In saline-alkali and coastal areas, cement soil faces various threats from salt erosion, and these environmental conditions can significantly impact the mechanical properties of cement soil. To counter external erosion, the addition of graphene oxide (GO) nanomaterials to cement soil is considered an effective solution. This study systematically investigates the strength variations of GO cement soil after erosion in different concentrations of NaCl solution (0 g/L, 4.5 g/L, 18 g/L, 30 g/L), Na2SO4 (0 g/L, 4.5 g/L, 18 g/L, 30 g/L), and a composite salt solution of both (0 g/L, 4.5 g/L, 18 g/L, 30 g/L) at different times (7d, 14d, 30d, 60d) through salt immersion tests, unconfined compressive strength tests, and SEM scanning electron microscope tests. Simultaneously, the study analyzes the mass change rate, stress-strain curves, peak stress of unconfined compressive strength, and modulus of elasticity changes in cement soil samples after erosion. The internal erosion mechanism of cement soil samples is explored at the microscopic level. When the GO cement soil was eroded in different concentrations of NaCl solution for 14 days, a consistent trend of mass decrease was observed. However, after 7, 30, and 60 days of erosion in various concentrations of NaCl solution, the mass showed an increasing trend. When immersed in pure water for 7d, 14d, 30d, and 60d, as well as in a 4.5 g/L NaCl solution for 7d and 14d erosion, the peak stress of GO cement soil samples shows an increasing trend, while it decreases under other conditions, especially significantly in Na2SO4 solution. Simultaneously, Na2SO4 has the greatest impact on the modulus of elasticity of cement soil. SEM test results reveal that due to nucleation effects, GO promotes the generation of hydration product C-S-H, enhancing the resistance of cement soil samples to external erosion. Furthermore, it is observed that under the influence of SO42-, C-S-H undergoes decalcification to generate AFt, while the impact of Cl- on C-S-H is relatively small.

In coastal and saline-alkali regions, cement soil materials face significant challenges from salt erosion and both dynamic and static loads, threatening their structural stability. To enhance the mechanical properties of cement soil, this study explores the incorporation of graphene oxide (GO). We subjected GO cement soil specimens to various concentrations of a composite salt solution (with a NaCl to Na2SO4 mass ratio of 1:1) in erosion experiments lasting 7 and 30 days. The specimens were analyzed through unconfined compressive strength tests, split Hopkinson pressure bar (SHPB) tests, and scanning electron microscopy (SEM) to examine changes in stressstrain curves, peak stress, and energy dissipation. The results indicate that the dynamic and static peak stresses, energy absorption, and energy absorption efficiency of the GO cement soil specimens are inversely related to the concentration of the mixed salt solution. Notably, in a 4.5 g/L erosion environment after 7 days, an increasing trend was observed in static peak stress, energy absorption, and energy absorption efficiency. Additionally, when the salt concentration was fixed, these properties showed a positive correlation with impact gas pressure. SEM analysis revealed that the nucleation effect of GO and its strong bonding with the cement matrix significantly improved the microstructure of the specimens by reducing pores and defects, thus enhancing density and overall performance. Furthermore, in an 18 g/L erosion environment, a notable presence of ettringite (AFt) was identified in the GO cement soil specimens.

In cold and saline soil areas, concretes usually experience multi-factor erosions, such as freezing- thawing cycles (FTCs), drying-wetting cycles (D-Ws), and salt erosion. To promote green and sustainable development of the construction industry, municipal solid waste incinerator bottom ash (MSWIBA) was adopted as a partial replacement for conventional fine aggregates in concretes. In this study, the coupled effects of the D-Ws and salt erosion (i.e., 5 % NaCl solution and 5 % Na2SO4 2 SO 4 solution) were experimentally conducted to investigate the mechanical and micro- structural properties of ordinary and MSWIBA concretes. The results showed that D-Ws had a negative effect on the mechanical properties of concretes. The depth and width of cracks in concretes increased with the D-Ws raised. During the D-Ws, the influence of salt solution on concretes could be divided into two stages. Initially, the filling effect of salt crystals was beneficial to the development of concrete strength. Subsequently, salt crystals accumulated in concretes caused cracks, and accelerated the deterioration of concrete specimens. Meanwhile, sodium sulphate reacted with hydration products in concretes to produce some expansive substances, the evident diffraction peaks of expansive substances (e.g., gypsum and ettringite) had been clearly observed after D-Ws. Thus, the damage effect of 5 % Na2SO4 2 SO 4 solution (SS) to concrete structure was more serious than that of water (WT) and 5 % NaCl solution (CS). Furthermore, the total porosity of the concrete specimens generally decreased with the MSWIBA substitution rate increased. There was an optimal MSWIBA content for concretes to obtain the excellent mechanical and microstructural properties. In detail, when the substitution rate of MSWIBA was between 0 % and 33.0 %, it had an excellent effect on improving the pore structure of concretes. Specifically, the compressive strength of concretes was larger than 35.0 MPa when the substitution rate of MSWIBA with natural river sand was between 24.8 % and 57.8 %, whereas the substitution rate of MSWIBA should not exceed 33.0 % exposed to D-Ws. This study could provide a significant reference for the sustainable development of concretes in cold and saline soil areas, as well optimization and innovation usage of MSWIBA.

In cold and saline soil regions, freeze-thaw (F-T) cycles and salt erosion are two major factors determining the durability of concrete structures. This paper aims to investigate the influential mechanism and deterioration of the mechanical and microstructural properties for the concretes modified with nano-TiO2 (NT) and nano-SiO2 (NS) exposed to the coupled environment conditions of the F-T cycles and salt erosion. 180 F-T cycles were conducted on the concretes immersed in five kinds of environment media, namely, water (WF), air (AF), solution with a concentration of 5% Na2SO4 (SSF), solution with a concentration of 5% NaCl (SCF), and a mixture solution with the concentration of 5% Na2SO4 and 5% NaCl (HSF). The results indicate that the added nanoparticles and media significantly influence the overall performance of concrete samples. The SCF has the greatest influence on the degradation of concretes, following by the HSF, SSF, WF, and AF. Meanwhile, the compressive strength of concretes modified with NT is lower than that modified with NS. There is an optimal nanoparticles ratio for the nano-concrete samples to resist coupled effect of the F-T actions and salt erosion, and the optimal nanoparticles ratios for the concretes modified with NS and NT are 1% and 2%, respectively. Moreover, the filling effect on pore structure for the concretes modified with NS is better than that with NT, more hydration products and corrosion products occur on the concrete surfaces, and the crystals on the surface of concretes modified with NS are larger than that modified with NT. Furthermore, for the concretes modified with nanoparticles in the first 90 F-T actions, the gel micro-pores (5000 nm) decrease. However, the gel micro-pores decrease and the macro-pores increase within the 90-150 F-T cycles. This research would provide significant instructions on the exploration of the anti-erosion and frost-resistance of nano-concretes in marine and cold region engineering.