Performance of Coating Mortars with Partial Replacement of Natural Aggregate by Açaí Seed Residual Ash from the Amazon Region

This study evaluated external rendering mortars with partial replacement of natural sand by açaí seed residual ash (ASRA). Initially, through a pilot study, mortars containing 0, 10, 20, and 30% ASRA were tested, analyzing their properties in both fresh and hardened states. Considering the demand for sustainable solutions for agro-industrial residues, this research aims to corroborate, with technical and scientific evidence, the feasibility of using ASRA as a substitute for sand in mortars. Based on the pilot study analysis, it was found that the mixture with 20% replacement (ASRA20) exhibited the best rheological and mechanical performance. Subsequently, an external rendering mortar with 20% ASRA was produced and compared, in terms of performance, with a reference mortar widely used in Brazil (plasticized mortar without ash). Both mortars (REF and ASRA20) were applied to vertical masonry panels built with ceramic blocks, where the following aspects were assessed: cracking, surface friability, permeability, and direct tensile bond strength. In addition, microstructural analyses were carried out using scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). The results, analyzed through statistical methods, demonstrated that the ASRA20 mortar presented improved particle cohesion, higher plasticity, a lower cracking index, greater resistance to surface wear (scratch test), reduced permeability, and bond strength values exceeding the requirements established by standards. These findings indicate that ASRA has strong potential for application in cementitious matrices, contributing to the reuse of an abundant residue from the Amazon region and providing a sustainable alternative for construction materials.