Mortars containing eucalyptus wood ash and sewage sludge: eco-efficiency optimization using a central composite design and the desirability function

The increasing generation of industrial solid waste demands sustainable solutions for its reuse. The literature still lacks studies focused on optimizing the use of eucalyptus wood ash and sewage treatment plant (STP) sludge in cement-lime mortars. This study aims to fill this gap by optimizing the eco-efficiency of cement-lime mortars incorporating these residues, thereby promoting more sustainable practices in the construction industry. A Central Composite Design (CCD) was elaborated to define the mortar compositions to be investigated, along with the evaluation of compressive strength and flexural tensile strength. The statistical desirability function (DSJ) was applied to balance mechanical performance and sustainable resource consumption, seeking the most suitable formulation for the mixtures. Eco-efficiency optimization was conducted under practical masonry workability constraints rather than aiming at maximum mechanical strength without complying with standardized mortar consistency requirements. The results indicated that the lime addition played a predominant role in the mechanical strength of the mortars, whereas the addition of residues showed a less significant effect. The application of the desirability function enabled the identification of the most eco-efficient mortar composition. Regression analyses with coefficients of determination exceeding 80% demonstrated a good correlation between experimental data and the developed mathematical models. These findings contribute to the development of sustainable cementitious materials, demonstrating that the combined use of eucalyptus wood ash and STP sludge in mortar production is technically feasible and environmentally advantageous. This approach promotes the valorization of industrial residues without compromising mortar strength, advancing sustainable construction practices.