Early Age Concrete Thermal and Creep effects: Relevance to Anchorage Zones of Post-tensioned Members

Highly concentrated stresses are imposed on maturing concrete slab local anchorage zones when post-tensioning (PT) load is applied. The prime nonlinear phenomena of the concrete while hydrating are the evolution of stiffness, the thermal strains, the visco-elastic nature of the concrete and cracking. Thermal and visco-elastic effects are more pronounced in early ages due to a higher rate of hydration reaction and the different phases present. The stresses associated with these effects may cause minor cracks in concrete, even prior to the application of the PT load. Finite Element simulation of early-age concrete behaviour is presented representing about four days of concrete curing in a plywood box. The thermal evolution is validated using experimental data obtained for the same mix. Results demonstrate that hydration reaction and viscoelastic effects can produce tensile stresses at critical times when the PT load is being applied. These stresses can have significant effects to the “spalling” stresses when a concentrated load is applied to the concrete section.