Alkali-activated-blast furnace slag–rock interface strengthening via bio-mediated polysaccharide–mineral networks

The interfacial transition zone (ITZ) between alkali-activated blast furnace slag (AABFS) and rock is commonly regarded as the weakest component in geopolymer-based infrastructure due to microstructural discontinuities and chemical incompatibility. To overcome these limitations, this study proposed a bio-mediated polysaccharide–mineral hybrid approach by integrating chitosan-assisted enzyme-induced carbonate precipitation (EICP) to enhance interfacial cohesion and durability. The results demonstrated that the chitosan-assisted EICP treatment exhibited the highest interfacial shear strength and cohesion, increasing by up to 91% compared with the control. This improvement was primarily attributed to enhanced chemical bonding and microstructural densification rather than changes in frictional behavior. Nanoindentation and EDS results revealed that the hybrid-treated interface transformed from a porous and mechanically weak zone into a continuous gradient structure, with the ITZ width reduced from 19.8 μm to 10.2 μm. Thermal and XRD analyses further indicated that the hybrid modification promoted the transformation of metastable vaterite into stable calcite and facilitated the formation of a thermally stable organic–inorganic hybrid network. Overall, the synergistic interaction between chitosan and EICP stabilized the carbonate phase and established a cohesive polysaccharide–mineral framework, providing an effective and sustainable route for improving the mechanical integrity of AABFS–rock composite systems.