## 1 Introduction  
In recent decades, the construction of plastic and polycarbonate greenhouses has expanded. The total global area occupied by greenhouses has grown to 1.3 million hectares [1]. According to this analysis, the country with the largest area of intensive greenhouse agriculture in the world is China. In Europe, the countries with the largest areas are Spain, Italy, the Netherlands and France. Spain is the second country in the world with the largest extension of greenhouses, and Almeria, in the Autonomous Community of Andalusia, is the region with the highest concentration of greenhouses [2]. According to the comparative study carried out by the Regional Ministry of Agriculture, Livestock, Fisheries and Sustainable Development on the cartography of greenhouses in Almeria, Granada and Malaga in 2020, Almeria concentratesmost of the area with greenhouses. This province has a total of 32,554 hectares, mainly located in the regions of Campo de Dalias, Campo de Nijar and Bajo Andarax. In Granada, an estimated greenhouse area of 3381 hectares is located mainly in the region of La Costa. In Malaga, it has been estimated that a total of 777 hectares have greenhouses, concentrated mainly in the Velez-Malaga region [2]. Because of this great extension of greenhouses and considering the annual crop rotation to supply consumer demand, the production of vegetable residue per year in the Almeria region is 2,013,210 tons of fresh residue that corresponds to 269,770 tons of dry residue [3]. The largest amount of vegetable residue generated are tomato, pepper, zucchini, cucumber, watermelon and aubergine plants (Figure 1). It should be noted that watermelon plant residue was discarded for this study, as it is a seasonal crop and was only available at the recycling plant in spring [4]. Furthermore, the annual production of the polypropylene residue that appears intertwined with the crop stems, in order to maintain the verticality of the plant and improve plant exposure to sunlight, is 4.813 tons [5]. Regarding the agricultural residue production, the European Directive EU 2018/851 [6] aims to move towards a circular economy, as well as to improve the traceability of the residue, preventing it from ending up in landfills or being illegally burned [7]. To comply with this regulation, several residue management companies and recycling plants have emerged in recent years in Andalusia, especially in Almeria, the region with the highest concentration of intensive agriculture in Europe [2; 5; 8]. Currently, agricultural residue is often burned to produce energy, used as animal feed or as a natural fertiliser [9; 10]. It is worth noting that agricultural residues can also be promising feedbacks for materials development, as they come from renewable sources and are widely available [11; 12]. In line with this situation and in order to make use of these residues in the field of construction, this research proposes the use of agricultural residues as reinforcement in construction materials. Thus, these residues can be by-products for the development of these materials. In this context, construction materials reinforced with plant fibres are currently of great interest due to their lower dependence on non-renewable energy resources, biodegradable behaviour and very interesting specific mechanical characteristics [13; 14; 15]. In addition to the advantages of the use of fibres from a sustainable development point of view, fibres bring additional benefits such as reduction in linear shrinkage and cracking. This is shown in other studies on both compacted earth walls and earth concrete materials [16; 17; 18; 19]. However, the effectiveness of fibre reinforcement varies with soil type and the quantity of reinforcement fibres [20]. In addition, clay reinforced with natural fibres shows higher water absorption at low humidities [21]; this may be due to the high water absorption capacity of the fibres.