Use of organic residual ash and PET fibers on the mechanical properties and durability of a solid slab

Plastic waste and industrial by-products present an increasing environmental challenge due to their accumulation and limited reuse. This study investigates a sustainable alternative by assessing the individual and combined effects of eucalyptus wood ash (EWA) and recycled PET fibers (FPET) on the mechanical properties and durability of concrete for solid slab applications. The innovation lies in combining both organic and plastic waste, a topic rarely explored, particularly in terms of durability. Concrete mixes were designed following ACI 211.1, targeting a compressive strength of 21 MPa. EWA was used as a partial cement replacement at 2.50–4.00% by weight, with the ash ground to pass through a No. 200 sieve (75 µm). FPET fibers, sourced from plastic bottles, were added at 0.15–0.75% by volume, with lengths of 50–60 mm and widths of 2–3 mm, randomly dispersed in the mix. Experimental tests assessed workability, unit weight, air content, and mechanical performance (compressive, tensile, and flexural strength, and elastic modulus). The optimal proportions were identified as 3% EWA and 0.75% FPET, yielding the best mechanical performance. These mixes were used to prepare cylindrical slab specimens (0.80 m diameter × 0.075 m height) to evaluate durability through impact energy, electrical resistivity, water absorption, and water penetration. At 28 days, the results showed a 12.05% reduction in water absorption, a 15.89% decrease in water penetration under pressure, and a 19% increase in electrical resistivity. The combined use of EWA and FPET enhanced ductility, energy absorption, and impermeability, highlighting their synergistic effect and potential as eco-efficient materials for durable concrete applications.