Water Transport Properties of Hybrid Binder Concrete Containing Activated Copper Slag and Recycled Concrete Aggregate

Abstract

Advanced design of eco-friendly concrete is very urgent in view of the vital fight against climate change. An interesting eco-efficient strategy is the combination of (1) alternative low carbon hybrid binders with a low clinker factor and the inclusion of alkali activators, (2) substituting natural aggregate by recycled aggregate and (3) securing satisfactory durability performance. Transport properties of concrete are reliable indexes concerning the ingress rate of aggressive agents though the pore structure. The present study analyses the water transport properties of concrete made with hybrid binders and recycled concrete aggregate. Copper slag (70 wt% binder) and copper slag + ground granulated blast-furnace slag (GGBFS) (50 and 20 wt% binder, respectively) were used as precursors with a tailored activator based on sodium sulfate and Portland cement. Coarse recycled aggregate (category Rcu 90 according to EN 12620) was used as 50% of total content of coarse aggregate (particle size range 4/32 mm). The examined properties include capillary absorption rate, water penetration under pressure, and accessible porosity by vacuum saturation at curing ages of 28 and 90 days. Concrete performance was dominated by the type of binder, whereas the impact of the recycled aggregate on the transport properties was in second place. A limited content of GGBFS in the binder system proved efficient to improve concrete performance. Overall, these preliminary results reflect promising capabilities of the combined strategy of using low carbon hybrid binders and recycled aggregates in concrete.