In recent years, expanded polystyrene (EPS) lightweight soil has been widely used as subgrade in soft soil areas because of its light weight and environmental protection. This study aimed to investigate the dynamic characteristics of sodium silicate modified lime and fly ash treated EPS lightweight soil (SLS) under cyclic loading. The effects of EPS particles on the dynamic elastic modulus (E_d) and damping ratio (λ) of SLS were determined through dynamic triaxial tests at various confining pressures (σ₃), amplitudes, and cycle times. Mathematical models of the E_d of the SLS, cycle times, and σ₃ were established. The results revealed that the EPS particle content played a decisive role in the E_d and λ of the SLS. The E_d of the SLS decreased with an increase in the EPS particle content (EC). The E_d decreased by 60% in the 1–1.5% range of the EC. The existing forms of lime fly ash soil and EPS particles in the SLS changed from parallel to series. With an increase in σ₃ and amplitude, the E_d of the SLS gradually decreased, the λ generally decreased, and the λ variation range was within 0.5%. With an increase in the number of cycles, the E_d of the SLS decreased. The E_d value and the number of cycles satisfied the power function relationship. Additionally, it can be found from the test results that 0.5% to 1% was the best EPS content for SLS in this work. In addition, the dynamic elastic modulus prediction model established in this study can better describe the varying trend of the dynamic elastic modulus of SLS under different σ₃ values and load cycles, thereby providing a theoretical reference for the application of SLS in practical road engineering.

Diatomite is a non-metallic mineral resource rich in SiO₂, which can be used to modify coastal cement soil. In order to explore the mechanical modification effect of diatomite on coastal cement soil at the age of 7 days, based on coastal cement soil with cement content of 5% (mass fraction), diatomite of 0%, 5%, 10%, 15% and 20% (mass fraction) was mixed for modification. Through the unconfined compressive strength test, the triaxial unconsolidated undrained test, backscattered electron imaging (BSE), and energy-dispersive spectroscopy (EDS) technology, the influence of diatomite content and confining pressure on the peak strength of modified coastal cement soil was explored. The empirical formula between the peak strength of the DE specimen and the content of diatomite and confining pressure was established by curve fitting, and the fitting effect was ideal. When diatomite was mixed with coastal cement soil, the optimal dosage of diatomite was 5% from the perspective of mechanical properties and economic benefits of the maximum growth rate of compression and shear. The unconfined compressive strength test showed that the peak strength and elastic modulus of the modified coastal cement soil with 5% diatomite content were 37% and 57% higher than those of cement soil, respectively. The triaxial unconsolidated undrained test showed that the internal friction angle of the modified coastal cement soil was stable at about 30°, and cohesion of DE-5, DE-10, DE-15, and DE-20 increased by 28%, 48%, 78%, and 97%, respectively, compared to cement soil. The microscopic test found that the pore distribution of modified coastal cement soil is closely related to the strength change. The results show that the addition of diatomite can effectively improve the mechanical properties of soil-cement.

Fluidized solidified soil (FSS) is a cement-based engineering matergood working performance and mechanical properties. Based on fixed cement and desulphurisation gypsum (DG), fly ash (FA) and ground granulated blast furnace slag (GGBS) were added as admixtures to the construction slurry to prepare three types of FSS: namely cement-GGBS-DG FSS (CGD-FSS), cement-FA-GGBS-DG FSS (CFGD-FSS), and cement-FA-DG FSS (CFD-FSS). Considering 7 d, 14 d, and 28 d three curing times, compressive, flexural, scanning electron microscopy (SEM), and x-ray diffraction (XRD) analyses were conducted to explore the time-dependent mechanical properties and microscopic characterisation of FSS. The mechanical test showed that CFGD-FSS doped with FA and GGBS had better fluidity, compressive strength, and flexural strength than CGD-FSS doped with FA alone and CFD-FSS doped with GGBS. The CFGD-FSS specimen with a cement:FA:GGBS:DG ratio of 30: 10: 40: 20 in the curing agent had the best mechanical properties, i.e., the CFGD01 specimens. It has fluidity of 189 mm, compressive strength of 671 kPa, and flexural strength of 221 kPa with a 28d curing time, which can meet the working requirements of FSS for filling narrow engineering spaces. And compared with other specimens, it has the shortest setting time, which can effectively shorten the construction period. Microscopic analysis showed that a large number of hydration products, such as calcium silicate hydrate, calcium aluminate hydrate, and ettringite (Aft), were well-formed in the FSS, resulting in good mechanical properties, especially for the CFGD-01 specimens. Finally, two empirical models were established to describe the compressive strength–porosity and flexural strength–porosity relationships. Moreover, the investigated data agreed well with the modelling results.

The recycling and reuse of construction waste have not only effectively protected natural resources but also promoted the sustainable development of the environment. Therefore, in this article, waterborne polyurethane (WPU) as a promising new polymer reinforcement material was proposed to reinforce the road demolition waste (RDW), and the mechanical performance of WPU-reinforced RDW (named PURD) was investigated using triaxial unconsolidated and undrained shear (UU) and Scanning Electron Microscope (SEM) tests. The results showed that under the same curing time and confining pressure, the shear strength of PURD increased with the increase in WPU content. When the WPU content was 6%, the WPU presented the best reinforcement effect on RA. The failure strain of PURD increased with the increase in confining pressure, but increased first and then reduced with the increase in WPU content. The specimens with 5% WPU content showed the best ductility. At the curing time of 7 and 28 days, the internal friction angle and cohesion of PURD increased with the increase in WPU content, and they reached a maximum when the WPU content was 6%. The internal friction angle barely budged, but the cohesion increased obviously. The enhancement effect of WPU was attributed to the spatial reticular membrane structure produced by wrapping and bonding particles with the WPU film. Microscopic analysis showed that with the increase in WPU content, the internal pore and crack size of PURD gradually decreased. As the WPU content increased, the WPU film became increasingly thicker, which increased the adhesion between WPU and RA particles and made the structure of PURD become increasingly denser.

In order to study the mechanical modification effect of nano-MgO on cement-reinforced recycled fine aggregate (CRA), direct shear tests and triaxial shear tests were carried out. In the test of recycled fine aggregate reinforced by nano-MgO modified cement (MCRA), the cement content was fixed at 2%, and the nano-MgO content varied between 0%, 0.5%, 1.0%, 1.5% and 2.0%. The test results showed that adding nano-MgO can greatly increase both the direct shear strength and triaxial shear strength of MCRA. This increase in direct shear strength was mainly attributed to the increase in cohesion. However, this increase in triaxial shear strength was attributed to the simultaneous increase in the cohesion and friction angle.

Seeking ways to effectively utilise iron tailings within the green building sector is a pressing issue at present. In this study, using iron tailings as the main raw material and cement as the auxiliary cementitious material, the effects of sodium silicate (SS) content and carbonation curing on the compressive strength, stiffness, microstructure and mineral composition of cemented iron tailings (SSCIT) were investigated. The results showed that a certain amount of SS could increase the strength and stiffness of SSCIT. By adding 6% SS, the strength and stiffness of SSCIT reached the maximum value. The addition of SS promoted the dissolution of silicate minerals, and the generated geopolymerised gel binder filled the pores of specimens, enhanced the bonding force between the interfaces of soil particles, and improved the specimen compactness. However, carbonation curing adversely affected the strength of SSCIT. Carbonation caused the hydration products of SSCIT to change, and the decalcification and decomposition of the C-S-H gel increased the porosity of SSCIT, leading to a decrease in strength. In addition, using iron tailings for road base materials is an efficient and feasible method of utilisation.