To address scour hazards surrounding offshore foundations, a new method employing novel alkali-activated cementitious grout (AACG) has been proposed for improvement of seabed soil. Ground granulated blastfurnace slag (GGBFS) was replaced by fly ash (FA), steel slag (SS) or FA + SS to prepare precursors, the replacement amounts were 10 %, 20 %, 30 % and 40 %. Fresh-state and mechanical properties, minerals and microstructures were investigated. A novel scour simulation test device was developed to simulate engineering conditions of scour and remediation. Flow-soil coupled scour resistance tests were conducted, shear tests and SEM measurements of solidified soil were carried out. The results showed that the optimal ratio of GGBFS:FA:SS was 6:2:2 for AACG. The optimized AACG has better fluidity and lower brittleness, and its 28 d unconfined compressive strength (UCS) achieves 13.5 MPa. For AACG solidified soil, the maximum scour depth was reduced by 33.3 % and the maximum sediment transport amount was decreased by 53.2 %, which were compared to those of cement - sodium silicate (C-S) double slurry. Moreover, the increase degrees of internal friction angle, cohesion and critical shear stress were 700 %, 7.9 % and 786 %, respectively. The scour resistance of AACG solidified soil was superior. The inherent relationship between UCS and critical shear stress was discussed. UCS can be used to rapidly assess the scour resistance of consolidated soil. This study introduced an eco-friendly AACG as an innovative stabilizer for soil reinforcement around offshore structural foundations, offering significant application and environmental values for scour control.

This investigation addresses the reinforcement of rammed earth (RE) structures by integrating carpet polyacrylic yarn waste (CPYW) generated from the carpet production process and employing Ground Granulated Blast-Furnace Slag (GGBS) as a stabilizer, in conjunction with alkali activators potassium hydroxide (KOH), to enhance their mechanical properties. The study included conducting Unconfined Compressive Strength (UCS) tests and Brazilian Tensile Strength (BTS) tests on plain samples, GGBS-stabilized (SS) samples, CPYW-reinforced (CFS) samples, and samples reinforced with a combination of GGBS and CPYW (SCFS). The results showed that the mechanical and resistance properties of the CFS and SCFS samples were improved; these findings were confirmed by the presence of more cohesive GGBS gel and fibers as seen in FE-SEM and microscopic images. Therefore, the use of GGBS and CPYW, both separately and in combination, is suggested as a viable approach to enhance mechanical performance and reduce the brittle failure propensity of RE structures. This study achieved significant improvements in the mechanical behavior of RE structures by integrating CPYW and alkali-activated GGBS. Results showed a 370% improvement in UCS and a 638% increase in BTS than the plain sample. These enhancements demonstrate the potential for using industrial waste in eco-friendly, high-performance construction materials.

The use of OPC as a construction material is currently being reconsidered owing to the generation of greenhouse gases during production. Geopolymers or alkali-activated cement (AAC) have been proposed as partial replacements because of their excellent chemical and mechanical properties, which are equal to or superior to those of OPC. The use of these alkaline types of cement in soil stabilization has also gained significant interest in the academic community because of the possibility of it being derived from industrial waste. In this study, clay soil stabilized with AAC using waste stone wool fiber (SW) as a precursor and stabilized with hybrid alkali-activated cement (HAAC) using SW and OPC was prepared and subsequently evaluated mechanically and chemically after 28 days of curing. The results showed a significant increase in soil strength with both stabilization processes. The maximum achieved unconfined compressive strength (UCS) in the soil stabilized with AAC was 0.9 MPa (15 % SW), while the strength achieved with HAAC was 1.7 MPa (10.5 % SW- 4.5 % OPC). The California Bearing Ratio (CBR) of the latter combination was also determined, finding a value of 133 %, well above that of the soil without treatment (3.32 %). Through XRD, the A-type zeolite was identified as a product of the alkaline reaction, whereas the formation of N-A-S-H and C-A-S-H gels was observed via SEM. EDS mapping showed an increase in the atomic percentages of Si and Al in the soil specimens with HAAC, indicating the formation of Si-O-Si and Si-O-Al bonds. In addition to the potential application of this material in civil infrastructure related to soils (e.g., embankments and wall fillings), a sustainable construction material using industrial waste SW with a lower percentage of OPC is proposed.

The present investigation explores the potential of alkali-activated slag as a novel method for stabilizing and enhancing the mechanical properties of loose sandy soils. To achieve this, unconfined compression tests were performed on samples with varying slag content, activator solution parameters, and curing conditions. A predictive model was developed to estimate UCS based on these factors. The microstructural analyses using field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy elucidated the development of gels contributing to improved mechanical properties of the treated samples. Additionally, UCS tests demonstrated that increased slag content, activator concentration, and curing time significantly increase strength, stiffness, and brittleness. Notably, the findings show that samples treated with alkali-activated slag achieved substantially higher strength than those treated with ordinary Portland cement. These findings highlight the superior efficiency of this method in soil stabilization.

This paper presents a study on the stabilization of hazardous tin mine tailings (TMT) using a metakaolin-based geopolymer binder for their potential reuse as geomaterials in geotechnical works. The extensive laboratory testing evaluated the mechanical properties, such as unconfined compressive strength, and the durability properties, including mass loss during freezing-thawing and wetting-drying cycles. Environmental assessment included the analysis of leached heavy metal concentration using Toxicity Characteristic Leaching Procedure (TCLP). Additionally, Scanning Electron Microscopy (SEM) was conducted to investigate the microstructure of the stabilized TMT. Satisfactory results show that improvements in mechanical and durability properties depend on variations in metakaolin content, NaOH molarity, and compaction density. The novel porosity/binder index (eta/Biv) has proven to be effective in predicting the behavior of mixtures. Additionally, it demonstrated that freezing-thawing cycles have a more adverse impact on the durability of the examined mixtures. Laboratory results for mechanical strength, durability, and immobilization of hazardous heavy metals demonstrate the potential performance of TMTs for safe reuse in geotechnical works, specifically as a geomaterial for subbase and base layers of pavement exposure to severe environment and climate of the Andean highlands.