Potential application of geopolymers as protection coatings for marine concrete: II. Microstructure and anticorrosion mechanism

The excellent anticorrosion property of geopolymers in sea water and their efficient bonding to hardened cement paste did not only depend on the chemical compositions but were also influenced by the microstructure. This study presents an investigation into the interfaces between the geopolymer and cement paste and mortar and the pore structure of geopolymers by scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and Brunauer–Emmett–Teller (BET) nitrogen adsorption. The interface between the geopolymer and cement paste was compact and its chemical composition changed due to the reaction between the geopolymer slurry and the surface of cement. Open pores in the geopolymer synthesized with 90% metakaolin (MK) and 10% granulated blast furnace slag (GBFS) were < 15 nm in an average, thus much smaller than the average open pore size in ordinary Portland cement (OPC) paste. The compact microstructure of the geopolymer made it difficult for sea water to penetrate. The amorphous aluminosilicate geopolymeric gels, which were chemically stable in sea water or in air, provided a sustainable protection for marine concrete structures.