PSI - Issue 11

Pablo Benítez et al. / Procedia Structural Integrity 11 (2018) 60–67 Benítez et al./ Structural Integrity Procedia 00 (2018) 000 – 000

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preserve its performance over its lifespan, which leads to the need for a broad knowledge about maintenance of these structures. The maintenance of structures has engaged the interest of structural engineers since the end of the last century, introducing concepts and theories such as reliability, life-cycle analysis, and the adaptation of new materials to the durability requirements, among others. Carbonation in RC structures is a natural process of reaction between the hydration of cement and the atmospheric carbon dioxide (CO 2 ) forming calcium carbonate. As a result of this process, shrinkage is generated under certain moisture conditions that generate micro-cracks, which facilitates the passage of carbon dioxide and other harmful agents into the structure that may cause corrosion of the reinforcing steel (Broomfield 2007). Studies have found that maintenance and repair activities expend multibillion USD (United States Dollar) per annum in terms of infrastructures corrosion. The estimated annual cost of corrosion worldwide exceeds the value of 1.8 trillion USD, which translates into a 3-4 % of the Gross Domestic Product (GDP) of the industrialized countries. Nevertheless, is estimated that between 25% and 30% of those expenditures could be preserved if optimised techniques in the corrosion treatment were employed (Schmitt et al. 2009). Carbonation-induced corrosion is definitely a source of significant and expensive degradation, directly related to climatic parameters such as CO 2 , temperature and relative humidity. In this way, climate change and its effects play an important role in terms of environmental exposure that determines the durability of infrastructure elements. A study concerning structures degradation in several cities around the world has clearly demonstrated that climate change would play an important role in the lifespan reduction of RC structures due to the carbonation-induced corrosion (Talukdar and Banthia 2013). The damage risks induced by carbonation can increase by more than 16% by the year 2100, which means that one in six structures will suffer additional and costly corrosion damage due to climate change. Moreover, the corrosion rate could increase by 15% if the temperature increases by 2 °C, in addition to an increase in the ultimate carbonation depth in some parts of the world (Peng and Stewart 2016). Regarding the carbonation front advance through concrete structures, this study has been based on the method developed in 1993 by Häkkinen (Sarja and Vesikari 2005) to calculate the carbonation rate corresponding to the case studies herein presented. This method considers variables such as air content, environmental exposure, the concrete strength and parameters associated with the cement type, relating them in a relatively simple way. From a socio economic perspective, Paraguay is a developing country where the construction industry is having an important growth since the end of the last century. However, an important weakness of this development is the lack of control during the construction stage of projects that calls into question the concrete structure quality. Hence, when countries experiment a rapidly developing infrastructure, a poor quality control procedures in construction often leads to poor quality concrete and low concrete cover leading to carbonation problems (Broomfield 2007). The aim of this paper is to present a study about the concrete structures degradation located in the urban area of Asunción, the capital city of Paraguay. For that purpose, a set of real carbonation test report has been collected in order to develop an analysis regarding the carbonation-induced degradation in this city. In order to face this issue, the solution has been formulated in terms of effective inspection planning as part of a maintenance strategy. Therefore, an optimisation problem is formulated through a quantification of cost components over the lifespan of structures, where the optimal inspection plan is considered when a minimum total expected cost of intervention is accomplished. Thereby, this research gives an outlook for optimal inspection strategies regarding this mechanism of degradation that will be useful to preserves the durability of infrastructures in Paraguay. 2. Carbonation in Paraguay – Case Study The analysis herein conducted corresponds to real cases of measurement of carbonation depth and cover thickness in RC structures located in the urban area of the city of Asunción, Paraguay. In order to characterise these structures, it should be noted that this set of data corresponds mostly to concrete structures of commercial and office buildings, even though some of them are schools building, apartments, and residential constructions. Moreover, in some cases, these structures were from unfinished buildings, where a different consideration of exposition must be taken into account in a deterioration analysis. Regarding environmental conditions, Paraguay has an annual average temperature of 24 °C and high thermal variations, where a tropical savannah climate and humid subtropical climate are predominant. Another important parameter for carbonation-induced corrosion is the relative humidity, for which the average value in Asunción is around 73.4% (DNEEC 2014; Peel, Finlayson, and McMahon 2007).