Evaluación medioambiental a través de la metodología de Análisis de Ciclo de Vida en la utilización de residuos procedentes de procesos industriales y agrícolas para la producción de morteros y hormigones

Abstract

The current construction sector is in a development phase to achieve environmental sustainability in the future. In this context, specifically regarding concrete and mortar materials, an effective strategy is to reduce the quantity of the primary materials of which they are composed. In other words, reducing the amount of cement, natural aggregates and additives and substituting them in an appropriate way with potential waste from different sectors such as industry or agriculture. In this way, waste is reused and reintroduced into the value chain, applying the concept of circular economy. In this Doctoral Thesis in which the main objective is the generation of environmental results associated with the production of 1m3 of concrete or mortar. Where a series of potential wastes have been used as a substitute for fine aggregate and natural coarse aggregate or as a dopant element in other cases. In order to obtain the environmental results, the Life Cycle Assessment methodology was applied. The case studies investigated in this Doctoral Thesis have a productive scope, i.e. from cradle to gate, although simulations have been carried out on certain wastes in their use phase. There are five wastes treated and investigated in this Doctoral Thesis, three of them from the industrial sector and two from the agricultural sector. These waste materials have been applied either as recycled fine aggregates in a mortar matrix such as crumb rubber from end-of-life tyres and ground olive stones. Also, the use of recycled coarse aggregates in a concrete matrix generated from surplus concrete mixes in a manufacturing plant. The environmental feasibility of these first three waste materials as recycled aggregates replacing natural fine/coarse aggregates has been systematically assessed. Subsequently, the use of metallic fibres generated in machining operations and their incorporation into a concrete matrix as a dopant element is also being investigated. Finally, a new line of research is to be started with the possibility of revaluing vine shoot waste to produce charcoal and use it in mortar/concrete matrices, in order to define its mechanical, thermal, acoustic and environmental characteristics in future lines of research. Among the most relevant results of this Doctoral Thesis is the identification of those key internal processes that negatively affect the environmental profitability of using this type of recycled aggregates. These key processes are transport and the waste treatment process to convert them into recycled aggregates. However, despite this, the case studies identified reductions in environmental impacts with a cradle-to-gate production scope. In particular for recycled aggregate such as crumb rubber and using a percentage of 40% replacement of fine aggregate in 1m3 of mortar, it is evident that for the impact category of Global Warming Potential, the reduction of CO2 eq emissions is 37%. This corresponds to a 100 kg of CO2 eq reduction per cubic metre of composite mortar with these properties. And along the same lines, the ground olive stone, where 20% is used to replace the natural fine aggregate in 1m3 of mortar and for its respective simulation over a period of 35 years in the facade of a building, demonstrates a net balance of CO2 eq emissions for this study horizon of -87.53 kg CO2 eq/m3, and in other impact categories such as the Depletion of Fossil Fuels with an energy saving of 2,138.88 MJ/m3. This Doctoral Thesis has generated knowledge in environmental results in the field of the use of recycled aggregates and the incorporation of waste into mortar and concrete matrices, which is currently in the development phase due to the construction sector's need to achieve the concept of sustainable construction.