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 purpose of this study was to evaluate the sustainability benefits of Class F fly ash (FA), lime sludge (LS), and ground granulated blast furnace slag (GGBS)-based geopolymer-stabilized Edgar plastic kaolin (EPK) clay using the sustainability index (ISus) approach. Geotechnical engineering operations usually precede most infrastructural projects, making pavement construction an integral contributor to various environmental effects, due to the production of enormous quantities of greenhouse gas emissions through soil stabilization activities. To nip these concerns in the bud, effective integration of these environmental implications must be achieved during the geotechnical planning phase. The life cycle assessment (LCA) method was used to assess a wide range of environmental effects of a project, from raw material procurement, manufacturing, transportation, construction, and maintenance to final disposal. It is a well-recognized tool for designing environmentally sustainable projects. Experimental results from the geopolymer-stabilized EPK clay showed a notable improvement in unconfined compressive strength of the geopolymer-stabilized clay with 15% (FA + LS) and 5% (FA + GGBS) contents of up to 697% and 464%, respectively, after 28 days of curing at elevated temperature, 70 degrees C. The sustainability index (ISus) of geopolymer and lime treatment methods was analyzed based on the concept of environmental, resource consumption, and socioeconomic concerns, which quantifies the sustainability through greenhouse gas emission, environmental impacts, and the cost of utilizing FA, LS, and GGBS in soil stabilization compared with traditional lime. LCA was conducted for traditional lime treatment, FA-LS, and FA-GGBS geopolymer-stabilized subgrades to determine the most sustainable treatment method. From the sustainability analysis, using FA, LS, and GGBS as geopolymer stabilizers for kaolin clay reduced the global warming potential by 98.03% and 77.55% over the traditional lime stabilizers at 8% dosage. More importantly, results from the sustainability index (ISus) computations showed that FA-LS (ISus = 12.88) and FA-GGBS (ISus = 29.72) geopolymer treatment methods of EPK clay subgrade soils are more sustainable alternatives compared to the traditional lime (ISus = 48.07) treatment method.

Sulfate soils often caused foundation settlement, uneven deformation, and ground cracking. The distribution of sulfate-bearing soil is extensive, and effective stabilization of sulfate-bearing soil could potentially exert a profound influence on environmental protection. Ground granulated blast furnace slag (GGBS)-magnesia (MgO) can be an effective solution to stabilize sulfate soils. Dynamic cyclic loading can be used to simulate moving vehicles applied on subgrade soils, but studies on the dynamic mechanical properties of sulfate-bearing soil under cyclic loading are limited. In this study, GGBS-MgO was used to treat Ca-sulfate soil and Mg-sulfate soil. The swelling of the specimens was analyzed by a three-dimensional swelling test, and the change in compressive strength of the specimens after immersion was analyzed by an unconfined test. The dynamic elastic properties and energy dissipation of GGBS-MgO-stabilized sulfate soils were evaluated using a fatigue test, and the mineralogy and microstructure of the stabilized soils were investigated by X-ray diffraction and scanning electron microscopy. The results showed that the maximum swelling percentage of stabilized Ca-sulfate soil was achieved when the GGBS:MgO ratio was 6:4, resulting in an expansion rate of 14.211%. In contrast, stabilized Mg-sulfate soil exhibited maximum swelling at GGBS:MgO = 9:1, with a swelling percentage of 5.127%. As the GGBS:MgO ratio decreased, the dynamic elastic modulus of stabilized Ca-sulfate soil diminished from 2.8 MPa to 2.69 MPa, and energy dissipation reduced from 0.02 MJ/m3 to 0.019 MJ/m3. Conversely, the dynamic elastic modulus of stabilized Mg-sulfate soil escalated from 2.16 MPa to 6.12 MPa, while energy dissipation decreased from 0.023 MJ/m3 to 0.004 MJ/m3. After soaking, the dynamic elastic modulus of Ca-sulfate soil peaked (4.01 MPa) and energy dissipation was at its lowest (0.012 MJ/m3) at GGBS:MgO = 9:1. However, stabilized Mg-sulfate soil exhibited superior performance at GGBS:MgO = 6:4, with a dynamic elastic modulus of 0.74 MPa and energy dissipation of 0.05 MJ/m3. CSH increased significantly in the Ca-sulfate soil treated with GGBS-MgO. The generation of ettringite increased with the decrease in the GGBS-MgO ratio after immersion. MSH and less CSH were formed in GGBS-MgO-stabilized Mg-sulfate soil compared to Ca-sulfate soils. In summary, the results of this study provide some references for the improvement and application of sulfate soil in the field of road subgrade.