Microwave Curing of FA- and MK-Based Geopolymer Gels: Effects on Pore Structure, Mechanical Strength, and Heavy Metal Leachability

Microwave curing has proven to be a highly effective method for enhancing the structural integrity, compressive strength, and heavy metal immobilization performance of geopolymer (GP) gels. For fly ash-based GP gels, optimal compressive strength (126.84 MPa) and minimal heavy metal ion leaching (0.01 mg/L) were achieved under microwave irradiation at 100 W for 75 s. Similarly, metakaolin-based GP gels reached peak compressive strength (76.84 MPa) and reduced heavy metal leaching (0.44 mg/L) under 440 W irradiation for 60 s. Microwave energy significantly accelerates geopolymerization by promoting the aggregation of dispersed particles, rapidly forming a dense, block-like matrix. This accelerated densification enhances the mechanical properties of GP gels within minutes. Moreover, the dense matrix structure effectively encapsulates heavy metal ions, minimizing their leaching through a combination of physical encapsulation and chemical bonding. In summary, microwave treatment significantly enhances both mechanical performance and heavy metal immobilization, offering a practical pathway for sustainable applications.