Updating Thermal Data Sets to Better Evaluate Thermal Effects of Concrete

The thermal behavior of concrete has long been studied to reduce cracking, especially in massive members, where heat generation is great. Heat dissipation and restraint create volume changes that can induce stresses at an early age, when strength and modulus are low. Many designers and contractors use Figure 31 of Reclamation Engineering Monograph (EM) No. 34 “Control of Cracking in Mass Concrete Structures” or Figure 4.1 of ACI 207.2R “Thermal and Volume Change Effects on Cracking of Mass Concrete” when preparing their temperature control plan for mass concrete. These figures were generated from pre 1960’s data and can be traced back to the 1936 Boulder Canyon studies. Due to changes in physical and chemical properties of cement over the years, these figures no longer provide accurate guidance to designers. In an effort to provide a reliable set of thermal properties, nine (9) concrete mixtures were tested for adiabatic temperature rise, diffusivity, conductivity and thermal expansion. This study includes mixtures containing various amounts of OPC, Class F fly ash, and Grade 100 Slag.