Life cycle assessment applied to the sustainable design of prestressed bridges in coastal environment

Resumen

Sustainability has gained relevant presence in our society since its first definition in 1987 by the Brundtland Commission. Ever since, the scientific community has put significant efforts in the development of standards, tools and criteria to reach sustainable designs. Notwithstanding the above, such efforts have not been enough to outline a truly sustainable future in the short term. As a response to the actual, insufficient state of development, the United Nations have recently established the Sustainable Development Goals to be reached by 2030. In such Goals, explicit attention is paid to the role of infrastructures, which are revealed as key elements to ensure the achievement of the mentioned Goals. However, despite the relevant implications of infrastructure design, and despite the fact that most infrastructures are designed to serve a significant group of people over an intergenerational period of time, the design of sustainable and resilient infrastructures is still lacking of a standarised methodology to determine their sustainability along their life cycles from a holistic perspective. Currently, both the environmental and the economic life cycle assessment methodologies show a relatively mature state of development. However, the social dimension is still considered to be in an embryonic state, thus compromising the use of multidimensional sustainability assessment methods. The present thesis proposes an extended methodology based on the environmentally oriented ISO 14040 standard to evaluate the life cycle sustainability of infrastructures through the simultaneous and consistent consideration of the three dimensions of sustainability, namely environment, economy and society. A new methodology is suggested here so as to assess infrastructures from a social dimension, while integrating such assessments into an ISO 14040 based framework. A multi criteria decision making technique is then applied to integrate the three sustainability dimensions into one single assessment. So as to take into consideration the non-probabilistic uncertainties involved in subjective weighting techniques, a novel neutrosophic approach for group AHP weights determination is proposed here. The sustainable design of a prestressed concrete bridge in a coastal environment is assumed as a conducting case study on which to construct the proposed methodology. The holistic approach in the sustainability assessment of infrastructures reveals itself to be essential rather than the usually conducted sustainability assessments based on the sole consideration of the environmental dimension. It has been observed that preventive maintenance results in better life cycle sustainability performance values when compared with reactive maintenance strategies. This thesis provides a guide for the sustainable design of concrete structures, although the suggested methodology can be applied to any type of infrastructure.