Effect of in-situ alkali activator treatment of polypropylene fiber on the corrosion resistance of geopolymer coatings: test and mechanistic analysis

This study addresses crack propagation-induced corrosion resistance degradation in geopolymers. Although economical polypropylene (PP) fibers demonstrate crack mitigation potential, their poor dispersion and weak interfacial bonding with the geopolymer matrix limit their performance. To overcome this issue, PP fibers were treated via an in-situ alkali activation process to form a surface-deposited inorganic layer that improved fiber dispersion and interfacial adhesion. A systematic evaluation of the fiber modification degree and dosage revealed that the optimal modified fiber content of 0.4 wt% (MPFGC0.4) resulted in substantial improvements versus unmodified counterparts: an 18.8 % increase in compressive strength, 8.1 % flexural strength enhancement, 42.5 % water absorption reduction, and a 67.8 % decrease in the chloride diffusion coefficient. The microstructural analysis confirmed that SiO₄^4- species and inorganic groups on fiber surfaces optimize fiber dispersion and enhance bonding with the matrix. As a steel coating, the modified geopolymer exhibited the lowest mass loss ratio after salt-spray testing, with the profilometric analysis verifying improved fracture resistance. This work advances corrosion-resistant coating strategies for reinforced concrete in aggressive service environments.