Workability, rheology, and geopolymerization of fly ash geopolymer: Role of alkali content, modulus, and water-binder ratio

The performance of fresh and hardened geopolymer pastes is significantly influenced by parameters, such as alkali admixture (A/F), activator modulus (Ms), and water-binder ratio (w/b). In this work, the effects of A/F, Ms, and w/b on the properties of fresh and hardened fly ash geopolymers (FAGs) are characterized using rheological, strength, and microstructural tests. The Bingham and Herschel-Bulkley (H-B) equations were uti-lized to match the rheological curve of the fresh FAG paste. Experimental results showed that the rheological behavior of the FAG paste conformed to the H-B model. However, the rheological model of the FAG paste did not change with variations in A/F, Ms, and w/b. In addition, A/F, Ms, and w/b regulated the geopolymerization and microstructure of the FAG. By decreasing Ms, increasing A/F, and adjusting w/b, the properties of the FAG paste effectively improved while maintaining strength. When Ms and A/F were 1.2 and 6%, the FAG setting time decreased by 94.5%; moreover, the fluidity and 28-d compressive strength increased by 11.7% and 31.3%, respectively, compared with those when Ms and A/F were 1.4 and 8%.