One-part pastes and mortars of CaO-Na2CO3 activated blast furnace slag: Microstructural evolution, cost and CO2 emissions

The mechanical properties and a thorough characterization of the reaction products were studied in one-part blast furnace slag (BFS) binders activated with 4, 6 and 8 % of a blend of CaO-Na2CO3 (with molar ratios of 1:1) in relation to the BFS. Pastes and mortars were cured for 24 h at 20 degrees C or 60 degrees C; with subsequent exposure at 20 degrees C up to 90 days. The compressive strength indicated that curing at 20 degrees C was beneficial for the advancement of the reactions; binders with 8 % CaO-Na2CO3 developed 45 MPa after 90 days, while the other regime reached 35 MPa. Mortars with aggregate:binder proportions of 2:1 and 3:1 developed 24 MPa and 21 MPa at 28 days, respectively. XRD, thermal analysis, SEM, FT-IR and Si-29 and Al-27 NMR evidenced the consolidation of micro-structures with low porosity, formed by C-(A-)S-H-type gel, hydrotalcite phases and calcite; the later occurred by reaction of Ca2+ and CO32- ions supplied by the alkaline activator. The assessed binders are environmentally friendly and cost effective compared to a blended Portland cement (BPC) paste and mortar.

Automated summary

The research focused on the mechanical properties and characterization of reaction products in one-part blast furnace slag (BFS) binders. The study examined the effects of 4, 6, and 8% CaO-Na2CO3 blend activation on the BFS binders. The results showed that curing at 20 degrees Celsius promoted the reactions, leading to improved compressive strength and consolidated micro-structures with low porosity.