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.

To assess the stabilizing effect of sodium alginate (SA) on cement soil subjected to dry-wet cycles, a comprehensive study was conducted involving UCS tests, dynamic triaxial tests, SEM analysis, and XRD analysis. The results showed that after 11 dry-wet cycles, the residual strength of the cement soil was 11.25 kPa with a 90.1% strength loss rate, while the SA-modified soil had a 72% loss rate and a residual strength of 432 kPa. Dynamic strain increased and dynamic elastic modulus decreased with higher dynamic stress, while higher loading frequencies reduced dynamic strain and increased dynamic elastic modulus. Increased cycle counts led to higher dynamic strain and lower dynamic elastic modulus. The damping ratio curves shifted downward with higher frequencies and moved rightward with more cycles. SEM and XRD analyses revealed that SA formed reticular cementitious materials that encapsulated soil particles and aggregated fines into larger particles. Sodium alginate significantly enhanced the soil's resistance to dry-wet cycles, providing valuable insights for coastal and soft soil subgrade engineering design.

Ground granulated blast furnace slag (GGBS), calcium carbide slag (CS), and phosphogypsum (PG) were combined in a mass ratio of 60:30:10 (abbreviated as GCP) to solidify dredged sludge (DS) with high water content. The long-term strength characteristics of solidified DS under varying curing agent dosage and initial water contents, as well as its durability under complex environmental conditions, were investigated via a series of mechanical and microstructural tests. The superior performance of GCP-solidified DS (SDS-G) in terms of strength and durability was demonstrated in comparison to solidified DS using ordinary Portland cement (SDS-O). The results indicated that the unconfined compressive strength (UCS) of SDS-G was approximately 3.0-4.5 times greater than that of SDS-O at the same dosage and curing ages, exhibiting a consistent increase in strength even beyond 28 days of curing. Additionally, the strength and deformation modulus (E50) of SDS-G increased initially and then decreased during wet-dry cycles, with reductions in mass, volume, and strength significantly were smaller than those observed in SDS-O. Furthermore, the reductions in UCS and E50 induced by freeze-thaw cycles were considerably smaller for SDS-G than for SDS-O, with strength losses of 50.7 % and 88.3 %, respectively, after 13 freeze-thaw cycles. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that the enhancements observed in SDS-G were attributed to the formation of ettringite (AFt), which effectively fills larger pores between agglomerated soil particles, thereby creating a denser and more stable microstructure in conjunction with hydrated calcium aluminosilicate (C- (A)-S-H) gels.

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.

The composite rapid soil stabilizer (CRSS) is a newly developed material for rapid curing of sludge with fast setting, fast hardening, and high strength properties. CRSS was used to solidify the sludge, and the durability test of the solidified sludge under the action of sulfate erosion was carried out to analyze the influence of erosion time and Na2SO4 and MgSO4 concentration on the physical and mechanical properties of the solidified sludge. The research results showed that as the erosion time increased, the mass of soaked samples increased gradually. Additionally, the strength of samples soaked in clear water continued to rise, while the strength of samples soaked in sulfate increased first and then decreased. After 112 days of erosion, the higher the concentration of SO42-, the greater the mass of the soaked sample and the lower the strength. At the same concentration, the mass of the soaked sample with MgSO4 was the largest, but the strength was the lowest. Under the action of sulfate attack, the soaked samples produced a large number of expansive products, and the cumulative pore volume first decreased and then increased. The microstructure of the MgSO4-soaked samples suffered the most damage due to the double corrosion of Mg2+ and SO42-. Based on the macroscopic and microscopic test results, the microscopic evolution mechanism of the durability of solidified sludge under Na2SO4 and MgSO4 erosion environments was revealed. The solidified sludge with CRSS has good sulfate resistance durability, which lays a theoretical foundation for the engineering application of CRSS.

Stabilizing and improving weak and poorly graded soils in road construction projects is a widely used and highly interesting technology. This research study utilizes paper sludge ash (PSA) residues as a geopolymer waste material to stabilize loose and poorly graded sands (SP), improve mechanical properties, and support sustainable pavement development. Geotechnical tests using the unconfined compressive strength test (UCS), Young's modulus (Es), California bearing ratio (CBR), and a direct shear test (DST) assessed the performance and strength development of geopolymer-stabilized soil. The stabilized soil's microstructure and chemical mineralogy were also examined using SEM and XRD. Additionally, a laboratory testing apparatus was designed and developed to assess the permanent strain behavior of subgrade soil and geopolymer-stabilized soil layers under cyclic loading. The research analysed variables including curing duration (1, 3, and 7 days), PSA concentration (5, 10, and 15%), and the type and concentration of alkaline activators (NaOH or Na2SiO3). Soil samples treated with PSA and Na2SiO3 geopolymers showed higher UCS, Es, and CBR values, leading to improved strength from increased N-A-S-H and C-A-S-H gel formation among sand soil particles. On the contrary, the NaOH solution enhanced the strength parameter of geopolymer-stabilized soil samples. The results showed that geopolymer-stabilized soil significantly improved its resistance to permanent deformation after applying loads. The mineralogical examination also shows a high concentration of lime and cubic aluminate, which may be active cementitious pozzolanic material. This research reflects that PSA has promising potential to stabilize sandy soil and improve the design and maintenance of roads and infrastructure in areas with weak soils.

This study investigates the evolution of the dynamic characteristics of a solidified dredge sludge, including the resilient modulus (MR), accumulative plastic strain (epsilon p) and damping ratio (lambda) during long-term traffic loadings considering influences of environmental actions (dry-wet, DW, and freeze-thaw, FT cycles), stress states (confining stress sigma cand deviator stress sigma d) and loading frequency (f). The experimental results indicate that the dynamic characteristics continuously change with increasing loading cycles and the influences of environmental actions, external stress state, and loading frequency are coupled. The resistance of the solidified sludge against traffic loading decreases after both DW and FT cycles, which is manifested by the decrease in the MR and the increase in the lambda and epsilon p. DW cycles induce greater reductions in the dynamic characteristics than the FT cycles. The increasing sigma c improves the resistance of the soil against cyclic loadings, resulting in higher MR and lower epsilon p and lambda. Besides, their rates of change with loading cycles (i.e., delta MR, delta epsilon p and delta lambda) reduce. The MR, epsilon p, lambda, and delta ap increase while the delta MR and delta lambda decrease with the sigma d, indicating that the increase in the cyclic loading level contributes to the accumulation of plastic strain and energy assumption while the resultant densification effect leads to the increase in the MR and decrease in the delta MR and delta lambda. The soil dissipates less energy when loaded under higher f, resulting in higher MR and lower epsilon p and lambda. Results reported in this paper are helpful for better understanding the dynamic responses of solidified sludge under complex loading and environmental conditions.

This study explores the valorisation of alum sludge, a byproduct of water treatment processes, as a sustainable reinforcement material in Poly(butylene adipate-co-terephthalate) (PBAT) composites. The research aims to address industrial waste challenges by developing eco-friendly composite materials while promoting circular economy principles. Alum sludge particles, classified into two size distributions (<63 m and <250 m), were incorporated into PBAT matrices at varying concentrations. The composites were characterised for their mechanical, thermal, crystallographic, and moisture adsorption properties; and their biodegradation behaviour was evaluated through soil burial tests over 60 days. The results revealed that the 63 mu m particle size fraction exhibited superior performance compared to the 250 mu m fraction, demonstrating improved mechanical properties, reduced degradation rates, and enhanced interfacial bonding. Composites with 5 wt.% alum sludge achieved a balance between reinforcement and processability, outperforming the other filler concentrations examined. This innovative approach highlights the potential of upcycling alum sludge into functional materials, advancing sustainable waste management and composite manufacturing. Furthermore, the observed variation in degradation rates suggests that these composites can be tailored for applications requiring controlled compostability.

Phosphogypsum (PG), phosphate sludge (PS), and sewage sludge (SS) are regarded by-products produced in huge amounts. However, PG, PS and SS are no longer considered as waste, but as valued resources in accordance with the circular economy's rules. Their management provides a serious environmental problem. In order to assess the impacts of SS, PS, and PG on soil physico-chemical parameters (pH, EC, OM, nutrients, and heavy metals) in response to diverse experimental settings, the purpose of the current study was to conduct a meta-analysis on previously published results. The VOSviewer program was used to construct bibliometric maps using the VOS mapping and grouping techniques. The findings indicated that there were statistically significant changes (P < 0.05) in electrical conductivity (EC), organic matter (OM), and pH in connection to the different by-products employed. The application of SS considerably elevated pH by 46.15% compared to the control. Furthermore, a beneficial effect on P and K was detected, regardless of the by-product used. Moreover, Cd, Pb, and Ni concentrations in SS treatments had a substantial reduction of 30.46%, 30.70%, and 18.07%, respectively. Cd, Pb, and Cu concentrations in PG treatments revealed a substantial decrease of 47.71%, 36.14%, and 46.01%, respectively. Based on the acquired data, PG, PS, and SS need to be regularly monitored and regulated. This study serves as an early investigation for the construction of a new approach to restore damaged land on mine sites by employing phosphate industry by-products and sludge for revegetation objectives.

The increasing generation of industrial waste sludge poses a serious worldwide problem with detrimental effects on the environment and the economy. Effective utilization of waste sludge in sustainable construction practices offers a universal solution to mitigate environmental impacts. As the mining industry continues to extract clay from clay mines, the demand for sustainable practices in both clay mineral extraction and brick production is growing. Bricks are fundamental in masonry construction, and current research is exploring the integration of industrial waste materials into fired clay bricks to enhance their properties and mitigate environmental impacts. This study investigates the incorporation of waste sludge in brick manufacturing to assess its potential for reducing environmental burdens while maintaining technical performance. X-ray Fluorescence Spectrometry (XRF) analysis reveals that both clay soil and mosaic sludge contain high levels of silicon dioxide (SiO2) and aluminum oxide (Al2O3), supporting their suitability as partial substitutes for clay soil. Incorporating up to 30% of body mill sludge (BS) and polishing sludge (PS) into the brick mix significantly enhances physical and mechanical properties, resulting in reduced shrinkage, increased porosity, and improved compressive strength, reaching up to 25 N/mm(2). Initial rate of suction tests shows values below 5 g/mm(2), indicating optimal water absorption characteristics. Various leachability assessments, including the Toxicity Characteristic Leaching Procedure (TCLP), Synthetic Precipitation Leaching Procedure (SPLP), and Static Leachate Test (SLT), confirm that bricks containing up to 30% BS and PS comply with United States Environmental Protection Agency (USEPA) and Environment Protection Authority Victoria (EPAV) standards for heavy metals, making them environmentally safe for use. Additionally, indoor air quality assessments confirm that these bricks meet Industry Codes of Practice on Indoor Air Quality (ICOP-IAQ) guidelines. This study demonstrates that using BS and PS as alternative raw materials offers a sustainable, cost-effective solution aligned with Sustainable Development Goals (SDGs), promoting cleaner production practices in brick manufacturing.