Evaluation of the total replacement of natural coarse aggregate with mining waste coarse aggregate in the production of Portland cement structural concrete: physical and mechanical properties

Background: Following the concern of proposing solutions to minimize the environmental impacts caused by the mining industry in the state of Pará, in partnership with the company HYDRO S.A., this research was guided by the study of Fernandes, which analyzed the production stages of different types of coarse aggregates derived from bauxite, clay, and silica waste. The study utilized the coarse aggregate produced in the third production cycle, which had the highest percentage of waste in its composition, designated as AGS90. Materials and Methods: This work presents an evaluation of the characterization results of the synthetic coarse aggregate (AGS) with normal specific mass compared to the natural coarse aggregate (AGN), considering their physical, chemical, and mechanical properties. Furthermore, a correlation is established between these factors and their influence on the mechanical strength and modulus of elasticity of Portland cement concrete with a normal strength class. Results: Through the characterization of AGS, a disadvantage was identified, as it is still a type of aggregate with higher porosity in its structure and, consequently, greater water absorption compared to AGN. This condition negatively affected the mechanical properties of the concrete with synthetic aggregate (CAGS) up to 28 days of age. However, from the tests conducted at 91 and 277 days, an intrinsic consolidation of the composite occurred, and the results for axial compressive strength, indirect tensile strength, flexural tensile strength, and modulus of elasticity became equivalent to those of concrete with natural coarse aggregate (CAGN). Conclusion: The study confirmed the technical feasibility of fully replacing natural aggregate (AGN) with synthetic aggregate (AGS) derived from bauxite waste in structural concrete of class C30. Despite the higher porosity and water absorption of AGS, the mechanical properties of the composite (CAGS) equaled those of conventional concrete (CAGN) from 91 days onward, meeting technical standards. Microstructural analysis confirmed adequate adhesion at the matrix-aggregate interface without deleterious reactions, while adjustments in binder water highlighted the need for dosage optimization. Aligning with COP30 goals, the use of AGS demonstrates sustainable potential to reduce the extraction of natural resources and repurpose mining waste. However, long-term durability studies and methods to minimize the porosity of synthetic aggregate are essential for practical applications in regions such as the Amazon.