Expansive soil is widely distributed and often needs to be improved for engineering and construction needs. Using blast furnace slag and fly ash as precursors and NaOH as an alkali activator, a geopolymer was prepared to solidify expansive soil, and the effect of nano-SiO₂ on the compressive strength and water stability of the geopolymer-solidified expansive soil was further studied. The effects of alkali addition ratio, nano-SiO₂ addition ratio, and curing agent addition ratio on the unconfined compressive strength and water stability of the cured soil were studied through unconfined compressive strength tests, and the curing mechanism was analyzed by electron microscopy scanning. The experimental results showed that the unconfined compressive strength and water stability of geopolymer-stabilized soil first increased and then decreased with an increase in alkali activator dosage. The optimal dosage of alkali activator was found to be 12.5%. Furthermore, it was found that adding nano-SiO₂ can further enhance the strength and water stability of solidified soil. When the content of nano-SiO₂ was 3%, the unconfined compressive strength was increased by 15%. With an increase in the content of nano-SiO₂ doped polymer (GFNS), the unconfined compressive strength and water stability of the solidified soil showed a trend of first increasing and then decreasing, reaching a peak at a content of 20%. The cementitious materials, such as hydrated calcium silicate and hydrated calcium silicate aluminate, generated by the reaction between nano-SiO₂ and geopolymer played a role in bonding and filling in the solidified soil. Under the joint action of the two, the structural arrangement between the solidified soil particles became more compact, which improved the strength of the solidified soil.

This study prepares solid-waste-based alkali-activated material (AAM) concrete using ground granulated blast furnace slag (GGBFS), fly ash (FA), steel slag (SS), and desulfurized gypsum (DG) as primary raw materials, with Na₂SiO₃ as the activator. Taking the GGBFS content (X₁), Na₂SiO₃ content (X₂), and water-to-binder ratio (X₃) as independent variables and the 3-day, 7-day, and 28-day compressive strengths and slump as response values, it investigates the influence of each factor and their interactions, constructs a response surface prediction model, screens for the optimal mix proportion with comprehensive performance, and explores the microstructural characterization and strength formation mechanism of the AAM concrete via SEM and EDS. The results indicate the following: (1) compared with binary and ternary mixtures, the use of the quaternary solid waste mixture not only enhances strength and optimizes the microstructure but also increases the utilization rate of low-quality solid wastes; (2) the regression coefficients (R²) of the response surface models are all greater than 0.98, exhibiting good goodness of fit and rationality. Experimental validation confirms that each model shows excellent predictive capability; (3) AAM concrete exhibits comprehensively superior mechanical properties to ordinary cement, with leading early- and late-stage compressive strengths and splitting strengths, albeit with a slightly lower slump; (4) the performance synergy is prominent. Combined with microscopic analysis (highly polymerized C-S-H gels and a dense structure), the superiority of its macroscopic mechanical properties stems from the optimization of the microstructure, reflecting the intrinsic correlation of the “microscopic densification-macroscopic high strength.

To address environmental concerns related to cement-stabilized expansive soil and the safety risks of caustic-activated blast furnace slag, this study explores the use of lime-activated blast furnace slag as an alternative stabilizer in northern Hebei, China. The effects of slag dosage, curing time, and osmotic pressure on the expansion, osmotic properties, and strength of the improved soil were evaluated through free expansion rate, permeability coefficient, and unconfined compressive strength tests. Results show that adding slag-lime significantly reduces soil expansion. As slag content increases, the free expansion rate decreases exponentially. During the curing period of 3–7 days, expansion declines and stabilizes between 7–14 days. Similarly, the permeability coefficient permeability coefficient decreases with higher slag content, following a quadratic trend. Under osmotic pressures of 0.1–0.2 MPa, the permeability coefficient permeability coefficient increases but stabilizes between 0.2–0.4 MPa.Furthermore, slag-lime significantly enhances unconfined compressive strength, which increases linearly with slag content. The stress–strain curve follows a logistic function in the rising stage and a rational fractional equation in the descending stage.This study demonstrates that lime-activated blast furnace slag is a sustainable and effective alternative for stabilizing expansive soils while reducing dependence on cement.

To investigate the relationship between the three-dimensional size of a structure and the impact of the traveling wave effect, models derived from an orthographic quadrangle flat grid based on a practical engineering case were established and validated. The plane size (ranging from 30 m to 90 m), height (ranging from 0 m to 9 m), and space of the supporting columns (ranging from 6 m to 12 m for peripheral columns and from 18 m to 24 m for internal columns) were changed. The time history method was used to perform a statistical analysis of the proportion and distribution of special bars and to investigate their seismic response under multiple-support excitation along the length of the structure and single excitation. The results show that an increase in the structural length and decreases in the structural span and the height and distance of the columns lead to an increase in the traveling wave effect, with special bars spreading from the supports to the peripheries and from the edge to the middle along the span. It is concluded that the traveling wave effect can be regarded as an additional dynamic load according to the excitation time differences among supporting columns along the propagation direction of the seismic wave, which spreads from supports to peripheries in a manner similar to energy radiation. The smaller the apparent wave velocity, the larger the time difference, the larger the additional dynamic load, and the larger the degree and range of the traveling wave effect. Increasing the plane and the height and space of the supporting columns to certain sizes will lead to a decrease in the traveling wave effect due to its limited range.