Reactive magnesium oxide (MgO) and ground granulated blast furnace slag (GGBS) are cementitious materials introduced into sludge solidification, which not only reutilizes solid waste but also reduces cement consumption. Through the carbonation of reactive MgO and GGBS, the strength of the solidified sludge is further improved and CO2 is stably sequestrated in carbonate minerals. This paper investigates the strength and microstructural development and CO2 uptake of solidified sludge with varying water content, binder content, and ratio of MgO to GGBS. According to unconfined compressive strength (UCS) tests, when the binder content is 20% and the ratio of reactive MgO to GGBS is 2 & ratio;8, the strength of carbonated samples increases the most, which is six times that of the sample without reactive MgO. With binder content, the CO2 uptake of sample increases up to 2.1 g. Scanning electron microscope (SEM), X-ray diffractometer (XRD), and thermogravimetry-differential thermogravimetry analysis (TG-DTG) tests were conducted to systematically elucidate the micromechanism of carbonation of sludge solidified by reactive MgO and GGBS. Various carbonation and hydration products enhance the soil strength through filling pores and integrating fine particles into bulk aggregates. As the ratio of reactive MgO to GGBS increases, dypingite and hydromagnesite were converted into nesquehonite with better morphological integrity, and thus strengthens the soil skeleton. Diverse calcium carbonate polymorphs from carbonated GGBS also promote sludge strength growth and CO2 sequestration. Test results indicate that the addition of reactive MgO further improves the hydration and carbonation properties of GGBS, so the CO2 uptake grows with the ratio of reactive MgO to GGBS. The synergistic effect of reactive MgO and GGBS increases the carbonation performance of the mixed binder, so likewise the compressive strength.

Lysimeters are frequently employed to replicate environmental conditions in landfill scenarios due to their relatively economical nature and brief study duration. Lysimeters frequently exhibit varying geometrical characteristics that modify the physical and thermodynamic attributes, potentially influencing waste material's decomposition rate and leaching dynamics. Based on the results of the lysimeter tests, lysimeters effectively evaluate and predict the impact of magnesium oxide (Mgo), a material suitable for constructing landfill liners. The findings substantiate that lysimeter investigations can significantly contribute to landfill engineering by identifying optimal strategies for waste containment and selecting appropriate materials for fabricating landfill barriers. Throughout the experimental procedure, the lysimeter was subjected to leachate application. In each hour of the experiment, the quantities of moisture, electric conductivity value (EC), temperature, settlement, pressure reaching the liner, and the total volume and pH of the obtained effluents were measured each week. This research explores and analyzes the role of magnesium oxide (C-M) in reducing permeability and measuring the shear strength properties of the composite material by utilizing a triaxial test. The sensor results demonstrated that MgO-enhanced liners provided superior long-term performance compared to clay. EC sensors showed MgO liners had lower and more stable conductivity. Moisture content sensors indicated that MgO-treated soil maintained better moisture regulation, reducing leachate. LVDT sensors revealed that MgO liners had minimal settlement, while clay experienced greater and prolonged settlement. Temperature sensors confirmed MgO's consistent thermal stability. In contrast, pressure, Total Dissolved Solid (TDS), pH, and flow rate sensors highlighted MgO's better structural integrity, lower dissolved solids, and controlled permeability over time.

Dredged marine soils are increasingly recognized as a valuable resource amidst growing environmental concerns and the need for sustainable waste recycling. This study presents an innovative soil stabilization technique combining recycled aggregate (RA) and magnesium oxide (MgO) with a dual focus on enhancing soil properties and promoting carbon dioxide (CO2) sequestration. The stabilizing effects of RA and MgO were evaluated independently and synergistically under varied curing conditions and durations, with microstructural and mechanical properties analysed using scanned electron microscopy, X-ray diffraction, and uniaxial tests. Carbonation experiments quantified CO2 fixation potential, with the formation of hydration and carbonation products, along with dynamic moisture content and pH conditions, playing a significant role in enhancing the structural reinforcement of the soil. The combined RA-MgO treatment achieved superior mechanical stability (1.28-3.02 MPa) and a CO2 sequestration capacity of up to 11 g/kg without compromising performance. This study highlights the dual environmental and structural benefits of utilizing RA and low-content MgO for marine soil stabilization, offering a sustainable pathway to reduce carbon emissions, promote waste recycling, and support resilient infrastructure development.

Generally, nanotechnology plays an very important role in various applied scientific fields. Iron and magnesium nanoparticles (NPs) can cause positive or negative changes in soil physical and mechanical properties, especially in long periods. The aim of this study was to investigate the multi-year effects of NPs on soil water retention and aggregate tensile strength. A wheat farm loamy soil was amended with 1%, 3%, and 5% (weight/weight) of magnesium oxide (MgO) and iron oxide (Fe3O4) NPs in three replications and incubated for three years. Water contents were measured at different matric suctions of 0, 10, 20, 40, 60, 100, 300, 1 000, and 15 000 cm. The van Genuchten model was fitted to the moisture data. Tensile strength was measured on the 2-4 mm aggregates at matric suctions of 300 (i.e., field capacity) and 15 000 (i.e., permanent wilting point) cm. The results showed that the levels of 1% and 3% Fe3O4 NPs significantly increased water retention, compared to the no NP application control and 5% MgO NPs, which is probably due to the increase of adsorption surfaces in the treated soils. Water contents at field capacity and permanent wilting point in the 5% MgO NP treatment decreased compared to those of the other treatments, due to the increased soil vulnerability and reduced soil fine pores. The application of Fe3O4 NPs did not have any significant effect on soil tensile strength. Based on the results of this study, soil physical and mechanical properties could be affected by NP application.

Red mud (RM) is an industrial waste generated in the process of aluminum refinement. The recycling and reusing of RM have become urgent problems to be solved. To explore the feasibility of using RM in geotechnical engineering, this study combined magnesium oxide (MgO) (or calcium oxide (CaO)) with RM as an RM-based binder, which was then used to stabilize the soil. The physical, mechanical, and micro-structural properties of the stabilized soil were investigated. As the content of MgO or CaO in the mixture increased, the unconfined compressive strength (UCS) of the RM-based cementitious materials first increased and then decreased. For the soils stabilized with RM-MgO or RM-CaO, the UCS increased and then decreased, reaching a maximum at RM:MgO = 5:5 or RM:CaO = 8:2. The addition of sodium hydroxide (NaOH) promoted the hydration reaction. The UCS enhancement ranged from 8.09% to 66.67% for the RM-MgO stabilized soils and 204.6% to 346.6% for the RM-CaO stabilized soils. The optimum ratio of the RM-MgO stabilized soil (with NaOH) was 2:8, while that of the RM-CaO stabilized soil (with NaOH) was 4:6. Freeze-thaw cycles reduced the UCS of the stabilized soil, but the resistance of the stabilized soil to freeze-thaw erosion was significantly improved by the addition of RM-MgO or RM-CaO, and the soil stabilized with RM-MgO had better freeze-thaw resistance than that with RM-CaO. The hydrated magnesium silicate generated by the RM-MgO stabilized soil and the hydrated calcium silicate generated by the RM-CaO stabilized soil helped to improve the UCS of the stabilized soil. The freeze-thaw cycles did not weaken the formation of hydration products in the stabilized soil but could result in physical damage to the stabilized soils. The decrease in the UCS of the stabilized soil was mainly due to physical damage.