PSI - Issue 77

João Custódio et al. / Procedia Structural Integrity 77 (2026) 447–456 João Custódio, et al. / Structural Integrity Procedia 00 (2026) 000–000

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reinforcement of the concrete usually involves adding linear or laminar elements made of steel or advanced composite materials, either passive or active, as well as concrete lining, which can be simple, reinforced, and/or pre-stressed. In cases of severe deterioration, the demolition and complete reconstruction of the structure may be necessary, often involving new structures with different and optimised structural solutions. Finally, adding a redundant structural system may also be an option, depending on the type of affected structure. The new structural system should be activated when the concrete degradation caused by ASR and/or DEF reaches a certain level, at which point the structural load should be transferred to the new system. 5.1. Examples of interventions in existing Portuguese structures affected by ASR and DEF In Portugal, various structures affected by either ASR or DEF have been intervened in to mitigate their long-term consequences. The Aguieira dam road network, which includes seven bridges built in 1976-1979, was subjected to rehabilitation works (Rodrigues et al. , 2021). The ASR and DEF caused significant cracking, as well as a reduction of the mechanical performance of the concrete of these bridges, especially in their foundations and piers. From 2013 to 2014, major works were carried out to rehabilitate and reinforce the piers and foundations of the bridges over the river Mondego at Cunhedo (Cunhedo bridge), over the Mortágua stream (Mortágua bridge) and over the river Dão at Santa Comba Dão (Santa Comba Dão bridge). The rehabilitation of these bridges consisted of executing a single shaft on each pier, while retaining the existing cap beam. The new shaft walls ensure clearance throughout the perimeter of the existing piers, allowing for their expansion without restriction due to the swelling reactions that may continue to occur. The foundation consists of a set of twelve micro piles with high load capacity, headed by a circular pile cap built, as the shaft, around the existing pier. The micro piles were constructed from the surface, intersecting the existing footings. At the top (cap beam), the new shaft is connected to the existing one through bolts along the entire perimeter of the shaft (Rodrigues et al. , 2021). From 2015 to 2017, major works were also undertaken to rehabilitate the piers and replace/reinforce the foundations of the bridges over the river Breda (Criz I bridge), the river Criz (Criz II bridge), and the river Mondego at São João das Areias (São João das Areias bridge). The rehabilitation of Criz I and Criz II bridges involved deactivating the existing foundations and shaft pier sections that were immersed in the reservoir. This was achieved by installing a set of piles, headed by a prestressed pile cap in reinforced concrete, which transferred the load from the shafts to the new foundation. The rehabilitation of São João das Areias bridge was similar to the one adopted for the Criz I and Criz II bridges. The structural intervention took place in the submerged areas of the piers below the reservoir's operational top level. It created a redundant system that ensures structural stability and adequate performance in service, even if ASR and DEF continue to develop in the original concrete elements (Rodrigues et al. , 2021). In 2015, the bridge over the river Dão in Foz do Dão (Foz do Dão bridge) was replaced with a new bridge (Fig. 1). In this case, rehabilitation was not possible, owing to the considerable depth of the river where the columns and foundations were situated.

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(b) Fig. 1. (a) View of Foz do Dão bridges, with the new bridge in the foreground and the decommissioned bridge in the background; (b) View of Foz do Dão bridges, with the new bridge on the right and the decommissioned bridge on the left.