Behavior in the fresh state, in the hardened state and microstructural characteristics of alkali-activated fly ash cement pastes

Abstract

Fly ash is one of the main precursors for alkali-activated cement. However, the combined use of fly ash and bottom ash is not common and little information is present. Therefore, this paper focuses on investigating the fresh and hardened properties of alkali-activated pastes with the addition of fly ash and bottom ash. In the fresh state, setting time, fluidity and plasticity were evaluated. In the hardened state, mechanical, chemical, and microstructural properties were evaluated. The incorporation of bottom ash up to 50% improves the workability of the pastes, in addition to acting as a retardant for setting. Mechanical strength tends to decrease with increasing ash content. However, the paste containing 100% bottom ash was 14.4 MPa, indicating potential for application. The main reaction product was identified in chemical and microstructural analyses as the N-A-S-H gel. In general, the blend based on bottom ash and fly ash has the potential for alkali activation, so a higher valorization of these by-products can be obtained, especially of the bottom ash.