Development of Fly Ash-Based Geopolymer Lightweight Aggregates

This research delves into the utilization of microwave hybrid heating as a curing technique for producing fine aggregates from fly ash. Various concentrations of alkali activator solutions were employed as binders to pelletize the fly ash (ranging from 0% to 10%). The resultant green fly ash-based geopolymer (FAG) aggregates were subjected to a 15-minute microwave kiln treatment. The microwave-sintered FAG fine aggregates, varying in sizes from 0.60 to 2.36 mm, were then utilized to fabricate 50 mm cubic cement mortar samples. Findings indicated that the density of FAG aggregates was approximately 36% lower than that of natural sand, while the water absorption capacity of FAG aggregates exhibited a fivefold increase compared to natural sand. Notably, cement mortar samples made with FAG aggregate of 4% alkali activator exhibited maximum compressive strengths of 31, 37, and 42 MPa at 7, 14, and 28 days of curing, respectively. These compressive strengths were only 12% lower than those of cement mortars made with natural sand across all curing periods. The use of microwave hybrid heating to transform fly ash into aggregates with sufficient strength appears viable, suggesting that these manufactured FAG aggregates could serve as substitutes for natural aggregates in concrete production