Multi-source industrial waste-based binder for marine soft clay: mechanical performance and microstructural mechanisms

Abstract

Marine soft clays, characterized by high compressibility, low shear strength, and water sensitivity, pose significant challenges for the construction of coastal infrastructure. This study develops and evaluates an alkali-free, Ca-based alkali-activated binder (GFPC) composed of ground granulated blast furnace slag (GGBS), fly ash (FA), phosphogypsum (PG), and calcium carbide slag (CCS), all derived from industrial by-products. A D-optimal mixture design was employed to optimize component proportions and assess synergistic effects on mechanical performance. Unconfined compressive strength tests at various curing ages and after 20 freeze–thaw cycles, combined with XRD and SEM–EDS analyses, were conducted to evaluate strength development, durability, and microstructural evolution. The optimal mix (68.4 % GGBS, 10 % FA, 11.6 % PG, 10 % CCS) achieved a 28-day UCS of 4.24 MPa, which is 36.8 % higher than that of cement-stabilized soil, and retained 2.41 MPa after 20 freeze–thaw cycles, 52.5 % higher than the corresponding value for cement stabilization. Strength loss was most pronounced during the first five cycles (38.44 %) and then stabilized. Microstructural analyses revealed abundant C-(A)-S-H gels and ettringite filling pores and densifying the soil skeleton. Environmental and economic assessments indicated 97.8 % lower carbon emissions and a 67.5 % lower unit strength cost compared with cement stabilization. These results demonstrate that the proposed alkali-free GFPC binder, derived from multiple industrial waste streams, provides a high-performance, low-carbon, and cost-effective alternative for marine soft clay stabilization, supporting more sustainable and resilient coastal infrastructure.