Coating performance, durability and anti-corrosion mechanism of organic modified geopolymer composite for marine concrete protection

Geopolymer has excellent chemical resistance, while the high shrinkage prohibited its application in marine concrete coating. To solve this problem, organic modified metakaolin based geopolymer (MG) composites were synthesized with waterborne epoxy resin (WR) at 10%, 20% and 30%, and three types of silane coupling agents (SCA) at 1%, respectively. Multiple coating performance related properties were assessed, with the organic-inorganic interaction explored using SEM-EDS, XRD, FTIR and MIP. The organic-MG composites presented apparent enhancement in coating performance, with 30% WR- and 1% S823- modified MG having the most promising properties. Particularly, MG-WR performed better in shrinkage reduction, adhesion, anti-abrasion and Cl− corrosion resistance; while MG-SCA had better durability in seawater and carbonation conditioning. These were attributed to the more compact microstructure configurated through (i) pore filling of WR in geopolymer matrix; (ii) hydrogen bonds formed between waterborne hardener, epoxy resin, geopolymer and water; and (iii) SCA-geopolymer crosslinked networks formed via silanol-aluminosilicate condensation, respectively.