Chloride Diffusion in Limestone Flash Calcined Clay Cement Concrete

This study aims to assess the influence of using a flash-calcined clay and limestone blend as a supplementary cementitious material on the chloride diffusion resistance of concrete. A limestone and calcined-clay blend was used as any other supplementary cementitious material (SCM) in Australia is by straight replacement of general purpose cement in the concrete mixture without any optimization of sulfate content or alkalinity of the blended cement to reduce the time for the adoption of limestone and flash-calcined-clay blends in the industry. The bulk diffusion test results show that the resistance of concrete containing a flash-calcined clay and limestone blend (LC3 concrete) to chloride diffusion is greatly improved compared to that of a reference general purpose cement-based concrete. The apparent chloride diffusion coefficient of LC3 concrete is more than four times lower due to the increase in its chloride binding capacity and refinement of pore structure. Chloride binding capacity is not captured by the rapid chloride penetration test (RCPT) or rapid migration test (RMT). Hence, accelerated test protocols involving externally applied electrical voltage greatly underestimate the resistance of LC3 concrete to chloride diffusion. Keywords: accelerated test; binding capacity; chloride diffusion; flash calcined clay; Friedel's salt; limestone-calcined clay-cement (LC3); limestone.