Sustainable low-cement blends featuring blast furnace slag, metakaolin and nanosilica show remarkable long-term durability against chlorides for one day curing age

Current cement production routes are facing an environmental challenge given the large amount of CO 2 emissions. With the objective of decreasing its carbon footprint, herein, low-cement blended mixtures containing pozzolanic ground blast furnace slag, metakaolin and nanosilica or a combination thereof have been studying referred to the mechanical properties and the long-term durable behaviour. The mixtures underwent chloride exposure for an initial curing age as critical as is 1 day and were subsequently subjected to extensive characterization of their durable behavior at intervals of 3, 6, 12, and 18 months. Regardless of their final composition, the substitution of cement with slag, metakaolin and nanosilica allowed reduction of cement by 75-80% and the resulting blended mixtures successfully met the standard mechanical properties displayed by the Portland cement (OPC) 42.5 R type I in some cases with a decrease of only 5%. Blended mixtures combining all three pozzolanic components showed the highest electrical resistivity, 4 and 10 times higher than the reference for 7 and 28 days of ccuring age respectively. Compositions with reduced cement content show chloride migration coefficients with a 50% reduction compared to the reference at one day of cure and of the same order as this composition but for 28 days curing age. For chloride diffusion, the differences in apparent and effective coefficients are much larger than for migration, being several orders of magnitude smaller for the reduced cement content samples at all exposure ages in the study and even when compared to the 28-day cured reference. Sustainable blends show diffusion and migration characterization. Even after 18 months of exposure, these blended mixtures exhibited outstanding durability, surpassing the standard reference cement. Finally, we found that the optimal performing blend had a composition in wt.% including 25 cement, 65 blast furnace slag, 8 metakaolin and 2 nanosilica. This novel chloride durability study is critical as it is carried out for exposure periods as long as 18 months and with a curing age of 1 day for sustainable compositions with a very low cement content of 20-25 wt. % demonstrating that sustainable alternatives to conventional cement may pave the way towards environmentally friendly construction materials. • Blends with slag, metakaolin and/or nanosilica with low cement content (20-25 wt. %) shows good mechanical and durable behavior. • Samples showed a compressive strength higher than the nominal value required for reference for 28 days. • Mortars for 1 day of curing showed chloride diffusion coefficients much lower than reference one exposed for 3,6, 12 and 18 moths. • Blend with all the pozzolanic additions for very early curing age shows a chloride migration coefficient similar to reference mortar with 28 days of curing. • These mixtures show excellent expectations for use as a sustainable alternative to Portland cement.