The Effect of Fly Ash on the Sulfate Resistance of Concrete

The durability of concrete is determined by its ability to endure the physical and environmental surroundings without losing the functional properties and structural integrity of the original design. Concrete containing fly ash can be proportioned to meet the durability requirements of a wide range of applications, such as concrete for mass structures, pavements, structural members, and high strength applications. One area where the long term performance of concrete containing fly ash is not clearly understood is in sulfate environments. The sulfate attack mechanism in concrete containing fly ash has been related in recent years to the mineralogical and chemical composition of the cementitious and pozzolanic material. This study investigated the interrelationship between the physical, mineralogical and chemical characteristics of portland cement, fly ash, and their proportions, and the sulfate resistance of concrete containing fly ash. Eighteen fly ashes and five portland cements have been studied at four levels of volumetric replacement of fly ash for portland cement. Other variables studied were workability, air content, curing conditions, and permeability. The fly ashes were characterized by performing chemical, physical and mineralogical analyses. Over 700 specimens were measured for expansion, mass change, and cracking. The study has revealed a strong correlation between the glassy composition of fly ash and the sulfate resistance of concrete.