Use of biomass-fired power plant bottom ash as an addition in new blended cements: Effect on the structure of the C-S-H gel formed during hydration

The identification of new supplementary cementitious materials (SCMs) for use in blended cements is an area of major interest to the scientific community. The industry is equally keen for, given the vast amounts of raw materials and emission of large volumes of greenhouse gases involved in cement manufacture, it is under pressure to reduce its environmental footprint. This study explored hydration in blended cements bearing 20 wt% bottom ash (BBA) from three biomass-fired power plants. The results showed that the OPC-BBA blended and the neat OPC pastes exhibited similar degrees of hydration (~90%) and their C-S-H gels similar Al/Si ratios (0.08–0.09), while the mean chain length of the C-S-H gels was slightly higher in the former (5.15–5.30 for blended cement vs. 4.71 for OPC). The presence of pozzolanic activity in the BBA pastes, in turn, was confirmed by their lower CH and higher C-S-H gel content than would be expected on the grounds of the dilution of the amount of cement used