PSI - Issue 17

João Custódio et al. / Procedia Structural Integrity 17 (2019) 80–89

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João Custódio et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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phenomenon heat-induced internal sulphate attack, also referred in the literature as delayed ettringite formation, DEF). From the 60 large concrete dams, being monitored in Portugal, there are 19 in which the concrete swelling phenomena has already been identified. In terms of bridges and viaducts it is expected that the number of ISR affected structures will very soon surpass that of dams. In Portugal, a dam was demolished and replaced by a new one in 2014 due to ASR induced expansion and distress, a bridge was decommissioned and replaced by a new one in 2015 due to deleterious development of ASR and DEF, and several bridges had to suffer expensive rehabilitation works to keep them operational. Moreover, there are newly built structures that will eventually suffer from ISR deterioration either because existing guidance was not followed or simply due to limitations of available recommendations. As such, ISR affected structures will continue to wave our infrastructure for years to come. Existing knowledge on ISR does not allow for a complete assessment of the actual condition of an affected structure and an accurate prediction of the mechanical properties deterioration and, consequently, of the period during which the structure will effectively perform its function, essential for the timely and cost-effective planning of the necessary mitigation, rehabilitation or reconstruction works. Because of that, the diagnosis and prognosis of ISR in existing structures are not currently covered by any European standard or regulation. Therefore, to help surpassing this situation, research is being conducted at LNEC to contribute to the establishment of a method for a more accurate determination of the current level of ISR progression and of the deterioration of the concrete mechanical properties (Custódio, et al ., 2013; Custódio & Ribeiro, 2014; Custódio & Ribeiro, 2015; Custódio, 2015-2019, 2017-2021). These are essential to the adequate overall appraisal of an affected structure, which requires development of structural models using the actual concrete performance. The results allow structural integrity analyses of damaged structures and useful information on the potential for further deterioration due to other mechanisms, need for mitigation or remediation actions, and remaining life of the affected structure. This paper aims to contribute to the ongoing discussion of this topic by the scientific community and, therefore, presents the methodology followed to assess the condition of the concrete from an ISR-affected motorway underpass in Portugal. It includes a comprehensive experimental campaign, performed to concrete cores extracted from the structure, comprising the latest advances in the field, to allow for an adequate diagnosis and prognosis of the swelling reactions development in the concrete. The results obtained in the study evidenced the utility of such a methodology on the appraisal of the actual expansion level attained to date in the concrete from ISR-affected structures.

2. Case study

2.1. Structure ’s characteristics

The structure evaluated in the present study is a motorway underpass in Portugal, designed and built in the early 2000’s. The underpass, 48 meters long and 18 meters wide, has three spans (12 m + 24 m + 12 m). The pre-stressed reinforced concrete deck is composed of a slab with three beams, 1 meter high and a width varying between 1.8 m and 2.6 m, connected monolithically to cylindrical columns (1 m in diameter) and simply supported in the abutments.

2.2. Structure ’s concrete

The concrete prescribed for the underpass was of the strength class C25/30 (IPQ, 1993) for the footings and abutments, and of the strength class C30/37 (IPQ, 1993) for the deck and columns. The minimum cement content was 300 kg/m 3 for all structural elements.

2.3. Evidences of the swelling phenomenon

The visual symptoms of ISR in the structure consisted mostly of cracking in the deck, more specifically in the slab, the longitudinal beams, and in the transverse beam at the abutments. The pattern of cracking varied with the geometry of the concrete member; but it was, in general, aligned with the reinforcement and the direction of the major stress fields, for instance, longitudinal cracking was observed in the pre-stressed reinforced concrete deck beams.