Comparative Life Cycle Assessment of Concrete with Coarse Natural and Recycled Concrete Aggregates for Household Construction, Case Study in the Hamburg Area

Abstract

Society’s awareness of sustainability has been increasing in the last years, hence the use of recycled materials is becoming crucial in order to avoid negative impacts of human activities on the planet. Concrete is one of the most important building material in the construction industry. For the sake of concrete sustainability, the introduction of recycled concrete aggregate (RCA) in new concrete represents a possibility of avoiding construction waste and saving resources. The aim of this study is to evaluate the environmental impacts of three different sources of coarse aggregates for concrete production through a comparative Life Cycle Assessment (LCA). Two aggregates are produced with recycled construction and demolition waste, also known as RCA, and the third is produced from natural gravel also referred as natural concrete aggregate (NCA). The analyzed products are several concrete mix designs, covering different strength classes which are commonly used for household construction. The level of RCA replacement for the mix designs were established to a German guideline. The processes and materials evaluated comprehend the concrete production in a ready-mix plant located in Hamburg, Germany. Based on a data collection from the literature and different datasets out of the databases Ecoinvent version 3.7 and ELCD version 3.2, a LCA-Model has been developed. The results are presented using five midpoint indicators calculated by the CML-baseline and ReCiPe Method. During the evaluation of the LCA-results, it was found that the inclusion of RCA does not inevitably reduce the environmental impacts of concrete. Depending on the considered impact categories, it is possible that additional strains are eliminating the emerging benefits of RCA contribution. Supplementary transportations, changes in the mix design, compressive strength, and general demands for recycling old demolition waste are in focus of the discussion. In order to improve the sustainable performance of RCA in concrete some factors need to be considered.