To improve the limitations of lime-treated subgrade soil (LS), a series of unconsolidated and undrained triaxial tests were conducted to investigate the improvement effect of fiber modified lime-treated soil (PLS) and fly ash modified lime-treated soil (FLS). The test results showed that (1) The deviatoric stress-strain curves of LS, PLS, and FLS were basically of the softening type. (2) The addition of fiber and fly ash improved the ductility and stiffness of LS. The ductility of PLS increased by 134% compared with LS, while the mechanical strength of FLS increased by 53%. (3) The microscopic tests showed that a denser skeleton structure was generated inside LS with the addition of fiber and fly ash. (4) The deviatoric stress-strain curves of LS, PLS, and FLS under different confining pressures were better characterized with the CES curve model. The above results indicate that fiber and fly ash can effectively improve the mechanical characteristics of lime-treated subgrade soil.

To observe the effect of recycled sand and nano-clay on the improvement of the early strength of soil-cement (7d), 0%, 10%, 15% and 20% recycled sand were added. While maintaining a fixed moisture content of 30%, the ratios of each material are specified in terms of soil mass percentage. The shear strength of CSR (recycled sand blended soil-cement) was investigated by direct shear test and four groups of specimens (CSR-1, CSR-2, CSR-3 and CSR-4) were obtained. In addition, 8% nano-clay was added to four CSR groups to obtain the four groups of CSRN-1, CSRN-2, CSRN-3 and CSRN-4 (soil-cement mixed with recycled sand and nano-clay), which were also subjected to direct shear tests. A detailed analysis of the modification mechanism of soil-cement by recycled sand and nano-clay was carried out in combination with scanning electron microscopy (SEM) and IPP (ImagePro-Plus) software. The test results showed that: (1) CSR-3 has the highest shear strength due to the “concrete-like” effect of the incorporation of recycled sand. With the addition of 8% nano-clay, the overall shear strength of the cement was improved, with CSRN-2 having the best shear strength, thanks to the filling effect of the nano-clay and its high volcanic ash content. (2) When recycled sand and nano-clay were added to soil-cement, the improvement in shear strength was manifested in a more reasonable macroscopic internal structure distribution of soil-cement. (3) SEM test results showed that the shear strength was negatively correlated with the void ratio of its microstructure. The smaller the void ratio, the greater the shear strength. This shows that the use of reclaimed sand can improve the sustainable development of the environment, and at the same time, the new material of nano-clay has potential application value.

To remove graphene oxide from wastewater, we used batch experiments with calcareous sand to recover GO. The adsorption properties and mechanisms of GO by calcareous sand were investigated by different characterization techniques. In this paper, the relationship between the coagulation of GO on calcareous sand and pH, calcareous sand content, GO initial concentration, and temperature was studied. The results show that calcareous sand can effectively adsorb GO from aqueous solution, the interaction of GO with calcareous sand achieved interaction equilibrium in 5 h, and the adsorption of GO by calcareous sand strongly depends on pH. The isotherm data fitted to a Langmuir equation. A possible mechanism can be expressed from FT-IR, XRD, Raman spectra, SEM, EDS, TEM, AFM, and XPS results. The test results indicate that calcareous sand is a potentially recoverable GO material.

Magnetic carbon-supported metal nickel has been successfully synthesized by solvothermal method and heat treatment for highly effective adsorption of various reactive dyes. Structure characterization and composition analysis demonstrated that the metal nickel nanoparticles with the size of 1–2 nm were embedded into the pore of carbon spheres. It is helpful to prevent the agglomeration and falling off of metal nickel nanoparticles on the surface of carbon spheres. The adsorption performance of the carbon-supported metal nickel nanospheres for reactive brilliant yellow R-4GLN was studied by changing the pH value and initial concentration of the solution, adsorption time, adsorption temperature, and the amount of adsorbent. The carbon-supported metal nickel showed fast and efficient adsorption activity. After 5 min of adsorption, the removal efficiency of 10 mL 25 mg·mL⁻¹ reactive brilliant yellow R-4GLN was close to 100%. The carbon-supported metal nickel composite was reused 20 times, and the removal efficiency of dye remained above 98%. It also showed good adsorption performance on various reactive dyes with wide universality, which has a certain adsorption effect on most dyes with a high utilization value in wastewater treatment.

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 effects of recycled aggregate with different particle gradations and different contents on the mechanical properties of cement soil modified by nano-MgO, unconfined compressive strength and scanning electron microscope (SEM) tests were carried out. The cement content was fixed at 15% and the nano-MgO content was 1.5%. The effects of two ages, three recycled aggregate contents, and three recycled aggregate particle gradations were considered. The test results show that the unconfined compressive strength of natural graded (RA), recycled coarse aggregate (SRA), and recycled fine aggregate (TRA) reached the maximum when the content of recycled aggregate was 20%, and the unconfined compressive strength of SRA was higher than that of TRA and RA. The residual strength of RA and SRA samples first increased and then decreased with the increase in recycled aggregate content, and the residual strength of TRA samples increased gradually with the increase in recycled aggregate content. The variation law of peak strain and peak strength of the three particle graded samples was consistent, and the variation law of brittle failure degree was highly consistent with that of residual strength. When the recycled aggregate content of RA, SRA, and TRA samples was 20%, the deformation resistance and stiffness of the samples were the best. In addition, SRA samples showed the best deformation resistance, followed by TRA samples and, finally, RA samples. The smaller the porosity of the sample, the tighter the sample structure and the stronger the bearing capacity of SRA. The unconfined compressive strength of the WPRA sample was represented by an exponentially negative power function of the porosity.