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.

This work compares the effectiveness of different biogrout agents to improve the mechanical properties (strength and stiffness) of two sandy soils. Based on the results of unconfined compressive strength tests for different curing times (3-180 days), the results obtained from microbial induced calcium carbonate precipitation using two bacteria (Sporosarcina pasteurii and Idiomarina insuliasalsae) are compared with employing urease to promote calcium carbonate precipitation and the use of the biopolymer xanthan gum (3-28 days). Additionally, the methodologies of calcite precipitation and the use of xanthan gum are also analyzed by examining scanning electron microscopy images. For a curing time of 28 days, the results show that the use of urease is the best of the three bio-based methodologies to improve sand, while the least efficient methodology is the use of the biopolymer xanthan gum. The use of both bacteria increases the unconfined compressive strength during the curing time (until 180 days); regarding the use of urease and xanthan gum, the unconfined compressive strength remains approximately constant for a curing time longer than 7-14 days. In terms of stiffness, the use of the bacteria Idiomarina insuliasalsae and urease result in a better improvement, while the use of the bacteria Sporosarcina pasteurii and xanthan gum has only a marginal effect on the stiffness.