What is a "massive" concrete structure at early ages? Some dimensional arguments

The risk of early-age concrete cracking depends on the capacity of hardenin g concrete to support the thermal stresses caused by the exothermic nature of the hydration process. This has been recognized for "massive" concrete s tructures. However, with the increasing use of high performance concretes, it is apparent that this problem also concerns traditionally "thin" structu ral members (columns, beams). The definition of a "massive" concrete struct ure, and how the structural dimension affects intensity and occurrence of c hemically-induced structural degradation is the main focus of this paper. B ased on dimensional analysis of the governing equations, a characteristic L ength scale, the hydration heat diffusion length, is derived; beyond this l ength the structure needs to be considered as "massive," and latent hydrati on heat effects affect the long-term structural integrity. From experimenta l data of normal strength concrete and high performance concrete, it is sho wn that this hydration heat diffusion length of high performance concrete i s of the order of e(h) = 0.2 m, and l(h) = 0.3 m for normal strength concre te. Through a number of case studies, the relevant similarity parameters of the risk of early-age concrete cracking are identified, which allow's the monitoring of the structural performance of early-age concrete structures.