This paper presents the experimental investigation of the influence of fly ash on fresh concrete and hardened concrete mechanical properties, i.e., compressive, tensile, and bond strength. The fly ash content was used from a 5 replacement to a 50 replacement of OPC. The optimum replacement level of fly ash was observed between 15 to 30 for achieving high compressive strength. Whereas highest bond strength was achieved using 10 to 15 fly ash. The effects of fly ash were much pronounced after 28 days curing, such as at 90 and 180 days. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021.