Considerations for Handling of Mass Concrete: Control of Internal Restraint

This paper presents the findings of an investigation in which the finite element method was used to assess the effects of various construction procedures on the cracking performance of a hydrating massive concrete element. A 1.07 x 1.07 x 1.07 m (3.5 x 3.5 x 3.5 ft) concrete block is modeled using a commercially avaialable finite element analysis software and the inputs for the mechanical and thermal properties of early-age concrete based on values obtained experimentally from a concrete mixture used in the construction of mass concrete in Florida. It was shown that, for insulation with a given thermal resistance, as the size of concrete placement increases, greater reduction of the temperature differential can be achieved by simply using additional layers of polystyrene foam or insulating blankets. The study also found that the attained tensile strength of concrete should be considered before the formwork and accompanying insulation used in mass concrete applications are removed to ensure that the stresses that result from the sudden cooling of the concrete surface are sufficiently lower, thereby reducing the likelihood of thermal cracking.