PSI - Issue 17

João Custódio et al. / Procedia Structural Integrity 17 (2019) 80–89 João Custódio et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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The estimated values for the total free expansion, attained to date in the sampled concrete, vary substantially with the sampling location. The higher values were calculated for the concrete sampled in locations L5, L3, L4 and L1, and the lowest in location L9. The different levels of expansion determined for the concrete sampled throughout the deck are likely to be related with the local concrete composition, the different environmental service conditions ( i.e. , temperature and moisture), and the stress fi eld. The SDT performed to the “as received specimens” allowed estimating that, in average, the ASR is likely to have caused, in the sampled concrete, an expansion that, in unrestrained conditions, would have reached 3800x10 -6 . Tough, it should be noted that this estimate was performed with data from laboratory studies (Custódio & Ribeiro, 2014, 2015; Custódio, 2015-2019, 2017-2021); therefore, it aims only at providing an order of magnitude of the potential concrete dimensional variations that result in variation of the mechanical behaviour. This paper analysed and discussed very succinctly a subset of the data produced from the characterization and testing of 12 cores extracted from a motorway underpass in Portugal. This paper aimed at providing the scientific and technical community an example of a practical application of several test methods, current available, for the diagnosis and prognosis of ASR and DEF in large long-service life concrete structures. The combination of the various test methods allowed determining that: (i) the aggregate has potentially alkali reactive constituents and also constituents that may release alkalis into the concrete pore solution, which in turn will promote ASR development; (ii) the concrete is affected by both ASR and DEF, but mainly by ASR; (iii) the concrete alkali content is favourable for ASR further development, provided that sufficient moisture and reactive silica are available; (iv) the cement sulphate content indicates that the analysed concrete might be susceptible to the deleterious devolvement of DEF, if it was exposed to high temperatures during curing and sufficient moisture is available; (v) the potential for continued deterioration due to ISR is negligible to moderate, depending on the location; (vi) the ISR have not yet evolved to an extent so that they result in a detectable reduction of the concrete compressive strength; (vii) the SDT evidenced that the ISR have resulted in a relevant decrease in the modulus of elasticity of the concrete sampled in all locations; (viii) the SDT performed to the “as received specimens” allowed to estimate that, in average, the ASR is likely to have caused, in the sampled concrete, an expansion that, in unrestrained conditions, would reach 3800x10 -6 . The ASR residual reactivity tests revealed that the rate of the expansion that might still occur in service should not be higher than 50x10 -6 per year, it might actually be lower due to the eventual leaching of the alkalis and the depletion of the available alkali-reactive silica. Nevertheless, the SDT has shown that the residual expansion may lead to an additional degradation of the concrete. In terms of DEF, the residual expansion that might still occur can also lead to an additional degradation of the concrete, but only if favourable conditions for its development exist in the structure; however, since this phenomenon has not yet manifested itself in a relevant manner in sampled concrete, it is likely that the above scenario only occurs if the impermeability conditions of the structure change or if the cracking reaches a significant depth in the structural elements. Consequently, the eventual occurrence of an additional expansion of the deck ’s concrete that might result in the progression of the existing cracks, with repercussion in the structure performance, cannot be completely ruled out, at least in some locations. Hence, it is important that the evolution of this pathology continues to be carefully accompanied in the structure. Finally, it was concluded that a methodology, such as the one described in the paper, is useful for any long-life structure where concrete swelling deterioration mechanisms are observed visually or structurally. Moreover, the gathered data can be used, in the future, as input values on modelling for structural assessment, to assist in the definition of eventual rehabilitation solutions that ensure the structure safety, and also as reference data in future assessments of the structure’s concrete. 5. Conclusions

Acknowledgements

João Custódio carried out the work in the scope of the FCT Investigator Project IF/00595/2015, financed by the Fundação para a Ciência e a Tecnologia, FCT (Portugal); the author wishes to acknowledge this financial support.