Potential application of geopolymers as protection coatings for marine concrete: I. Basic properties

Coatings can extend the service life of concrete structures exposed to marine environments by inhibiting the intrusion of corrosive ions. In the present paper, the possibility of using geopolymer as an innovative inorganic coating for marine concrete protection was evaluated by 5 basic properties: setting time, permeability, anticorrosion and bond strength as well as volume stability. Fresh coat needed about 2 h to finally set at 25 °C. A compound geopolymer was developed by adding 10% granulated blast furnace slag (GBFS) in metakaolin as starting materials at the liquid/solid ratio of 0.60 ml/g. The presence of GBFS had a beneficial effect on reducing the permeability of the geopolymer. Although the strength development was relatively slower under the condition of seawater curing, it convincingly confirmed that geopolymer had excellent anticorrosion property. Furthermore, the average bond strength between geopolymer and cement paste or between geopolymer and mortar was higher than 1.5 MPa, which could be explained by the coexistence of calcium silicate hydrate (C–S–H) gels in cement and geopolymer matrix under strong alkaline condition. In addition, the large shrinkage of the geopolymer was controlled by using polypropylene (PP) fiber and self-prepared MgO expansion agent, later of which could produce a shrinkage compensating effect.