Combined FI-SAM-Micro-CT analysis of entrained air void systems in processed and blended fly ash concrete

Motivated by the dwindling supply of high-quality fly ash (FA) and the growing interest to use harvested coal combustion ash (CCA), this research investigates how a processed Class F fly ash blended with Class C fly ash compares to a blend of standard Class C and F at 20 and 40% OPC replacement. Three techniques were used to assess the entrained air void systems: (1) FI-derived AEA dosage, (2) Super Air Meter (SAM) to quantify air content in fresh concrete, and (3) X-ray micro-computed tomography (micro-CT) of paste (50 mm × 100 mm) and field-scale (100 mm × 200 mm) concrete cylinders. Mechanical performance of the concrete cylinders was evaluated through compressive strength testing, while post-failure micro-CT was used to assess fracture localization to the pre-existing entrained air-void structure. The results show oxidizable fraction strongly influenced AEA demand, air entrainment behavior, strength development, and post-failure fracture characteristics. Increasing FA replacement reduced fresh-state air content from approximately 6.3% to 4.3% and increased SAM number, indicating reduced air void system stability at higher FA replacement levels despite FI-guided AEA dosage selection. Among the tested materials, the processed FA blend exhibited more favorable behavior than the standard FA blend, suggesting that material processing may improve the practical usefulness of lower-quality legacy CCA in air-entrained concrete.

Duke Scholars

Author Laura Elizabeth Dalton Civil and Environmental Engineering