Sodium hydroxide (NaOH)-sodium silicate-GGBS (ground granulated blast furnace slag) effectively stabilises sulfate-bearing soils by controlling swelling and enhancing strength. However, its dynamic behaviour under cyclic loading remains poorly understood. This study employed GGBS activated by sodium silicate and sodium hydroxide to stabilise sulfate-bearing soils. The dynamic mechanical properties, mineralogy, and microstructure were investigated. The results showed that the permanent strain (epsilon(p)) of sodium hydroxide-sodium silicate-GGBS-stabilised soil, with a ratio of sodium silicate to GGBS ranging from 1:9 to 3:7 after soaking (0.74%-1.3%), was lower than that of soil stabilised with cement after soaking (2.06%). The resilient modulus (E-d) and energy dissipation (W) of sodium hydroxide-sodium silicate-GGBS-stabilised soil did not change as the ratio of sodium silicate to GGBS increased. Compared to cement (E-d = 2.58 MPa, W = 19.96 kJ/m(3)), sulfate-bearing soil stabilised with sodium hydroxide-sodium silicate-GGBS exhibited better E-d (4.84 MPa) and lower W (15.93 kJ/m(3)) at a ratio of sodium silicate to GGBS of 2:8. Ettringite was absent in sodium hydroxide-sodium silicate-GGBS-stabilised soils but dominated pore spaces in cement-stabilised soil after soaking. Microscopic defects caused by soil swelling were observed through microscopic analysis, which had a significant negative impact on the dynamic mechanical properties of sulfate-bearing soils. This affected the application of sulfate-bearing soil in geotechnical engineering.

The soft soil in the coastal region of South China is taken as the research object, and the slag/fly ash activated by sodium silicate is used to solidify it. Results show that the single-doped slag or fly ash has a limited effect on enhancing the strength of silt soft soil. However, with a 28-day curing age, the strength of solidified soil increases with slag content but decreases with the increase in fly ash content. Incorporating sodium silicate significantly affects the strength of the solidified soil, with reinforced soil strength gradually rising with the sodium silicate content. The maximum strength achieved by solidifying the soft soil sample with slag activated by sodium silicate reaches 850 kPa, 2.55 times higher than that of single-doped slag. The optimal sodium silicate content for samples with 5 % and 10 % and 15 % and 20 % slag content are 4 % and 3 %, respectively. Similarly, the maximum strength obtained by solidifying the soft soil sample with fly ash activated by sodium silicate is 483 kPa, 1.71 times higher than that of single-doped fly ash. The optimal sodium silicate content for samples with 5 % and 10 % and 15 % and 20 % fly ash is 3 % and 4 %, respectively. Furthermore, the solidification effect of sodium silicate-activated slag on soft soil is superior to that of sodium silicate-activated fly ash. Microscopic testing reveals the formation of cementing material within the solidified soil, binding the soil particles together. This cementing material corresponds to the hydration product C-(A)-S-H. Due to the higher alkali activity of slag compared to fly ash, it generates a greater amount of C-(A)-S-H hydration cementitious material, filling the pores and enhancing the cementation between soil particles, thereby improving the strength of the solidified soil. Consequently, the solidification effect is enhanced.

To study scour-resistant applicability, 6-10% mass ratio of polyurethane (PU) was added to sulphoaluminate cement (SAC) and ordinary Portland cement (OPC) grouts to generate OPCPU and SACPU. Sodium silicate (SS) with slurry volume ratio of 1:1-5:1 was added to SAC and OPC grouts to generate OPCSS and SACSS. The water-cement ratio (w/c) of grout was 0.8-1.5. Fresh-state properties and mechanical properties were investigated. Hydrated minerals and microstructures were analyzed, scouring tests were conducted considering key formulations. The results indicated that SACSS and OPCSS have a shorter setting time and higher strength, which makes them suitable as scour resistance materials. At the w/c of 1.0, OPCSS with a volume ratio of 3:1 and SACPU with 6% PU were selected for scour resistance tests. It showed that maximum scour depths and sediment transports were 7.0-12.2 and 1.1-1.2% as those without reinforcing conditions. The critical shear stress on the seabed under reinforcement is similar to 103 times greater than the bed shear stress. This inhibits the occurrence of scouring. The study evaluated the applicability of cementitious reinforcement for scour resistance. This study analyzed material and mechanical properties, hydrated minerals, and microstructures, and conducted scour tests to optimize grouting material ratios for seabed scour protection, providing references for soil reinforcement and grouting protection.

To enhance the resistance to local scour around offshore wind turbine monopiles, 15 mixtures were designed based on Response Surface Methodology (RSM). Cement content, sodium silicate content, and rubber powder content were selected as independent variables. After determining their flowability, the compressive strength and shear strength were measured after curing in pure water and artificial seawater for 3 days, 7 days, 14 days, and 28 days. Experimental results indicate significant improvement in the mechanical properties of the modified soil, including increased Unconfined Compressive Strength (UCS), internal friction angle, and cohesion. The optimal mix ratio is identified as CSR40-10-15, consisting of 40% cement, 10% sodium silicate, and 15% rubber powder. The strength variation mechanism is elucidated from both macroscopic and microscopic perspectives. Finally, numerical simulations using Computational Fluid Dynamics (CFD) software validate the scour resistance performance based on the optimal mix ratio of flowable solidified soil, offering a new approach for local scour protection around offshore wind turbine monopile.

To address the issues of low early strength in cement-stabilized soft soil, as well as the high pollution, energy consumption, and costs associated with cement binder application, one-part geopolymer (OPG) is prepared by using solid sodium silicate (Na2O center dot SiO2, NS) to activate a mixture of binary precursors, namely fly ash (FA) and ground granulated blast furnace slag (GGBFS), along with water. The factors, including FA dosage, solid NS molarity, alkali molar concentration, and water-cement ratio, are considered for assessing the physical and mechanical properties of OPG. Based on this, optimized proportioning tests were conducted to determine the best mixing ratio of OPG for soft soil stabilization. The effects of the FA/GGBFS ratio in the precursor and curing ages on the unconfined compressive strength (UCS), porosity, and pore size distribution of OPG-stabilized soft soil were further investigated. Micro-analysis was performed using mercury intrusion porosimetry (MIP), scanning electron microscope-energy dispersive spectrometer (SEM-EDS) to reveal the stabilization mechanism. The results indicated that the OPG prepared with solid NS could effectively stabilize soft soil, with hydrated gels (N-A-S-H, C-A-H, C-S-H, and C-A-S-H) effectively bonding soil particles and contributing to the formation of a denser soil skeleton. The mixing proportion of FA/GGBFS of 0.1, water-cement ratio of 0.8, NS molarity of 1.0, and molar concentration of 3 mol/L was found to be optimal for soft soil stabilization. The corresponding OPG had good workability and achieved a UCS of 4.4 MPa. This study extends the application of solid sodium silicate-inspired one-step geopolymers in deep mixing techniques, providing guidance on the theoretical basis for the reinforcement treatment of soft ground foundations.

The present work investigates the feasibility of producing boards, with unconventional materials, namely hazelnut shells as a high-mass bio-aggregate and a sodium silicate solution as a no-toxic adhesive, and discusses possible applications based on an extensive characterization. The aim is to define a feasible reuse of a largely produced agro-industrial by-product to reduce the high environmental impact caused by both the construction and the agriculture sectors, by proposing a building composite that improves indoor comfort. The presented combination of aggregate-adhesive generated a product with characteristics interesting to explore. The thermal conductivity is moderated, and the composite achieved values of sigma max = 0.39 N/mm2 for flexural strength and sigma max = 2.1 N/mm2 for compressive strength, but it showed high sorption capacity with a moisture buffering value of about 3.45 g/(m2 %RH), and a peak of sound absorption between 700 and 900 Hz. Therefore, the boards' most promising performance parameters seem to be their high hygroscopicity and acoustic absorption behaviour, namely in the frequency range of the human voice. Hence, the proposed composite could improve indoor comfort if applied as an internal coating board.