Rheological benefits of biomass fly ash as filler replacement in cement-based materials

Biomass Fly Ash (BFA) represents a significant waste, which needs to find a new way of recovery. Their use as replacement for cement remains difficult because these ashes are generally non-reactive and lead to low resistance for cementitious materials. This study explores the feasibility of valorizing these biomass ashes as replacement for limestone filler, generally used in concrete to improve rheological stability of mixtures. An experimental program, based on a progressive replacement of limestone filler (LF) with biomass ash, is proposed. The rheological behavior of BFA were studied from a Blast Furnace Slag cement (BFS) and an ordinary Portland cement (OPC). The incorporation of BFA in replacement of LF increase the non-linearity of flow behavior depending of the shear rate intensity. A loss of workability with BFA is observed, associated to the difference in water demand between BFA and LF. In addition, BFA-based mixtures present more shear thinning behavior in comparison with the limestone filler. This study provides a rheological basis for functional aspects of a possible replacement of limestone filler by BFA in the future and demonstrates the use of BFA can improve working performance of cement-based materials.