Corrosion resistance of steel bar and chloride binding capacity of cementitious materials with internal chloride: A comparative study on Portland cement, geopolymer, inter-ground and gap-graded blended cements

摘要

During the construction of islands and reefs far from the mainland, local marine materials are expected to be used in concrete from the viewpoint of economy, rapid and convenient construction. As abundant chloride with local marine materials is involved into concrete, ordinary Portland cements are not recommended due to their low chloride binding capacity and poor corrosion resistance of steel bar. In the present study, geopolymer, gap-graded blended cement as well as Portland cement and inter-ground blended cement as references were mixed directly with NaCl to simulate the chloride in local marine materials, their hydration process, mechanical properties, corrosion resistance of steel bar and microstructure were compared. The results showed that the hydration processes of blended cements were accelerated after introducing NaCl, resulting in a dramatic increase in early strengths. In contrast, the compressive strengths of Portland cement and geopolymer kept constant, whereas the late flexural strengths reduced gradually. Geopolymer had slightly better corrosion resistance of steel bar than Portland cement due to low porosity and pore size refinement, and gap-graded blended cement presented a superior corrosion resistance of steel bar even in chloride-rich environment, as the chloride binding capacity of gap-graded blended cement paste was about 4 times higher than that of geopolymer.