Efeito da substituição parcial da areia por resíduo de PEBD em argamassas geopoliméricas para a produção de chapas cimentícias

Abstract

The Sustainable Development Goals (SDGs) include targets related to the preservation of natural resources and air quality. Given that sand consumption in the construction industry contributes to environmental degradation as it is a non-renewable mineral resource, along with the improper disposal of plastic waste, this study investigates the effects of partially replacing sand with Low-Density Polyethylene (LDPE) waste in geopolymer mortars for the production of cementitious plates. The objectives are to: analyze the microstructure of geopolymer mortars with partial sand replacement by LDPE waste; study the physical and mechanical properties of the produced mortars and cementitious plates; analyze the results of the mechanical resistance of mortars as a function of Analysis of Variance (ANOVA); and classify the cementitious plates for sealing applications according to the parameters outlined in NBR 15498:2021. LDPE waste replaced sand at levels of 0%, 25%, 50%, 75%, and 100%. The cementitious plates were produced using metakaolin-based geopolymers synthesized at 650°C, activated with sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). The materials were characterized using X-Ray Fluorescence (XRF), Thermogravimetric Analysis (TGA/DSC), X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and laser particle size analysis. The mortars were further analyzed by XRF, TGA, XRD, FTIR, SEM-FEG/EDS, and compressive strength testing. The plates were characterized through flexural tensile strength, bulk density, water absorption, and porosity tests. Statistical analyses were conducted using ANOVA and Tukey's test on compressive strength and flexural tensile strength evaluations. XRF results indicated an aluminosilicate content of 95.68% in the metakaolin. TGA/DSC and FTIR analyses confirmed the successful transformation of kaolin into metakaolin. In the mortars, XRD analyses revealed that the progressive incorporation of LDPE waste reduced crystallinity. SEM analysis showed that highly reactive matrices produced denser mortars, while less reactive matrices exhibited higher porosity. The 25% sand replacement demonstrated good mechanical performance, achieving a compressive strength of 44.68 MPa, second only to the 0% replacement, which reached 72.91 MPa. The flexural tensile strength ranged from 11.71 MPa to 5.95 MPa, meeting the acceptance criteria established by NBR 15498:2021. Furthermore, replacing sand with LDPE produced lighter plates with an apparent density of 2.51 g/cm3 for 25% and 1.93 g/cm3 for 100% plastic waste.