed bridges under parametric excitation. Considering the sag, damping of BFRP cables, and the coupled interactions between stayed cables and the main girder, the nonlinear coupling vibration model of the BFRP cable–beam composite structure has been established. Taking the longest cable of Sutong Bridge as a case study, the nonlinear coupled vibration behavior of BFRP cables under parametric excitation has been numerically analyzed using the finite difference method. The analysis results indicate that (1) under parametric excitation, the large amplitude nonlinear vibration of the BFRP cable will be induced with an evident “beat” phenomenon. (2) Under the same parametric excitation, the nonlinear coupling vibration response and the beta frequency of the BFRP cable were both smaller than that of the traditional steel cable. (3) The nonlinear coupling vibration response of the BFRP cable increased with an increment in excitation amplitude and a decrement in cable force. With the increase in the excitation frequency, weight per unit length, and axial stiffness, the nonlinear vibration response of the BFRP cable increased first and then decreased. Meanwhile, the damping ratio of the BFRP cable had no significant influence on the nonlinear coupling vibration.

With the rapid advancement of urbanization, the reuse of waste concrete has become more and more important. Recycled aggregate inevitably develops microcracks during the crushing process of waste concrete, resulting in undesirable characteristics such as low density and strong water absorption. This study employed an external calcium source combined with wet carbonation to optimize the performance of recycled fine aggregate (RFA). A series of microscopic analytical techniques, including scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), and the Brunauer–Emmett–Teller (BET) method, were used to elucidate the underlying mechanisms. The results indicate that calcium-rich leachate can be obtained by soaking alkali residue in 0.3 mol/L acetic acid at a solid-to-liquid ratio of 1:6. When this leachate was further used to soak the aggregate at a solid-to-liquid ratio of 1:2, followed by carbonation in a carbonation chamber, the carbonation effect reached its optimum. Under these conditions, the saturated water absorption of the recycled fine aggregate decreased to 16%, the carbon sequestration efficiency increased by 66.8%, and pores smaller than 50 nm accounted for 62.9% of the total pore volume. Furthermore, a Bacillus strain capable of producing carbonic anhydrase was introduced to enhance the carbonation reaction. The results demonstrated that when Bacillus was added to acetic acid-modified recycled fine aggregate, the saturated water absorption further decreased to 14.6%, while the carbon sequestration efficiency significantly increased to 109.04%. Additionally, pores smaller than 50 nm constitute 79.2% of the total pore volume. These findings suggest that utilizing calcium-containing industrial waste as a calcium source for recycled fine aggregate, followed by carbonation modification, is highly effective. This approach not only improves the performance of recycled aggregates but also promotes the reutilization of industrial waste, contributing to sustainable construction practices.