# Green Manufacturing of UHPFRC Made with Waste Derived from Scrap Tires and Oil Refineries
After the onset of a crack, the fibers exert their exertions to arrest the crack using a bridging action and in turn improve the post-peak and residual strength of the structural elements [18]. The initial high cost of UHPFRC is due to the use of steel fibers. In addition to material costs, sustainability problems in steel production should be taken into account [19]. Each ton of steel is estimated to emit 1.9 tons of CO\({}_{2}\)[20]. Therefore, the use of steel fibers recovered from scrap tires could be beneficial in terms of reducing the initial cost and increasing the sustainability of UHPFRC mixes. The performance of UHPFRC containing different amounts of this recovered steel fiber (RSF) has been studied in the literature [8]. The increase in the amount of RSF has been shown to adversely affect not only the workability but also the homogeneity of the fresh mixture [21]. During mixing, the fibers will tend to agglomerate, and this balling effect reduces the workability of fresh mixes [22]. Some recommendations have been proposed to avoid this balling effect, such as the addition of incremental fiber [23], scattering after wet mixing [24], and using a fiber aspect ratio of 200 [25]. The importance of rubber being attached to RSF with regards to concrete performance has been highlighted. A decrease in compressive strength was reported from 136 MPa to 130 MPa in the case of RSF with rubber attached, while a decrease of 5% in compressive strength was reported at 141 MPa in the case of fibers without rubber attached [23]. In the case of the flexural toughness of UHPFRC containing RSF, a gradual increase in post-peak behavior was reported by increasing the percentage of fiber [26]. The beneficial use of RSF has also been reported to provide crack bridge and crack-arresting actions to improve the post-peak behavior of tested beams under flexural load [27]. A relatively small amount of residual flexural strength, as well as softening responses, was revealed with a lower content of fiber use [28], with a significant improvement in flexural strength being observed when the amount of steel fiber was increased [29]. Improvements in the first crack by 60% and maximum load by 20% were reported when using 60 kg/m\({}^{3}\) of RSF [30]. Recently, the mechanical performance of affordable and eco-efficient UHPFRC containing RSF was studied [31]. In addition to studying short fiber and the effect of clarity, different UHPFRCs containing 2%, 3%, and 4% of fiber were proposed. Fibers less than 9 mm were found to significantly reduce the mechanical strength of the proposed mixtures, and the clarity of the fiber was also shown to improve performance [32]. Furthermore, a significant cost and environmental benefit of using RSF in the production of UHPFRC was highlighted in paper [33]. An economic solution for recycling ECAT and RSF would be their utilization in the production of concrete mixes for infrastructure applications. The synergistic effects of the RSF and ECAT dose on the optimization, performance, and environmental impacts of the UHPFRC have not yet been studied. To fill this research gap, UHPFRC samples containing different amounts of ECAT and RSF were tested in this study. Their rheological, mechanical, and microstructural properties were evaluated using flow table apparatus, a universal testing machine, and a scanning electron microscope. The economic and environmental impacts of the developed UHPFRC were also highlighted with regards to cement-based mixes that are pertinent to the Polish construction industry, together with a discussion of the different limits of the concrete system and the conversion factors involved. These findings can allow for the development of sustainable UHPFRCs in the European market, where the availability of RSF and ECAT is abundant and the demand for bridge deck construction is high.