Afşin Elbistan / Kahramanmaraş thermal power plant waste C type fly ash (UK) was used in this study. This ash was ground and 6 different fineness values were obtained. With different fineness values of fly ash, reference concrete samples with and without fly ash admixture were prepared by using 10%, 30% and 50% substitution rates instead of cement in concrete. Abrasion and carbonation resistance tests were performed to determine the effect of fly ash fineness on hardened concrete samples. Abrasion resistance was applied on concrete samples which have completed curing time of 28, 56 and 90 days according to Rotating Cutter method stated in ASTM C 944-99 standard. For carbonation resistance, the samples were left in a dense medium for 360 days and the carbonation depth was determined. According to the experimental results obtained; In 10% and 50% fly ash substitute concrete samples, grinding time did not have much effect on bending strength, but it was found that fly ash substitution increased the strength according to the reference sample. Furthermore, it is seen that the grinding time increases slightly the tensile splitting strength in 30% fly ash substitute concrete samples, but this mixture ratio is below the resistance value obtained by the reference sample. The depth of carbonation increased with the increase of fly ash content added to concrete mixtures. The highest carbonation depth value is in the 50% UK substituted concrete sample (1.0 cm) with 0, 20, 30 and 45 minutes grinding time, the lowest carbonation depth value (0.3 cm) is 10% UK substituted with 10 and 45 minutes grinding time concrete samples. According to the results obtained; It was found that the grinding time of UK used in concrete mixtures did not cause much changes on the carbonation depth. The maximum wear rate in the 10, 30 and 50% UK substituted concrete mixtures occurred during the curing period of 28 days. It can be said that the 28-day curing time increases the wear amount of the samples as the grinding time increases in the 10% UK-substituted concrete mixture, but it is not very effective in curing times of 56 and 90 days. In other UK substitution rates (30 and 50%), it cannot be said that the abrasion amounts of the samples with a curing time of 28, 56 and 90 days are increased as the grinding time increases.