Influence of Fly Ash, Slag Cement and Specimen Curing on Shrinkage of Bridge Deck Concrete

Cracks occur in bridge decks due to restrained shrinkage of concrete materials. Concrete materials shrink as cementitious materials hydrate and as water that is not chemically bonded to cementitious materials migrates from the high humid environment of the concrete to an environment with lower humidity. Reinforcing steel and structural supporting members provide restraint to this shrinkage which causes tensile stress in the concrete. When these tensile stresses exceed the tensile strength of the concrete, cracks occur and provide relief for these stresses. MDOT engineers wanted to determine the usefulness of supplementary cementitious to reduce shrinkage of concrete materials and subsequent cracking. This research project investigates length change of concrete as influenced by supplementary cementitious materials including Class C fly ash, Class F fly ash, and slag cement. The use of liquid membrane and 7-day, 14-day, and 28-day moist curing periods were also investigated to determine the influence of curing on length change of standard prism specimens.