Nuevo modelo de evaluación de la sostenibilidad de estructuras de hormigón

Abstract

The most rigorous method for assessing sustainability is the so-called Life Cycle Analysis (LCA), applicable not only to the environmental, but also to the social and economic aspects. This method is based in the quantification of different parameters, called indicators. For instance, among others, the CO2 emissions in metric tons, the employment generated or the production cost of each metric ton of a specific type of concrete, with a particular dosage. The most important problems of LCA are, firstly, that most professionals in any country, including the advanced ones, do not have the adequate education or training to carry out these studies. Secondly, that there is still no global agreement on how to perform an LCA. In third place, that there is a lack of complete databases to quantify all the key indicators; this is the case, among others, of job creation. And finally, in fourth place, that the LCA result is a mere list of indicator quantifications, that in many cases is not enough for making decisions, since each design alternative will have specific advantages and drawbacks. These were the main reasons for establishing a sustainability assessment model not based in LCA, when the Spanish Structural Concrete Code (EHE-08) was developed. On the contrary, it was decided to employ parameters well known by all the professionals of the sector, together with a multicriteria decision support technique, the MIVES method (Integrated Value Model for Sustainability Assessment, in Spanish), for integrating the several indicators in a single, global sustainability index: the ICES (Index of Contribution of the Structure to Sustainability, in Spanish). The previously alluded reasons also led to the focus of the present work, again employing the same type of parameters and the MIVES method, but assuring that the results of applying the new model were always consistent with an LCA. It should be noted that the EHE-08 model is not only a pioneer one, but also the only sustainability assessment method employed in a structural concrete code, up to the moment. For many reasons, especially related to time, the project carried out to create the EHE-08 model did not include in its scope the comparison of its results with the ones of applying LCAs. As just mentioned, this is something that has been solved in this work. After analyzing the literature related to the EHE-08 model and the detailed study of that model and its applications, several questions were posed in this Doctoral Thesis. The first was: as for the sustainability of the structure under analysis, does the relevance of each ICES parameter correspond to its real importance?. In this work it has been studied whether the relevance of each aspect included in the EHE-08 model is consistent with the results of an environmental life cycle analysis (LCA). And the answer to this first question is negative, according to the conclusions of that study. The second question was: are there relevant aspects of sustainability that have not been taken into account in the EHE-08 model and, on the other hand, does that model include indicators that, in reality, are hardly influential for the purposes of sustainable development?. In this work it has been analyzed the completeness of the environmental, economic and social aspects encompassed by the EHE-08 model, and the answer to this second question is positive, according to the conclusions of that analysis. The last question was: does it make sense to propose a new evaluation model, of the same type as the existing one, which would provide more reliable information for making decisions in the sustainable design of concrete structures? Given the answers to the previous questions, the response to this query was positive. Therefore, the last objective of this work was to propose a new model for assessing sustainability of concrete structures, based on the existing one, but including solutions to the detected problems. A new model is proposed here, generically conceived, not necessarily for its integration in a structural code. However, it can be included in that framework, without problems. It is a very complete model, consistent with potential LCA’s of the structure under analysis. The results of this work can be useful for designers and clients wishing to construct sustainable reinforced or prestressed concrete structures, whether in a code framework, or in other ones. They will also be useful for the development of future research projects derived from this work and framed within the scope of structural sustainability. A new Spanish Structural Code (SSC), adapted to the Eurocodes, is currently under development. It will replace the EHE-08 and the Spanish Structural Steel Code (EAE), including a new sustainability assessment model. Despite of this, the new SSC model has not yet been disseminated. One of the future developments of this work will be, therefore, to make comparisons between the SSC model and the one here proposed, to draw conclusions on the matter, and to suggest solutions for the problems detected.