This study delves into the multifaceted effects of multi-walled carbon nanotubes (MWCNT) incorporation on phosphogypsum's properties. We investigated the phase composition and morphology of phosphogypsum and observed the influence of MWCNT on the setting time, flexural strength, compressive strength , water resistance, and hydration process. The results demonstrated that MWCNT significantly abbreviates the setting time of phosphogypsum, enhances its absolute dry flexural strength and compressive strength, and improves water resistance, with optimal effects occurring at a MWCNT content of around 1.00%. Nonetheless, these benefits diminish and can even be counterproductive if MWCNT content is excessively high. The enhanced properties of phosphogypsum upon MWCNT addition can be ascribed to the filling effect and mechanical interlocking facilitated by MWCNT. Additionally, MWCNT promoted the hydration of phosphogypsum, as evidenced by calorimetric measurements.

The mechanical behavior of sand–fines mixtures is governed by their limiting void ratios, which are sensitive to fines content and particle morphology. Conventional empirical correlations often fail to generalize to a wide range of soils, limiting their applicability in engineering design. This study develops an integrated approach combining laboratory calibration, discrete element method (DEM) simulations incorporating realistic particle morphologies and machine learning to predict maximum and minimum void ratios. Glass beads were first tested to validate DEM contact parameters, after which sand particles obtained through 3D scanning were employed to capture morphological effects. Correlation and partial least squares analyses confirmed fines content as the dominant factor, while particle shape also contributed to packing behavior. A fully connected neural network (FCNN) was trained to establish predictive relationships, demonstrating closer agreement with DEM simulations than traditional empirical formulations. The proposed approach provides a reliable and generalizable tool for evaluating packing characteristics and offers new insights into the role of particle morphology in the mechanical response of sand–fines mixtures.

The wave impeding board (WIB) is frequently integrated beneath dynamic machinery, tracks, and subgrades to counteract vibrations emanating from artificial sources. However, conventional WIBs have exhibited a limited isolation frequency band due to their dependence on the soil cut-off frequency of soil. Furthermore, the vibration sources typically encompass intricate frequency components spanning low, medium, and high frequencies. To overcome the technical limitations of WIBs relying on the cut-off frequency of soil, a new periodic structural wave impeding board (PSWIB) is proposed based on the principles of phononic crystals. Theoretical and numerical analyses demonstrate that PSWIB exhibits bandgap characteristics, with the attenuation range achieved by finite periodic structures aligning with the bandgap of an infinite PSWIB. Maximum amplitude reductions of 47 dB and 65 dB are achieved within the vibration attenuation range. Compared to traditional WIB, PSWIB surpasses the constraints imposed by the cut-off frequency of soil and allow for the design of constituent parameters based on the characteristics of the vibration source, enabling effective isolation of the target frequency vibrations.