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Durability of Concrete Utilizing Blended Cements with Elevated Levels of Fly Ash


The benefits of using fly ash have been increasingly recognized for the last 25 years. Additions of fly ash result in improved resistance to sulphate attack, mitigation against alkali-silica reactivity, decreased permeability, and improved resistance to thermal cracking. Partial replacement of Portland cement with fly ash contributes to sustainability by increasing the recycled materials content of blended cements, reducing greenhouse gas emissions, conserving raw material resources, and reducing landfill volumes and disposal costs. Fly ash has many benefits; however, there remains some reluctance within the industry to use elevated levels of fly ash in concrete production. While the long-term improvement of durability and increased service life of structures is well recognized, higher levels of fly ash replacement frequently result in slower strength gain, additional curing requirements, and the perception of delayed construction schedules. This paper presents the results from a comprehensive study to determine the effect of binary blends with Class F fly ash on the properties of concrete. The properties of concrete with different levels of fly ash replacement were compared to concrete with an interground blend of general use (type GU) hydraulic cement and fly ash. The microstructure of concretes with blended and interground cementitious materials was analyzed by scanning electron microscopy (SEM), and the impact on concrete durability is discussed. The results of the study demonstrate that excellent early age durability of concrete can be achieved with fly ash replacement at a level that satisfies LEED requirements by intergrinding Portland cement clinker with fly ash. 

Conference Paper Details

Session title:
Bozena Czarnecki
Ward Johnston
Walter Dobslaw