Monitoring the structural effects of internal swelling reactions in Aguieira bridges

São João das Areias Bridge and Criz II Bridge, located in the reservoir of Aguieira dam, in the centre of Portugal, were affected by internal swelling reactions of concrete, which particularly affected their piers and foundations. Laboratory tests diagnosed both alkali–aggregate reaction and delayed ettringite formation as the causes of the expansions. This situation motivated important rehabilitation works on the piers and foundations of both bridges. These rehabilitation works were based on the construction of six piles around the footing of every pier founded on the riverbed. The corresponding pile cap was connected to the immersed part of the pier. In the course of these works, a structural health monitoring system was installed on both bridges in order to characterise the structural effects of the swelling reactions, both in the loss of rigidity and the temporal evolution of this degradation. The instrumentation applied on the bridges is described in this paper and the preliminary results achieved are presented.