Time-depth dependent chloride diffusion coefficients of self-compacting concrete

Chloride attack severely impacts the performance of reinforced concrete. The total and free chloride ion concentrations (CICs) of self-compacting concrete (SCC) prepared with three supplementary cementitious materials (SCMs) - fly ash (FA), blast furnace slag (BS), and silica fume (SF) – were measured through the accelerated salt immersion tests. The apparent chloride diffusion coefficients (CDCs) at any exposure time and erosion depth were calculated using the Boltzmann-Matano method. The influence of the type and content of SCMs, the water-binder ratio (W/B), and the type of salt solution on CICs and CDCs were investigated. Both introducing SCMs and reducing W/B effectively reduced the CIC. The SCM that most effectively reduced CIC was SF, followed by BS and then FA. Free CICs were reduced to a greater degree than total CICs in FA and BS concrete, but the opposite was true for SF concrete. Presence of calcium chloride in salt solution increased total CICs while reducing free CICs. Apparent free CDC dropped over exposure time and initially increased with erosion depth but eventually stabilized. A model of apparent free CDC considering the time-depth dependence was created, which shows that time reduction factors of CDC is larger in SCM-containing SCC than in control SCC.