Industrial symbiosis is a process that takes wastes or by-products from an industrial process or an industry and turns it into raw material for another process or industry. This concept provides a more sustainable material utilization and promotes the development of a circular economy, which is a pivotal target of the ‘European Commission’s Circular Economy Action Plan’. The circular economy helps in the reduction of the environmental footprints of industries, limits the requirement of virgin materials, and restricts the need for landfill disposal, leading to the value addition of the wastes. Numerous studies have been conducted on the utilization of different kinds of industrial wastes in different fields – agriculture, road and building construction, and so on. Lately, due to their inherent constituents, a few industrial wastes have also been implemented as possible ingredients in friction material formulations for automotive braking applications like fly ash, red mud, and metallurgical slags. These wastes displayed exceptional friction and wear behavior when added to conventional formulations at a varying range of testing conditions. With desirable friction and wear properties, the next step is to extensively evaluate the non-exhaust particulate matter emissions generated during the testing of these formulations with different wastes. In this expansive study, different types of industrial wastes produced in Italy and Czechia in huge magnitudes with limited options for disposal were added in friction material formulations to understand their friction, wear, and emission properties and to determine their possible utilization and potential inclusion in automotive braking applications. Three types of industrial wastes were selected – wastes produced during the aluminum anodization process (AAW) provided by Ossicolor, Italy, wastes produced during the plasma cutting operations of Al sheets provided by Valcom’s, Italy, and three kinds of metallurgical slags from blast and steel furnaces from Czechia. The wastes were added in two types of formulations – the first was a basic in-house formulation with minimum constituents to understand the waste characteristics/nature and the second was a commercial, highly optimized formulation, which was selected to obtain results in a ‘real-world braking scenario’. Initially, the three wastes were characterized using different tools like XRD, SEM/EDS, and FTIR to obtain their complete constitution. Next, the friction, wear, and emission analyses were conducted on a pin on disc tribometer at 1.51 m/s sliding velocity and 1 MPa contact pressure to replicate mild braking conditions. With the basic formulation, it was seen that all wastes behaved as an abrasive, which was determined by an increase in the friction coefficient magnitude when compared to the original composition. The wastes were added in varying quantities from 6 to 38 wt.% in the commercial friction material formulation to determine the most desirable content concerning friction, wear, and emission characteristics, when compared to the original composition. In the case of the waste generated during plasma cutting, the composition containing the ideal waste content was also subjected to subscale dynamometric analysis to observe results in varying testing conditions. The worn mated surfaces were subjected to SEM/EDS analysis to understand the influence of the wastes on the extension, quality, and sustenance of secondary contact plateaus. The focus of these analyses was to have a critical understanding of the scope, potential, pros, and cons of the utilization of different types of industrial wastes in brake pad formulations and the possibility of replacing the conventional constituents with these wastes, leading to a circular economy and sustainability.

Dr. Priyadarshini Jayashree, Researcher, University of Trento; Mr. Stefano Candeo, Doctoral Student, University of Trento, Italy; Prof. Vlastimil Matejka, Associate Professor, VSB - Technical University of Ostrava, Czech Republic; Dr. Roberto Masciocchi, Administrator, Ossicolor Srl, Autonomous Province of Trento; Dr. Carlo Fidelio, Chief Executive Officer, Valcom's SpA, Padova; Dr. Mara Leonardi, Materials Development Specialist, Brembo SpA, Italy; Prof. Giovanni Straffelini, Professor, University of Trento, Italy