Modeling the Effect of Unsaturated Conditions on Chloride Penetration in One-Part Alkali-Activated Slag Concrete

In this study, the effect of unsaturated conditions and curing time before exposure to an unsaturated environment on the properties of one-part alkali-activated slag concrete (O-AAS) and Ordinary Portland cement concrete (OPCC) was investigated. The samples were cured in water saturated with alkaline materials for 7, 28, 56, and 360 days. However, the specimens cured for 7, 28, and 56 days were stored in an unsaturated environment with 50% relative humidity until they reached 360 days of age. Compressive strength and rapid chloride migration tests (RCMT) were conducted at various ages up to 360 days, and corrosion initiation time was estimated by solving Fick's second law using the finite difference approach and results from RCMT. Results show that reducing the curing time before unsaturated exposure significantly decreased O-AAS's compressive strength and increased its chloride ion diffusion coefficient more significantly than OPCC. Chloride penetration modeling indicates that exposure to an unsaturated environment has a more pronounced effect on reducing the corrosion initiation time of O-AAS compared to OPCC. Also, increasing the curing time from 7 days to 56 days before exposure to an unsaturated environment caused a 186.7% increase in the estimated corrosion initiation time of O-AAS and a 20.4% increase in the estimated corrosion initiation time of OPCC. The required curing time for the O-AAS mixture to eliminate the effect of an unsaturated environment with a relative humidity of 50% on the compressive strength and chloride ion diffusion coefficient on standard specimens is 56 days, and for the OPCC mixture is 28 days.