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.

The development of eco-friendly and efficient alternative binder to conventional Portland cement is a challenging issue that deserves to be paid more attention. The mineral additive-modified magnesium potassium phosphate cement mixture was introduced in sediment solidification recycled as alternative roadbed material. The feasibility of mineral additive-MKPC blend in solidifying sediment and its mechanical performance were probed into deeply through unconfined compressive strength, durability, microstructural and mineralogical tests. The results demonstrated that it existed an optimal mineral additive content where the peak strength was achieved, and an excessive amount caused the strength degradation. The unconfined compressive strength of solidified sediment increased with curing age and exhibited a growing potential. Struvite-k crystals were identified as the major cementing phase in mineral additive-MKPC solidified sediment. C-S-H gels and Ca2P2O7 c 2H2O were recognized as secondary phases for fly ash-MKPC blend and MgSiO3 for silica fume-MKPC blend. As the molar ratio of M/P and curing age grew, the total porosity was reduced due to the pore filling of mineral grains and densification of hydrated phases. The strength of solidified sediment after durability tests showed a tendency of first decline and then increase with durability period. Overall, the superior benefits including excellent strength performance, strong resistance to external environmental damage and highly densified microstructure could be expected for mineral additive-MKPC blend in sediment solidification as a promising roadbed filling.

The traction force of the tracked miner is primarily determined by the shear characteristics of deep-sea sediments. The influence of different parameters on the shear characteristics of deep-sea sediments and the particles change law of the soil-track interface are discussed. By constructing the relationship between the particles horizontal displacement and residual shear strength, a novel shear rheological damage model of deep-sea sediments considering the influence of grounding pressure is proposed, and the microscopic mechanism of shear displacement of deep-sea sediments is explained. The results show that the peak shear strength and residual shear strength increase significantly with the increase of grounding pressure, track length, grouser height and shear speed. Moreover, the particles within the soil-track interface move along the lower right of the vehicle operating direction during the shearing process under different working conditions, the change of particle spacing shows a non-linear trend, and a quantitative equation for the horizontal deformation of soil-track interface under the experimental conditions is constructed. Additionally, the new shear model has a high level of accuracy in fitting with the experimental data, the internal particle migration changes on the soil-track interface can be divided into four characteristics: compaction, failure, deformation and translation.

Traditional lime -solidified loess presents the issue of high carbon dioxide emissions. This paper presents the development of a kind of cementitious material using industrial solid waste: slag-white mud-CCR (calcium carbide residue). The slag mainly contains CaO, SiO2, and Al2O3, with a 10.6 pH value. The white mud and CCR mainly contain CaCO3 and Ca(OH)2, respectively. We further assessed the efficacy of slag-white mud-CCR in solidified loess and employed SEM and TG/DTG to explore their micromechanisms. The pH value of the CB4 sample (slag-white mud-CCR with the lowest CCR content) was 42.3 % higher than that of pure loess. Considering the 3 -day and 28 -day compressive strength and the material costs, the optimal mortar mixture ratio was found to be slag-white mud-CCR = 60:32:8, and this mixture was used to solidify loess. The unconfined compressive strength of 15 % slag-white mud-CCR-solidified loess is almost 5.0 times and 6.0 times higher than that of lime -solidified loess at 7 and 28 days of curing age, respectively. The durability of the solidified loess after freeze-thaw and wet-dry cycles was significantly improved compared with that of lime- or slag -solidified loess. Specifically, 10 % and 15 % slag-white mud-CCR-solidified loess maintained a high compressive strength after eight freeze-thaw and wet-dry cycles. SEM and TG/DTG analyses of the mortar and solidified loess confirmed the formation of hydration products of C-S-H- and C-A-(S)-H-type gels. The compressive strength results were obtained using a dual mechanism: the cementation of loess particles through the formation of hydration products and their subsequent filling action.

Although cemented soil as a subgrade fill material can meet certain performance requirements, it is susceptible to capillary erosion caused by groundwater. In order to eliminate the hazards caused by capillary water rise and to summarize the relevant laws of water transport properties, graphene oxide (GO) was used to improve cemented soil. This paper conducted capillary water absorption tests, unconfined compressive strength (UCS) tests, softening coefficient tests, and scanning electron microscope (SEM) tests on cemented soil using various contents of GO. The results showed that the capillary water absorption capacity and capillary water absorption rate exhibited a decreasing and then increasing trend with increasing GO content, while the UCS demonstrated an increasing and then decreasing trend. The improvement effect is most obvious when the content is 0.09%. At this content, the capillary absorption and capillary water absorption rate were reduced by 25.8% and 33.9%, respectively, and the UCS at 7d, 14d, and 28d was increased by 70.32%, 57.94%, and 61.97%, respectively. SEM testing results demonstrated that GO reduces the apparent void ratio of cemented soil by stimulating cement hydration and promoting ion exchange, thereby optimizing the microstructure and improving water resistance and mechanical properties. This research serves as a foundation for further investigating water migration and the appropriate treatment of GO-modified cemented soil subgrade.

The Loess Plateau is highly susceptible to gully headward erosion, highlighting the urgent need for soil stabilization. In this study, a series of physical and mechanical properties, water physical properties and microstructure tests were carried out to explore the loess improvement for potential control of headward erosion in loess gullies. Experimental results reveal that the addition of the Consolid System to loess soil leads to an increase in the plastic limit and liquid limit of the soil, while the soil retains its characteristics as a type of low plasticity soil. The dry density of the stabilized loess soil decreases, while the unconfined compressive strength increases. Regarding the water-physical properties, the swelling and shrinkage properties of modified loess soil were significantly improved while the permeability coefficient slightly decrease. Furthermore, the surface energy decreased, resulting in increased water repellency, while the pore volume remains relatively unchanged. A recommended minimum mixing ratio of the Consolid System is 1.5% to resist water erosion. In conclusion, the implementation of the Consolid System not only enhances the strength of loess soil and its water repellency, but also preserves the advantageous water drainage characteristics inherent to loess soil. Consequently, loess soil stabilized by the Consolid System holds promising potential for applications in areas covered with loess soil.