Microstructure of cementitious materials under the coupling effects of Cl− and Mg2+ in a marine tidal environment

Abstract

To reveal the deterioration mechanism of cementitious materials serving in the marine tidal environment, this study investigates the microstructures of cementitious materials under the coupling effects of Cl− and Mg2+. This study mainly analyzes the phase composition, pore structure distribution, and micromorphology of the hardened cementitious materials with 30 % fly ash (FA), 30 % ground granulated blast furnace slag (GGBS), or a combination of 15 % FA and 15 % GGBS under different Mg2+ concentrations. The effects of Mg2+ concentration and mineral admixture type on chemically bound chloride ions and their microstructures are investigated. The results show that a large amount of Friedel’s salt is formed under the coupling effects of 0.6 mol/l Cl− and 0.1 mol/l Mg2+. A corrosive solution with a high concentration of Mg2+ is not conducive to the forming of Friedel’s salt. In a Cl− or Cl−-Mg2+ environment, GGBS can chemically bind more chloride ions than FA. With the increase of Mg2+ concentration, more pores and cracks appear on the sample surface. In a Cl−-Mg2+ corrosive solution, cementitious materials with mineral admixtures are more porous than pure cementitious materials. Cementitious materials hardened with GGBS are more porous than those materials hardened with FA. Thus, GGBS is more conducive to improving the materials’ resistance to chloride ions than FA.