Early age behaviour of massive concrete piers

In the proposed work the study of the structural effects of hydration heat and differential shrinkage on structures realized by means of massive concrete castings is presented. The object of the study are several circular piers of a viaduct built in Northern Italy. In the first weeks after the removal of the scaffoldings an evident crack pattern was noticed on the body of a great number of piers. The crack opening was of a few tenth of millimeters. The formation of the cracks also occurred before the dead load of the girder and the service loads were applied. Aim of this work is the numerical simulation of what occurred to the structure in the first hours after the casting and in the following days, in order to establish the causes of the unforeseen cracking. A diffused cracking phenomenon rising in the first days after the casting with a pattern similar to the one seen in situ has been numerically reproduced by means of a non linear finite element coupled thermal and mechanical analysis. Crack width was then calculated according to Model Code 90 and Eurocode 2 formulations, obtaining results in good agreement with the values measured in site. The result obtained gives a clear answer of what were the main causes of the damage: hydration heat, absence of curing, dimension of the casting, differential shrinkage, evolution of concrete mechanical properties in time during the hardening reaction.