## 1 Introduction  
Currently, facing the challenge of reducing the environmental impact resulting from our economic and social activities is a priority at all levels. The waste that is generated daily across the world is known. This waste has been studied in depth and new alternatives for recycling have granted some of its parts a second life cycle, e.g., recycled aggregates from construction and demolition waste, bottom ash from biomass combustion, or ash from solid urban waste. All of these examples refer to recycled materials that can be applied to engineering infrastructure. In addition, another example could be the utilisation of waste products for the manufacturing of recycled concrete: waste products, such as discarded tiles, glass, steel, burnt foundry sand, and coal combustion by-products, have provided specific effects on the properties of fresh and hardened concrete [1]. However, there are numerous types of waste that are being generated in high quantities but, from an environmental point of view, they are not reused at acceptable rates. This is the case for plastic wastes coming from plastic food packaging, which is the subject of the present study. Plastic packaging is widely used in the food sector due to several properties: it is flexible and adaptable in form, hygienic, light, cost-effective, high versatility, and does not easily degrade [2]. Increasing its recycling potential is a priority. In recent years, the circular economy of plastic has been increasing year by year and, in the specific case of plastic recycling, for the first time in Spain (in 2017), the number of tons of recycled plastic exceeded that of plastic deposited into landfills. These data demonstrate the increase in society's awareness, as well as the efforts and improvements of the collection systems, the modernisation of recycling processes, and the innovation of the plastics industry, which is incorporating more recycled material into new products. The plastics recycling sector in Spain is one of the most mature and powerful in Europe, with more than 120 companies and between 3500 and 4000 direct jobs, currently. The recycling of plastics will continue to grow and it is estimated that, in 2030, with the recycling of 55% of plastic containers in Europe, savings of 14.8 million tons of CO\({}_{2}\) emissions will be achieved [3]. On the other hand, the construction sector is continuously evolving and reinforced concrete is an example of an innovative solution. Compared to other building materials, such as metal and polymers, concrete is significantly more brittle and exhibits poor tensile strength [4]. To overcome this deficiency, fibres have been added to concrete in recent decades [5; 6], increasing the productivity and adapting more rational production techniques [7]. Fibre reinforced concrete (FRC) is composite material containing fibres in a cement matrix, either in an orderly manner or a randomly-distributed manner. Its properties are largely dependent on the type of fibre, fibre geometry, fibre content, orientation and distribution of the fibres, mixing and compaction techniques of the concrete, and size and shape of the aggregate [4]. The most common applications are pavements (slabs, industrial floors, or roadways), precast elements, and structural reinforcements. Different types of fibres have been used extensively in FRC (steel, polypropylene, glass, asbestos, polyester, etc.) [8], although steel and polypropylene are the most commonly used ones [9; 10; 11; 12]. Polypropylene fibres (PF) are generally used in FRC structures to enhance shrinkage cracking resistance, impact strength, spalling resistance, splitting tensile strength, and other properties [8; 12; 13; 14; 15]. [PERSON] et al. [16] observed that an additive amount of 0.1% PF in concrete had a 44% increase in its flexural toughness. [PERSON] and [PERSON] [17] reported that compressive strength increased by about 25% at 0.5% volume fraction of PF in the concrete mixture design.