The fresh and engineering properties of alkali activated slag as a function of fly ash replacement and alkali concentration

• Under the same conditions increasing alkaline activator besides making the flow time of gerpolymers longer.
• The compressive strength of the geopolymer paste increases with age and alkaline solutions, and the optimal compressive strength is 93.06 MPa.
• The polymerization rate increases with the strongly alkaline solution; therefore, the internal structure is compact and the ultrasonic pulse velocity is increased.
• When alkaline activator 0.5% compared to 1.5% is more weight loss, we know higher alkaline activator less prosity, and higher durability relatively is better.

Geopolymers are novel, environmentally friendly and economical materials. These materials are produced from industrial wastes, such as fly ash and slag. The geopolymer material used in this study is made from recycled materials, including fly ash and slag, and aqueous solution of NaOH and silicate. All of the specimens are produced using a fixed liquid-to-solid ratio (L/S = 0.5), different ratios of fly ash and slag (fly ash replaces slag by 0%, 20%, 40%, and 60%) and various alkaline solutions (0.5%, 1% and 1.5%). The engineering properties of slump, flow, slump flow, flow time, setting time, compressive strength, ultrasonic pulse velocity and anti-sulfate attack are tested at different curing ages 1, 3, 7 and 28 days.The findings show that when the replacement of fly ash is fixed, the slump value, flow value and slump flow increase with the alkalinity of the solutions. The slump value (98 mm) before replacement with 1.5% alkaline solutions 1.5% is increased by approximately 20 mm compared with different replacements of fly ash. Before the addition of any additive with a slow setting effect, the setting time can be shortened by reducing the alkaline solutions. When the alkaline solution increases from 0.5% to 1.0% or 1.5%, the compressive strength quickly develops. The ultrasonic pulse velocity increases with the addition of alkaline solutions. When alkaline activator 0.5% compared to 1.5% of an alkaline activator sulfate, they get more weight loss. The result shows more alkaline activator, less porosity, higher strength, durability relatively is better. These results are expected to upgrade the technical level of slag-based geopolymer with fly ash to further develop Taiwan’s energy saving, carbon reduction and environmentally friendly recycled admixtures.