Strength, Flow, Setting, and Antiwashout Performance of Alkali-Activated Soil-Fly Ash-GGBS Grout for Scouring Protection of Marine Structures

Abstract

Local scour of the seabed around the marine structures severely threatens the structure’s safety. Most previous studies utilized cement as a binder material to prevent scouring. However, the use of cement contributes to the carbon footprint and exhibits little resistance to harsh marine environment conditions. Therefore, this study develops an alkali-activated cementitious material (AACM) using dredged river sediments (DRS), fly ash (FA), and ground granulated blast-furnace slag (GGBS) to prevent scour around wind turbine foundations. An alkali-activated sediments-FA-GGBS (AASFG) slurry was prepared using a mixture of DRS (70%) and FA and GGBS (30% in 1 ∶ 1 ), activated by sodium silicate solution and NaOH. Further, the AASFG slurry was amended with 0.1% polyacrylamide (PAM) to enhance its performance. The slurries were prepared at a modulus value of 1, 1.2, and 1.4 and 6%, 8%, and 10% Na 2 O content. The performance of AASFG and PAM amended AASFG (P-AASFG) slurry was tested for fluidity, setting time, turbidity (antidispersion test), washout resistance, and unconfined compressive strength (UCS) at 3- and 28-day curing periods, and then the optimal mix was determined. The AASFG slurry with 0.1% PAM shows a 1.7% to 12% decrease in fluidity and a 60% to 70% reduction in turbidity, enhancing the washout resistance (97.84%–99.66%) and producing UCS values between 1.87 and 7.48 MPa and an antiwashout strength ratio higher than 90%. The results revealed that the performance of both slurries depends on the modulus ratio and Na 2 O content. The sample M1.2N10 demonstrates optimum performance considering all parameters. Microstructural analysis revealed that the coexistence of ettringite, N─ A─ S─ H gel, C─ A─ S─ H gel, and C─ S─ H gel provides strength to the slurry. The characteristics of the P-AASFG slurry affirm its efficacy as a robust antiscouring material.