In the two last decades, world production of pig iron and steel has undergone a significant increase. In 2018, 1252.87 and 1806.46 million tons of pig iron and steel, respectively, were produced as compared to the 575.78 and 809.94 million tons of 2000. Consequently, the amount of the different types of slags deriving from these production processes has also increased considerably. In relation to the principles of sustainability and circular economy, the available literature suggests several possible reuses for these slags (bituminous conglomerates, hydraulic engineering, metallurgy, fertilizers, etc.). This paper aims to provide an overview of the iron and steel slags production and their reuse in concrete (for example as replacement of cement, fine or coarse aggregates). The characteristics of slags are analyzed in terms of chemical, physical, and mechanical properties. Mechanical and durability tests (both from material and structures point of view) carried out in the different studies and research are shown as well. Particular attention was devoted to electric arc furnace slags (EAF) since they are the most produced in Italy. Based on this deep literature review, the gaps that still require further studies have been identified and discussed.

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A greater reuse of steel slags would bring considerable benefits both from an environmental and economic point of view. The development of tools and strategies to monitor at different scales resources and waste flows would allow for better resource planning and a more sustainable management on territory. The aim of this study is to investigate and analyse the supply chain that deals with the management of steel slags at meso-level, in order to investigate the state of implementation of industrial symbiosis (IS), its potential and its improvement. A Mass Flow Analysis (MFA) has been implemented, through big data analysis coming from the integration of regional and provincial databases with a careful data processing from questionnaires. This integrated methodology has proved to be a valid tool to monitor the recovery and reuse, the implementation of industrial symbiosis and to plan improvement actions. This paper reports a representation of the current situation regarding the production, recovery and reuse of these materials in production processes for which they are suitable, with a view to their full exploitation, following the principles of circular economy and an analysis of the mutual exchange that occur among steelmaking plants and other business partners in a network of industrial companies. The results showed that most of the steel slags managed at meso-level (Province of Brescia, Italy) is still unfortunately destined for landfill with low percentage of them classified as by-product highlighting as the IS is not adequately applied. Of the slag destined for treatments and recovery processes, almost all of them are Electric Arc Furnace slag, which are mainly reused for hydraulically bound base layers and road sub-bases (about 85% of the total recovered) and as aggregates for the production of cement and bituminous mixes (about 15% of the total recovered). Results shows as further effort should be made in term of policies and strategies to incentivize IS and to increase the recovery. Graphical abstract

Volume 36 RILEM, The International Union of Laboratories and Experts in Construction Materials, Systems and Structures, founded in 1947, is a non-governmental scientific association whose goal is to contribute to progress in the construction sciences, techniques and industries, essentially by means of the communication it fosters between research and practice. RILEM's focus is on construction materials and their use in building and civil engineering structures, covering all phases of the building process from manufacture to use and recycling of materials. More information on Preface 2021, back to the "face-to-face" FRC.BEFIB2021 is the X edition of the series of specific international symposia focused on covering all aspects related to fibre-reinforced concrete (FRC) such as definition, technology, mechanical characterisation, structural design, numerical simulation, and cases studies analysed from the scientifical to the practical point of view.Unfortunately, one year ago, we decided to postpone the BEFIB2020 edition due to the global pandemic situation. Despite such a difficult decision, we pledged to publish the already presented papers as BEFIB2020 Proceedings: we considered that the performed advances should be published as soon as possible as recognition of the research activity of the authors and dissemination of all the new achievements among the scientific community.The postponement decision entailed a new call for papers for the "one-year-after" BEFIB2021 edition, with some fear and risk but relying on the ability our FRC community to research and produce new technological and scientific advances for publication. Despite all these issues caused by the global pandemic, and after the peer review process, we obtained 83 scientific papers for the BEFIB2021 Proceedings incorporating the work of 229 authors from 32 countries around the world. This new volume entitled "Fibre Reinforced Concrete: Improvements and Innovations II" concludes the publication of the research works and knowledge of FRC in the frame of BEFIB from 2020 to 2021.This BEFIB2021 edition has been organised to be a face-to-face event that will take place in the Universitat Politècnica de València (UPV) facilities. I would like to focus your attention on the significance of a "face-to-face" BEFIB2021 celebration. A symposium is not only the presentation of our paper and attending the rest of presentations. A symposium also represents the possibility of discussing and meet other researchers or practitioners in your field. Although this situation may usually occur in the plenary sessions (easy to be adapted with a proper streaming server), the best networking results occur in most cases out of the sessions rooms (which is more difficult to replicate online) such as during the coffee breaks, chance encounters in the hallway, or even during the social programme activities like v technical tour or banquet dinner. This is a market: the option of meet the people you want to connect and the possibility to meet other unforeseen people, meeting old and...