The use of fly ash in concrete has received significant attention during recent years, owing to environmental concerns regarding its disposal, and, to its potential use as a supplementary cementitious material due to its ability to improve concrete performance. Although a fly ash content of less than 25% of the total cementitious content is routinely used in concrete. This thesis presents an assessment of high volume fly ash concrete using thermal power plant fly ash at replacement levels of 30, 40, 50, 60 and 70 percent of cement with constant w/cm ratio of 0.45. Tests were performed on fresh and hardened concrete to determine their properties in terms of workability, strength and durability. The study discloses that incorporation of high volume of fly ash in concrete improves the quality of concrete and enhances its performance in terms of workability, strength and long term durability.