Fluidized bed combustion ash utilization: CFBC fly ash as a pozzolanic additive to portland cement concrete

Atmospheric fluidized bed combustion (CFBC) produces spent bed fly ash and bottom ash consisting primarily of lime (CaO), anhydrite (CaSO ₄), calcined clay materials and quartz. These materials have a much larger surface areas than conventional pulverized coal combustion (PCCA) fly ash. But, problems with swelling and strength loss have limited their usefulness. The potential of the CFBC fly ash as a pozzolanic additive to portland cement was investigated. The pre-hydrated CFBC fly ash was tested "as received" and as beneficiated by hydraulic classification or screening to remove the >200 mesh materials. The CFBC was also blended with PCCA fly ash. The mortar bar tests indicated that the CFBC fly ash was dimensionally stable and beneficiating the ash further reduced expansion. The CFBC materials did not lower water demand. The CFBC fly ash initially retarded strength development but by 7 days this was not a major factor. The CFBC materials performed well in concrete.