# Mechanical Performance of Concrete Made with the Addition of Recycled Macro Plastic Fibres
[23] proved the feasibility of substituting up to 10% by volume of sand for recycled plastics in the manufacture of concrete. Elsewhere, [PERSON] et al. [24] detected a lack of adhesion between recycled plastic and cementitious matrix, explaining the loss of mechanical properties as ratio incorporation increased. In addition, authors such as [PERSON] went even further, studying the use of PET plastic waste in strips of large size [25] or in grids of macro-strips [26] as reinforcements in concrete, suggesting the possibility of being considered for the reinforcement of concrete in place of steel. Within this sector, recycled plastic fibres can be used in FRC, which allows improvement of the concrete properties, in addition to the environmental benefits that this entails [4; 18; 27; 28]. The global value of the packaging industry is around EUR 345 million, of which the EU accounts for one-third, and of which 50% is related to food packaging. Forecasts indicate that the sector will continue to grow both in size and in importance [29]. In terms of structure, monolayer and multilayer can be distinguished: monolayer films consist of a thermoplastic polymer sheet made mostly of PE, PP, or PET, with a range from 20 to 200 \(\upmu\)m of thickness, while multilayer films are made up of a different number of sheets that can be polymeric (thermoplastics) or non-polymeric materials (paper or aluminium foils) [30]. Multilayer plastic waste used in food packaging does not enter the waste recycling stream due to the wide variety of materials, its multilayer composition [31], and the colours that make up the food packaging; hence, a call for a circular economy is proposed [32]. Currently, the technical feasibility of recycling this waste at low cost is not close to being achieved [31; 33]. Indeed, due to the fact that it is not always managed properly, the recycling process is quite complex and, with the great environmental concern attached, the plastic sector is encouraged to participate in projects to deal with this issue [34; 35]. This confirms the need to address studies such as the present work, which are essential in finding solutions that transform plastic waste from packaging into new resources, enabling not only contribution to the circular economy, but also the production of innovative materials for civil construction. In particular, this study deals with the analysis of the mechanical behaviour of concrete with the addition of macro-fibres obtained by cutting plastic sheets; specifically, measurements such as crack mouth opening displacement (CMOD) and toughness were obtained. Three different levels of fibre addition were used in the production of concrete (2 kg/m\({}^{3}\), 4 kg/m\({}^{3}\), and 6 kg/m\({}^{3}\)), and two reference concretes were produced (one without fibre, and another with a commercial fibre). The main novelty of this research consists of having used not commercial plastic fibres, but waste material derived from the processing of plastic for food packaging. These multilayer plastic wastes are difficult to recycle due to their heterogeneous composition. Hence, this work aims to valorise this waste, contributing to a circular economy.