Rheology and setting of self-compacting concrete incorporating high volume of fly ash and internal curing via coal and wood bottom ash

Abstract

The continuous development of innovative high performance concretes is encouraging the use of new and sophisticated techniques to study their performance. In this article, a rheometer is used to determine the rheological parameters (dynamic yield stress, viscosity, yield stress at rest and thixotropy) of an internally cured self-compacting concrete with fly ash blended cement. This research is motivated by the scarcity of rheological studies regarding internally cured concretes. Coal bottom ash (CBA) and wood bottom ash (WA) were used as internal curing water reservoirs. Air content, setting times and temperature rise under semi-adiabatic conditions were also analysed. The results indicate that ball bearing effect of fly ash decreased the amount of high range water reducer admixture added to the mortars to get similar workability. Furthermore, all the rheological parameters increased when using coal bottom ash and, more remarkably, wood ash, due to their irregular shape, rough texture and some minor water absorption. Internal curing of fly ash blended cement concrete has no detrimental effects on the fresh state properties, but special attention must be paid to the pre-wetting of porous aggregates. If the internal curing water reservoirs are wetted below their water absorption capacities, their use reduces workability and setting times. Therefore, the practicality of the proposed mixtures relay mainly on the care taken during their design and materials conditioning. The future research efforts should focus on the development of new mixes with different supplementary cementitious materials and new conditioning techniques that guarantee a precise pre-wetting. © 2025 The Authors