PSI - Issue 54

João Custódio et al. / Procedia Structural Integrity 54 (2024) 271–278

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

If one compares the mean values of R.H. recorded at locations L2 and L3, before (2019/02/07-08, 2020/07/20-21, 2020/11/05-07) and after the coating application (2021/05/10-12, 2022/02/07-09, 2022/06/30-2022/07/01), i.e. – 83 % (18 ºC) and 74 % (22 ºC) for L2 and 98 % (16 ºC) and 95 % (14 ºC) for L3, it appears that there was a reduction of the moisture level of the concrete in those two locations, more expressive in L2 than in L3. To better clarify the above considerations regarding the effect of the coating on the concrete moisture content, made with one-off readings and performed at the referred dates but at different times of the day, an extensive measurement campaign was performed in July 2023, and another one will be carried out in December 2023. In these two campaigns, the readings are made over a larger area, and involve leaving the probes in the holes for 5 days, over which three readings are made per day. These results will be presented on a future publication. 4. Conclusions This paper presented the general criteria that may be used to select coating systems for the mitigation of ASR and DEF in concrete structures. In addition, the paper presented the preliminary results of an in-situ study concerning the performance evaluation of a coating system in terms of its capacity to control humidity in concrete. The main findings obtained so far can be summarised as follows: • The relative humidity values in concrete are considered sufficient to sustain the deleterious development of ASR and DEF, both in the column and in the footing. • The relative humidity values are sometimes below what is, generally, considered as the threshold for the deleterious development of ASR (80 %) and DEF (92-95 %), hence there are periods of the year in which these reactions may slow down or even stop in the structure; at least at the depths assessed, and more so in the column than in the footing. • The coating system appears to have resulted in a decrease of the concrete moisture content, at the locations and depths assessed. • The final decision on the usefulness of applying such a coating in the piers will be made after the measuring campaigns are finished and all the data analysed, including the available structural monitoring data. References CEN 2004. EN 1504-2:2004 Products and systems for the protection and repair of concrete structures. Definitions, requirements, quality control and evaluation of conformity. Part 2: Surface protection systems for concrete. Brussels, Belgium: European Committee for Standardization (CEN). Custódio, J., Silva, H., Bettencourt Ribeiro, A., Paula Rodrigues, M. & Cabral-Fonseca, S. 2022. Performance evaluation of a coating protection system for concrete structures affected by internal expansive reactions. MATEC Web of Conferences, 361. Fournier, B. & Bérubé, M.-A. 2000. Alkali-aggregate reaction in concrete: a review of basic concepts and engineering implications. Canadian Journal of Civil Engineering, 27, 167-191. Geng, G., Barbotin, S., Shakoorioskooie, M., Shi, Z., Leemann, A., Sanchez, D. F., Grolimund, D., Wieland, E. & Dähn, R. 2021. An in-situ 3D micro-XRD investigation of water uptake by alkali-silica-reaction (ASR) product. Cement and Concrete Research, 141, 106331. Leemann, A. 2022. Alkali silica reaction - sequence, products and possible mechanisms of expansion. 16th International Conference on Alkali Aggregate Reaction – ICAAR 2020-2022. Lisbon, Portugal. LNEC 2021. Especificação LNEC E 461:2021 Betões. Metodologias para prevenir reações químicas expansivas de origem interna (LNEC Specification E 461:2021 Concrete. Methodologies to prevent expansive chemical reactions of internal origin) (in Portuguese), Lisboa, Portugal: Laboratório Nacional de Engenharia Civil, I.P. (LNEC). Nixon, P. J. & Sims, I. (eds.) 2016. RILEM Recommendations for the prevention of damage by alkali-aggregate reactions in new concrete structures (State-of-the-Art Report of the RILEM Technical Committee 219-ACS), Dordrecht, NL: Springer. Poyet, S., Sellier, A., Capra, B., Foray, G., Torrenti, J. M., Cognon, H. & Bourdarot, E. 2007. Chemical modelling of Alkali Silica reaction: Influence of the reactive aggregate size distribution. Materials and Structures, 40, 229-239. Poyet, S., Sellier, A., Capra, B., Thèvenin-Foray, G., Torrenti, J.-M., Tournier-Cognon, H. & Bourdarot, E. 2006. Influence of Water on Alkali Silica Reaction: Experimental Study and Numerical Simulations. Journal of Materials in Civil Engineering, 18, 588-596. Rajabipour, F., Giannini, E., Dunant, C., Ideker, J. H. & Thomas, M. D. A. 2015. Alkali – silica reaction: Current understanding of the reaction mechanisms and the knowledge gaps. Cement and Concrete Research, 76, 130-146. Renaud-Pierre, M., Bazin, C. & Toutlemonde, F. 2012. Alkali aggregate reaction and delayed ettringite formation: common features and differences. 14th International Conference on Alkali-Aggregate Reaction – ICAAR 2012. France.