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.

Alkali-activated materials have gained increasing popularity in the field of soil barrier materials due to their high strength and low environmental impact. However, barrier materials made from alkali-activated materials still suffer from long setting times and poor barrier performance in acidic, alkaline, and saline environments, which hinders the sustainable development of green alkali-activated materials. Herein, coconut shell biochar, sodium silicate-based adhesives, and polyether polyol/polypropylene polymers were used for multi-stage material modification. The modified materials were evaluated for barrier performance, rapid formation, and resistance to acidic, alkaline, and saline environments, using metrics such as compressive strength, permeability, mass loss, and VOC diffusion efficiency. The results indicated that adhesive modification reduced the material's setting time from 72 to 12 h. Polymer modification improved resistance to corrosion by 15-20%. The biochar-containing multi-stage modified materials achieved VOC diffusion barrier efficiency of over 99% in both normal and corrosive conditions. These improvements are attributed to the adhesive accelerating calcium silicate hydration and forming strength-enhancing compounds, the polymer providing corrosion resistance, and biochar enhancing the volatile organic compounds (VOC) barrier properties. The combined modification yielded a highly effective multi-stage green barrier material suitable for rapid barrier formation and corrosion protection. These findings contribute to evaluating multi-level modified barrier materials' effectiveness and potential benefits in this field and provide new insights for the development of modified, green, and efficient alkali-activated barrier materials, promoting the green and sustainable development of soil pollution control technologies.

The efficiency of alkali-activated ground granulated blast furnace slag in stabilizing dredged sediments with high water contents is suboptimal because the activators become diluted. To improve stabilization efficiency, additives such as nano-CaCO3 are proposed. However, some of the proposed additives may not be practical owing to their high costs. This study experimentally investigates the addition of Na2CO3 for the stabilization of dredged sediment with high water contents (i.e., 100%) using Ca(OH)2-activated slag. Experimental results show the optimal content of Na2CO3 to obtain the highest 28-day unconfined compressive strength of stabilized sediments is 0.2% gravimetrically. Below the optimal content, the strength increases with Na2CO3 content. Above the optimal content, a decrease in strength is observed. By examining the reaction products and microstructure of the stabilized dredged sediments, it is observed that the coupling mechanism of cation exchange and calcite precipitation promotes the development of finer capillary pores, leading to a reduction in interpore connectivity and lower structural heterogeneity of the fine capillary pores. Experimental evidence from this study broadens the practical applications of sustainable soil stabilization using additives.

Alkali-activated cementitious materials present an environmentally beneficial and high-performance option in the domain of soil solidification and stabilization. This research focused on granulated blast-furnace slag (GGBFS), a predominant byproduct and solid waste from iron manufacturing that has a limited utilization rate. Due to its high content of calcium (Ca), silicon (Si), and aluminum (Al), slag has emerged as an effective soil curing agent. This study investigated sandy silt by employing alkali-activated slag to examine its solidification and stabilization properties. We assessed the unconfined compressive strength (UCS), deterioration strength, and solidification mechanism of alkali-activated slag-stabilized sandy silt through unconfined compressive strength tests and various microscopic analyses, including X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FITR), and scanning electron microscopy (SEM). These findings indicate that using slag alone for solidifying sandy silt is inefficient. However, following alkali activation, the UCS of solidified soil with sandy silt generally increases with increasing GGBFS content and initially increases, then decreases with increasing alkali-activator content. The ideal proportions of GGBFS and alkali-activator are between 12 %-14 % and 6 %-9 %, respectively. Upon exposure to ordinary and triple-concentration artificial seawater, the strength of the solidified soil generally diminishes over time. It is worth noting that the strength of the samples in group GGBFS14 exhibited an initial increase, followed by a decrease, as the deterioration time increased. With alkali-activator contents of 6 % and 9 %, the strength and durability of the solidified soil remain relatively stable, maintaining robust mechanical properties even after seawater erosion. The resistance of the solidified soil to seawater deterioration increases as the GGBFS content increases. Microscopic tests revealed the presence of amorphous hydration gel products (C-A-S-H). The optimal GGBFS and alkali-activator contents for sandy silt solidification in this study were determined to be 12 %-14 % and 6 %-9 %, respectively. At these optimal levels, the strength of the solidified soil at a curing age of 28 days can reach 13.49 MPa (GGBFS16AA6). This suggests that alkali-activated slag holds potential as a substitute for ordinary Portland cement (OPC) in engineering applications and offers a strategy for reusing GGBFS.

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.

Gold mine tailings (GMTs) pose significant environmental challenges, and while alkali-activated materials (AAMs) have been widely used as sustainable alternatives to Portland cement for stabilizing geotechnical materials, further research is needed to optimize their composition and performance, particularly by incorporating traditional industrial waste residues to develop composite alkali-activated materials (CAAMs) with improved mechanical properties and reduced environmental impact. Different CAAMs admixtures (i.e., 0%, 3%, 5%, and 8%) and gold mine tailings were prepared, and the samples were solidified under saturated water and no air. In order to investigate the mechanical characteristics of CAAMs-stabilized GMTs, laboratory direct shear tests were carried out on samples after curing them for 3, 7, 14, and 28 days, respectively. The test results showed that with the extension of curing time, the brittleness of the samples increased, and the stress-displacement curves for all the cured specimens changed from plateau type to peak type. Both curing time and CAAMs content are conducive to improving the shear strength of CAAMs-stabilized GMTs samples, but the increase rate decreased as the vertical confining stress increased. Furthermore, the influence of CAAMs content on shear strength increment was larger than that of curing periods. The exponential growth model could well describe the change of shear strength with the curing periods under different vertical stresses. The paper can provide theoretical support for the application of CAAMs to enhance the stability of tailings dams.

With the rapid growth of shield-discharged soil (SDS), there is an increasing demand for effective recycling and transformation methods. This study aims to develop an alkali-activated controlled low-strength material (CLSM) by utilizing ground granulated blast furnace slag (GGBFS) and fly ash (FA) as precursors, SDS as fine aggregate, and sodium hydroxide (NaOH) solution as an activator. The Box-Behnken design (BBD) within the response surface methodology (RSM) framework was employed, considering liquid-to-solid ratio, alkali equivalent, aggregate-to-binder ratio, and foam agent content (FC) in SDS as key factors. Regression models were constructed to analyze the effects of these factors on flowability, bleeding rate, setting time, compressive strength, elastic modulus, and water absorption. The results confirmed the effectiveness of RSM in determining optimal conditions for material performance. In addition, microscopic analyses were conducted to explore hydration products, microstructural characteristics, and pore distribution. The findings revealed that the fresh density of the CLSM ranged from 1460 to 1740 kg/m(3), classifying it as a low-density material. The 28-day compressive strength varied from 1.837 to 7.884 MPa, while the setting time ranged between 1.2 and 5.6 hours. These properties comply with the ACI 229 standard and are suitable for practical applications. Interestingly, when the aggregate-to-binder (A/B) ratio was between 0.2 and 0.4, increasing the ratio did not lead to a consistent reduction in mechanical properties. Instead, the properties initially decreased and then improved. Moreover, an increase in foam agent content (FC) extended the setting time and reduced mechanical strength. The correlation coefficients of all models exceeded 0.98, with a coefficient of variation below 10 % and a signal-to-noise ratio greater than 4, demonstrating strong reliability and accuracy of the models. Additionally, the average relative error between predicted and experimental values in six scenarios was under 6 %, validating the feasibility of optimizing the design of alkali-activated CLSM using RSM. The formation of Ca(OH)(2) crystals facilitates early strength development, resulting in final cementitious materials reticular, fibrous C-S-H, C-A-H, and other gel-like hydration products. Calcium promotes the formation of gels such as C-S-H, shortening the setting time and enhancing microstructural density. This study provides valuable insights for optimizing the design of alkali-activated CLSM containing SDS, thereby expanding methods for utilizing construction and demolition waste.

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.

To decrease the environmental impact and increase the high-quality resource utilization of construction spoil (CS), the alkali-activated slag (AAS) was selected to solidify CS and prepare solidified construction spoil (SCS). SCS with certain working and mechanical properties can be used as building materials, such as unsintered bricks. However, the preparation of SCS is inefficient, mainly because the properties of SCS are affected by various factors, and the formula is difficult to determine. This study intensively investigated the effects of the liquid-solid ratio (W/ (B + S)), clay content of CS, and binder-soil ratio (B/S) on the flowability and compressive strength of SCS. It was found that W/(B + S) was the main factor controlling compressive strength, and both W/(B + S) and clay content significantly affected the flowability of SCS. Based on an assumption for the flowability prediction method and the relationship between flowability and liquid-solid ratio of CS, AAS, and SCS, a method to predict the flowability of SCS was proposed and validated. Additionally, the extended Abrams' law was applied to fit the compressive strength variation of SCS. Combining the flowability prediction method and the extended Abrams' law, a novel formula design method for SCS was proposed and proven effective in validation experiments.

Excavated rock and soil from tunnelling (ERST), fly ash (FA), and slag are one of the largest sources of solid waste and play an important role in reducing dependence on natural resources and solving the problem of solid waste accumulation. This study verifies the feasibility of highperformance ecological geopolymer concrete (HPEGC) incorporating ERST, FA and slag for engineering applications. The effects of different binding material to machine-made sand ratio (BMMSR) and SN/FS (the total mass of sodium silicate and NaOH solids to the total mass of the powdered raw material) on the slump, compressive strength, tensile strength, drying shrinkage, salt corrosion resistance of concrete and the microstructural deterioration process before and after salt corrosion were analysed by indoor tests and microscopic tests. The results showed that the hydration products generated at SN/FS of 10, 12, and 15 % could effectively fill the pores of HPEGC and improve the pore structure and interfacial properties of HPEGC by microminiaturisation of the pore size. HPEGC formed a dense three-dimensional reticulated polysilicaaluminate-like structure due to the coexistence of C-S-H gel, C-A-S-H gel, N-A-S-H amorphous gel, and Na2Al2Si3O10. 2 Al 2 Si 3 O 10 . HPEGC with SN/FS of 12 % and BMMSR of 0.36 showed 29.5 % and 18.9 % improvement in compressive and tensile strengths, better resistance to sulfate attack, and 4.5 % and 45 % reduction in economic cost and GHG emission, respectively, compared with ordinary Portland cement concrete (OPCC). The results of the study proved that the engineering application of HPEGC incorporating ERST, FA and slag as raw materials is promising, providing new solutions for global underground excavation materials and industrial solid waste, and effectively promoting the sustainable development of the construction industry.