Alkali Activation of High MgO BFS with Sodium Carbonate Added Dry Vs. Wet

The use of sodium carbonate to alkali activate blast furnace slag has several advantages over the typically used sodium silicate, including for example easier, safer handling and less negative environmental impacts. In this study, sodium carbonate (SC)-activated blast furnace slag (BFS) pastes and concretes were produced using a high MgO content BFS activated with 3, 5, 10 and 14 wt.% (by binder) of SC. The activator was added either as a dry powder or dissolved in water one hour before mixing. The setting time, workability and compressive strength after 1,7 and 28 days were determined. Concrete cubes were cured in two setups: sealed specimens at 65 ˚C for 24 hours followed by storage at laboratory conditions (20±2˚C), or simply sealed storage at laboratory conditions (20±2˚C and 50-55% RH), until testing. The results showed that, increasing the dosage of SC decreases the initial and the final setting time regardless of whether the mixing procedure was dry or wet. However, addition of the SC dissolved in water increased the slump at higher SC dosage, while increasing addition of the dry SC resulted in a lower slump. A higher dose of SC increased the 28d compressive strength when added as a dry powder or wet, with higher values in laboratory curing compared with heat curing.ISBN för värdpublikation: 978-2-35158-223-7; 978-2-35158-218-3;Finansiär: Iraqi Ministry of Higher Education and Scientific Research