Chloride diffusivity change of inadequate cured mortar subjected to sulphate attack using mini-migration method

This study examines the impact of insufficient curing conditions, characterized by large diurnal temperature variations and severe drying, on the diffusivity of mortar samples after 30–90 days of accelerated sulfate attack. The accelerated mini-migration test (ACMT) was employed to measure the effective diffusivity of thin mortar plates under steady-state conditions, focusing on local microstructural changes. Results indicated that insufficient curing led to significant initial microcracks and increased porosity. The effective chloride diffusion coefficient (D_eff) initially decreased after 30 days of sulfate exposure due to further hydration and ettringite formation filling capillary and gel pores. However, prolonged exposure 90 days resulted in microstructural degradation caused by crystalline pressure of ettringite and dissolution of calcium hydroxide, leading to significant increased D_eff over time. The coupled effect of temperature variations and drying caused the most severe initial damage and subsequent degradation, followed by individual dry curing and temperature variation conditions.