Using sucrose for improvement of initial and final setting times of silica fume-based activating solution of fly ash geopolymer concrete

This study investigates the initial and final setting times of fly ash-based geopolymer concrete using an activating solution that was a mixture of silica fume, sodium hydroxide, and water. The addition of sucrose (sugar) was implemented to improve the initial and final setting times. The effects of including sucrose on the mechanical, microstructure, and potential durability properties were observed. Sucrose was considered a viable solution to extending hardening times because it is readily available and affordable. Three different percentages were observed: 3%, 6%, and 9%. In order to eliminate the need for external heat, 10% of the fly ash was replaced by Portland cement. The results showed that when 10% of the fly ash weight was replaced by Portland cement, the initial and final setting times were 10 min and 25 min. The final and initial setting times were enhanced by more than 100% to reach more than 60 min when 3%, 6%, and 9% of sucrose were included. For instance, the final setting time reached 65 min when 3% of sucrose was added, 320 min for 6%, and 755 min for 9%. The reason for the delay is because the sucrose increased the viscosity leading to a postponement in the initiation of the geopolymerization process. The results showed that when sucrose was included in the mixtures, the compressive strength was not affected, and absorption and permeable void ratios were reduced.