Chloride permeability and chloride binding capacity of nano-modified concrete

Chloride permeability and chloride binding capacity are two important factors for assessment of the rebar corro-sion risk in reinforced concrete structures. In this work, the chloride permeability and chloride binding capacity of concrete modified with nano-SiO2 (NS), nano-CaCO3 (NC), multi-walled carbon nanotubes (CNT) were evaluated. The results demonstrate that incorporation of nanomaterials significantly decreases the chloride diffusion coefficients by refining the pore structure and reducing the pore volume. The experimental data strongly suggest the existence of a percolation threshold (critical porosity), below which the chloride permeability decreases dramatically. Addition of NS compromises the chloride binding capacity due to decreased pH value of pore solution, which results in dissolution of Friedel's salt. XRD suggests that adding NC restrains the formation of AFm phase, which is mainly responsible for the chemical binding. TG/DTG analyses confirm that adding CNT facilitates the formation of more amount of hydrates, thus enhancing the chloride binding. Addition of NS and NC leads to a decreased amount of Friedel's salt and thereby weakens the chemical binding.