Effects of Fineness and Dosage of Fly Ash on the Fracture Properties and Strength of Concrete

This study focuses on evaluating the effects of the fineness of fly ash on the strength, fracture toughness, and fracture resistance of concrete. Three fineness levels of fly ash that respectively pass sieves—no. 175, no. 250, and no. 32—were used. In addition to the control concrete mixture without fly ash, two fly ash replacement levels of 10% and 20% by weight of the cementitious material were selected for the concrete mixture. The experimental results indicate that the compressive strength of the fly ash concrete decreases with the increase in the replacement ratio of fly ash but increases in conjunction with the fineness level of fly ash. The presence of finer fly ash can have beneficial effects on the fracture energy (GF) of concrete at an early age (14 days) and attain a higher increment of GF at a later age (56 days). The concrete containing finer fly ash was found to present larger critical stress intensity factors (KSIC) at various ages, and the KSIC also increases in conjunction with the fineness levels of fly ash.