Influence of the Fly Ash Content on the Fresh and Hardened Properties of Alkali-Activated Slag Pastes with Admixtures

A study on the influence of the inclusion of slag or fly ash and five types of superplasticizers on the fresh and hardened properties of alkali-activated cements is presented. Three alkali-activated slag formulations with different fly ash content (0, 15, and 30%) in the presence of five admixtures (vinyl copolymer, melamine, and three polycarboxylates with different chain lengths) were assessed for fluidity control and setting adjustment without loss of mechanical properties. Solid sodium metasilicate was used as an alkaline activator. Their fresh and hardened properties were studied through slump, setting time, isothermal calorimetry, mechanical strengths, and porosity tests. The results showed that the increase of fly ash content delayed the reaction and improved workability but reduced compressive strengths. Concerning the admixtures, these maintained fluidity especially for the one based on polycarboxylate with very long chains. The melamine and polycarboxylate with very long chain admixtures did not have a drastic impact on mechanical properties at early ages; even a gain of flexural and compressive strength was noted.