The feasibility of lightweight construction materials by incorporating a waste that is difficult to recycle, based on waste from intensive agriculture: vegetable fibers and propylene, is presented. This innovative material consists of a mixture of Alhambra Formation soil (Granada, SE of Spain) reinforced with vegetable fibres from tomato, pepper, zucchini, cucumber, aubergine and polypropylene fibres. The fibres were used in the mixture at a ratio of 2.5%, 5.0%, 7.5% and 10.0%. These values were then compared with control test samples that did not contain any residues. The compatibility of the fibres with the soil of the Alhambra Formation was then evaluated in terms of its physical-mechanical properties, specifically in relation to uniaxial compression and longitudinal deformation. Due to the highly hygroscopic nature of plant fibres, their absorption was measured and the techniques of presoaking and non-soaking the fibres before mixing them with the soil of the Alhambra Formation were investigated. The results of the unconfined compression tests show that the increase in fibre volume leads to a significant decrease in compressive strength. The highest compressive strength from a residue ratio >= 7.5 % was achieved with the cucumber residue and the non-pre-soaking technique. This residue ratio reached an average value of 1.82 MPa, which is 4% lower than the reference specimen without additives. Notwithstanding the decline in mechanical strength with elevated residue quantities, the resulting Alhambra Formation soil composite blended with a 7.5 % cucumber ratio may be regarded as a prospective candidate for implementation using the Projected Earth System technique.

Modern construction is largely dependent on steel and concrete, with natural materials such as earth being significantly underutilised. Despite its sustainability and accessibility, earth is not being used to its full potential in developed countries. This study explores innovative building materials using Alhambra Formation soil (Granada, Spain) reinforced with difficult-to-recycle agricultural waste: polypropylene fibres contaminated with organic matter and leachates. Fibres were added at a ratio between 0.20 and 0.80% of the soil mass, leachates at a ratio between 4.25 and 8.50%, and lime was incorporated at 2.00% and 4.00% for specimens with higher residue content. Physico-mechanical properties, including uniaxial compressive strength and longitudinal strain, were analysed together with the microstructure. The results showed that polypropylene fibres, in comparison to the use of leachates, improved compressive strength and ductility, reaching a compressive strength of 1.76 MPa with a fibre content of 0.40%. On the other hand, this value is 7.4% lower than the reference sample without additives. The fibre-reinforced samples showed a higher porosity compared to the samples with leachates or without additives. This approach highlights the potential of agricultural waste for the development of sustainable construction materials, offering enhancements in the strength and ductility of reinforced soils.