Hybrid Mortars Activated with Alternative Steel-Compatible Salts: Impact on Chloride Diffusion and Durability

Eco-friendly mortars have been manufactured with hybrid binders made of blast furnace slag and a reduced amount of clinker. The objective is to explore new formulations suitable for reinforced structures. Previous studies are mainly focused on activation with sulfates, a salt that is corrosive to reinforcing steel. Sodium nitrate and sodium carbonate, easily implementable in construction, have been used as activators in two different concentrations that involve similar Na content. A Type II PC mortar is used as reference. The dimensional stability of the mortars during curing (at 99% RH) and subsequent drying at 40% RH, has been evaluated, as well as their porosity and mechanical properties. Böhme tests revealed that studied hybrid binders have lower wear resistance than PC mortar. Activation with Na₂CO₃ allows the obtention of mortars with reduced porosity and good compression resistance, but generates microcracking that favors chloride diffusion. Activation with nitrates favors precipitation of AFm phases identified through differential thermal analysis. Nitrates in moderate amounts (4% w/w) allow manufacturing hybrid mortars with good resistance to chloride penetration and reasonably good mechanical properties. Hence, this binder can be a promising option for reinforced structures. Higher amounts of nitrates (8%) for activation give rise to more porous mortars.