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Description
Construction and demolition waste (CDW) is a complex combination of materials, including concrete, mortar, tiles, bricks, and ceramic flooring, representing approximately 50% of urban solid waste in medium and large cities. The final disposal of these materials constitutes a serious environmental problem, with a high incidence of illegal dumping, triggering studies on recycling and reuse processes. Recycled construction and demolition waste (CDW-R) can be reused as soil remineralizers, an alternative aligned with the principles of the circular economy, which allows for the reduction of the extraction of natural raw materials, in line with the Sustainable Development Goals (SDGs) of the United Nations' 2030 Agenda. Remineralizers are materials of mineral origin, generally volcanic or silicate rocks, applied to the soil to improve its physicochemical properties and biological activity, with a long-term effect to promote plant growth. Brazilian legislation (IN5/2016) specific to soil remineralizers limits maximum values for potentially toxic elements such as As, Cd, Hg, and Pb, as well as minimum levels of CaO, K2O, and MgO. Sampling campaigns of recycled construction and demolition waste were carried out in recycling companies in different regions of Brazil. The chemical characterization of these materials was carried out using neutron activation analysis (NAA) technique. Analytical portions of 200 mg were placed in high-purity polyethylene capsules, along with certified reference materials used for analytical quality control, and irradiated under a thermal neutron beam in the IEA-R1 nuclear research reactor (IPEN/CNEN), in São Paulo. At CENA/USP, induced radioactivity was measured by high-resolution gamma spectrometry using hyperpure germanium detectors with 50% relative efficiency at the 1332 keV photopeak of ⁶⁰Co. Spectral deconvolution and mass fraction calculations were performed using Quantu software, based on the k0 method. Twenty-two chemical elements - As, Ca, Ce, Co, Cr, Cs, Eu, Fe, Hf, K, La, Na, Rb, Sb, Sc, Sm, Ta, Tb, Th, U, Yb, and Zn - were determined in all samples. The results indicate that the recycled construction and demolition waste have a chemical composition compatible with agricultural use as remineralizers and reinforce the potential of NAA as an analytical tool to assess the quality and safety of these materials.