New approach for coupled chloride/moisture transport in non-saturated concrete with and without slag

Over the paste decades a considerable research effort has been attributed to chloride ingress into reinforced concrete in order to understand the transport mechanisms and to predict its durability.In saturated concrete, chloride ions enter through diffusion (concentration gradient), whereas in partially saturated concrete, a part of the invading chloride is transported along with the salty water that was sucked by capillary absorption into the dried concrete. This study examines the effects of cyclic drying and wetting with chloride sodium on chloride ingress into non-saturated concrete. For this aim, a new automatic experimental setup has been developed to apply cyclic movement of chloride solution in controlled environmental conditions ambiance. Likewise, a new astute test method to control the concrete moisture content has been presented. As results, the first part of our study concerns chloride binding and water vapour adsorption isotherms. Results showed that Blast Furnace Slag (BFS), used as partial substitution of cement, increases the performances of concrete (BFSC60). Furthermore, the interaction chloride/concrete matrix seems to increase the adsorbed water vapour. In the second part of this research work, the influence of the moisture content, the number of cycles, the water-to-binder ratio and the slag’s addition on chloride profiles has been investigated and analysed. The results showed that the decreasing of relative humidity from 90% to 50% enabled to increase by ≈2–9 times the apparent chloride diffusion coefficient, which decreased when the number of cycles increased. A correlation between apparent diffusion coefficient and relative humidity has been obtained.

► A new experimental setup has been developed for cyclic wetting/drying.
► A new astute test method to control the concrete moisture content is proposed.
► Slag increases chloride binding.
► The interaction chloride/concrete matrix increases its water vapour adsorption.
► Decreasing relative humidity increases the chloride diffusion coefficient.