Correlations between porosity, chloride diffusivity and electrical resistivity in volcanic pumice-based blended cement pastes

This paper reports the results of an investigation on the chloride diffusivity of volcanic pumice (VP)-blended hardened cement pastes with varying curing age of up to 1 year. The pastes had 0, 20 and 40% VP as cement replacement and water to binder ratios (W/B) of 0·40, 0·50 and 0·60. The accelerated chloride ion diffusion test was used to calculate the chloride ion diffusion coefficient (D_i) of pastes using the Nernst–Plank equation for steady-state condition. In addition, electrical resistivity, mercury intrusion porosimetry, and differential scanning calorimetry (DSC) tests were also conducted. Good correlations were found between D_i, total pore volume and electrical resistivity of the pastes. The Di values of VP-blended pastes were within the range of 10⁻⁷–10⁻⁹ cm²/s. It was also found that blending cement with VP 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 VP-blended pastes as observed from the DSC tests. Pastes with 40% VP showed better performance in terms of chloride ion diffusivity. The water to binder 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.