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

The risk of early-age concrete cracking depends on the capacity of hardening concrete to support the thermal stresses caused by the exothermic nature of the hydration process. This has been recognized for ''massive'' concrete structures. However, with the increasing use of high performance concretes, it is apparent that this problem also concerns traditionally ''thin'' structural members (columns, beams). The definition of a ''massive'' concrete structure, and how the structural dimension affects intensity and occurrence of chemically- induced strucctural degradation is the main focus of this paper. Based on dimensional analysis of the governing equations, a characteristic length scale, the hydration heat diffusion length, is derived; beyond this length the structure needs to be considered as ''massive,'' and latent hydration heat effects affect the long-term structural integrity. From experimental data of normal strength concrete and high performance concrete, it is shown that this hydration heat diffusion length of high performance concrete is of the order of < h = 0.2 m, and lh = 0.3 m for normal strength concrete. 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.