**1. Introduction**

Corrosion of reinforcing steel in concrete structures is one of the most important durability problems associated with this material. Currently, construction companies of different countries state that the refurbishment and maintenance of buildings represents up to 30% of the activity of the construction sector [1]. The poor durability of many concrete structures, which results in short structural service lives, is not sustainable [2] neither in social nor in economic terms. In recent times, it has been common practice to deal with concrete deterioration mechanisms once the problem is detected and not before it arises. Such kinds of strategies result in greater socio-economic impacts, since they require more material in the long term than a design based on prevention. Although there are several mechanisms that may degrade concrete in severe environments, experience demonstrates that the most critical threat to concrete structures exposed to marine environments is chloride-induced corrosion of the reinforcing steel bars [3–5]. Research has been carried out on this specific mechanism for many years [6–9], leading to the development of different preventive measures to increase resistance to corrosion from the beginning of the structure life cycle, thus resulting in less maintenance-demanding solutions.

Some of the measures developed to prevent chloride corrosion focus on the reinforcement itself and others seek to prevent corrosion by reducing the porosity of the concrete cover. Corrosion can also be prevented by isolating the structure from the environment by means of surface protection treatments or by altering the kinetics of the reactions or electrochemical potential of the affected metals. Although the degree of knowledge associated with some of these measures is still precarious, the use of preventive measures such as those mentioned above is common when a concrete structure is exposed to chlorides. It is the task of the designer to find the solution that entails the lowest cost and consumption of resources [10–13]. Regarding durability, decision support techniques, such as Life

Cycle Cost Assessment (LCCA) can be used to find a durable solution with the minimum associated costs [14].

Cost comparison is the usual procedure for selecting the best design alternative. However, when only considering the costs derived from implementing a particular solution, it may happen that the costs associated to the maintenance operations of the structure can exceed the initial investment, thus tilting the balance in favor of other alternatives with higher initial investment costs [15] but lesser maintenance. This leads to the consideration of LCCA techniques in order to evaluate the costs generated throughout every stage of the life cycle of a structure. In addition, the economic costs deferred over time have associated social costs that can also be evaluated by means of Social Life Cycle Assessment (SLCA) techniques. When applied to the choice of the most appropriate prevention measure, it is common practice to overlook the social impacts generated. In urban environments, this impact may lead to adopting preventive measures that are more expensive in economic terms, but that require fewer interventions and, consequently, generate less social costs. Thus, the integration of social criteria in decision making is presented as an effective step towards a sustainable structural design [16,17].

It is possible to integrate both methodologies when choosing between different prevention measures. The present paper proposes an LCCA based methodology for decision-making regarding the most appropriate preventive measure for concrete structures exposed to chlorides, taking into account economic and social criteria. The economic and social costs considered in the proposed methodology are described below.

#### **2. Materials and Methods**
