Modelling of concrete at early ages: Application to an externally restrained slab

In view of the growing use of High Performance Concrete, with large hydration-induced volumetric changes (both thermal and shrinkage related), numerical modelling of concrete at early ages has become an important issue, regarding the possible formation of cracks, with undesirable consequences on aesthetics and structural durability. In this paper a thermo-mechanical model based on the framework of finite element techniques is presented, and involves the consideration of phenomena such as the heat production induced by the cement hydration, the evolving properties of concrete during hydration and early-age creep. A numerical application is presented, focused on the thermo-mechanical behaviour of a slab strongly restrained by the supporting piles, which has been monitored during the construction phase. For this particular problem it is shown that by making a reasonable thermal and mechanical characterization of concrete, the thermo-mechanical model provides results that are well correlated with the observed in situ measurements, namely the temperatures and the strains.