Chloride diffusivity of volcanic ash blended hardened cement paste

This paper reports the results of investigations on the chloride diffusivity of volcanic ash (VA) blended hardened cement pastes with varying curing age of up to one year. The pastes had 0, 20 and 40% VA as cement replacement by mass and water/binder ratios of 0·40, 0·50 and 0·60 by mass. The ACID test was used to calculate the chloride ion diffusion coefficient D_i , of pastes using the Nernst–Plank equation for steady state conditions. In addition, electrical resistivity, mercury intrusion porosimetry, and differential scanning calorimetry (DSC) tests were also conducted. Good correlations were found among D_i , total pore volume and electrical resistivity of the pastes. The D_i of VA blended pastes was within the range of 10⁻⁷ and 10⁻⁹ cm²/s. It was also found that blending cement with VA significantly reduced the long-term chloride ion diffusion coefficient and hence increased the long-term corrosion resistance of pastes. This fact was also supported by the presence of lower quantity of Ca(OH)₂ and higher quantity of Friedel's salt in the VA blended pastes as observed from the DSC tests. Pastes with 40% VA showed better performance in terms of chloride ion diffusivity. W/b ratio was also found to affect the D_i at the early ages of curing, but became less important at the later ages of curing.