Foamed lightweight soil with red mud (FLS-RM), a new type of subgrade material commonly used in projects such as bridge backfill. In engineering applications, FLS-RM tends to crack after pouring to weaken its properties, which limits its further application, and this situation can be improved by adding fiber into FLS-RM. Thus, this study developed a new type of FLS-RM reinforced by polypropylene fibers, polyester fibers, and kenaf fibers to investigate the changes in the mechanical properties of FLS-RM and its deterioration mechanism. The experimental results showed that the mechanical properties of FLS-RM could be enhanced by the fibers, and the compressive and flexural strengths of FLS-RM specimens reinforced by polypropylene fiber reached 0.87 MPa and 0.85 MPa, respectively, when the fiber length was 12 mm and the content was 0.75 wt% and 1.00 wt%. Design Expert was used to analyze the experimental data to obtain the pattern of the effect of different fiber conditions on the strength of FLS-RM and optimal fiber conditions, and to establish the strength equation. The EDS results revealed that the red mud can be excited to generate an aluminosilicate gel filling in the skeleton under alkaline conditions. The results of the microscopic analysis indicated that the close bonding between the fibers and the matrix increased the friction and mechanical bite between the independent blocks and enhanced the strength of the specimens.

As an emerging environmentally friendly solid waste-based composite foam lightweight soil, saponified slag fly ash (SS-FA) foam lightweight soil has a wide range of application prospects in road engineering. In this paper, the dynamic characteristics of SS-FA foam light soil material were investigated. Dynamic triaxial tests under different cyclic loading conditions were designed to analyze the variation rules of dynamic elastic modulus and damping ratio. The results showed that the stress-strain curve of SS-FA foam lightweight soil can be divided into three stages: elastic stage, plateau stage, and stress yielding stage. Under cyclic dynamic load, with the increase of dynamic stress amplitude, the dynamic elastic modulus of 400-700 kg/m3 samples gradually increased to the maximum, reaching 235.24 MPa, 324.54 MPa, 356.45 MPa, 379.67 MPa, respectively. The damping ratio, on the other hand, shows a tendency to first decrease and then slowly increase to stabilize. The dynamic elastic modulus is positively correlated with density grade, confining pressure and loading frequency. The damping ratio decreases with the increase of density grade and loading frequency, and increases with the increase of confining pressure. The electron microscope test was designed and image processing and data statistics were carried out. Through the grey correlation analysis, the correlation degree between the microstructure parameters of SS-FA foamed lightweight soil and the macroscopic mechanical properties is basically above 0.6, indicating that the two have a significant correlation. A normalized prediction formula model between the dynamic elastic modulus of materials and the conditional parameters was established. The R2 of the linear fitting of the predicted value is 0.964, indicating that the prediction model has a high degree of fitting and a good prediction effect. The research results revealed the dynamic mechanical properties of foamed lightweight soil, and provided a reference for the application of SS-FA foamed lightweight soil in subgrade engineering.

Foamed lightweight soil (FLS) is frequently used for roadbed backfilling; however, excessive cement use contributes to higher costs and energy consumption. Desulfurized gypsum (DG), a by-product of industrial processing with a chemical composition similar to natural gypsum, presents a viable alternative to cement. This study evaluates the potential of DG to replace cement in FLS, creating a new material, desulfurized gypsum foamed lightweight soil (DG-FLS). This article is conducted on DG-FLS with varying DG content (0-30%) to assess its flowability, water absorption, unconfined compressive strength (UCS), durability, and morphological characteristics, with a focus on its suitability for roadbed backfilling, though its performance over the long term in engineering applications was not evaluated. Results show that as DG content increased, flowability, water absorption, and UCS decreased, with values falling within the range of 175-183 mm, 8.24-12.49%, and 0.75-2.75 MPa, respectively, all of which meet embankment requirements. The inclusion of DG enhanced the material's plasticity, improving failure modes and broadening its applicability. Durability tests under wet-dry and freeze-thaw cycles showed comparable performance to traditional FLS, with UCS exceeding 0.3 MPa. Additionally, the incorporation of SO42- in DG-FLS reduced sulfate diffusion, decreased C-S-H content, and increased calcium sulfate content, improving sulfate resistance. After 120 days of exposure to sulfates, the durability coefficient of DG-FLS surpassed 100%, with a 25% improvement over traditional FLS. A sustainability analysis revealed that DG-FLS not only meets engineering strength requirements but also offers economic and environmental benefits. Notably, DG-12 showed a 20% reduction in environmental impact compared to conventional FLS, underscoring its potential for more sustainable construction.

Using air-cement-treated clay (ACTC) as a subgrade material for flexible pavements has gained widespread interest and acceptance. The mechanical properties of ACTC, including its compressive strength and elastic modulus (i.e., equivalent elastic modulus, Eeq\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$E_{{{\text{eq}}}}$$\end{document}) are required to realistically model its behavior in simulating pavement structure. This paper investigates the impact of different mixing proportions, particularly cement content and unit weight, on the mechanical properties of ACTC. These properties include its unconfined compressive strength (qu\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$q_{{\text{u}}}$$\end{document}) and elastic moduli (initial modulus (E0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$E_{{0}}$$\end{document}), secant modulus (E50\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$E_{{{50}}}$$\end{document}), and Eeq\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$E_{{{\text{eq}}}}$$\end{document}). The aim of the current study is to develop an equation for estimating the Eeq\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$E_{{{\text{eq}}}}$$\end{document}, which is essential for analyzing pavement structures under cyclic loading. The study involves applying continuous monotonic and cyclic loads to evaluate the mechanical properties of ACTC mixtures with varying cement contents (35-135%) and controlled unit weights (8, 10, and 12 kN/m3). Our study findings indicate that both qu\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$q_{{\text{u}}}$$\end{document} and the elastic moduli are significantly influenced by cement content and unit weight, and are well described using the effective void ratio (est\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$e_{{{\text{st}}}}$$\end{document}) parameter. The ranges for qu\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$q_{{\text{u}}}$$\end{document}, E0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$E_{{0}}$$\end{document}, and E50\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$E_{{{50}}}$$\end{document} were 51.9-411.2 kPa, 42.8-289.4 MPa, and 33.9-183.1 MPa, respectively. Eeq\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$E_{{{\text{eq}}}}$$\end{document} varied between 37.6 and 289.4 MPa, depending upon the cement content, unit weight, and applied stress level. Notably, Eeq\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$E_{{{\text{eq}}}}$$\end{document} values decreased with increasing vertical stress. A simplified equation, accounting for the combined effects of cement content and unit weight on the Eeq\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$E_{{{\text{eq}}}}$$\end{document} variation under different stress levels, is developed and recommended for practical use in designing ACTC mixtures for pavement analysis.

Foamed lightweight soil is widely used in subgrade engineering as a lightweight, high fluidity material. However, due to the use of cement as the main raw material, its cost is relatively high. Therefore, the preparation of foamed lightweight soil by mixing muck excavated at the project site with iron ore tailings (IOT) is not only helpful to reduce costs, but also can promote the efficient and comprehensive utilization of inactive solid waste. In this paper, the fluidity, wet density, compressive strength and specific strength of muck-IOT foamed lightweight soil with different content were tested, and the optimal mixing ratio was selected according to the engineering specifications. Then, through uniaxial and triaxial compression tests, the strength and deformation characteristics of muck-IOT foamed lightweight soil under different dosage, wet density and confining pressure conditions were studied. Finally, the influence mechanism of muck and IOT on the strength and structure of foamed lightweight soil was revealed through Scanning Electron Microscope (SEM) analysis. The research results show that the wet density of foamed lightweight soil prepared by the optimal mixing amount (20% muck and 10% IOT) is 894 kg/m3, and the uniaxial compressive strength is 4.6 MPa. While meeting the requirements of fluidity, the mixing amount of solid waste is higher, with the specific strength increased by 28.12%. In the triaxial compression test, for every 100 kg/m3 increase in wet density, the peak strength and residual strength increase by 1.30 MPa and 1.00 MPa, respectively; For every 200 kPa increase in confining pressure, the peak strength and residual strength increase by 0.27 MPa and 0.32 MPa, respectively. In addition, the shear strength levels of muck-IOT foamed lightweight soil under different normal stress conditions under different wet densities were determined by establishing the linear equations of c and phi related to the wet density. From the microstructure, it can be seen that the pores in the muck-IOT foamed lightweight soil are evenly distributed, resulting in a denser structure and reduced stress concentration, which significantly enhances the material's compressive strength.

This study explores the influence of the water-cement ratio and fiber content in engineered cementitious composite (ECC) on the mechanical characteristics of foamed lightweight soil (FLS) through experimental analysis. Two types of cementitious materials-ECC and ordinary Portland cement (OPC)-were utilized to create FLS specimens under identical parameters to examine their mechanical performance. Results indicate that ECC-FLS exhibits superior toughness, plasticity, and ductility compared to OPC-FLS, validating the potential of ECC as a high-performance material for FLS. To assess the influence of the ECC water-cement ratio, specimens were constructed with varying ratios at 0.2, 0.25, and 0.3, while maintaining other parameters as constant. The experimental results indicate that as the water-cement ratio of ECC increases, the flexural strength, compressive strength, flexural toughness, and compressive elastic modulus of the lightweight ECC-FLS gradually increase, exhibiting a better mechanical performance. Moreover, this study investigates the effect of basalt fiber content in ECC on the mechanical properties of FLS. While keeping other parameters constant, the volume content of basalt fibers varied at 0.1%, 0.3%, and 0.5%, respectively. The experimental results demonstrate that within the range of 0 to 0.5%, the mechanical properties of FLS improved with increasing fiber content. The fibers in ECC effectively enhanced the strength of FLS. In conclusion, the adoption of ECC and appropriate fiber content can significantly optimize the mechanical performance of FLS, endowing it with broader application prospects in engineering practices. ECC-FLS, characterized by excellent ductility and crack resistance, demonstrates versatile engineering applications. It is particularly suitable for soft soil foundations or regions prone to frequent geological activities, where it enhances the seismic resilience of subgrade structures. This material also serves as an ideal construction solution for underground utility tunnels, as well as for the repair and reconstruction of pavement and bridge decks. Notably, ECC-FLS enables the resource utilization of industrial solid wastes such as fly ash and slag, thereby contributing to carbon emission reduction and the realization of a circular economy. These attributes collectively position HDFLS as a sustainable and high-performance construction material with significant potential for promoting environmentally friendly infrastructure development.

This study investigated the small-strain dynamic properties of expanded polystyrene (EPS) lightweight soil (ELS), a low-density geosynthetic material used to stabilize slopes and alleviate the subgrade settlement of soft soil. Resonant column tests were conducted to evaluate the effects of EPS's granule content (20-60%), confining pressures (50 kPa, 100 kPa, and 200 kPa), and curing ages (3 days, 7 days, and 28 days) on the dynamic shear modulus (G) of ELS within a small strain range (10-6-10-4). The results indicate that ELS exhibits a high dynamic shear modulus under small strains, which increases with higher confining pressure and longer curing age but decreases with an increasing EPS granule content and dynamic shear strain, leading to mechanical property deterioration and structural degradation. The maximum shear modulus (Gmax) ranges from 64 MPa to 280 MPa, with a 60% reduction in Gmax observed as the EPS granule content increases and increases by 11% and 55% with higher confining pressure and longer curing ages, respectively. A damage model incorporating the EPS granule content (aE) and confining pressure (P) was established, effectively describing the attenuation behavior of G in ELS under small strains with higher accuracy than the Hardin-Drnevich model. This study also developed an engineering testing experiment that integrates materials science, soil mechanics, and environmental protection principles, enhancing students' interdisciplinary knowledge, innovation, and practical skills with implications for engineering construction, environmental protection, and experimental education.

Saline soil, common in the western China, poses a significant threat to road engineering due to its salt swelling characteristics. Therefore, studying the water-salt migration patterns within saline soil subgrades and developing methods to interrupt this migration are crucial for road safety prevention and control. Based on the utilization of excavated waste soil, a new type of foamed lightweight soil based on saline soil is proposed as a subgrade separation fault in saline soil areas. Using self-developed equipment, we tested internal temperature changes, vertical displacements, and water and salt distribution after freeze-thaw cycles. The objective was to evaluate its salt insulation and swelling suppression capabilities and to explore the microstructure-based mechanisms underlying salt inhibition. Results indicate that under a temperature gradient, water and salt in the saline soil sample migrate upward, accumulating mainly in the middle and upper sections. Notably, the novel foamed lightweight soil separation fault effectively blocks water and salt migration, significantly suppressing salt swelling. Interestingly, a higher soil salt content results in a more pronounced anti-swelling effect. The porous structure of the foamed lightweight soil can not only store salt effectively, but also block salt migration, allowing salt crystallization within the soil, thereby reducing salt swelling damage.

Sustainable foam lightweight soil (FLS) with the introduction of solid waste-based binders and dredged mud has shown high engineering and environmental value in expressway reconstruction and extension projects. Accelerated testing through high-temperature curing is considered a crucial method for early-stage assessment of sustainable FLS construction quality. This study aims to explore the curing temperature effect on the strength development of the FLS with different mix proportions and the applicability of accelerated curing method. Strength tests were first conducted on kaolin clay-based FLS with three wet densities and three water contents under different curing temperatures (T), and the strength of the dredged mud-based FLS was also tested to broaden the applicability. Results indicate that higher T and increased wet density significantly enhance the strength of clay-based FLS at any curing age, while higher water content reduces it. The wet density and water content of the proposed FLS recommended in this study considering the strength and lightweight requirements are 800 kg/m3 and 100%, respectively. Moreover, the effectiveness of the accelerated aging method for clay-based FLS is demonstrated by the fact that no dramatic strength loss occurs due to foam expansion and collapse at elevated T of up to 50 degrees C. On this basis, a strength prediction model based on the concept of activation energy is proposed for both kaolin clay-based and dredged mud-based FLS considering the temperature effect. Changes in wet density have a minimal impact on model parameters, but variations in soil type and water content require updating these parameters to ensure prediction accuracy. Finally, an early quality control method is introduced for applying the sustainable FLS in field projects.

The flexural behavior of geogrid-reinforced foamed lightweight soil (GRFL soil) is investigated in this study using unconfined compressive and four-point bending tests. The effects of wet density and reinforcement layers on flexural performance are analyzed using load-displacement curves, damage patterns, load characteristics, unconfined compressive strength, and flexural strength. A variance study demonstrates that increasing the wet density significantly increases unconfined compressive strength. Bond stress mechanisms enable geogrid integration, efficiently reroute stresses internally, and greatly increase flexural strength. With a maximum unconfined compressive strength of 3.16 MPa and a peak flexural strength increase of 166%, this reinforcement increases both strength and ductility by changing the damage pattern from brittle to ductile. The principal load is initially supported by the foamed lightweight soil, and in later phases, geogrids take over load-bearing responsibilities. Additionally, the work correlates the ratio of unconfined compressive to flexural strength with wet density and informs the development of predictive models for unconfined compressive strength as a function of reinforcing layers and wet density.